Serum samples from hypocomplementemic MPGN patients with or without C3 nephritic factor (C3NeF) were examined for the nature of C3 splitting factor and the levels of complement component. Totally 10 patients showed the existence of C3 splitting factor, 5 patients were detected C3bBb stabilizing activity (C3NeF) from their sera, other 5 cases were not detected C3NeF activity. Purified IgG from these C3NeF negative cases did not agglutinate the EAC4b3bBb cell except one case and indicated the different pattern of complement profiles from C3NeF positive cases. In C3NeF positive cases, both the pattern of complement profiles and the nature of C3 splitting activity cannot be explained by C3NeF only. These results suggest the variety of mechanism that causes hypocomplementemia in MPGN.
