Platelet adhesion to fibrinogen in response to ephrinB1 or EphA4 is mediated by α_IIbβ₃. (A-B) Platelets were preincubated for 30 minutes with recombinant monomeric proteins corresponding to the exodomain of either (A) EphB1 (10 μg/mL) or (B) ephrinA4 (10 μg/mL) and then stimulated with GST-EphB1, GST-ephrinA4, or GST for an additional 20 minutes. Mean ± SEM for 3 experiments. (C) Platelets were incubated with GST-EphB1 or GST-ΔEphB1 for 20 minutes. Mean ± SEM for 6 experiments. (D-F) Platelets were preincubated for 30 minutes with the monoclonal anti-α_IIbβ₃, A2A9, or with RGDS, and then stimulated with GST-EphB1 or GST-ephrinA4 for 20 minutes as indicated. Mean ± SEM for 3 to 4 experiments.