Fig 1: IAV infection alters cell surface expression of ligands for NK cell receptors. A549 cells were infected with FM-MA, PR8, or CA/07 at an MOI of 1. At 17 h, cells were fixed and immunostained to determine cell surface levels of NK cell ligands; cells were subsequently permeabilized for immunostaining of intracellular IAV proteins. (A) Flow cytometry analysis of cells immunostained with a pan-HLA-A/B/C antibody, or antibodies specific for class I HLA proteins HLA-B, HLA-C, or HLA-E or isotype antibody controls. (B) Flow cytometry analysis for cells immunostained with antibodies to detect NK cell-activating ligands MICA/B and CD155/PVR, or inhibitory ligand CD113/NECTIN3, or isotype antibody controls. Representative histograms (top) show results of a single experiment; the vertical lines represent the expression level of the target in uninfected cells. (Bottom) Mean fluorescence intensity (MFI) relative to uninfected cells. Each data point represents an independent experiment. Means ± SD are shown. *, P < 0.05; *2, P < 0.01; *3 P < 0.001. (C) A549 cells were mock infected or infected with PR8 for 16 h or CA/07 for 15 h at an MOI of 1, fixed, permeabilized, and stained with polyclonal antibodies specific for IAV proteins (green). DNA was stained with Hoechst-33342 (blue). Scale bar represents 20 µm.