alpha IIb integrin, a novel marker for hemopoietic progenitor cells

Integrin alpha IIb beta 3 (abbreviated as alpha IIb), also known as GPIIb-IIIa or CD41/CD61, is a cell adhesion molecule expressed on cells belonging to the megakaryocytic lineage. Aiming to identify new markers of hemopoietic progenitor cells (HPC), we undertook a developmental study of this molecule since it remains controversial if this integrin is expressed by various progenitors. We reported the expression pattern of two integrins, in both of which the beta 3 chain is present, respectively associated with alpha V and alpha IIb in the chick embryo. While at E3.5, the earliest time at which these integrins can be detected, alpha V beta 3 becomes expressed by endothelial cells in the aorta (and only in the aorta), alpha IIb beta 3 becomes detected in the well-defined intra-aortic clusters made up of HPC. The latter were found to be multilineage progenitors when sorted for alpha IIb expression and analyzed by means of clonogenic assays. In mice also, alpha IIb is expressed in the intra-embryonic site of HPC generation, the intra-arterial clusters in the embryo proper, as well as in sites where HPC migrate. Finally we provided the first evidence in two species that multipotent HPC expressing alpha IIb are able to differentiate not only into cells of the erythroid and myeloid lineages but also into lymphocytes. These cell populations actually coexpress alpha IIb and c-Kit. These data establish alpha IIb as a novel marker for HPC, which appears at very early stages in the embryo. Capitalizing on this finding, other investigators confirmed it and suggested that alpha IIb plays a role in regulating hematopoietic development.