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PubMed1979

[Immunologic factors and platelet vessel wall interactions (author's transl)].

Platelet subendothelium interaction is an essential step in thrombosis and hemostasis which can be modulated by immunoglobulins, immune complexes, complement, and leukocytes. Antiplatelet antibodies can induce thrombocytopenia which is accompanied by a reduced vascular wall thickness and an increased fenestration. Antigen-antibody complexes can activate platelets inducing platelet release and aggregation. This reaction is amplified by the first component of complement C1q. Cytotoxic antibodies directed against endothelial cells have been observed in transplantation. These antibodies can be directed against HL-A antigens or specific endothelial antigens. Anticollagen antibodies have been detected in patients with leprosy. The C1q component can inhibit adhesion of platelets to collagen and platelet aggregation induced by collagen. The association of acquired or congenital C1q deficiency and vasculitis has been reported. C3a is taken up by endothelial cells and metabolized. C3a and C5a can modify vessel wall permeability and activate granulocytes which can become toxic for endothelial cells. Leukocyte cationic protein can reduce platelet aggregation. An anti-von Willebrand antibody could be the origin of hemostatic abnormalities and endothelial lesions. The involvement of immunologic factors in platelet vessel wall interactions is complex. Immune complexes and some antibodies seem capable of promoting thrombosis, while a component of complement (C1q) may also have an antithrombotic role.

Antibodies↗
PubMed1978

The reaction between the complement subcomponent C1q, IgG complexes and polyionic molecules.

The strength of the bond between 125I-labelled C1q and immune complexes, Fc piece, dextran sulphate, polyglutamic acid and polylysine has been investigated. The binding of C1q to Fc piece, small molecular weight (less than 10,000) dextran sulphate, polyglutamic acid and polylysine have value; for the functional affinity constant (Ko) in the range of 0.2-1.5 X 10(4) M-1. In contrast the binding of C1q to immune complexes and large molecular weight polyions (greater than 100,000 is much greater and lies in the range 3 X 10(7)--4 X 10(8) M-1. The differences in the binding constants between the two groups can be explained if the Fc piece and small molecular weight compounds bind to only 1 head of the C1q molecule but the immune complexes and large molecules bind to 2 heads. There are probably 6 binding sites on the C1q molecule for dextran sulphate. The enhancement of the binding affinity of C1q by reduction in ionic strength and the reaction with polyions, indicate that ionic groups are present near or within the binding sites.

Antigen-Antibody Complex↗
PubMed1996

[Acquired generalized cutis laxa with paraproteinemia (IgG lambda). Immunofluorescence study, clinical and histologic findings with review of the literature].

A 49-year-old patient developed acquired generalized cutis laxa, manifest as involvement of the elastic fibres of the dermis and the internal organs, leading to pulmonary emphysema, bilateral inguinal hernia and two oesophageal diverticula. The patient's serum levels of IgG lambda paraprotein were elevated. Direct immunofluorescence examination revealed intensive linear deposits of IgG lambda light chains, an early component of complement C1q and discrete C3 deposits. The deposits were found along the preserved elastic fibres in the dermis, especially in the papillary dermis, at the dermoepidermal junction around the sweat and sebaceous glands and in the walls of small vessels. Dermal alterations of this kind have not been described previously.

Basement Membrane↗
PubMed1996

Aortobifemoral surgery induces complement activation and release of interleukin-6 but not tumour necrosis factor-alpha.

The aim of the present study was to determine the inflammatory response by an extended analysis of complement in 16 patients undergoing aortobifemoral bypass surgery. The patients were randomized to receive either a bifurcated expanded polytetrafluoroethylene graft (n = 8; group I) or a collagen-impregnated knitted Dacron graft (n = 8; group II) to determine whether differences in graft surface properties might influence the inflammatory response during and after the procedure. The following components of complement: C1q, C4, C3, C3d, C5a and terminal complement complexes were all analysed. C-reactive protein and interleukin-6 were also determined to assess the acute phase response. The complement data were corrected for haemodilution, which was assessed from alpha 2-macroglobulin concentrations. A significant decrease of C1q (P < 0.0001) and an increase in C5a (P < 0.0005) was observed in both groups. C4 and C3 levels showed slight fluctuations in group I, whereas in group II these proteins increased significantly (P < 0.05, P < 0.005, respectively) between 2 and 7 days after surgery. Terminal complement complexes remained unchanged in both groups. Interleukin-6 levels peaked at 12-24 h and the C-reactive protein at 24-72 h. Higher interleukin-6 levels (P < 0.05) were found in group II 6 h after surgery compared with group I; no release of tumour necrosis factor-alpha was identified. An early inflammatory response was found in all patients. The patterns of the complement proteins varied with a C1q depletion and a C5a increase, interpreted as complement activation. Whether the variations between the two graft groups represent any differences in graft surface properties has to be further elucidated.

Aged↗
PubMed1983

Plasma fibronectin-C1q complex formation and its effect on C1q inhibition of collagen-induced platelet aggregation.

The first component of complement (C1q) contains a collagen-like structure which evidently accounts for its ability to bind to platelets and to inhibit collagen-induced platelet aggregation. This present investigation explored the interaction among C1q, plasma fibronectin (Pl Fn) and platelets. Gel filtration chromatography (Sepharose 2B and 4B) of preincubated mixtures of C1q and Pl Fn yielded evidence of complex formation. Preincubation of Pl Fn with platelets did not affect collagen-induced platelet aggregation nor did preincubation of Pl Fn with C1q significantly affect C1q-mediated inhibition of collagen-induced platelet aggregation. These observations may indicate that the site of interaction between Pl Fn and C1q is different from the site of interaction between C1q and platelets.

Blood Platelets↗
PubMed1993

Structural features of human immunoglobulin G that determine isotype-specific differences in complement activation.

Although very similar in sequence, the four subclasses of human immunoglobulin G (IgG) differ markedly in their ability to activate complement. Glu318-Lys320-Lys322 has been identified as a key binding motif for the first component of complement, C1q, and is present in all isotypes of Ig capable of activating complement. This motif, however, is present in all subclasses of human IgG, including those that show little (IgG2) or even no (IgG4) complement activity. Using point mutants of chimeric antibodies, we have identified specific residues responsible for the differing ability of the IgG subclasses to fix complement. In particular, we show that Ser at position 331 in gamma 4 is critical for determining the inability of that isotype to bind C1q and activate complement. Additionally, we provide further evidence that levels of C1q binding do not necessarily correlate with levels of complement activity, and that C1q binding alone is not sufficient for complement activation.

Amino Acid Sequence↗
PubMed1993

Effector functions of a mouse IgG that lacks the entire CH1 domain. C1q binding and complement fixation in the absence of antigen.

C1q binding and complement fixation were examined of a short-chain IgG2a antibody that lacks the entire CH1 domain. This short-chain antibody has been reported to have a low level of constitutive complement-activating activity in the absence of Ag. Two-dimensional SDS/PAGE and cation-exchange chromatography have demonstrated that two types of IgG2a proteins are secreted by the short-chain IgG2a antibody producing cell line. It has been shown that 1) the difference between these two types of the IgG2a proteins is whether the two L chains are linked by a disulfide bridge or not, and 2) C1q-binding and complement-activating activities are expressed only when the inter L chain disulfide bridge does not exist. A molecular model is presented for the active form of the short-chain IgG2a antibody.

Animals↗
PubMed1982

Characterization of various immunoglobulin preparations for intravenous application. II. Complement activation and binding to staphylococcus protein A.

14 immunoglobulin preparations for intravenous use were tested to assess functions of their Fc portion. Inhibition of the hemolytic activity of complement, C1q binding and the interaction of IgG subclasses with Staphylococcus protein A were investigated. Complement studies were done on both the ready-for-infusion and the heat-aggregated preparations. Three groups of products could be distinguished: (1) Enzymatically and chemically treated products were devoid of complement-activating capacity, both when tested and ready-for-infusion and as heat-aggregated preparations. The chemically treated preparations showed atypical binding properties to Staphylococcal protein A. (2) The poly-(ethylene glycol) (PEG)-treated preparations and the untreated reference activated complement before and after heat-aggregation. (3) The albumin protected and the pH 4-treated product did not spontaneously activate complement in the ready-for-infusion state but did so after heat-aggregation. These results suggest that only the albumin-protected and the pH 4-treated products can be expected both to be well tolerated when given intravenously to high-risk agammaglobulinemic patients and to exhibit normal Fc functions in vivo.

Complement Activating Enzymes↗
PubMed2000

Complement receptor 1/CD35 is a receptor for mannan-binding lectin.

Mannan-binding lectin (MBL), a member of the collectin family, is known to have opsonic function, although identification of its cellular receptor has been elusive. Complement C1q, which is homologous to MBL, binds to complement receptor 1 (CR1/CD35), and thus we investigated whether CR1 also functions as the MBL receptor. Radioiodinated MBL bound to recombinant soluble CR1 (sCR1) that had been immobilized on plastic with an apparent equilibrium dissociation constant of 5 nM. N-acetyl-d-glucosamine did not inhibit sCR1-MBL binding, indicating that the carbohydrate binding site of MBL is not involved in binding CR1. C1q inhibited MBL binding to immobilized sCR1, suggesting that MBL and C1q might bind to the same or adjacent sites on CR1. MBL binding to polymorphonuclear leukocytes (PMNs) was associated positively with changes in CR1 expression induced by phorbol myristate acetate. Finally, CR1 mediated the adhesion of human erythrocytes to immobilized MBL and functioned as a phagocytic receptor on PMNs for MBL-immunoglobulin G opsonized bacteria. Thus, MBL binds to both recombinant sCR1 and cellular CR1, which supports the role of CR1 as a cellular receptor for the collectin MBL.

Binding Sites↗
PubMed1992

Antibodies against C1q in anti-glomerular basement membrane nephritis.

The prevalence of antibodies against the collagen-like region of the subcomponent of the first component of complement, C1q, was investigated in 11 patients with anti-glomerular basement membrane (GBM) nephritis. Anti-C1q antibodies (anti-C1qAb) were detected in seven patients. IgG anti-C1qAb were found in four and IgA anti-C1qAb in five patients. During follow up of the patients a relationship was observed between the levels of IgG anti-C1qAb and the levels of anti-GBM antibodies (anti-GBMAb). Gelfiltration experiments indicated that both IgG anti-C1qAb as well as IgG anti-GBMAb were monomeric and that binding also occurred with the F(ab')2 fragments of the antibodies. Although anti-C1qAb and anti-GBMAb are both directed against a collagen-like structure, it was demonstrated by means of inhibition experiments that anti-C1qAb and anti-GBMAb are directed against different antigenic sites. Comparison of patients with anti-GBM nephritis with and without anti-C1qAb revealed that there were no differences in disease activity or disease severity. Therefore, the results of this study suggest that anti-C1qAb do not play a direct pathogenetic role in anti-GBM nephritis.

Adult↗
PubMed1994

Antibodies to the collagen-like region of C1q and type II collagen are independent non-cross-reactive populations in systemic lupus erythematosus and rheumatoid arthritis.

The collagen-like region (CLR) of the first component of complement, C1q, and type II collagen are structurally similar, raising the possibility of epitopes in common, and of the existence of autoantibodies that are cross-reactive. Accordingly, antibodies to the CLR of C1q and to type II collagen were measured in patients' sera with systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) by an ELISA. IgG antibodies to the CLR of C1q were present in 17% of patients with SLE but none with RA, and IgA antibodies were present in 10% and 8% of patients with SLE and RA, respectively. IgG antibodies to type II collagen were present in 15% and 25% of patients with SLE and RA, respectively, and IgA antibodies in 15% and 28% of patients with SLE and RA, respectively. There was no correlation in either disease between the serum levels of antibodies to the CLR of C1q and antibodies to type II collagen. For sera with antibodies to both antigens, neither competitive inhibition by ELISA nor preabsorption with the alternative antigen affected the level of reactivity to the other antigen. Thus antibodies to the CLR of C1q and antibodies to type II collagen are independent and non-cross-reactive populations, and presumably occur by different types of immunogenic stimulation.

Antibody Specificity↗
PubMed1995

Solid-phase C1q-directed bacterial capture followed by PCR for detection of Chlamydia trachomatis in clinical specimens.

An antigen capture system based on the binding of bacteria to solid-phase immobilized complement C1q followed by PCR for detection of Chlamydia trachomatis in clinical samples was developed and clinically evaluated. Comparison of C1q-directed antigen capture PCR with cell culture and direct PCR on 71 consecutive clinical specimens revealed an identical sensitivity. In this group, all 11 cell culture-positive samples were positive by direct PCR and C1q-directed antigen capture PCR. In addition, two samples found negative by cell culture were found positive by both direct PCR and C1q-directed antigen capture PCR. To further assess the sensitivity of C1q-directed antigen capture PCR, 20 clinical samples with one to five inclusions in cell culture and 20 clinical samples with 6 to 20 inclusions in cell culture were tested. Results obtained showed sensitivities of 95 and 90% for clinical samples with 6 to 20 and 1 to 5 inclusions in cell culture, respectively. Using C1q-coated solid phases, C1q-binding Chlamydia particles can be concentrated from large volumes with concomitant removal of inhibitors of PCR, allowing the use of large volumes of clinical samples for clinical testing. Since C1q has been shown to bind to a range of gram-negative bacteria, the newly developed technique has utility for a broad range of bacteria.

Antigens, Bacterial↗
PubMed1995

Follicular dendritic cells, interdigitating cells, and cells of the monocyte-macrophage lineage are the C1q-producing sources in the spleen. Identification of specific cell types by in situ hybridization and immunohistochemical analysis.

In a mouse model, we have shown previously that macrophages are the principal source of complement C1q. Furthermore, spleen, heart, and brain were found to contain substantial levels of murine C1q-specific mRNA, whereas liver, kidney, lung, and small intestine contained only trace amounts of C1q-specific mRNA. This work addresses the identification of C1q-expressing spleen cells in the rat, using Northern blotting and in situ detection of rat C1q mRNA combined with immunohistochemical analysis. The complete sequence of mRNA encoding the B chain of rat C1q was established. The cloned cDNA was found to hybridize primarily with spleen-derived mRNA of 1.2 kb, and additionally with a novel mRNA species of 3 kb. In situ hybridization together with immunohistochemistry revealed most of the C1q-expressing cells to be located in the red pulp of the spleen, and to be mainly of the monocyte-macrophage lineage, as indicated by coexpression of ED-1, an established marker for this type of cell. In addition, C1q was expressed in S-100-positive but ED-1-negative cells, in germinal center follicular dendritic cells, and in some interdigitating dendritic cells of the periarteriolar lymphatic sheath (PALS). These results indicate that the spleen, containing the above APCs that are all involved to a major extent in the adaptive immune response and are all capable of synthesizing C1q that is involved intimately in the innate immune response, may provide the site at which the innate and adaptive immune systems merge.

Amino Acid Sequence↗
PubMed1992

Immunomodulatory action of propolis: IV. Prophylactic activity against gram-negative infections and adjuvant effect of the water-soluble derivative.

The efficacy of the water-soluble derivative (WSD) of natural propolis (bee glue) was examined for augmentation of host resistance against experimental infections caused by Gram-negative pathogens (Klebsiella pneumoniae, Proteus vulgaris, Escherichia coli, Pseudomonas aeruginosa). The substance was found to induce significant non-specific protection, but did not inhibit the in vitro growth of the same strains. Pretreatment with WSD prior to the standard scheme for tumour necrosis factor (TNF) induction (BCG and two weeks later lipopolysaccharide (LPS)) provoked an interval-dependent reduction in the lytic capacity of serum against L 929 target cells. The replacement of the triggering or priming signal with WSD markedly increased TNF production. In vivo administration of WSD led to a rapid and route-dependent change in the alternative complement pathway haemolysis. The alteration in C1q complement component and total protein synthesis, and also in nitroblue tetrazolium reduction, suggests that macrophage activation makes a major contribution to the capacity of WSD to prevent infections.

Adjuvants, Immunologic↗
PubMed1982

Structures of the asparagine-linked sugar chains of subcomponent C1q of the first component of bovine complement.

Bovine C1q, a subcomponent of the first component of complement, contains six asparagine-linked sugar chains in 1 molecule. The sugar chains are exclusively distributed in the noncollagenous regions. The sugar chains were liberated as radioactive oligosaccharides from the polypeptide portion by hydrazinolysis followed by N-acetylation and NaB[3H]4 reduction, and their structures were studied by sequential exoglycosidase digestion in combination with methylation analysis. Bovine C1q was shown to contain equal amounts of neutral and acidic oligosaccharides with the following structures: (formula, see text) where NeuG1 is N-glycolylneuraminic acid.

Animals↗
PubMed1999

C1q inhibits autoantibody binding to calreticulin.

Calreticulin (CR) is a new rheumatic disease-associated autoantigen that is intimately associated with the Ro/SS-A ribonucleoprotein. CR autoantibodies are frequently observed in patients with photosensitive forms of lupus erythematosus (LE). CR has been shown to be highly homologous to cC1q-R, the cell surface receptor that binds the collagenous domain of the first component of complement, C1q. C1q has also been shown to directly bind to CR. We therefore asked whether the binding of C1q to CR might interfere with the binding of CR autoantibody to CR. Full-length recombinant human CR, an E. coli fusion proteins was used as antigen in a direct enzyme-linked immunosorbent assay (ELISA). CR autoantibody-containing sera were assayed before and after C1q removal by two different methods: by heating sera at 56 degrees C for 30 min or adding monoclonal anti-C1q antibodies. ELISA optical density (OD) values were found to be consistently higher in sera depleted of C1q by both methods compared to unmodified sera. The addition of purified C1q to C1q-depleted sera resulted in ELISA OD values similar to those of unmodified sera. These results suggest that C1q levels present in human serum can inhibit the binding of CR autoantibody to CR. One can speculate that the failure of C1q to mask CR autoepitopes in individuals with genetic deficiency of C1q could contribute to the high rate of photosensitive LE that occurs in such individuals.

Antibodies, Monoclonal↗
PubMed1991

[Angioedema due to acquired complement-C1-inhibitor deficiency in a female patient with non-Hodgkin lymphoma and autoimmune hemolytic anemia].

A case of angioedema due to acquired deficiency of the regulatory protein C1-esterase-inhibitor (C1-INH) is reported. The edematous attack occurred 3 1/2 weeks after initiation of successful therapy for autoimmune-hemolytic anemia in the course of long-standing non-Hodgkin's lymphoma. At the time of acute edema the complement profile was typical: virtual absence of C1-INH function was associated with diminished concentrations of the components of the classical pathway of complement (C1q, C1r, C1s, C2, C4) and reduced complement hemolytic activity (CH50). Anti-C1-INH-autoantibodies were not detected. The angioedema lasted for about one week, and no further attacks occurred during the five-months follow-up period. Although there was only a minor adjustment to the therapy, the C1q, C2, C4 and CH50 values gradually increased to levels close to the lower limit of the normal range, while C1r and C1s showed normal values. In contrast to most other reports, this case was characterized by angioedema which was precipitated only after initiation of appropriate treatment for the underlying disease rather than before therapy or even diagnosis of the underlying disease.

Aged↗