FIG. 4.

Contribution for perforin-mediated cytotoxicity in clearance of influenza virus but not in homeostatic regulation of the CD8⁺ T-cell responses in the absence of antibody. (A) IgM^−/−-P^−/−, IgM^−/−-FasL^−/−, or control IgM^−/− mice were infected with 10⁴ PFU A/Mem, and virus titers were measured at the time points indicated. Data shown are means ± standard errors of the means (SEM) of the log₁₀ TCID₅₀ per gram of lung of 5 to 10 mice. In the case of IgM^−/−-P^−/− mice, variation in viral titers was observed. Symbols in the middle panel represent individual mice with detectable viral titers (○) or mice with viral titers below the detection limits (•), with the number of mice falling into each group indicated for each time point. (B) Parallel total numbers of NP366-374, NS2114-121, or PA224-233 peptide-specific CD8⁺ T cells in the BAL fluid were measured by staining with MHC tetramers (•) or for intracellular IFN-γ production (○) following peptide stimulation. Total numbers of virus-specific CD8⁺ T cells (sum of NP366-374, NS2114-121, and PA224-233 peptide-specific T cells) were determined by staining with tetramers (•) or by intracellular IFN-γ staining following short-term culture with virus-infected DC2.4 cells (○) as described above (Fig. 2). Data shown are mean ± SEM log₁₀ virus-specific T cells per lung of 5 to 10 mice.