Ifnar^−/− NK cells proliferate normally but undergo greater apoptosis during MCMV infection. (A) Ly49H⁺ NK cells from WT:Ifnar^−/− chimeric mice were labeled with CTV, transferred into a Ly49H-deficient host, and infected with MCMV. Proliferating cells were analyzed at day 4 PI. Bar graph shows percentages of divided and nondivided NK cells at day 4 PI for each group. (B) FLICA incorporation is shown in plots, and bar graph shows percentages of FLICA⁺ NK cells in each group. Data are mean ± SEM and representative of three independent experiments with at least n = 3 biological replicates per condition. *, P < 0.05 using paired Student’s t test.