MePDN treatment inhibits perforin release: correlation with the impairment of NK receptor–mediated cytotoxicity. (A) NK cells were cultured for 4 days in IL-2 (100 U/mL) or IL-15 (20 ng/mL) in the presence (white bars) or absence (gray bars) of MePDN (0.5 μg/mL). They were then stimulated by cross-linking the indicated NK receptors with appropriate mAbs. After overnight incubation at 37°C in the presence of RPMI + FCS alone, supernatants were collected and analyzed in an ELISA assay for quantitative determination of perforin release. Data are expressed in pg/mL. (B) The activating NK receptors analyzed in panel A were also tested for their ability to induce cytotoxicity in a redirected killing assay using the FcR-γ⁺ murine P815 cell line. NK cells derived from the same cultures as in panel A were analyzed after 4 days of culture. The E/T ratio was 5:1. Gray bars indicate IL-2– or IL-15–cultured control NK cells; white bars, MePDN-treated NK cells. This experiment is representative of 4 performed.