CONSTITUTIVE EXPRESSION OF E-SELECTIN AND VASCULAR CELL-ADHESION MOLECULE-1 ON ENDOTHELIAL-CELLS OF HEMATOPOIETIC TISSUES

The first step in the homing of hematopoietic progenitor cells (HPCs) from the peripheral blood to the bone marrow involves an adhesion mole cule-dependent contact with human bone marrow endothelial cells (HBMEC s). In the present study we describe the constitutive expression of tw o of these molecules, E-selectin and vascular cell adhesion molecule-1 (VCAM-1), on endothelial cells of hematopoietic tissues. Immunophenot ypic analysis of tissue sections of hematopoietically active (human ad ult and fetal bone marrow, fetal spleen, fetal liver, and adult spleen with extramedullary hematopoiesis) and inactive tissues (human adult spleen, lymph node, appendix, and liver; and fetal lung and fetal inte stine) revealed that E-selectin and VCAM-1 are selectively expressed o n endothelial cells of adult and fetal hematopoietic organs. These res ults were validated by means of reverse-transcriptase polymerase chain reaction. Adhesion studies revealed that binding of normal mobilized peripheral blood HPCs to HBMECs was completely inhibited by preincubat ion of HBMECs with anti-E-selectin (ENA2), whereas no effect of anti-V CAM-1 (1G11B1) was detected. These results suggest that E-selectin pla ys a role in the homing of HPCs and that its constitutive expression o n endothelial cells of hematopoietic organs may be essential in the in itial step of the homing process.