Mesenchymal stem cells attenuate acute liver injury by altering ratio between interleukin 17 producing and regulatory natural killer T cells

Mesenchymal stem cells (MSCs) are, due to immunomodulatory characteristics, considered as novel agents in the treatment of immune‐mediated acute liver failure. Although it is known that MSCs can regulate activation of T lymphocytes, their capacity to modulate function of neutrophils and natural killer T (NKT) cells, major interleukin (IL) 17–producing cells in acute liver injury, is still unknown. By using 2 well‐established murine models of neutrophil and NKT cell–mediated acute liver failure (induced by carbon tetrachloride and α‐galactoceramide), we investigated molecular and cellular mechanisms involved in MSC‐mediated modulation of IL17 signaling during acute liver injury. Single intravenous injection of MSCs attenuate acute hepatitis and hepatotoxicity of NKT cells in a paracrine, indoleamine 2,3‐dioxygenase (IDO)–dependent manner. Decreased levels of inflammatory IL17 and increased levels of immunosuppressive IL10 in serum, reduced number of interleukin 17–producing natural killer T (NKT17) cells, and increased presence of forkhead box P3 + IL10–producing natural killer T regulatory cells (NKTregs) were noticed in the injured livers of MSC‐treated mice. MSCs did not significantly alter the total number of IL17‐producing neutrophils, CD4+, and CD8 + T lymphocytes in the injured livers. Injection of mesenchymal stem cell–conditioned medium (MSC‐CM) resulted with an increased NKTreg/NKT17 ratio in the liver and attenuated hepatitis in vivo and significantly reduced hepatotoxicity of NKT cells in vitro. This phenomenon was completely abrogated in the presence of IDO inhibitor, 1‐methyltryptophan. In conclusion, the capacity of MSCs to alter NKT17/NKTreg ratio and suppress hepatotoxicity of NKT cells in an IDO‐dependent manner may be used as a new therapeutic approach in IL17‐driven liver inflammation. Liver Transplantation 23 1040–1050 2017 AASLD.