Type I IFN protects against perforin- and NKG2D-dependent NK cell fratricide during viral infection. (A) NK cells from WT:Ifnar^−/− chimeric mice were labeled with CTV and transferred into WT, Prf1^−/−, or NKp46^Cre × R26^DTA recipients followed by infection with LCMV. Bar graph shows percentages of transferred cells in the spleen for each group at day 7 PI. (B) NK cells from WT:Ifnar^−/− chimeric mice were labeled with CTV and transferred into WT or Ncr1^gfp/gfp hosts followed by LCMV infection. Bar graph shows percentages of transferred cells for each group in spleen at day 3 PI. (C) NK cells from WT:Ifnar^−/− chimeric mice were labeled with CTV and transferred into WT hosts receiving an anti-NKG2D antibody or PBS followed by LCMV infection. Bar graph shows percentages of transferred cells for each group in the spleen at day 3 PI. (D) WT:Ifnar^−/− chimeric mice were directly infected with LCMV. The expression of NKG2D ligands is shown at day 2 PI. Data are mean ± SEM and representative of three independent experiments with at least n = 3 biological replicates per condition. MFI, mean fluorescent intensity. *, P < 0.05 using paired Student’s t test. ns, not significant.