Three Cases of Platelet Alloimmunisation Associated with the Presence of a Novel Platelet Specific Antibody

Abstract Background and Objectives : In three cases of platelet alloimmunisation, a platelet‐specific alloantibody was detected which could not be classified within the known human platelet alloantigen or HLA systems. The first case was of a family in which two siblings suffered neonatal alloimmune thrombocytopenia at birth. In the second case, the newborn was suffering from phocomelia with hypoplastic thrombocytopenia. The third case was a male who became refractory to transfusions of HLA‐matched platelets after a related bone marrow transplantation. Materials and Methods : The serum samples were investigated by: enzyme‐linked immunosorbent assay, platelet suspension immunofluorescence test (PSIFT), monoclonal antibody immobilisation of platelet antigens assay (MAIPA), and by the lymphocytotoxicity test. Results : The antibody gave positive reactions with 26% of normal donor platelets. Surprisingly, no platelet‐specific antibody was detected by PSIFT or by MAIPA and there was no evidence found to support classifying the antibody within the HLA system. Conclusion: The reactivity pattern of the antibody detected and the clinical presentation of the three cases described, strongly suggest the presence of an additional platelet specific alloantigen system.