Peripheral blood dendritic cells, but not monocyte-derived dendritic cells, can augment human NK cell function.

Dendritic cells (DCs) are essential antigen-presenting cells with a wide variety of functions relating to both adaptive and innate immunity. Recently, interactions of DCs with natural killer (NK) cells and NK1.1-positive T cells have been reported in mice. However, in humans, this interaction is not well understood. Here we report the use of a coculture method to analyze the modulation of NK cell function in antitumor immunity by DCs. We found that peripheral blood DCs (PDCs) enhanced NK cell activity in cytotoxicity assay, even without direct contact between DC and NK cells. In contrast, neither monocyte-derived DCs (MoDCs), nor TNF-alpha-treated MoDCs, stimulated NK lytic activity. Secretion of IL-12 and TNF-alpha into the PDC-NK coculture supernatant was increased. However, blocking antibodies against these cytokines could not completely abolish the upregulation of NK activity, suggesting the presence of other soluble factor(s) that affect DC-NK cell interaction. To summarize, this study demonstrates for the first time the direct activation of human NK cells by DC-NK cell interaction in vitro, suggesting that DCs may have a central role linking the innate and adaptive immune responses. Moreover, in stimulating NK cell function, PDCs appear to have a different potential from MoDCs.