title: Investigation of the mechanisms of monoclonal antibody-induced platelet activation.
abstract: Antiplatelet antibodies can activate platelets causing platelet aggregation and the release reaction. However, the pathway of activation by these antibodies is unknown and several potential mechanisms are possible. In this report, we describe studies investigating potential pathways of platelet activation by IgG antibodies. We tested 16 different IgG monoclonal antibodies (MoAbs) against a variety of platelet surface components and found that six antibodies were capable of causing platelet aggregation and release. These included MoAbs against glycoprotein (GP) IIb/IIIa, CD9, GPIV, and two other not well-characterized platelet components. There was no relationship between the number of platelet binding sites and the ability of an MoAb to activate the platelets. By adding intact and F(ab')2 preparations of the MoAb to control or Fc receptor-blocked platelets, we found that in all instances the MoAbs initiated platelet activation via interacting with the platelet Fc receptors. Clustering of the platelet protein components using a secondary antibody did not cause activation. Studies into the pathway of Fc-dependent activation demonstrated that the MoAbs were capable of activating platelets by occupying Fc receptors on adjacent platelets (interplatelet activation), as well as on the same platelet (intraplatelet activation).
authors.affiliation: Departments of Medicine, McMaster University Medical Centre, Hamilton, Ontario, Canada.
authors.forename: P
authors.initials: P
authors.lastname: Horsewood
authors.forename: C P
authors.initials: CP
authors.lastname: Hayward
authors.forename: T E
authors.initials: TE
authors.lastname: Warkentin
authors.forename: J G
authors.initials: JG
authors.lastname: Kelton
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology / Q000494:pharmacology*; D015703:Antigens, CD / Q000276:immunology; D000943:Antigens, Differentiation / Q000276:immunology; D001792:Blood Platelets / Q000276:immunology* / Q000502:physiology; D018955:CD36 Antigens; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000494:pharmacology; D007074:Immunoglobulin G / Q000494:pharmacology; D007163:Immunosorbent Techniques; D008562:Membrane Glycoproteins; D051379:Mice; D008807:Mice, Inbred BALB C; D015539:Platelet Activation; D010974:Platelet Aggregation; D010980:Platelet Membrane Glycoproteins / Q000276:immunology; D011961:Receptors, Fc / Q000276:immunology / Q000502:physiology; D012701:Serotonin / Q000378:metabolism; D060245:Tetraspanin 29
chemical_list: D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D000943:Antigens, Differentiation; D018955:CD36 Antigens; C554869:CD9 protein, human; C554870:Cd9 protein, mouse; D007140:Immunoglobulin Fab Fragments; D007074:Immunoglobulin G; D008562:Membrane Glycoproteins; D010980:Platelet Membrane Glycoproteins; D011961:Receptors, Fc; D060245:Tetraspanin 29; D012701:Serotonin