Fig. 1. P-selectin and P-selectin glycoprotein ligand 1 (PSGL1) blockade inhibit aggregation in thrombin receptor activating peptide–activated whole blood. Whole-blood samples were incubated in the presence and absence of P-selectin, PSGL1, or immunoglobulin (Ig)G isotype control antibodies for 20 min. Aggregation in response to thrombin receptor activating peptide was then measured by impedance aggregometry as described in Methods. (A ) P-selectin antibody experiments. (B ) PSGL1 antibody experiments. In each set of experiments, data were significantly different by repeated-measures analysis of variance (P < 0.0001; n = 13); * P < 0.001 versus  no antibody and IgG control by Bonferroni post hoc  test.