Angioneurotic edema with acquired C1- inhibitor deficiency and autoantibody to C1- inhibitor: response to plasmapheresis and cytotoxic therapy.

A patient with severe acquired angioneurotic edema had essentially no C1- inhibitor activity in his serum and nearly died of cardiopulmonary arrest during an acute episode of facial, oral, and pharyngeal edema. This patient had an antibody directed against C1- inhibitor and C1- inhibitor-anti-C1- inhibitor complexes in his serum. The antibody required a normal residue (Arg) in the reactive center of the inhibitor for its optimal interaction with the inhibitor. Plasmapheresis with 5% human serum albumin replacement relieved him of his antibody load and the edema; additional treatment with pulsed cyclophosphamide has provided a sustained remission. The 5% albumin solution that was used contained functional C1- inhibitor; other lots that were tested contained only traces or none. No underlying disease has yet been identified. During this acute episode of edema, the C1- inhibitor in the patient's plasma was a 92 kd component, and on recovery, a 105 kd component reappeared. C1- inhibitor isolated from the patient's plasma, which was obtained before pheresis, was mainly in lower molecular weight forms (56 kd and 45 kd). The antibody in the patient's serum appeared to render C1- inhibitor susceptible to proteolysis, for when purified antibody was added to normal serum, a cleaved form of C1- inhibitor was generated.