Modified C-reactive protein interacts with platelet glycoprotein Ibα

Herein, we investigated the possible mechanisms by which recombinant modified CRP (mrCRP) modulates blood platelet function. Modified CRP could activate blood platelets and stimulate their adhesion and aggregation in the absence of any other physiological stimuli. Pre-incubation of isolated blood platelets with mrCRP at a concentration as low as 2 µg/ml resulted in significant platelet degranulation (fraction of CD62-positive platelets increased 2-fold, p < 0.0002), and at concentrations of 20 µg/ml and 100 µg/ml, increased exposure of the platelet procoagulant surface was observed (expression of annexin V-positive platelets increased to 5.7 ± 1.0% and 10.4 ± 2.2%, respectively, p < 0.03, vs. 2.9 ± 0.2% in control). Furthermore, mrCRP (100 µg/ml) strongly augmented spontaneous and ADP-induced fibrinogen binding to platelets (p < 0.05), platelet adhesion to fibrinogen and platelet aggregation. Using the Biacore™ surface plasmon resonance technique and glycoprotein Ibα (GPIbα) immobilized on the sensor surface, we demonstrated direct binding between platelet GPIbα and mrCRP. Binding of mrCRP to GPIbα and C1q was also observed by ELISA, irrespective of the immobilized ligand. These outcomes strongly support a role of the GPIb-IX-V complex in the interactions of mrCRP with blood platelets.