ENDOTHELIAL P-SELECTIN AND VCAM-1 EACH CAN FUNCTION AS PRIMARY ADHESIVE MECHANISMS FOR T-CELLS UNDER CONDITIONS OF FLOW

This study demonstrates that endothelial P-selectin and vascular cell adhesion molecule 1 (VCAM-1), but not intercellular adhesion molecule 1 (ICAM-1), are capable of supporting extensive primary adhesion of T cells under flow. To address this issue, we used human umbilical vein endothelial cells (HUVECs) stimulated with histamine, interleukin-4 (I L-4), or interferon-gamma (IFN-gamma) that provide essentially a P-sel ectin, VCAM-1, or ICAM-1 surface, respectively, in a physiologically r elevant cell type. Monoclonal antibody (mAb) blockade studies were car ried out to confirm the specificity of these adhesive interactions and rule out a number of other potentially important adhesion molecules. Quantitation of adhesion showed that almost all of the interacting T c ells rolled on histamine-stimulated HUVECs or CHO-P cell monolayers, I n contrast, similar to 20% of the total interacting T cells with 24-h IL-4-treated HUVECs were firmly adherent, mAb blocking experiments rev ealed that T cell adhesion to IL-4-treated HUVECs is alpha(4)-VCAM-1 d ependent. Furthermore, mAb 4B9 directed against domain 1 of VCAM-1 eli minated adhesion, suggesting that alpha(4) integrins may not interact with either the alternatively spliced domain 4 of VCAM-1 or fibronecti n in this process. At a wall shear stress of 2 dyn/cm(2), the mean T c ell rolling velocities were significantly lower on 24-h IL-4-activated HUVECs (10.2 +/- 2.6 mu m/s) compared with either CHO-P cells (15.6 /- 3.1 mu m/s) or histamine-stimulated HUVECs (16.6 +/- 6.1 mu m/s). I CAM-1, expressed on the surface of 24-h IFN-gamma-activated HUVECs pre treated with an anti-VCAM-1 mAb to eliminate any VCAM-1-dependent cont ribution, did not support T cell adhesion under shear conditions. Toge ther these data indicate that T cell primary adhesion can be mediated by both endothelial P-selectin and VCAM-1 but not ICAM-1. alpha(4) as integrins are highly versatile molecules, capable of initiating T cell rolling interactions and mediating firm arrest on activated endotheli um.