Evidence that an autoantibody of IgG3 subclass against C3b discloses a C3 Nef activity in a pateint with partial lipodystrophy and glomerulonephritis.

Immunoglobulins of IgG3 subclass were purified from the serum of a patient with partial lipodystrophy and glomerulonephritis. The immunochemical data clearly showed that the immunoglobulins were directed against newly-formed determinants on C3 molecule when activation of complement occurred. This autoantibody property was related to the C3 nephritis factor activity present in the serum of the patient. Furthermore, this serum was unable to destroy cell bound C3b. This result suggested that this patient would presented a deficiency of C3b inactivation system.