[Clinical significance of platelet antigens]

During the last years, platelet immunology has shown an accelerated progress associated with the development of new highly specific and sensitive techniques. This progress has allowed the description of many new "platelet specific" alloantigens. In 1990, an International Workshop on Platelet Serology of the ISBT and ISH grouped the accepted alloantigens into five systems, named HPA-1 to HPA-5. Recent progress in molecular genetics techniques has also enabled the definition of the primary molecular structure of platelet glycoproteins which carry the specificity of the platelet-specific antigens. From the clinical point of view, the role of immunization against platelet-specific alloantigens has been established in neonatal alloimmune thrombocytopenia and in posttransfusion purpura, with anti-PIA1 (anti-HPA-1) being the antibody most frequently involved. An adequate diagnosis and management of these conditions can avoid devastating consequences like severe bleeding and even death. Associated with an increase in the administration of platelet transfusions, immunological refractoriness to platelet transfusions limits the benefits of such therapy, in most cases associated with HLA antibodies. Refractoriness can be efficiently prevented to large extent by using leucocyte-poor blood components in multitransfused patients.