[Anti PLA or anti HPA-1 platelet allo-immunization]

The HPA-1 platelet antigenic system (PLA/Zw) is involved in most cases of antiplatelet alloimmunization. The two alleles HPA-1a and HPA-1b are likely to differ only at the amino acid position 33. This difference is probably due to a unique mutation at base pair position 196 on the glycoprotein IIIa gene which encoded this antigen. Anti HPA-1a alloimmunization is responsible for neonatal thrombocytopenia and post-transfusion purpura. Most immunized women belong to the HLA DR3, DRw52a phenotype, suggesting that this class II molecule may play a role in the presentation of HPA-1a peptide to specific helper T cells.