[Platelet alloantigenic systems].

Platelet-specific alloantigen systems are located on glycoproteins expressed at the surface of platelet membrane. These di-allelic systems are due to an amino acid substitution. An official nomenclature was adopted in 1990 by the Working Party on Platelet Serology ICST/ISBT which defined the following rules: (1) platelet-specific antigen systems are called HPA for "Human Platelet Antigens"; (2) they are numbered chronologically according to the date of publication; (3) the most frequent allele is designated by the letter a and the less frequent by the letter b (i.e., HPA-1a 1b). Since the introduction of molecular biology techniques, the nomenclature has become insufficiently precise and an adjustment will probably be required in a near future.