Eri1 is required for Ly49H⁺ NK-cell expansion and control of viral titers in MCMV infection. (A) Anti-Eri1 mAb immunoblot of Ly49H⁺ NK cells pooled from 3-4 mice and sorted at various time points after MCMV infection. Data are representative of 2 independent experiments. (B-D) B6 WT CD45.1⁺ lethally irradiated hosts were reconstituted with a 1:1 mixture of congenic WT (CD45.1⁺ CD45.2⁺) and Eri1^−/− (CD45.2⁺) fetal liver cells. At 8-15 weeks, chimeras were infected with MCMV. WT (CD45.1⁺CD45.2⁺) and Eri1^−/− (CD45.1⁻CD45.2⁺) NK cells (NK1.1⁺ CD3ϵ⁻) were analyzed for (B) intracellular IFN-γ and (C) cell-surface CD69 and NKG2D expression. (D) Absolute numbers of WT and Eri1^−/− Ly49H⁺ and Ly49H⁻ NK cells in the spleen and liver at various time points after infection. Error bars in panels B and D indicate SD (N = 3 mice). (E-F) CD45.2⁺Eri1^−/− splenic Ly49H⁺ NK cells from reconstituted fetal liver chimeras or B6 mice were mixed 1:1 with splenic Ly49H⁺ NK cells from CD45.1⁺CD45.2⁺ or CD45.1⁺ WT B6 mice. Mixed splenocytes were labeled with CellTrace Violet and transferred into B6 CD45.1⁺Ly49H^−/− hosts. (E) CellTrace Violet dilution before and after MCMV infection. (F) Percentage of Ly49H⁺ NK cells transferred at day 0 (mean ± SEM, N = 13 infected and 4 uninfected mice from 4 independent experiments). **P ≤ .001, paired Student t test. (G-H) B6 WT CD45.1⁺ lethally irradiated hosts were reconstituted with CD45.2⁺ WT or Eri1^−/− fetal liver cells and infected with MCMV at 12 weeks. (G) Absolute numbers of WT and Eri1^−/− CD45.2⁺ splenocytes over the course of infection (mean ± SD, N = 3 mice). (H) Viral titers in the spleen and liver were determined at day 3.5 p.i. by plaque assays. Horizontal line indicates the mean of each group (N = 3 mice). *P ≤ .05; 2-tailed Mann-Whitney U test.