Effect of phorbol ester and calcium ionophore on human thymocytes

Positive selection of immature thymocytes is a developmental process in whi ch TCR ligation with low avidity induces generation of mature T cells. In m ouse thymocytes, CD4(+)8(+) double-positive (DP) cells which were created w ith a proper combination of calcium ionophore ionomycin and phorbol 12-myri state 13-acetate (PMA) have been reported to differentiate into CD4 single positive cells. However, in human thymocytes the effects of PMA and ionomyc in have remained unclear. Here we report that DP cells that were treated wi th PMA and ionomycin up-regulated bcl-2 and down-regulated CD1 expression. However, CD3 expression remained low. This treatment induced prolonged CD4 down-regulation in DP cells which was an effect also seen in mature periphe ral blood T cells. PMA/ionomycin-treated DP cells showed high cell prolifer ation and resistance to dexamethasone-induced apoptosis. These results indi cate that PKC activation and calcium elevation may be part of the biochemic al signals that induce positive selection of human DP cells and the system described in this paper may be a useful model to study the signals involved in the selection of human thymocytes. Human Immunology 62 771-781 (2001). (C) American Society for Histocompatibility and Immunogenetics, 2001. Publi shed by Elsevier Science Inc.