Immunologic studies in IgA nephropathy.

Circulating immune complexes (CIC) were detected in 43.6% of 78 patients with primary IgA nephropathy by the solid-phase Clq radioimmunoassay. The IC were intermediate (9 to 17S) in size and contained IgA, IgG, and less commonly IgM. CIC were often present intermittently, correlating with episodes of macroscopic hematuria. Elevated serum IgA concentrations (38.7%) did not correlate with the detection of CIC. Similar findings were observed in sera samples from patients with Henoch Schonlein purpura and in IgA glomerulonephritis associated with alcoholic cirrhosis and/or portal systemic shunts. The factors responsible for the mesangial localization of the IC are not clear, but elevations in serum antibody titers to respiratory pathogens (mycoplasma pneumoniae, herpes virus, influenza), gut flora (E. coli 07), and bovine serum albumin suggest that common exogenous antigens may be involved in the pathogenesis. Primary defects in either mucosal antigen exclusion or reticuloendothelial IC sequestration are proposed to account for these findings.