Human platelet HPA-1 polymorphism is embedded in the N-terminal plexin/semaphorin/integrin (PSI) domain of the 3 chain of the platelet integrin IIb 3. HPA-1 polymorphism is responsible for neonatal alloimmune thrombocytopenia (NAITP). T-helper response drives anti-HPA-1a production and the putative dominant T-helper epitope is likely to be an important contributory factor in the immunogenicity of HPA-1a. This book provides detailed insight into the molecular mechanism behind of anti-HPA-1a platelet alloimmunization."