High programmed death 1 expression on T cells in aplastic anemia.

Programmed death 1 (PD-1) has been reported to be associated with aberrant regulation of T cells activation in aplastic anemia (AA). However, the connection between PD-1 expression status and AA needs to be further explored. The aim of this study is to investigate PD-1 expression status on T cells in AA patients and to explore the effect of PD-1 on apoptosis of T cells and BMHSCs. The concentration of platelet, lymphocyte and hemoglobin in peripheral blood of AA patients and healthy volunteers was detected by automatic blood-counter system. Mononuclear cells (MNCs) of peripheral blood and marrow were isolated from AA patients and healthy volunteers. PD-1 expression level on CD3+, CD4+, CD8+, CD4+CD25+FOXP3+ T cells and bone marrow hematopoietic stem cells (BMHSCs) and B7-H1 expression level on peripheral blood mononuclear cells (PBMCs) and BMHSCs were detected by flow cytometry (FCM). Cell apoptosis on T cells and BMHSCs was also detected by FCM. PD-1, B7-H1, Bax and Bcl-2 mRNA expression levels on T cells of peripheral blood were detected by real-time PCR. MNCs from healthy volunteers were treated with ammonium pyrrolidine dithiocarbamate (PDTC) to block the nuclear factor (NF)-кB pathway. Our results showed that in AA patients, T cells had high levels of PD-1 expression and apoptosis rate. In BMHSCs, apoptosis rate was also higher than healthy volunteers. The expression of PD-1 on T cells was correlated with lymphocyte count and hemoglobin level. PD-1 was highly expressed on CD4+CD25+FOXP3+ T cells of AA patients and PD-1 expression was negatively correlated with the percentage of CD4+CD25+FOXP3+ T cells in AA patients. B7-H1, the ligand of PD-1, was also highly expressed on T cells, B cells, PBMCs and BMHSCs. When the NF-κB pathway was blocked by PDTC, the apoptosis of T cells and BMHSCs was reduced in a dose-dependent manner and PD-1 expression was also decreased in a dose-dependent manner. In conclusion, PD-1 was up-regulated in T cells in AA patients compared with healthy volunteers. The NF-κB pathway participated in the process of apoptosis of CD4+CD25+FOXP3+ T cells and BMHSCs induced by PD-1 in AA patients.