Induction of apoptosis of activated murine splenic T cells by cycloprodigiosin hydrochloride, a novel immunosuppressant.

Two types of immunosuppressants, cycloprodigiosin hydrochloride (cPrG) and L-leucyl-L-leucine methyl ester (LeuLeuOMe), both have the ability to selectively inhibit the lysosomal function, and a related compound to cPrG, prodigiosin 25-C, and LeuLeuOMe have been reported to selectively inhibit the T cell function in vitro. We therefore examined the cell-type specificity of cPrG and LeuLeuOMe using murine splenocytes. Concanavalin A (Con A)- and lentil lectin-induced proliferation was suppressed by cPrG more profoundly than lipopolysaccharide-induced proliferation. At the optimal concentration, Con A induced the proliferation of both CD4+ and CD8+ cells, whereas at a supra-optimal concentration Con A induced rather selective proliferation of CD8+ cells. Irrespective of the dose of Con A, CD4+ and CD8+ cells were equally affected by cPrG. In contrast, LeuLeuOMe induced the selective loss of CD8+ cells. cPrG enhanced the apoptosis of murine splenocytes and nylon fiber column-purified T cells cultured in the presence of Con A, as shown by the decrease in cell size and/or DNA fragmentation. Overall, this study revealed that the cell-type specificity of cPrG is different from that of LeuLeuOMe, and that the immunosuppression by cPrG is associated with apoptosis.