EVIDENCE FOR AN EXPRESSION OF BLOOD-GROUP-A ANTIGEN ON PLATELET GLYCOPROTEIN-IV AND GLYCOPROTEIN-V

Blood group ABO antigens are known to be carried by several platelet g lycoproteins (GP), e.g. GPIb, GPIIa, GPIIb, GPIIIa and PECAM. Beside t hese proteins, we recently observed that blood group A antigen was als o expressed on some other uncharacterized platelet proteins (70-90 kDa ) having electrophoretic mobilities closely resembling those of GPIV a nd GPV. These findings prompted us further to characterize these latte r ABO-expressing platelet proteins. By antigen capture ELISA, wherein the monoclonal antibodies (mAbs) CLB-IVC7 and CLB-SW16 were used to ho ld the corresponding antigens GPIV and GPV, human anti-A specifically bound to these proteins derived from Al-platelets; neither GPIV nor GP V derived from A(2)-, B- or O-platelets bound anti-A. In a Western blo t assay using immunoprecipitated GPIV and GPV as antigens, mAb anti-A immunostained GPIV and GPV precipitated from A(1), but not from A(2) a nd O platelets. These results conclusively demonstrate that blood grou p A antigen is expressed on platelet GPIV and GPV.