To see the other types of publications on this topic, follow the link: C3b.
Journal articles on the topic 'C3b'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 journal articles for your research on the topic 'C3b.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse journal articles on a wide variety of disciplines and organise your bibliography correctly.
1
Quigg, R. J., J. J. Alexander, C. F. Lo, A. Lim, C. He, and V. M. Holers. "Characterization of C3-binding proteins on mouse neutrophils and platelets." Journal of Immunology 159, no. 5 (September 1, 1997): 2438–44. http://dx.doi.org/10.4049/jimmunol.159.5.2438.
Full textAbstract:
Abstract In the mouse, MCR1 and MCR2 on B lymphocytes are encoded by alternatively spliced Cr2 gene transcripts. Immune adherence receptors that bind C3 are present on mouse platelets and unstimulated neutrophils, yet they are not MCR1 or MCR2. To examine C3b- and C3d-binding proteins on mouse platelets and neutrophils, we performed C3b and C3d affinity chromatography as well as immunoprecipitation studies using previously described Ab to MCR1/MCR2 (mAb clones 8C12, 7G6, and 7E9 and polyclonal Ab BRN-1). Mouse neutrophils contained a 190-kDa membrane protein that specifically bound to C3b-Sepharose. Preabsorption of neutrophil proteins with anti-MCR1/MCR2 Ab did not affect the recovery of the 190-kDa C3b-binding protein by subsequent C3b affinity chromatography. Thus, this protein is immunologically distinct from the previously described MCR1 and MCR2 proteins. By virtue of its size and C3b-binding capacity, the 190-kDa protein was named C3bR-190. C3bR-190 was also apparent on platelets, but in reduced amounts. BRN-1 anti-MCR1/MCR2 Ab immunoprecipitated proteins of 125 and 150 kDa from surface-radiolabeled mouse platelets, which specifically bound to C3d-Sepharose. However, these proteins were not identified by mAb to MCR2, thus distinguishing them from previously described MCR2. These proteins were named C3dR-125 and C3dR-150. Therefore, we have identified a 190-kDa C3b-binding protein on mouse neutrophils and 125- and 150-kDa C3d-binding proteins on mouse platelets. These appear to be distinct from the heretofore identified mouse B lymphocyte MCR1 and MCR2. The identity of these C3b- and C3d-binding proteins on mouse neutrophils and platelets awaits further study.
2
Sahu, A., B. K. Kay, and J. D. Lambris. "Inhibition of human complement by a C3-binding peptide isolated from a phage-displayed random peptide library." Journal of Immunology 157, no. 2 (July 15, 1996): 884–91. http://dx.doi.org/10.4049/jimmunol.157.2.884.
Full textAbstract:
Abstract We have screened a phage-displayed random peptide library for binding to C3b, the proteolytically activated form of complement component C3, and have identified a novel peptide that suppresses complement activation. This phage-displayed peptide bound to C3, C3b, and C3c, but not to C3d, indicating that it binds to the C3c region of C3. A synthetic 27-amino acid peptide corresponding to the phage-displayed peptide also bound to C3 and C3 fragments and inhibited both the classical and alternative pathways of complement activation. The inhibition of complement activation was reversible. Studies with overlapping peptides indicated that the functional activity was located in the cyclic 13-amino acid N-terminal region (ICVVQDWGHHRCT) of the parent peptide. Reduction and alkylation of this 13-residue synthetic peptide destroyed its inhibitory activity. Analysis of the mechanism of inhibition revealed that the peptide inhibited C3 cleavage in normal human serum as well as when the alternative pathway was reconstituted with purified complement components, and the observed inhibition was not due to sterically hindered access to the C3a/C3b cleavage site. Further, the peptide did not inhibit the cleavage of factor B, indicating that it did not affect the interaction of CA with factor B or the formation of C3b,Bb. The peptide also had no effect on the binding of properdin to C3, demonstrating that the observed inhibition of C3 cleavage in normal human serum was not due in part to its effect on the properdin-stabilized C3 convertase, C3b,Bb,P. These results indicate that the peptide we have identified interacts with C3 to inhibit its activation.
3
Farries, T. C., P. J. Lachmann, and R. A. Harrison. "Analysis of the interactions between properdin, the third component of complement (C3), and its physiological activation products." Biochemical Journal 252, no. 1 (May 15, 1988): 47–54. http://dx.doi.org/10.1042/bj2520047.
Full textAbstract:
The interactions of properdin with both surface-bound and fluid-phase C3 (the third component of complement) and its activation products have been investigated by using a purified preparation of the ‘native’ form. At physiological ionic strength, a weak interaction with cell-bound C3b (the larger activation fragment of C3) could be demonstrated. In the presence of Factor B this interaction was enhanced, and further enhancement was seen when C3bBb sites were formed on the erythrocytes. The avidities of properdin for cell-bound iC3b (the initial product of Factors I and H action on C3b) and C3b were compared at low ionic strength, with that measured for iC3b being less than that for C3b. In contrast, the affinities of properdin for fluid-phase C3b, iC3b and C3c (the larger product of Factors I and H or CR1 (the C3b receptor) action on iC3b) were all very similar, and apparently much weaker than that for cell-bound C3b. No interaction with either native C3 or, more surprisingly, C3i (haemolytically inactive C3) could be detected. Properdin also inhibited Factor I binding to, and action upon, cell-bound C3b, but did not inhibit Factor I action on fluid-phase C3b. These data permit a more detailed description of the roles of properdin in the alternative pathway of complement activation, emphasizing its importance in concentrating activation at the activating surface.
4
Fries, L. F., G. M. Prince, T. A. Gaither, and M. M. Frank. "Factor I co-factor activity of CR1 overcomes the protective effect of IgG on covalently bound C3b residues." Journal of Immunology 135, no. 4 (October 1, 1985): 2673–79. http://dx.doi.org/10.4049/jimmunol.135.4.2673.
Full textAbstract:
Abstract We have shown previously that C3b resides in a protected site when it is covalently bound to IgG (C3b-IgG). Such C3b displays a reduced affinity for factor H, with consequent enhanced survival in the presence of factors H and I and increased capacity for promoting alternative pathway consumption of C3. Because erythrocyte CR1 may be a major co-factor for factor I-mediated inactivation of immune complex-borne C3b in blood, we have examined the effect of covalently bound IgG on the C3b-CR1 interaction. Binding of monomeric C3b and C3b-IgG to human erythrocyte CR1 demonstrates identical ionic strength dependence for both species. Identical numbers of binding sites with indistinguishable affinities are detected by both ligands. Cleavage of the alpha'-chain of C3b and the alpha'-heavy chain of C3b-IgG proceeds at the same rate when erythrocyte CR1 serves as co-factor for factor I. Unlike factor H, CR1 supports a second cleavage of fluid-phase iC3b alpha'1 chain (free or bound to IgG) that generates C3c and a 33,000 m.w. fragment, which bears antigenic markers characteristic of C3g. Inactivation of C3b and C3b-IgG by CR1 and factor I also occurs at physiologic ionic strength, but proceeds very slowly relative to rates attainable with sub-physiologic inputs of factor H. CR1 does not recognize IgG-bound C3b as being in a protected site but, because of low binding affinity at physiologic ionic strength, is probably highly dependent on multivalent ligand-receptor interactions to efficiently exert its co-factor functions. Thus, inactivation of C3b-IgG heterodimers or small immune complexes bearing limited numbers of C3b residues may remain largely factor H-dependent in vivo, with resultant enhanced C3b survival.
5
Tamerius, J. D., M. K. Pangburn, and H. J. Müller-Eberhard. "Detection of a neoantigen on human C3bi and C3d by monoclonal antibody." Journal of Immunology 135, no. 3 (September 1, 1985): 2015–19. http://dx.doi.org/10.4049/jimmunol.135.3.2015.
Full textAbstract:
Abstract A neoantigen was detected on human C3bi and C3d by using the monoclonal antibody (MoAb) 130. The antibody bound to EC3bi and EC3d cells but not to EC3b. Although highly purified C3bi or C3d strongly inhibited the binding of the antibody to EC3d, highly purified C3c had no such effect. Native C3, C3b, or C3(H2O) inhibited this binding only weakly. The neoantigen was also detected in serum after activation with zymosan or heat-aggregated IgG, and it was found bound to the aggregated IgG and zymosan particles. Plasma samples from patients with immunologic disorders were tested for this neoantigen, and 25 out of 43 samples tested were found to have levels of neoantigen corresponding to 2 to 11.5% complement activation, whereas 13 out of 14 normal donor plasmas contained amounts of neoantigen indicating much less than 1% complement activation.
6
Kostavasili, I., A. Sahu, H. M. Friedman, R. J. Eisenberg, G. H. Cohen, and J. D. Lambris. "Mechanism of complement inactivation by glycoprotein C of herpes simplex virus." Journal of Immunology 158, no. 4 (February 15, 1997): 1763–71. http://dx.doi.org/10.4049/jimmunol.158.4.1763.
Full textAbstract:
Abstract Glycoprotein C (gC) of both herpes simplex virus type 1 (HSV-1) and HSV-2 interacts with complement C3b and protects the virus from complement-mediated neutralization. To study the mechanism by which gC modulates complement activation, we expressed both gC-1 and gC-2 in a baculovirus expression system. Baculovirus recombinants containing gC genes spanning the entire gC-1 sequence (gC-1-TMR) or only the extracellular domain(s) of gC-1, gC-2, or a deletion mutant of gC-1 lacking residues 33 through 123 were expressed in sf9 insect cells. Binding of the expressed proteins to human C3 and C3 fragments was assessed by direct and competition ELISA. All four expressed proteins bound to C3, C3b, and C3c but not to C3d, suggesting 1) that the binding sites for these proteins are located in the C3c region of C3; and 2) that gC, in contrast to other C3-binding proteins, interacts with native C3. We have also examined the interaction of native C3 with gC-1 expressed on the HSV-1-infected cells. Analogous to recombinant proteins, gC-1 expressed on the infected cells also bound to native C3. The ability of baculovirus-expressed gCs to inhibit the interaction of C3b with its ligands was also analyzed. We found that gC-1, but not gC-2, inhibited the binding of C5 and properdin to C3b and also inhibited the alternative pathway-mediated lysis of rabbit erythrocytes. Inhibition of alternative pathway-mediated lysis and properdin binding to C3b, but not of C5 binding to C3b, required the transmembrane segment of the gC-1. The specificity of gC interactions was examined by studying the interaction of gC with C3 from various species. In contrast to properdin, both gCs bound to cobra C3; this finding suggests that gC-1 and properdin bind to different sites on C3b. Further analyses suggested that gC-1 sterically hindered access of C5 and properdin to C3b.
7
Villiers, Marie-Bernadette, Christian L. Villiers, Anne-Marie Laharie, and Patrice N. Marche. "Amplification of the Antibody Response by C3b Complexed to Antigen Through an Ester Link." Journal of Immunology 162, no. 6 (March 15, 1999): 3647–52. http://dx.doi.org/10.4049/jimmunol.162.6.3647.
Full textAbstract:
Abstract Complement C3 has been described as playing an important role in the cell-mediated immune response. C3b has the capacity to covalently bind Ag and then to stimulate in vitro Ag presentation to T lymphocytes. To verify this observation in vivo, we prepared and purified covalent human C3b-Ag complexes using lysozyme (HEL) as Ag. The characterization of these HEL-C3b complexes indicates that they are representative of those susceptible to be generated in physiological conditions. Mice were immunized with 0.1 to 0.6 μg of either free HEL, HEL + C3b, HEL-C3b, or HEL + CFA. Response was assessed after two i.p. injections by quantification of specific Ab production. Immunization with either HEL-C3b complexes or HEL + CFA leads to anti-HEL IgG production whereas free HEL or HEL + C3b was ineffective. Either HEL-C3b or HEL + CFA immunizations led to a similar Ig subclasse patterns, including IgG1, IgG2a, IgA, and IgM. Our experiments provide the first evidence for modulation of specific Ab response by C3b when it is bound to Ag through a physiological-like link. Taken together with previous data concerning Ab response following recombinant HEL-C3d immunization, cellular events such as processing of C3b-Ag by APC and recognition by T lymphocytes, this present result underlines the importance of C3b and its fragments in stimulation of the immune system, through the multiplicity and complementarity of its interactions.
8
Sahu, Arvind, Stuart N. Isaacs, Athena M. Soulika, and John D. Lambris. "Interaction of Vaccinia Virus Complement Control Protein with Human Complement Proteins: Factor I-Mediated Degradation of C3b to iC3b1 Inactivates the Alternative Complement Pathway." Journal of Immunology 160, no. 11 (June 1, 1998): 5596–604. http://dx.doi.org/10.4049/jimmunol.160.11.5596.
Full textAbstract:
Abstract Vaccinia virus complement control protein (VCP) is a virulence determinant of vaccinia virus that helps protect the virus from the complement attack of the host. To characterize the interaction of VCP with C3 and C4 and understand the mechanism by which VCP inactivates complement, we have expressed VCP in a yeast expression system and compared the biologic activity of the purified protein to that of human factor H and complement receptor 1 (CR1). Recombinant VCP bound to C3 and the proteolytically cleaved form of C3 (C3b), but not to the 135,300-m.w. fragment of C3 generated using elastase (C3c) and the 35,000-m.w. fragment of C3 generated using elastase (C3d) and inhibited both the classical and alternative pathways of complement activation. Although rVCP was less effective at inhibiting the alternative pathway than factor H or CR1, it was more effective than factor H at inhibiting the classical pathway. Unlike factor H, rVCP was unable discriminate between alternative pathway-mediated lysis of rabbit and sheep E. A comparison of the cofactor activity in factor I-mediated cleavage of C3b suggested that in contrast to factor H and CR1, which displayed cofactor activity for the three sites, rVCP displayed cofactor activity primarily for the first site, leading to generation of C3b cleaved by factor I between Arg1281-Ser1282 (iC3b1). Its cofactor activity for C4b cleavages was similar to that of soluble complement receptor type 1. Purification and functional analysis of iC3b1 showed that it was unable to interact with factor B to form the alternative pathway C3 convertase, C3b,Bb. These results suggest that the interaction of VCP with C3 is different from that of factor H and CR1 and that VCP-supported first cleavage of C3b by factor I is sufficient to render C3b nonfunctional.
9
Risitano, Antonio M., Caterina Pascariello, Luigi Del Vecchio, Christopher J. Horvath, Masha Fridkis-Hareli, V. Michael Holers, Margaret A. Lindorfer, and Ronald P. Taylor. "C3-Mediated Extravascular Hemolysis In Paroxysmal Nocturnal Hemoglobinuria: An In Vitro Model to Dissect Complement C3 Activation Comparing the Effects of Complement Inhibitors Eculizumab, 3E7 and TT30 on C3 Fragment Processing and Hemolysis of PNH Erythrocytes." Blood 116, no. 21 (November 19, 2010): 637. http://dx.doi.org/10.1182/blood.v116.21.637.637.
Full textAbstract:
Abstract Abstract 637 PNH is characterized by complement (C)-mediated chronic intravascular hemolysis (IVH) due to the absence of CD55 and CD59 on erythrocytes (E) and subsequent impaired C regulation. C alternative pathway (CAP)-derived normal ongoing low level activity (termed the tickover mechanism) is the pivotal initial step, which subsequently leads to C3 fragment (C3frag) deposition on E followed by membrane attack complex (MAC)-mediated IVH. C3frag processing on E proceeds from the initially covalently attached C3b form that is serially converted through proteolysis, mediated on E by factor I and cofactors factor H and complement receptor 1 (CR1), to iC3b and then to C3d as forms that all remain membrane-bound. To develop an improved mechanistic understanding of this process in PNH, which results in C3frag accumulation and extravascular hemolysis (EVH) in vivo during eculizumab (Ecu) treatment, herein we exploited an in vitro model to characterize and dissect C3frag generation after CAP activation on PNH E. We used monoclonal antibodies (mAbs) specific for the different C3 fragments, including C3b/iC3b (mAbs 2C5, 3C11, 3E7, 7C12 and 8E11) and C3b/iC3b/C3d (mAbs A702, 1H8 and 14A10). We also investigated the effect of the C inhibitors (C-Inh) Ecu, 3E7 (a CAP-inhibitory anti-C3b/iC3b mAb) and TT30 (a cell surface-targeted CAP-inhibitory complement receptor 2/factor H fusion protein) on C3frag accumulation and hemolysis of PNH E. E from PNH patients, either naïve or on Ecu treatment, were washed and incubated in ABO-matched acidified normal human serum (aNHS). Assessment of hemolysis and C3 activation and processing was performed by serial flow cytometry analyses of both intact E and E ghosts, as previously described (Risitano et al, Blood 2009; Lindorfer et al, Blood 2010). We first studied E from PNH patients on Ecu, which were known to be C3frag+ using an anti-C3 polyclonal Ab (pAb). Only the anti-C3b/iC3b/C3d mAbs A702, 1H8 and 14A10 demonstrated binding to these PNH E, with a pattern overlapping with that of the anti-C3 pAb, while the anti-C3b/iC3b mAbs 2C5, 3C11, 3E7, 7C12 and 8E11 did not bind. To investigate the kinetics of generation of specific C3frag on PNH E, fresh E from untreated PNH patients that did not show either membrane-bound C3b/iC3b or C3d were exposed in vitro to aNHSs. Analysis at 1h and 24h revealed that intact E, which remained C3frag-negative, progressively decreased and finally disappeared, being transformed into C3b/iC3b+ and C3d+ ghosts. In the presence of Ecu (using serum from patients on Ecu treatment, drawn within 1h of dosing), the same experiments revealed a dramatic reduction of hemolysis, but residual CAP-mediated hemolysis in a process of pharmacodynamic breakthrough was confirmed by the presence of C3b/iC3b+, C3d+, CD59− E ghosts. More interestingly, intact E showed substantial C3frag deposition which progressed over time, initially characterized by the presence of C3b/iC3b and C3d, and subsequently converting after 24h exclusively into C3d+ E, with an identical phenotype as found in C3frag+ PNH E obtained from patients on Ecu. This result demonstrates that PNH E, despite exhibiting only C3d when recovered from patients, pass through an earlier phase where C3b/iC3b frag are present that can interact with their cognate receptors on fixed cells in liver and spleen during EVH in vivo. Both 3E7 and TT30 completely inhibited hemolysis, with an IC50 of 120 μg/mL for 3E7 and 30 μg/mL for TT30; consistent with their mechanism of action, both 3E7 and TT30 bound to PNH RBCs. No C3b/iC3b nor C3d was detected on surviving PNH E at any time, indicating that 3E7 and TT30 effectively inhibit the earliest phases of CAP activation involved in EVH. Similar results were obtained when E from PNH patients on Ecu were challenged in vitro with aNHS in the presence or absence of C-Inh. In conclusion, we demonstrate that CAP-mediated C3b/iC3b fixation to PNH RBCs is the early event leading to IVH or, in presence of Ecu, to C3frag deposition and subsequent EVH in vivo. Unlike Ecu, use of 3E7 or TT30 resulted in complete inhibition of hemolysis as well as CAP-mediated C3 activation, preventing C3b/iC3b and C3d deposition on intact PNH E. Thus, use of this model will allow assessment of the roles of both endogenous and therapeutic C regulators in CAP activation and C3 processing (and subsequent EVH) in PNH. Preclinical data suggest that TT30 is an optimal candidate agent to assess in vivo the effect of CAP inhibition in PNH patients. Disclosures: Risitano: Taligen Therapeutics: Consultancy, Research Funding. Horvath:Taligen Therapeutics: Employment. Fridkis-Hareli:Taligen Therapeutics: Employment. Holers:Taligen Therapeutics: Employment, Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties.
10
Kaidoh, T., and I. Gigli. "Phylogeny of C4b-C3b cleaving activity: similar fragmentation patterns of human C4b and C3b produced by lower animals." Journal of Immunology 139, no. 1 (July 1, 1987): 194–201. http://dx.doi.org/10.4049/jimmunol.139.1.194.
Full textAbstract:
Abstract Functional and structural studies of the activated proteins of the complement system C4b and C3b have led to the identification of cleavage products resulting from the effect of the regulatory proteins, factor I, H, and C4b binding protein (bp). In this paper we report the results of studies that investigated the capacity of plasma or serum from a wide range of phylogenetic species to yield similar cleavage products. Sera and plasma from mammals, reptiles, amphibia, and fishes are capable of cleaving fluid phase human C4b and C3b, generating apparently the same fragments as observed using normal human serum: alpha 2, alpha 3, alpha 4 from the alpha' chain of C4b: and alpha-68, alpha-46, alpha-43, and alpha-30 from the alpha' chain of C3b. When C3b bound to a cell membrane is used C3c and C3dg are generated. The generation of these fragments from C3bi is a dose-dependent reaction. There is no correlation between the evolution of the species and the quantitative capability to degrade the substrates. Birds possess only a limited capability to degrade the alpha' chain of C4b and have no cleaving activity for C3b, whereas sera from more primitive vertebrate species (chondrichthyes and agnatha) fail to participate in the reaction. Contrary to other species, the proteins in fish serum or plasma responsible for the degradation of C4b and C3b show a unique requirement for Ca2+ ions. Magnesium and barium are less effective, and in their presence a 65,000 dalton intermediate product is observed. These results demonstrate that protein(s) displaying proteolytic activity for products of complement activation, probably related to I, H, and C4bp, are present in plasma of species whose evolution have preceded humans by 300 million years. Moreover, the recognition of human substrates and the generation of fragments identical to those produced by human serum suggests that human C4b and C3b share structural characteristics with their evolutionary ancestors in the serum or plasma of the species studied.
11
Seya, T., and J. P. Atkinson. "Functional properties of membrane cofactor protein of complement." Biochemical Journal 264, no. 2 (December 1, 1989): 581–88. http://dx.doi.org/10.1042/bj2640581.
Full textAbstract:
Membrane cofactor protein (MCP or gp45-70) of the complement system is a cofactor for factor I-mediated cleavage of fluid-phase C3b and C3b-like C3, which opens the thioester bond. In the present study the activity of MCP was further characterized. Unexpectedly, in the absence of factor I, MCP stabilized the alternative- and, to a lesser extent, the classical-pathway cell-bound C3 convertases and thereby enhanced C3b deposition. Soluble MCP, if added exogenously, hardly functioned as cofactor for the cleavage of erythrocyte-bound C3b to iC3b; i.e. its activity, compared with the cofactor activity of factor H, was inefficient, since less than 10% of the bound C3b was MCP-sensitive. Further, exogenously added soluble MCP was also a weak cofactor for the cleavage of C3b bound to zymosan. Likewise, factor I, in the presence of cells bearing MCP, cleaved fluid-phase C3b inefficiently. These results imply that MCP has very little extrinsic cofactor activity for factor I. In contrast, exogenously added MCP and factor I mediated efficient cleavage of erythrocyte-bound C3b if the concentration of Nonidet P40 was sufficient to solubilize the cells. Interestingly, soluble MCP and factor I degraded C3b attached to certain solubilized acceptor membrane molecules more readily than others. The cleavage reaction of fluid-phase and cell-bound C3b by soluble MCP and factor I produced iC3b, but no C3c and C3dg. These and prior data indicate that soluble MCP has potent cofactor activity for fluid-phase C3b or C3b bound to solubilized molecules, but acts inefficiently towards C3b on other cells. This functional profile is unique for a C3b/C4b binding protein and, taken together with its wide tissue distribution, suggests an important role for MCP in the regulation of the complement system.
12
Almajhdi, Fahad N. "Hemagglutinin-Neuraminidase Gene Sequence-Based Reclassification of Human Parainfluenza Virus 3 Variants." Intervirology 58, no. 1 (2015): 35–40. http://dx.doi.org/10.1159/000369208.
Full textAbstract:
The most comprehensive phylogenetic classification of human parainfluenza virus 3 (HPIV-3) was recently developed [PLoS One 2012;7:e43893]. This classification included three distinct clusters (A, B and C) with subdivision of cluster C into four subclusters (C1-4). In the present report, the classification of HPIV-3 was refined by inclusion of 27 overlooked beside newly characterized Saudi variants. The new phylogram was developed and included the same clusters described before, in which cluster A remained unchanged and cluster B contained more recent isolates. The organization of cluster C was altered through inclusion of a new subcluster (C5), subdivision of C1 into two lineages C1a and C1b and subdivision of C3 into three lineages C3a, C3b and C3c. The majority of Saudi variants were classified as members of subcluster C1b, whereas only one variant was placed in each of subclusters C2 and C5. This study illustrates an up-to-date phylogenetic classification of HPIV-3 variants.
13
Currie, MS, PK Rustagi, R. Wojcieszak, L. Ziolkowski, GD Ross, and GL Logue. "Effect of antigen site and complement receptor status on the rate of cleavage of C3c antigen from red cell bound C3b." Blood 71, no. 3 (March 1, 1988): 786–90. http://dx.doi.org/10.1182/blood.v71.3.786.786.
Full textAbstract:
Abstract C3b was bound to human red cells when serum complement was activated by addition of antibodies directed against different red cell antigens, and the rate of cleavage to C3dg was determined by assay for loss of bound C3c antigens using radiolabeled monoclonal anti-C3c. When C3b was bound by antibodies to antigens on branched-chain glycoproteins, cleavage to C3dg occurred more rapidly than when C3b was bound by antibodies to antigens closer to the red cell lipid bilayer. The rate of cleavage to C3dg also correlated directly with the number of complement receptors (CR1) per red cell, reflecting their role as cofactors in the cleavage of iC3b by factor I. Thus, the life span of C3b/iC3b on human red cells, which may be important for determining the rate and mechanism of clearance of C3-coated red cells, appears to depend on the CR1 status of the red cells and the characteristics of the antigen sites around which complement is bound.
14
Currie, MS, PK Rustagi, R. Wojcieszak, L. Ziolkowski, GD Ross, and GL Logue. "Effect of antigen site and complement receptor status on the rate of cleavage of C3c antigen from red cell bound C3b." Blood 71, no. 3 (March 1, 1988): 786–90. http://dx.doi.org/10.1182/blood.v71.3.786.bloodjournal713786.
Full textAbstract:
C3b was bound to human red cells when serum complement was activated by addition of antibodies directed against different red cell antigens, and the rate of cleavage to C3dg was determined by assay for loss of bound C3c antigens using radiolabeled monoclonal anti-C3c. When C3b was bound by antibodies to antigens on branched-chain glycoproteins, cleavage to C3dg occurred more rapidly than when C3b was bound by antibodies to antigens closer to the red cell lipid bilayer. The rate of cleavage to C3dg also correlated directly with the number of complement receptors (CR1) per red cell, reflecting their role as cofactors in the cleavage of iC3b by factor I. Thus, the life span of C3b/iC3b on human red cells, which may be important for determining the rate and mechanism of clearance of C3-coated red cells, appears to depend on the CR1 status of the red cells and the characteristics of the antigen sites around which complement is bound.
15
Devaux, Patricia, Dale Christiansen, Sébastien Plumet, and Denis Gerlier. "Cell surface activation of the alternative complement pathway by the fusion protein of measles virus." Journal of General Virology 85, no. 6 (June 1, 2004): 1665–73. http://dx.doi.org/10.1099/vir.0.79880-0.
Full textAbstract:
Measles virus (MV)-infected cells are activators of the alternative human complement pathway, resulting in high deposition of C3b on the cell surface. Activation was observed independent of whether CD46 was used as a cellular receptor and did not correlate with CD46 down-regulation. The virus itself was an activator of the alternative pathway and was covered by C3b/C3bi, resulting in some loss in infectivity without loss of virus binding to target cells. The cell surface expression of MV fusion (F), but not haemagglutinin, envelope protein resulted in complement activation of the Factor B-dependent alternative pathway in a dose-dependent manner and F–C3b complexes were formed. The underlying activation mechanism was not related to any decrease in cell surface expression of the complement regulators CD46 and CD55. The C3b/C3bi coating of MV-infected cells and virus should ensure enhanced targeting of MV antigens to the immune system, through binding to complement receptors.
16
Hack, C. E., J. Paardekooper, R. J. Smeenk, J. Abbink, A. J. Eerenberg, and J. H. Nuijens. "Disruption of the internal thioester bond in the third component of complement (C3) results in the exposure of neodeterminants also present on activation products of C3. An analysis with monoclonal antibodies." Journal of Immunology 141, no. 5 (September 1, 1988): 1602–9. http://dx.doi.org/10.4049/jimmunol.141.5.1602.
Full textAbstract:
Abstract Hydrolysis of the internal thioester bond in native C3 is thought to be a key event in initiating the alternative pathway of C activation, because the resulting C3(H2O) acquires "C3b-like" properties. Therefore, disruption of the internal thioester bond is probably accompanied by conformational changes in the C3 molecule. In this study, we demonstrate that such conformational changes indeed occur; 7 of the 19 mAb raised against C3 or C3 activation products recognized epitopes exposed on C3(H2O) but not on native C3. One of these epitopes is located on the C3a part, three on the C3c part, and another three on the C3d,g part. Because the 7 mAb bound equally well to C3 incubated either with MgCl2 or with methylamine (which primarily disrupts the thioester), the conformational changes detected by the mAb apparently occur after disruption of the thioester. Furthermore, the epitopes were also present on the corresponding C3 activation products. Immunoblotting experiments revealed that the epitopes for the three anti-C3d,g mAb were located on the C3d part, C-terminal to the thioester. The epitopes for 2 of the 3 anti-C3c mAb were located on the C-terminal alpha-chain fragment of C3c. Thus, this study provides immunochemical evidence for the biologic resemblance between C3(H2O) and C3 activation products. Implications of these findings for the activation process of C3 are discussed.
17
Ekdahl, K. N., U. R. Nilsson, and B. Nilsson. "Inhibition of factor I by diisopropylfluorophosphate. Evidence of conformational changes in factor I induced by C3b and additional studies on the specificity of factor I." Journal of Immunology 144, no. 11 (June 1, 1990): 4269–74. http://dx.doi.org/10.4049/jimmunol.144.11.4269.
Full textAbstract:
Abstract The factor I-mediated cleavage of C3b, using factor H as a cofactor was completely inhibited by diisopropylfluorophosphate (DFP) when factor I and C3b were incubated with DFP before the addition of factor H. Inhibition, although to a lesser degree, was observed when factor H was present during DFP-exposure. No inhibition in factor I activity was seen when factor I and H were incubated with DFP either alone or together. It was also demonstrated that the 38-kDa subunit of factor I bound radiolabeled DFP when factor I and C3b together were exposed to DFP. These observations suggest that factor I interacts with C3b in a manner that exposes its catalytic site to DFP, an interaction that is independent of factor H. The inhibitory effect by DFP on factor I led us to further investigate the factor I cleavage products of iC3b, inasmuch as previous reports were ambiguous as to whether digestion occurs in the presence of DFP. Digestion of C3b bound to activated thiol Sepharose (ATS-C3b) in the presence of factor H at low pH and ionic strength and in serum by complement activation produced C3d,g-like fragments with apparent molecular mass of 41 and 43 kDa. These fragments were shown to have three different N-terminal and two different C-terminal ends. The major fragments had N-terminal sequences starting with Glu933, as shown by sequence determination. Traces of fragments extending beyond this point were also found, shown by Western blot analysis using a panel of mAb previously shown to bind to epitopes exposed within a region of C3 spanning residues 929 to 943, as well as a shorter fragment starting with Glu938. When digestion of C3b is carried out in the presence of DFP, the factor I level necessary for digestion is elevated and may explain how the first two cleavages producing iC3b but not the following giving C3d,g, can occur. The finding of several factor I cleavage sites in the C3d,g region of C3 demonstrates that factor I has a broad specificity, mainly for arginyl bonds. It has also been shown to digest a lysyl bond exposed in ATS-bound C3b.
18
Manthei, U., M. W. Nickells, S. H. Barnes, L. L. Ballard, W. Y. Cui, and J. P. Atkinson. "Identification of a C3b/iC3 binding protein of rabbit platelets and leukocytes. A CR1-like candidate for the immune adherence receptor." Journal of Immunology 140, no. 4 (February 15, 1988): 1228–35. http://dx.doi.org/10.4049/jimmunol.140.4.1228.
Full textAbstract:
Abstract Immune adherence is the attachment of C-bearing immune complexes via the major activation fragment of the third component of C(C3b) to C3b binding membrane proteins. On primate E, the C3b-R, termed CR1, mediates immune adherence. In nonprimates, immune adherence involves platelets instead of E. However, these functional data have not been corroborated by the identification of the binding protein. In this work, we have identified a C3b/iC3 binding protein of rabbit platelets and characterized it as a single chain structure with a Mr of 150 kDa (nonreducing) or 175 kDa (reducing). This protein binds to rabbit iC3 or C3b but not C3d. This specificity of binding and the ability to rebind to a second column of iC3- or C3b-thiol-Sepharose are comparable to human CR1. Also, a molecule with the identical Mr as well as other structural and binding characteristics is present on rabbit PBMC. No such protein was isolated from rabbit E. Our data strongly suggest that the C3b/iC3 binding protein of rabbit platelets is the homologue of human CR1. If so, this represents an interesting evolutionary switch in the tissue specific expression of the immune adherence R from platelets in the nonprimate to E in the primate.
19
Lutz, HU, P. Stammler, E. Jelezarova, M. Nater, and PJ Spath. "High doses of immunoglobulin G attenuate immune aggregate-mediated complement activation by enhancing physiologic cleavage of C3b in C3bn- IgG complexes." Blood 88, no. 1 (July 1, 1996): 184–93. http://dx.doi.org/10.1182/blood.v88.1.184.184.
Full textAbstract:
Abstract Intravenously applied human IgG has beneficial effects in treating inflammatory diseases, presumably because it has a complement attenuating role. This role of IgG was studied in vitro by following C3 activation and inactivation in sera that were supplemented with exogenous human IgG and incubated with immune aggregates. IgG added at 2 to 10 mg/mL stimulated the physiologic inactivation of C3b-containing complexes twofold to threefold in 20% sera. This, in turn, lowered the overall C3 activation by 28%, as new C3 convertases primarily assembled on C3b-containing complexes. Exogenous IgG (5 mg/mL) also stimulated inactivation of purified C3b2-IgG complexes, whereby their half-life dropped from 3–4 to 1.5 minutes in 20% serum. IgG appeared to act like a modulator of factor H and I because it did not stimulate inactivation of C3b-containing complexes in factor I-deficient serum. Thus, the known partial protection of C3bn-IgG complexes from inactivation by factor H and I was downregulated by high concentrations of IgG. The ability of high doses of IgG to stimulate complement inactivation is a novel regulatory role of IgG. This may be one of the molecular principles for its therapeutic efficacy in treating complement-mediated inflammations.
20
Lutz, HU, P. Stammler, E. Jelezarova, M. Nater, and PJ Spath. "High doses of immunoglobulin G attenuate immune aggregate-mediated complement activation by enhancing physiologic cleavage of C3b in C3bn- IgG complexes." Blood 88, no. 1 (July 1, 1996): 184–93. http://dx.doi.org/10.1182/blood.v88.1.184.bloodjournal881184.
Full textAbstract:
Intravenously applied human IgG has beneficial effects in treating inflammatory diseases, presumably because it has a complement attenuating role. This role of IgG was studied in vitro by following C3 activation and inactivation in sera that were supplemented with exogenous human IgG and incubated with immune aggregates. IgG added at 2 to 10 mg/mL stimulated the physiologic inactivation of C3b-containing complexes twofold to threefold in 20% sera. This, in turn, lowered the overall C3 activation by 28%, as new C3 convertases primarily assembled on C3b-containing complexes. Exogenous IgG (5 mg/mL) also stimulated inactivation of purified C3b2-IgG complexes, whereby their half-life dropped from 3–4 to 1.5 minutes in 20% serum. IgG appeared to act like a modulator of factor H and I because it did not stimulate inactivation of C3b-containing complexes in factor I-deficient serum. Thus, the known partial protection of C3bn-IgG complexes from inactivation by factor H and I was downregulated by high concentrations of IgG. The ability of high doses of IgG to stimulate complement inactivation is a novel regulatory role of IgG. This may be one of the molecular principles for its therapeutic efficacy in treating complement-mediated inflammations.
21
Ekdahl, K. N., and B. Nilsson. "Phosphorylation of complement component C3 and C3 fragments by a human platelet protein kinase. Inhibition of factor I-mediated cleavage of C3b." Journal of Immunology 154, no. 12 (June 15, 1995): 6502–10. http://dx.doi.org/10.4049/jimmunol.154.12.6502.
Full textAbstract:
Abstract Phosphorylation of C3 in vitro has been shown previously to lead to significantly altered function of the protein. Platelets are known to contain and release considerable amounts of protein kinases and ATP, which are prerequisites for protein phosphorylation. The aim of the present study was to investigate whether C3 is phosphorylated extracellularly by human platelets. Platelet-rich plasma was stimulated by human aggregated gamma-globulin or ADP. The remaining cells were removed by centrifugation, and the plasma was incubated with [gamma-32P]ATP. After precipitation with Sepharose-bound Abs to C3c followed by SDS-PAGE, it was shown that C3 was phosphorylated in the alpha-chain by a protein kinase dependent on Mn2+, Ca2+, or Mg2+ ions. The supernatant from washed, activated platelets was incubated with purified C3 or soluble or activated thiol Sepharose-bound C3b, together with [gamma-32P]ATP. Phosphorylation was seen in the alpha-chain of C3, and to the same extent in the alpha'-chain of both C3b preparations. The analysis of acid hydrolysate demonstrated that C3 contained 32P-labeled Thr and 32P-labeled Ser. After extensive proteolysis with trypsin, the major phosphorylation site was located to a peptide of 3 to 4 kDa that was bound to the activated thiol Sepharose via the free sulphydryl group in the C3d fragment. Incubation of phosphorylated C3b with factors I and H showed that phosphorylation inhibited the cleavage of the alpha'-chain of C3b. The results in this study suggest that phosphorylation is a regulator of C3 during platelet activation induced, for example, by immune complexes.
22
JELEZAROVA, Emiliana, Anna VOGT, and Hans U. LUTZ. "Interaction of C3b2–IgG complexes with complement proteins properdin, factor B and factor H: implications for amplification." Biochemical Journal 349, no. 1 (June 26, 2000): 217–23. http://dx.doi.org/10.1042/bj3490217.
Full textAbstract:
Nascent C3b can form ester bonds with various target molecules on the cell surface and in the fluid phase. Previously, we showed that C3b2-IgG complexes represent the major covalent product of C3 activation in serum [Lutz, Stammler, Jelezarova, Nater and Späth (1996) Blood 88, 184-193]. In the present report, binding of alternative pathway proteins to purified C3b2-IgG complexes was studied in the fluid phase by using biotinylated IgG for C3b2-IgG generation and avidin-coated plates to capture complexes. Up to seven moles of properdin ‘monomer’ bound per mole of C3b2-IgG at physiological conditions in the absence of any other complement protein. At low properdin/C3b2-IgG ratios bivalent binding was preferred. Neither factor H nor factor B affected properdin binding. On the other hand, properdin strongly stimulated factor B binding. Interactions of all three proteins with C3b2-IgG exhibited pH optima. An ionic strength optimum was most pronounced for properdin, while factor B binding was largely independent of the salt concentration. C3b2-IgG complexes were powerful precursors of the alternative pathway C3 convertase. In the presence of properdin, C3 convertase generated from C3b2-IgG cleaved about sevenfold more C3 than the enzyme generated on C3b. C3b2-IgG complexes could therefore maintain the amplification loop of complement longer than free C3b.
23
Mishra, Meenu, Adam Ressler, Larry S. Schlesinger, and Daniel J. Wozniak. "Identification of OprF as a Complement Component C3 Binding Acceptor Molecule on the Surface of Pseudomonas aeruginosa." Infection and Immunity 83, no. 8 (May 11, 2015): 3006–14. http://dx.doi.org/10.1128/iai.00081-15.
Full textAbstract:
Pseudomonas aeruginosais a versatile opportunistic pathogen that can cause devastating persistent infections. Complement is a highly conserved pathway of the innate immune system, and its role in the first line of defense against pathogens is widely appreciated. One of the earliest events in the complement cascade is the conversion of C3 to C3a and C3b, the latter typically binds to one or more acceptor molecules on the pathogen surface. We previously demonstrated that complement C3b binding acceptors exist on theP. aeruginosasurface. In the current study, we utilized either C3 polyclonal or C3b monoclonal antibodies in a far-Western technique followed by mass spectroscopy to identify the C3b acceptor molecule(s) on theP. aeruginosasurface. Our data provide evidence that OprF (an outer membrane porin, highly conserved in thePseudomonadaceae) binds C3b. AnoprF-deficientP. aeruginosastrain exhibits reduced C3 deposition compared to the wild type. We observed reduced internalization ofoprF-deficient bacteria by neutrophils after opsonization compared with wild-typeP. aeruginosa. Heterologous expression of OprF significantly enhanced C3b binding and increased serum-mediated bactericidal effects in complement-susceptibleEscherichia coli. Furthermore, the predicted secondary structure of the C-terminal, surface-exposed region of OprF has high structural identity to the OmpA domain of several other Gram-negative bacteria, one of which is known to bind C3b. Therefore, these findings provide new insights into the biology of complement interactions withP. aeruginosaand other Gram-negative bacteria.
24
Quigg, R. J., and V. M. Holers. "Characterization of rat complement receptors and regulatory proteins. CR2 and Crry are conserved, and the C3b receptor of neutrophils and platelets is distinct from CR1." Journal of Immunology 155, no. 3 (August 1, 1995): 1481–88. http://dx.doi.org/10.4049/jimmunol.155.3.1481.
Full textAbstract:
Abstract In the mouse, CR1 and CR2 on B lymphocytes are encoded by alternatively spliced Cr2 gene transcripts. Immune adherence receptors that bind C3b are present on mouse platelets and unstimulated neutrophils, but they are not CR1. In this study, rabbit anti-mouse CR1/CR2 Ab immunoprecipitated a 145- to 150-kDa CR2 protein from rat platelets, neutrophils, and splenocytes, but not a approximately 200-kDa CR1 protein. By Northern analysis, cDNA for mouse CR2 hybridized to mRNA of 3.7 and 5.2 kb from both mouse and rat splenocytes. The murine decay-accelerating factor and membrane cofactor protein analogue Crry was present in rat platelets, neutrophils, E, and splenocytes as two distinct proteins of 65 to 70 kDa and 75 to 85 kDa. Rat platelets, neutrophils, and splenocytes contained a novel 200-kDa cell membrane protein that specifically bound to a rat C3b-Sepharose column. We have named this protein C3bR-200. C3bR-200 was not identified by anti-mouse CR1/CR2 or anti-human CR1 Ab. Rat E lacked C3bR-200. Rat neutrophils and splenocytes also contained an 80-kDa C3b-binding protein that was distinct from Crry, which we have named C3bR-80. Therefore, CR2 and Crry are present in the rat, and have similar qualities to those from the mouse, except that CR2 is located on rat platelets and neutrophils, which is not the case in the mouse. Rat platelets, neutrophils, and splenocytes have a 200-kDa C3b-binding protein, C3bR-200, that is likely to be the rodent immune adherence receptor.
25
Edberg, J. C., L. Tosic, E. L. Wright, W. M. Sutherland, and R. P. Taylor. "Quantitative analyses of the relationship between C3 consumption, C3b capture, and immune adherence of complement-fixing antibody/DNA immune complexes." Journal of Immunology 141, no. 12 (December 15, 1988): 4258–65. http://dx.doi.org/10.4049/jimmunol.141.12.4258.
Full textAbstract:
Abstract We have studied the turnover of the third component of C (C3) and capture of the major cleavage fragment of C3 produced during C activation (C3b) that occurs when soluble antibody/DNA immune complexes (IC) active C. We used the Amersham RIA kit for the minor cleavage fragment of C3 produced during C activation (C3a), and a new assay utilizing mAb to C3b to measure the fraction of active C3 in a C source after the IC activate C. These mAb, along with a mAb to human IgG, allowed us to measure IC stoichiometries. The efficiency of C3 turnover by the IC is quite high, and under conditions of Ab excess, the maximum number of IgG bound per dsDNA corresponds to 1 IgG/20 to 30 base pairs. The maximum number of C3b found in the IC corresponds to less than 1 C3b/IgG, and the vast majority of the captured C3b is bound to the IgG, and not to the DNA. We identified several IC that consumed large amounts of C3, and captured large amounts of C3b, but did not bind to human E via C3b receptors (C receptor type 1). This finding suggests that the ability of IC to bind to human E depends upon the number and distribution of captured C3b molecules and the conformation and size of the DNA Ag, which reflects the need for multivalent binding between several properly arrayed C3b and a "cluster" of C receptor type 1 on the human E membrane. IC that activate C3 but do not bind to E would presumably "escape" the E IC clearance mechanism, but could deposit in susceptible organs and tissues and play a role in the pathogenesis of SLE because of their potential to generate the inflammatory products of C activation.
26
Panneerselvam, M., S. Welt, L. J. Old, and C. W. Vogel. "A molecular mechanism of complement resistance of human melanoma cells." Journal of Immunology 136, no. 7 (April 1, 1986): 2534–41. http://dx.doi.org/10.4049/jimmunol.136.7.2534.
Full textAbstract:
Abstract The susceptibility of human melanoma cells to lysis by human complement after sensitization with the R24 murine IgG3 monoclonal antibody to the GD3 ganglioside antigen was investigated. It was found that the melanoma cell lines were either susceptible (greater than or equal to 70% cytotoxicity) or resistant (less than or equal to 30% cytotoxicity) to complement-mediated killing. We determined the kinetics of binding of C3 to and its subsequent fate on the melanoma cells. We found that on susceptible cell lines, maximal binding of C3 occurred within 10 min of incubation. At that time, approximately 90% of the bound C3 was in the form of C3b. During the subsequent incubation, the C3b was slowly inactivated, apparently generating the physiologic degradation products iC3b, C3dg, and C3d. However, this degradation of C3b could be inhibited without affecting the final degree of cytotoxicity, indicating that it is of no apparent consequence for the killing of susceptible melanoma cells. Very different results were obtained with resistant melanoma cells. Bound C3b was rapidly inactivated, and C3d was the predominant form of C3 on resistant cells throughout the incubation. Therefore, rapid inactivation of C3b was identified as a protective mechanism of human melanoma cells against complement attack. In addition, we found that resistance to complement is not an inherent property of the cells but depends on the antibody used for sensitization, because the resistant cell lines could be lysed after sensitization with polyclonal antiserum.
27
Molina, H., T. Kinoshita, C. B. Webster, and V. M. Holers. "Analysis of C3b/C3d binding sites and factor I cofactor regions within mouse complement receptors 1 and 2." Journal of Immunology 153, no. 2 (July 15, 1994): 789–95. http://dx.doi.org/10.4049/jimmunol.153.2.789.
Full textAbstract:
Abstract Human and murine CR1 and CR2 are defined as evolutionary homologues on the basis of their in vitro activities and a shared structural motif known as a short consensus repeat (SCR). To identify additional similarities between the two species, we analyzed the functional domains within the mouse receptors by constructing mouse-human chimeric cDNAs in which the C3 binding site of human CR2 has been replaced by different regions within the first eight SCRs of mouse CR1. Rosette analysis of cells expressing chimeric proteins, with erythrocytes bearing different mouse C3 fragments, coupled with rosette inhibition studies using specific anti-mouse CR1/CR2 mAbs reveal a weak C3b binding site within SCRs 1 and 2 of mouse CR1. There is no independent C3b interacting domain within SCRs 3 to 6, but their presence enhances C3 binding. A molecule that contains only the first six SCRs of mouse CR1 also binds C3b, but with less efficiency. There is no C3d binding area within the first six SCRs, but our data confirms previous studies indicating an additional C3b/C3d binding region within SCRs 7 and 8 of mouse CR1 (SCRs 1-2 of mouse CR2). The presence of SCRs 1 to 4 is required for C3 cofactor activity. 8C12, a mAb which blocks C3b erythrocyte rosette binding and the C3 cofactor activity of mouse CR1, binds only to chimeras containing SCRs 3 to 4.(ABSTRACT TRUNCATED AT 250 WORDS)
28
Kinoshita, T., S. Lavoie, and V. Nussenzweig. "Regulatory proteins for the activated third and fourth components of complement (C3b and C4b) in mice. II. Identification and properties of complement receptor type 1 (CR1)." Journal of Immunology 134, no. 4 (April 1, 1985): 2564–70. http://dx.doi.org/10.4049/jimmunol.134.4.2564.
Full textAbstract:
Abstract We identified on the membrane of mouse spleen cells a polypeptide of Mr 190,000 (S190), with binding affinity for the mouse third component of the complement system (C3). S190, purified by affinity chromatography on C3-Sepharose, has properties resembling those of the human C3 receptor type 1 (CR1). Thus, S190, like CR1, served as a cofactor for the C3b inactivator (I)-mediated cleavage of fluid-phase C3b into iC3b, and had cofactor activity comparable to that of serum factor H (H). S190 also acted as a cofactor for the cleavages of membrane-bound C3b or membrane-bound iC3b into C3c (Mr 140,000) and C3dg (Mr 40,000) by serum factor I. As is the case with CR1, the specific activity of S190 for the cleavages leading to C3c-C3dg formation was approximately 100-fold greater than that of H. We therefore conclude that S190 and CR1 are analogous proteins.
29
Bieber, T., D. Hanau, E. Heid, and M. D. Kazatchkine. "Histiocytosis-X cells express C3b, C3d, and C3bi receptor (CR1, CR2, and CR3) antigens." Archives of Dermatological Research 277, no. 6 (1985): 496–98. http://dx.doi.org/10.1007/bf00510069.
Full text
30
Birmingham, D. J., and F. G. Cosio. "Characterization of the baboon erythrocyte C3b-binding protein." Journal of Immunology 142, no. 9 (May 1, 1989): 3140–44. http://dx.doi.org/10.4049/jimmunol.142.9.3140.
Full textAbstract:
Abstract E from primates demonstrate type 1 CR (CR1) with binding specificities for C3b and C4b. In the present study we characterized the E C3b-binding protein of baboons. We showed that three out of four mouse mAb and one polyclonal antiserum, raised against human E CR1, cross-reacted with baboon E. In addition, one anti-human CR1 mAb (1B4) and a polyclonal anti-human CR1 inhibited the binding of C3b opsonized immune complexes to baboon E. Finally, a mAb to human CR1 (E11) recognized epitopes on E of a variety of nonhuman primates, including baboons. SDS-PAGE analysis of biochemically purified baboon E membrane fractions reactive with E11 demonstrated a 65-kDa protein as a major component. Affinity absorption and elution experiments verified this protein to be E11 reactive as well as a C3b binding protein. E surface radiolabeling, followed by C3i affinity purification, confirmed that this 65-kDa protein is the only C3b-binding protein present on the baboon E membrane. We postulate that the baboon E 65-kDa protein is the equivalent of the human E CR1. In addition, there appear to be antigenic similarities between the baboon E 65-kDa protein and the human E CR1.
31
Umnyakova, E. S., I. A. Krenev, S. V. Legkovoy, A. V. Sokolov, O. N. Rogacheva, T. V. Ovchinnikova, V. N. Kokryakov, and M. N. Berlov. "THE INTERACTION OF ARENICIN-1 WITH C3B COMPLEMENT PROTEIN." Medical academic journal 19, no. 1S (December 15, 2019): 187–88. http://dx.doi.org/10.17816/maj191s1187-188.
Full textAbstract:
The complement system and antimicrobial peptides (AMPs) are known to be vital humoral factors of innate immunity. Earlier we showed the double-sided influence of arenicin-1 (Ar-1), the AMP from a sea polychaeta Arenicola marina, on the complement activation. In this work we studied the binding of Ar-1 to C3b protein, the fragment of the central complement component C3, using surface plasmon resonance. We also performed molecular docking and molecular dynamics of interaction between C3b fragment - C3c - and Ar-1. All these data showed that the influence of Ar-1 on complement activation might be realized through the interaction with C3b, the most important component for complement activation. Ar-1 may be used for the design of new complement regulators for treating complement-related diseases.
32
Newman, S. L., and L. K. Mikus. "Deposition of C3b and iC3b onto particulate activators of the human complement system. Quantitation with monoclonal antibodies to human C3." Journal of Experimental Medicine 161, no. 6 (June 1, 1985): 1414–31. http://dx.doi.org/10.1084/jem.161.6.1414.
Full textAbstract:
Monoclonal antibodies were used to determine the number and molecular form of C3 bound to particulate activators of the complement (C) system by human serum. Sheep erythrocytes (E) coated with IgM (EIgM) and IgG (EIgG) were used to study activation of the classical pathway (CP). Yeast (Y), rabbit erythrocytes (ER), and five species of bacteria (Escherichia coli, Staphylococcus aureus, Streptococcus pneumoniae type 3, Streptococcus pyogenes, and Hemophilus influenzae type b) were used to study activation of the alternative pathway (AP). The deposition of C3b onto EIgM and EIgG incubated in C7-deficient human serum was dependent on the serum concentration. At all serum concentrations tested, there was complete conversion of C3b to iC3b. Kinetic analysis of C3b deposition and conversion to iC3b indicated that these events occurred almost simultaneously; the reaction was completed by 15 min. The deposition of C3 onto the AP activators ER and Y was also dependent on serum concentration, and ER, but not Y, required the presence of Mg-EGTA and thus the activation of only the AP. C3b deposition and conversion to iC3b on Y was complete in 15 min, with 82% of bound C3 converted to iC3b. For ER, maximum C3 deposition required 30 min in both the presence and absence of Mg-EGTA. However, after 1 h of incubation, 74% of bound C2 was iC3b in the absence of Mg-EGTA, compared with only 52% in the presence of Mg-EGTA. Thus, even on AP activators, a large portion of C3b may be converted to iC3b, and this conversion is probably controlled by elements on the particle's surface. Studies with the five species of bacteria yielded similar results. Approximately 3-5 X 10(4) molecules of C3 were bound per microorganism, with opsonization being completed in 30 min. Remarkably, only 16-28% of bound C3 was in the form of iC3b, even after 2 h of incubation. The presence or absence of Mg-EGTA, or the addition of purified CR1 to the reaction mixture, did not significantly effect the ratio of C3b to iC3b. Finally, SDS-PAGE and autoradiography of particle-bound 125I-C3 fragments confirmed that there was no conversion of iC3b to C3d,g or C3d. The data obtained about the opsonization of bacteria suggest that the predominant form of C3 that is encountered by inflammatory phagocytes may be C3b.
33
Peterson, Erica A., Jonathan H. Foley, Michael J. Krisinger, and Edward Conway. "Plasmin Cleaves Complement iC3b, Preventing CR3/4 Mediated Phagocytosis By Macrophages." Blood 122, no. 21 (November 15, 2013): 1105. http://dx.doi.org/10.1182/blood.v122.21.1105.1105.
Full textAbstract:
Abstract Introduction The plasmin(ogen) and complement systems are activated at sites of tissue injury and are involved in hemostasis, wound healing, inflammation and immune surveillance. Although the mechanisms are poorly understood, dysregulation of these systems underlie the pathogenesis and progression of inflammatory and vascular diseases. We aimed to characterize the relevant molecular interactions between the plasmin(ogen) and complement pathways. The three complement pathways converge with formation of C3-convertases that cleave C3 into C3a and C3b. C3a is liberated as an anaphylatoxin while C3b participates in further formation of the C3 and C5 convertases, thereby amplifying complement activation. To dampen the system, negative regulatory mechanisms exist. C3b is degraded to iC3b by the factor I (FI)/FH complex, which in turn is degraded to C3dg by the FI/complement receptor 1 (CR1) complex. iC3b and C3dg induce cellular responses by binding to complement receptors CR3 / CR4 / CR2, and CR2, respectively. Interactions of iC3b with CR3 or CR4 induce phagocytosis by macrophages, and binding of iC3b or C3dg to CR2 promotes B-cell responses. Recent studies show that plasmin proteolyses C3b and iC3b. We further characterized the plasmin cleavage sites in iC3b and evaluated the functional consequences in vitro. Methods and Results Plasmin cleavage of iC3b was examined over a range of concentrations and times. Plasmin (50 nM) generated a 40 kDa iC3b cleavage fragment (946TLD – PSR1303) which was notable for containing both C3dg (1002HLI – PSR1303) and the C3 thioester domain, necessary for opsonic binding to surfaces. We tested the relevance of this cleavage in phagocytosis assays using immunofluorescence and flow cytometry (Figure 1). C3b bound to the surface of fluorescent (Alexa 488) zymosan particles (C3b-zym), was treated with FI/FH to generate iC3b-zym, and subsequently incubated with FI/CR1 or plasmin to yield C3dg-zym or 946TLD – PSR1303-zym, respectively. Western blots confirmed that plasmin generated 946TLD – PSR1303 from iC3b-zym. The C3 fragment-zymosan species (C3b-zym, iC3b-zym, C3dg-zym and 946TLD – PSR1303-zym) were each incubated with macrophages (PMA-differentiated THP-1 cells) for 90 minutes. Cells were washed, stained and fixed for immunofluorescence, or suspended for flow cytometry. Figure 1, panel A shows macrophages stained with CellMask (red, cell membrane) and DAPI (blue, nucleus). Fluorescent zymosan is seen in green. No phagocytosis was detected with zymosan lacking C3 (zym alone), but there was a small amount with C3b-zym. In contrast, iC3b-zym was highly effective in inducing phagocytosis by most macrophages. This effect of iC3b-zym was abolished with FI/CR1 or plasmin, i.e. little phagocytosis was detected with C3dg-zym or 946TLD – PSR1303-zym. Flow cytometry-based quantitative analyses confirmed the preceding findings (Figure 1, panel B), with a similar pattern of phagocytosis induced by the zymosan-bound fragments. No phagocytosis was detected with zymosan lacking C3. Phagocytosis of C3b-zym and iC3b-zym was 7±2% and 17±1% of cells, respectively. C3dg-zym and 946TLD – PSR1303-zym induced phagocytosis was <5%. We also evaluated the role of the complement receptors in mediating the effect of the C3b/iC3b fragments using CR3/4 and CR1 blocking antibodies. These confirmed that phagocytosis of iC3b-zym and C3b-zym is mediated by CR3/4 and CR1, respectively. Conclusions Plasmin cleaves iC3b to form a redundant complement regulatory pathway with the FI/CR1 complex, but which notably does not require a cellular cofactor. Further studies will delineate the role of this and other plasmin-generated complement fragments in modulating innate immune and inflammatory responses. Disclosures: No relevant conflicts of interest to declare.
34
Vulich, S. A., E. G. O'Riordan, and J. P. Hanrahan. "Use of n-alkanes for the estimation of herbage intake in sheep: accuracy and precision of the estimates." Journal of Agricultural Science 116, no. 2 (April 1991): 319–23. http://dx.doi.org/10.1017/s0021859600077741.
Full textAbstract:
SUMMARYTwo experiments at Belclare, Co. Galway, in late autumn 1988, evaluated the use of herbage and dosed n-alkanes for estimating herbage intake by sheep. The first experiment examined faecal recoveries of dosed and herbage n-alkanes. The second experiment assessed the accuracy and precision of herbage intake estimates obtained using the n-alkane technique, and tested the effect of supplying n-alkanes to animals either in gelatine. capsules (containing different ratios of n-alkane: cellulose fibre) or in pellets prepared from shredded paper onto which the n-alkanes had been adsorbed. Individually penned wether lambs were offered freshly cut herbage ad libitum (+ 10%) and actual dry matter intake was recorded daily. Intake was estimated using the C31:C32 and C33:C32 (natural:dosed) n-alkane ratios.There was no significant effect of n-alkane chain length on faecal recovery rate for either the dosed n-alkanes (C32 and C36), the herbage odd-chained n-alkanes (C29, C31, C33 and C36) or those used for the estimation of herbage intake (C31, C32 and C33). The accuracy and precision of the n-alkane technique for estimating herbage intake were unaffected by whether the dosed n-alkane was supplied in capsules or pellets or by the n-alkane:cellulose fibre ratio in the capsules. The bias in the estimated intake was – 8% (± 1·1%) and + 3% (± 1·2%) for estimates based on C31:C32 and C33:C32 ratios, respectively. The estimates based on C31:C32 and C33:C32 exhibited similar precision in the estimation of herbage intake, with a R.S.D. of 6% in actual intake when adjusted for variation in estimated intake and a correlation of +0·92 between actual and estimated herbage intake. The C.V. for actual herbage intake was 17%. The repeatability of actual dry matter intake over three consecutive 6-day periods was 0·54 while those of estimated intake were 0·57 and 0·60 for estimates based on C31:C32 and C33:C32, respectively. The results show that the n-alkane technique can provide an accurate and precise estimate of herbage intake.
35
Morikis, D., and J. D. Lambris. "Structural aspects and design of low-molecular-mass complement inhibitors." Biochemical Society Transactions 30, no. 6 (November 1, 2002): 1026–36. http://dx.doi.org/10.1042/bst0301026.
Full textAbstract:
We present a mini-review on the structure-based design of three promising complement inhibitors. Firstly, we review compstatin, a 13-residue cyclic peptide that binds to C3 and inhibits the cleavage of C3 to C3a and C3b. Secondly, we review a six-residue cyclic peptide that binds to C5aR and antagonizes the binding of C5a to its receptor C5aR. Finally, we review three small molecules that bind to Factor D and inhibit the enzymic action of Factor D, during which Factor D proteolytically cleaves Factor B in complex with C3 or C3b.
36
Hong, K., T. Kinoshita, P. Pramoonjago, Y. U. Kim, T. Seya, and K. Inoue. "Reconstitution of C5 convertase of the alternative complement pathway with isolated C3b dimer and factors B and D." Journal of Immunology 146, no. 6 (March 15, 1991): 1868–73. http://dx.doi.org/10.4049/jimmunol.146.6.1868.
Full textAbstract:
Abstract C5 convertase of the alternative complement pathway is a trimolecular complex consisting of two molecules of C3b and one molecule of Bb. We previously proposed a model of the alternative pathway C5 convertase in which the second C3b molecule binds covalently to the first C3b molecule bearing Bb, and the C5 molecule binds to each C3b molecule of the covalently linked C3b dimer, resulting in its appropriate presentation to the catalytic site on Bb. In the present study, we purified the covalently linked C3b dimer and reconstituted the C5 convertase with the C3b dimer and factors B and D to obtain evidence in support of this model. An insoluble glucan, OMZ-176, was incubated with human serum to activate the alternative pathway and to allow formation of the alternative C5 convertase on the surface of the glucan, and the glucan bearing the C5 convertase was then solubilized by incubation with glucosidases. In this way, the covalently linked C3b dimer was obtained in solution without using a detergent. The C3b dimer was then separated from enzymes, C3b monomer, C3b oligomer, and other materials by chromatographies. SDS-PAGE analysis demonstrated that the purified C3b dimer had intact alpha'-chains. Alternative pathway C5 convertase was reconstituted when the isolated C3b dimer was incubated with factors B and D. The presence of P enhanced C5 convertase formation threefold. These results support the notions that the formation of the covalently linked C3b dimer is a general phenomenon associated with activation of the alternative pathway and that the C3b dimer acts as a part of the C5 convertase.
37
Fearon, Douglas T. "Human Complement Receptors for C3b (CR1) and C3d (CR2)." Journal of Investigative Dermatology 85, no. 1 (July 1985): S53—S57. http://dx.doi.org/10.1111/1523-1747.ep12275473.
Full text
38
Li, Qingfang, Qiqi Li, Yongping Du, Lei Zhang, Hongzhe Pan, and Haifeng Wang. "Tuning electronic properties in the C3N/C3B lateral heterostructures." Physica E: Low-dimensional Systems and Nanostructures 126 (February 2021): 114497. http://dx.doi.org/10.1016/j.physe.2020.114497.
Full text
39
Morikis, D., A. M. Soulika, B. Mallik, J. L. Klepeis, C. A. Floudas, and J. D. Lambris. "Improvement of the anti-C3 activity of compstatin using rational and combinatorial approaches." Biochemical Society Transactions 32, no. 1 (February 1, 2004): 28–32. http://dx.doi.org/10.1042/bst0320028.
Full textAbstract:
Compstatin is a 13-residue cyclic peptide that has the ability to inhibit the cleavage of C3 to C3a and C3b. The effects of targeting C3 cleavage are threefold, and result in hindrance of: (i) the generation of the pro-inflammatory peptide C3a, (ii) the generation of opsonin C3b (or its fragment C3d), and (iii) further complement activation of the common pathway (beyond C3) with the end result of the generation of the membrane attack complex. We will report on our progress on: (i) rational design of more active compstatin analogues based on the three-dimensional structure of compstatin, (ii) experimental combinatorial design based on the generation of a phage-displayed peptide library partially randomized with the implementation of structure-induced restraints, and (iii) theoretical combinatorial design based on a novel computational optimization method, structure-induced restraints and flexible structural templates. All three approaches have resulted in analogues with improved activities. Currently, the lead analogue has the sequence acetyl-I[CVYQDWGAHRC]T-NH2 (where the brackets denote cyclization), and is 16-fold more active than the parent peptide. We will also report on our progress towards understanding the dynamic character of compstatin using molecular dynamics simulations. The identification of an ensemble of interconverting conformers of compstatin with variable populations is a first step towards the incorporation of dynamic elements in the design of new analogues using dynamics–activity relationships in addition to structure–activity relationships.
40
Koistinen, V. "Effect of complement-protein-C3b density on the binding of complement factor H to surface-bound C3b." Biochemical Journal 280, no. 1 (November 15, 1991): 255–59. http://dx.doi.org/10.1042/bj2800255.
Full textAbstract:
Various amounts of the activation fragment C3b of the complement (C) protein C3 were coupled to Sepharose 4B by catalysis with the C3 convertase of the alternative pathway of C. The binding of radioactively labelled C proteins B and H (= factor H) to the C3b-carrying particles was assayed. It was found that the relative binding of H, but not of B, fell rapidly with decreasing densities of solid-phase C3b, suggesting a sigmoidal relationship between C3b density and binding of H. To study the phenomenon in more detail, preformed C3b was coupled to activated thiopropyl-Sepharose 6B at various densities. By using this model system, it was shown that the binding of H/unit amount of C3b was positively correlated to C3b density up to a C3b concentration of about 0.5 mg/ml of gel, whereas binding of B was independent of C3b density. The results show that accumulation of high densities of C3b on a surface creates high-affinity binding sites for H. Because H has recently been shown to form dimers in solution, the interaction of dimeric H with neighbouring C3b molecules is a likely explanation for the phenomenon. The C3b density effect may be a regulatory mechanism keeping the activation of the alternative pathway of C on activating surface within reasonable limits.
41
Feng, Shuju, Michael H. Kroll, and Vahid Afshar-Kharghan. "Von Willebrand Factor Is a Cofactor in Complement Regulation." Blood 124, no. 21 (December 6, 2014): 109. http://dx.doi.org/10.1182/blood.v124.21.109.109.
Full textAbstract:
Complement, besides its involvement in eliminating microbes, participates in such diverse processes as synapse maturation, clearance of immune complexes, angiogenesis and tissue regeneration. Delicate balance between complement activation and regulation contributes to complement’s role in physiology. Any trigger that tips this balance can induce self-attack. Atypical hemolytic uremic syndrome (aHUS) is a systemic disease characterized by non-immune hemolytic anemia, thrombocytopenia, and renal impairment. In over 50% of cases, aHUS is known to be caused by uncontrolled activation of the complements. Von Willebrand factor (VWF) is a large multimeric glycoprotein that plays an important role in stopping the escape of blood from vessels following vascular injury. VWF and VWF cleavage enzyme ADAMTS13 gene defects have been identified in patients with aHUS, raising the possibility that VWF could have contributed to complement regulation. To examine the role of VWF in complement activation, we investigated whether VWF functions as a cofactor for FI-mediated C3b cleavage through in vitro assay. We found that C3b binds to VWF. In the presence of plasma-purified VWF (pVWF), FI cleaves C3b to 68kD and 43kD degradation products (iC3b) (Figure (A)). VWF alone, or FI alone, did not have any effect on C3b cleavage. C3b, not C3 or iC3b, was the mainly substrate for FI/VWF proteolysis. Increasing VWF concentration or prolonging the incubation time with VWF enhanced FI-mediated C3b cleavage. To remove the possibility that another plasma protein co-purified with pVWF that affects our results, we used recombinant VWF dimers purified from human embryonic kidney (HEK) 293 cell expressing VWF-Dpro cDNA, and detected a similar cofactor activity (Figure (B)).To investigate whether the size of VWF multimers have any effect on C3b cleavage, we compared the cofactor activity of pVWF, recombinant VWF dimers, and ULVWF multimers. While pVWF and dimer VWF enhanced C3b cleavage by FI, ULVWF did not have any effect on C3b cleavage (Figure (B)). In plasma, complement proteins Factor B and Factor D coexist with the inhibitory protein FI. To investigate the effect of VWF on complement activity in the presence of both pro-activation and inhibitory complement proteins, we incubated C3, FB, FD, and FI with VWF. In the presence of FB and FD, C3 be activated and resulted in the generation of C3a and C3b. Addition of recombinant VWF put a brake on complement activation and shifted C3 toward the generation of iC3b (Figure (C)). We conclude that normal plasma VWF, function as a cofactor, prevents complement activation through steers the complement pathway toward the generation of inactive iC3b. ULVWF multimers, as are present in patients with thrombotic microangiopathy, lack an inhibitory effect on complement and permit complement activation. Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.
42
Fröschen, Frank Sebastian, Sophia Schell, Matthias Dominik Wimmer, Gunnar Thorben Rembert Hischebeth, Hendrik Kohlhof, Sascha Gravius, and Thomas Martin Randau. "Synovial Complement Factors in Patients with Periprosthetic Joint Infection after Undergoing Revision Arthroplasty of the Hip or Knee Joint." Diagnostics 11, no. 3 (March 4, 2021): 434. http://dx.doi.org/10.3390/diagnostics11030434.
Full textAbstract:
The role and diagnostic value of the synovial complement system in patients with low-grade periprosthetic joint infection (PJI) are unclear. We sought to evaluate, for the first time, the usefulness of synovial complement factors in these patients by measuring the individual synovial fluid levels of complement factors (C1q, C3b/iC3b, C4b, C5, C5a, C9, factor B, factor D, factor H, factor I, properdin, and mannose-binding lectin [MBL]). The patients (n = 74) were classified into septic (n = 28) and aseptic (n = 46). Receiver-operator characteristic curves and a multiple regression model to determine the feasibility of a combination of the tested cytokines to determine the infection status were calculated. The synovial fluid levels of C1q, C3b/C3i, C4b, C5, C5a, MBL, and properdin were significantly elevated in the PJI group. The best sensitivity and specificity was found for C1q. The multiple regression models revealed that the combination of C1q, C3b/C3i, C4b, C5, C5a, and MBL was associated with the best sensitivity (83.3%) and specificity (79.2%) for a cutoff value of 0.62 (likelihood ratio: 4.0; area under the curve: 0.853). Nevertheless, only a combined model showed acceptable results. The expression patterns of the complement factors suggested that PJI activates all three pathways of the complement system.
43
del Conde, Ian, Miguel A. Crúz, Hui Zhang, José A. López, and Vahid Afshar-Kharghan. "Platelet activation leads to activation and propagation of the complement system." Journal of Experimental Medicine 201, no. 6 (March 21, 2005): 871–79. http://dx.doi.org/10.1084/jem.20041497.
Full textAbstract:
Inflammation and thrombosis are two responses that are linked through a number of mechanisms, one of them being the complement system. Various proteins of the complement system interact specifically with platelets, which, in turn, activates them and promotes thrombosis. In this paper, we show that the converse is also true: activated platelets can activate the complement system. As assessed by flow cytometry and immunoblotting, C3 deposition increased on the platelet surface upon cell activation with different agonists. Activation of the complement system proceeded to its final stages, which was marked by the increased generation of the anaphylotoxin C3a and the C5b-9 complex. We identified P-selectin as a C3b-binding protein, and confirmed by surface plasmon resonance binding that these two proteins interact specifically with a dissociation constant of 1 μM. Using heterologous cells expressing P-selectin, we found that P-selectin alone is sufficient to activate the complement system, marked by increases in C3b deposition, C3a generation, and C5b-9 formation. In summary, we have found that platelets are capable of activating the complement system, and have identified P-selectin as a receptor for C3b capable of initiating complement activation. These findings point out an additional mechanism by which inflammation may localize to sites of vascular injury and thrombosis.
44
Mold, C., B. M. Bradt, G. R. Nemerow, and N. R. Cooper. "Epstein-Barr virus regulates activation and processing of the third component of complement." Journal of Experimental Medicine 168, no. 3 (September 1, 1988): 949–69. http://dx.doi.org/10.1084/jem.168.3.949.
Full textAbstract:
Serum incubated with purified EBV was found to contain C3 cleavage fragments characteristic of C3c. Since the cofactors necessary for such cleavage of C3b by factor I are not normally present in serum, EBV was tested for factor I cofactor activity. Purified EBV from both human and marmoset EBV-producing cell lines was found to act as a cofactor for the factor I-mediated breakdown C3b to iC3b and iC3b to C3c and C3dg. EBV also acted as a cofactor for the factor I-mediated cleavage of C4b to iC4b and iC4b to C4c and C4d. EBV from both the human and marmoset cell lines accelerated the decay of the alternative pathway C3 convertase. The classical pathway C3 convertase was unaffected. Multiple lines of evidence eliminated the possibility that marmoset or human CR1 was responsible for the functional activities of EBV preparations. The spectrum of activities was different from CR1 in that EBV and EBV-expressing cell lines failed to rosette with C3b or particles bearing C3b, the primary functional assay for CR1, and EBV did not accelerate classical pathway C3 convertase decay, another property of CR1. In addition, CR1 could not be detected immunologically on marmoset or human EBV-expressing cells and mAbs to CR1 failed to alter EBV-produced decay acceleration and factor I cofactor activities, although the antibodies blocked the same CR1-dependent functional activities. The multiple complement regulatory activities exhibited by purified EBV derived from human and marmoset cells differ from those of any of the known C3 or C4 regulatory proteins. These various activities would be anticipated to provide survival value for the virus by subverting complement- and cell-dependent host defense mechanisms.
45
Mehta, R. L., H. Takahashi, R. A. Rudick, and D. W. Knutson. "Binding and catabolism of aggregated immunoglobulins containing C3b by U937 cells." Journal of Immunology 136, no. 5 (March 1, 1986): 1765–71. http://dx.doi.org/10.4049/jimmunol.136.5.1765.
Full textAbstract:
Abstract We studied Fc receptor and C3b receptor (CR1) function on U937 cells, a human monocyte cell line. C3b was incorporated into stable soluble heat aggregates of 125I-IgM (A-IgM) and 125I-IgG (A-IgG) by using functionally pure classical pathway components. C3b incorporation was verified by the ability of aggregates to bind to human red cells and by cosedimentation of 125I and 131I during ultracentrifugation. Cell uptake and degradation of A-IgG X C3b was increased up to twofold compared with A-IgG not containing C3b molecules. However, A-IgG X C3b bound to CR1 after Fc receptors were blocked with nonradiolabeled A-IgG were also not endocytosed and catabolized. Moreover, A-IgM X C3b was bound but not degraded by U937 cells. As expected, uptake of A-IgM without C3b was negligible. CR1-mediated binding of A-IgM X C3b was specifically inhibited both by a murine monoclonal antibody against the human CR1 that blocks C3b binding and by C3b oligomers generated by trypsin activation of C3, but not by monoclonal antibodies against the iC3b receptor (CR3). We conclude that CR1 on U937 cells cause increased binding of A-IgG, and this increased binding leads to increased Fc-mediated endocytosis and catabolism of model immune complexes. However, binding of soluble ligands by CR1 alone, even when binding is multivalent, does not lead to endocytosis and degradation of soluble ligands bearing C3b.
46
Farries, T. C., P. J. Lachmann, and R. A. Harrison. "Analysis of the interaction between properdin and factor B, components of the alternative-pathway C3 convertase of complement." Biochemical Journal 253, no. 3 (August 1, 1988): 667–75. http://dx.doi.org/10.1042/bj2530667.
Full textAbstract:
The interactions between Factor B (B), its activation products Ba and Bb, properdin (P) and C3i or C3b, components that together form the alternative-pathway C3 convertase enzyme of human complement, have been analysed. Fluid-phase complexes of the purified components C3i, B and P were probed with the homobifunctional cross-linking reagent disuccinimidyl tartarate, and efficient cross-linking of B to P was observed. The 140 kDa B-P conjugate formed was cleaved by Factor D to yield a single product of 85 kDa. This is consistent with a Ba-P heterodimer, and suggests that the initial interaction of B and P includes an interaction of P with the Ba domain of intact B. (The Ba fragment is not retained in the active P-stabilized complex, C3bBbP). By contrast, no cross-linking of P to the Bb domain of B could be demonstrated. Binding studies on cellular intermediates also provided evidence for a site of interaction between B and P, with high concentrations of B inhibiting P binding to EAC3b (sheep erythrocytes coated with antibody and C3b). Neither isolated Ba nor Bb had any effect on the P-EAC3b interaction. High concentrations of B also accelerated the decay of the functional EAC3bBbP complex. These data indicate that the positive co-operativity of binding to C3i or to C3b between B and P is mediated, at least in part, through a direct interaction between B and P.
47
Rahkola, Dina, Tiina Lipitsä, Hanna Siiskonen, Anita Naukkarinen, and Ilkka T. Harvima. "Sequential Increase in Complement Factor I, iC3b, and Cells Expressing CD11b or CD14 in Cutaneous Vasculitis." Analytical Cellular Pathology 2022 (June 14, 2022): 1–9. http://dx.doi.org/10.1155/2022/3888734.
Full textAbstract:
Mast cells contribute to the pathogenesis of cutaneous vasculitis through complement C3 that is cleaved to C3b and then to iC3b by complement factor I. The receptor of iC3b, CD11b, is expressed on neutrophils and monocytes and CD14 on monocytes. Their role in vasculitis is obscure. In this study, frozen skin biopsies from the nonlesional skin, initial petechial lesion, and palpable purpura lesion from 10 patients with immunocomplex-mediated small vessel vasculitis were studied immunohistochemically for complement factor I, iC3b, CD11b, and CD14. Peripheral blood mononuclear cells from 5 healthy subjects were used to study cell migration and cytokine secretion. Already, the nonlesional skin revealed marked immunostaining of complement factor I, iC3b, CD11b, and CD14, and their expression increased sequentially in initial petechial and palpable purpura lesions. Mast cell C3c correlated to iC3b, and both of them correlated to CD11b+ and CD14+ cells, in the nonlesional skin. The stimulation of mononuclear cells with 0.01-0.1 μg/ml iC3b induced cell migration in the transwell assay. C3a stimulated slightly interleukin-8 secretion, whereas 1 μg/ml iC3b inhibited it slightly, in 4/5 subjects. In conclusion, the C3-C3b-iC3b axis is activated already in the early vasculitis lesion leading to progressive accumulation of CD11b+ and CD14+ cells.
48
Mitomo, K., T. Fujita, and K. Iida. "Functional and antigenic properties of complement receptor type 2, CR2." Journal of Experimental Medicine 165, no. 5 (May 1, 1987): 1424–29. http://dx.doi.org/10.1084/jem.165.5.1424.
Full textAbstract:
This is the first report demonstrating that C3d receptor (CR2) has functional activity in regulating complement cascade. Purified CR2 was examined for its cofactor activity in factor I-mediated cleavage of membrane-bound iC3b. CR2 plus C3b inactivator (I) released C3c from EA 125I-iC3b, and the release was inhibited when CR2 was preincubated with OKB7 monoclonal anti-CR2. Furthermore, immunoelectroblotting analysis showed crossreactivity of CR2 with 57H anti-CR1. These results indicate that CR2 has functional and antigenic similarity to CR1, thus providing a supporting evidence for placement of CR2 as a member of the recently defined gene family of C3- and C4-regulatory proteins composed of CR1, C4-binding protein, and factor H.
49
Pangburn, M. K. "Analysis of the mechanism of recognition in the complement alternative pathway using C3b-bound low molecular weight polysaccharides." Journal of Immunology 142, no. 8 (April 15, 1989): 2759–65. http://dx.doi.org/10.4049/jimmunol.142.8.2759.
Full textAbstract:
Abstract The human complement (C) system recognizes bacterial, fungal and viral activators of the alternative pathway following covalent attachment of the protein C3b to carbohydrates (CHO) on the surface of the organisms. Recognition first manifests itself as a 3- to 10-fold reduction in the affinity of C3b for factor H, a regulatory protein of C. This report describes the use of a fluorimetric assay which is sensitive to the C3b-H interaction to study the characteristics of recognition. Fluid phase C3b covalently bound to CHO (C3b-CHO) was prepared by activating C3 in the presence of the small homopolymers dextran (alpha 1-6 polyglucose) or inulin (beta 1-2 polyfructose). In particulate form both polysaccharides are activators of C. The conjugates exhibited increased resistance to inactivation in the factor H-dependent assays compared to C3b not bound to CHO and to C3b bound to mono- or disaccharides. The dextran-induced restriction of inactivation was partially reversed by treatment of the conjugate with dextranase. C3b-CHO conjugates failed to bind to factor H-Sepharose and when introduced into serum behaved as though C3b was attached to particulate activators of C, suggesting that the fluorimetric assay accurately reports recognition. The results suggest that the recognition site which induces a reduction in the affinity of C3b for factor H is distinct from the thioester site of C3b and can recognize structural features of polysaccharides including size, sialic acid content, and possibly aspects of three-dimensional oligosaccharide structure.
50
Kalli, K. R., J. M. Ahearn, and D. T. Fearon. "Interaction of iC3b with recombinant isotypic and chimeric forms of CR2." Journal of Immunology 147, no. 2 (July 15, 1991): 590–94. http://dx.doi.org/10.4049/jimmunol.147.2.590.
Full textAbstract:
Abstract CR2 is a component of a signal transduction complex on B lymphocytes that augments B cell responses to Ag. We have quantitatively assessed binding by the two isotypic forms of CR2 for two of its ligands, the polymerized iC3b (p(iC3b)) fragment of C3, and gp350/220, the EBV membrane protein. The recombinant 15-SCR or 16-SCR forms of CR2 bound p(iC3b) with identical affinities. Full binding activity of CR2 for p(iC3b) was observed with a chimera comprised of SCR-1 and -2 of CR2 fused to SCR-17 through -30 of CR1. Therefore, the alternatively spliced SCR-10a has no role in binding p(iC3b), and the binding activity of wild type receptor for iC3b can be reconstituted with SCR-1 and -2 of CR2. The binding affinities of the two isoforms of CR2 for soluble gp350/220 were also similar. Additional sites in the C3c region of C3 have been postulated also to interact with CR2. However, monomeric iC3b and C3d were equally effective in inhibiting the binding of p(iC3b) to CR2, indicating that the C3c region of iC3b does not contribute to the interaction of iC3b with CR2. Finally, the relative abilities of C3b and iC3b to bind to CR1 and CR2 were compared. The conversion of C3b to iC3b generated a ligand with an approximate 100-fold decrease in affinity for CR1 and a 10-fold increased affinity for CR2, resulting in a 1000-fold greater likelihood for binding to the latter receptor that may then promote B cell activation.