B lymphocytopenia and Bregs in a not-to-die murine sepsis model

Sepsis is a leading cause of mortality in intensive care units due to multi-organ failure caused by dysregulated immune reactions. In this study, kinetic changes in the immune system were analyzed for 72 h in cecal ligation and puncture (CLP)-induced septic mice while preventing animal death by keeping body temperature. Increase of myeloid cells and decrease of B cells in circulation at 6 h after CLP were markedly observed. At the same time point, interleukin (IL)-10 expressing CD5+ regulatory B cells (Bregs) appeared. IL-10 and programmed death-ligand 1 (PD-L1) mRNA as well as IL-1β, IL-6 and interferon γ (IFNγ) mRNA was increased in the spleen at 6 h. A gradual decrease in Bcl-2 and abrupt increase of Bim expression in the spleen at the late phase were also found. These results showed that B lymphocytopenia with the appearance of Bregs is the earliest event, likely leading to immunoparalysis in sepsis. •Kinetic changes in the immune system were analyzed for 72 h in septic mice.•Animal death was prevented by keeping body temperature.•Decrease of total B cells in circulation at 6 h after the onset of sepsis were marked.•IL-10-expressing presumable regulatory B cells appeared at 6 h.•B lymphocytopenia and the IL-10-expressing Bregs may induce immunoparalysis.