title: Human platelet-specific antigen, Siba, is associated with the molecular weight polymorphism of glycoprotein Ib alpha.
abstract: Platelet-specific antigen Sib(a) has been highly implicated in the pathogenesis of refractoriness to human leukocyte antigen (HLA)-matched platelet transfusions in Japan. We provide evidence that the Sib(a) antigen is located on the glycoprotein (GP) Ib alpha and has a close association with the molecular weight (mol wt) polymorphism of GPIb. In modified antigen-capture ELISA (MACE), anti-Sib(a) antibody reacted only with GPIb/IX held by a murine anti-GPIb/IX monoclonal antibody (MoAb). The reactivity of anti-Sib(a) antibody to Sib(a)-positive (Sib(a+)) platelets was abolished after they were treated with Serratia marcescens protease. Platelets from 50 healthy volunteers were semiquantitatively phenotyped for Sib(a) antigen by MACE and divided into three distinct groups: strongly positive, positive, and negative. They were also analyzed by sodium dodeyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and periodic acid-silver staining for mol wt polymorphism of GPIb, phenotyped as A, B, C, or D. Without exception, Sib(a+) platelets showed larger phenotypes (A or B). Removal of sialic acid from Sib(a+) platelets did not reduce the binding of anti-Sib(a). Finally, anti-Sib(a) antibody specifically immunoprecipitated A and B phenotypes of GPIb from Sib(a+) platelets. Thus, Sib(a) antigen evidently is located in the region of glycocalicin that is present only on the A and B phenotypes of GPIb.
authors.affiliation: Second Department of Internal Medicine, Shinshu University School of Medicine, Nagano, Japan.
authors.forename: F
authors.initials: F
authors.lastname: Ishida
authors.forename: H
authors.initials: H
authors.lastname: Saji
authors.forename: E
authors.initials: E
authors.lastname: Maruya
authors.forename: K
authors.initials: K
authors.lastname: Furihata
mesh_terms: D016824:Antigens, Human Platelet / Q000032:analysis* / Q000235:genetics; D001792:Blood Platelets / Q000276:immunology*; D004591:Electrophoresis, Polyacrylamide Gel; D004797:Enzyme-Linked Immunosorbent Assay; D005434:Flow Cytometry; D006801:Humans; D016130:Immunophenotyping; D007163:Immunosorbent Techniques; D008970:Molecular Weight; D009439:Neuraminidase / Q000494:pharmacology; D010375:Pedigree; D010980:Platelet Membrane Glycoproteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D011110:Polymorphism, Genetic
chemical_list: C071221:2b alloantigen, human; D016824:Antigens, Human Platelet; D010980:Platelet Membrane Glycoproteins; D009439:Neuraminidase