NK T cells stimulated with a ligand for TLR2 at least partly contribute to liver injury caused by Escherichia coli infection in mice

Fas ligand (Fas L) expression was induced on intrahepatic NK1.1⁺ T cells in vivo after an intraperitoneal inoculation of Escherichia coli. Liver injury after E. coli infection, as assessed by serum GPT level and histological examination, was significantly reduced in Jα281^-/- mice lacking NK1.1⁺ T cells or in gld/gld mice bearing mutated Fas L, indicating that NK T cells at least partly contribute to E. coli-induced liver injury in a Fas/Fas L-dependent manner. Bacterial numbers in organs and cytokine levels in serum of Jα281^-/- mice did not differ from those of Jα281^+/+ mice following E. coli infection. Intrahepatic NK1.1⁺ T cells, which preferentially expressed Toll-like receptor 2 (TLR2) mRNA, responded in vitro to synthetic lipoprotein, a ligand for TLR2, by inducing Fas L expression on their surface. In a manner analogous to E. coli infection, lipoprotein and LPS could additively induce Fas L expression on NK1.1⁺ T cells, leading to liver injury in vivo in normal mice but not in gld/gld mice. In conclusion, it is suggested that induction of Fas L on NK T cells in response to bacterial components such as lipoproteins plays an important role in pathogenesis of E. coli-induced liver injury in mice.