PRF1 and infection: A small increase in CD69+ NK cells was observed in the lungs only at 24 hours and 72 hours (S2C and S2D Fig), but no increase of Perforin+ and Granzyme B+ cells was detected at both 24 and 72 hours post-infection (Figs 2B and 2C, MFI in S2C and S2D).