The Role of Thymic Immunity and Insulitis in the Development of Streptozocin-induced Diabetes in Mice

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Abstract
This article is concerned with the role of thymic immunity in the development of diabetes experimentally induced by multiple injections of subdiabetogenic doses of streptozocin (STZ). Euthymic + / +, + /nu, and athymic nu/nu mice of CD-1 and BALB/cAJcl origin were studied. Daily intraperitoneal (i.p.) injections of 30 mg /kg body wt of STZ for 5 consecutive days in CD-1 + / + and + /nu mice resulted in hyperglycemia and mononuclear cell infiltrations of islets (insulitis). The CD-1 nu/nu mice developed neither insulitis nor hyperglycemia after the same treatment. In the nu/nu mice, when thymic immunity was restored by thymus grafting, both insulitis and hyperglycemia developed, thus demonstrating that thymic immunity was a prerequisite for the development of insulitis and hyperglycemia. There was a positive correlation among the degrees of thymic immunity, insulitis, and hyperglycemia in CD-1 + /nu,nu/nu with thymus grafts, and nu/nu mice, indicating that thymic immunity may amplify the diabetogenic effect of STZ by eliciting insulitis. In contrast, in BALB/cAJcl mice, a nonsusceptible strain to insulitis, no significant differences in plasma glucose levels were observed between the + /nu and nu/nu or between the nu/nu and thymus-grafted nu/nu mice. Furthermore, no significant difference was found in plasma testosterone levels between the + /nu and nu/nu mice of both CD-1 and BALB/cAJcI origin. In conclusion, our data indicate that thymic immunity enhances the diabetogenic effect of STZ by eliciting insulitis in susceptible mice.

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