Abstract: Objective: To observe the influence of Th1 cytokines IL-2,IFNγ,and Th1 induced cytokine IL-12 on the phagocytosis of human peripheral blood neutrophils using flowcytometry.Methods: Escherichia coli(E.coli) and Staphylococcus aureus(S.aureus) were labeled with different concentrations of fluorescein isothiocyanate(FITC) in carbonate buffer(CB,pH 9.5) or phosphate buffer saline (PBS,pH 7.2).The FITC labeling rates of the two bacteria were measured by flowcytometry.The whole fresh peripheral blood of the healthy adults were incubated with FITC labeled bacteria for 5 min to 20 min at 37℃,followed by washing and lysing of red blood cells.The percentages of phagocytosis of bacteria by neutrophils were measured by flowcytometry.The whole blood was pretreated with IL-2(20 u/ml),IFN-γ(50 u/ml) or IL-12(30 u/ml) for 2 hours before incubation with FITC labeled bacteria for 5 min at 37℃.The increment of phagocytosis of bacteria by neutrophils was measured and calculated in comparison with control group.Results: The labeling rate of E.coli was higher in alkaline CB,and that of S.aureus was higher in PBS.The percentages of phagocytic neutrophils for E.coli and S.aureus at 5 min were 45% and 38%,respectively,and reached plateau at 15 min to 20 min,with the percentages of 86%-88% and 83%-89% for E.coli and S.aureus,respectively.Pretreated with IL-2(20 u/ml),IFN-γ(50 u/ml) or IL-12(30 u/ml),the phagocytosis rates for E.coli by neutrophils increased by 19%,19%,and 26%,respectively;and that for S.aureus increased by 25%,23%,and 35%,respectively.Conclusions: Th1 type cytokines IL-2,IFN-γ,and Th1 induced cytokine IL-12 can increase human neutrophil phagocytosis,which demonstrates that Th1 type related cytokines enhance the role of neutrophils in innate immunity.