Platelet interaction with surface-immobilized IgG induces the secretion of surface bound microparticles and fragmentation of the cells

Exposure of fibrinogen-adherent platelets to plasma proteins: a new method for studying protein interactions with platelets

To understand the effects of mediators in coagulating blood at biomaterial surfaces, it is important to use methods that resemble the normal sequence of events in wound healing around implants. The initial adhesion of platelets from whole blood onto material surfaces is mediated by the fibrinogen receptor glycoprotein IIb/IIIa, as shown in a previous study (Broberg et al., J Lab Clin Med 2002; 139:163-172). In this study, isolated platelets were adhered to fibrinogen and exposed to IgG, von Willebrand factor, or thrombin. The response was detected as the number of adherent platelets, the spreading of platelets, the exposure of CD62P (P-selectin), and the release of platelet factor 4 (PF4), ADP, and ATP. These results were compared to the response of platelets adhering to surfaces coated with the same proteins. Fibrinogen-adherent platelets exposed to thrombin generated the significantly highest exposure of CD62P and release of PF4, ADP, and ATP. When platelets were adhered to different protein coatings, von Willebrand factor generated the most CD62P exposure, IgG generated the most PF4 release, and thrombin generated the highest concentration of ADP. These results indicate that protein interactions with platelets may generate different results, depending on the mode of protein exposure.

Platelets stimulated by IgG-coated surfaces bind and activate neutrophils through a selectin-dependent pathway

Blood platelets bind rapidly to foreign surfaces and interact with adsorbed proteins and neutrophil granulocytes. We demonstrate by use of luminol-amplified chemiluminescence under stirred and non-stirred conditions that platelets at IgG-coated surfaces amplify the neutrophil extracellular release of reactive oxygen species (ROS). The neutrophil response involved tyrosine phosphorylation, but was only in part induced by neutrophil F(c gamma)-receptor stimulation. The platelet mediated effects were contact-dependent since the respiratory burst was inhibited when the IgG-stimulated platelets were removed by filtration, but not when they were fixed in paraformaldehyde. Bodipyphallacidin-staining of filamentous actin (F-actin) revealed that an actin-dependent platelet adhesion supported the subsequent adhesion and spreading of neutrophils. The neutrophil ROS-response was lowered when the interaction between platelet P-selectin (CD62P) and neutrophil P-selectin glycoprotein ligand-l (PSGL-1 or CD162) was inhibited. The blocking of L-selectin (CD62L) or blocking of the interaction between platelet glycoprotein (Gp) IIb/IIIa and neutrophil complement receptor 3 (CR3) showed no effect. We conclude that platelet activation on immobilized IgG trigger a contact-dependent "frustrated" phagocytosis by neutrophils, associated with a release of toxic ROS.