This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bleeding disorders, Subject name: Pediatrics
In Alloimmune thrombocytopenia antigen against which antibody is found? 
Select and explain. 
A. HPA 1a, B. HPA 1b, C. HPA 2a, D. HPA 2b
A: HPA 1a
Answer: A: HPA 1a 
Explanation: Neonatal alloimmune thrombocytopenic purpura (NATP): - Caused by development of maternal antibodies against antigens present on fetal platelets that are shared from father & recognized as foreign by maternal immune system. - The most common cause is incompatibility for the platelet alloantigen HPA-1a.