Serum immunoglobulin sedimentation patterns and circulating immune complexes in IgA glomerulonephritis and Schönlein-Henoch nephritis.

Sera from 8 patients with IgA glomerulonephritis and from 6 patients with Schönlein-Henoch nephritis were investigated by the C1q-binding assay (C1q-BA) test and by sucrose gradient centrifugation followed by sensitive solid phase radioimmunoassay determinations of IgA, IgG and IgM in each fraction obtained. Abnormal sedimentation profiles were found in sera from 3 of 8 patients with IgA nephritis and in 3 of 6 patients with Schönlein-Henoch nephritis. The abnormal fraction consisted of low molecular weight IgA in 2 patients, IgG in 1 patient and IgM in 4 patients. The absolute level of polymeric IgA was increased in 3 of 8 patients with IgA nephritis, but the relative distribution was normal. An abnormal sedimentation pattern of immunoglobulins was correlated to a positive C1q-BA test (p less than 0.001).