Integrin expression profiles during erythroid differentiation

To study the expression of integrins at the erythroid progenitor level we isolated selected populations of cells from human fetal liver after immunoadherence to anti-beta 2 integrin (CD18) coated plates. These CD18 adherent cells (CD18-Ad), in contrast to CD18 nonadherent cells (CD18-NAd), have a blastlike cell morphology and are highly enriched in all progenitor types (14% to 37% progenitors). By several criteria progenitor cells present in CD18-Ad cells appear to have a higher proliferative potential and diversity than the ones found in CD18-NAd, which were mostly later erythroid progenitors. Positivity of CD18-Ad cells with the common beta 2 integrin (CD18) is largely attributable to expression of alpha L (CD11a) chain, rather than alpha M (CD11b). CD11a is present in all types of progenitors, but it is selectively lost at later stages of erythroid differentiation/maturation. By contrast, CD11b appears to be virtually absent from all progenitors but it has an enhanced expression during granulomonocytic differentiation/maturation. In addition to beta 2 integrins, CD18-Ad cells express several other cytoadhesion molecules (VLA-4, VLA-5, I-CAM, H-CAM) as well as other progenitor cell antigens (CD34, HLA-DR, CD38). Cells expressing all these antigens were selectively enriched in CD18-Ad cells. Our data add new information on the regulation of CD11a and CD11b molecules in hematopoiesis and on the composite profile of integrin expression at several stages of erythroid differentiation.