Anti-PSI mAbs inhibited fibrinogen binding to purified human integrin αIIbβ3 as demonstrated by BFP technique. (A) A αIIbβ3-bearing bead and fibrinogen-bearing bead were repeatedly brought into contact with a ∼15 pN compressive force for 0.1-5 seconds, which allowed for bond formation, and was then retracted for adhesion detection. The effective affinity (m_rm_lA_cK_a) of αIIbβ3-fibronogen binding fitted and calculated from BFP adhesion frequency curves. (B) BFP detection of fibrinogen-αIIbβ3 binding in a purified system. BFP “Adhesion frequency vs Contact Time” plots integrin αIIbβ3 binding to fibrinogen. The experiments were performed in the absence of (orange) or presence of bacitracin (green) or DTNB (purple). (i-v) The antibodies PSI A1 (ii), PSI B1 (iii), PSI C1 (iv), or PSI E1 (v) were added into the experimental environment, respectively. The site densities of αIIbβ3 (m_r) and fibrinogen (m_l) are marked in the lower left corner. Mean ± SEM; *P < .05; **P < .01; ***P < .001; n = 4.