Acquired C1-inhibitor deficiency in essential cryoglobulinemia and macrocryoglobulinemia.

In 5 patients with mixed cryoglobulinemia, 3 with Waldenström's disease and 2 with essential cryoglobulinemia, a C1-inhibitor (C1-INH) deficiency was discovered. The complement profile was characteristic of the acquired type: the total hemolytic activity and the early components were reduced, C3 was diminished in 1 patient only, C5 and C9 were normal or elevated. 1 atient with Waldenström's disease and 1 with essential cryoglobulinemia experienced episodes of angioedema. Circulating immune complexes were found in all patients' sera by the 125I-radiolabelled C1q binding activity (C1q BA) test. The values of the C1q binding activity were correlated with the depletion of the early complement components and that of C1-inh. 4 patients showed circulating 7S IgM. Our data support the hypothesis of a complement activation by the cryoprecipitating immune complexes; the C1-INH depletion is secondary to its consumption following C1 activation.