<prompt> In Alloimmune thrombocytopenia antigen against which antibody is found?HPA 1aHPA 1bHPA 2aHPA 2b  <response>: 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. 