BACKGROUND: Natural killer (NK) cells are an important component of the innate immune defense against viruses, including hepatitis C virus (HCV). The cell culture system using HCV-permissive Huh-7.5 cells make studies on interaction of NK cells and HCV-infected target cells possible. We used this system to characterize interactions of HCV-infected Huh-7.5 cells and NK cells from healthy controls and patients with acute HCV infection. METHODS: IFNα- and IL-2 stimulated NK cells were cultured with HCV-infected hepatoma cells and subsequently analyzed (for degranulation and cytokine production) via multicolour flow cytometry. Luciferase assyas have been used to study inhibition of HCV replication. Further, PBMC from patients with acute hepatitis C as well as HCV-infected Huh7.5 cells have been analyzed via flow cytometry for expression of NK cell receptors and ligands, respectively. RESULTS: After interferon (IFN) α stimulation, NK cells from healthy controls and patients with acute hepatitis C efficiently recognized both HCV-infected and uninfected hepatoma cells. Subsequent dissection of receptor-ligand interaction revealed a dominant role for DNAM-1 and a complementary contribution of NKG2D for NK cell activation in this setting. Furthermore, IFN-α-stimulated NK cells effectively inhibited HCV replication in a DNAM-1-dependent manner. CONCLUSIONS: Human NK cells recognize HCV-infected hepatoma cells after IFN-α stimulation in a DNAM-1-dependent manner. Furthermore, interaction of IFN-α-stimulated NK cells with HCV-infected hepatoma cells efficiently reduced HCV replication. This study opens up future studies of NK cell interaction with HCV-infected hepatocytes to gain further insight into the pathogenesis of human HCV infection and the therapeutic effects of IFN-α.