INCIDENCE OF THE NAK(A)-NEGATIVE PLATELET PHENOTYPE IN AFRICAN-AMERICANS IS SIMILAR TO THAT OF ASIANS

Background: About 5 to 10 percent of Asians have platelets that lack t he major membrane glycoprotein (GP) IV (CD36, GPIIIb) that carries the isoantigen Nak(a). The GPIV-negative platelet phenotype is extremely rare among whites, but its frequency in persons of African ancestry ha s not yet been determined. Isoimmunization against GPIV can occur in G PIV-negative persons and can lead to platelet transfusion refractorine ss. Therefore, the expression of GPIV on platelets from unrelated Afri can Americans was studied. Study Design and Methods: Platelets were ob tained from 250 African American and 280 white blood donors. Flow cyto metry was used to determine the ability of these platelets to bind a m onoclonal antibody that reacted with GPIV. Platelets that failed to re act with this probe were tested with other GPIV-specific monoclonal an tibodies and with anti-Nak(a), an isoantibody that recognizes an epito pe on GPIV. Results: Platelets from 6 of the 250 African American dono rs (2.4%) lacked GPIV and failed to bind anti-Nak(a), whereas platelet s from all of the white donors were GPIV positive (p > 0.05). No plate let-reactive antibodies were identified in the serum of the GPIV-negat ive donors. Conclusion: The frequency of the GPIV-negative platelet ph enotype in African Americans is comparable to that in Asians and much greater than that in whites. Studies are needed to determine the frequ ency with which African Americans become isoimmunized to GPIV by trans fusions and the possible contribution of this isoimmunization to plate let transfusion refractoriness in this population.