Immunofluorescent staining of platelet suspensions and detection of antiplatelet antibody in patients with idiopathic thrombocytopenic purpura.

Direct immunofluorescent staining of 31 specimens of platelets obtained from 13 cases of idiopathic thrombocytopenic purpura (ITP) revealed positive staining on the surface of platelets for both immunoglobulins (Igs) and human B1C globulin in 9 specimens, for only Igs in 1 specimen and for human B1C alone in 5 specimens. The pattern of the positive immunofluorescent staining was granular. Indirect immunofluorescent staining of normal platelets in serum obtained from patients with ITP was positive for antiplatelet antibody in 9 out of 31 specimens. This suggests that platelets in patients with ITP may be damaged by an antiplatelet autoantibody acting directly on the platelet surface and/or by antigen antibody complexes binding via Fc IgG receptors on the surface of the platelets.