NKG2D-mediated immunosensing of metabolically stressed hepatocytes by innate-like T cells is essential for initiation of NASH and fibrosis

Metabolic-associated fatty liver disease (MAFLD) comprises a spectrum of clinical entries ranging from benign steatosis to cirrhosis. A key event in the pathophysiology of MAFLD is the development of non-alcoholic steatohepatitis (NASH) that may lead to fibrosis and hepatocellular carcinoma. What triggers inflammation in MAFLD is unknown. We find that lipid accumulation in hepatocytes induces expression of ligands for the activating immune receptor NKG2D. Tissue-resident innate-like T cells are activated through NKG2D and secrete IL-17A. IL-17A licenses hepatocytes to produce chemokines that recruit pro-inflammatory cells into the liver, causing NASH and fibrosis. NKG2D-deficient mice did not develop fibrosis in a dietary model for NASH and had a marked decrease in the incidence of hepatic tumors. Importantly, the frequency of IL-17A+ γδ T cells in the blood MAFLD patients correlated with liver pathology. Our findings identify a key molecular mechanism through which stressed hepatocytes trigger inflammation in context of MAFLD. Gene expression analysis using total RNA isolated from murine livers of Klrk1-/- or C57BL6/J mice fed with normal chow diet (NCD) or steatosis-steatohepatitis SSD diet.