Serum or plasma levels of C3, factor H and C3d in patients with amebic liver abscess.
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Complement Activation↗
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Immune reactive C3d on the surface of myelin sheaths in neuropathy.
Immunofluorescence studies of sural nerve demonstrated immune reactive C3d and IgM on the surface of myelin sheaths in seven patients with neuropathy and an anti-myelin-associated glycoprotein (MAG) IgM M-protein. Similar deposits of C3d and sometimes IgM were found in four of six patients with acute or chronic inflammatory demyelinating polyneuropathy and in three of six patients with vasculitic neuropathy (including one with acquired immunodeficiency syndrome (AIDS)). C3d was not found in 80 patients with other peripheral nerve disorders except for two with metachromatic leukodystrophy. None of the C3d deposits contained immune reactive C3c implying substantial degradation of C3b. C3d is a sensitive index of complement activation in nerve and may be useful in classification of neuropathies.
Antibodies, Monoclonal↗
The gene encoding decay-accelerating factor (DAF) is located in the complement-regulatory locus on the long arm of chromosome 1.
Delay-accelerating factor (DAF) protects host cells from complement-mediated damage by regulating the activation of C3 convertases on host cell surfaces. Using a panel of hamster-human somatic cell hybrids, the DAF gene was mapped to human chromosome 1. In situ hybridization studies using human metaphase cells further localized the gene to bands 1q31-41, with the largest cluster of grains at 1q32. This establishes the close linkage of the DAF gene to genes for four other proteins (C3b/C4b receptor or complement receptor 1, C3d receptor or complement receptor 2, factor H, and C4-binding protein) that share 60-amino-acid homologous repeats as well as complement-regulatory or -receptor activity, thereby enlarging the complement-regulatory gene family on the long arm of human chromosome 1.
CD55 Antigens↗
Diabetes and autonomic neuropathy: an immunological association?
Lymphocytic infiltration of autonomic ganglia found at autopsy and a strong clinical association with iritis suggests that diabetic autonomic neuropathy might have an immunological basis. We measured levels of circulating immune complexes, complement (C3, C4), complement breakdown products (C3d), and insulin antibodies in diabetics with autonomic neuropathy and a history of iritis (n = 17), compared to diabetics of similar age and duration with autonomic neuropathy but no history of iritis (n = 20), and with uncomplicated insulin-dependent diabetics (n = 23), together with normal controls (n = 26). We found higher levels of circulating immune complexes in patients with autonomic neuropathy (irrespective of iritis) compared to normal controls, and differences in C3d levels suggesting complement activation. C4 levels were unexpectedly normal in the diabetics with autonomic neuropathy, in contrast to the uncomplicated insulin-dependent diabetic controls. Insulin antibody levels showed no difference between the three groups of diabetics. These findings suggest that immunological mechanisms may be implicated in the aetiology of diabetic autonomic neuropathy and that further studies are indicated.
Adult↗
Pathways to complement activation during cardiopulmonary bypass.
Complement activation was assessed in 34 patients undergoing cardiopulmonary bypass. Arterial concentrations of complement fragments Ba and C3d rose in all patients, the increase in Ba preceding that of C3d. At the same time as complement fragments were being generated the arterial neutrophil count fell. These findings suggest (a) that complement activation is initiated by the alternative pathway during cardiopulmonary bypass and (b) that complement activation mediates loss of neutrophils during bypass. Complement mediated loss of neutrophils during the analogous setting of haemodialysis is the result of leucosequestration in the pulmonary vasculature. During cardiopulmonary bypass the lungs are out of circuit, so that activated leucocytes may sequester in other target organs. This may be an aetiological factor in the multi-organ failure occasionally seen after uneventful cardiopulmonary bypass.
Adult↗
C3 degradation products (C3d) in normal pregnancy.
Plasma C3 degradation products (C3d) were measured in 65 normal pregnancies and compared with those of non-pregnant women. No significant difference was detected between the two groups, although a difference had been previously reported. Plasma C3d estimations give an indication of complement activation and may be used as an indicator of disease activity in patients with systemic lupus erythematosus (SLE), irrespective of pregnancy.
Complement C3↗
Expression of specific binding sites on Candida with functional and antigenic characteristics of human complement receptors.
Receptors for C3 degradation fragments (CR1, CR2, and CR3) are present on many human cells including phagocytes and lymphoid cells and may be critical in the attachment of invading microorganisms. In these studies Candida were found to mimic the human CR by binding erythrocytes coated with specific human C3 fragments. Yeast forms of Candida species were adhered to glass slides and were allowed to germinate. Sheep erythrocytes (E) were coated with IgM (EA) and human complement components to prepare EA, EAC14, EAC3b, EAC3bi, and EAC3d. These test cells were then examined for adherence to the organism. Antibodies to human CR1, CR2, and CR3 were used to evaluate their potential for blocking adherence of the test erythrocytes to Candida. Fluorescein-labeled antibodies to human complement receptors were also used to characterize the binding sites. EAC3bi and EAC3d, but not E, EA, or EAC14, bound extensively to the germ tubes and pseudohyphae of Candida albicans and C. stellatoidea. EAC3b bound infrequently. Other Candida species, generally considered less pathogenic, bound significantly fewer specific test erythrocytes than C. albicans. Monoclonal antibodies to human CR1 and CR3 (3D9, 1B4, C511, 2B6, anti-B2, Mo1, and anti-Mac-1), in general, did not block adherence of test erythrocytes. Blocking of adherence of EAC3bi and EAC3d test erythrocytes coated with small quantities of C3 fragments occurred with high concentrations of monoclonal (anti-CR2) HB-5 and polyclonal (anti-CR2) anti-GP 140. Immunofluorescence studies demonstrated binding of Mo-1 to the germinated forms of the organism, whereas binding of the other antibodies was not seen. These studies suggest a surface constituent on the organism similar to CR on human cells. Additional studies are necessary to further define the molecular nature of the binding site. The ability of organisms to mimic human CR may be more generalized than previously known and may serve as a mechanism for modification of the inflammatory and immune response.
Antibodies, Monoclonal↗
Membrane receptors for IgG and complement (C4, C3b and C3d) on human eosinophils and neutrophils and their relation to eosinophilia.
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Animals↗
Development and clinical application of electroimmunoassays for the direct quantification of the complement C3 split products C3c and C3d.
The present report describes the development of electroimmunoassays for the direct quantification of C3d and C3c, split products of the third complement factor (C3). Both methods were developed as rocket immunoelectrophoreses, using two antibody preparations with specificities against the C and D epitopes on C3. A stable calibrator preparation for C3c and C3d was produced by autolytic cleavage of C3. Investigations of patients with anaphylactic reactions or chronic immunological disorders showed that quantification of C3c and C3d in plasma by these methods reflected the degree and rate of complement activation. C3d determination was found to be the most sensitive and reliable indicator of C activation, both during acute and chronic activation since C3c is eliminated considerably faster from the circulation than C3d (estimated half lives of 2 h and 4 h, respectively). Treatment of rheumatoid arthritis patients with prednisolone caused a prompt decrease of plasma C3d values, indicating that the clinical effect may be due to inhibition of complement activation.
Antibody Specificity↗
Structural requirements for C3d,g/Epstein-Barr virus receptor (CR2/CD21) ligand binding, internalization, and viral infection.
The structure of CR2, the human C3d,g/EBV receptor (CR2/CD21) consists of 15 or 16 60-70 amino acid repeats called short consensus repeats (SCRs) followed by a transmembrane and a 34-amino acid intracytoplasmic domain. Functions of CR2 include binding the human complement component C3d,g when it is covalently attached to targets or cross-linked in the fluid phase. In addition, CR2 binds the Epstein-Barr virus (EBV) and mediates internalization of EBV and subsequent infection of cells. In order to explore functional roles of the repetitive extracytoplasmic SCR structure and the intracytoplasmic domain of CR2, we have created truncated CR2 (rCR2) mutants bearing serial deletions of extracytoplasmic SCRs and also the intracytoplasmic tail. We then stably transfected these rCR2 mutants into two cell lines, murine fibroblast L cells and human erythroleukemic K562 cells. Phenotypic analysis of these expressed mutants revealed that 1) The C3d,g- and EBV-binding sites are found in the two amino-terminal SCRs of CR2, 2) expression of SCRs 3 and 4 is further required for high affinity binding to soluble cross-linked C3d,g, 3) the intracytoplasmic domain of CR2 is not required for binding C3d,g or EBV but is necessary for internalization of cross-linked C3d,g as well as for EBV infection of cells, 4) monoclonal anti-CR2 antibodies with similar activities react with single widely separated epitopes, and 5) no functional roles can yet be clearly assigned to SCRs 5-15, as rCR2 mutants not containing these SCRs show no major differences from wild-type rCR2 in binding or internalizing cross-linked C3d,g or mediating EBV binding and infection.
Animals↗
Protection of gingival epithelium against complement-mediated damage by strong expression of the membrane attack complex inhibitor protectin (CD59).
Adult periodontitis (AP) is a chronic inflammatory disease of the tooth-supporting apparatus. Activation products of the inflammation-inducing complement system have been detected in the gingival crevicular fluid at the site of gingival inflammation. In the present study, we examined whether evidence for ongoing complement activation in gingival tissues of patients with AP can be obtained. In light of the potential tissue-damaging effects of the complement system, we also examined how the gingival tissue is protected against the cytolytic activity of complement. Surgical and autopsy samples of AP (n = 18) and healthy (n = 11) gingiva were analyzed for the expression or deposition of the complement regulators protectin (CD59) and vitronectin (S-protein) and complement components C3d and C9 by indirect immunofluorescence microscopy with specific antibodies. In healthy gingiva, protection was strongly expressed on the membranes of epithelial cells and on the vascular endothelia of the underlying connective tissue. In AP, protectin was also strongly expressed by endothelial cells, but in the epithelia the expression was granular and weaker than in the healthy gingiva. Coarse granular deposits of complement components were seen in the subepithelial tissues of 61% (C3d), 39% (C9), and 33% (vitronectin) of AP patients, compared with 9% (one case in 11) in healthy controls. In addition, deposits of C3d, C9, and vitronectin were observed on the basement membranes of both pocket and oral epithelium of healthy and AP gingiva but not at sites of protectin expression. The results suggest an increased turnover of the complement system in the gingival tissues of AP patients. The gingival epithelium and connective tissue endothelia are well-protected against damage by the membrane attack complex of complement (MAC). Protection of the underlying connective tissue is insufficient, however, and may allow for deposition of MAC and autologous tissue damage in AP.
Adult↗
[Value of the determination of C3d and the hemolytic activity of C4 (C4H) during systemic lupus erythematosus].
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Adult↗
Antibody-dependent enhancement of simian immunodeficiency virus (SIV) infection in vitro by plasma from SIV-infected rhesus macaques.
Plasma from two rhesus macaques (Macaca mulatta) experimentally infected with the simian immunodeficiency virus (SIV; isolate SIVmac251) enhanced SIVmac infection of a human CD4+ lymphoblastoid cell line, MT-2. Prechallenge plasma samples from these animals and serum from SIV-negative macaques did not enhance infection. Compared with controls, infection enhancement was characterized by the rapid appearance of syncytium formation (3 to 4 days sooner), reverse transcriptase release (10-fold increase), and cytopathic effect (60% cell killing). Enhancement of activity was dependent on the presence of diluted, fresh SIV-negative macaque serum as a source of complement. A requirement for complement was shown by the absence of enhancement in heat-inactivated serum and by dose-dependent inhibition of enhancement in the presence of polyclonal antibody to monkey complement component C3. Monoclonal antibody to CD4 (OKT4a) blocked enhancement completely, while monoclonal antibody to the human complement component C3d receptor CR2 (OKB7) reduced enhancement by greater than 50%, indicating a requirement for CD4 and CR2 in mediating this phenomenon. SIV infection-enhancing activity appeared in macaques soon after experimental inoculation (28 days). The titer increased over time and peaked just prior to the death of both macaques from opportunistic infections and lymphoma. In vitro SIV infection enhancement is nearly identical to the in vitro complement-mediated, antibody-dependent enhancing (C'-ADE) activity observed in human immunodeficiency virus-positive human sera (Robinson et al., Lancet i:790-794, 1988; Robinson et al., J. Acq. Immun. Def. Synd. 2:33-42, 1989). These observations validate the macaque-SIV model for studies of C'-ADE.
Animals↗
Antisera with anti-pan C3 receptor reactivity which block complement C3b, C3bi and C3d receptors.
Antisera directed at human C3 receptors were prepared by 2 different methods. In method I rabbits were immunized with EAC coated with C3 receptors of tonsil cells (AC3RS type I). In method II rabbits were immunized with insoluble aggregates of tonsil membrane constituents containing significant amounts of C3 receptors. After appropriate absorptions both types of AC3RS showed a selective reactivity with those cells known to express C3 receptors. With the EAC rosette inhibition test it is demonstrated that both types of AC3RS contain antibodies against the binding sites of C3b, C3bi and C3d receptors. The antibody titer was consistently higher in AC3RS of type II.
Animals↗
Quantification of C3d in biological fluids by an enzyme-linked immunosorbent assay.
Using a commercial source of peroxidase-labelled anti-C3d antibody (Dakopatts), an enzyme-linked immunosorbent assay (ELISA) has been developed to quantify the complement fragment C3d. The technique enables the detection of C3d in plasma, urine and cerebrospinal fluid (CSF). The C3d-ELISA therefore provides a very sensitive technique for the evaluation of complement activation in biological fluids. In both plasma and urine the technique is able to discriminate between samples from normal controls and patients with rheumatoid arthritis in whom complement activation is known to occur. A good correlation was found between results obtained by ELISA and those by laser nephelometry (r = 0.91, P less than 0.0001). Microtitre plates pre-coated with anti-C3d antibody and subsequently stored at -70 degrees C retained the ability to perform in this assay. The sensitivity, short assay time and use of commercial reagents and pre-coated plates give this technique numerous potential applications in the evaluation of complement activation.
Arthritis, Rheumatoid↗
Monoclonal anti-human C3d antibodies: stabilization of the alternative pathway C3 convertase.
IgG mouse monoclonal antibody (mAb) was prepared by fusion of spleen cells from mice immunized with human C3d (mAb:C3d) using syngeneic thymocytes as feeder cells. mAb:C3d was assessed for its effect on the stabilization of the cell-bound alternative pathway C3 convertase EAC3bBb. It bound to cell-bound C3b and stabilized C3bBb at 30 degrees in the presence of EDTA-GVB. The plasma protein H reduced the stabilization effect of the stabilized C3 convertase. These results suggest that binding of antibody to C3d may stabilize C3bBb. It seems likely that such antibody induces in C3b conformational change, which increases the C3bBb complex stability.
Antibodies, Monoclonal↗
Influence of time, temperature and coagulation on the measurement of C3, C3 split products and C4.
Quantitative and qualitative immunoelectrophoretic analyses of circulating C3, C3 split products and C4 were performed in matched EDTA plasma and serum obtained from 5 normal subjects and stored for up to 48 h at room temperature (18 degrees C-22 degrees C) and 4 degrees C. Fluctuations in apparent levels of C3 were greater in serum than plasma stored at room temperature, a fall in levels seen by 24 h being followed by a significant increase. By contrast, levels of C3 did not alter if stored at 4 degrees C. C4 levels in both EDTA plasma and serum remained unchanged for 24 h, a slight decrease being seen at 48 h. Levels of C4 remained constant if samples were stored at 4 degrees C. Crossed immunoelectrophoresis revealed a significant progressive decrease in C3 levels and a simultaneous increase in C3c occurring after 4 h in serum and 8 h in EDTA plasma, stored at room temperature. In studies conducted at 4 degrees C, similar but delayed fluctuations were seen. A progressive and significant increase in C3d levels was seen in both plasma and serum samples stored at room temperature, levels rising to 276% (plasma) and 308% (serum) of levels seen at zero time. At 4 degrees C marginal increases in C3d levels only were observed. These results suggest that in vitro degradation of C3 and C4 are readily facilitated by temperature, time and coagulation, and that conditions of collection and storage of samples must be optimized for the accurate definition of activation of the complement cascade.
Adult↗
[Evaluation of C3d in primitive chronic glomerular nephritis (author's transl)].
Plasma levels of C3d, which is liberated by enzymatic cleavage of C3, are determined in 97 patients with primitive chronic glomerular nephritis. This level is indicative of an abnormally high consumption of C3. In all cases where C3 is low, C3d is found at abnormally high levels. When the level of C3 is normal, C3d may, however, be elevated: a more subtle interpretation of the pathologic significance of C3 in immune disease is thus possible.
Complement C3↗