These can stimulate production of alloantibodies (that is, antibodies against other people's antigens) in recipients of transfused platelets from donors with different HPAs.
[1] A nomenclature was devised by International Society of Blood Transfusion (ISBT), platelet working party to overcome problems generated by many different nomenclatures in use.
Since inception of this list, a greater number of antigens have been described and the molecular basis of many has been resolved.
[citation needed] To date, 24 platelet-specific alloantigens have been defined by immune sera, of which 12 are grouped in six biallelic systems (HPA-1, -2, -3, -4, -5, -15).
In all but one of the 22, the difference between self and non-self is defined by a single amino acid substitution generally caused by a single-nucleotide polymorphism (SNP).