IAV infection of epithelial cells increases class I HLA gene expression. (A) Expression of NK cell ligands from 18 publicly available gene expression data sets from in vitro IAV infection of A549 cells and primary human lung cells. NK ligands are classified as activating (green), ambiguous function (orange), and inhibitory (red). Class I HLA proteins are indicated in blue. Data are presented as the log2 fold change relative to uninfected controls for each data set; median values with interquartile range (IQR) are shown. Vertical dashed lines indicate 2-fold change thresholds. (B) A549 cells were infected with PR8 or FM-MA or mock-infected for 17 h, and RNA was harvested for RT-qPCR. The relative expression of NK cell ligands was expressed as log2 fold change relative to mock-infected controls. Vertical dashed lines indicate 2-fold change thresholds. N = 3; *, P < 0.05; **, P < 0.01; ***, P < 0.001.