Three cases of platelet alloimmunisation associated with the presence of anovel platelet-specific antibody

Background and Objectives: In three cases of platelet alloimmunisation, a p latelet-specific alloantibody was detected which could not be classified wi thin the known human platelet alloantigen or HLA systems. The first case wa s of a family in which two siblings suffered neonatal alloimmune thrombocyt openia at birth. In the second case, the newborn was suffering from phocome lia with hypoplastic thrombocytopenia. The third case was a male who became refractory to transfusions of HLA-matched platelets after a related bone m arrow transplantation. Materials and Methods: The serum samples were invest igated by: enzyme-linked immunosorbent assay, platelet suspension immunoflu orescence test (PSIFT), monoclonal antibody immobilisation of platelet anti gens assay (MAIPA), and by the lymphocytotoxicity test. Results: The antibo dy 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 sy stem. Conclusion: The reactivity pattern of the antibody detected and the c linical presentation of the three cases described, strongly suggest the pre sence of an additional platelet-specific alloantigen system.