Differential effect of cyclosporin A on activation signaling in human T cell lines.

Different T cell lines, which can be induced to secrete interleukin 2 (IL-2) in vitro, were used to dissect the effect of cyclosporin A (CsA). The T leukemia cell Jurkat requires an increase in cytoplasmic calcium concentration ([Ca++]i) and phorbol myristate acetate (PMA) for the induction of IL-2 production, which is completely blocked by CsA. Another T cell line, HUT 78, also produces IL-2 in response to a rise in [Ca++]i and PMA; however, in HUT 78, PMA alone induces low levels of IL-2 production that is not blocked by CsA. After treatment with 5-azacytidine, HUT 78 cells produced maximal levels of IL-2 in response to PMA alone without requiring [Ca++]i increasing stimuli. In these cells no inhibitory effect of CsA on PMA-induced activation could be demonstrated. In addition, CsA does not inhibit PMA-induced translocation of protein kinase C. These data suggest that CsA does not globally inhibit IL-2 gene expression, but rather interferes with signaling events of T cell activation.