RESUMEN
The third component of complement, the central protein of the complement cascade, occurs in two principal allotypes, C3S and C3F. An excess frequency of the F allotype has been implicated in a number of disease states, including some forms of glomerulonephritis. These associations have been explained by functional differences between C3S and C3F. We examined several complement functions, using purified preparations of C3S or C3F. The C3S allotype was 1.3 times more efficient than C3F in a hemolytic assay employing sensitized sheep erythrocytes; this difference was shown to arise from a slightly more efficient deposition of C3F on the cell surface. These differences are trivial and of much less magnitude than the functional differences between C4A and C4B. There were no differences between allotypes in their ability to be converted to inactive C3b (C3bi) by complement factors H and I or by CR1 and factor I. No significant differences were seen between the allotypes and their ability to support solubilization of preformed immune complexes.
Asunto(s)
Complemento C3/genética , Polimorfismo Genético , Animales , Complejo Antígeno-Anticuerpo/genética , Proteínas Sanguíneas/análisis , Bovinos , Complemento C3/análisis , Proteínas Inactivadoras del Complemento C3b/farmacología , Complemento C4/análisis , Factor H de Complemento , Factor I de Complemento , Eritrocitos/inmunología , Hemólisis/genética , Humanos , Fenotipo , Conejos , Serina Endopeptidasas/farmacología , Ovinos , SolubilidadRESUMEN
Inhibition of complement mediated solubilization (CMS) of preformed immune complexes was previously demonstrated in the serum of patients with systemic lupus erythematosus. We studied the ability of serum from patients with MPGN I or III to inhibit the solubilization of preformed BSA- anti-BSA aggregates by pooled normal human serum. Inhibition of CMS was found in the sera of 20/35 patients; the inhibition was more dramatic in those with active disease (9/9), as compared to those in remission (8/21) or with renal failure (3/5). The inhibition did not seem to be related to corticosteroid therapy, nephrotic syndrome, circulating immune complexes or hypocomplementaemia. In only one patient was inhibition associated with the presence of C3 nephritic factor activity and decomplementation of the target serum.