Nephropathy and mixed cryoglobulinemia: evidence for an immune complex pathogenesis.

Mixed IgM-IgG cryoglobulins were present in the serum of a patient with the nephrotic syndrome, recurrent purpura, chronic active hepatitis and ascites. A renal biopsy demonstrated deposition of IgM, IgG, and complement components C3 and C4 in intracapillary 'coagula' and glomerular capillary walls. No glomerular deposition of alternate complement pathway components was noted. Serum levels of C3 and C1q were depressed, and the cryoprecipitate which contained monoclonal chi-type IgM and polyclonal IgG, behaved as an immune complex by in vitro C3 conversion tests. It is suggested that the renal disease resulted from entrapment of circulating cryoglobulin 'aggregates' having immunopathologic effects similar to those of immune complexes.