Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Complement C4b”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 271 records · Page 15Linked to original sources
PubMed1983

Cell-bound C4b resists reduction by reducing agents: analysis by chain structure and by hemolytic activity.

EA3H-C4hu treated with 2-mercaptoethanol (MSH) or dithiothreitol (DTT) were analyzed for residual chains and hemolytic activity. MSH treatment resulted in no loss of the chains of C4b and no loss of reactivity with a polyclonal anti-human C4 rabbit antibody, and the cells did not lose their ability to generate SAC4b2a. DTT-treated cells lost about 70% of the gamma-chain and over 95% of C4b activity; there was no loss of alpha' and beta chains or the ability to react with anti-C4 antibody. Kinetic studies indicated that the remaining 30% of the gamma-chains could not be removed by prolonged incubation with DTT, implying heterogeneity of cell bound C4b. The data also imply that the gamma-chain is important in the generation of SAC4b2a.

Animals↗
PubMed1989

Probing the C4-binding site on C1s with monoclonal antibodies. Evidence for a C4/C4b-binding site on the gamma-domain.

The catalytic site for C4 of C1s has been presumed to consist of a C4-binding domain and a proteolytic domain. A mAb to C1s, M81, blocked C4 activation and C4 binding to C1s. M81 recognized the H chain of C1s. Using M81 as a probe, we tried to define C4-binding site on C1s. Plasmin digestion of C1s generated four products of Mr 58,000 (P1), 48,000 (P2), 37,000 (P3), and 27,000 (P4). These products, except for P2, all possessed a 26,000-Da H chain fragment (26k-HF) connected to variable-sized L chain pieces. 26k-HF alone had an ability to interact with M81. Amino-terminal amino acid analysis of 26k-HF mapped the epitope for M81 to domain IV and/or V of gamma-domain of C1s. The gamma-domain therefore contains the C4-binding site. The confirm and further elucidate the role of the C4-binding site for C4, we used a substrate-blotting technique in which labeled C4 was incubated with nitrocellulose membrane-fixed C1s and its fragments. C4 was successfully blotted onto C1s and P1, but not P2-P4; i.e., further degradation of the L chain led to the loss of C4-binding. During the incubation, most of the added C4 was converted to C4b. The binding was augmented, if the proteolytic activity of C1s and P1 was blocked, so that the added C4 remained intact. Although C4b also bound to C1s and P1, its binding was less effective and abolished by the addition of cold C4. Based on these results, the gamma-domain and the L chain constitute the catalytic site of C1s to activate C4 to C4b. Moreover, the generated C4b, although it still has weak affinity for C1s, can be replaced by newly coming C4.

Antibodies, Monoclonal↗
PubMed1988

Ligand-loaded but not free complement receptors for C3b/C4b and C3d co-cap with cross-linked B cell surface IgM and IgD.

We have performed experiments to investigate possible physical interactions between C receptors (CR) and surface Ig (sIg) on the B cell plasma membrane. These molecules were found to be independent, non-linked, B cell surface structures, because capping CR1, CR2, sIgM, or sIgD with a specific antibody did not affect the distribution of the remainder of these molecules. Both CR1 and CR2, if bound by antibodies that did not independently cap CR, however, became associated with cross-linked sIg because CR that have been bound by intact anti-CR antibodies or their Fab fragments co-capped with sIgM or sIgD that had been bound by divalent anti-IgM or anti-IgD antibody. CR1 that had bound C3b similarly co-capped with sIg when sIg was cross-linked. Ligand-bound or even cross-linked CR did not associate with non-cross-linked sIg because sIgD, bound by a univalent Fab fragment of anti-IgD antibody, did not co-cap with CR that had been cross-linked by a sandwich of mouse anti-CR antibody and goat anti-mouse Ig. Other surface molecules, such as B1 and HLA-DR Ag, when bound by specific antibodies, did not cap with cross-linked sIg, and sIgD, when bound by a univalent Fab fragment of anti-IgD antibody, did not co-cap with cross-linked sIgM. Interactions between CR and sIg were not mediated by an association with IgG FcR because co-capping of CR and sIg was observed when F(ab')2 fragments of both anti-CR and anti-Ig antibodies were used. These results demonstrate that B cell surface CR can become associated with sIg, but only if sIg is cross-linked and CR is bound by anti-CR antibody or has bound its natural ligand.

Animals↗
PubMed1986

Mesangial glomerulonephropathy with decreased circulating C4 and predominant mesangial C4 deposition in association with one null gene at the C4B locus.

We report a case of mesangial glomerulonephropathy associated with decreased circulating C4 in a young man with recurrent microscopic hematuria and one null gene at the C4B locus. Mesangial deposits moderately reactive with anti-C4 and weakly reactive with anti-C3 and anti-IgA were found on renal biopsy. No evidence was found to support a diagnosis of IgA nephropathy or any other of the recently described mesangial glomerulonephropathies with immunoglobulin and complement deposition. This case apparently represents a unique, heretofore undescribed variant of mesangial glomerulonephropathy associated with mesangial C4 deposition and C4 hypocomplementemia.

Adolescent↗
PubMed1986

HLA haplotypes with C4B5; evidence for further allelic heterogeneity.

Twenty-three individuals from various disease groups and normal controls were identified by immunofixation with anti-C4, C4-dependent lysis, determination of Rg (Rodgers) and Ch (Chido) phenotypes, and immunoblotting with C4-specific mouse monoclonal antibody. We found that one haplotype predominates with the C4B*5 allele, HLA-A11, B22(55), Cw3, Bf*S, C4A*4B*5, which also carries the Ch1,-2, 3 haplotype. The B5 allotype was also found with HLA-B60, HLA-B35 in Caucasoids, and HLA-B18 in non-Caucasoids; these carried the Ch-1, -2, -3 haplotype. Our results are in accord with an earlier report of two B5 subtypes, B5Rg+ and B5Rg- (Roos et al. 1984). The specificity of the mouse monoclonal antibodies IC4 and 2B12 had been previously related to C4A and C4B, respectively, but our results suggest that they relate more closely to Rg and Ch determinants.

Alleles↗
PubMed1989

Sandwich enzyme-linked immunosorbent assays for the quantification of the C4 isotypes (C4A and C4B) in human plasma.

Sandwich enzyme-linked immunosorbent assays were developed to determine the concentration of the isotypes of the fourth component of human complement (C4A and C4B) in human plasma. In the case of C4A a monoclonal antibody against a common determinant of the alpha chain was used to capture the protein. The bound antigen was then detected with a biotinylated monoclonal antibody reacting exclusively with the C4A isotype, followed by peroxidase labeled avidin. For the quantification of C4B, C4B-specific monoclonal antibodies were coated onto a microtitration plate in order to capture the protein. Bound antigen was then detected with a biotinylated monoclonal antibody directed against C4 followed by peroxidase labeled avidin. The assays, which were rapid, selective and specific for C4A and C4B, respectively, provide an alternative to gel electrophoresis and blot procedures for the study of unexpressed alleles ('null alleles') at each of the C4 loci.

Antibodies, Monoclonal↗
PubMed1996

C4 polymorphism and extended HLA haplotypes in Namibian San and Khoi and in South African Xhosa.

We studied C4A and C4B polymorphisms and HLA-B and -DR associations in the San, Khoi and Xhosa. C4A and C4B alleles were determined using conventional protein allotyping methods. The C4A*3, C4B*1 haplotype had a high frequency (30-55%) in all populations. The frequency of C4A*3, C4B*Q0 was 7-19%. The C4A*Q0, C4B*1 haplotype was frequent (15%) in the Khoi but very rare in the San (P < 0.001). C4A*12 A*91, C4B*Q0 was frequent in the Xhosa (15%) but rare in the San and Khoi (P < 0.001). Alleles C4A*5 and C4A*6, and the C4B*2 B*92 duplication were only found in the Xhosa. C4A alleles A*4, A*45, A*58, A*12, A*14, A*19 and the C4A*3 A*91 duplication were only found in the San/Khoi population group. In the San, fourteen extended haplotypes were found in a relatively high frequency (2-7%). In the Xhosa, one extended haplotype (B42, C4A*12 A*91, C4B*Q0, DR18) was found in a very high frequency (13%) and was characteristic for this group; five other extended haplotypes were found with a low frequency (< 3%).

Complement C4a↗
PubMed1977

Inhibition of complement by mouse serum: selective inactivation of the fourth component of human complement.

Bound human C4b on EAC4 is rapidly inactivated in the presence of murine serum reagents. The functional characteristics of this inactivation suggest that it is probably caused by factor(s) homologous to human C3bI-C4bI: inactivation is temperature-dependent and occurs without concomitant consumption of the inactivator(s); loss of hemolytic function is associated with the cleavage of the bound C4b into C4c, which is released, and C4d, which is retained on the cell membrane. Murine serum reagents inhibit bound human C4b far more efficiently than C3b and may therefore be employed to selectively inhibit C4b.

Animals↗
PubMed1988

Identification of distinct C3b and C4b recognition sites in the human C3b/C4b receptor (CR1, CD35) by deletion mutagenesis.

Complementary DNA clones encoding the NH2-terminal region of human CR1 have been isolated and sequenced. The deduced complete amino acid sequence of the F allotype of human CR1 contains 2,039 residues, including a 41-residue signal peptide, an extracellular domain of 1,930 residues, a 25-amino acid transmembrane domain, and a 43-amino acid cytoplasmic region. The extracellular domain is composed exclusively of 30 short consensus repeats (SCRs), characteristic of the family of C3/C4-binding proteins. The 28 NH2-terminal SCRs are organized as four long homologous repeats (LHRs) of seven SCRs each. The newly sequenced LHR, LHR-A, is 61% identical to LHR-B in the NH2-terminal two SCRs and greater than 99% identical in the COOH-terminal five SCRs. Eight cDNA clones were spliced to form a single construct, piABCD, that contained the entire CR1 coding sequence downstream of a cytomegalovirus promoter. COS cells transfected with piABCD transiently expressed recombinant CR1 that comigrated with the F allotype of erythrocyte CR1 on SDS-PAGE and that mediated rosette formation with sheep erythrocytes bearing C4b and C3b. Recombinant CR1 also had factor I-cofactor activity for cleavage of C3(ma). Analyses of six deletion mutants expressed in COS cells indicated that the NH2-terminal two SCRs of LHR-A contained a site determining C4 specificity and the NH2-terminal two SCRs of LHR-B and -C each had a site determining C3 specificity. The presence of these three distinct sites in CR1 may enable the receptor to interact multivalently with C4b/C3b and C3b/C3b complexes generated during activation of the classical and alternative pathways.

Amino Acid Sequence↗
PubMed1984

C4 polymorphism: use of a monoclonal antibody to distinguish C4A and C4B locus products.

A monoclonal antibody reactive against C4B locus products was used in a passive immunoblotting technique to distinguish C4B from C4A electrophoretic variants. The technique is simple and has the advantage of being able to distinguish clearly those C4B variants which may be either difficult to define by conventional hemolytic assay alone or which would normally be designated as C4B products on account of their lack of hemolytic function. Patterns detected by immunoblotting can be compared directly with patterns obtained by immunofixation with anti-C4 from the same gel.

Alleles↗
PubMed1990

Hypomorphic C4B* 15 variant of the fourth component of complement.

We report a rare 'hypomorphic' C4 allotype detected during routine screening in controls for the Rogers:1 epitope. C4B* 15 was distinguished by having only faint staining when using polyclonal anti-C4 antibody on agarose immunoelectrophoresis (e.g. hypomorphic), having relatively weak hemolytic activity but being strongly reactive with monoclonal antibody to Rodgers 1. TaqI restriction fragment length polymorphism (RFLP) demonstrated that C4B* 15 segregated with 7 kb and 5.4 kb C4 gene fragments and with the haplotype HLA-A2,C-, B50,BW6,DR7,DQ2,DR52,SO7C2(1,15). The 5.4-kb fragment was more intense than the 7.0-kb fragment, suggesting duplication of the 5.4-kb fragment. This hypomorphic C4 allotype (genotype frequency = 0.0088) has diminished expression of C4 epitopes commonly recognized by polyclonal anti-C4 and may be missed by standard phenotyping methods.

Adult↗
PubMed1986

Monoclonal anti-human C4b antibodies: stabilization and inhibition of the classical-pathway C3 convertase.

Two IgG mouse monoclonal antibodies (MAbs), Abs 242 and 463, were prepared by fusion of spleen cells from mice immunized with human C4b with a myeloma cell line, P3/ X 63-Ag 8.653. They were assessed for their effect on the activation and stability of the cell-bound classical-pathway C3 convertase, EAC14b2a and on the binding of C2 and C4bp to EC4b. Ab 242 recognized a conformational neoantigen which appeared upon activation of C4 with C-1s and disappeared after chain separation of C4b, while Ab 463 recognized a linear epitope in the beta-chain of C4b. Ab 242 was found to be a C4bp-like MAb: it accelerates the decay-dissociation of C3 convertase and interferes with the binding of C2 to C4b. It also interfered with the binding of C4bp to C4b. These results suggest that Ab 242 recognizes an epitope which is closely related to the C2- and C4bp-binding sites in C4b. Ab 463, on the other hand, was found to be a nephritic factor like MAb: it prolongs the half-life of C3 convertase from 8 to 30 min at 37 degrees C.

Animals↗
PubMed1996

Investigation of mechanism-based inhibitors of complement targeting the activated thioester of human C3.

An intramolecular thioester bond in complement protein C3 is vital for covalent attachment of C3b (the proteolytically activated form of C3) to biological surfaces and for activation of the complement system. Proteolytic removal of C3a from C3 activates the thioester in the C3b fragment. Activated C3b primarily forms ester bonds with hydroxyl groups of carbohydrates on complement activating surfaces, but it has also been shown to react with the hydroxyl group of tyrosine and with specific Ser and Thr residues on IgG and on complement protein C4b. To examine the reactivity of the thioester, several families of hydroxylated compounds were examined. Reactivity of a series of substituted phenols varied over two orders of magnitude and demonstrated a linear correlation between reactivity and the Hammett substituent constants. Hydroxylated drugs including members of the L-DOPA/epinephrine family and hydroxamic acids also were examined. Compounds were identified that were 20,000 times more reactive than carbohydrates. These compounds were found to inhibit both the classical and alternative pathways of complement activation. Although the specificity of the thioester for its natural biological targets appears to be determined by many structural features, the data presented here demonstrate that increasing the nucleophilic character of the target hydroxyl group can increase the potency of a synthetic inhibitor many orders of magnitude.

Complement C3↗
PubMed1991

The influence of venous occlusion on the status of protein S.

In the present study the effect of perturbation of the vessel wall by venous occlusion on protein S release, was evaluated in 10 healthy male volunteers. A 9% (P less than 0.01) increase in free protein S and a 7% (NS) in total protein S over the baseline were observed 7 min after venous occlusion, whereas von Willebrand factor antigen (vWF:Ag)--a known release product of vascular endothelium--increased by 11% (P less than 0.01). In addition, the possibility of free protein S release from unstimulated platelets was investigated in pre- and post-occlusion samples incubated at room temperature for 24 h as whole blood or platelet-rich plasma. An increase in the mean free protein S was observed in the pre-occlusion samples which peaked after 4 h of incubation--121% at time 0 to 130% (P less than 0.05) of the normal pooled plasma whereas total protein S increased by only 4% (NS). In the post-occlusion samples, a similar peak in mean free protein S levels was observed after 12 h of incubation--132% at time 0 increased to 142% (P less than 0.01) of the normal human plasma pooled and the total protein S was increased by 8.55 (P less than 0.05). Small but significant increases in vWF:Ag levels were observed at 2 h and 6 h for the pre- and post-occlusion samples, respectively. No changes in C4b-binding protein were observed throughout the study. We conclude that, firstly, venous occlusion causes release of protein S in addition to vWF:Ag and, secondly, unstimulated platelets release protein S in addition to vWF:Ag.

Adolescent↗
PubMed1982

A study of a covalent-like interaction between soluble nascent C4b and C4-binding protein.

In the classical pathway of complement, the interaction between C4b and C4bp can be considered as a control of the C3 convertase formation. Purified C4-binding protein (C4bp) interacts with soluble nascent C4b to form covalent-like complexes; the interaction is also possible with nascent C4b-like C4, but not with C4, C4b or C4b-like C4. Formation of the complexes upon incubation of C4bp, C4 and C1s appears to involve a single link between a subunit of C4bp and the alpha' chain of C4b, as observed by SDS-polyacrylamide gel electrophoresis in reducing conditions (160 000 dalton band). In non-reducing conditions, a mixture of C4b-C4bp complexes is observed as a function of the C4b:C4bp molar ratio, with apparent molecular weights differing by a value of 210 000 and reflecting different C4b-C4bp associations. A maximum of five molecules of C4b are bound per molecule of C4bp, which appears to consist of 10 subunits of apparent molecular weight 72 000. The link between C4b and C4bp is partially destroyed by 1 M hydroxylamine at pH 9.0; its formation is strongly inhibited by 3.5 mM hydroxylamine or 60 mM methylamine at pH 9.0. These findings suggest an ester or amide bond between the activated carboxyl group of the thioester bridge in the alpha' or alpha chain of nascent C4b or C4b-like C4 and a hydroxyl or amino group of C4bp. Thus, C4bp might compete with other C4b acceptors such as membranes or IgG.

Carrier Proteins↗
PubMed1992

Tumour necrosis factor B gene polymorphism in relation to complotype in couples with spontaneous abortions and in control families.

NcoI restriction fragment length polymorphism (RFLP) of the tumour necrosis factor B (TNFB) gene gives two allelic fragments of 5.5 and 10.5 kb, corresponding to the TNFB*1 and TNFB*2 alleles, respectively. The frequencies of these alleles were analysed in 121 healthy Finns and 56 Finnish couples suffering from recurrent spontaneous abortions (RSA). In the healthy Finns the frequency of TNFB*1 was 37% and that of TNFB*2 63%, of which the frequency of TNFB*1 was significantly increased compared with the Danish population. No deviation was seen between the RSA couples and the Finnish controls. TNF genes are located in major histocompatibility complex class III region close to complement (BF, C4A and C4B) genes. Some complotypes associated most often with the TNFB*1 (S01, S30, S02) and some (S31, F320) with the TNFB*2 allele in the healthy Finns. The combination of the TNFB and the C4 'null' allele differed between the RSA couples and the Finnish controls.

Abortion, Habitual↗
PubMed1990

Marked shortage of C4B DNA polymorphism among insulin-dependent diabetic patients.

TaqI, BamHI and HinddIII polymorphisms of the C4 genes were studied with a 500-bp C4 cDNA probe (pAT-A153) specific for the 5' end of the gene. The restriction patterns obtained were correlated with the C4A and C4B genotypes in 35 patients suffering from insulin-dependent diabetes mellitus (IDDM), and results were compared to those from 40 healthy individuals. The controls, all Caucasian, were genotyped for HLA-A, B, C, DR, Bf, C2 and C4, together with 10 diabetics and their families; haplotypes for the other patients had been deduced using DNA and protein polymorphism, and taking into consideration linkage disequilibrium for neighbouring loci. No significant difference between genotypes at the C4A locus was seen in either population. The C4A gene deletion, associated with a C4B "short" gene (66.7%), was found mainly in the haplotype B8,Cw7,DR3,BfS,C2C, C4AQOB1, and the C4B gene deletion in the haplotype B18,Cw5,DR3,BfF1, C2C,C4A3BQO. When diabetic patients were compared with normal individuals, we observed, at the C4B locus, a decrease in the C4B "long" gene (22% vs. 49% respectively, p less than 0.001). A compensatory increase was observed in patients vs. controls for the frequency of C4BQO, both in the deleted and intact form (26% vs. 10% respectively, p less than 0.03).

Alleles↗