Human platelet antigens

Many antigens on platelets are shared with other cells (eg, ABO and HLA class I antigens). There are 24 platelet-specific alloantigens:

12 have been grouped into 6 biallelic systems (HPA-1, -2, -3, -4, -5 and -15)
12 antigens do not, as yet, have antithetical partners.

Human platelet antigen (HPA) systems are shown below. The most important, HPA-1a and HPA-1b, reside on the platelet membrane glycoprotein GP IIIa. Patients with Glanzmann’s thrombasthenia Type I, who lack this glycoprotein, do not express HPA-1 antigens.

HPA can be targeted by different types of antibodies, including autoantibodies, alloantibodies and drug-dependent antibodies. HPA alloantibodies are responsible for the following clinical conditions:

Platelet immunofluorescence test (PIFT) and capture assays, such as the Monoclonal Antibody Immobilisation Platelet Antigen (MAIPA) assay, can detect platelet alloantibodies.

Human Platelet Antigen Systems(1,2)
System	Antigen	Other published name	Antigen frequency (%)*
HPA-1	HPA-1a HPA-1b	Zw^a, PL^A1 Zw^B, PL^A2	97.9 28.8
HPA-2	HPA-2a HPA-2b	Ko^b Ko^a, Sib^a	>99 13.2
HPA-3	HPA-3a HPA-3b	Bak^a, Lek^a Bak^b	80.95 69.8
HPA-4	HPA-4a HPA-4b	Yuk^b, Pen^a Yuk^a, Pen^b	>99.9 <0.1
HPA-5	HPA-5a HPA-5b	Br^b, Zav^b Br^a, Zav^a, Hc^a,	99.0 19.7
	HPA-6bw	Ca^a, Tu^a	0.7
	HPA-7bw	Mo	0.2
	HPA-8bw	Sr^a	<0.01
	HPA-9bw	Max^a	0.6
	HPA-10bw	La^a	<1.6
	HPA-11bw	Gro^a	<0.25
	HPA-12bw	ly^a	0.4
	HPA-13bw	Sit^a	0.25
	HPA-14bw	Oe^a	<0.17
HPA-15	HPA-15a HPA-15b	Gov^b Gov^a	74 81
	HPA-16bw	Duv^a	<1
	Va^a	<0.4
	Mou^a	26
Note: *Frequencies are based on studies in Caucasians.

References

Allen DL, et al. Platelet and neutrophil antigens. In Murphy MF and Pamphilon DH (eds). (2005) Practical Transfusion Medicine, 2nd ed. Blackwell Publishing Ltd. USA, 2005.
Metcalfe P, et al. Nomenclature of human platelet antigens. Vox Sanguinis 2003;85:240–245.

Updated on 30 August 2010

Australian Red Cross Blood Service

Human platelet antigens

References