摘要Background Regulatory T cells (Treg) have been shown to play an important role in the regulation of hematopoietic activity. However, there is no information about the effect of Treg cells in the pathogenesis of polycythaemia vera (PV).Methods In this study, we investigated the percentage and function of Treg cells in the peripheral blood of 21 PV patients and 25 healthy donors. Treg cells were identified and characterized as CD4+CD25+FOXP3+ by flow cytometry.The suppressive activity of CD4+CD25+ Treg cells was assessed by the proliferation and cytokine secretion of the co-cultured CD4+CD25- fractions.Results The results showed that the percentage of Treg cells in the peripheral blood of PV patients significantly increased compared to healthy controls ((10.93±4.02)% vs (5.86±1.99)%, P <0.05). Moreover, the mRNA and protein expression of FOXP3 was higher in CD4+CD25+ Treg cells. Coordinately, when co-cultured with the activated CD4+CD25-cells, the CD4+CD25+ Treg cells showed enhanced suppressive function in PV. Yet, the underlying mechanism for the increased frequency and function of CD4+CD25+ Treg cells is still to be clarified.Conclusion Treg cells expansion might account for the abnormal T cell immunity in PV patients and thus contribute to the pathogenesis of PV.