IMMUNOCHEMICAL CHARACTERIZATION OF THE PLATELET-SPECIFIC ALLOANTIGEN LEKA - A COMPARATIVE-STUDY WITH THE PLA1 ALLOANTIGEN

  • 1 January 1984
    • journal article
    • research article
    • Vol. 64  (6) , 1212-1219
Abstract
The immunochemical characterization of a new platelet-specific alloantigen detected using an IgG antibody isolated from the serum of a patient with posttransfusion purpura (PTP) was reported. In indirect immunoprecipitation experiments, the antibody, termed anti-Leka, predominantly precipitated glycoprotein (GP) IIb from Triton X-100 lysates of normal human platelets. In an immunoblot procedure, which involved the transfer of platelet polypeptides separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis to nitrocellulose membrane, anti-Leka bound exclusively to GP IIb. Under identical conditions, 4 anti-PIA1 antibodies each reacted with GP IIIa. No binding of anti-Leka IgG occurred to Leka (-) platelets or to their separated polypeptides although GP IIb was normally detected by Coomassie blue staining. After electrophoresis of reduced platelet proteins, the Leka determinant was localized to the IIb.alpha. chain. Unlike the PIA1 antigen, the Leka determinant was not destroyed by disulfide reduction. Analysis of platelets from a patient with Glanzmann''s thrombasthenia revealed little or no binding in the GP IIb position. Anti-Lek permitted the identification of 76,000 and 60,000 dalton fragments of GP IIb retained by the platelet following chymotrypsin treatment. The immunogenicity of the GP IIb-IIIa complex was shown. Antibodies against GP IIb apparently can cause the thrombocytopenia observed in PTP and anti-PIA1 antibodies do not account exclusively for the pathophysiology of this immune disorder.

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