Male Sprague-Dawley rats were fasted 18 h and given streptozocin (STZ; 60 mg/kg body wt i.p.). The resultant diabetes mellitus, not treated with insulin, was associated with persistent manifoldly increased plasma IgA levels, as measured by single-radial immunodiffusion after reduction with dithiothreitol and alkylation with iodoacetamide. Also observed were concurrent increases in plasma levels of secretory IgA (sIgA) and of C3- and IgA-containing immune complexes (C3-IgA-CIC). After 104 days without insulin treatment, six of the diabetic rats were given daily injections of 2 U of insulin for 11 days. Insulin treatment was associated with a precipitous decrease in plasma levels of IgA, sIgA, and C3-IgA-CIC. Cessation of insulin treatment resulted in restoration of greatly increased levels of all three IgA-containing species. Histoimmunofluorescence studies of kidneys from untreated rats with diabetes of 192–324 days revealed glomerular capillary wall and mesangial deposits reacting strongly with anti-IgA (α-chain-specific) antiserum. Kidneys from two of the diabetic rats (324 days) were tested with anti-rat C3 and anti-rat secretory component (SC) antisera, and they reacted positively. Control kidneys from normal rats examined simultaneously were negative. The concurrent changes in plasma levels of three IgA-containing species in the untreated STZ-induced diabetic rat and the demonstration of abnormal immunoreactive IgA-containing renal glomerular deposits make this experiment an attractive model for studying the possible role of disturbed IgA metabolism in the pathogenesis of diabetic nephropathy.

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