HEMATOPOIETIC PROGENITOR-CELL ROLLING IN BONE-MARROW MICROVESSELS - PARALLEL CONTRIBUTIONS BY ENDOTHELIAL SELECTINS AND VASCULAR CELL-ADHESION MOLECULE-1

We have used intravital microscopy to study physiologically perfused m icrovessels in murine bone mallow (BM). BM sinusoids and venules, but not adjacent bone vessels, supported rolling interactions of hematopoi etic progenitor cells. Rolling did not involve L-selectin, but was par tially reduced in wild-type mice treated with antibodies to P- or E-se lectin and in mice that were deficient in these two selectins. Selecti n-independent rolling was mediated by alpha 4 integrins, which interac ted with endothelial vascular cell adhesion molecule (VCAM)-1. Paralle l contribution of the endothelial selectins and VCAM-1 is not known to direct blood cell trafficking to other noninflamed tissues. This comb ination of constitutively expressed adhesion molecules may thus consti tute a BM-specific recruitment pathway for progenitor cells analogous to the vascular addressins that direct selective lymphocyte homing to lymphoid organs.