[Analysis of polymorphism at the human class I MHC locus, HLA-G]

Abstract

HLA-G is one of the non-classical HLA class I gene and its expression has been identified in cytotrophoblasts and in some choriocarcinoma cell lines. It encodes apparently non-polymorphic antigen and is considered to play an important role in the fetomaternal immune system. However, the monomorphism of the HLA-G gene has not been established firmly. In order to examine the polymorphism of the HLA-G locus, a clone 7.0E was isolated from a genomic library using a probe derived from 3' untranslated region of HLA-G (Orr). Additionally, PCR/SSCP analysis of the HLA-G 3' untranslated region was carried on 35 DNA samples of unrelated individuals taking advantage of the fact that HLA-G (Orr) and 7.0E differed in 14bp length in the amplified fragments. The nucleotide sequence of 7.0E was homologous to HLA-G (Orr), but the sequence was more closely related to a cDNA sequence of BeWo-G7 which has been cloned from mRNA of BeWo cells. Among these 3 clones no amino acid substitution was found in the coding region, Thus, 7.0E should represent a genomic clone of BeWoG7. PCR/SSCP analysis showed that 33 out of 35 samples (94%) contained 7.0E gene, 29 contained HLA-G (Orr) gene (83%). Two samples (6%) contained only HLA-G (Orr), and 6 samples contained only 7.0E (17%). Among 29 DNA samples containing HLA-G (Orr), 3 samples showed the shift in electrophoretic mobility in HLA-G (Orr), suggesting minor sequence differences in HLA-G alleles. From these results it is concluded that HLA-G antigen is monomorphic, but there are several alleles recognizable by DNA sequence and/or SSCP analysis.