Expression of CD41 on CD34+ primitive yolk sac hematopoietic progenitors

The phenotype of primitive hematopoietic cells varies during murine ontogeny. CD41 is an integrin alpha chain involved in platelet aggregation and generally considered a platelet lineage marker. Recently, CD41 has been identified as a cell surface marker of primitive hematopoietic cells in the chick. The purpose of the present experiments was to characterize CD41 expression on primitive hematopoietic cells (CD34+ cells including repopulating stem cells) in the murine yolk sac. CD41 was expressed on 65% of CD34+ cells and CD41+CD34+ represent 4.5% of fresh yolk sac cells. Cells were isolated by collagenase/dispase digestion of yolk sacs from timed-pregnant females. Plating of 500 CD41+CD34+ and 5000 CD41-CD34+ cells in progenitor or high proliferative potential colony forming cell (HPP) assays revealed that essentially all HPP and committed progenitor activity resides in the CD41+CD34+ fraction of E9 yolk sac cells (HPP: 10±1 vs. 0 for CD41−CD34+). No HPP or progenitors were observed in the CD41+CD34− or CD41−CD34− populations. All megakaryocyte progenitors are present in the CD41+CD34+ population (BFU-Meg: 2±1, CFU-Meg 8±1). In ongoing studies, 500–1000 CD41+CD34+ or 10,000 CD41−CD34+ cells were transplanted into busulfan conditioned newborn congenic pups for evidence of repopulating ability (pending). Of interest, CD41 is expressed on 86% of cKit+CD34+ cells which contains long-term repopulating cells. In summary, CD41 is expressed on primitive hematopoietic cells and not restricted to the megakaryocyte lineage.