Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Complement C1r”

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 307 records · Page 17Linked to original sources
PubMed1997

Complement classical pathway expression by human skeletal myoblasts in vitro.

Human myoblasts express immunological properties in vitro and we have previously reported that they produce Complement (C) components of the alternative pathway. Myoblasts activate the classical pathway but are fully protected against C attack by the expression of major C regulators. In order to fully understand the relationship between myoblasts and C, we here report the biosynthesis of C components of the classical pathway by skeletal muscle cells. Human myoblasts in vitro produced C1q, C1r, C1s, C2 and C4 constitutively and all syntheses were upregulated after stimulation with IFN-gamma. We suggest that human myoblasts may constitute a local source of C and therefore C could be implicated in inflammatory or physiopathological processes developed in skeletal muscle.

Blotting, Western↗
PubMed2005

Inhibition of classical pathway of complement activation with negative charged derivatives of bisphenol A and bisphenol disulphates.

In order to obtain strong inhibitors of classical pathway of complement activation the low weight negative charged compounds have been investigated. On the basis of bisphenol A anionic derivatives with one or two carboxylic, sulphate and phosphate groups the critical role of negative charged groups for complement-inhibiting activity has been established. It was determined that two sulphate or phosphate groups in the molecule provide the most inhibiting effect. At the next stage a set of bisphenol disulphates of varying structures has been synthesized and investigated. Bulky hydrophobic groups (cyclohexyliden, fluorenyliden, anthronyliden) at the central part of the bisphenol molecule it was found to increase complement-inhibiting activity markedly. The replacement of the ortho-positions to the charged group by halogens or alkyl groups (allyl, propyl) increases the inhibiting effect. It was showed by ELISA that several compounds studied interact with C1q, C1r /C1s components of complement. For the set of bisphenol disulphates the QSAR equation with hydrophobic coefficient and electronic parameters has been formulated. Both hydrophobic and electrostatic interactions it was established to have a great significance for the inhibition of classical pathway of complement activation.

Animals↗
PubMed1978

Activation of the first component of human complement (C1) by antibody-antigen aggregates.

The activation of subcomponents C1r and C1s in the first component of complement, C1, when bound to antibody-antigen complexes was investigated. Activation was followed both by the splitting of the peptide chains of subcomponents C1r and C1s and by the development of proteolytic activity. For the maximum rate of activation to occur, all components must be present in approximate molar proportions of antibody: C1q:C1r:C1s of 13:1:5:5. For activation of subcomponent C1s, subcomponents C1r or C1r, but not C1r inactivated with iPr2P-F (di-isopropyl phosphorofluorideate), are effective. For activation of subcomponent C1r, subcomponents C1s, C1s or C1s inactivated with iPr2P-F are effective. Subcomponent C1s is activated by C1r, and C1r is activated autocatalytically, probably through the formation of an intermediary C1r. in which the peptide chain is unsplit but a conformational change caused by interaction with the other components has led to the formation of a catalytic site able to split subcomponent C1r to C1r.

Antigen-Antibody Complex↗
PubMed1983

Complement components, C1 activation and disease activity in SLE.

Laboratory parameters were studied in 8 systemic lupus erythematosus patients during periods of high and low disease activity, mainly as defined by clinical criteria. Renal manifestations were present in 6 patients 5 of which showed antibodies to native DNA. C-reactive protein was raised in 3 patients. Only 1 of these showed a superimposed bacterial infection. Markedly high concentrations of C1r-C1s-C1 inactivator cOmplexes (C1r-C1s-Cl IA) in the sera provided direct evidence of C1 activation independent of disease activity. During active disease. C1r-C1s-C1 IA were correlated with C1q binding immune complexes as measured by solid phase, but not by fluid phase assay. Immunochemical concentrations of C1q, C4 and C3 and functional C2 were decreased in active SLE, consistent with sequential activation of the classical pathway. Discrepancies were noted between functional and immunochemical assay for C2 but not for factor B. Although essentially within the normal range, the levels of C1s, C4 binding protein, C5 and properdin were lower during active than during inactive disease. The concentrations of the factors B, I and H did not suggest involvement of the alternative pathway. 1 exceptional patient showed low factor B, a relative decrease of factor I and the presence of Bb fragments in plasma during active SLE. Markedly high factor D values were found. This could partly be explained by reduced renal function.

Adolescent↗
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↗
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↗
PubMed1994

In vitro activation of the classical pathway of complement by a streptococcal lipoteichoic acid.

The purpose of this study was to find whether a glycerolphosphate-containing lipoteichoic acid prepared from Streptococcus sobrinus OMZ 176 cells would activate the classical pathway of complement while in solution. Reference activators were lipopolysaccharide from Escherichia coli 0111:B4 and heat-aggregated immunoglobulin G. Serum samples were taken from healthy students. Analysis through crossed immunoelectrophoresis showed that lipoteichoic acid caused an almost complete dissociation of the C1qrs macromolecule. All activators decreased the area of and slowed the electrophoretic mobility of the C4 protein peaks, with lipoteichoic acid causing the most pronounced alterations. Electroimmunoassays showed that lipoteichoic acid separately, yielded detectable amounts of free C1r2s2 subunits; it also generated significantly more trimer complexes between C1r, C1s and C1 inhibitor (C1INH) than did the other two activators. Lipoteichoic acid was, however, a comparatively weak inducer of tetramer C1INH-C1r-C1s-C1INH complexes. Analysis through Western blotting showed that all activators accelerated consumption of C1r, induced complex formations between C1INH and C1s and produced cleavage products of C2. Altogether, the immunochemical analysis gave clear evidence of classical pathway activation by lipoteichoic acid, but its activation profile differed from those seen with lipopolysaccharide and aggregated immunoglobulin G.

Analysis of Variance↗
PubMed1986

Human complement component C1s. Partial sequence determination of the heavy chain and identification of the peptide bond cleaved during activation.

Human C1s proenzyme (Mr 83 000) was isolated by a rapid two-stage method involving affinity chromatography of C1 on IgG-Sepharose and isolation of subcomponent C1s by ion-exchange chromatography on DEAE-Sephacel. Single-chain C1s proenzyme was activated to two-chain C1s with self-activated C1r. After reduction and S-carboxamidomethylation the heavy chain of C1s (Mr 57 000) was isolated by ion exchange chromatography on DEAE-Sephacel. Cleavage of C1s heavy chain with CNBr yielded five fragments whose N-terminal sequences were determined. The alignment of the fragments within the heavy chain was established by tryptic peptides containing methionine. C1s heavy chain comprises about 470 amino acid residues and 42% of its sequence was determined. An intrachain sequence homology and a homology to the alpha 2 chain of human haptoglobin were identified. The C-terminal CNBr fragment comprising 44 amino acid residues was completely sequenced. From BNPS-skatole cleavage of reduced and alkylated C1s proenzyme a fragment was isolated which overlaps the C1s heavy and light chain parts and which contains the peptide bond cleaved during activation. The results show that this is an Arg-Ile bond and that under standard conditions of activation no peptide material is liberated from this portion of the molecule. The sequence data and homology to two-chain serine proteases indicate a single interchain disulfide bond in C1s.

Amino Acid Sequence↗
PubMed1986

Functional model of subcomponent C1 of human complement.

The domain organization of the zymogen subunits of the first component of human complement C1s, C1r2 and the complex C1s-C1r2-C1s was studied by electron microscopy. In the absence of Ca2+, monomeric C1s was visualized as a dumb-bell-shaped molecule consisting of two globular domains (center-to-center distance 11 nm) connected by a rod. One of the globular domains is assigned to the light chain (B-chain) of the activated molecule, which is homologous to trypsin and other serine proteases. The second globular domain and the rod are assigned to the heavy chain (A-chain) of CIs. The subunit C1r is a stable dimer in the presence or absence of Ca2+. This dimer C1r2 was visualized as composed of two dumb-bells of dimensions similar to those observed for C1s. These are connected near the junctions between the rod and one of the globular domains. This leads to the structure of an asymmetrical X with two inner closely spaced globules (center-to-center distance 7 nm) and two outer globules at a larger distance (14 nm). By comparison with fragment C1rII2, in which part of the A-chain is removed, the inner globular domains were assigned to the catalytic B-chains. This characteristic structure of C1r2 is readily recognized in the central portion of the thread-like 54 nm long C1s-C1r2-C1s complex formed in the presence of Ca2+. By affinity-labeling of C1s with biotin and visualization of avidin-ferritin conjugates in the reconstituted complex, it was demonstrated that C1s forms the outer portion of the complex. A detailed model of C1s-C1r2-C1s is proposed, according to which two C1s monomers bind to the outer globes of C1r2 by contacts between their heavy chains and those of C1r. According to this model the catalytic domains of C1r are located in the center and those of C1s at the very tips of the C1s-C1r2-C1s complex. On the basis of the structure of C1s-C1r2-C1s, we derived a detailed model of the C1 complex (composed of C1q and the tetrameric complex) and we discuss this model with a view to finding a possible activation mechanism of C1.(ABSTRACT TRUNCATED AT 400 WORDS)

Complement Activating Enzymes↗
PubMedDate not supplied

Effect of fibronectin on the haemolytic activity of complement.

Sheep erythrocytes were coupled with trinitophenyl sulphonate, sensitized with anti-TNP (or-DNP) IgM monoclonal antibodies, and exposed to components of the classical pathway of complement activation. When human fibronectin (FN) was added after C1q, but before addition of C1r and C1s (subunits of the first complement component), inhibition of haemolytic activity was observed which was strictly dependent upon the dose of FN. When FN was added after addition of C1 (reconstituted from C1q, C1r and C1s), the haemolytic activity of complement was not affected by the presence of FN. These data suggest that FN binds on C1q by interfering with C1r and C1s fixation. In addition, FN was unable to displace the activated subcomponents (C1r and C1s) from their binding site on C1q. When using other systems (sheep erythrocytes sensitized with anti-Forssman IgM monoclonal antibodies), the quantity of FN required to inhibit complement haemolytic activity was greater than in the TNP system. In normal plasma, there is a 50-fold excess of FN compared to free C1q.

Animals↗
PubMed1996

Serum complement determinations in patients with quiescent systemic lupus erythematosus.

OBJECTIVE: To determine whether complement component analyses during a period of inactive disease can define clinically important subgroups and predict morbidity in patients with systemic lupus erythematosus (SLE). METHODS: We identified 277 patients with SLE whose disease became clinically inactive at some point after diagnosis. Serum samples were obtained at that time and tested for total complement activity (CH100) and antigenic levels of C1q, C1r, C1s, C3 and C4. Results of complement determinations were correlated with demographic characteristics and clinical findings in the followup period (mean observation period 4.25 years). RESULTS: We identified 25 (9%) patients with multiple complement determinations below the normal range. 24 other patients (8.5%) had a very low level of a single complement component. The group with multiple complement determinations below the normal range was much more likely than the normocomplementemic SLE controls to progress to renal insufficiency. In other respects, complement component determinations were neither reflective nor predictive of clinical course. CONCLUSION: In this group of patients with inactive SLE, complement component analyses did not generally correlate with longterm outcome; however, multiple low complement component determinations during disease quiescence was associated with increased risk of renal insufficiency.

Autoantigens↗
PubMed1996

Inhibition of the hemolytic activity of the first component of complement C1 by an Escherichia coli C1q binding protein.

Molecular mimicry is a well established mechanism via which bacteria protect themselves from complement-mediated killing. We have previously demonstrated that a number of human cells express receptors for C1q (C1qR) and that the soluble form of this receptor inhibits activation of the classical pathway of complement. We now investigated whether Escherichia coli possesses a C1qR-like protein that protects these bacteria from complement-mediated injury. By FACS analysis it was shown that approximately 60% of the bacteria bound C1q directly in the absence of Abs. With ELISA we confirmed that the bacterial cell envelope was able to bind C1q in a dose-dependent fashion. We isolated a cell envelope associated C1q binding protein (C1qBP) by C1q affinity chromatography, then by anion exchange chromatography and gel filtration chromatography. On SDS-PAGE, the m.w. of C1qBP appeared to be 57 kDa and 51 kDa under reducing and nonreducing conditions, respectively. It was demonstrated that C1qBP specifically binds C1q and inhibits the hemolytic activity of C1q in both a dose- and time-dependent fashion. The binding of C1qBP to C1q is inhibited by C1q itself and also by the collagen-like stalks and the globular heads of C1q. In this respect, bacterial C1qBP is different from human C1qR because the binding of C1q to C1qR is only inhibited by the collagen-like stalks of C1q and not by the globular heads of C1q. C1qBP, when bound to C1q, prevents the assembly with C1r and C1s to form a functional C1 complex. The occurrence of C1qBP is not limited to certain E. coli strains, but is also found on Staphylococcus aureus, Citrobacter freundii, and Pseudomonas aeruginosa. Also, the binding of 125(I)-labeled C1q to these bacteria is specific because the binding of C1q to these bacteria is inhibitable with isolated soluble C1qBP. These findings provide evidence for the existence of a C1qR-like protein on bacteria that might protect them from complement-mediated damage.

Animals↗
PubMed1998

Structural and functional studies on C1r and C1s: new insights into the mechanisms involved in C1 activity and assembly.

C1r and C1s, the enzymes responsible for the activation and proteolytic activity of the C1 complex of complement, are modular serine proteases featuring similar overall structural organizations, yet expressing very distinct functional properties within C1. This review will initially summarize available information on the structure and function of the protein modules and serine protease domains of C1r and C1s. It will then focus on the regions of both proteases involved in: (i) assembly of C1s-C1r-C1r-C1s, the Ca(2+)-dependent tetrameric catalytic subunit of C1; (ii) expression of C1 catalytic activities. Particular emphasis will be aid on recent structural and functional studies that provide new insights into the complex mechanisms involved in the assembly, activation, and proteolytic activity of C1.

Calcium↗
PubMed1997

Secreted chondroitin sulfate proteoglycan of human B cell lines binds to the complement protein C1q and inhibits complex formation of C1.

We recently characterized a species of proteochondroitin sulfate (CSPG) secreted by human B cell lines that closely resembles in its structure the serum-derived C1q inhibitor (C1qI). These proteoglycans have in common a molecular mass of approximately 130 to 150 kDa with a core protein of 30 kDa to which up to four chondroitin sulfate chains each of approximately 26 kDa are attached. Since this B cell-derived CSPG is a potential source for serum C1qI, we measured its capacity to interact with C1q in solid-phase binding and complex electrophoresis assays. B cell CSPG purified from culture supernatants of the two human B cell lines JOK-1 and U266 strongly bound to C1q. In contrast to the secreted form, cellular proteoglycan of the myeloma cell line U266 did not interact with C1q. Binding of C1q to CSPG was competitively inhibited by free glycosaminoglycans (GAG) in the order dextran sulfate > heparin > heparan sulfate > chondroitin-6-sulfate (CS-C) > dermatan sulfate (CS-B) > chondroitin-4-sulfate (CS-A). B cell CSPG inhibited the hemolytic activity of C1q and C1. In addition, B cell CSPG blocked C1q receptor binding in a dose-dependent manner. The proteoglycans did not influence the activity of C1 complex already bound to EAC4 target cells. By interaction of CSPG with solid-phase-bound C1q, formation of the C1 complex upon the addition of C1r and C1s was impaired. Strong binding of B cell CSPG to C1q, its inhibition of C1q activity, and its structural similarities to the previously described human serum C1qI indicate that B cells produce a soluble CSPG, which may act as C1qI under physiologic conditions.

B-Lymphocytes↗
PubMed2001

The human gene for mannan-binding lectin-associated serine protease-2 (MASP-2), the effector component of the lectin route of complement activation, is part of a tightly linked gene cluster on chromosome 1p36.2-3.

The proteases of the lectin pathway of complement activation, MASP-1 and MASP-2, are encoded by two separate genes. The MASP1 gene is located on chromosome 3q27, the MASP2 gene on chromosome 1p36.23-31. The genes for the classical complement activation pathway proteases, C1r and C1s, are linked on chromosome 12p13. We have shown that the MASP2 gene encodes two gene products, the 76 kDa MASP-2 serine protease and a plasma protein of 19 kDa, termed MAp19 or sMAP. Both gene products are components of the lectin pathway activation complex. We present the complete primary structure of the human MASP2 gene and the tight cluster that this locus forms with non-complement genes. A comparison of the MASP2 gene with the previously characterised C1s gene revealed identical positions of introns separating orthologous coding sequences, underlining the hypothesis that the C1s and MASP2 genes arose by exon shuffling from one ancestral gene.

Base Sequence↗
PubMed2002

Increased expression and secretion of r-Gsp protein, rat counterpart of complement C1s precursor, during cyclic AMP-induced differentiation in rat C6 glioma cells.

The gene, termed r-gsp, was originally isolated during identification of differentiation-associated molecules in rat C6 glial cells. Its mRNA expression was markedly increased during cAMP-induced glial cell differentiation. The deduced amino acid sequence of r-gsp was homologous to those of complement C1s precursors of hamsters and humans. In the present study, we raised anti-peptide antibody against r-Gsp protein and analyzed its change during cAMP-induced differentiation. The 90-kDa r-Gsp protein increased time-dependently and reached the maximal level ( approximately 7.6-fold increase) at 24 h in response to dibutyryl cyclic AMP (dbcAMP) and theophylline. Moreover, it was secreted into the medium and then was cleaved to form disulfide-linked fragments, one of which was 30 kDa, similar to C1s, suggesting its processing in the extracellular space. In fact, the partially purified r-Gsp from culture medium was cleaved by active human C1r to form a 30-kDa polypeptide. Moreover, secreted r-Gsp protein cleaved human C4alpha to yield C4alpha' and associated with human serum C1-esterase inhibitor, strongly suggesting that r-Gsp protein is rat C1s. However, in C6 cells overexpressing r-Gsp, their morphology and proliferation rate were similar to those in parent C6 cells. These results suggest that r-Gsp protein could not induce glial differentiation alone, and suggest that r-Gsp protein was secreted as a proenzyme and processed in culture medium. Its possible role in glial cell differentiation will be discussed.

Animals↗
PubMed1994

Unique C1 inhibitor dysfunction in a kindred without angioedema. I. A mutant C1 INH that inhibits C1-s but not C1-r.

We have described hereditary incomplete deficiency of the fourth component of complement (C4) in 10 members of a large kindred. C4 deficiency in this kindred is not linked to C4 loci in the HLA region. C4 synthesis is decreased, and C4 catabolism is normal in kindred members with low serum C4 levels. We have discovered a uniquely dysfunctional C1 inhibitor in all C4-deficient members of this kindred. C1 inhibitor dysfunction is revealed by incubating sera of affected members with EDTA, which destroys all C4 activity in these sera, but not in normal sera or sera from individuals with partial C4 deficiencies. The M(r) of C1 inhibitor purified from affected members is normal, but approximately 50% of this C1 inhibitor resists cleavage by trypsin (0.14 microM) at arg444, suggesting a substitution at this position. Moderate increases in trypsin, however, result in cleavage of the resistant molecules, which would not be expected if arg444 were the site of the mutation. All molecules in C1 inhibitor purified from affected members' plasma bind to activated C1s (C1-s), but approximately 50% of molecules in these preparations do not bind to activated C1r (C1r). These findings show that affected kindred members have a unique mutation in C1 inhibitor. The mutant C1 inhibitor does not prevent the activation of C1s by C1-r when serum Ca2+ is chelated by EDTA, but its inhibition of C1-s is normal in vivo, as shown by normal C2 levels, normal C4 catabolism, and absence of angioedema in C4-deficient members. The nature of the mutation, its selective failure to inhibit C1-r, and its relationship to decreased C4 synthesis remain to be defined.

Angioedema↗
PubMed1999

[Activation of plasma cascade systems in sepsis: role of C1 inhibitors].

During sepsis the complement system, the contact activation system and the coagulation cascade are activated. Activation of these plasmatic cascades contributes to the development of multiple organ failure and the high mortality rate of severe sepsis and septic shock. C1-inhibitor is the main inhibitor of the classical pathway of the complement system (C1s and C1r), of the contact activation system (factor XIIa and kallikrein) and of the intrinsic pathway of coagulation (factor XIa). During sepsis, C1-inhibitor is proteolytically inactivated. The increase of inactivated C1-inhibitor in plasma correlates positively with mortality in septic patients. C1-inhibitor substitution has been shown to reduce the mortality in experimental animals with severe sepsis or septic shock. Only a few cases of C1-inhibitor substitution in patients with severe sepsis or septic shock have been reported. C1-inhibitor has been shown to attenuate the activation of the complement system and the contact activation system and to improve hypotension. Based on this convincing pathophysiological concept and the results of the animal studies, we initiated the "Bernese C1-inhibitor study", a randomised double-blind and placebo-controlled pilot study involving administration of C1-inhibitor to patients with severe sepsis or septic shock. If the results of this pilot study confirm the results of the reports mentioned above, they will serve as a base for larger multicentre studies.

Complement Activation↗