Figure 7.

Lung natural killer (NK) cells expand and are activated rapidly after respiratory infection. C57BL/6 mice were infected intranasally with 0·1 haemagglutination units of influenza A virus (PR8 strain), 1 × 10⁷ colony-forming units (CFU) of Staphylococcus aureus (S. a) or 1 × 10⁷ CFU of Klebsiella pneumoniae (K. p), respectively. At days 0, 1, 2 and 3 post-infection, mice were killed, and lymphocytes were isolated from lung and spleen. (a, b) The changes of the frequency (a) and number (b) of NK cells in the lung and spleen are shown. (c) Flow cytometry assay determined the expression of CD69 on NK cells (CD3⁻ NK1.1⁺), and the mean fluorescence intensity values are shown as mean ± SEM. Histograms are representative of three independent experiments using three mice per group at each time-point, the shadow histogram is the isotype control. dpi, days post-infection. *P < 0·05; **P < 0·01; ***P < 0·001; NS, not significant.