β₁ integrin–dependent adhesion is defective in LADV cells and is partially corrected by cation substitution and β₁ integrin–activating antibody.

Wells were coated overnight with fibronectin (3 μg/well; 60 μg/mL), and adhesion of LADV cells (2 different populations from separate transformations, LADV-1 [■] and LADV-2 [░]) or control lymphoblastoid cells (▪) was measured after a 20-minute incubation at 37°C in the presence of control buffer, PMA (10⁻⁷ M), the β₁-activating mAb TS2/16 (final 1:14 dilution of hybridoma supernatant), Mn⁺⁺ (1 mM) or Mn⁺⁺ and the β₁ blocking mAb p4C10 (10 μg/mL). The error bars represent the standard deviation of triplicate determinations. In the experiment shown here, cation substitution did not result in increased adhesion of the control cell line to FN because of high basal binding. However, in additional experiments using the same control lymphoblastoid cells washed in HBSS containing the chelator EDTA (1 mM) there was a 2- to 4-fold increase in adhesion to FN in response to Mn⁺⁺ substitution compared with buffer alone (not shown). The results with the LADV-1 and LADV-2 cells shown are representative of 3 separate experiments.