TIGIT and viral hepatitis: For example, TIGIT has been identified as a protective factor that facilitates liver cell regeneration by interfering with the interaction between NK cells and hepatocytes in a mouse model (14); the expression of TIGIT on murine NK cells is up-regulated during the early stages of acute viral hepatitis and negatively regulates NK cell activation (25); and the over-expression of TIGIT inhibits NK-mediated killing of the NK cell lymphoblastic leukemia/lymphoma cell line, YTS (20).