FIG. 1.

Influenza virion inhibits primary human NK cell cytotoxicity. Influenza H1N1 virus was inactivated by UV or heat at 100°C. Fresh primary human NK cells were treated with the inactivated virus at an MOI of 2 (A, C, and D) or the indicated MOI (B) for 1 h, extensively washed, and then cultured for 24 h. (A and B) NK cells were collected and examined for their cytotoxicity against K562 cells. Samples were analyzed by flow cytometry for the percentage of specific lysis. (C and D) After being treated by inactivated influenza virus, NK cells were examined by flow cytometry for annexin V binding and PI uptake (C) or surface NKp46 expression (D). The data shown are means ± SEM from four different donors. *, P < 0.05; **, P < 0.01; ***, P < 0.001. Images are representatives of at least three independent experiments.