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PubMed1991

Characterization and organization of the genes encoding the A-, B- and C-chains of human complement subcomponent C1q. The complete derived amino acid sequence of human C1q.

A partial cDNA clone for the A-chain of human complement subcomponent C1q was isolated from a monocyte library. Use of the A-chain cDNA clone, and a previously characterized B-chain cDNA clone [Reid (1985) Biochem. J. 231, 729-735] allowed the isolation of overlapping cosmid clones that were shown to contain the genes encoding the A-, B- and C-chains of human C1q. The three genes were found to be aligned, 5'----3', in the same orientation, in the order A-C-B on a 24 kb stretch of DNA on chromosome 1p. The A-, B- and C-chain genes are approx. 2.5, 2.6 and 3.2 kb long respectively, and each contains one intron, located within a codon for a glycine residue found half-way along the collagen-like region present in each chain. These glycine residues are located just before the point where the triple-helical portions of the C1q molecule appear to bend when viewed in the electron microscope. Southern-blot analyses indicated that there is only one gene per chain, and preliminary examination of genomic DNA from several C1q-deficient patients showed no evidence for major deletions or insertions within the A-, B- or C-chain genes. The DNA sequence of the coding region of the C-chain gene allows the completion of the entire derived amino acid sequence for the human C1q molecule. The globular, C-terminal, regions of the chains of C1q show a strong similarity in amino acid sequence to the non-collagen-like, C-terminal, regions of the type VIII and type X collagens, indicating structural and evolutionary relationships between these three molecules.

Amino Acid Sequence↗
PubMed1983

The binding properties of human complement component C1q. Interaction with mucopolysaccharides.

Quantitative measurements have been made of the interaction of human complement subcomponent C1q with mucopolysaccharides. The binding of C1q to heparin was quantitatively examined by utilizing an assay that employs a 125I-labeled low molecular weight heparin glycosaminoglycan (LMW-Hep) (Mr = 8500). Two classes of binding sites were detected. The first class of sites bound 2.02 mol of LMW-Hep/mol of C1q with a Kd of 76.6 nM. The second class of sites complexes with 12 mol of LMW-Hep with a Kd of 1.01 microM. The higher affinity-binding site for LMW-Hep could be assigned to the collagenous region of C1q (C1q-c); 2.2 mol of 125I-LMW-Hep were bound/mol of purified isolated C1q-c with a Kd = 381 nM. In contrast, the isolated C1q globular region did not bind to 125I-LMW-Hep. The binding of LMW-Hep to C1q and the C1q-c region was confirmed by fluorescence polarization experiments; C1q and C1q-c bound 2.3 and 2.02 mol of fluorescamine-labeled LMW-Hep/mol of protein, respectively. A variety of mucopolysaccharides were able to inhibit interaction of C1q with 125I-LMW-Hep, the most effective being heparan sulfate and dermatan sulfate. LMW-Hep (2.5 nM) inhibited the ability of C1q (0.5 nM) to recombine with C1r (1.4 nM) and C1s (1.6 nM) to form hemolytically active C1. At 250 mM, LMW-Hep inhibited the hemolytic activity of reconstituted C1. The ability of mucopolysaccharides to interact with purified C1q suggests a role for such molecules in the regulation of the first component of complement.

Centrifugation, Density Gradient↗
PubMed1988

Macromolecular organization of natural and recombinant lung surfactant protein SP 28-36. Structural homology with the complement factor C1q.

The macromolecular structure of the pulmonary surfactant apolipoprotein SP 28-36 has been determined. For SP 28-36 isolated from dog lung lavage, a flower bouquet-like hexameric structure with six globular domains connected by short stalks to a common stem was revealed by electron microscopy, using the rotary shadowing technique. This structure is very similar to that published for the subcomponent C1q of the first component of complement C1. The lavage material was compared with the homologous human recombinant SP 28-36 by the same technique. Mostly smaller aggregates like di-, tri- and tetramers as well as very high aggregates were observed. Mild reduction of the recombinant material revealed the lollipop-shaped monomers composed of a globular domain and a tail with a discrete kink in the middle portion. The collagenous nature of the tail was demonstrated by circular dichroism spectroscopy. This implies that the mammalian expression system assembles the monomeric subunits correctly. Assembly into the hexameric structures, however, does not proceed quantitatively.

Animals↗
PubMed1989

Biosynthesis of normal and low-molecular-mass complement component C1q by cultured human monocytes and macrophages.

High levels of low-molecular-mass complement component C1q (LMM-C1q), a haemolytically inactive form of C1q, are found in serum of individuals with inherited complete (functional) C1q deficiency and in serum of patients with systemic lupus erythematosus, whereas lower levels are present in normal serum [Hoekzema, Hannema, Swaak, Paardekooper & Hack (1985) J. Immunol. 135, 265-271]. To investigate whether LMM-C1q is a (by-)product of C1q synthesis or the result of degradation of C1q, cultures of blood monocytes and of alveolar macrophages, which secrete functional C1q, were studied. A considerable portion of C1q-like protein secreted by these cells was found to be LMM-C1q. In contrast with the C1q fragments that resulted from degradation of normal C1q during phagocytosis, culture-derived LMM-C1q appeared to be identical with LMM-C1q found in serum, as judged by sedimentation behaviour, subunit structure and recognition by poly- and mono-clonal antibodies raised against C1q. The presence of LMM-C1q in cytoplasmic organelles compatible with the Golgi apparatus and the inability to generate LMM-C1q by impeding hydroxylation and triple-helix formation of C1q further argues against degradation as its source. Monocyte cultures of homozygous probands from two families with complete functional C1q deficiency reflected the abnormalities in serum, i.e. absence of functional C1q, but increased levels of LMM-C1q. By contrast, secretion of C1q and LMM-C1q by cells from healthy individuals was clearly co-ordinate, indicating that LMM-C1q in serum may provide a unique marker of C1q synthesis in vivo.

Cells, Cultured↗
PubMed1989

Interaction between complement subcomponent C1q and bacterial lipopolysaccharides.

The heptose-less mutant of Escherichia coli, D31m4, bound complement subcomponent C1q and its collagen-like fragments (C1qCLF) with Ka values of 1.4 x 10(8) and 2.0 x 10(8) M-1 respectively. This binding was suppressed by chemical modification of C1q and C1qCLF using diethyl pyrocarbonate (DEPC). To investigate the role of lipopolysaccharides (LPS) in this binding, biosynthetically labelled [14C]LPS were purified from E. coli D31m4 and incorporated into liposomes prepared from phosphatidylcholine (PC) and phosphatidylethanolamine (PE) [PC/PE/LPS, 2:2:1, by wt.]. Binding of C1q or its collagen-like fragments to the liposomes was estimated via a flotation test. These liposomes bound C1q and C1qCLF with Ka values of 8.0 x 10(7) and 2.0 x 10(7) M-1; this binding was totally inhibited after chemical modification of C1q and C1qCLF by DEPC. Liposomes containing LPS purified from the wild-strain E. coli K-12 S also bound C1q and C1qCLF, whereas direct binding of C1q or C1qCLF to the bacteria was negligible. Diamines at concentrations which dissociate C1 into C1q and (C1r, C1s)2, strongly inhibited the interaction of C1q or C1qCLF with LPS. Removal of 3-deoxy-D-manno-octulosonic acid (2-keto-3-deoxyoctonic acid; KDO) from E. coli D31m4 LPS decreases the binding of C1qCLF to the bacteria by 65%. When this purified and modified LPS was incorporated into liposomes, the C1qCLF binding was completely abolished. These results show: (i) the essential role of the collagen-like moiety and probably its histidine residues in the interaction between C1q and the mutant D31m4; (ii) the contribution of LPS, particularly the anionic charges of KDO, to this interaction.

Acetates↗
PubMed1985

Molecular modelling of human complement subcomponent C1q and its complex with C1r2C1s2 derived from neutron-scattering curves and hydrodynamic properties.

Models for the structures of subcomponent C1q of first component C1 of human complement and its complex with subunit C1r2C1s2 are compared with experimental neutron-scattering curves. The length of the C1q collagenous arm is closer to 14.5 nm than to 11.5 nm proposed from electron microscopy, and this is consistent with the primary sequence of C1q. The mean C1q base-arm angle is 40-45 degrees and C1q is found to be flexible: the base-arm angle can vary up to 30 degrees from equilibrium at any moment. The complex of C1r2C1s2 and C1q requires a large shape change in C1r2C1s2. Ring-like models for C1r2C1s2 are not as successful at rationalizing the scattering data as are models that involve C1r2C1s2 binding to one side of C1q. Hydrodynamic calculations of the sedimentation coefficients for C1q and C1 are generally consistent with these neutron models.

Complement Activating Enzymes↗
PubMed1996

Complement subcomponent C1q modulation of TNF-alpha binding to L929 cells for enhanced TNF-mediated cytotoxicity.

Complement subcomponent C1q has been recently implicated in the modulation of autocrine binding of TNF-alpha to murine macrophages for induction of nitric oxide synthase. In the present study, the putative role of C1q in increasing TNF-alpha binding to L929 cells to mediate cytotoxicity was explored. TNF-sensitive L929 cells (L929-S) had higher total endogenous cellular and surface C1q levels and bound correspondingly more phycoerythrin-labelled rTNF-alpha (PE-TNF) than did a TNF-resistant L929 variant (L929-R). Pretreatment of L929-S with soluble C1q increased their sensitivity to TNF-mediated cytotoxicity coincident with increased binding of PE-TNF, but similar treatment of L929-R had no effect. Pretreatment of L929-S with an inhibitor of C1q secretion, 3,4 dehydro-D,L-proline (DHP), resulted in a decrease in their TNF-mediated cytotoxicity, as well as reduced binding of PE-TNF. Subsequent exposure of DHP-treated L929-S with exogenous soluble C1q restored their TNF-mediated cytotoxicity and binding of PE-TNF. These results provide evidence for the modulation of TNF-alpha binding to TNF sensitive tumour targets L929 by either endogenously synthesized or exogenously added C1q to promote TNF-mediated cytotoxicity by mechanisms which remain to be elucidated.

Animals↗
PubMed1991

Kinetics of the biosynthesis of complement subcomponent C1q by murine macrophages: LPS, immune complexes, and zymosan alone and in combination with interferon-gamma.

We investigated the effects of bacterial lipopolysaccharide (LPS), immune complexes (IC), and C3b opsonized zymosan (AZ) alone and in combination with interferon-gamma (IFN-gamma) priming on macrophage synthesis and secretion of C1q. Our results indicated that LPS, IC, and AZ alone stimulated C1q mRNA and secretion in the absence of IFN-gamma. The increase in mRNA accumulation was detectable after 3 h, peaked at 6 h and was maintained at constitutive levels for 24 h. There was a corresponding early burst of increased secretion of functional C1q after 3 to 6 h which declined rapidly after 9 to 24 h culture of LPS-stimulated macrophages. Priming of macrophages with IFN-gamma and simultaneous triggering with LPS, IC, or AZ produced additive rather than synergistic increases in C1q mRNA accumulation. These same agents inhibited constitutive secretion of C1q in the absence of IFN-gamma priming as determined by autoradiographic analysis of metabolically radiolabeled secretory C1q. Triggering of IFN-gamma primed macrophages with LPS, IC, or AZ also markedly suppressed the increased rate of C1q secretion induced by IFN-gamma in a dose-related fashion. A corresponding dose-dependent increased accumulation of endogenous C1q in cell lysates was detected by Western blot analysis of macrophages which had been stimulated by LPS, IC, or AZ alone or in combination with IFN-gamma. Our findings indicate that LPS as well as FcR and C3bR triggering agents stimulate early and sustained C1q synthesis accompanied by an early and short-lived burst of C1q secretion which rapidly diminished and results in an increased intracellular accumulation of C1q due to ongoing synthesis. IFN-gamma appeared to further amplify the same kinetics of increased C1q mRNA accumulation and decreased extracellular accumulation mediated by LPS, IC, and ZM. Our results suggest that LPS, IC, and AZ alone or in combination with IFN-gamma stimulate early C1q production to modulate macrophage effector functions followed by an inhibition of C1q secretion when the activation process has been culminated.

Animals↗
PubMed1995

Complement components C1q, C1r/C1s, and C1INH in rheumatoid arthritis. Correlation of in situ hybridization and northern blot results with function and protein concentration in synovium and primary cell cultures.

OBJECTIVE: To analyze the synovial site and the cell types expressing C1q, C1r/C1s, and C1-esterase inhibitor (C1INH) and to characterize newly synthesized C1q in patients with rheumatoid arthritis (RA). METHODS: Tissue and primary cell cultures of synovium from RA patients were analyzed for C1q, C1r/C1s, and C1INH by Northern blotting, in situ hybridization, and pulse-chase experiments for C1q. RESULTS: The de novo synthesis of C1q, C1r/C1s, and C1INH in synovium and primary cell cultures was proven by Northern blot and by antigenic and functional analysis. In in situ hybridization experiments, the synovial lining cell layer was identified as the site of C1q, C1r, and C1INH expression. In contrast, immunohistologic analysis showed that C1q, C1s, and C1INH proteins were present in a thin film covering the synovial lining cells. In situ hybridization performed on primary cell cultures provided evidence that only macrophages were able to express C1q, whereas fibroblasts and stellate cells synthesized C1r. CONCLUSION: The synovium is important for the synthesis and secretion of C1q and C1r/C1s, as well as the control protein C1INH, which supports the idea of a locally occurring inflammatory process in RA patients.

Arthritis, Rheumatoid↗
PubMed1991

Kinetics of the biosynthesis of complement subcomponent C1q by murine macrophages: effects of stimulation by interferon-gamma.

The effects of interferon-gamma (IFN-gamma) on the kinetics of biosynthesis of complement subcomponent C1q by mouse inflammatory peritoneal macrophages were determined. Stimulation of macrophages with various concentrations of IFN-gamma produced a dose-dependent increase in C1q mRNA accumulation which was detected as early as 3 h and sustained through 24 h, as determined by Northern blot analysis. A corresponding early increase in the extracellular accumulation of functional C1q was detected in culture supernatants after 3-9 h stimulation of macrophages with IFN-gamma that was sustained for 24-48 h as determined by a complement hemolytic assay. Autoradiographic analysis of [35S]methionine-labeled secretory C1q confirmed the protracted dose-dependent secretion of C1q by IFN-gamma stimulated macrophages during 24-48 h of culture. Western blot analysis of macrophage lysates indicated no significant changes in endogenous C1q levels following stimulation with IFN-gamma either after 3-9 h or 24-48 h when both C1q mRNA and extracellular accumulation were at their peak. Our results indicate that IFN-gamma promotes early and protracted mRNA accumulation and secretion of C1q by macrophages without intracellular accumulation, presumably due to the rapid rate of secretion of newly synthesized C1q. It is apparent that priming of macrophages with IFN-gamma provides a rapid and abundant source of secretory C1q for potential interaction with various macrophage triggering agents which also bind C1q.

Animals↗
PubMed1991

Binding of the human complement subcomponent C1q to hybrid mouse monoclonal antibodies.

Activation of the classical pathway of the complement system is initiated by the binding of C1q to antibody complexes. Here we evaluated the C1q binding capacity of series of monospecific and bispecific hybrid mouse monoclonal antibodies (mAb) and compared them with parental (conventional) mAb. The hierarchy in C1q binding capacity of the bispecific anti-HuIgA1/HRP mAb with homologous H-H chain combinations (IgG2a-2a, IgG2b-2b and IgG1-1) and the parental anti-HuIgA1 or anti-HRP mAb was identical; IgG2a greater than IgG2b much greater than IgG1. Hybrid IgG1-2a mAb bind intermediate amounts of C1q when compared with the IgG1 and IgG2a parental antibodies. IgG1-2b and IgG1-1 hybrid mAb did not bind any C1q, like the IgG1 mAb. We could not observe any difference in C1q binding efficiency between monovalently bound IgG1-2a, IgG2a-2a and IgG2b-2b anti-HuIgA1 HRP mAb and the bivalently bound IgG1-2a, IgG2a-2a and IgG2b-2b anti-HuIgA1 mAb, respectively. Furthermore, these hybrid ms anti-HuIgA1 and bs anti-HRP/HuIgA1 mAb were able to lyse HuIgA1-coated erythrocytes, in the presence of 50% human serum, as efficiently as their parental counterparts. These data indicate that a simultaneous binding of both F(ab') fragment to antigen is not a necessary prerequisite for binding and activation of C1q.

Antibodies, Monoclonal↗
PubMed1983

Biosynthesis in vitro of complement subcomponents C1q, C1s and C1 inhibitor by resting and stimulated human monocytes.

The capacity of cultured human monocytes to synthesize and to secrete the subcomponents of C1 and C1 inhibitor was examined. Non-stimulated monocytes secreted C1q and C1s from day 5 of culture. C1s reached a plateau immediately at its maximum level, whereas C1q secretion increased progressively until the end of the second week. Between day 12 and day 25, C1q secretion remained nearly constant (1-15 fmol/day per microgram of DNA, depending on the donor), whereas C1s secretion decreased and even in some cases stopped. C1r and C1 inhibitor were not secreted in detectable amounts by these resting cells. Stimulation of monocytes by yeasts, immunoglobulin G-opsonized sheep red blood cells or latex beads did not modify consistently C1q and C1s secretion. Activation by conditioned media from mitogen-, antigen- or allogeneic-stimulated lymphocyte cultures increased C1q production from 2 to 7 times and re-activated C1s secretion. Under the same conditions of activation, C1 inhibitor was secreted (up to 300 fmol/day per microgram of DNA) and C1r became detectable in culture supernatants. Isolated human monocytes are thus able to synthesize the whole C1 subcomponents; C1, if assembled, could be protected from non-immunological activation by locally produced C1 inhibitor. Activated monocytes appear to be a good tool for studying the assembly of C1 subcomponents and the role of C1 inhibitor in this process.

Cells, Cultured↗
PubMed1987

Modulation of FcR function by complement: subcomponent C1q enhances the phagocytosis of IgG-opsonized targets by human monocytes and culture-derived macrophages.

We have investigated the interaction of C1q, a subunit of the first component of complement, with human monocytes and culture-derived macrophages. Adherence of these mononuclear phagocytes to surfaces coated with C1q induced a marked enhancement of the phagocytosis of sheep erythrocytes opsonized with IgG anti-Forssman antibody (EA-IgG). This C1q-mediated enhancement of phagocytosis was dose dependent, and was specifically blocked by pretreatment of the C1q-coated surfaces with F(ab')2 anti-C1q. The augmentation of FcR-mediated phagocytosis by C1q was determined to be a result of the interaction between the C1q and the phagocytic effector cell, and was not due to interaction between the surface-bound C1q and the EA-IgG. Neither resting nor N-formyl-methionyl-leucyl-phenylalanine-stimulated polymorphonuclear leukocytes were induced by C1q to increase FcR-mediated phagocytosis. Experiments conducted with purified fragments of C1q suggest that the C1q phagocytosis enhancement signal resides in the collagen-like tail domain of the molecule. This region is the same portion of the molecule previously shown to interact with the cell surface C1q receptor. Native type I collagen was unable to enhance FcR-mediated phagocytosis by mononuclear phagocytes. It has been demonstrated that C1q can be localized to areas of inflammation, and additionally C1q can be secreted by macrophages in culture. In view of these findings and the results of our present study, we hypothesize that C1q could provide local, direct, and non-opsonic enhancement of phagocytosis by mononuclear phagocytes in areas of infection and inflammation.

Cell Adhesion↗
PubMed2026

Proteomic profiling of cephalic vein reveals potential biomarkers for arteriovenous fistula neointimal hyperplasia in ESRD patients.

Arteriovenous fistula (AVF) is the preferred vascular access for patients with end-stage renal disease; however, its failure is primarily due to neointimal hyperplasia. Five patients who underwent initial AVF surgery served as the control group, and another five patients with failed AVF surgery served as the experimental group. Herein, we employed mass spectrometry (MS)-based quantitative proteomics coupled with tandem mass tag labeling to screen differentially expressed proteins (DEPs) in the anastomotic cephalic vein, followed by bioinformatics analyses and verification experiments. A total of 121 DEPs were identified in the failed AVF group. GO analysis was primarily enriched in protein binding, nucleic acid binding, enzyme binding, mRNA binding, cadherin binding, catalytic activity, and cell adhesion molecule binding. KEGG pathways were mainly enriched in cell aggregation and adhesion, actin cytoskeleton, extracellular matrix-receptor interaction, PI3K-Akt signaling pathway, complement and coagulation cascades, and cholesterol metabolism. Protein-protein interaction network consisted of 86 (71.07%) DEPs, including complement VII (C7), factor IX (F9), SERPINC1, microfibril-associated glycoprotein 4 (MFAP4), complement C1s subcomponent, complement C1q subcomponent subunit A, complement C1q subcomponent subunit B, tissue factor, and von Willebrand factor, which interacting with numerous other proteins. In the expanded validation for different patients, C7, F9, SERPINC1, and MFAP4, were verified by immunohistochemical staining and Western blotting, which were consistent with the proteomics results. Collectively, this study identifies a series of potential diagnostic biomarkers, and explores the underlying mechanisms associated with AVF dysfunction.

Humans↗
PubMedDate not supplied

Contribution to the mode of action of univalent gold.

Au+ binds to the collagen structure and, therefore, the authors studied the kinetics of the interaction between sodium gold thiosulphate (SGTS) and C1q complement subcomponent, the structure of is partially collagenous. The kinetics was evaluated densitometrically and compared with that of collagen and SGTS. On the basis of those results, the effect of SGTS upon collagen type-II-induced arthritis (CIA) was investigated in Wistar rats. SGTS (20 mg per kg of body weight weekly) was administered i.m. starting i) with the first immunization dose, ii) with the second immunization dose, and iii) after the onset of arthritis. Regardless of the timing of drug administration the manifestation of arthritis was decreased, but the decrease was more expressed in the first two groups. It was concluded that SGTS administration is capable of inhibiting CIA, provided that the drug is applied sufficiently early. Since formation of antibodies to type-II collagen remained unaffected, it is feasible that the mode of action of gold complexes is based mainly on blocking the activation of complement system.

Animals↗
PubMed1987

In vivo immunosuppression by pan-T cell antibodies relates to their isotype and to their C1q uptake.

There is considerable interest in the use of monoclonal anti-T cell antibodies for immunosuppression during organ transplantation. However, the in vitro cytotoxic titers of these monoclonal reagents do not correlate with their immunosuppressive potency when injected in vivo. A relationship nevertheless seems to exist between immunosuppression and the isotype of anti-mouse Thy-1 antibodies, because among several anti-Thy-1 antibodies of mouse and rat origin, the only two found to cause immunosuppression in vivo belonged to the rat IgG2b and mouse IgG2a isotype. We show here that a quantitative positive correlation exists between an antibody-induced humoral effector mechanism and immunosuppression. We measured the uptake of the C1q complement subunit by polyclonal rabbit and rat anti-thymocyte globulin and also seven monoclonal anti-Thy-1 antibodies in an immunohistochemical assay or a radioimmunoassay. Immunosuppression was studied in a murine graft-vs-host and skin allograft model. Our results suggest strongly that a stable association between the C1 protein and a potential binding antibody is an essential prerequisite of antibody-dependent cell inhibition in vivo that suppresses the immunoresponse against strongly incompatible transplantation antigens.

Animals↗
PubMed1994

[Conformational analysis and hemolytic activity of immunoglobulin G fragment 285-292 and its analogs].

Theoretical conformational analysis was carried out for the 285-292 fragment of human immunoglobulin G (His-Asn-Ala-Lys-Thr-Lys-Pro-Arg) and its analogues containing Arg, Glu, Gly, Lys, or Trp residue instead of the His residue in position 1. Spectropolarimetic investigation of these peptides showed the analogues to have different activities in the C1q-mediated erythrocytes hemolysis assay. Comparison of the low-energy structures sets of the compounds tested allowed to suggest a model of the "biological active" conformation for the peptide molecule in the course of the C1q complement component binding.

Complement C1q↗
PubMed1990

[Autoantibodies against the complement component C1q in systemic lupus erythematosus].

Autoantibodies against C1q, a subcomponent of the first complement component C1, could be detected in 49.4% of sera from patients with systemic lupus erythematosus (SLE). They are directed against the collagen-like portion of the C1q molecule and recognize only bound, but not fluid-phase C1q. The appearance of these autoantibodies in the course of SLE correlates with the detection of IgG in the C1q-Solid-Phase-Binding-assay, with high titres of dsDNA-antibodies and with depressed total complement activity (CH50) and C1q-values. Our investigations show that autoantibodies against the collagen-like portion of bound C1q but not immune complexes are the main constituent of C1q-binding IgG in SLE.

Autoantibodies↗