There is increasing evidence that the function of NK cells in patients with chronic hepatitis B (CHB) infection is impaired. The underlying mechanism for the impaired NK cell function is still unknown. Since myeloid dendritic cells (mDC) are potent inducers of NK cells, we investigated the functional interaction of mDC and NK cells in CHB and the influence of antiviral therapy. Blood BDCA1(+) mDC and NK cells were isolated from 16 healthy controls or 39 CHB patients at baseline and during 6 months of antiviral therapy. After activation of mDC with poly(I (.) C) and gamma interferon (IFN-gamma), mDC were cocultured with NK cells. Phenotype and function were analyzed in detail by flow cytometry and enzyme-linked immunosorbent assay. Our findings demonstrate that on poly(I (.) C)/IFN-gamma-stimulated mDC from CHB patients, the expression of costimulatory molecules was enhanced, while cytokine production was reduced. In cocultures of poly(I (.) C)/IFN-gamma-stimulated mDC and NK cells obtained from CHB patients, reduced mDC-induced NK cell activation (i.e., CD69 expression) and IFN-gamma production compared to those in healthy individuals was observed. Antiviral therapy normalized mDC activity, since decreased expression of CD80 and CD86 on DC and of HLA-E on NK cells was observed, while poly(I (.) C)/IFN-gamma-induced cytokine production by mDC was enhanced. In parallel, successful antiviral therapy resulted in improved mDC-induced NK cell activation and IFN-gamma production. These data demonstrate that CHB patients display a diminished functional interaction between poly(I (.) C)/IFN-gamma activated mDC and NK cells due to impaired mDC function, which can be partially restored by antiviral therapy. Enhancing this reciprocal interaction could reinforce the innate and thus the adaptive T cell response, and this may be an important step in achieving effective antiviral immunity.