title: Allelic imbalance modulates surface expression of the tolerance-inducing HLA-G molecule on primary trophoblast cells.
abstract: The HLA-G molecule is expressed on trophoblast cells at the feto-maternal interface, where it interacts with local immune cells, and upholds tolerance against the semi-allogeneic fetus. Aberrant HLA-G expression in the placenta and reduced soluble HLA-G levels are observed in pregnancy complications, partly explained by HLA-G polymorphisms which are associated with differences in the alternative splicing pattern and of the stability of HLA-G mRNA. Of special importance is a 14 bp insertion/deletion polymorphism located in the 3'-untranslated region of the HLA-G gene. In the current study, we present novel evidence for allelic imbalance of the 14 bp insertion/deletion polymorphism, using a very accurate and sensitive Digital droplet PCR technique. Allelic imbalance in heterozygous samples was observed as differential expression levels of 14 bp insertion/deletion allele-specific mRNA transcripts, which was further associated with low levels of HLA-G surface expression on primary trophoblast cells. Full gene sequencing of HLA-G allowed us to study correlations between HLA-G extended haplotypes and single-nucleotide polymorphisms and HLA-G surface expression. We found that a 1:1 expression (allelic balance) of the 14 bp insertion/deletion mRNA alleles was associated with high surface expression of HLA-G and with a specific HLA-G extended haplotype. The 14 bp del/del genotype was associated with a significantly lower abundance of the G1 mRNA isoform, and a higher abundance of the G3 mRNA isoform. Overall, the present study provides original evidence for allelic imbalance of the 14 bp insertion/deletion polymorphism, which influences HLA-G surface expression on primary trophoblast cells, considered to be important in the pathogenesis of pre-eclampsia and other pregnancy complications.
authors.affiliation: Centre for Immune Regulation and Reproductive Immunology (CIRRI), Department of Clinical Biochemistry, Copenhagen University Hospital (Roskilde) and University of Copenhagen, Denmark.
authors.forename: S
authors.initials: S
authors.lastname: Djurisic
authors.affiliation: Depatment of Obstetrics and Gynaecology, Copenhagen University Hospital (Roskilde) and University of Copenhagen, Denmark.
authors.forename: S
authors.initials: S
authors.lastname: Teiblum
authors.affiliation: Depatment of Obstetrics and Gynaecology, Herlev University Hospital, Denmark.
authors.forename: C K
authors.initials: CK
authors.lastname: Tolstrup
authors.affiliation: Fertility Clinic 4071, Rigshospitalet, Copenhagen University Hospital, Blegdamsvej 9, DK-2100 Copenhagen, Denmark.
authors.forename: O B
authors.initials: OB
authors.lastname: Christiansen
authors.affiliation: Centre for Immune Regulation and Reproductive Immunology (CIRRI), Department of Clinical Biochemistry, Copenhagen University Hospital (Roskilde) and University of Copenhagen, Denmark tvh@regionsjaelland.dk.
authors.forename: T V F
authors.initials: TV
authors.lastname: Hviid
mesh_terms: D020413:3' Untranslated Regions; D000029:Abortion, Legal; D000483:Alleles; D022981:Allelic Imbalance; D017398:Alternative Splicing; D001483:Base Sequence; D005260:Female; D059951:HLA-G Antigens / Q000235:genetics* / Q000378:metabolism; D006239:Haplotypes; D006579:Heterozygote; D006801:Humans; D054643:INDEL Mutation; D007108:Immune Tolerance; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction / Q000379:methods; D011110:Polymorphism, Genetic; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D061251:Primary Cell Culture; D017422:Sequence Analysis, DNA; D014327:Trophoblasts / Q000276:immunology / Q000378:metabolism* / Q000473:pathology
chemical_list: D020413:3' Untranslated Regions; D059951:HLA-G Antigens
keywords: 3′ untranslated region; HLA-G; allelic imbalance; polymorphism; pregnancy