Rescue of human T cells by interleukin-9 (IL-9) from IL-2 deprivation-induced apoptosis: Correlation with alpha subunit expression of the IL-9 receptor

Interleukin-9 (IL-9) is a Th2-derived cytokine that uses the gamma-chain of the IL-2 receptor for signaling. Therefore, the responsiveness of human Th 1 and Th2 cell clones to IL-9 was measured by examining the ability of this cytokine to prevent apoptosis induced by IL-2 deprivation. A time course s tudy demonstrated that both subsets of T cell clones underwent apoptosis wi th similar kinetics when deprived of IL-2 and that viability could be maint ained by the addition of either IL-4 or IL-7. Interestingly, IL-9 prevented apoptosis in only 2 (Th2) of 14 clones tested. Analysis of IL-9R alpha sub unit expression on 18 T cell clones revealed that IL-9 responsiveness was d irectly proportional to the expression of the high-affinity receptor. IL-9 responsiveness was also dependent on long-term culturing because neither fr eshly isolated nor 3-day phytohemagglutinin (PHA) stimulated peripheral blo od lymphocytes (PBL) expressed IL-9R alpha. In summary, the data showed tha t IL-9 can rescue only a small subset of Th2 cells from apoptosis induced b y growth factor withdrawal and that expression of IL-9R alpha is required f or the antiapoptotic signals mediated by this cytokine.