Persistent grossly elevated plasma immunoglobulin A levels in untreated streptozocin-induced diabetic rats.

Experimental diabetes mellitus was induced in adult male and female rats by injecting streptozocin (STZ; 60 mg/kg i.p.) in preparation for a screening survey of changes in the pattern of undenatured plasma proteins, as revealed by two-dimensional (2-D) gel electrophoresis followed by silver staining. As early as 8-12 days later, the 2-D gels revealed three high-molecular-weight plasma protein spots, which persisted for 150 days in the blood of untreated diabetic rats. Such spots were not seen in plasma of normal control rats. Evidence is presented for the presumptive characterization of these proteins as oligomers of immunoglobulin A (IgA). Specific measurement of total IgA content of diabetic plasma samples by single-radial immunodiffusion, after reduction with dithiothreitol and alkylation with iodoacetamide, reveals that IgA content increases linearly from control values of 11.1 +/- 4.6 to 358 +/- 249 mg/dl (means +/- SE) 21 days after STZ and persists at these high levels for as long as 150 days. Diabetic rats injected daily with insulin showed IgA levels only two to four times higher than normal. Neither experiments designed to quantitate the rates of clearance (catabolism plus excretion) of 125I-labeled secretory IgA from the circulation of normal and diabetic rats nor measurement of total IgA in the bile from diabetic and normal bile fistula rats supports the view that slowed clearance from the circulation or impaired biliary excretion in the diabetic rat causes observed gross hyperimmunoglobulinemia A.

Increased plasma IgA, sIgA, and C3- and IgA-containing immune complexes with renal glomerular deposits in diabetic rats.

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 (alpha-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.

Preferential localization and rate of loss of labeled alloantibody from rat tumors and skin transplants carrying the corresponding alloantigen.

125I-Labeled rat histocompatibility antibody was prepared from sera of Buffalo rats immunized with a transplantable fibrosarcoma induced by methylcholanthrene in a Fischer 344 rat. After i.v. injection this antibody was shown to localize with high specificity in transplants of a second Fischer 344 tumor or Fischer 344 skin grafts onto immunosuppressed Buffalo rats. These represent conditions such that only tumor or skin grafts carry the corresponding antigen. In skin transplants localization at 24 hr corresponded to 80% and in tumor to 30% of the injected dose in tissue equal to 1% of the rat weight. However, rapid loss of the 125I label from the target tissues indicated that degradation of antibody fixed to target cells was rapid and that the half-time of the intact antibody was less than 2 days.