Fig. 3

Aged HMPV-specific CD8⁺ T cells co-express inhibitory receptors and produce less granzyme B. A CD8⁺ N11 tet⁺ cells from aged infected mice had increased expression of all 4 inhibitory receptors PD-1, TIM-3, LAG-3, and 2B4 compared to young infected mice. B Pie charts represent SPICE software analysis of inhibitory receptor co-expression on CD8⁺ N11 tet⁺ T cells in BAL of infected aged and young mice on day 7 post-infection. Asterisks indicate statistically significant differences between aged and young. C Aged CD8⁺ tet⁺ cells in BAL had increased mean fluorescence intensity (MFI) of PD-1 at day 7 post-infection while there was no difference in MFI in other inhibitory receptors. D CD8⁺ cells from aged infected mice had decreased production of granzyme B in lung (shaded bars). In BAL (open bars) aged CD8⁺ T cells produced significantly less IFNγ with a trend towards decreased production of granzyme B and IL-2. E & F Representative flow plots and histograms of granzyme B production in young and aged infected lung at day 7 post-infection with NP366 flu irrelevant as control. G Aged CD8⁺ T cells in lung were less polyfunctional. Functional markers measured: granzyme B, IFNγ, TNF, perforin, and CD107a. *P < 0.05, **P < 0.001, unpaired t-test