A new screening test for C3 nephritis factor based on a stable cell bound convertase on sheep erythrocytes

C3 nephritis factor (C3nef) activity was measured by the incubation of sheep erythrocytes with a mixture of normal human serum and patient's serum in EGTA followed by lysis of the washed cells with rat C in EDTA. The C convertase activity on the cells was dependent on the dose of patient's serum. Activation of human C3–C9 by the washed cells was shown by lysis of susceptible target cells (chicken erythrocytes). The test is specific for C3nef.