Myd88ΔT mice mount greatly reduced CD8 T-cell responses to LCMV infection. (A) Splenocytes were isolated from a Myd88ΔT mouse, T and B cells were FACS purified, and MyD88 expression was examined by Western blot. (B-C) Myd88^flox/flox, Myd88ΔT, and Myd88^−/− mice were examined 8 days after infection with LCMV-Arm. Data represent the means ± SD of 4 mice per group. (B) The number of splenic CD8 T cells was determined. (C) The frequency of H2-D^b-gp33–specific (left panel) and H2-D^b-np396–specific (right panel) cells among gated CD8 T cells from the indicated tissues was measured using tetramers. (D) Naive Myd88^flox/flox and Myd88ΔT mice and mice that had been primed with LCMV-Arm 60 days earlier were infected with LCMV-CL13. Six days after CL13 infection, splenocytes were restimulated with the indicated peptides and antigen-specific IFNγ production was assessed. Data represent the means ± SD of at least 3 mice per group.