L-SELECTINS AND P-SELECTINS, BUT NOT CD49D (VLA-4)-INTEGRINS, MEDIATEMONOCYTE INITIAL ATTACHMENT TO TNF-ALPHA-ACTIVATED VASCULAR ENDOTHELIUM UNDER FLOW IN-VITRO

Monocyte adhesion to the vascular endothelium is a pivotal step during their egress to tissues at sites of inflammation and immune reactions , and during atherogenesis. In this study, an in vitro flow model and blocking mAb were used to define the role of adhesion molecules in mon ocyte interactions with activated HUVEC under flow conditions. By vide omicroscopy, freely flowing monocytes abruptly halted (initial attachm ent) on 6-h TNF-alpha-activated HUVEC under flow via L- and P-selectin , whereas E-selectin was not involved. CD49d/CD29 integrin (VLA-4), wh ich can mediate initial attachment of certain T cells to VCAM-1 under flow, did not support monocyte initial attachment. Once initially atta ched, a small number of monocytes began rolling at 9 mu m/s through a mechanism involving L-selectin, as well as CD49d and CD11/CD18 integri ns, while the remaining monocytes became firmly adherent, or released to the flow stream. Monocyte stable arrest and subsequent transendothe lial migration occurred rapidly and efficiently through either CD49d o r CD18 integrin adhesion pathways. Transendothelial passage was also d ependent on PECAM-1 (CD31). These data reveal monocytes initially atta ch to activated endothelium via an L-selectin-dependent mechanism, wit h a smaller contribution from P-selectin and no contribution by CD49d. Subsequent monocyte rolling, arrest, and transmigration require overl apping functions between multiple members of the selectin, integrin, a nd Ig gene families.