PROBLEM: Human leukocyte antigen (HLA)-G is uniquely expressed on extravillous cytotrophoblasts of the placenta and is postulated to be a mediator of maternal immune tolerance. Although it was originally considered to be nonpolymorphic, variations of the HLA-G DNA sequence have been reported, and a limited number of HLA-G alleles been defined.
METHOD OF STUDY: The HLA-G wild-type sequence was compared with HLA-A2 with regard to the conservation of functionally essential parts of classical HLA-I molecules. HLA-G polymorphisms were analyzed under the aspect of ethnic differences, site, and consequences for postulated molecule functions.
RESULTS: HLA-G exhibits a high degree of conservation relative to HLA-A2 in functionally relevant sites of HLA-class I molecules. However, polymorpahic sites in HLA-G and classical HLA loci are not congruent.
CONCLUSION: The type and localization of HLA-G polymorphisms suggest that different parts of the HLA-G molecule underlie different selective constraints.