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Abstract
P
latelets, the smallest of blood cellular elements, have a critical role in the cellular mechanisms of primary hemostasis. More than 45 different membrane structures are found on resting platelets and it contains a wide range of membrane glycoproteins. Platelet membrane can be divided into four groups including integrins, leucine-rich glycoproteins, selectins and immunoglobulin superfamily.
Platelets express a number of alloantigens. Some are non specific being not restricted to the megakaryocyte lineage, including major histocompatibility (MHC) molecules and ABH blood group determinants. Platelets express MHC Class I but not Class II antigens, and anti-HLA Class I antibodies are the major cause of refractoriness to platelet transfusion. Also Platelet membrane glycoproteins carry ABH blood group antigens that include the glycoprotein (GP) Ib complex and the integrins (platelet cohesion receptor) and (platelet collagen receptor).
Human platelet specific allo antigens (HPA) are specific antigens exclusively present on platelets and megakaryocytes and carried out by platelet glycoproteins whose genes show single nucleotide polymorphism. HPA can induce alloantibodies bringing about alloimmune response.