The dialogue between natural killer cells and dendritic cells

Natural killer (NK) cells play an important role in the early innate response against cancer and infections whereas dendritic cells (DC) are critical in the initiation of adaptive immune responses through their unique antigen presentation capacities. It was discovered in 1999 by Fernandez et al. that DC and NK cells make functional interactions. In vitro, IL-12/IL-18, IL-15 and IFN-α/β production by activated DC enhance NK cell IFN-γ production, proliferation and cytotoxic potential, respectively. Activated NK cells induce DC maturation either directly or in synergy with suboptimal levels of microbial signals. NK cell-induced DC activation is dependent on both TNF-α/IFN-γ secretion and a cell-cell contact. Finally, immature DC appear susceptible to autologous NK cell-mediated cytolysis while mature DC are protected. Thus, the outcome of NK/DC cross-talk is likely to influence both innate and adaptive immune responses. In vivo, NK/DC interactions occur at least in lymphoid organs and promote Th1 differentiation. Thus, DC and NK cells are equipped with complementary sets of receptors that allow the recognition of various pathogenic agents, rendering the cross-talk between the two partners mandatory.