Plasma-treated skin tumor cells stimulated the secretion of inflammatory mediators upon co-culture with NK-cells. (a) simplified scheme and consequences of NK-cell-tumor cell interaction; (b) granzyme B quantification in supernatants of co-cultures (±plasma treatment) at 4 h, 6 h, and 24 h (A431 and A375) and 24 h (HaCaT); (c–e) quantification of cytokines in co-cultures in supernatants of untreated (vehicle) and plasma-treated A431 (c), A375 (d), and HaCaT (e) cells at 24 h as a ratio to the respective single tumor cell or HaCaT keratinocyte culture. Data are the mean of three independent experiments. Statistical analysis was performed using t-test or two-way ANOVA (* = p < 0.01, ** = p < 0.01, *** = p < 0.001, ns = not significant).