IL-2 can enhance the cyclosporin A-mediated inhibition of Theileria parva-infected T cell proliferation.

The effect of cyclosporin A on the continuous proliferation of Theileria parva-infected T cells was tested and compared with its effect on the Con A-induced proliferation of bovine lymph node cells. The effect of rIL-2 on cyclosporin A-treated cells was also tested. Whereas the Con A-induced proliferation of bovine lymph node cells was completely inhibited by cyclosporin A, the continuous growth of T. parva-infected cells was only partly inhibited. In both cases the inhibition was accompanied by a reduction in the level of IL-2R/Tac mRNA and surface IL-2R expression. The cyclosporin A-mediated inhibition of Con-A stimulated lymphoblasts was, over a period of 5 days, largely abrogated by human rIL-2. In the short term, rIL-2 could also alleviate the growth inhibition of T. parva-infected cells caused by treatment with cyclosporin A. In the long term, however, rIL-2 enhanced the cyclosporin A-mediated inhibition of T. parva-infected cells, gradually leading to their complete growth arrest. This enhanced inhibition was accompanied by a further reduction in surface IL-2R expression, but not by a further decrease in the levels of steady state IL-2R/Tac mRNA. The fact that IL-2 can enhance the inhibition caused by cyclosporin A could be of relevance for the immunosuppressive activity of cyclosporin A.