C3 Nephritic Factor Stabilization of the Classic C3 Convertase: A Role for C2 in C3 Nephritic Factor Activity 1

Summary

The C3 Nephritic Factor (C3Nef) from two patients with partial lipodystrophy was partially isolated in order to study the role of early classic C-complement components in C3Nef activity. Both C3Nef preparations were C2 dependent for C3 inactivation, although one C3Nef was C2 dependent only following dilution of the C3Nef preparation. Reconstitution of C2-deficient sera with either human or guinea pig C2 restored C3Nef activity in C2-deficient sera. C3Nef prolonged the decay of the classic complement C3 convertase (EAC142gp) in a dose-dependent manner, and this function of C3Nef may explain, in part, the role of C2 in C3Nef activity.