Prothymosin alpha enhances interleukin 2 receptor expression in normal human T-lymphocytes.

We investigated whether the enhancement, by prothymosin alpha (Pro alpha), of the phytohaemagglutinin-stimulated proliferation of human peripheral blood mononuclear cells (PBMC) is due to its affect on the number of cells expressing the interleukin 2 receptor (IL-2R) or the surface density of IL-2R on PBMC. Peripheral blood mononuclear cells were obtained from 21 donors. For both an optimal phytohaemagglutinin (PHA) concentration (H) and a 10-fold dilution (L), their responses fell in two classes, high (h) and low (l), making four dose--response situations. Pro alpha significantly increased the number and IL-2R density of cells expressing IL-2R only when the response in its absence was about half maximal, i.e. for PBMC responding well to the low PHA stimulus (group Lh) or PBMC responding poorly to the optimal stimulus (group Hl). The enhancement of IL-2R expression in group Lh by Pro alpha was dose-dependent and paralleled by increased proliferative response. It appears not to be mediated by IL-2, since it was unaffected when IL-2 production was suppressed by cyclosporin A. The early interaction of Pro alpha with lymphocytes did not require the presence of macrophages, but macrophages were necessary during lymphocyte activation for modulation of PHA-stimulated IL-2R expression to be affected. The immunoregulatory activity of Pro alpha may prove useful for improving the decreased T-cell function associated with immunodeficiency, or for restoration of normal IL-2R expression by the lymphocytes of aged individuals.