Microbiota-Driven Activation of Intrahepatic B Cells Aggravates NASH Through Innate and Adaptive Signaling

BACKGROUND AND AIMS: Nonalcoholic steatohepatitis is rapidly becoming the leading cause of liver failure and indication for liver transplantation. Hepatic inflammation is a key feature of NASH but the immune pathways involved in this process are poorly understood. B lymphocytes are cells of the adaptive immune system that are critical regulators of immune responses. However, the role of B cells in the pathogenesis of NASH and the potential mechanisms leading to their activation in the liver are unclear. APPROACH AND RESULTS: In this study, we report that NASH livers accumulate B cells with elevated proinflammatory cytokine secretion and antigen-presentation ability. Single-cell and bulk RNA sequencing of intrahepatic B cells from mice with NASH unveiled a transcriptional landscape that reflects their pro-inflammatory function. Accordingly, B-cell deficiency ameliorated NASH progression, and adoptively transferring B cells from NASI I livers recapitulates the disease. Mechanistically, B-cell activation during NASH involves signaling through the innate adaptor myeloid differentiation primary response protein 88 (MyD88) as B cell-specific deletion of MyD88 reduced hepatic T cell-mediated inflammation and fibrosis, but not steatosis. In addition, activation of intrahepatic B cells implicates B cell- receptor signaling, delineating a synergy between innate and adaptive mechanisms of antigen recognition. Furthermore, fecal microbiota transplantation of human NAFLD gut microbiotas into recipient mice promoted the progression of NASI I by increasing the accumulation and activation of intrahepatic B cells, suggesting that gut microbial factors drive the pathogenic function of B cells during NASH. CONCLUSION: Our findings reveal that a gut microbiota- driven activation of intrahepatic B cells leads to hepatic inflammation and fibrosis during the progression of NASH through innate and adaptive immune mechanisms.