title: Liberation of surface and internal platelet-associated IgG (PA-IgG) during platelet activation.
abstract: The relationship between platelet-associated IgG (PA-IgG) of intact platelets to that of lysed platelets has been studied using a competitive ELISA. In platelets from 20 normal individuals mean surface PA-IgG constituted 35% of mean total PA-IgG and showed a significant linear relationship with total PA-IgG. In platelets from 61 patients with various forms of thrombocytopenia including that with immune causes, 38 showed a similar proportion of PA-IgG on the surface after storage at 2 degrees C, as seen in normal platelets, while in 23, levels of surface and total PA-IgG were equal. Normal platelets activated with thrombin or calcium ionophore A23187, also had levels of surface PA-IgG close to total PA-IgG. Supernatants of platelet suspensions activated with aggregating agents contained increased amounts of IgG and when the platelets were washed, both total and surface PA-IgG were decreased. Liberation of IgG from platelets was slower than that of [14C]serotonin but was decreased by release reaction inhibitors. Platelets treated at 2 degrees C with soluble heat-aggregated IgG, which binds to the Fc gamma receptor, showed increased surface PA-IgG, but, after incubation at 37 degrees C, although [14C]serotonin was released, PA-IgG levels were no longer increased. Thus since platelet activation, including that mediated by IgG binding to the Fc gamma receptor, causes PA-IgG release, levels of both surface-located and total PA-IgG may be affected by platelet activation, either in vivo, or in vitro during sample preparation and assay.
mesh_terms: D001792:Blood Platelets / Q000187:drug effects / Q000276:immunology*; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D007074:Immunoglobulin G / Q000378:metabolism*; D066298:In Vitro Techniques; D010974:Platelet Aggregation; D011947:Receptors, Antigen, B-Cell / Q000378:metabolism; D012701:Serotonin / Q000378:metabolism; D013921:Thrombocytopenia / Q000276:immunology
chemical_list: D007074:Immunoglobulin G; D011947:Receptors, Antigen, B-Cell; D012701:Serotonin