Abstract
The classical pathway C3 convertase (C4b2a) is regulated by the action of two components. C4 binding protein (C4bp) accelerates its intrinsic decay and acts as a cofactor with the C3 inactivator (I) in the cleavage of C4b. We examined the possibility that an equilibrium existed between the serum concentration of the components (“C”[C4 and C2]) and regulators (“R”[C4bp and I]) of the classical C3 convertase.
Complete measurement of serum complement components was made in 184 normals. The r value of C vs R (each expressed as 7, normal) was +0.64; the 95% confidence interval was defined as the normal classical convertase C vs R relationship (CCC vs R).
A normal CCC vs R was found in 23/25 patients with heterozygous genetic deficiency of C2, C4, I, or C4bp and 11/13 newborns with low complement levels in cord sera. These data suggest that hypocomplementemia in the absence of complement consumption would not disturb the CCC vs R. In situations of classical pathway mediated complement consumption, the CCC vs R was usually abnormal (19/23 SLE, 2/2 bacteremla, 8/8 HANE, and 14/24 MPGN I). Patients with MPGN II with evidence of alternative pathway activation, however, generally had normal values of CCC vs. R (10/13).
Simultaneous examination of C4bp and I along with C4 and C2 may help to document the contribution of classical pathway activation to hypocomplementemia.
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Welch, T., Forristal, J., Beischel, L. et al. 1036 THE RELATIONSHIP BETWEEN THE COMPONENT AND REGULATORY PROTEINS OF THE CLASSICAL PATHWAY C3 CONVERTASE. Pediatr Res 19, 283 (1985). https://doi.org/10.1203/00006450-198504000-01066
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DOI: https://doi.org/10.1203/00006450-198504000-01066