Dynamic IFN-γ responses from human NK cells to heterologous influenza virus restimulation.

<p>(<b>A</b>) Fresh PBMCs from vaccinated (subject #4) and unvaccinated (subject #8) donors were cultured with or without inactivated influenza A/PR8 at the indicated time points. Intracellular IFN-γ production from gated CD3⁻CD56⁺ human NK cells was detected 18 hours later by FACS. (<b>B</b>) Long-term monitoring of NK cell—derived IFN-γ from vaccinated (subjects #1–6) and unvaccinated (subjects #7, #8) donors. Plots represent NK cells from individual donors against A/PR8 (red) or unstimulated control (black) at each time point. (<b>C</b>) IFN-γ⁺ NK cell percentage detected before and after vaccination (n = 6). (<b>D</b>) Absolute IFN-γ⁺ cell number from NK (red) or CD3⁺ T (blue) cells to the total number of IFN-γ⁺ cells responding to A/PR8 at different time points. Numbers above each column represent the mean proportion of IFN-γ⁺ NK cells (n = 6). (<b>E</b>) Fresh PBMCs from subjects 2 months after vaccination were cultured with or without (control) the corresponding influenza virus for 18 hours, and intracellular IFN-γ production on gated CD3⁺CD56⁻ human NK cells was detected by flow cytometry (n = 3). (<b>F</b>) Plasma was obtained from vaccinated subjects before (day 0, blue) and after (2 months, red; 6 months, green) vaccination, and the influenza-specific antibodies were investigated by the hemagglutination inhibition (HI) assay (n = 6). The data in C, D, E and F are presented as the mean ± SEM. *<i>P</i> < 0.05, **<i>P</i> < 0.01, ***<i>P</i> < 0.005; Student’s <i>t</i>-test.