Abstract: Objective: To detect the proportions of interleukin-9 producing cells in different lymphocyte subpopulations of peripheral blood of healthy subjects by intracellular cytokine measuring technique using flow cytometry.Methods: Twenty-three peripheral blood of healthy adults was stimulated by PMA and ionomycin,followed adding monensin for total 6 hours.The stimulated cells were stained with fluorescent antibodies,anti-CD3,anti-CD8,anti-TCRγδ,anti-CD19,and anti-CD56,followed hemolysing,fixed and membrane permeabilization,and stained intracellular cytokine with fluorescent anti-IL-9,anti-IL-17 antibodies.The proportion of IL-9 producing cells in different T cell subsets and other lymphocyte populations were detected and analyzed by Flow cytometry.Results: IL-9 producing cells were detected among all lymphocyte subpopulations,the percentages of which in total T cells(CD3⁺T),CD4⁺ T cells,CD8⁺ T cells and γδ T cells were 0.35±0.31,0.22±0.13,0.31±0.29 and 1.07±1.05,respectively.The proportion of IL-9 producing γδ T cells was significantly the highest(P<0.01).There was also the small proportion of IL-9 producing cells in NK cells.In addition,few amount of IL-9 and IL-17 co-expressing cells were detected among CD3⁺ T cells and CD4⁺T and CD8⁺T cells,but the small proportion of which in γδ T cells.Conclusions: The frequency of IL-9 producing cells detected by flow cytometry indicates that there exist IL-9 producing cells not only in CD4⁺ T cells,but also in CD8⁺T cells,γδ T cells and NK cells.