The polymorphonuclear leukocyte--a new target for erythropoietin

A previous study from our laboratory has shown that erythropoietin (EPO), beside its traditional role in erythropoiesis, acts as an alleviator of oxidative stress and inflammation in chronic hemodialysis (HD) patients, conferred in part by activated polymorphonuclear leukocytes (PMNLs). To substantiate this phenomenon, the existence of EPO receptors (EPO-Rs) on PMNL membrane was examined at the transcriptional and translational levels. mRNA for EPO-R was detected in PMNLs using specific primers directed towards the extracellular region of human EPO-R cDNA. The predicted 300-bp fragment was amplified by reverse transcriptase-polymerase chain reaction. Subcloning and sequence analysis revealed 100% homology of this fragment with human EPO-R. The receptor protein was detected on the surface of intact PMNLs using (125)I-EPO. The protein was further demonstrated by flow cytometric analysis using a fluorescent monoclonal anti-EPO-R. The percentage of PMNLs expressing EPO-R showed a strong correlation with the level of EPO in the serum, suggesting an upregulation of the receptor by the hormone. Taken together with our recent findings that EPO attenuates the oxidative stress and inflammation contributed by PMNLs in HD patients, the detection of functional EPO-R expression in PMNLs places these cells among the nonerythroid, EPO-responsive target populations.