NK cells have well-established functions in immune defense against virus infections and cancer through their cytolytic activity and production of cytokines. In this study, we examined the frequency of NK cells and their influence on T cell responses in mice given variants of lymphocytic choriomeningitis virus that cause acute or persisting infection. We found increased frequencies of circulating NK cells during disseminating infection compared with uninfected or acutely infected mice. Consistent with recent reports, we observed that the depletion of NK cells in mice with disseminated infection increased peak numbers of virus-specific cytokine producing CD8(+) T cells and resulted in the rapid resolution of disseminated infection. Additionally, we show that NK cell depletion sustained T cell responses across time and protected against T cell exhaustion. The positive effects of NK cell depletion on T cell responses only occurred when NK cells were depleted within the first 2 d of infection. We find that the improved CD8(+) T cell response correlated with an enhanced ability of APCs from NK cell-depleted mice to stimulate T cell proliferation, independently of the effects of NK cells on CD4(+) T cells. These results indicate that NK cells play an integral role in limiting the CD8 T cell response and contribute to T cell exhaustion by diminishing APC function during persisting virus infection
