Cytokine production and CD107a expression on NK cell after stimulation by S100A9 monomer and tetramer proteins. (A) Intracellular expression of TNF-α and IFN-γ and surface expression of CD107a on NK cells unstimulated, stimulated by S100A9 monomers or tetramers for 4 hours at 37°C (black, grey and white bars respectively). Graph shows cumulative results from 7 independent experiments. (B) NK cells were stimulated with S100A9 tetrater or with an equimolar combination of CD85j-Fc + S100A9 tetramer for 4 h at 37°C. For the later stimulation, CD85j-Fc and S100A9 tetramer were co-incubated for 2 hours at 37°C prior stimulation of NK cells. Graph represents the percentage of increase in TNF-α expression following stimulation compared to the unstimulated NK cells. Graph shows cumulative results from 4 independent experiments. (C) Expression of intracellular TNF-α and IFN-γ and surface CD107a by NK cells unstimulated, pre-stimulated by S100A9 monomer or tetramers (black, grey and white bars respectively) following a secondary stimulation by K562 target cells for 4 h at 37°C. For the blocking experiment regarding intracellular TNF-α expression, NK cells were stimulated with an equimolar combination of CD85j-Fc + S100A9 tetramer. Graph shows cumulative results from 8 independent experiments. Results are expressed as mean ± SE and p values are indicated.