Excessive supply of fatty acid suppresses NK cell metabolism. (A-C) Splenic NK cells were isolated and expanded with IL-15 in vitro, and effects of palmitic acid (PA) on NK cell metabolism were examined. NK cells were pre-treated with IL-15 + 500 µM PA or BSA control for 24 hours, and stimulated with IL-12 + IL-15 + IL-18 for 20 hours in the presence of fatty acid (FA). (A) 2-NBDG uptake of NK cells measured by flow cytometry (n = 9). (B) Basal extracellular acidification rate (ECAR) and (C) basal oxygen consumption rate (OCR, left), OCR linked to ATP production (middle) and maximal OCR (right) as measured by metabolic flux assay. Fold changes were calculated against IL-15 + BSA controls (n = 6). (A-C) Data show mean ± SEM; statistical significance (*P < .05; **P < .01; ***P < .001; ****P < .0001; NS, not significant) was determined by Mann-Whitney test.