UV-C irradiation induces β₁ integrin–mediated adhesion of HL-60 cells to Fn. HL-60 cells were incubated in wells coated with Fn and stimulated with PMA or irradiated with UV-C in the presence of different antibodies. Addition of control IgG (□) did not inhibit adhesion. Blocking of α_mβ₂ with MoAb 44a (■) also had no effect on adhesion. Blocking of α₄β₁ and α₅β₁ with MoAbs HP2/1 and SAM-1 () completely prevented adhesion to Fn. Data represent the mean plus or minus SD of 3 experiments.