Ythdf2-deficient NK cells have impaired antiviral functions. (A and B) Viral titers in the spleen (A) and liver (B) on day 7 after infection were analyzed by qPCR. Mice injected with PBS were used as control (n = 5 mice for MCMV groups; n = 3 for PBS groups). (C and D) The percentage (C) and absolute number (D) of NK cells from Ythdf2^WT and Ythdf2^ΔNK mice in the blood on days 0, 4, and 7 after MCMV infection (n = 3 at days 0 and 4; n = 5 at day 7). (E) Quantification of annexin V⁺ NK cells in spleen and blood from Ythdf2^WT and Ythdf2^ΔNK mice on day 7 after MCMV infection (n = 3 mice per group). (F and G) The percentage (F) and absolute number (G) of Ly49H⁺ NK cells in blood from Ythdf2^WT and Ythdf2^ΔNK mice on days 0, 4, and 7 after MCMV infection (n = 3 at days 0 and 4; n = 5 at day 7). (H–K) The percentage (H and J) and the absolute number (I and K) of Ly49D⁺ NK cells in the spleen (H and I) and blood (J and K) from Ythdf2^WT and Ythdf2^ΔNK mice on days 0, 4, and 7 after MCMV infection (n = 3 at days 0 and 4; n = 5 at day 7). (L–Q) The percentage (L–N) and the absolute number (O–Q) of Ly49D⁺Ly49H⁻ NK cells, Ly49D⁺Ly49H⁺ NK cells, and Ly49D⁻Ly49H⁺ NK cells in the spleen from Ythdf2^WT and Ythdf2^ΔNK mice on days 0, 4, and 7 after MCMV infection (n = 3 at days 0 and 4; n = 5 at day 7). (R–W) The percentage (R–T) and the absolute number (U–W) of Ly49D⁺Ly49H⁻ NK cells, Ly49D⁺Ly49H⁺ NK cells, and Ly49D⁻Ly49H⁺ NK cells in the blood from Ythdf2^WT and Ythdf2^ΔNK mice on days 0, 4, and 7 after MCMV infection (n = 3 at days 0 and 4; n = 5 at day 7). (X) Quantification of granzyme B expression by NK cells in the spleen and blood from Ythdf2^WT and Ythdf2^ΔNK mice on day 7 after MCMV infection (n = 5 mice per group). (Y) Quantification of IFN-γ expression by NK cells in the spleen from Ythdf2^WT and Ythdf2^ΔNK mice on days 0, 4, and 7 after MCMV infection (n = 3 at days 0, 4, and 7). Data are shown as mean ± SD and were analyzed by one-way ANOVA with Šídák post-test (A and B) or two-way ANOVA with Šídák post-test (C–Y). Data are representative of at least two independent experiments. *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001.