Effects of neutral pepsin on the deposition of dietary antigens in glomeruli from IgA nephropathy.

Recently we reported on the participation of dietary antigens in the pathogenesis of IgA nephropathy. Particularly, the glomerular deposition of dietary antigens (casein, soybean protein, rice protein) was observed in some cases with IgA nephropathy. It is known that human urinary pepsin (HUP) prepared from the urine of a healthy adult acts as an immune complexase at neutral pH. In this study, the effects of incubation with HUP on the glomerular deposition of dietary antigens was investigated by an immunofluorescence technique in 48 patients with IgA nephropathy, four patients with Henoch-Schönlein purpura nephritis and 69 with other glomerulonephritides. In 33 cases (68.8%) soybean protein and in 12 (25.0%) casein was found in biopsies of patients with IgA nephropathy. After a 3-day incubation with HUP there was no change in the deposition of IgA in 12 cases, a decrease in 22 and complete elimination in 14 cases. The deposits of soybean protein increased in 12 cases, did not change in 20, decreased or was abolished in five and was positively converted in 11. Exceptionally, in five patients treated with HUP, the deposition of soybean protein appeared concomitantly with the disappearance of IgA deposits. Such a concomitance did not occur either in other glomerulonephritides or in studies of other dietary antigens. Thus it appears that soybean protein may be deposited in the glomerular mesangium as an antigen in some patients with IgA nephropathy.