Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Complement C1”

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 109 records · Page 6Linked to original sources
PubMed1988

Antibody-independent activation of the complement system by mitochondria is mediated by cardiolipin.

Non-immune activation of the first component of complement (C1) by the heart mitochondrial inner membrane has been investigated. Cardiolipin, the only strong activator of C1 among phospholipids, is present in large amounts in the heart mitochondrial inner membrane. We therefore studied its contribution to C1 activation by mitochondria. The proteins of the mitochondrial inner membrane were found to activate C1 only weakly, in contrast with the phospholipid fraction which induces strong C1 activation. Furthermore, the digestion of mitochondrial inner membranes with proteolytic enzymes did not affect C1 activation. Additional support in favour of cardiolipin being the responsible activator came from competition experiments with mitochondrial creatine kinase (mt-CPK) and adriamycin, known to bind to cardiolipin. Both mt-CPK and adriamycin displaced C1q from the mitochondrial inner membrane. In addition, C1q displaced mt-CPK bound to mitoplasts.

Animals↗
PubMed1980

Kinetic measurement of the interaction of rheumatoid factor with IgG-coated latex particles and the influence of the first component of human complement.

Interaction between isolated rheumatoid factor (RF) of the IgM class or sera from patients with rheumatoid arthritis (RA) and IgG-coated latex particles has been studied kinetically by means of standard aggregometer equipment. The agglutination of particles mediated by isolated RF or RA-sera is inhibited by fresh normal human serum (NHS). The RF-inhibiting principle is heat-labile and recovered in the high molecular weight fractions of NHS separated on a G-200 column. Partially purified first component of complement, C1, also inhibits RF-mediated particle agglutination and disintegrates preformed RF-IgG-latex particle agglutinates. Addition of C1 to heated (56 degrees C, 30 min) NHS restores its RF-inhibiting activity. The most probable basis of this serum activity is competition between C1 with higher affinity for IgG bound to particles and RF. After about 5 min of incubation of NHS with IgG-latex particles the RF-inhibiting activity is gradually lost and interpreted to mean that C1 during the activation of the complement system is discharged from IgG bound to particles. The RF-inhibiting activity of NHS gradually decreases by incubation of serum with increasing doses of activators of the classical complement pathway probably due to the inability of activated C1 to hinder RF-interaction with IgG-particles. The presence in certain RA-sera of C1 in mainly activated form explains why such sera, even if they are fresh are able to agglutinate IgG-particles.

Complement Activation↗
PubMed1984

Characterization of C1q by monoclonal antibodies.

The effect of a purified monoclonal anti-C1q antibody (Ab 242 G3) on the function of C1q, a subcomponent of the first component of complement C1, was studied. No inhibition of purified activated C1 was observed, whereas binding of the Ab to fluid phase C1q, to C1q bound to immune complexes (EAC1q), or to serum C1 in fluid phase resulted in a dose-dependent inhibition of the hemolytic activity of C1. In contrast, when the effect of the Ab on serum C1 bound to immune complexes (EAC1) was measured, no inhibition but a dose-dependent enhancement of the hemolytic activity was obtained. The dose-response curve of the Ab-treated cell bound serum C1 was indistinguishable from that of activated C1. Isolated Fab fragments of this Ab did not cause an increase in C1 activity. After separation of the A, B, and C chains of C1q by SDS-PAGE, Ab 242 G3 reacted in immunoblotting selectively within the C chain. These data indicate that cross-linking of C1q via the C chain of C1q might lead to an internal activation of C1. One out of seven monoclonal antibodies generated against mouse macrophages (M phi was found) to recognize isolated heterologous C1q. This antibody was shown to be cytotoxic and to react in a strain independent way with mouse M phi derived from bone marrow cells as well as with M phi from the peritoneal activity. However, it did not react with mouse granulocytes, thymocytes, T- and B-lymphocytes. The hemolytic activity of fluid phase C1q was inhibited to 50% at a 2 X 10(-4) dilution of hybridoma supernatant, whereas a 100-fold higher concentration was required to inhibit C1q bound to immune complexes (EAC1q) to the same extent. It was demonstrated that this antibody recognizes the isolated globular, Fc-binding portions of the C1q molecule and react with the A and B chains. Since M phi have been shown to synthesize C1q, the Fc-recognizing subcomponent of the first component of complement, evidence was provided that endogenous C1q can serve as an Fc receptor on M phi during secretion. This was demonstrated by a dose-dependent inhibition of Fc receptor activity for EIgG by the F (ab')2 fragment of this monoclonal antibody. In a fluorescence activated cell sorter (FACS) analysis Ab 146 F (ab')2 recognizes up to 75% of unstimulated NMRI peritoneal exudate cells (PEC), 60% and 53% of cells stimulated by thioglycollate and ConA, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1977

Further studies on the identification of the subcomponents of the first component of complement after affinity chromatography of human serum on IgG-sepharose.

Affinity chromatography of serum on IgG covalently linked to Sepharose results in the retention of the proteins of the first component of complement (C1). A fraction called pool II is eluted from this column with 0.025 M EDTA and has previously been shown to contain C1s and a novel protein believed to be part of the C1 complex and called C1t. C1r has now been located in pool II and these three proteins were purified by DEAE cellulose chromatography. C1r and C1s were recovered in the proenzyme form and their identity was established by SDS polyacrylamide gel electrophoresis before and after reduction and alkylation, and on the basis of their esterolytic activities toward different substrates. The properties of C1r from pool II are contrasted with those of the protein recovered from the pool III eluate of the affinity column and previously thought to be C1r.

Chromatography, Affinity↗
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↗
PubMed1984

Differential precipitation of the Clq subcomponent of the first complement component (C1) by polyethylene glycol from normal human serum and sera of patients with collagen diseases.

Sera were, under strictly standardized conditions, centrifuged in the presence of 0-5% PEG and the Clq concentration in the precipitates was measured by radial immunodiffusion. The presence of circulating immune complexes and rheumatoid factor(s) resulted in a shift of Clq precipitation to lower PEG concentrations. Clq precipitation at 1.5% PEG was shown to be specific for sera containing immune complexes. Under similar conditions addition of aggregated IgG to normal human serum gave rise to Clq precipitation directly proportional to the amount of aggregated IgG. Precipitation of endogenous Clq at 1.5% PEG and assay by radial immunodiffusion may therefore be useful for the detection and quantitation of immune complexes in human serum.

Antigen-Antibody Complex↗
PubMed1976

Studies on vasculitis. VII. C-reactive protein as a substance perpetuating chronic vasculitis. Occurrence in lesions and concentrations in sera.

Previous findings were confirmed that C-reactive protein (C-RP) occurs in some vasculitis lesions, particularly those infiltrated mainly by neutrophils (necrotizing vasculitis). The C-RP was usually in lesions also containing complement C1 or C3c, and in some, IgG was present. Using a procedure that reliably detected 200 ng C-RP/ml serum, C-RP was found in sera of many normal persons, and the amount was influenced by the occupation of the donor. Sera of thirty-one persons with vasculitis with mainly mononuclear cell-infiltrated lesions had about four-fold more C-RP (mean 28, 200 ng/ml serum) than found in normal persons, and sera of thirty-nine persons with mainly neutrophil-infiltrated lesions had eight times the normal amount (mean 56,400 ng C-RP/ml). The amount of C-RP was influenced by the severity, extent and duration of the disorder in most patients. Experimental data suggests that C-RP may contribute to the perpetuation of inflammation in chronic vasculitis.

Animals↗
PubMed1988

Assignment of the complement serine protease genes C1r and C1s to chromosome 12 region 12p13.

C1r and C1s are distinct, but structurally and functionally similar, serine protease zymogens responsible for the enzymatic activity of the first component of complement (C1). Recent comparisons indicate a significant degree of sequence similarity between C1r and C1s and support the hypothesis that they are related by gene duplication. Complementary DNA probes for human C1r and C1s do not cross-hybridize even at mild stringency conditions and are therefore gene-specific. Using a panel of 25 human-rodent cell hybrids, we have independently assigned the C1r and the C1s genes to chromosome 12. In situ hybridization analyses were consistent with these assignments, showing in addition that both C1r and C1s are located on the short arm of the chromosome in the region p13. These data suggest that the homologous C1r and C1s genes have remained closely linked after duplication of a common ancestor. The C1r and C1s loci also provide useful polymorphic DNA markers for the short arm of chromosome 12.

Animals↗
PubMed1985

Activation of C1 by monoclonal antibodies directed against C1q.

Eleven monoclonal antibodies directed against the subcomponent C1q of the first component of human complement, C1, were prepared and tested for binding to intact C1q and to the collagenous portion, the C1q stalks. All of the monoclonals bound well to the intact C1q. Eight out of the eleven exhibited strong binding to the collagenous stalks, while three bound very weakly, if at all, to the stalks and, thus, were presumed to bind to the pepsin-sensitive region which includes the C1q heads. For one of the latter monoclonals, this was confirmed by electron microscopy. Five of the monoclonals were purified by C1q affinity chromatography. When tested with C1 reassembled from its subunits, two of these purified monoclonal antibodies markedly enhanced the rate of spontaneous activation.

Antibodies, Monoclonal↗
PubMed1978

Demonstration and quantitation of activation of the first component of complement in human serum.

Activation of the first component of human complement (C1) in human sera can be readily detected in double immunodiffusion studies with anti-C1q, anti- C1r, and anti-C1s as it produces a characteristic pattern quite different from that of precursor C1. Native macromolecular C1 gives a continuous line of precipitation with antisera to C1q, C1r, and C1s in double diffusion studies. After activation of C1 by incubation of serum with complement activators, three major changes occurred in the Ouchterlony pattern. First, spurring of the C1s precipitin line over that of macromolecular C1, indicating release of C1s from C1, was observed with low doses of activator. Release of C1s was quantitated by single radial diffusion and shown to be complete with the highest activator dose examined. Second, C1q was released with larger activator doses as shown also by spurring of the precipitin line due to this component over the remaining macromolecular C1. Third, and most surprising, C1r antigenicity was progressively lost as the activator dose was increased and no C1r line remained with the highest dose of activator tested. This was not true with C1s as there was no change in the total C1s concentration in serum incubated with various activator doses. These observations provide two approaches to the quantitation of C1 activation in human serum. First, C1r and C1s can be quantitated by single radial diffusion. A decrease in the C1r:C1s ratio correlates with activation. Second, C1s released by the activation can be quantitated by single radial diffusion if the agarose contains high concentrations of anti-C1q to confine C1, also containing C1s, to the area near the application well, and lesser concentrations of anti-C1s to permit free C1s to produce a measurable ring. The extent of release of C1s also correlates with activation. These immunochemical techniques to quantitate C1 activation directly inserum do not require specialized reagents. It is hoped that they will be useful in screening pathological sera and in monitoring the status of the complement system in patients.

Complement C1↗
PubMed1987

Autoantibody-mediated acquired deficiency of C1 inhibitor.

During the past 25 years, three forms of deficiency of the inhibitor of the first component of complement (C1 inhibitor) with angioedema have been recognized; two forms are hereditary and one is acquired. As compared with hereditary angioedema, the syndrome of acquired C1-inhibitor deficiency is rare, and it is usually associated with lymphoproliferative diseases. We report another type of acquired C1-inhibitor deficiency with angioedema. Two patients with recurrent angioedema but no associated diseases were found to have IgG1 autoantibodies against C1 inhibitor. The anti-C1-inhibitor antibodies prevented binding of C1 inhibitor to activated C1s. Both patients had 60 to 70 percent of normal levels of C1 inhibitor, but it was functionally inactive, with a molecular weight of 96,000 (normal C1 inhibitor, 105,000). In vitro studies of the patients' serum revealed degradation of 125I-labeled 105,000-dalton C1 inhibitor into the inactive 96,000-dalton molecule, caused by activated C1s and not found in normal human serum. We conclude that these cases of acquired C1-inhibitor deficiency resulted from a blockade of C1-inhibitor function by the anti-C1-inhibitor antibodies and from subsequent inactivation of C1 inhibitor by the now uncontrolled enzyme, activated C1s. As in other forms of C1-inhibitor deficiency, the unopposed activation of the complement system led to angioedema.

Adult↗
PubMed1983

Heparin-stimulated modification of C1-inhibitor by subcomponent C1s of human complement.

C1-inhibitor and C1s form a very stable complex which migrates with an apparent molecular mass of 180 kDa in dodecyl sulfate gel electrophoresis. A small fraction of the inhibitor (100 kDa) was found to be converted to a large (95 kDa) and a small (2 to 5 kDa) fragment during this reaction. It is concluded that C1-inhibitor is modified by C1s in a similar way as are the related plasma inhibitors alpha 1-proteinase inhibitor, antithrombin III and antiplasmin by their specific proteinases. The fraction of modified C1-inhibitor increased when heparin was present during complex formation. This reaction was complete after 15 s and is comparable with the fast heparin induced formation of modified antithrombin III. Treatment with hydroxylamine led to a complete dissociation of the inhibitor-enzyme complex by dodecyl sulfate. The large inhibitor fragment (and not unmodified inhibitor as reported by other authors) was released.

Complement Activating Enzymes↗
PubMed1986

An examination of the structural and biological properties of three intravenous immunoglobulin preparations.

Three commercial preparations of immunoglobulin G prepared for administration by the i.v. route were tested for their physical integrity and in vitro biological activity. Size exclusion chromatography by HPLC in native and denaturing buffers together with SDS-PAGE analysis were used to determine whether covalent-bond cleavage had occurred as a result of procedures used in their preparation. C1 complement binding assays and measurements of competitive binding to an Fc receptor-bearing promonocyte cell line U937 were used to assess whether such changes had altered the capacity of these preparations to engage biological effector functions. A purified IgG1 myeloma protein was used as a reference standard. WinRho, an unmodified IgG, consisted almost wholly of monomeric IgG by HPLC size exclusion and showed no evidence of proteolytic fragments in denaturing buffers or on SDS-PAGE. Sandoglobulin, a product treated at pH 4 with pepsin, contained about 10% dimeric protein and, as revealed under denaturing conditions, about 2% fragments. Relative affinity of binding to U937 cells was similar to WinRho. C1 binding by Sandoglobulin showed normal activity with 50% inhibition at 2.8 nM. Gamimune, modified by partial reduction and alkylation, contained about 15% dimers. Between 20 and 30% of the preparation retained covalent interchain disulfides. Binding to U937 cells was two-fold weaker than the other preparations and binding to C1 was also diminished and modified. This accords well with previous reports of the deleterious effect of reduction and alkylation on Fc function.

Cells, Cultured↗
PubMed1983

[Hereditary angioedema. A hereditary disorder in the synthesis of the complement system].

Hereditary angioedema is characterized by recurrent attacks of painless, non itching edema of the face and limbs and sometimes by abdominal symptoms. It is due to a deficiency of functional inhibitor of the first component of complement (C1 Inh). We present a case where a normal antigenic level of C1 Inh was found but no functional activity was present (B variant). A short review is given of the pathogenesis, heredity, diagnosis and treatment of the disease.

Adult↗
PubMed1991

Synthesis of C1 inhibitor in fibroblasts from patients with type I and type II hereditary angioneurotic edema.

Patients with hereditary angioneurotic edema (HANE) have serum levels of functionally active inhibitor of the first component of complement (C1 INH) between 5 and 30% of normal, instead of the 50% expected from the single normal allele. Increases in rates of catabolism have been documented in patients with HANE and certainly account for some of decrease in C1 INH level. A possible role for a decrease in synthesis of C1 INH in producing serum levels of C1 INH below the expected 50% of normal has not been well studied. We studied the synthesis of C1 INH in skin fibroblast lines, which produce easily detectable amounts of C1 INH. In type I HANE cells, C1 INH synthesis was 19.6 +/- 4.0% (mean +/- SD) of normal, much less than the 50% predicted. In type II HANE cells, the total amount of C1 INH synthesis (functional and dysfunctional) was 98.9 +/- 17% of normal; the functional protein comprised 43% of the total. Thus, type II HANE cells synthesized functional C1 INH at a much greater rate than for the type I cells. In both type I and II HANE cells, amounts of steady-state C1 INH mRNA levels paralleled rates of C1 INH synthesis, indicating that control of C1 INH synthesis occurred at pretranslational levels. Both type I and type II fibroblasts synthesized normal amounts of C1r and C1s. These data suggest that the lower than expected amounts of functionally active C1 INH in type I HANE may be due, in part, to a decrease in rate of synthesis of the protein, and that the expressions of the normal C1 INH allele in HANE is influenced by the type of abnormal allele present.

Adult↗
PubMed1980

Complement studies in children with treated coeliac disease after gluten challenge.

Changes of the complement components in the sera of 13 children with treated coeliac disease were studied after gluten challenge. The levels of C 1 and C3-activator (factor B) were significantly decreased at 4 h after the challenge, as were the levels of total complement (CH 50) and the components C 1, C 4 and C 1-inactivator at 8 h. After 24 h most values returned to normal but there was another significant decrease in serum C 4 after 24 h, and for CH 50, C 1, C 2 and C 4 after 48 h.

Celiac Disease↗