Extracellular Inosine Induces Anergy in B Cells to Alleviate Autoimmune Hepatitis.

BACKGROUND & AIMS: Dysregulation of naïve B cell receptor (BCR) signaling and the generation of antibody-secreting B cells (ASCs) have been implicated in the development of autoimmune diseases. Anergic B cells (B(ND)s) are naïve B cells with a low-density of surface IgM-BCR, thus demonstrating attenuated autoantigen responsiveness. However, potential regulatory mechanisms of B cell anergy and their roles in autoimmune hepatitis (AIH) remain unestablished. METHODS: The frequency of circulating B cell subsets and comparative phenotypic analyses were conducted using flow cytometry. Primary human CD19(+) B cells were differentiated in vitro with inosine or specific inhibitors, followed by quantitative polymerase chain reaction (qPCR), Western blotting, and flow cytometry analyses. The effects of inosine were evaluated in a concanavalin A-induced AIH mouse model, and a specific equilibrative nucleoside transporter 1 (ENT1) inhibitor was utilized both in vitro and in vivo. RESULTS: An elevated frequency of ASCs but a diminish of B(ND)s were observed in AIH. B(ND)s showed attenuated activated status compared with C(NB)s. B(ND)s uniquely exhibited high-level expression of CD73, the rate-limiting enzyme in purinergic metabolism. Inosine, as the end-product of the extracellular purinergic pathway, significantly enhanced B(ND)s expansion and inhibited ASCs differentiation in vitro. Mechanically, extracellular inosine was taken up via ENT1, promoting surface IgM internalization by inhibiting the PARP14-STAT6 signaling pathway. Pharmacological inhibition of ENT1 with dipyridamole reversed therapeutic effects of inosine both in vitro and in vivo. CONCLUSIONS: Our findings revealed that inosine was a crucial metabolite that induced immune tolerance of B cells, thus proposing a potential intervention strategy for AIH.