Effect of an anti-sulfatide single-chain antibody probe on platelet function

Sulfatide (galactocylceramide-3'-sulfate), a cell surface glycosphingolipid interacts with several cell adhesion molecules including fibrinogen, von Willebrand factor (VWF), P-selectin, thrombospondin (TSP) and laminin, which are involved in haemostasis. We have used a sulfatide-specific single-chain fragment variable (scFv) antibody probe PA38 and sulfatide-deficient mice to investigate the role of membrane sulfatide in platelet function. PA38 bound to platelets and binding increased following platelet activation. Sulfatide was localized as a large cluster towards the center of the platelet surface when examined in a confocal microscope. PA38 (20 microg/ml) inhibited the adhesion of activated platelets to fibrinogen, VWF, P-selectin, TSP1 and laminin by 30%, 30%, 75%, 20% and 35%, respectively, compared to a control scFv (p < 0.05). Furthermore, PA38 inhibited collagen, ADP, thrombin and ristocetin-induced platelet aggregation in PRP by 25%, 30%, 18% and 20%, respectively, compared to the control scFv (p < 0.05). In a PFA-100 platelet function assay, PA38 prolonged the occlusion time by 25% (p < 0.05). Under flow PA38 decreased the thrombus formation on collagen by 31%, (p < 0.01). Sulfatide-deficient mice displayed an extended lag-phase in collagen-induced platelet aggregation compared to wild type (p < 0.05), though in-vivo haemostasis did not differ significantly. Thus, this study provides new evidence for a role for membrane sulfatide in platelet function.