Immunopathologic study of minimal change glomerular disease with mesangial IgM deposits

Renal biopsies from 21 patients with minimal change nephrotic syndrome and mesangial IgM deposits were investigated by means of fluorescence, light and electron microscopy; elution of tissue-bound antibody; and fixation of heterologous (guinea pig) complement. In 12 patients complement and IgM deposits were associated and, in 4 of these, electron dense deposits conforming to immune complexes were detected in mesangia. Antibody elution and heterologous complement fixation studies in tissues suggested that such immune reactants may represent interaction of complement-fixing antibody and antigen. Long-term follow-up studies are needed to determine the clinical relevance of IgM deposits in minimal change nephrotic syndrome.