HPA-5b (Br-a) 抗原感作による血小板輸血不応例

A 65-year-old female MDS patient Y. M showed refractoriness to transfusions of HLA-matched platelets in 4 out of 72 occasions. Analysis of Y. M serum by a monoclonal antibody specific immobilization of platelet antigens (MAIPA) assay revealed that the serum contained anti-HPA-5b antibody directed against an epitope on platelet glycoprotein (GP) Ia/IIa. The Y. M serum was tested for its reactivity against ineffective as well as effective platelets by MAIPA assay. The serum was reactive to the platelet antigen against an epitope on GP Ia/IIa of ineffective platelets, but not against an epitope on GP IIb/IIIa, GPIb or GPIV. The serum was not reactive to any of GPs of effective platelets. Platelet typing of patient Y. M and four ineffective HLA-matched donors showed that patient Y. M was HPA-5a/a, whereas four ineffective donors were HPA-5a/b. The results indicate that HPA-5 antigen is responsible for the refractoriness to the platelet transfusion.