Functional heterogeneity of alloantibodies against the human platelet antigen (HPA)-1a.

The integrin alphaIIbbeta is the major fibrinogen receptor on the platelet membrane and plays a crucial role for platelet aggregation. The beta3-subunit carries the human platelet alloantigen (HPA)-1a, which is the main target for alloantibodies (alloabs) responsible for foetal and neonatal alloimmune thrombocytopenia (FNAIT) and post-transfusion purpura (PTP). Whereas PTP is almost invariably associated with severe bleeding, the clinical presentation of FNAIT ranges from mild thrombocytopenia to severe haemorrhagic diathesis.