PSGL-1 antibodies enhance adhesion of neutrophils to fibrinogen. Washed neutrophils were incubated with 10 μg/mL mouse IgG (mIgG), KPL-1 (a leukocyte adhesion-blocking mAb to PSGL-1), PL1 (a leukocyte adhesion-blocking mAb to PSGL-1), or PL2 (a leukocyte adhesion-nonblocking mAb to PSGL-1) before they were added to the wells without fibrinogen coating (control) or the wells immobilized with fibrinogen. For inhibition experiments, neutrophils were preincubated with IB4 (a leukocyte adhesion-blocking mAb to β2 subunit). Other steps of the cell adhesion assay were carried out as described for Figure 1. All results are expressed as the mean ± SD values of the adherent cells determined in triplicate measurements of 3 separate experiments.