Adhesion of activated natural killer cells to tumor necrosis factor-alpha-treated endothelium under physiological flow conditions.

Adhesion of activated natural killer (A-NK) cells to activated and nonactivated endothelial cells in vitro was studied under dynamic flow conditions. Endothelial cells grown on glass slides were either treated with tumor necrosis factor-alpha (TNF alpha) or medium, then placed into a flow chamber over which suspensions of A-NK cells were passed using a range of defined shear stress levels. Significant numbers of binding cells could be consistently observed at shear stress levels less than 3 dyn/cm2 on TNF alpha-activated endothelium or at 0.59 dyn/cm2 on nonactivated endothelium. Stable adhesion occurred rapidly following the initial interaction of the following cells with the endothelium in the absence of detectable rolling. Pretreatment of the A-NK cells with monoclonal antibodies directed against CD18 (LFA-1) or CD49d (VLA-4) resulted in a significant reduction in the number of binding cells. Simultaneous treatment with both monoclonal antibodies eliminated all A-NK adhesion occurring over 0.5 dyn/cm2. Pretreatment of the endothelial cells with antibodies against E- or P-selectin resulted in a small but significant reduction in binding only at 0.5 dyn/cm2. The binding efficiency of the A-NK cells was similar to that previously observed for T lymphocytes under the same conditions. Once bound, approximately half of the adherent cells could resist detachment when exposed to wall shear stresses over 12 dyn/cm2. These findings indicate that A-NK cell adhesion to activated endothelium can occur under shear stress conditions which are representative of postcapillary venules and that this binding is mediated principally by both CD18 and CD49d. A-NK cell adhesion also occurs to nonactivated endothelium but only at wall shear stress levels less than 1 dyn/cm2.