Enhancement of human cord blood CD34(+) cell-derived NK cell cytotoxicity by dendritic cells

NK cells and dendritic cells (DCs) are both important in the innate host de fense. However, the role of DCs in NK cell-mediated cytotoxicity is unclear , In this study, we designed two culture systems in which human cord blood CD34(+) cells from the same donor were induced to generate NK cells and DCs , respectively. Coculture of the NK cells with DCs resulted in significant enhancement of NK cell cytotoxicity and IFN-gamma production. However, NK c ell cytotoxicity and IFN-gamma production were not increased when NK cells and DCs were grown together separated by a transwell membrane. Functional s tudies demonstrated that 1) concanamycin A, a selective inhibitor of perfor in/granzyme B-based cytolysis, blocked DC-stimulated NK cytotoxicity agains t K562 cells; and 2) neutralizing mAb against Fas ligand (FasL) significant ly reduced DC-stimulated NK cytotoxicity against Fas-positive Jurkat cells. In addition, a marked increase of FasL mRNA and FasL protein expression wa s observed in DC-stimulated NK cells. The addition of neutralizing mAb agai nst IL-18 and IL-12 significantly suppressed DC-stimulated NK cell cytotoxi city. Neutralizing IFN-gamma Ab almost completely inhibited NK cell cytotox icity against Jurkat cells. These observations suggest that DCs enhance NK cell cytotoxicity by up-regulating both perforin/granzyme B- and FasL/Fas-b ased pathways. Direct interaction between DCs and NK cells is necessary for DC-mediated enhancement of NK cell cytotoxicity. Furthermore, DC-derived I L-18 and IL-12 were involved in the up-regulation of NK cell cytotoxicity, and endogenous IFN-gamma production plays an important role in Fas-mediated cytotoxicity.