C3 and kidney disorder: To demonstrate that IgG of MIg-C3G patients directly enhance the C3 cleavage into C3b without the influence of auto-antibodies, purified C3, FB, FD were incubated with total IgG from controls (Healthy-donors (HD) and patients with MIg without kidney disease) and MIg-C3G patients and tested in solution or on IgG-coated plate in presence of EGTA-Mg2+.