Increased mTOR cancels out the effect of reduced Xbp-1 on antibody secretion in IL-1α-deficient B cells.

IL-1α in vitro promotes immunoglobulin secretion by inducing proliferation of mature B cells, whereas IL-1α deficiency has no effect on in vivo antibody production. However, the reason IL-1α deficiency does not reduce in vivo antibody production is still unclear. In this study, we found that similar as in vivo data, IL-1α deficiency did not affect antibody production in in vitro LPS-stimulated B cells. Surprisingly, LPS-stimulated IL-1α-/- B cells reduced a key antibody production-related transcription factor X-box binding protein 1 (Xbp-1) expression. Furthermore, we found that IL-1α deficiency up-regulated mTOR expression, which bypassed Xbp-1 for immunoglobulin secretion. Finally, we showed that Xbp-1 suppressed mTOR expression, whereas mTOR suppressed the activation of Xbp-1 promoter via JunB. Together, these data suggest that IL-1a deficiency reduced Xbp-1 and up-regulated mTOR. This may explain why IL-1α deficiency has no effect on antibody production.