Functionality of NK-cell subsets in naive and SIV-infected macaques. Percentages of peripheral blood NK-cell subsets positive for intracellular IFN-γ, TNF-α, MIP-1β, and CD107a in response to 721.221 cells. Horizontal bars indicate medians. Only significant P values are shown for naive versus SIV-infected comparisons. Mann-Whitney test; *P < .05; **P < .01; ***P < .001.