Studies of platelet-bound and serum platelet-bindable immunoglobulins in dogs with idiopathic thrombocytopenic purpura.

Canine idiopathic thrombocytopenic purpura (ITP) is clinically analogous to chronic ITP in human beings. The objective of this study was to investigate the pathogenesis of canine ITP by determining whether immunoglobulins bound to the surface of platelets from dogs with ITP (platelet-bound immunoglobulins) were directed against host platelet antigen and whether platelet glycoproteins (GP) IIb and IIIa were target antigens in dogs with ITP. Thirty-two dogs with ITP were studied. Increased platelet-bound immunoglobulin concentrations were detected in 30 cases (94%), and increased concentrations of serum platelet-bindable immunoglobulins were detected in 11 cases (34%). Immunoglobulins eluted from the surface of platelets from dogs with ITP bound to homologous normal canine platelets in 11 of 19 cases (58%). Immunoglobulins against platelet membrane GP IIb and/or IIIa were detected in serum from four of 17 affected dogs. This study provides evidence that immunoglobulins bound to surface of platelets from some dogs with ITP are directed against host platelet antigens and that platelet target antigens are, in some cases, GP IIb and IIIa. This supports the hypothesis that canine ITP is an autoimmune disease, similar to the pathogenesis of chronic ITP in human beings.