SUSCEPTIBILITY TO ALLOIMMUNIZATION TO PLATELET HPA-1A ANTIGEN INVOLVES TAP1 POLYMORPHISM

The alloimmunization against platelet HPA-la antigen in mothers of thrombocytopenic neonates is strongly associated with HLA class II structures (DR3 and DR13) and especially with HLA-DR52a antigen (98% of the cases reported here). Because new genes have recently been mapped within the MHC class II region, we typed TAP1 and TAP2 gene polymorphisms by ARMS-PCR in order to characterize more effectively MHC genes involved in this alloimmunization. Our re suits showed that TAP1*0102 allele was significantly associated with NAIT only in the population of HLA-DR13-DR52a-immunized women (50%) versus HLA-DR13-DR52a controls (20%) (p < 0.05), and not in HLA-DRS-DRS 2a-immunized women versus HLA-DR3-DR52a controls. There is no linkage disequilibrium between TAP1*0102 and DRB1*13 alleles (Delta = -0.0063) that could account for this result. The higher frequency of TAP1*0102 allele among HLA-DR13-DR52a-immunized women suggests that HPA-1a antigen presentation and recognition may be influenced by nonclassic HLA class II gene polymorphisms, or that other linked but yet unknown genes could interfere.