Virus-induced type IIFN stimulates generation of immunoproteasomes at the site of infection

IFN-gamma is known as the initial and primary inducer of immunoproteasomes during viral infections. We now report that type IIFN induced the transcription and translation of immunoproteasome subunits, their incorporation into the proteasome complex, and the generation of an immunoproteasome-dependent CD8 T cell epitope in vitro and provide in vivo evidence that this mechanism occurs prior to IFN-gamma responses at the site of viral infection. Type I IFN-mediated generation of immunoproteasomes was initiated by either poly(I:C) or HCV RNA in human hepatoma cells and was inhibited by neutralization of type IIFN. In serial liver biopsies of chimpanzees with acute HCV infection, increases in immunoproteasome subunit mRNA preceded intrahepatic IFN-gamma responses by several weeks, instead coinciding with intrahepatic type IIFN responses. Thus, viral RNA-induced innate immune responses regulate the antigen-processing machinery, which occurs prior to the detection of IFN-gamma at the site of infection. This mechanism may contribute to the high effectiveness (95%) of type IIFN-based therapies if administered early during HCV infection.