Clonal expansion is severely compromised in MyD88^−/− and TLR2^−/− clone 4 CD8 T cells in response to viral infection in vivo. A total of 10⁴ naive WT, MyD88^−/−, or TLR2^−/− clone 4 CD8 T cells (Thy1.1⁺) were transferred into WT (WT→WT, MyD88^−/− →WT, or TLR2^−/−→WT) or MyD88^−/− (WT→MyD88^−/−) recipient mice (Thy1.2⁺) that were either left uninfected (naive) or infected with 5 × 10⁵ pfu rVV-HA intraperitoneally. Seven days after infection, splenocytes were analyzed for the expansion of clonotypic T cells and their function by IFN-γ intracellular staining. (A) The percentages of clonotypic T cells among total lymphocytes (top) and IFN-γ–producing clonotypic T cells among total CD8⁺ T cells (bottom) in rVV-HA infected mice are indicated. (B) The absolute cell number per spleen of CD8⁺Thy1.1⁺ clonotypic T cells in both uninfected and rVV-HA infected hosts with SDs are indicated (n = 4 per group). For all groups: naive versus rVV-HA, P < .001. For rVV-infected hosts: WT→MyD88^−/− versus WT→WT, P < .05; MyD88^−/−→WT or TLR2^−/−→WT versus WT→WT, P < .001. (C) The mean fluorescence intensity (MFI) of IFN-γ–producing clonotypic cells is indicated. WT→MyD88^−/−, MyD88^−/−→WT, or TLR2^−/−→WT versus WT→WT, P > .05. Data shown are representative of 3 independent experiments.