IFN-γ/STAT1 acts as a proinflammatory signal in T cell-mediated hepatitis via induction of multiple chemokines and adhesion molecules: a critical role of IRF-1

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Abstract
We have previously shown that IFN-γ/STAT1 plays an essential role in concanavalin A (ConA)-induced T cell hepatitis via activation of apoptotic signaling pathways. Here we demonstrate that IFN-γ/STAT1 also plays a crucial role in leukocyte infiltration into the liver in T cell hepatitis. After injection of ConA, leukocytes were significantly infiltrated into the liver, which was suppressed in IFN-γ−/−and STAT1−/−mice. Disruption of the IFN regulatory factor-1 (IRF-1) gene, a downstream target of IFN-γ/STAT1, abolished ConA-induced liver injury and suppressed leukocyte infiltration into the liver. Additionally, ConA injection induced expression of a wide variety of chemokines and adhesion molecules in the liver. Among them, expression of ICAM-1, VCAM-1, monokine induced by IFN-γ (Mig), CC chemokine ligand-20, epithelial cell-derived neutrophil-activating peptide (ENA)-78, IFN-inducible T cell-α chemoattractant (I-TAC), and IFN-inducible protein-10 (IP-10) was markedly attenuated in IFN-γ−/−, STAT1−/−, and IRF-1−/−mice. In primary mouse hepatocytes, Kupffer cells, and endothelial cells, in vitro treatment with IFN-γ activated STAT1, STAT3, and IRF-1, and induced expression of VCAM-1, ICAM-1, Mig, ENA-78, I-TAC, and IP-10 mRNA. Induction of these chemokines and adhesion molecules was markedly diminished in STAT1−/−and IRF-1−/−hepatic cells compared with wild-type hepatic cells. These findings suggest that in addition to induction of apoptosis, previously well documented, IFN-γ also stimulated hepatocytes, sinusoidal endothelial cells, and Kupffer cells partly via an STAT1/IRF-1-dependent mechanism to produce multiple chemokines and adhesive molecules responsible for promoting infiltration of leukocytes and, ultimately, resulting in hepatitis.

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