Figure 1.

Cell surface–bound SDF-1 augments VLA-4–mediated capture and arrest of lymphocytes on endothelial VCAM-1 under physiological shear flow. (A) The frequency of PBTLs perfused at a shear stress of 1.5 dyn/cm² over HUVECs stimulated for either 18 h (top) or 40 h (bottom) are capable of tethering transiently, or tether and roll or arrest on the cell monolayers. These different categories are depicted in stacked bars. SDF-1 (1 μg/ml in binding medium) was overlaid for 10 min on each monolayer and washed extensively before PBTL perfusion. Indicated cell monolayers were pretreated for 10 min with the E-selectin blocking mAb BB11 (at 10 μg/ml). Indicated PBTL samples were pretreated with the α4-integrin subunit mAb, HP1/2, to block their VLA-4–dependent interactions with endothelial VCAM-1. Where indicated, PBTLs were perfused over the endothelial monolayers in the presence of 1 mM EDTA. Standard deviation of total tethering values between multiple experiments on the different TNF-activated HUVECs was <10% of the mean. Asterisk indicates that chemokine-dependent augmentation in total tethering to activated HUVECs was highly significant (n = 5, P < 0.001). (B) Frequency of different categories of tethers initiated by PBTLs on VCAM-1–expressing CHO cells at 1.5 dyn/cm². SDF-1 (1 μg/ml) was overlaid on the CHO monolayer as described for panel A. Data shown in B are representative of four independent experiments.