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PubMed2001

Ellipsometric in vitro studies on the activation of complement by human immunoglobulins M and G after adsorption to methylated silicon.

Human serum immunoglobulin M (IgM) or human immunoglobulin G (IgG) were adsorbed to dichlorodimethyl silane (DDS) treated silicon. Subsequently, the model surfaces were incubated in normal-, complement factor 1q (C1q)-complement factor B or complement factor 2 (C2)-depleted human sera at 37 degrees C for up to 1.5 h. The serum deposition and binding of selected polyclonal complement antibodies into this layer were then quantified by null ellipsometry. Both types of precoated surfaces bound large amounts of anti-complement factor 3c (anti-C3c), anti-properdin and anti-C3d, after incubation in normal serum. In contrast to IgG coated surfaces, IgM coated surfaces bound no anti-C1q after the serum incubations and no anti-C3c deposition lag time was observed after incubations in EGTA serum. Upon immersions of IgM coated surfaces in the different sera, a rapid complement activation via a C1q factor B, and Ca(2+)-independent, but C2 dependent pathway, was indicated. When IgM was instead immobilized to APTES/glutaraldehyde surfaces, anti-C3c deposition was lower after incubations in EGTA than normal serum. The results suggest that, under the present experimental conditions, human IgM and IgG activate the complement system differently.

Journal Article↗

PubMed1984

Epstein-Barr virus receptor of human B lymphocytes is the C3d receptor CR2.

Identity of the Epstein-Barr virus (EBV) receptor with the complement receptor type 2 (CR2) was established in three sets of experiments using the monoclonal antibodies, HB-5 and anti-B2, which recognize a Mr 145,000 B-lymphocyte membrane protein that is CR2. First, the rank order for binding of fluoresceinated EBV to four lymphoblastoid cell lines (SB, JY, Raji, and Molt-4) was identical to the rank order for binding of HB-5 and anti-B2 by analytical flow cytometry. Second, pretreatment of cells with HB-5 followed by treatment with goat F(ab')2 fragments to mouse IgG blocked binding of fluoresceinated EBV on SB, a B-lymphoblastoid cell line. Virus attachment was not inhibited by HB-5 alone, second antibody alone, rabbit anti-C3b receptor, or UPC10 (an irrelevant monoclonal antibody). Third, transfer of CR2 from SB to protein A-bearing Staphylococcus aureus particles, to which HB-5 had been absorbed, conferred on them the specific ability to bind 125I-labeled EBV. We conclude that CR2 is the EBV receptor of human B lymphocytes.

Antibodies, Monoclonal↗

PubMed1980

Xenoantiserum to human C3 receptors: its preparation and effect on the C3b and C3d receptors of tonsil cells and the C3b receptors of erythrocytes and neutrophils.

Antisera directed against complement (C3) receptors on human tonsil cells were prepared and tested for their capacity to block specifically C3 receptors on various types of human cells. The antisera were capable of blocking both membrane-bound and solubilized C3 receptors of human tonsil cells. The C3b receptors of human erythrocytes and granulocytes were also blocked by the anti-C3 receptor sera. Sheep erythrocyte rosette formation was not affected. IgG-EoxA rosette formation was only slightly reduced by the anti-C3 receptor sera. Immunofluorescent staining with anti-C3 receptor sera revealed only a faint or negative staining of T cells and a distinct staining of EAC-reactive tonsil cells, lymphocytic leukaemia cells, and granulocytes. Absorption of the antisera with human serum proteins, brain, thymus, liver, EU-1 cell line cells, or trypsinized tonsil cells did not influence the capacity of the anti-C3 receptor sera to inhibit C3 receptors, whereas absorption with splenic tissue or tonsil cells completely removed the blocking activity of the anti-C3 receptor sera. Absorption with human erythrocytes or kidney removed only the inhibitory effect of the antisera on C3b receptors of tonsil cells, human erythrocytes, and granulocytes, but not on C3d receptors of tonsil cells. The results indicate that (a) the antisera prepared with the described procedure contained significant amounts of antibody against C3 receptors, (b) the receptors for C3b and C3d differe in antigenicity, and (c) the C3b receptors of tonsil cells, human erythrocytes, granulocytes, and probably glomerular cells have common antigenic sites.

Complement C3↗

PubMedDate not supplied

Activation mechanism of brain microglia in patients with diffuse neurofibrillary tangles with calcification: a comparison with Alzheimer disease.

Diffuse neurofibrillary tangles with calcification (DNTC) is an atypical dementia and is characterized pathologically by diffuse neurofibrillary tangles (NFTs) without senile plaques (SPs). In this study, we investigated the distribution of human leukocyte antigen (HLA)-DR-positive activated microglia in postmortem brain tissue of six patients with DNTC and six patients with Alzheimer disease (AD). HLA-DR-positive activated microglia were observed to associate with SPs in AD. In the DNTC brain, which lacks SPs, HLA-DR-positive microglia were mainly accumulated around weakly tau-positive NFTs, which were also positive for anti-amyloid-P and anti-C3d antibodies. The results of this study suggest that the complement pathway is also activated in the DNTC brain and that immune and inflammatory responses, including microglia activation, may occur around extracellular NFTs in DNTC patients.

Aged↗

PubMed1983

The Epstein-Barr virus receptor is distinct from the C3 receptor.

Polyvalent serum directed against C3 receptors was employed in an attempt to block Epstein-Barr virus (EBV) binding to virus receptor-containing cell lines. The serum eliminated 90% of virus binding to Daudi and BJAB, lines which express only the C3d receptor. Raji and Ramos cells, which express the C3d, C3b and C3bi receptors, still adsorbed 70% of their virus capacity in the presence of excess antiserum. These effects were independent of the virus strain. In the light of previous reports, these data imply that, although the two receptors, EBV and C3d, are closely associated, the binding sites of EBV and complement are distinct. Additionally, an unusual EBV substrain-specific receptor found on U698 and P3HR-1/ASNP lines was shown to be independent of complement receptors.

Animals↗

PubMed1989

Evaluation of the complement split product C3dg in synovial fluid as a possible diagnostic guide in inflammatory arthropathies.

Analyses of C3 split products with C3d specificity (C3dg) were performed in 157 synovial fluids (SF) of 129 patients with various known joint diseases. Considerable overlap between all inflammatory infectious, and crystal induced disease categories confines the value of such measurements as a diagnostic guide to only a few clinical situations. In seronegative as well as in seropositive rheumatoid arthritis no correlation between SF C3d levels and erythrocyte sedimentation rate could be found.

Arthritis↗

PubMed1984

Magnitude of bacteremia and complement activation during Neisseria meningitidis infection: study of two co-primary cases with different clinical presentations.

Two co-primary cases of schoolchildren with acute meningococcal disease due to infection with Neisseria meningitidis serogroup B are described. The first patient presented with septic shock and purpura fulminans, bacteremia greater than 10(5) organisms/ml blood, low C3 and factor B levels and an elevated level of C3d. The second patient had meningitis, negative blood cultures, normal levels of serum complement components but more than 10(4) organisms/ml in CSF. A comparison of the quantitative bacteriology data and complement profiles for these patients suggests that the degree of activation of complement during meningococcemia is directly related to the number of organisms in the blood. This association may determine the different clinical syndromes.

Adolescent↗

PubMed2003

Administration of a soluble recombinant complement C3 inhibitor protects against renal disease in MRL/lpr mice.

Complement receptor 1-related gene/protein y (Crry) in rodents is a potent membrane complement regulator that inhibits complement C3 activation by both classical and alternative pathways. To clarify the role of complement in lupus nephritis, MRL/lpr mice were given Crry as a recombinant protein (Crry-Ig) from 12 to 24 wk of age. Control groups were given saline or normal mouse IgG. Sera and urine were collected biweekly. Only 1 of 20 (5%) Crry-Ig-treated mice developed renal failure (BUN > 50 mg/dl) compared with 18 of 38 (47.4%) mice in control groups (P = 0.001). BUN levels at 24 wk were reduced from 68.8 +/- 9.7 mg/dl in control groups to 38.5 +/- 3.9 mg/dl in the Crry-Ig-treated group (P < 0.01). Urinary albumin excretion at 24 wk was also significantly reduced from 5.3 +/- 1.4 mg/mg creatinine in the control groups to 0.5 +/- 0.2 mg/mg creatinine in the Crry-Ig-treated group (P < 0.05). Of the histologic data at 24 wk, there was a significant reduction in scores for glomerulosclerosis and C3d, IgG, IgG3, and IgA staining intensity in glomeruli in complement-inhibited animals. Crry-Ig-treated animals were also protected from vasculitic lesions. Although there was no effect on relevant autoimmune manifestations such as anti-double stranded DNA titers or cryoglobulin IgG3 levels, circulating immune complex levels were markedly higher in complement-inhibited animals. Thus, inhibition of complement activation with Crry-Ig significantly reduces renal disease in MRL/lpr lupus mice. The data support the strategy of using recombinant complement C3 inhibitors to treat human lupus nephritis.

Albuminuria↗

PubMed1988

Enhancing effect of autologous human erythrocytes on generation of C3 cleavage products beyond iC3b.

The in vitro formation of C3d and C3c in fresh normal human serum (NHS) after addition of five different activators of the complement (C) system was studied. Following C-activation in NHS (n = 53) by Sephadex G-200 beads, the conversion of C3 was found to proceed to iC3b with a variable but restricted generation of C3d. Similar results were obtained by use of heat-aggregated IgG, Escherichia coli, zymosan, and cobra venom factor. However, comparing the C3d concentration following activation in the presence and absence of autologous red blood cells (RBC) at 37 degrees C the generated C3d was found to be 2- to 3-fold higher in the presence of RBC after 30, 60, and 210 min. Preincubation of RBC with polyclonal anti-CR1 antibodies resulted in a dose-dependent reduction of the amount of C3d generated. C-activation induced by Sephadex G-200 beads, in the absence of RBC, generated iC3b without a significant production of C3d. After removal of the activator beads, addition of RBC resulted in a decrease of iC3b and a clear increase in the C3c and C3d concentration within 3 h. Western blotting analysis of the C3d produced in the presence of RBC showed that the molecular weight (36 kilodaltons) was similar to that of C3d formed in vivo.

Blotting, Western↗

PubMed1997

Complement and the immune response.

This past year has seen a major advance in our understanding of how the complement system enhances the adaptive immune response. The use of in vivo models has revealed that direct coupling of C3d to antigen is sufficient to dramatically reduce the amount of antigen required for a secondary response. At least one important requirement for the enhancing effect was determined to be expression of the CD21 (C3d receptor) on B cells.

Animals↗

PubMed1986

Complement (C3) metabolism in systemic lupus erythematosus in relation to the disease course.

Metabolic turnover studies of complement components (C3) provide a direct insight into the dynamics of the complement regulation (synthesis and catabolism). To obtain information about the role of the complement system in relation to the disease course in patients with systemic lupus erythematosus (SLE), a prospective study was performed. The results of the C3 turnover studies were also correlated to the complement levels (C3) and to the presence of C3 conversion products (C3d) in circulation. In nearly all SLE patients (in 21 of the 26 metabolic turnover studies) a C3 hypercatabolism was found, with a quantitative difference depending on the disease phase. In the period preceding an exacerbation an impaired C3 synthesis was observed (in three of the four studies), in contrast to SLE patients in stable disease phase where in one case only a decrease C3 synthesis was calculated (1 out of 15 observations). A linear correlation was found between the serum C3-levels and the ratio of C3d/C3, suggesting that both serologic parameters are quantitatively indicative for C3 hypercatabolism. The study shows that in all SLE patients, irrespective of the disease stage, an increased C3 consumption is found, which supports the concept that a chronic inflammatory process is constantly present.

Adult↗

PubMed1978

Immunoadherence and complement in cancer-bearing mice.

Shortly after grafting of Ehrlich ascites carcinoma cells, the serum of tumour-bearing mice loses the capacity to mediate immunoadherence phenomena, because of a sharp decrease in the concentration of C3b and C3d, while the cellular receptors for such factors are unaffected by tumour growth. It is suggested that complement is consumed through the alternative pathway which is activated during the inflammatory responses accompanying tumour growth.

Animals↗

PubMed2006

Factor I-mediated processing of complement fragments on HIV immune complexes targets HIV to CR2-expressing B cells and facilitates B cell-mediated transmission of opsonized HIV to T cells.

Our study demonstrates that binding of complement-opsonized HIV to complement receptor type 1 on human erythrocytes (E) via C3b fragments is followed by a rapid normal human serum-mediated detachment of HIV from E. The release was dependent on the presence of factor I indicating a conversion of C3b fragments to iC3b and C3d on the viral surface. This in turn resulted in an efficient binding of opsonized HIV to CR2-expressing B cells, thus facilitating B cell-mediated transmission of HIV to T cells. These data provide a new dynamic view of complement opsonization of HIV, suggesting that association of virus with E might be a transient phenomenon and the factor I-mediated processing of C3b to iC3b and C3d on HIV targets the virus to complement receptor type 2-expressing cells. Thus, factor I in concert with CR1 on E and factor H in serum due to their cofactor activity are likely to be important contributors for the generation of C3d-opsonized infectious HIV reservoirs on follicular dendritic cells and/or B cells in HIV-infected individuals.

B-Lymphocytes↗

PubMed1991

Herpes simplex virus glycoprotein C is a receptor for complement component iC3b.

Herpes simplex virus type 1-infected cells bind C3b and iC3b, but not C3d, at the cell surface. Herpes simplex virus type 2 (HSV-2)-infected cells bind none of these C3 fragments. A transfection assay was used to demonstrate that binding of iC3b was to gC1. Although iC3b did not bind to HSV-2-infected cells, it did bind to mammalian cells transfected with the gC2 gene. Using linker insertion mutants, three domains on gC2 that are important for binding iC3b were mapped; these regions were similar to previously defined regions involved in binding C3b. These results suggest that some of the functions served by gC may be similar to those of CR3, the mammalian receptor for iC3b.

Amino Acid Sequence↗

PubMed1984

Study on C3-like factor in the serum of a C3-deficient subject.

Analysis of the serum of an individual having a deficiency of C3 (C3D) revealed that despite the fact that the C3 could not be detected immunochemically, a small amount of C3 haemolytic activity and total complement activity was indeed found to be present. The present study was performed to analyse the C3-like factor, responsible for this C3 activity in C3D serum. It was found that the C3-like factor was not neutralized by anti-C3 but was neutralized by anti-C5. The electrophoretic mobility of the C3-like factor corresponded to that of purified C5. Thus, C3-like factor was shown to have the antigenicity and electrophoretic mobility of C5. This factor was found in the sera of three other C3D subjects and even in pooled normal human serum (NHS). These findings suggest that, in cases of C3D, C5 compensates for the genetic lack of C3 and serves a protective function and that sensitized erythrocytes (EA) may be lysed by complement components without participation of C3.

Complement C3↗

PubMed1991

Binding of CD 35, CD 21 and CD 11B monoclonal antibodies and EAC complexes to lymphocytes. A comparative histochemical study.

Using cryostat sections of human tonsils after various pretreatments, the adherence of sheep erythrocyte--antisheep erythrocyte (EA) complexes coated with either fresh mouse complement (EACm) or fresh human complement (EACh) has been compared with the binding of monoclonal antibodies (MAbs) against C3b (CD 35), C3d (CD 21) and iC3b (CD 11b) receptors (clusters). After periodic acid oxidation the binding of MAbs to CD 35, CD 21 was well preserved, whereas EACm and EACh complex adherence and CD 11b binding were abolished. These findings seem to prove that the binding sites for EACm and EACh complexes, as well as those for CD 35, CD 21 clusters (antigenic structure of the C3b and C3d receptors) are different.

Animals↗

PubMed1986

Impaired humoral immune response in complement C3-deficient guinea pigs: absence of secondary antibody response.

A recently described genetically controlled C3 deficiency (C3D) in guinea pigs (GP) provided a unique model for studying the role of C3 in the afferent limb of the humoral immune response in a direct manner. These C3D animals, which have only 5-7% of normal serum C3 level, were immunized with the bacteriophage phi chi 174, a T cell-dependent antigen, followed by a booster injection after 4 weeks (1.5 X 10(9) plaque-forming units/kg). The formation of IgM and IgG antibody in the course of the primary and secondary response was determined and compared with a control group of inbred strain 2 GP. The C3D animals showed a markedly diminished antibody response to this antigen. Amplification of the antibody titer as well as regular isotype switching from IgM to IgG was absent in the secondary response. Increasing the amount of antigen to a high dose (1 X 10(10) plaque-forming units/kg) led to a normalization of the antibody response. The impairment in antibody formation resembles closely the impaired antibody response in C4-deficient or C2-deficient GP, which both have a block in activation of C3 via the classical pathway. However, in contrast to C4D GP or C2D GP the C3D GP do not exhibit serological characteristics of immune complex disease. They have normal levels of total serum IgM, of IgM anti-2,4-dinitrophenyl antibodies and of IgM rheumatoid factors.

Animals↗

PubMed1993

Subinvolution of the uteroplacental arteries: an immunohistochemical study.

Subinvolution of uteroplacental arteries is a well-recognized cause of hemorrhage in the postpartum period. Although the physiological changes in these arteries during pregnancy are well documented, the sequence of events in normal involution is largely unknown. A recent immunohistochemical study has raised the possibility of an abnormal interaction between maternal uterine cells and fetal trophoblast in subinvolution. An indirect immunoperoxidase technique was used to compare deposition of complement components and immunoglobulin in subinvoluted and normally involuted uteroplacental arteries in 25 cases of postpartum hemorrhage. Deposits of C1q, C3d, C4, and C9 were detected within the walls of normally involuted vessels, whereas deposition of C1q, C3d, and C4 was absent in subinvoluted vessels; C9 was detected only focally. Deposition of immunoglobulins G, A, and M mirrored those described for complement components. The results suggest that immunological factors are necessary for the process of normal involution of uteroplacental arteries and are deficient in subinvoluted vessels.

Arteries↗