Cyclosporin A inhibits helper/inducer surface antigen expression on activated human lymphocytes

Helper/inducer (H/I) and cytotoxic/suppressor (C/S) subpopulations of human peripheral blood mononuclear lymphocytes (PBL) were cultured with Concanavalin A (Con A) and Cyclosporin A (CsA) to determine effects on proliferation and surface marker expression. After 72 h in culture, CsA strongly inhibited Con A induced proliferation of H/I and C/S subpopulations in a manner similar to that observed for whole PBL. By flow cytometric analysis, enhanced expression of both the Leu-2a (C/S) and Leu-3a (H/I) surface markers was observed on PBL from con A treated cultures. Addition of CsA to these cultures inhibited the enhanced expression of Leu-3a more than that of Leu-2a. Studies showed that this CsA inhibition of enhanced Leu-3 antigen expression occurred in a concentration dependent manner, was statistically significant throughout a 4 day culture period and did not require addition of C/S cells to mediate the effect. The data suggest that CsA blocks Con A induced blastogenesis at an early stage of activation.