Human anti-idiotypic antibody responses to autoantibody against the alternative pathway C3 convertase.

Anti-idiotypic antibodies to autoantibody against the alternative pathway C3 convertase (C3NeF) were isolated and purified from normal human serum as well as from serum from six patients with membrano-proliferative glomerulonephritis (MPGN). All preparations of anti-id antibody blocked C3NeF deposition on EC3bBb as well as C3NeF stabilization of EC3bBb functional activity. The Ka of these ant-id antibodies for C3NeF was 10(9) liters/mol which is comparable to the Ka of C3NeF for its antigen. In addition, 90% of anti-id antibody isolated from patients with MPGN and 20% isolated from normal individuals resembled Bb and bound to C3b as well as to antibody specific for the Bb portion of Factor B. These anti-id antibodies also resembled C3b and bound to antibody specific for the C3c portion of C3b. Immunization of rabbits with this latter form of anti-id antibody led to the production of functionally active C3NeF. These data indicate that C3NeF anti-idiotypic antibodies exist in two distinct forms, with and without internal imagery of C3bBb, and can occur in both normal individuals and patients with MPGN.