NKG2D and MICA/B interaction promotes C4 synthesis. rIL-2-activated NK3.3 and Huh7.5 cells stably transfected with HCV core or NS5A were preincubated for 30 min with anti-NKG2D, anti-MICA/B, or negative-control antibody and cocultured for 24 h. Nonadherent NK cells were removed, and the Huh7.5 cell monolayer was washed and analyzed for C4, IRF-1, USF-1, and actin expression by Western blotting. Cellular actin was used for comparison of protein load in each experiment.