Different expression of adhesion molecules on myeloid and B‐lymphoid CD34+ progenitors in normal bone marrow

The expression of adhesion molecules was studied on B lymphoid and myeloid CD34+ precursors in normal bone marrow. Bone marrow aspirates were labelled in a double fluorescence procedure with the CD34 monoclonal antibody 43A1 and with antibodies directed against maturation and differentiation antigens and adhesion molecules. Three clusters of CD34+ cells could be distinguished by their light scatter characteristics in flow cytometry. The population with the lowest forward scatter contained B-lymphoid precursors while the two others showed phenotypic characteristics of, respectively, early and late myeloid precursors. Nearly all CD34+ cells in the 3 subpopulations expressed VLA-4, VLA-5, LFA-3 and H-CAM. B-lymphoid progenitors showed a higher density of VLA-4 and VLA-5 than the myeloid progenitors. Myeloid precursors, and particularly the late subset, expressed more HCAM than the B-lymphoid progenitors. The majority of the CD34+ cells also expressed LFA-1 and L-selectin. Higher numbers of positive cells were found in the myeloid subset. The early myeloid subset showed the highest positivity for L-selectin. We conclude that B lymphoid and early and late myeloid CD34+ precursors in normal bone marrow show a different profile of adhesion molecules. These profiles could reflect a higher tendency of the myeloid CD34+ precursors to circulate.