Differential activation of hepatic iNKT cell subsets plays a key role in progression of nonalcoholic steatohepatitis

Innate immune mechanisms play an important role in inflammatory chronic liver diseases. Here, we investigated the role of type I natural killer T (or iNKT) cell subsets in the progression of nonalcoholic steatohepatitis (NASH). We used α-galactosylceramide (αGalCer)/CD1d tetramers and clonotypic mAb together with intracytoplasmic cytokine staining to analyze iNKT cells in CDAA-induced murine NASH model and in human PBMCs, respectively. Cytokine secretion of hepatic iNKT cells in CDAA-fed B6 mice altered from predominantly IL-17 + to IFNγ + and IL-4 + during NASH progression along with the down-modulation of TCR and NK1.1 expression. Importantly, steatosis, steatohepatitis and fibrosis were dependent upon the presence of iNKT cells. Hepatic stellate cell activation, infiltration of neutrophils, Kupffer cells and CD8 + T cells as well as expression of key pro-inflammatory and fibrogenic genes were significantly blunted in Jα18−/− mice and in B6 mice treated with an iNKT-inhibitory RAR-γ agonist. Gut microbial diversity was significantly impacted in Jα18−/− and in CDAA-diet fed mice. An increased frequency of CXCR3 + IFNγ + T-bet + and IL-17A + iNKT cells was found in PBMC from NASH patients in comparison to NAFL patients or healthy controls. Consistent with their in vivo activation, iNKT cells from NASH patients remained hypo-responsive to ex-vivo stimulation with αGalCer. Accumulation of plasmacytoid DC in both mice and NASH patients suggest their role in activation of iNKT cells. In summary, our findings indicate that the differential activation of iNKT cells play a key role in mediating diet-induced hepatic steatosis and fibrosis in mice and its potential involvement in NASH progression in humans.