Binding of naïve T cells to KM-H2 C/S-stimulated HUVECs is mediated by β2-integrin-ICAM-1 and CD44-hyaluronan interactions. C/S-stimulated HUVECs or naïve T cells were treated with function blocking mAbs for 30 and 10 minutes, respectively, prior to use in flow experiments. (A) Blocking of ICAM-1, but not VCAM-1 and E-selectin, expressed on C/S-stimulated HUVECs significantly inhibited naïve T-cell interactions. Treatment of C/S-stimulated HUVECs with mAb against MHC class I molecules was used as the binding nonblocking control. (B) Blocking of CD18 and L-selectin on the naïve T cells significantly reduced the interaction between the T cells and C/S-stimulated HUVECs. Naive T cells treated with purified mouse IgG (MuIgG) was used as the negative control. (C) Blocking of CD44 inhibited naïve T-cell interactions with C/S-stimulated HUVECs but had no effect on their interactions with TNF-α–stimulated HUVECs. Naïve T cells treated with purified rat IgG (RatIgG) was used as the negative control. (D) Treatment of C/S-stimulated HUVECs with hyaluronidase (50 µg/mL for 1 hour) resulted in a significant reduction in the number of interacting naïve T cells. Treatment with deactivated hyaluronidase was used as the vehicle control. Values shown are mean ± SEM from 3 different experiments. *P ≤ .05 compared with untreated controls. The clones of the mAb used are ICAM-1 (clone Hu5/3), VCAM-1 (clone E1/6), E-selectin (clone H18/7), CD18 (β2-integrin, clone LIA1/2), CD11a (clone HI111), CD44 (clone IM7), and L-selectin (clone DREG56).