Induction of Mx-2 in rat liver by toxic injury

Background/Aims: Mx proteins are supposed to be strictly regulated by viruses or interferon-alpha (IFN-alpha). We used a non-viral model of acute liver injury to study Mx expression. Methods: We induced toxic liver injury by CCl4, and studied the expression of IFN-alpha, IFN-gamma, and IFN-inducible antiviral genes (Mx-2; 2'-5' oligoadenylate synthetase, 2-5 A; double-stranded RNA-activated protein kinase, PKR). Results: Similar to 2-5 A and PKR, Mx-2 gene expression was biphasically induced after CCl4 administration with a maximum at 24 h, and a second peak at 72 h. On protein level, Mx-2 only was up-regulated. IFN-alpha remained constant for the first 24 h while IFN-gamma peaked at 6 h. Thereafter, IFN-alpha increased to a maximum at 72 h while IFN-gamma decreased to 77 +/- 4%. Small monocyte-like liver macrophages, but not large macrophages, expressed Mx-2 constitutively. In vitro, IFN-alpha but not IFN-gamma induced Mx-2 in different liver cell populations. IFN-gamma, instead, reduced the susceptibility of liver macrophages to the actions of IFN-alpha. Conclusions: Our data suggest that Mx expression does not invariably result from the presence of a viral particle or IFN-alpha synthesis but may represent an innate defensive armamentarium that may be up-regulated without antigen specificity upon liver injury. (C) 2003 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.