Interleukin-4-mediated protection of primary B cells from apoptosis through Stat6-dependent up-regulation of Bcl-xL.

Apoptosis is an integral aspect of B lymphocyte development and homeostasis and is regulated by the engagement of antigen costimulatory and cytokine receptors. Although it is well established that interleukin 4 (IL-4) is a potent anti-apoptotic cytokine for B lymphocytes, little is known about the IL-4-induced molecular events regulating cell survival. Stat6 is rapidly activated after IL-4 stimulation, but its role in B lymphocyte apoptosis has not been explored. In this report we demonstrate that Stat6 is a critical signaling molecule for IL-4 in protecting primary B cells from passive and Fas-induced cell death. We show that expression of the Bcl-2 family member, Bcl-xL, is induced maximally by IL-4 and anti-IgM/IL-4 in a Stat6-dependent manner. Additionally, we demonstrate that bcl-xL transcription is likely to be directly activated through a Stat6 binding site in the bcl-xL-flanking region. Finally, reconstitution of Stat6-deficient splenic B cells with Bcl-xL was able to protect those cells from Fas-induced cell death. These results suggest that the anti-apoptotic activity of IL-4 in B cells is mediated through the activation of Stat6 and subsequent transcription of Bcl-xL.