Flow cytometric analysis of STAT5 phosphorylation and CD95 expression in CD4+ T lymphocytes treated with recombinant human erythropoietin.

Erythropoietin receptor (EPO-R) appears on the cell surface in the early stages of erythropoiesis. It also has been found on human T and B lymphocytes and monocytes suggesting that EPO could directly influence these cells. Moreover, earlier reports have shown that treatment with recombinant human (rh) EPO in chronic renal failure (CRF) patients improves interleukin-2 production and restores CD4+ T lymphocyte functions. We decided to investigate possibility of direct action of rhEPO on these cells in vitro by phosphorylated signal transducer and activator of transcription 5 (pSTAT5) detection and changes in CD95 antigen expression observation. Flow cytometry was used for detection of pSTAT5 and CD95 expression in CD4+ T lymphocytes treated with rhEPO. Our results show that presence of rhEPO in cell culture of lymphocytes stimulated with anti-CD3 antibody increases percentage of CD4+ T lymphocytes expressing pSTAT5. Stimulating effect of rhEPO was dose dependent. RhEPO presence also increases CD95 expression on these cells but still activated T lymphocytes are resistant to CD95-mediated apoptosis. These observations show that EPO is able to directly influence CD4+ T lymphocytes' signaling pathways.