Thomas Vauvert F. Hviid

Polymorphism of exon 3 of the HLA-G gene

HLA-G is a non-classical MHC class I gene with a limited tissue distribution. The most pronounced expression is detected in the cytotrophoblast of first trimester placenta. It is possible to detect mRNA for HLA-G in preimplantation blastocysts where expression is correlated with a high cleavage rate of embryos. HLA-G seems to play an important role in the feto-maternal relationship. The polymorphism of the HLA-G locus is not fully clarified. One study has shown extensive nucleotide sequence variation in the exon 3 (alpha-2 domain) in healthy African Americans. A few studies in other populations have only revealed a limited polymorphism. We investigated the polymorphism of the exon 3 of HLA-G by means of Polymerase Chain Reaction (PCR)-Single Strand Conformation Polymorphism (SSCP)- and DNA sequencing analysis in a Danish population. We detected four single-base substitutions in exon 3 compared to the sequence of HLA-6.0 (G*01011); one of these has not been reported before. We also found a deletion of the first base of codon 130 or the third of codon 129 in a heterozygous individual. This study, together with previous results, suggests that the polymorphism of exon 3 of the HLA-G gene in Caucasians is limited, in contrast to that observed in Americans originating from Africa. Implications of this discrepancy and the detected deletion in relation to certain disorders of pregnancy are discussed.

HLA Class Ib Molecules and Immune Cells in Pregnancy and Preeclampsia

Despite decades of research, the highly prevalent pregnancy complication preeclampsia, “the disease of theories,” has remained an enigma. Indeed, the etiology of preeclampsia is largely unknown. A compiling amount of studies indicates that the pathological basis involves a complex array of genetic predisposition and immunological maladaptation, and that a contribution from the mother, the father, and the fetus is likely to be important. The Human Leukocyte Antigen (HLA)-G is an increasing focus of research in relation to preeclampsia. The HLA-G molecule is primarily expressed by the extravillous trophoblast cells lining the placenta together with the two other HLA class Ib molecules, HLA-E and HLA-F. Soluble isoforms of HLA-G have been detected in the early endometrium, the matured cumulus–oocyte complex, maternal blood of pregnant women, in umbilical cord blood, and lately, in seminal plasma. HLA-G is believed to be involved in modulating immune responses in the context of vascular remodeling during pregnancy as well as in dampening potential harmful immune attacks raised against the semi-allogeneic fetus. In addition, HLA-G genetic variants are associated with both membrane-bound and soluble forms of HLA-G, and, in some studies, with preeclampsia. In this review, a genetic contribution from the mother, the father, and the fetus, together with the presence and function of various immune cells of relevance in pregnancy are reviewed in relation to HLA-G and preeclampsia.

Detection of fetal‐specific DNA after enrichment for trophoblasts using the monoclonal antibody LK26 in model systems but failure to demonstrate fetal DNA in maternal peripheral blood

Trophoblast cells can be detected in maternal blood during normal human pregnancy and DNA from these cells may be used for non‐invasive prenatal diagnosis of inherited diseases. The possibility of enriching trophoblast cells from maternal blood samples using a monoclonal antibody (LK26) against a folate‐binding protein, which recognizes trophoblast in normal tissues, in conjunction with immunomagnetic cell sorting was investigated. Verification of the presence of fetal DNA in the sorted samples was done by detection of fetal/paternal‐specific short tandem repeat (STR) alleles using polymerase chain reaction (PCR) and automated fluorescence‐based genotyping. After successful initial experiments using retroplacental blood samples with a high number of trophoblast cells or an artificial mixture of trophoblast cells and blood, several versions of the enrichment method were attempted on peripheral maternal blood samples. However, it was not possible to detect fetal DNA sequences in these samples, most probably due to the extremely low number of trophoblast cells. Positive identification and retrieval of trophoblast cells in suspension or trophoblast nuclear material prepared on microscope slides after cell sorting procedures can be a solution to this problem. Copyright

HLA class Ib in pregnancy and pregnancy-related disorders

The HLA class Ib genes, HLA-E, HLA-F, and HLA-G, were discovered long after the classical HLA class Ia genes. The elucidation of their functions had a modest beginning. However, their basic functions and involvement in pathophysiology and a range of diseases are now emerging. Although results from a range of studies support the functional roles for the HLA class Ib molecules in adult life, especially HLA-G and HLA-F have most intensively been, and were also primarily, studied in relation to reproduction and pregnancy. The expression of HLA class Ib proteins at the feto-maternal interface in the placenta seems to be important for the maternal acceptance of the semi-allogenic fetus. In contrast to the functions of HLA class Ia, HLA-G possesses immune-modulatory and tolerogenic functions. Here, we review an accumulating amount of data describing the functions of HLA class Ib molecules in relation to fertility, reproduction, and pregnancy, and a possible role for these molecules in certain pregnancy complications, such as implantation failure, recurrent spontaneous abortions, and pre-eclampsia. The results from different kinds of studies point toward a role for HLA class Ib, especially HLA-G, throughout the reproductive cycle from conception to the birth weight of the child.

Distribution of HLA-G extended haplotypes and one HLA-E polymorphism in a large-scale study of mother-child dyads with and without severe preeclampsia and eclampsia.

The etiological pathways and pathogenesis of preeclampsia have rendered difficult to disentangle. Accumulating evidence points toward a maladapted maternal immune system, which may involve aberrant placental expression of immunomodulatory human leukocyte antigen (HLA) class Ib molecules during pregnancy. Several studies have shown aberrant or reduced expression of HLA‐G in the placenta and in maternal blood in cases of preeclampsia compared with controls. Unlike classical HLA class Ia loci, the nonclassical HLA‐G has limited polymorphic variants. Most nucleotide variations are clustered in the 5′‐upstream regulatory region (5′URR) and 3′‐untranslated regulatory region (3′UTR) of HLA‐G and reflect a stringent expressional control. Based on genotyping and full gene sequencing of HLA‐G in a large number of cases and controls (n > 900), the present study, which to our knowledge is the largest and most comprehensive performed, investigated the association between the HLA‐G 14‐bp ins/del (rs66554220) and HLA‐E polymorphisms in mother and newborn dyads from pregnancies complicated by severe preeclampsia/eclampsia and from uncomplicated pregnancies. Furthermore, results from extended HLA‐G haplotyping in the newborns are presented in order to assess whether a combined contribution of nucleotide variations spanning the 5′URR, coding region, and 3′UTR of HLA‐G describes the genetic association with severe preeclampsia more closely. In contrast to earlier findings, the HLA‐G 14‐bp ins/del polymorphism was not associated with severe preeclampsia. Furthermore, the polymorphism (rs1264457) defining the two nonsynonymous HLA‐E alleles, HLA‐E*01:01:xx:xx and HLA‐E*01:03:xx:xx, were not associated with severe preeclampsia. Finally, no specific HLA‐G haplotypes were significantly associated with increased risk of developing severe preeclampsia/eclampsia.

Endometrial immune markers are potential predictors of normal fertility and pregnancy after in vitro fertilization

Elucidating immune mechanisms in the endometrium, which lead to the success of implantation and pregnancy, is important in reproductive medicine. Studies of immune cell abundance have shown conflicting results, and the expression and importance of HLA class Ib proteins in pre‐implantation endometrium have not yet been investigated.

Human Leukocyte Antigen-G and Regulatory T Cells during Specific Immunotherapy for Pollen Allergy

Background: T_H2-biased immune responses are important in allergy pathogenesis. Mechanisms of allergen-specific immunotherapy (SIT) might include the induction of regulatory T cells (Tregs) and immunoglobulin (Ig) G₄ blocking antibodies, a reduction in the number of effector cells, and skewing of the cytokine profile towards a T_H1-polarized immune response. We investigated the effects of SIT on T cells, on immunomodulation of human leukocyte antigen (HLA)-G, which has been associated with allergy, on regulatory cytokine expression, and on serum allergen-specific antibody subclasses (IgE and IgG₄). Methods: Eleven birch and/or grass pollen-allergic patients and 10 healthy nonatopic controls were studied before and during SIT. Tregs, chemokine receptors, soluble HLA-G (sHLA-G), Ig-like transcript (ILT) 2, specific IgE, and IgG₄ were studied. Peripheral blood mononuclear cells (PBMCs) were stimulated with pollen extract in vitro and immune factors were evaluated. Results: During SIT, the main changes in the peripheral blood were an increase in CXCR3⁺CD4⁺CD25⁺CD127^low/- Tregs and a decrease in CCR4⁺CD4⁺CD25⁺CD127^low/- Tregs, an increase in allergen-specific IgG₄, and a decrease in sHLA-G during the first half of the treatment period. In the PBMC in vitro experiments, the following changes were observed upon allergen-stimulation: an increase in CD4⁺CD25⁺CD127^low/- Tregs and ILT2⁺CD4⁺CD25⁺CD127^low/- Tregs, an increase in IL-10 and IL-2 levels, and an increase in sHLA-G that was most pronounced at the start of SIT. Conclusions: The changes in CXCR3⁺CD4⁺CD25⁺CD127^low/- Treg, IgG₄, and sHLA-G levels in the peripheral blood and in ILT2⁺ Treg, IL-10, IL-2, and sHLA-G levels upon in vitro allergen stimulation suggest an upregulation in immunomodulatory factors and, to some degree, a shift towards T_H1 during SIT.

Expression and differential regulation of HLA-G isoforms in the retinal pigment epithelial cell line, ARPE-19

The purpose of this study was to examine if HLA-G is expressed in the retinal pigment epithelium (RPE) cells of the eye. The RPE comprises the outer most layer of the retina and as such defines the interface to the blood and contributes to the immune privilege in the posterior part of the eye. One way the RPE might be regulating the immune system could be by expressing the non-classical human leukocyte antigen (HLA) molecule, HLA-G. We therefore sought to define if the RPE cell line, ARPE-19, expressed HLA-G and analyse the regulation as a response to pro-inflammatory cytokines. This was done by digital droplet PCR, measuring the gene expression of HLA-G in total RNA. The protein expression was analysed by immunohistochemistry and by immunofluorescence followed by confocal microscopy and the expression of the HLA-G isoforms was explored by fragment analysis. In the current study, we show that HLA-G is expressed by ARPE-19 cells and is upregulated as a response to pro-inflammatory cytokines. Moreover, we are the first to describe a differential regulation of the HLA-G isoforms as a direct response to stimulation. These results might indicate that HLA-G can be part of the immune privilege of the posterior part of the eye, but further experiments on primary RPE cells are needed.

Associations between fetal HLA-G genotype and birth weight and placental weight in a large cohort of pregnant women – Possible implications for HLA diversity

Birth weight and placental weight are crucial parameters for the survival of fetuses and newborns in mammals. High variation in the MHC is important for an effective adaptive immune response. The maternal immune system must be controlled in relation to the semi-allogenic fetus. The immunoregulatory HLA/MHC class Ib gene, HLA-G, is strongly expressed on extravillous trophoblast cells. We investigated birth weight and placental weight of the newborns in mothers heterozygous for an HLA-G 14bp insertion (Ins)/deletion (Del) gene polymorphism. Separate analyses for pregnancies without preeclampsia (n=185), pregnancies complicated by preeclampsia (n=101), and both groups combined, were performed. Interestingly, we observed the highest mean birth weight and placental weight in homozygous 14bp Del/Del newborns, and the lowest in 14bp Ins/Ins newborns (P=0.008 and P=0.009). The 14bp Del/Del genotype is also associated with high expression of HLA-G on the trophoblast membrane. In theory, fetuses and newborns with intermediate weights and sizes would be an optimal compromise for both the fetus/father and the mother compared with very high and low weights. If such fetuses/newborns more often are heterozygous at the HLA-G gene locus, then newborns with two distinct HLA haplotypes are favored, leading to a higher degree of HLA diversity. The results of the study may indicate that a compromise between an intermediate birth weight and placental weight, induction of maternal tolerance by a fetal-derived non-polymorphic HLA class Ib molecule, and favoring of HLA heterozygous offspring, have evolved in humans.

The Pathophysiological Impact of HLA Class Ia and HLA-G Expression and Regulatory T Cells in Malignant Melanoma: A Review

Malignant melanoma, a very common type of cancer, is a rapidly growing cancer of the skin with an increase in incidence among the Caucasian population. The disease is seen through all age groups and is very common in the younger age groups. Several studies have examined the risk factors and pathophysiological mechanisms of malignant melanoma, which have enlightened our understanding of the development of the disease, but we have still to fully understand the complex immunological interactions. The examination of the interaction between the human leucocyte antigen (HLA) system and prognostic outcome has shown interesting results, and a correlation between the down- or upregulation of these antigens and prognosis has been seen through many different types of cancer. In malignant melanoma, HLA class Ia has been seen to influence the effects of pharmaceutical drug treatment as well as the overall prognosis, and the HLA class Ib and regulatory T cells have been correlated with tumor progression. Although there is still no standardized immunological treatment worldwide, the interaction between the human leucocyte antigen (HLA) system and tumor progression seems to be a promising focus in the way of optimizing the treatment of malignant melanoma.