Involvement of a CD47-dependent pathway in platelet adhesion on inflamed vascular endothelium under flow.

Resting platelet adhesion to inflammatory vascular endothelium is thought to play a causal role in secondary thrombus formation or microcirculatory disturbance after vessel occlusion. However, though adhesion receptors involved in platelet-matrix interactions have been extensively studied, the molecular mechanisms involved in platelet-endothelium interactions are incompletely characterized and have been mainly studied under static conditions. Using human platelets or platelets from wild-type and CD47-/- mice in whole blood, we demonstrated that at low shear rate, CD47 expressed on human and mouse platelets significantly contributes to platelet adhesion on tumor necrosis factor-alpha (TNF-alpha)-stimulated vascular endothelial cells. Using the CD47 agonist peptide 4N1K and blocking monoclonal antibodies (mAbs), we showed that CD47 binds the cell-binding domain (CBD) of endothelial thrombospondin-1 (TSP-1), inducing activation of the platelet alphaIIbbeta3 integrin that in turn becomes able to link the endothelial receptors intercellular adhesion molecule 1 (ICAM-1) and alphavbeta3. Platelet CD36 and GPIbalpha are also involved because platelet incubation with blocking mAbs directed against each of these 2 receptors significantly decreased platelet arrest. Given that anti-CD47 treatment of platelets did not further decrease the adhesion of anti-CD36-treated platelets and CD36 is a TSP-1 receptor, it appears that CD36/TSP-1 interaction could trigger the CD47-dependent pathway. Overall, CD47 antagonists may be potentially useful to inhibit platelet adhesion on inflamed endothelium.