Immunohistochemical study of cyclosporin-A on rat thymus after various treatment times.

The effects of the immunosuppressive agent cyclosporin A (CsA) after 4, 8, 15, and 21 days of treatment were investigated in the thymus of 12 week-old rats by an immunochemical method using the TRPM1 and TRPM2 monoclonal antibodies. Major changes were not observed after 4, 8 and 15 days' treatment. But thymus histology completely changed after 21 days: Interdigitating (TRPM1-positive) cells completely disappeared and only a small number of (TRPM1-positive) macrophages were observed in the thymus cortex. TRPM2-positive cells also decreased, most markedly in the outer cortex and cortex. These findings indicate that inhibition of T-lymphocyte maturation is linked to disappearance of interdigitating cells which produce cytokines with proliferative and differentiation properties.