Engagement of ICAM-3 potentiates the release of IFNγ, but not the cytotoxic activity, by NK cells. (A) NK cells were cultured alone or with neutrophils and then stimulated with LPS + IL-15/IL-18 in the presence or absence of αICAM-3 mAbs. (B-D) ICAM-3/Fc, αICAM-3 mAbs, or IgG1 was immobilized on plates prior to the addition of NK cells and subsequent incubation in the presence of IL-15/IL-18. (A-B) Extracellular IFNγ was measured in cell-free supernatants after 18 hours of culture (n = 3-6). (B) The fold increase was calculated as described in “Costimulation assays.” (A) **P < .01 and *P < .05 by 1-way ANOVA of paired samples. (C-D) After 18 hours, NK cells were co-incubated with K562 cells at different E:T ratios. The percentage of NK cells expressing CD107a was determined by flow cytometry (C), and the percentage of lysed K562 cells was determined by time-resolved fluorometry (D). One representative experiment (n = 3) is shown.