Circulating CD34+ cells in cord blood and mobilized blood hav a different profile of adhesion molecules than bone marrow CD34+ cells

The expression of adhesion molecules was studied on CD34+ hematopoietic precursors in cord blood, bone marrow and mobilized blood. The samples were labeled in a bouble immunofluorescence procedure with a CD34 monoclonal antibody and with antibodies against maturation and differentiation antigens and adhesion molecules. Myeloid precursors formed the majority of the CD34+ cells in all samples. In bone marrow a separate cluster of B-cell precursors with low forward scatter was present. Nearly all CD34+ cells in normal bone marrow expressed VLA-4 and VLA-5, PECAM-1, LFA-3 and HCAM. The majority of the CD34+ cells expressing the vitronectin receptor or the CD11c antigen were rare. Cord blood and mobilized blood CD34+ cells had a lower expression of VLA-2, VLA-3 and VLA5 and a higher expression of LFA-1, ICAM-1 and L-selectin than bone marrow CD34+ cells. Except for LFA-1, this was not due to the presence of more myeloid precursors in these samples. Low B1 integrin expression may lead to less adhession to the extracellular matrix. High expression of L-selectin may facilitate interaction with endothelial cells. Therefore, this phenotype may favour mobilization.