Interleukin-3 (IL-3)-dependent myeloid progenitor cell FDC.P2 is induced to undergo apoptotic cell death upon IL-3 depletion. Extracellular adenosine triphosphate (ATP) was found to prevent apoptosis and maintain cell viability of FDC.P2 cells upon IL-3 withdrawal. The antiapoptotic effect of ATP required extracellular Ca2+. Furthermore, FK506, a specific inhibitor of calcium/calmodulin-dependent protein phosphatase calcineurin, inhibited the antiapoptotic effect of ATP. As one of cytokines whose expression is dependent on the activation of calcineurin, interleukin-4 (IL-4) played a critical role in ATP-mediated cell survival of FDC.P2 cells because neutralizing antibody against IL-4 effectively abrogated the antiapoptotic activity of ATP. Moreover, ATP treatment induced a significant amount of secreted IL-4 that was sufficient to maintain cell viability. Taken together, our present results demonstrate that extracellular ATP triggers autocrine production of IL-4 through calcium-dependent activation of calcineurin and secreted IL-4 substitutes IL-3 in protecting FDC.P2 cells from apoptosis even in the absence of IL-3.