Memory T-cell expansion in response to secondary LCMV infection is MyD88 independent. cKO and cHet mice were infected with LCMV-Arm, treated as in Figure 4, and reinfected with LCMV-CL13 60 days after primary infection. (A-B) The frequency of CD44⁺ (A) and H2-D^b-np396–specific (B) YFP⁺ CD8 T cells was measured in the peripheral blood at the indicated time points. Data are the means ± SD of 9 mice per group. (C) The frequency of antigen-specific YFP⁺ CD8 T cells in the spleens of cKO and cHet mice was assessed 6 days after reinfection by tetramer staining. Data are representative of 9 mice per group. (D) YFP⁺ and YFP⁻ CD44⁺CD8 T cells were sorted from the spleens of reinfected cKO and cHet mice and MyD88 expression was measured by Western blot. (E) The viability of gated np396-specific YFP⁺ CD8 T cells from cKO and cHet mice was assessed by annexin V staining either directly ex vivo or after the indicated 18 hours of in vitro culture as indicated. Data are representative of 3 mice per group. (F) Splenocytes were restimulated with the indicated LCMV-derived peptides, and IFNγ production by YFP⁺ CD8 T cells was assessed by intracellular staining. (G) The frequency of YFP⁺ CD8 T cells producing the indicated combinations of IFNγ, TNFα, and IL-2 in response to stimulation with pooled LCMV peptide was determined. Data represent the means ± SD of 3 mice per group.