Interferon-gamma-stimulated genes, but not USP18, are expressed in livers of patients with acute hepatitis C

BACKGROUND & AIMS: Approximately 50% of patients with chronic hepatitis C (CHC) have a sustained virologic response to treatment with pegylated interferon (pegIFN)-alpha and ribavirin. Nonresponse to treatment is associated with constitutively increased expression of IFN-stimulated genes (ISGs) in the liver. Treatment of patients with acute hepatitis C (AHC) is more effective, with sustained virologic response rates greater than 90%. We investigated mechanisms of the different responses of patients with CHC and AHC to pegIFN-alpha therapy. METHODS: We analyzed IFN signaling and ISG expression in liver samples from patients with AHC, patients with CHC, and individuals without hepatitis C (controls) using microarray, immunohistochemical, and protein analyses. Findings were compared with those from primary human hepatocytes stimulated with IFN-alpha or IFN-gamma, as reference sets. RESULTS: Expression levels of hundreds of genes, primarily those regulated by IFN-gamma, were altered in liver samples from patients with AHC compared with controls. Expression of IFN-gamma-stimulated genes was induced in liver samples from patients with AHC, whereas expression of IFN-alpha-stimulated genes was induced in samples from patients with CHC. In an expression analysis of negative regulators of IFN-alpha signaling, we did not observe differences in expression of suppresor of cytokine signaling 1 or SOCS3 between liver samples from patients with AHC and those with CHC. However, USP18 (another negative regulator of IFN-alpha signaling), was up-regulated in liver samples of patients with CHC that did not respond to therapy, but not in AHC. CONCLUSIONS: Differences in expression of ISGs might account for the greater response of patients with AHC, compared with those with CHC, to treatment with pegIFN-alpha and ribavirin. Specifically, USP18 is up-regulated in liver samples of patients with CHC that did not respond to therapy, but not in patients with AHC