Studies on circulating immune complexes. II: Circulating immune complexes in primary IgA nephropathy and membranoproliferative glomerulonephritis.

A study of circulating immune complexes (CIC) was undertaken in 25 patients with primary IgA nephropathy and 13 patients with membranoproliferative glomerulonephritis (MPGN). Clinically, the 25 patients with IgA nephropathy were divided into two groups: the latent type, characterized by chance proteinuria and/or hematuria; and the acute onset type, revealing acute nephritic syndrome. Both the IgG class of CIC (IgG-IC) and the IgA class of CIC (IgA-IC) were measured by conglutinin binding enzyme immunoassay (C-assay). IgG-IC were found to be positive in 32% of the patients with IgA nephropathy, and in 77% of those with MPGN. IgA-IC were positive in 72% of the patients with IgA nephropathy, and in 54% of those with MPGN. Concerning the acute onset type of IgA nephropathy, IgG-IC and IgA-IC were found in 71% and 86% of the patients, respectively, which was more frequent than in the latent type group. Simultaneous presence of IgA-IC and glomerular IgA deposits detected by an immunofluorescence study was noted in 75% of the patients with IgA nephropathy. On the other hand, 78% of the patients with MPGN revealed IgG-IC and glomerular IgG deposits simultaneously. Thus, IgG-IC and IgA-IC appear to play important roles in the pathogenesis of MPGN and IgA nephropathy, respectively.