The recent report of EPO expression by trophoblast cells in the human placenta  prompted us to test whether the same cells also express the EPO-R. If so, then by analogy to erythroid precursors, important functions for this hormone related to survival, proliferation, and/or differentiation of placental trophoblast cells are possible. The findings of the present work provide evidence for the expression of EPO-R by trophoblast cells: 1) villous and extravillous cy-totrophoblast cells, as well as syncytiotrophoblast at all gestational stages, expressed immunoreactive EPO-R identified by immunohistochemistry; 2) placental tissues and isolated, immunopurified trophoblast cells of various gestational ages, as well as Jar trophoblast-derived choriocarcinoma cells, also expressed immunoreactive EPO-R by Western blot; 3) EPO-R mRNA was detected in the same placental tissues and trophoblast cells by RT-PCR; and 4) the EPO-R was shown to be functional, insofar as tyrosine phosphorylation of the receptor increased in response to exogenously administered EPO.
In the present investigation, we confirmed the localization of EPO-R to the endothelium of fetoplacental vessels by immunocytochemistry as originally described by An-agnostou et al. using the same m2her 16.5.1 monoclonal antibody. Indeed, this confirmation was an important ‘‘positive control’’ for our work. In the same term placental tissue sections, however, we also observed EPO-R immu-noreactivity associated with the trophoblast layer (Fig. 3), a finding not reported by Anagnostou and coworkers.