IgA-IgG cryoglobulinaemia with vasculitis.

A mixed IgA/IgG cryoglobulin complex was found in the serum of a 61-year-old man suffering from rheumatoid arthritis, Raynaud's phenomenon and vascular purpura. The purified complex was progressively insoluble at temperatures below 37°C. Reversible loss of cryoprecipitability was seen in conditions of extreme pH, in concentrated urea solutions and in 2-mercaptoethanol. Inactivation of complement at 56°C did not affect cryoprecipitability. The complex contained no complement and showed no anticomplementary activity. Analytical ultracentrifugation of the cryoglobulin at 37°C showed 7S and 11S components present in equal concentration. The component immunoglobulins of the complex were separated by anion exchange chromatography at 37°C. Crossmixing studies with purified normal immunoglobulins indicated that the patient's IgA component was essential for cryoprecipitability of the complex. RA latex tests for anti-IgG activity at 37°C showed strong agglutination with both cryoglobulin complex and the isolated IgA component; this protein was found to be monoclonal with type K light chains. Vasculitis, induced by skin testing the patient with his own plasma and isolated cryoglobulin was found to be histologically indistinguishable from that occuring spontaneously; reduction of symptoms paralleled reduction of cryoglobulin on treatment. These observations strongly support the hypothesis that the cryoglobulin complex is responsible for the patient's vasculitis.