Direct action of type I IFNs is critical for activation of NK cells following flu infection.

<p>Splenocytes from IFNAR<b>^+/−</b> or IFNAR<b>^−/−</b> (CD45.2<b>⁺</b>) were transferred into CD45.1<b>⁺</b> B6 WT recipients by i.v. injection prior to infection with flu. Splenic NK cells from indicated mice were analyzed post-infection. (A) Expression levels of IFN-γ (upper panels) and granzyme B (lower panels) were analyzed in NK cells after transfer and infection. Donor and recipient genotypes are indicated, and upper and lower quadrants for each dot plot represent the donor and host NK cells, respectively. Inset values indicate the percentages of IFN-γ<b>⁺</b> or granzyme B<b>⁺</b> NK cells. (B) CD69 expression of NK cells from infected (open histograms) and uninfected (shaded histograms) mice. Percentages of NK cells located within the CD69<b>⁺</b>gate are indicated. (C) IFN-γ and CD107a expression were analyzed after in vitro stimulation of splenocytes with YAC-1 cells. Numbers represent the relative percentages of CD107a<b>⁺</b> and IFN-γ<b>⁺</b> NK cells for donor and host cells. Data are representative of four separate experiments with 2–4 mice per group.