Inhibition of P-selectin expression in platelets following blocking of cell-surface ERP5. Binding of PE-conjugated anti-CD62p was measured by means of flow cytometry on platelets stimulated with the agonists convulxin or collagen. Prior to stimulation, platelets were incubated with anti-ERP5 antibodies, anti-PDI antibodies, or control antibodies from preimmune sera. (A) Histogram for fluorescence of PE anti-CD62p–labeled platelets in response to the agonist convulxin (100 ng/mL). Control IgG (12 μg/mL) is indicated by a filled histogram; anti-ERP5 antibody (12 μg/mL), by an empty histogram; and anti-PDI antibody (33 μg/mL), by a dotted-line empty histogram. (B,C) Data are presented as mean ± SE for 4 separate experiments. *P < .05. **P < .005. (Bi,Ci) Residual binding of PE anti-CD62p following incubation of platelets with preimmune IgG (12 μg/mL), anti-ERP5 antibody (12 μg/mL), anti-PDI antibody (33 μg/mL). Agonists were 100 ng/mL convulxin (Bi); and 10 μg/mL collagen (Ci). (Bii,Cii) Additive effect for inhibitory antibodies on residual binding of PE anti-CD62p following incubation of platelets with preimmune IgG (36 μg/mL); anti-ERP5 (12 μg/mL) plus preimmune IgG (19 μg/mL); anti-PDI (6 μg/mL) plus preimmune IgG (19 μg/mL); or anti-ERP5 (12 μg/mL) plus anti-PDI (6 μg/mL). Agonists were 300 ng/mL convulxin (Bii) and 4 μg/mL collagen (Cii).