Ligation of LFA-1 decreased cellular adhesion to VCAM-1 through a NADPH oxidase-dependent pathway. U937 cells were labeled with BCECF-am in the absence or presence of (A) DPI (5 μM), (B) rotenone (10 μM) or (C) allopurinol (4 μM) and then treated with anti-LFA-1 mAb TS1-18 and tested for binding to the recombinant VCAM-1-FC and FC. (D) After LFA-1 ligation with TS1-18 mAb, DPI-, allopurinol-, and rotenone-treated U937 cells were measured for their increase in production of ROSs with H2DCFDA fluorescence. The experiments were performed with 8 replicates and were repeated 3 times with similar results. Results showing significant differences in the comparison with negative controls are marked with ^** for P < .005 and ^* for P < .05. Data are expressed as mean ± SD.