STAT5-regulated autocrine IL-6 signaling dictates IL-10-dependent regulatory functions of neonatal B10 cells

Abstract

Abstract Neonates have suboptimal immune responses to immunization, resulting in higher susceptibility to microbial infection. B cells have a central role in humoral immunity to immunization, and antigen recognition by BCRs is essential for the activation and differentiation of B cells. Neonatal B cells, however, do not respond to BCR activation as robustly as adult cells do. Our hypothesis is that unique features of neonatal BCR signaling may contribute to suboptimal humoral responses. The aim of this project is to decipher the neonatal BCR signaling pathways and identify those that may be responsible for suboptimal B cell functions. Purified adult and neonatal B cells were stimulated with anti-IgM. RNA-seq analysis revealed that STAT3 and STAT5 signaling pathways were activated in neonatal B cells. STAT3 and STAT5 were phosphorylated in neonatal B cells. BCR-mediated STAT5 phosphorylation induces IL-6 production, which in turn activates STAT3 in an autocrine/paracrine manner. Moreover, IL-6-induced STAT3 activation led to the production of anti-inflammatory cytokine IL-10. Further underscoring the role of IL-6 in IL-10 production, neonatal B cells from IL-6-KO mice did not secrete IL-10. To assess whether the autocrine IL-6 is essential for IL-10-dependent immunosuppression, we incubated peritoneal macrophages with conditioned medium (CM) from adult, wild-type neonatal, or IL-6-KO neonatal B cells. We found that CM from wild-type neonatal B cells suppressed TNF-α production by macrophages in an IL-10-dependent manner, whereas CM from IL-6-KO neonatal B cells or adult B cells did not. Our studies unveiled the essential role for STAT5-induced autocrine IL-6 signaling in IL-10-mediated immunosuppressive functions of neonatal B cells.