HUMAN PLATELET ALLOANTIGEN TYPING - PCR ANALYSIS IS NOT A SUBSTITUTE FOR SEROLOGICAL METHODS

Currently, five platelet alloantigen (alloAg) systems have been establ ished (HPA-1, -2, -3, -4, -5). Three of these are expressed on the gly coprotein (GP) IIb-IIIa complex, HPA-1, HPA-3 and HPA-4, inherited in an autosomal codominant mode. Recent investigations of the molecular b asis of these platelet alloantigen systems have shown that only one nu cleic acid base substitution in the genes encoding for GP IIb and GP I IIa is responsible for the polymorphism. This substitution is reflecte d in a difference in restriction enzyme recognition allowing platelet alloantigen typing by restriction fragment length polymorphism (RFLP) analysis of DNA amplified by the polymerase chain reaction (PCR). To v alidate the PCR technology for platelet typing, we have compared PCR-R FLP with monoclonal-antibody-specific immobilization of platelet antig ens (MAIPA). For this purpose, we have studied different Glanzmann thr ombasthenic families and particularly heterozygous individuals, who ar e not lacking GP IIb-IIIa, as a model to detect the occurence of discr epancies between these two technologies. In two families, we have foun d differences between molecular biology and serological methods with t he lack of expression of one antigen on the platelet membrane surface. In the first family, the abnormality is related to the HPA-1 alloanti gen system with three informative members; in the second, the HPA-3 al loantigen system is concerned with two informative members. Considerin g these results, there may not always be a perfect correlation between molecular biology and serological methods, as an unknown molecular de fect could interfere with the PCR results and lead to false platelet t yping. In cases of suspected post-transfusion purpura (PTP) or fetuses at risk for neonatal alloimmune thrombocytopenia (NAITP), great care must be taken in the interpretation of the results if only PCR-RFLP te chniques are used.