3B). These experiments confirmed that the reduced response to FO-1 was dependent on the defective expression (Fig. 2A) of specific activating NK receptors. NVP-BEZ235 As expected, all the receptors analyzed (with the exception of CD16) also displayed lower capability of inducing target cell killing in “hypoxic” NK cells (see redirected killing assay in Supporting Information Fig. 2). In addition, “hypoxic” NK cells displayed a reduced ability to kill different

targets including MeCoP and FO-1 melanoma cell lines and the EBV+ 721.221 B-cell line (Fig. 4A). These results are in line with the concept that the activating NK receptors targeted by hypoxia are involved in the recognition and killing of a wide panel of NK target cells. Since our data indicate that hypoxia does not affect CD16 expression and function, we further analyzed whether “hypoxic” NK cells maintained ADCC capability. NK cells were cultured under normoxic or hypoxic conditions and tested in a cytolytic assay against the 721.221 HLA-DR+ selleckchem target cell

line with or without an anti-HLA-DR mAb (to promote ADCC). As shown in Figure 4B, NK cells exposed to hypoxia were not cytolytic against this target (see also Fig. 4A, right panel). In contrast, they acquired a strong killing capability upon the addition of the anti-HLA-DR mAb (Fig. 4B) thus indicating that hypoxia did not prevent NK cells from performing ADCC. Due to the lack of basal killing (i.e. in the absence of mAbs), the overall lytic activity of “hypoxic” NK cells remained lower than that of “normoxic” NK cells; nevertheless, similar increases

above controls (i.e. mAb-induced cytotoxicity) were detected under hypoxic and normoxic conditions (Fig. 4B). The aim of the present study was to assess how NK cells could be influenced in their killing capability by the variation of pO2 in the surrounding microenvironment. Our experiments demonstrate that low levels of pO2, comparable to those hypoxic areas of certain solid tumors or infection sites or even normal lymphoid tissues, may greatly interfere with the expression Resminostat and function of major activating NK-cell receptors. The receptors affected by hypoxia play a major role in recognition and lysis of a wide panel of NK-cell targets. Accordingly, under hypoxia, NK cells strongly reduced their ability to kill both EBV-infected and tumor cells. The inhibitory effects of hypoxia, together with a series of recently identified suppressive mechanisms occurring at the tumor site, suggest that the efficacy of NK cells in clearing pathogens or tumor cells in vivo may have been overestimated. Indeed, the assays to evaluate NK-cell-mediated cytolysis are routinely performed under atmospheric O2 concentration. Our experiments indicate that hypoxia can both influence NK cells in their “resting status” and effectively counteract the stimulatory effect of the main cytokines activating the NK-cell function (including IL-2, IL-15, IL-12, and IL-21).