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Results for “Complement C3-C5 Convertases”

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PubMed1979

Multiple effects of a diamidine (propamidine) on complement activation.

Propamidine, one of the diamidines used against infections with babesiae has inhibitory and enhancing effects on complement activation as assessed by immune haemolysis of sensitized sheep red cells. Utilization of C1 is powerfully, that of C3 weakly improved by propamidine while activation and/or fixation of C4, C5 and to a lesser degree of C8 and C9 are inhibited. At low concentrations of propamidine (less than 2 mM) the enhancing effects, at higher concentrations the inhibitory effects predominate. Inhibition is produced, in some cases certainly, in others likely, by interference of propamidine with binding properties of complement components. None of the complement enzymes, C1s, C42 or C3bBb was inhibited in its hydrolytic activity. The possible significance of propamidine actions is discussed.

Amidines↗
PubMed1979

Activation of the classical pathway of complement by the C3NeF-stabilized cell-bound amplification convertase.

C3 nephritic factor (C3NeF) has been shown to be composed of two heavy and two light chains, like IgG; in addition it shares antigenic determinants with IgG. C3NeF, purified from the sera of eight patients by incorporation of C3NeF into the stabilized fluid phase amplification C3 convertase, C3bBb(C3NeF), followed by its release after decay of convertase function, was investigated for its ability to bind 125I-C1q and to activate 125I-C1. It was found that although fluid phase C3b,Bb(C3NeF) is fully capable of binding 125I-C1q, it is not able to activate 125I-C1 even at concentrations of 1.3 x 10(12) C3bBb(C3NeF) complexs/ml. On the other hand, cell-bound C3bBb(C3NeF) is capable of both binding 125I-C1q and activating 125I-C1. This discrepancy between fluid phase and cell-bound, C3bBb(C3NeF) was found for C3NeF preparations from eight different patients and therefore seems to apply to all C3NeF preparations.

Binding Sites↗
PubMed1979

Activation of human complement by liposomes: a model for membrane activation of the alternative pathway.

Liposomal model membranes were found to activate the alternative pathway of human complement. Activation was measured by C3 conversion and component consumption in serum that had been incubated with liposomes. C3 conversion did not require C1 or C2 of the classical pathway, since it was observed in serum from a C1r-deficient patient, serum from a C2-dificient patient, and normal serum in buffer containing EGTA and MgCl2. The incubation of liposomes with C2-deficient serum resulted in consumption of components C3 through C9 with no consumption of C1 or C4 in a profile typical of alternative pathwya activation. The reaction was further shown to require alternative pathway factor D, and to be independent of antibody. Activation of the alterative pathway was dependent on the membrane composition of the liposomes. A positive charge was required for liposomes to produce C3 conversion. Liposomal cholesterol concentration and phospholipid fatty acyl chain length and unsaturation all influenced activation, suggesting the importance of membrane fluidity. Positively charged liposomes containing dimyristoyl phosphatidylcholine and cholesterol required the presence of certain glycolipids for C3 conversion. The activation of the alternative complement pathway by liposomes of defined membrane composition may provide a suitable model for the study of alternative pathway activation by cellular membranes.

Agammaglobulinemia↗
PubMedDate not supplied

Immunological studies of grain dust.

Epidemiological investigations of grain workers have suggested the presence of biological hazards in terminal grain elevators. Immunological assessments of the involved individuals, however, have produced inconclusive results. We have recently demonstrated in vitro a potential biological mechanism which could occur in vivo upon inhaling airborne graon dust, thereby constituting a potential inflammatory insult to the respiratory tracts of grain workers. Airborne dusts of similar size distributions generated by transporting grain in terminal grain elevators have been shown to activate the alternative pathway of complement in precipitin-negative pooled normal human serum. These dusts consumed hemolytic complement in a dose-response manner as quantified by both CH100 immunodiffusion and CH50 tube methods. The proactivator of C3 was converted to the activator form in the presence of the chelator EGTA, but conversion was prevented by EDTA. Likewise, serum from guinea pigs genetically deficient in C4, thereby lacking a functional classical complement pathway, showed complement consumption by grain dusts via the alternative pathway. Relative CH50 toxicity ranking of the various dusts was found to be unrelated to the amount of endotoxin present. Of interest, aged settled dust (20-30 years) remained relatively active against the alternative complement pathway as did 15 min aqueous extracts of ground whole rye.

Air Pollutants, Occupational↗
PubMed1977

[Complement].

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Complement Activating Enzymes↗
PubMed1977

The activation of the C3b feedback cycle with human complement components. II. Using components of the alternative pathway.

The C3 convertase of the C3b feedback cycle was generated in the fluid phase from C3b and factors B and D. It was shown to be an effective decomplementing agent when reacted with human serum. Many of the effects observed were dependent on the operation of the feedback during the ongoing reaction. Oxidization of factor B with iodine did not significantly increase the potency or the stability of the enzyme. Treatment of C3b with antrypol inhibited the formation of the enzyme. In preliminary experiments in the rat, the convertase was successfully formed in vivo, accompanied by cleavage of C3, consumption of C5, C6 and C7, and a biphasic change in the circulating neutrophils.

Animals↗
PubMed1979

Activation of the classical complement pathway by nephritic factor bound to the alternative pathway C3/C5 convertase.

Nephritic Factor (NF), the potent alternative pathway activator, which is occasionally found in association with certain types of nephritis has recently been identified as an IgG class autoantibody specific for the C3 convertase (C3bB) of the alternative pathway. In these studies we have examined the possibility that the cell-bound NF-stabilized C3 convertase (EC3 bBNF) binds and activates the first component of the classical pathway of complement. EC3bBNF bound C1q, and the extent of binding was dependent upon the number of NF molecules bound per cell and decreased parallel to the dissociation and release of NF from the cells. Interaction of C1 with bound NF resulted in its activation as shown by the proteolytic conversion of proenzyme C1s to its activated form C1s. As was the case with C1q binding, C1 activation was dependent on the number of NF molecules bound per cell. Thus the NF-stabilized C3 convertase binds and activates C1.

Binding Sites↗
PubMed1977

Is primary biliary cirrhosis an immune complex disease?

Large immune complexes are present in the circulation of patients with primary biliary cirrhosis and result in the activation of complement by the classical pathway. Such large complexes are capable of producing tissue damage. The granulomatous lesions surrounding the small bile-ducts within the liver of patients with primary biliary cirrhosis and the vasculitis, rheumatoid arthritis, and associated lesions are all compatible with immune complex injury. It is postulated that such large complexes could be formed in the vicinity of the bile-ducts by an antigen absorbed from the bile or biliary epithelium. Complexes reaching the systemic circulation might be responsible for the associated extra-hepatic diseases.

Antibody Formation↗
PubMed1979

[Description of an unusual enzymic activity cleaving the third component of complement].

A large enzymatic complex cleaving C3 (C3'ase) in the absence of magnesium (EDTA) has been partially characterized in two patients. On gel filtration EDTA-C3'ase was found in an 800 000 fraction containing antigenic C4, IgA and IgG in addition to alpha-2-macroglobulin and IgM normally present. EDTA-C3'ase was specifically neutralized by antibodies to IgG, IgA and C4. The characteristics of this unusual enzymatic complex are compatible with that of a C4b2a complex stabilized by its specific binding to an auto-antibody of the IgG and/or IgA class.

Chromatography, Gel↗