Oncostatin M (OSM) is released together with type I interferon (IFN) by activated dendritic cells, suggesting a concerted action of these cytokines in the biological response against infection. We found that OSM increases the antiviral effect of IFN-α in Huh7 hepatoma cells infected with hepatitis A or hepatitis C virus and synergizes with IFN-α in the induction of antiviral genes. The combination of OSM and IFN-α led to upregulation of both STAT1 and STAT3 together with intense and prolonged activation of STAT1, STAT3, and Jak1. OSM with or without IFN-α also activated p38 mitogen-activated protein kinase, which is known to enhance transcription of IFN-α-inducible genes. Interestingly, OSM combined with IFN-α strongly induced immunoproteasome genes and other genes involved in antigen processing and presentation. Moreover, OSM, alone or in combination with IFN-α, upregulated relevant innate immunity molecules and increased the expression of intracellular adhesion molecule 1 and interleukin-15 receptor alpha (IL-15Rα) in liver cells. Hepatoma cells transfected with a plasmid encoding a viral antigen were able to activate effector T cells when pretreated with IFN-α plus OSM but not with each cytokine separately. Also, OSM, more than IFN-α, augmented the ability of Huh7 cells to transpresent IL-15 to responding lymphocytes and increased the immunostimulatory activity of liver epithelial cells by presenting a short viral peptide to sensitized cytotoxic T cells. In conclusion, OSM enhances the antiviral effects of type I interferon and cooperates with it in the induction of adaptive immune responses to pathogens. These findings may have therapeutic implications
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