Lack of demonstrable effect of cyclosporin A on human epidermal Langerhans cell function

There is controversy about whether Cyclosporin A (CsA) affects antigen-presenting cell function. Within the skin, Langerhans cells (LC) are very potent antigen-presenting cells. We investigated the effect of CsA on alloantigen presentation by human LC using the in vitro mixed skin-cell lymphocyte reaction (MSLR). MSLR (6 day cultures) were performed in round-bottomed microplates and lymphocyte proliferation was assessed by 3H-thymidine incorporation during the final 18 h of culture. When CsA was added into the wells a dose-dependent inhibition of T-cell proliferation occurred. Similar results were obtained when crude or LC-enriched epidermal cells (EC) were incubated for 2 h in the presence of CsA and extensively washed. The inhibition caused by CsA treatment of EC was not overcome by the addition of indomethacin. However, when CsA-treated EC were added to a fresh MSLR, T-cell proliferation was impaired. Furthermore, supernatants from CsA-treated EC, that had been kept for 6 days in culture medium, were able to inhibit the T-cell proliferative assay. These supernatants were found to contain CsA by a radioimmunoassay. From these results, it is clear that inhibition of MSLR obtained after CsA pulsing of EC suspensions can be explained by a release of the drug into the supernatant and thus by a direct effect on T cells. These findings contrast with recent reports showing a direct effect of CsA on human LC function.