PSGL-1 mediates activated platelet/PMN adhesion. HE-loaded PMN were preincubated for 15 minutes at 4°C in the absence (control) or in the presence of the noninhibitory (PL2), the inhibitory (PL1) anti–PSGL-1, or with the anti-CD18 antibody (IB4) before addition of PFA-fixed BCECF-loaded thrombin-activated platelets. Data report the number of platelets bound by 100 PMN (PLT/100 PMN) and are expressed as percentage of the peak level (at 1 minute) of the untreated sample. At this time, 65.7 ± 5.3% of PMN bound 393 ± 55 platelets (means ± SEM, n = 2 to 5).