Detection and quantification of the soluble form of the human erythropoietin receptor (sEpoR) in the growth medium of tumor cell lines and in the plasma of blood samples

The erythropoietin receptor (EpoR) belongs to the cytokine superfamily and is a type I transmembrane protein. Like other members of this family, EpoR is also synthesized as a soluble form, and is subsequently secreted by the cell. To investigate whether soluble EpoR (sEpoR) is expressed in human tumor cell lines, we developed a sensitive quantitative ELISA, using an anti-human EpoR antibody and recombinant sEpoR as standard control. With this ELISA, sEpoR could be detected in the supernatant of human tumor cell lines. Analysis of blood samples showed that sEpoR was coprecipitated during coagulation. Therefore only plasma was suitable for analysis and first measurements of plasma samples were investigated. In conclusion, an ELISA to quantify the sEpoR was established and the expression of sEpoR in human tumor cell lines was demonstrated for the first time.