Mixed IgG-IgM cryoglobulinemia with glomerulonephritis. Immunochemical, fluorescent and ultrastructural study of kidney and in vitro cryoprecipitate.

Comparative studies of renal biopsy specimens and in vitro cryoprecipitate were carried out in a patient with mixed immunoglobulin G (IgG)-immunoglobulin M (IgM) cryoglobulinemia associated with glomerulonephritis. The IgM isolated from the cryoprecipitate was an antibody with anti-IgG activity. Proliferative endocapillary glomerulonephritis was found in the kidney, with large amorphous deposits in the capillary walls. On immunofluorescent examination, these deposits contained IgG and C3. Ultrastructural studies of both cryoprecipitate and glomerular deposits revealed unusual structures designated as "cylindrical or annular bodies." The morphologic characteristics of these bodies were exactly the same in the kidney and in the cryoprecipitate. These findings suggest an identity between the glomerular deposits and the circulating cryoglobulin, supporting the hypothesis that the glomerulonephritis reported here is an immune-complex disease.