Circulating immune complexes in steroid-responsive nephrotic syndrome.

We analyzed serums from 39 children with steroid-responsive nephrotic syndrome for the presence of circulating soluble immune complexes. Seventeen of 18 children in relapse had raised levels of IgG complexes: median titers were significantly higher in these patients than in control children (P less than 0.001) or in nephrotic children in sustained remission (P less than 0.001). Seven of nine children followed sequentially had raised complex levels in early remission but became normal after six weeks in remission. In contrast to patients with systemic lupus erythematosus these IgG complexes were not able to bind C1q. Serums from five patients in relapse contained complexes intermediate in size (2 to 2.5 X 10(6) daltons) as compared to those seen in systemic lupus erythematosus, and four of the five had small complexes as well (3 to 5 X 10(5) daltons). These findings suggest that immune complexes may have a pathologic role in steroid-responsive nephrotic syndrome, but the mechanism by which proteinuria is effected remains unclear.