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PubMed1987

Subunit interactions in the first component of complement, C1.

Interactions between C1q and other subunits of C1 were analyzed by sucrose gradient ultracentrifugation. A zone of dilute, radioiodine labelled C1q was sedimented through uniform concentrations of either C1r2C1s2, C1r2, C1r2 or C1s(2). The dissociation constants were found to be 3 x 10(-9) M and 6 x 10(-9) M for C1r2C1s2 and C1r2 binding respectively. Hill coefficients of 1 indicated no cooperativity in these bindings. Positive cooperativity was found in binding of C1s to C1q. Dissociation constants of 2 x 10(-6) M and 5 x 10(-8) M were obtained form computer modelling of a two step binding mechanism. No interaction was detected between C1q and activated C1r2. The data indicate that most of the interactions between C1q and C1r2C1s2 originates from a strong binding to the C1r2 moiety of the zymogen complex. This interaction is lost upon activation of C1r2.

Binding Sites↗
PubMed1986

Biosynthesis of complement C1 inhibitor by Hep G2 cells. Reactivity of different glycosylated forms of the inhibitor with C1s.

The biosynthesis of C1 Inh (C1 inhibitor) was studied in a human hepatoma cell line (Hep G2) by metabolic labelling, immunoprecipitation with anti-(C1 Inh) serum, analysis on SDS/polyacrylamide gel slabs and fluorography. Two forms of C1 Inh are secreted by Hep G2: a minor form of Mr 90,000 and a major form of Mr approximately 100,000. The latter form is also found in small amounts intracellularly in co-existence with an 80,000-Mr form. Accumulation of the 80,000-Mr C1 Inh is favoured when the cells are labelled at 23 degrees C instead of 37 degrees C or when they are treated with monensin. In the presence of tunicamycin, a compound that blocks the formation of N-asparagine-linked oligosaccharide chains, a decrease in Mr of both secreted and intracellular major forms is observed, indicating that secreted and intracellular C1 Inh contain N-linked oligosaccharide units. The 100,000 Mr secreted C1 Inh is sensitive to endoglycosidase F but resistant to endoglycosidase H, and it incorporates [3H]galactose, [3H]glucosamine and [3H]galactosamine, indicating the presence of both N-linked oligosaccharides of the complex type and O-linked oligosaccharides. The intracellular C1 Inh contains N-linked oligosaccharide units of the high-mannose type as demonstrated by endoglycosidase H-sensitivity. The functional activity of C1 Inh during its biosynthesis was tested by studying its reactivity towards C1s. Both secreted and intracellular C1 Inh form covalent-like complexes with purified plasma C1s. The underglycosylated C1 Inh secreted in presence of tunicamycin is still reactive with purified C1s. These results clearly show that sugars are not essential for this inhibitory activity of C1 Inh.

Acetylglucosaminidase↗
PubMed1992

Paramyosin inhibits complement C1.

We report here the results of studies showing that inhibition of C is a property of several invertebrate paramyosins. Paramyosins from Taenia solium, Schistosoma mansoni, and the mussel Mytilus edulis bind polymeric collagen and can be isolated from crude extracts of tissues by collagen affinity. These paramyosins inhibit C1 function whether the C1 is isolated or present in C2-deficient serum. Because T. solium paramyosin was the best inhibitor, we concentrated further studies on this molecule. T. solium paramyosin binds purified C1q in solution with a dose/response similar to C1r2S2. Further studies of the C1-paramyosin interaction indicate that: 1) C4 is not activated, 2) C4b2a decay is not affected, and 3) there is no effect on the efficiency of C3-9, as provided in EDTA-chelated guinea pig serum, in lysing SRBC. Thus, paramyosin inhibition is directed at the initiation of the classical pathway. The results suggest that paramyosins of helminthic parasites may have a role as modulators of the host immune response through C inhibition at C1.

Animals↗
PubMed1985

A simple two-step procedure for the preparation of the first component of human complement (C1) in its native form.

Native human C1 was purified from fresh human serum by affinity chromatography on protein A-bound Sepharose in the presence of 4-nitrophenyl-4-guanidinobenzoate hydrochloride (NPGB) taking advantage of the successive binding of IgG to protein A followed by C1 binding to IgG. After elution the C1 preparation contained IgG as a major contaminant as shown by SDS-PAGE. C1 was further purified by gel filtration. The yield of C1 was 12% and less than 4% of this C1 was activated during purification as assessed by a C4 consumption assay.

Chromatography, Affinity↗
PubMed1986

A simple one-step hemolytic assay of the first component of human complement (C1) with polyethylene glycol treated human serum: details of the assay procedures and its application to the C1 activation study.

C1 was removed from human serum by polyethylene glycol (PEG) precipitation and the supernatant (C1 deficient serum, C1D) was used for assay of C1 hemolytic activity (C1D method). Serum concentration of PEG 6,000 ranging from 3.5-4% was determined to be suitable for preparation of C1D, but C1D prepared by PEG 4,000 were proved unsatisfactory for use. Oxidation of C1D by iodine treatment increased C1 activity by two-fold. The C1D method was comparable in sensitivity to the conventional method, and the correlation between the 2 methods was good (r = 0.94). The C1D method was shown to be a useful tool for the study of C1 activation, since the method specifically measured C1, but not C1 activity. A half-life (T1/2) of C1 activity in fluid phase at 37 degrees C was 20 min under physiologic conditions.

Complement Activation↗
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↗
PubMed1986

Biosynthesis of the subcomponents C1q, C1r and C1s of the first component of complement (C1) by guinea pig hepatocyte primary cultures.

Thus far, the synthesis of C1q by liver cells has not been demonstrated. To investigate this possibility, viable hepatocytes were isolated from the liver of guinea pigs and primary cultures were established. The cells (10(6) cells/ml) were cultured under serum-free conditions for 8 days and the culture medium was changed every 24 h. The few contaminating Kupffer cells were lysed by preincubating the cell cultures with a monoclonal (22C4-8) antibody directed against a nonpolymorphic Ia determinant and preabsorbed rabbit serum. The hemolytic activity of C1 and its subcomponents C1q and C1r/C1s was tested in the supernatants. Guinea pig hepatocyte primary cultures synthesize and secrete up to 3 X 10(3) effective C1q molecules/cell/24 h and 34 X 10(3) effective C1r/C1s molecules/cell/24 h. The synthesis of C1q and C1r/C1s could be reversibly inhibited by cycloheximide (50 micrograms/ml). Furthermore, to demonstrate de novo synthesis of the C1q subcomponent, endogeneous labeling with 3H-proline (or 14C-proline) was performed. The immunoprecipitated C1q from cellular lysates and culture medium was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography. Compared to biosynthetically labeled guinea pig C1q from peritoneal macrophages, three corresponding bands (30, 28 and 24 kDa, respectively) were detectable in the fluorograph. The data show that guinea pig hepatocytes are able to synthesize C1 subcomponents, whereby the synthesis of C1q and C1r/C1s occurs independently.

Animals↗
PubMed1976

Role of C1 in the complement activating effect of Pseudomonas aeruginosa lipopolysaccharide preparations.

The complement consumption of endotoxin preparations extracted by the trichloroacetic acid or phenol-water method from different Pseudomonas aeruginosa strains was measured in normal human and guinea pig serum and in serum chelated with Mg2+-EGTA. In the chelated serum, which was essentially Ca2+-free, the first component of complement (C1) could not exert its function. All preparations tested consumed considerably less complement activity in chelated than in normal serum. The proportion of CH50 units fixed in Mg2+-EGTA and in normal serum was always higher in the tricholoracetic acid extract than in the phenol-water extract of the same strain. The part of LPS molecule that was able to activate the complement system in Ca2+-free serum was partially separated from the C1-requiring part by the combination of different extraction methods. The results suggest that on the LPS molecules two different sites are responsible for the complement activating effect through the classic and the alternative pathways.

Animals↗