BIP induces mice CD19hi regulatory B cells producing IL-10 and highly expressing PD-L1, FasL

• BIP can induced IL-10+, PD-L1hi and FasLhi B cells.
• IL-10+, PD-L1hi and FasLhi B cells induced by BIP share the CD19hi phenotype.
• CD40 signaling acts in synergy with BIP to induce regulatory B cells.

Many studies have shown that B cells possess a regulatory function in mouse models of autoimmune diseases. Regulatory B cells can modulate immune response through many types of molecular mechanisms, including the production of IL-10 and the expression of PD-1 Ligand and Fas Ligand, but the microenvironmental factors and mechanisms that induce regulatory B cells have not been fully identified. BIP (binding immunoglobulin protein), a member of the heat shock protein 70 family, is a type of evolutionarily highly conserved protein. In this article, we have found that IL-10+, PD-L1hi and FasLhi B cells are discrete cell populations, but enriched in CD19hi cells. BIP can induce IL-10-producing splenic B cells, IL-10 secretion and B cells highly expressing PD-L1 and FasL. CD40 signaling acts in synergy with BIP to induce regulatory B cells. BIP increased surface CD19 molecule expression intensity and IL-10+, PD-L1hi and FasLhi B cells induced by BIP share the CD19hi phenotype. Furthermore, B cells treated with BIP and anti-CD40 can lead to suppression of T cell proliferation and the effect is partially IL-10-dependent and mainly BIP-induced. Taken together, our findings identify a novel function of BIP in the induction of regulatory B cells and add a new reason for the therapy of autoimmune disorders or other inflammatory conditions.