Natural killer and natural killer T cells in liver fibrosis

► The liver lymphocyte population is enriched with NK and NKT cells. ► NK cells inhibit liver fibrosis by killing activated HSCs and by producing IFN-γ. ► IFN-α therapy enhances, while alcohol and TGF-β inhibit, NK cell killing of HSCs. ► NKT cells produce pro-fibrotic cytokines to promote liver fibrosis. ► NKT cells also produce anti-fibrotic cytokines to inhibit liver fibrosis.