Reduced MCMV-specific CD4⁺ and CD8⁺ T-cell frequency in the absence of Eri1. 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 and splenocytes were analyzed by flow cytometry at day 8 p.i. (A) Frequency of CD4⁺ and CD8⁺ cells among WT (CD45.1⁺ CD45.2⁺) or Eri1^−/− (CD45.1⁻ CD45.2⁺) splenocytes. (B) CD44 and CD62L expression on WT and Eri1^−/− CD4⁺ and CD8⁺ cells. (C) Frequency of WT and Eri1^−/− (day 8 p.i.) or WT control (uninfected) CD8⁺ cells labeled with M45-loaded H2-D^b:Ig dimer. (D-G) Splenocytes from infected mice were restimulated with indicated peptides or PMA and ionomycin. Flow cytometric plots show the average percentage of gated (D) CD8⁺ or (F) CD4⁺ cells producing intracellular IFN-γ. Summary graphs for Eri1^−/− splenic (E) CD8⁺ and (G) CD4⁺ T cells show mean IFN-γ expression relative to WT. Numbers indicate average values (A-C) ± SD or (E,G) SEM for 6 mice from 2 independent experiments. *P ≤ .05 **P ≤ .001; unpaired Student t test.