LFA-1 ligation induced U937 cells to produce ROSs that may modulate VCAM-1 binding. U937 cells were labeled with H2DCF-DA in the presence or absence of anti-LFA-1 antibody and the production of ROSs was measured by fluorescence intensity. After LFA-1 ligation, the production of ROSs increased in a time-dependent (A) and dose-dependent (B) manner. Adhesion experiments were then performed in the presence or absence of TS1-18, TS1-22, or immobilized ICAM-1-FC in the presence or absence of (C) catalase (0.3 U/μL) or (D) NAC (10 μM). Cellular binding to fibronectin, laminin, or vitronectin in the presence or absence of catalase was compared with the binding to VCAM-1-FC (E). The experiments in panels A-B were performed with 4 replicates and repeated 3 times with similar results. The experiments in panels C-E were performed with 8 replicates and were repeated 3 times with similar results. Data are expressed as mean ± SD and analyzed with 2-tailed Student t test. Results showing significant differences when compared with the baseline fluorescence are marked with ^** for P < .005 or ^* for P < .05.