Objective To examine PD-1expression in myelodysplastic syndromes(MDS)patients,analyze its correlation with some selected clinical parameters and explore its role in MDS pathophysiology.Methods Blood specimens from 44 MDS patients were collected,and specimens from 25 healthy volunteers were used as negative control(NC).Flow cytometry assay and RT-PCR were used to detect PD-1expression on T cells and PD-1mRNA expression in different T cell subsets,respectively,and ELISA was applied to detect soluble PD-1(sPD-1)in MDS patients serum.Then linear correlation analysis was performed to analyze the relationship between PD-1mRNA level and selected clinical parameters.Result The expression rate of PD-1of MDS patients and NC were 11.31±0.18% and 6.46±0.25%.Compared with NC,MDS patients had high expression of PD-1and PD-1mRNA in T cell subset including CD3+,CD4+and CD8+T cells.sPD-1in MDS patients was significantly high than that in NC group.In MDS patients,PD-1mRNA levels in CD3+ and CD8+T cells had positive correlation with LDH levels,whereas it mRNA level on CD4+T cells showed a positive correlation with CRP level.Conclusion PD-1overexpresses on T cells of MDS patients,which may play some role in the genesis of MDS.