HLA-E and immunobiology of pregnancy

DNA methylation dynamics during pregnancy

Pregnancy is a state of multiple physiological adaptations. Since methylation of DNA is an epigenetic mechanism that regulates gene expression and contributes to adaptive phenotypic variations, we investigated methylation changes in maternal blood of a longitudinal cohort of pregnant women from the first trimester of gestation to the third. Interestingly, during pregnancy, we found a gain of methylation in genes involved in morphogenesis, such as ezrin, while we identified a loss of methylation in genes promoting maternal-infant bonding (AVP and PPP1R1B). Together, our results provide insights into the biological mechanisms underlying physiological adaptations during pregnancy.

Advances in the study of HLA class Ib in maternal-fetal immune tolerance

The HLA class Ib molecule is an alloantigen that causes transplant rejection on behalf of individual human and plays an important role in maternal-fetal immune tolerance. Early studies on HLA class Ib focused on the mechanism of HLA-G-induced immune escape, but in recent years, studies on the mechanism of HLA-G have deepened and gradually explored the mechanism of HLA-E and HLA-F, which are also HLA class Ib molecules. In the maternal-fetal interface, trophoblast cells express HLA class Ib molecules to protect the fetus from maternal immune cells by binding to inhibitory receptors of decidual immune cells (DICs) and shifting Th1/Th2 balance toward Th2 bias. Further studies on the molecular mechanism of HLA class Ib molecules provide a reference for its application in the field of clinical assisted reproduction.

HLA-E*01:01 allele is associated with better response to anti-HCV therapy while homozygous status for HLA-E*01:03 allele increases the resistance to anti-HCV treatments in frequently transfused thalassemia patients

BACKGROUND

HLA-E binding to NKG2A/CD94 induces inhibitory signals that modulate NK cells cytotoxicity against infected targets. HCV-derived peptides stabilize HLA-E molecule that favours its higher expression. However, HLA-E stability and expression vary in different genotypes where the presence of HLA-E*01:03 allele is associated with higher HLA-E expression on targets that enhances NK cells inhibition and increases the chance of virus to escape from innate immune system. Here, we aimed to investigate whether HLA-E polymorphism affects HCV infection status or its treatment in major thalassemia patients who are more vulnerable to hepatitis C.

METHODS AND MATERIALS

Study included 89 cases of major thalassemia positive for HCV-antibody; of those 17 patients were negative for HCV-PCR (spontaneously cleared) and 72 patients were HCV-PCR positive (persistent hepatitis under different anti-viral treatment). 16 major thalassemia patients without hepatitis, negative for HCV-antibody were also considered as patients control group. Genomic DNAs extracted from whole bloods were genotyped for HLA-E locus using a sequence specific primer-PCR strategy.

RESULTS

In thalassemia patients, HLA-E*01:03 allele increased susceptibility to HCV infection [p = 0.02; 4.74(1.418-15.85)]. In addition, HLA-E*01:03/*01:03 genotype predicted more resistance to HCV treatment compared to other genotypes [p = 0.037; 3.5(1.1-11.4)]. In other words, we found that the presence of HLA-E*01:01 allele favors better response to anti-HCV therapy [p = 0.037; 3.5(1.1-11.4)].

CONCLUSION

From a mechanistic point of view, the associations between HLA-E polymorphisms and susceptibility to HCV infection or its therapeutic resistance in thalassemia patients may suggest potential roles for the innate and adaptive immune responses to this infection, which are manifested by the acts of HLA-E - NKG2A/CD94 axis in the modulation of NK cell inhibitory function as well as HLA-E associated CD8+ T cell cytolytic activity against HCV, respectively. Notably, from a clinical point of view, paying attention to these associations may not only be useful in increasing the effectiveness of current anti-HCV regimens comprising direct acting antivirals (DAAs) in more complicated patients, but may also suggest antiviral prophylaxis for patients more vulnerable to HCV infection.

Got your mother in a whirl: The role of maternal T cells and myeloid cells in pregnancy

Appropriate development of the placenta is required for healthy pregnancy to occur. After implantation of the fertilized blastocyst, fetal trophoblasts invade the endometrium and myometrium of the mother's uterus to establish placentation. In this process, fetal trophoblasts encounter maternal immune cells. In this review, we focus on the role of maternal T cells and myeloid cells (macrophages, dendritic cells) in pregnancy and their interaction with trophoblasts. To retain immunologic tolerization, trophoblasts evade immune recognition by T cells and produce factors that modulate their phenotype and function. On top of that, the local environment at the maternal-fetal interface favors expansion of regulatory T cells. Macrophages and dendritic cells are essential in maintaining a healthy pregnancy. They produce soluble factors and act as antigen-presenting cells, thereby interacting with T cells. Herein, M2 macrophages, immature dendritic cells, CD4⁺ Th2 cells, and regulatory T cells represent an axis that maintains a local immune tolerant environment. We consider outstanding issues concerning these cell types and their pathways, which need to be addressed in future investigations. Data from recent single-cell sequencing experiments of the placental bed, to study heterogeneity of maternal immune cells and to predict cell-cell interactions, are discussed. Novel ways for long-term culturing of primary trophoblasts allow for cell-cell interaction studies in a functional way. Future directions should include study of the functionality of currently known and newly identified decidual immune cell subsets in healthy and complicated pregnancies, and their interaction with and modulation by trophoblast cells.

Major histocompatibility complex-associated odour preferences and human mate choice: near and far horizons

The major histocompatibility complex (MHC) is a core part of the adaptive immune system. As in other vertebrate taxa, it may also affect human chemical communication via odour-based mate preferences, with greater attraction towards MHC-dissimilar partners. However, despite some well-known findings, the available evidence is equivocal and made complicated by varied approaches to quantifying human mate choice. To address this, we here conduct comprehensive meta-analyses focusing on studies assessing: (i) genomic mate selection, (ii) relationship satisfaction, (iii) odour preference, and (iv) all studies combined. Analysis of genomic studies reveals no association between MHC-dissimilarity and mate choice in actual couples; however, MHC effects appear to be independent of the genomic background. The effect of MHC-dissimilarity on relationship satisfaction was not significant, and we found evidence for publication bias in studies on this area. There was also no significant association between MHC-dissimilarity and odour preferences. Finally, combining effect sizes from all genomic, relationship satisfaction, odour preference and previous mate choice studies into an overall estimate showed no overall significant effect of MHC-similarity on human mate selection. Based on these findings, we make a set of recommendations for future studies, focusing both on aspects that should be implemented immediately and those that lurk on the far horizon. We need larger samples with greater geographical and cultural diversity that control for genome-wide similarity. We also need more focus on mechanisms of MHC-associated odour preferences and on MHC-associated pregnancy loss. This article is part of the Theo Murphy meeting issue 'Olfactory communication in humans'.

Donor HLA-E Status Associates with Disease-Free Survival and Transplant-Related Mortality after Non In Vivo T Cell-Depleted HSCT for Acute Leukemia

Previous studies have suggested that HLA-E may have a significant role in the outcome of matched unrelated hematopoietic stem cell transplantation (HSCT), especially for patients with acute leukemia. We used Center for International Blood and Marrow Transplant Research data and samples of 1840 adult patients with acute leukemia and their 10/10 HLA-matched unrelated donors to investigate the impact of HLA-E matching status as well as of donor/recipient (D/R) HLA-E genotype on post-HSCT outcome. Both patients and donors were HLA-E genotyped by next-generation sequencing. All patients received their first transplant in complete remission between 2000 and 2015. Median follow-up time was 90 months. Overall survival, disease-free survival (DFS), transplant-related mortality (TRM), and relapse incidence were primary endpoints with statistical significance set at .01. D/R HLA-E genotype analysis revealed a significant association of donor HLA-E*01:03/01:03 genotype with DFS (hazard ratio [HR] = 1.35, P = .0006) and TRM (HR = 1.41, P = .0058) in patients who received T cell replete (ie, without in vivo T cell depletion) transplants (n = 1297). As for D/R HLA-E matching, we did not identify any significant effect on any of the clinical outcome endpoints. In conclusion, this is the largest study to date reporting an improvement of DFS and TRM after matched unrelated HSCT by avoidance of HLA-E*01:03 homozygous donors in patients transplanted with T cell replete grafts for acute leukemia.

Dimorphism of HLA-E and its Disease Association

HLA-E is a nonclassical member of the major histocompatibility complex class I gene locus. HLA-E protein shares a high level of homology with MHC Ia classical proteins: it has similar tertiary structure, associates with β2-microglobulin, and is able to present peptides to cytotoxic lymphocytes. The main function of HLA-E under normal conditions is to present peptides derived from the leader sequences of classical HLA class I proteins, thus serving for monitoring of expression of these molecules performed by cytotoxic lymphocytes. However, opposite to multiallelic classical MHC I genes, HLA-E in fact has only two alleles—HLA-E*01:01 and HLA-E*01:03—which differ by one nonsynonymous amino acid substitution at position 107, resulting in an arginine in HLA-E*01:01 (HLA-E^R) and glycine in HLA-E*01:03 (HLA-E^G). In contrast to HLA-E^R,HLA-E^G has higher affinity to peptide, higher surface expression, and higher thermal stability of the corresponding protein, and it is more ancient than HLA-E^R, though both alleles are presented in human populations in nearly equal frequencies. In the current review, we aimed to uncover the reason of the expansion of the younger allele, HLA-E^R, by analysis of associations of both HLA-E alleles with a number of diseases, including viral and bacterial infections, cancer, and autoimmune disorders.

Extracellular vesicles in host-pathogen interactions and immune regulation - exosomes as emerging actors in the immunological theater of pregnancy

This review correlates and summarizes the role of the maternal-fetal interface in the immune tolerance of the fetus and the processes that lead to infection avoidance, emphasizing the participation of exosomes and other extracellular vesicles in both situations. Exosomes are released into the extracellular medium by several cell types and are excellent carriers of biomolecules. Host-derived exosomes and the transport of pathogen-derived molecules by exosomes impact infections in different ways. The interactions of exosomes with the maternal immune system are pivotal to a favorable gestational outcome. In this review, we highlight the potential role of exosomes in the establishment of an adequate milieu that enables embryo implantation and discuss the participation of exosomes released at the maternal-fetal interface during the establishment of an immune-privileged compartment for fetal development. The placenta is a component where important strategies are used to minimize the risk of infection. To present a contrast, we also discuss possible mechanisms used by pathogens to cross the maternal-fetal interface. We review the processes, mechanisms, and potential consequences of dysregulation in all of the abovementioned phenomena. Basic information about exosomes and their roles in viral immune evasion is also presented. The interactions between extracellular vesicles and bacteria, fungi, parasites and proteinaceous infectious agents are addressed. The discovery of the placental microbiota and the implications of this new microbiota are also discussed, and current proposals that explain fetal/placental colonization by both pathogenic and commensal microbes are addressed. The comprehension of such interactions will help us to understand the immune dynamics of human pregnancy and the mechanisms of immune evasion used by different pathogens.

Understanding the role of killer cell immunoglobulin-like receptors in pregnancy complications

Pregnancy is a unique immunological situation in which a fetus-bearing paternal histocompatibility antigens can survive in a maternal environment without apparent rejection. To face this challenge, cells of the uterine immune system show characteristic changes in absolute number and composition during pregnancy. Particularly relevant to this process are uterine natural killer (uNK) cells and their cell surface receptors, killer immunoglobulin-like receptors (KIRs). The main purpose of this review is to outline the current body of knowledge on the involvement of KIRs in the complications of pregnancy. Implantation depends on the invasion of embryonic trophoblast cells into maternal uterine tissue and remodeling of the uterine spiral arterioles, which is essential for placental perfusion and successful pregnancy. The proper interaction between maternal KIRs and their ligands human leukocyte antigen (HLA) class I molecules, expressed by the extravillous trophoblast cells, is crucial in this process. KIRs are a complex family that includes both activator and inhibitory receptors. The activation profile is genetically determined in each individual and leads to diverse levels of functionality for NK and T cells on engagement with specific HLA class I molecules. An association between different KIR alleles and HLA molecules has been reported in pregnancy complications, supporting the idea of a relevant role of these receptors in successful pregnancy.

HLA-E Peptide Repertoire and Dimorphism-Centerpieces in the Adaptive NK Cell Puzzle?

Adaptive Natural Killer (NK) cells, a heterogenous subpopulation of human NK cells with a unique phenotypic and functional signature, became arguably one of the central areas of interest in the field. While their existence seems closely associated with prior exposure to human cytomegalovirus (HCMV), many questions regarding their origin and regulation remain unanswered. However, a common denominator for the majority of adaptive NK cells is the expression of the activating heterodimeric receptor CD94/NKG2C that binds to HLA-E, a non-classical HLA molecule, that displays a comparably restricted expression pattern, very limited polymorphism and presents a distinct set of peptides. Recent studies suggest that-in analogy to T cell responses-peptides presented on HLA-E could play an unexpectedly decisive role for the biology of adaptive NK cells. Here, we discuss how this perspective on the CD94/NKG2C-HLA-E axis aligns with the existing literature and speculate about possible translational implication.

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.

Is HLA-E a possible genetic marker relevant for natural conception?

BACKGROUND

HLA-E products, class Ib human leukocyte antigens, act in the immunology of human reproduction as modulators of the maternal immune system during pregnancy.

AIMS

To evaluate HLA-E role in the establishment of a viable pregnancy.

MATERIALS & METHODS

HLA-E was genotyped by sequence-based typing (SBT) and analyzed for specific polymorphisms, comparing couples who underwent assisted reproduction treatment (ART) and fertile control couples.

RESULTS

There was a significant difference in HLA-E allele and genotype distributions between ART couples and control couples. The allele HLA-E*01:03 was observed in 63.2% of ART men and in 35.1% of fertile men (P = 0.0032).

CONCLUSION

These results suggest that HLA-E allelic variants may play a role in the modulation of immune responses in the context of the inability of natural conception and establishment of a viable pregnancy.

Human Leukocyte Antigen-E Alleles are Associated with Hepatitis C Virus, Torque Teno Virus, and Toxoplasma Co-infections but are not Associated with Hepatitis B Virus, Hepatitis D Virus, and GB Virus C Co-infections in Human Immunodeficiency Virus Patients

Context:

Data regarding the distribution of Human Leukocyte Antigen (HLA)-E alleles and their association with blood-borne pathogen infections/co-infections are limited for many populations, including Indonesia.

Aims:

The aim of this study was to analyze the association between HLA-E allelic variants and infection with blood-borne pathogens such as hepatitis B virus (HBV), hepatitis C virus (HCV), hepatitis D virus (HDV), torque teno virus (TTV), GB virus C (GBV-C), and Toxoplasma gondii (T. gondii) in Indonesian Javanese human immunodeficiency virus (HIV) patients.

Settings and Design:

A total of 320 anti-HIV-positive blood samples were analyzed for HBV, HCV, HDV, TTV, GBV-C, and T. gondii infection status and its association with HLA-E allelic variants.

Materials and Methods:

Nucleic acid was extracted from plasma samples and used for the molecular detection of HBV DNA, HCV RNA, HDV RNA, TTV DNA, and GBV-C RNA, whereas hepatitis B surface antigen, anti-HCV, immunoglobulin M and G (IgM and IgG) anti-T. gondii were detected through serological testing. The blood samples were genotyped for HLA-E loci using a sequence-specific primer-polymerase chain reaction.

Statistical Analysis Used:

Either the Chi-square or Fisher's exact test was performed to analyze the frequency of HLA-E alleles and blood-borne pathogen infections in the population. Odds ratios (ORs) were calculated to measure the association between the antibodies found and the participants’ possible risk behaviors. A logistic regression analysis was used to assess the associations.

Results:

HLA-E*101/0101 was associated with HCV/TTV co-infection (adjusted OR [aOR]: 3.5; 95% confidence interval [CI]: 1.156-10.734; P = 0.027) and IgM/IgG anti-Toxo positivity (aOR: 27.0; 95% CI: 3.626-200.472; P = 0.001). HLA-E*103/0103 was associated with TTV co-infection (aOR: 2.7; 95% CI: 1.509-4.796; P = 0.001).

Conclusions:

HLA-E alleles in Indonesian Javanese HIV patients were found to be associated with HCV, TTV, and toxoplasma co-infections.

HLA-E polymorphism and soluble HLA-E plasma levels in chronic hepatitis B patients

Chronic hepatitis B virus (HBV) infection occurs in association to a deregulation of immune system. Human leukocyte antigen E (HLA-E) is an immune-tolerant nonclassical HLA class I molecule that could be involved in HBV progression. To measure soluble (s) HLA-E in patients with chronic HBV hepatitis (CHB). We tested the potential association of HLA-E*01:01/01:03 A > G gene polymorphism to CHB. Our cohort consisted of 93 Tunisian CHB patients (stratified in CHB with high HBV DNA levels and CHB with low HBV DNA levels) and 245 healthy donors. Plasma sHLA-E was determined using enzyme-linked immunosorbent assay (ELISA). Genotyping was performed using polymerase chain reaction sequence-specific primer. No association between HLA-E*01:01/01:03 A > G polymorphism and HBV DNA levels in CHB patients was found. G/G genotype is less frequent in CHB patients without significance. sHLA-E is significantly enhanced in CHB patients compared with healthy controls (P = 0.0017). Stratification according to HBV DNA levels showed that CHB patients with low HBV DNA levels have higher sHLA-E levels compared with CHB patients with high HBV DNA levels. CHB patients with G/G genotype have enhanced sHLA-E levels compared with other genotypes (P = 0.037). This significant difference is maintained only for CHB women concerning G/G genotypes (P = 0.042). Finally, we reported enhanced sHLA-E in CHB patients with advanced stages of fibrosis (P = 0.032). We demonstrate, for the first time, the association of sHLA-E to CHB. Owing to the positive correlation of HLA-E*01:01/01:03 A > G polymorphism and the association of sHLA-E to advanced fibrosis stages, HLA-E could be a powerful predictor for CHB progression. Further investigations will be required to substantiate HLA-E role as a putative clinical biomarker of CHB.

Clinical Role of Human Leukocyte Antigen in Health and Disease

Most of the genes in the major histocompatibility complex (MHC) region express high polymorphism that is fundamental for their function. The most important function of human leukocyte antigen (HLA) molecule is in the induction, regulation of immune responses and the selection of the T cell repertoire. A clinician's attention is normally drawn to a system only when it malfunctions. The HLA system is no exception in this regard, but in contrast to other systems, it also arouses interest when it functions well - too well, in fact. Population studies carried out over the last several decades have identified a long list of human diseases that are significantly more common among individuals that carry particular HLA alleles including inflammatory, autoimmune and malignant disorders. HLA-disease association is the name of this phenomenon, and the mechanism underlying is still a subject of hot debate. Social behaviours are affected by HLA genes and preference for HLA disparate mates may provide 'good genes' for an individual's offspring. Also, certain HLA genes may be associated with shorter life and others with longer lifespan, but the effects depend both on the genetic background and on the environmental conditions. The following is a general overview of the important functional aspects of HLA in health and diseases.

HLA-E regulates NKG2C+ natural killer cell function through presentation of a restricted peptide repertoire

NK cells interact with the HLA-E molecule via the inhibitory receptor NKG2A and the activating receptor NKG2C. Hence, HLA-E can have a dual role in the immune response. In the present study, we aim to investigate the functional consequences of HLA-E for NKG2A and NKG2C expressing NK cell subsets by using a panel of HLA-E binding peptides derived from CMV, Hsp60 and HLA class I. PBMC derived from healthy subjects were used as targets for isolated NK cells and NK cell activation was examined by analysis of the expression of the degranulation marker CD107a. Peptide induced HLA-E expression inhibited degranulation of NKG2A+ NK cell subsets with almost all peptides, whereas NKG2A- NKG2C+ NK cell responses were enhanced only after incubation with four peptides; 1.3-fold with CMV(I), A80 and B13 and 3.2-fold with HLA-G derived peptide. In addition, the HLA-E:G peptide complex triggered NKG2C receptor internalization, as evidenced by reduction in the percentage of NKG2C+ NK cells when incubated with the peptide, which could be restored by addition of Bafilomycin.

IN CONCLUSION

in contrast to NKG2A, NKG2C is regulated by HLA-E only when HLA-E is in complex with a restricted peptide repertoire, especially in combination with the HLA-G leader peptide.

Immunology of hematopoietic stem cell transplant

Hematopoietic stem cell transplantation (HSCT) is a procedure in which infusion of hematopoietic stem cells is used to reestablish hematopoietic function in patients with damaged or defective bone marrow or immune systems. Early and late complications following allogeneic HSCT include acute and chronic graft-versus-host disease (GVHD), donor rejection, graft failure, relapse of primary malignancy, conditioning-related toxicity, immunodeficiency and infections. Immunology has a central role in allogeneic hematopoietic cell transplantation. Any appreciation of the immunological mechanism involved in engraftment, GVHD, the development of tolerance, immune reconstitution, and the control of malignancy requires some understanding of the immunologic basis for immune reactions provoked by grafting tissue from one individual to another. In the future it should be possible to learn what gene(s) must be activated and which must be repressed to force stem cells into division without maturation; to engineer a mechanism into the cells that stops proliferation and sets the stage for amplification; to search if there could be a universal donor cell line, neatly packaged and stabilized in sealed vials and distributed by the pharmaceutical industry; to modify the transplanted cells in such a way that they have a proliferative advantage over those of the host and to deliver the lethal blow against the neoplasm, perhaps the cells that are infused will be engineered in such a way as to be able to distinguish between normal host cells and tumor.

Do human leukocyte antigen E polymorphisms influence graft-versus-leukemia after allogeneic hematopoietic stem cell transplantation?

Hematopoietic-stem-cell transplantation (HSCT) is complicated by histocompatibility-dependent immune responses such as graft-versus-host disease, relapse, and graft rejection. The severity of these common adverse effects is directly related to the degree of human leukocyte antigen (HLA) incompatibility. In addition to the key role of classic HLA matching in influencing HSCT outcome, several lines of evidence suggest an important role for nonclassic major histocompatibility complex class I molecule, HLA-E. The interaction of HLA-E with NKG2A, its main receptor on natural killer cells, modulates cell-mediated cytotoxicity and cytokine production, an important role in innate immune responses. In addition, the HLA-E molecule can present peptides to different subtypes of T cells that may either support graft-versus-leukemia effects or be involved in bridging innate and acquired immunity. To date, the role of HLA-E and its polymorphisms in HSCT outcomes such as graft-versus-host disease, transplant-related mortality, and improved survival has been published by a number of groups. In addition, these data suggest an association between HLA-E polymorphisms and relapse. Whether the engagement of the HLA-E molecule in the modulation of donor T cells is involved in the graft-versus-leukemia effect, or whether a different mechanism of HLA-E dependent reduction of relapse is involved, requires further investigation.

HLA-E polymorphism and clinical outcome after allogeneic hematopoietic stem cell transplantation in Egyptian patients

Human leukocyte antigen-E (HLA)-E in a non-classical major histocompatibility complex (MHC) class I (Ib) molecule. HLA-E-peptide complex acts as a ligand for natural killer (NK) cells and CD8+ T lymphocytes playing a dual role in natural and acquired immune responses. The difference in expression levels between HLA-E alleles was suggested to have impact on transplantation outcome. The aim of the study is to evaluate the clinical effect of HLA-E alleles on transplantation in a group of Egyptian patients. HLA-E genotyping was analyzed in eighty-eight recipients of stem cell transplantation using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). HLA-E*01:03 allele showed a trend towards lower cumulative incidence of relapse at 2 years compared to homozygous HLA-E*01:01 genotype (8% versus 21.5%, p=0.09, HR: 0.30, 95% CI: 0.91-1.69). HLA-E was the only factor showing near significant association with relapse incidence. HLA-E polymorphism did not affect the cumulative incidence of acute GVHD grades II-IV at 100 days, the 2-year cumulative incidence of extensive chronic GVHD, transplant related mortality (TRM) or overall survival (OS).

CONCLUSION

the suggested association of HLA-E polymorphism with reduced risk of relapse needs verification in a larger cohort. However, its proposed role in GVL helps better understanding of alloreactivity of T cells and NK cells and their implication in immunotherapy post allogeneic hematopoietic stem cell transplantation.

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.

Worldwide HLA-E nucleotide and haplotype variability reveals a conserved gene for coding and 3' untranslated regions

The human leukocyte antigen-E (HLA-E) locus is a human major histocompatibility complex (MHC) gene associated with immune-modulation and suppression of the immune response by the interaction with specific natural killer (NK) and T cell receptors (TCRs). It is considered one of the most conserved genes of the human MHC; however, this low nucleotide variability seems to be a consequence of the scarce number of studies focusing on this subject. In this manuscript we assessed the nucleotide variability at the HLA-E coding and 3' untranslated regions (3'UTRs) in Brazil and in the populations from the 1000Genomes Consortium. Twenty-eight variable sites arranged into 33 haplotypes were detected and most of these haplotypes (98.2%) are encoding one of the two HLA-E molecules found worldwide, E*01:01 and E*01:03. Moreover, three worldwide spread haplotypes, associated with the coding alleles E*01:01:01, E*01:03:01 and E*01:03:02, account for 85% of all HLA-E haplotypes, suggesting that they arose early before human speciation. In addition, the low nucleotide diversity found for the HLA-E coding and 3'UTR in worldwide populations suggests that the HLA-E gene is in fact a conserved gene, which might be a consequence of its key role in the modulation of the immune system.

The impact of HLA-E polymorphisms on relapse following allogeneic hematopoietic stem cell transplantation

Since relapse following allogeneic hematopoietic stem cell transplantation (HSCT) can be due to the escape of the residual malignant cells from the graft-versus-leukemia (GvL) effect and given the role of NK cells in GvL and the importance of HLA-E in the modulation of NK cell function, we investigated whether polymorphisms of HLA-E molecule could impact on the incidence of relapse and the improvement of Disease-free Survival (DFS) after allogeneic HSCT. The study group included 56 pairs of donors and patients with malignant hematological disorders undergoing HLA-E matched allogeneic HSCT. The median follow-up was 43.6 (range 20.5-113.1) months. They were genotyped for HLA-E locus using a sequence-specific primer (SSP)-PCR. We found a lower incidence of relapse (p=0.02) in the patients with HLA-E*0103/0103 genotype compared to those with other genotypes of HLA-E. We also showed an association between HLA-E*0103/0103 genotype and a better DFS (p=0.001). Our results suggest a protective role for HLA-E*0103/0103 genotype against relapse and an association between this genotype and an improved DFS following HLA-E matched allogeneic HSCT.

Clinical significance of the HLA-E and CD94/NKG2 interaction

HLA-E belongs to the non-classical HLA (class Ib family) broadly defined by a limited polymorphism and a restricted pattern of cellular expression. So far, only two functional alleles differing at only one amino acid position (non-synonymous mutation) in the α2 heavy chain domain, where an arginine in position 107 in HLA-E*0101 is replaced by a glycine in HLA-E*0103, have been reported. The interaction between non-classical HLA-E molecule and CD94/NKG2A receptor plays a crucial role in the immunological response involving natural killer (NK) cells and cytotoxic T lymphocytes. All proteins forming CD94/NKG2 receptors are encoded by genes situated in the same cluster on chromosome 12, allowing tight control over the order of their expression. The inhibitory members of the NKG2 receptor family are available on the cell surface before activating the members to prevent autoimmune incidents during immune cells' ontogenesis. In the present review, the potential role of this interaction in viral infection, pregnancy and transplantation of allogeneic hematopoietic stem cells (HSC) is presented and discussed. The review will also include the effect of HLA-E polymorphism on the outcome of HSC transplants in humans.

Association between HLA-E *0101 homozygosity and recurrent miscarriage in Egyptian women

The objective was to investigate the frequency of human leucocyte antigen (HLA)-E alleles in Egyptian women with and without recurrent miscarriage (RM) to evaluate their role on the maintenance of pregnancy. A case-control study was adopted. HLA-E gene polymorphism typing was carried out by restriction fragment length polymorphism for 108 women with RM and 120 fertile female controls. The frequency of HLA-E *0101 allele was higher in patients with RM and HLA-E*0103 allele was higher in fertile controls, and the difference was statistically significant (P=0.003, P(c)=0.006). HLA-E*0101/0101 genotype was the most frequent genotype in patients (45.4%), followed by HLA-E*0101/0103 (44.4%) and finally HLA-E*0103/0103 genotype (10.2%). The difference in the frequency of HLA-E*0101/0101 homozygous genotype in patients with RM compared with that in the fertile controls was statistically significant (OR=2.02, 95% CI=1.13-3.62, P=0.011, P(c)=0.033). We found an increased frequency of homozygosity for HLA-E*0101 in Egyptian women with RM. HLA-E*0101 homozygosity may thus be a risk factor for RM.

HLA allele associations in idiopathic recurrent spontaneous abortion patients from India

BACKGROUND:

Rejection of semiallogenic foetus in recurrent spontaneous abortion (RSA) has been postulated to be a consequence of genetic and immunological phenomena.

AIM:

To evaluate the role of human leukocyte antigen (HLA) alleles in RSA in Indian couples.

SETTINGS AND DESIGN:

A case-control study.

MATERIALS AND METHODS:

Eighty-one randomly selected couples with unexplained three or more RSAs and a control group of 97 couples with live birth belonging to the same ethnic background, referred to the Gynaecology Department, KEM Hospital were included in the case-control study. Serological HLA A and B typing was done followed by molecular subtypes, defined using PCR-SSOP technique for HLA A, B, and C in 40 couples and DRB1* and DQB1* in 28 couples which were then compared with appropriate case 46 and 88 controls.

RESULTS:

Serologically A3 (15.43% vs. 4.43%; odds ratio (OR) = 4.34; P = 0.0002) and B17 (25.3% vs. 11.34%; OR = 3.49; P = 0.0001) were increased. Haplotype A1-B17 was significantly increased. Molecular subtyping revealed that A*030102 (11.25% vs. 4.34%; OR = 3.00; P = 0.07), B*5701 (11.25% vs. 1.08%; OR = 13.10; P = 0.003), Cw*120201 (25% vs. 4.34%; OR = 10.50; P = 2.05E-05), HLA DRB1*030101 (17.85% vs. 3.40%; OR = 7.6; P = 0.0001), DRB1*150101 (32.14% vs. 13.63%; OR = 4.8; P = 0.0003), and DQB1*060101 (35.71% vs. 29.34%; OR = 2.3; P = 0.004) were significantly increased in patients. A differential association was noticed when compared with reported world RSA patients.

CONCLUSION:

The HLA alleles A*030101, B*5701, Cw*120201, DRB1*030101, and DRB1*150101 as well as their associated ancestral haplotype may play a significant role in development of RSA in India.

Linkage disequilibrium between HLA-G*0104 and HLA-E*0103 alleles in Tswa Pygmies

Nonclassical human leukocyte antigen (HLA)-G and -E loci are separated by approximately 660 kb on the short arm of chromosome 6. Interestingly, some functional and expression characteristics are relatively identical or associated for both molecules. For example, expression of HLA-E on the cell surface has been linked to preferential binding of nonameric leader peptides derived from the signal sequence of HLA-G. It has been suggested that these two molecules act synergistically in modulating susceptibility to infectious or chronic inflammatory diseases. A possible explanation for these observations is that HLA-E and HLA-G are evolving under analogous selective pressures and have functions that place them under selective regimes differing from classical HLA genes. The purpose of this study was to investigate the consistency of this hypothesis based on the characterization of the molecular polymorphism of these two genes and their linkage disequilibrium (LD) in three populations, i.e. Southeastern French (n = 57), Teke Congolese (n = 84) and Tswa Pygmies (n = 74). Allelic frequencies observed for HLA-G and HLA-E and for 14-bp ins/del polymorphism in the three populations were similar to those observed in the literature for populations from corresponding geographic areas. Only one of the recently described HLA-G polymorphisms (HLA-G*01:07-01:16) was found, i.e. HLA-G*01:15 in one individual from Congo. We showed that two haplotypes in Tswa Pygmies, i.e. HLA-G*01:04-E*01:03:01 and G*01:04-E*01:01, exhibited highly significant positive and negative D' values respectively. Although these LD could have functional implications, it is more likely because of the genetic drift as the two other populations did not display any significant LD.

Innate immune natural killer cells and their role in HIV and SIV infection

The findings that early events during HIV-1 and SIV infection of Asian rhesus macaques dictate the levels of viremia and rate of disease progression prior to the establishment of mature and effective adaptive immune responses strongly suggest an important role for innate immune mechanisms. In addition, the fact that the major target of HIV and SIV during this period of acute infection is the gastrointestinal tissue suggests that whatever role the innate immune system plays must either directly and/or indirectly focus on the GI tract. The object of this article is to provide a general overview of the innate immune system with a focus on natural killer (NK) cells and their role in the pathogenesis of lentivirus infection. The studies summarized include our current understanding of the phenotypic heterogeneity, the putative functions ascribed to the subsets, the maturation/differentiation of NK cells, the mechanisms by which their function is mediated and regulated, the studies of these NK-cell subsets, with a focus on killer cell immunoglobulin-like receptors (KIRs) in nonhuman primates and humans, and finally, how HIV and SIV infection affects these NK cells in vivo. Clearly much has yet to be learnt on how the innate immune system influences the interaction between lentiviruses and the host within the GI tract, knowledge of which is reasoned to be critical for the formulation of effective vaccines against HIV-1.

Examination of genetic polymorphisms in newborns for signatures of sex-specific prenatal selection

Success rate in human pregnancies is believed to be very low and sex-specific mechanisms may operate in prenatal loss. Assuming a sex-differential in prenatal loss exists, we examined genetic markers in biologically plausible targets in the HLA complex, other immune system-related and iron-regulatory genes in 388 healthy newborns from Wales (UK) using one sex as a control group for the other. Genotyping of 333 single nucleotide polymorphisms (SNPs) from 107 genes was achieved mainly by TaqMan assays. Twenty-two of autosomal SNPs showed frequency differences between 187 male and 201 female newborns either individually or as part of a haplotype. Of these, six markers (RXRB rs2076310, HLA complex haplotype HLA-DQA1 rs1142316-HLA-DRA rs7192-HSPA1B rs1061581, HIST1H1T rs198844, IFNG rs2069727, NKG2D rs10772266 and IRF4 heterozygosity) showed statistically robust differences between male and female newborns and multivariable modeling confirmed their independence. There were fewer males homozygote for combined wildtype genotypes of LIF rs929271, TP53 rs1042522 and MDM2 rs2279744 compared with females [OR = 0.3, 95% confidence interval (CI) = 0.1-0.8; P < 0.01] although these SNPs did not show any association individually. It is unlikely that SNPs have clinical utility as single markers in any trait with complex etiology but polygenic predictive models remain a possibility. If their validity is confirmed in larger studies of different populations and functional mechanisms of these preliminary associations are elucidated, these markers from the HLA complex, NKG2D region and cytokines may cumulatively have sufficient predictive value for susceptibility to prenatal selection in each sex.

Cell bio-imaging reveals co-expression of HLA-G and HLA-E in human preimplantation embryos

The non-classical major histocompatibility complex (MHC) class Ib antigens, termed HLA-G and HLA-E, have been associated with fetal maternal tolerance. The role of HLA-G in the preimplantation embryo remains unclear although immunoprotection, adhesion and cell signalling mechanisms have been suggested. Unlike HLA-G, HLA-E protein expression has not been previously studied in preimplantation embryos. Embryos and model trophoblast cell lines JEG-3 and BeWo were labelled with the HLA-G- and HLA-E-specific monoclonal antibodies MEMG9 and MEME07. Flow cytometry, confocal microscopy and single particle fluorescence imaging techniques were employed to investigate the spatial and temporal expression of these receptors. Lipid raft analysis and adhesion assays were performed to investigate the role of these receptors in cell membrane domains and in promoting adhesion by cell-to-cell contact. HLA-E and HLA-G were co-localized in the trophectoderm of day 6 blastocysts. Analysis on trophoblast cell lines revealed that 37% of HLA-G and 41% of HLA-E receptors were co-localized as tetramers or higher order homodimer clusters. HLA-G receptors did not appear to play a role in either cell adhesion or immunoreceptor signalling via lipid raft platforms on the cell membrane. A possible role of HLA-G and HLA-E in implantation via immunoregulation or modulation of uterine maternal leukocytes is discussed.

MHC-linked and un-linked class I genes in the wallaby

BACKGROUND

MHC class I antigens are encoded by a rapidly evolving gene family comprising classical and non-classical genes that are found in all vertebrates and involved in diverse immune functions. However, there is a fundamental difference between the organization of class I genes in mammals and non-mammals. Non-mammals have a single classical gene responsible for antigen presentation, which is linked to the antigen processing genes, including TAP. This organization allows co-evolution of advantageous class Ia/TAP haplotypes. In contrast, mammals have multiple classical genes within the MHC, which are separated from the antigen processing genes by class III genes. It has been hypothesized that separation of classical class I genes from antigen processing genes in mammals allowed them to duplicate. We investigated this hypothesis by characterizing the class I genes of the tammar wallaby, a model marsupial that has a novel MHC organization, with class I genes located within the MHC and 10 other chromosomal locations.

RESULTS

Sequence analysis of 14 BACs containing 15 class I genes revealed that nine class I genes, including one to three classical class I, are not linked to the MHC but are scattered throughout the genome. Kangaroo Endogenous Retroviruses (KERVs) were identified flanking the MHC un-linked class I. The wallaby MHC contains four non-classical class I, interspersed with antigen processing genes. Clear orthologs of non-classical class I are conserved in distant marsupial lineages.

CONCLUSION

We demonstrate that classical class I genes are not linked to antigen processing genes in the wallaby and provide evidence that retroviral elements were involved in their movement. The presence of retroviral elements most likely facilitated the formation of recombination hotspots and subsequent diversification of class I genes. The classical class I have moved away from antigen processing genes in eutherian mammals and the wallaby independently, but both lineages appear to have benefited from this loss of linkage by increasing the number of classical genes, perhaps enabling response to a wider range of pathogens. The discovery of non-classical orthologs between distantly related marsupial species is unusual for the rapidly evolving class I genes and may indicate an important marsupial specific function.

Evidence that the bulge region is a site of relative immune privilege in human hair follicles

BACKGROUND

Recent gene profiling data suggest that, besides the anagen hair bulb, the epithelial stem cell region in the outer root sheath of hair follicles (HFs), termed the bulge, may also represent an area of relative immune privilege (IP).

OBJECTIVES

To investigate whether the human HF bulge is a site of relative IP within anagen VI HFs.

METHODS

Anagen VI HFs from normal human scalp skin were analysed using immunohistological staining techniques, quantitative histomorphometry and statistical analysis. For functional evidence we performed full-thickness human scalp skin organ cultures to investigate whether interferon (IFN)-gamma, a key inducer of IP collapse in hair bulbs, has a similar effect on the putative bulge IP.

RESULTS

Major histocompatibility complex (MHC) class Ia, beta(2)-microglobulin and MHC class II immunoreactivity are downregulated in the human bulge. The immunosuppressants alpha-melanocyte stimulating hormone, transforming growth factor-beta2, macrophage migration inhibitory factor and indoleamine-2,3-dioxygenase (IDO) are upregulated in the CD200+, stem cell-rich bulge region. These CD200+ cells also co-express HLA-E. Furthermore, IFN-gamma induces significant ectopic MHC class Ia expression in bulge cells of organ-cultured human scalp skin.

CONCLUSIONS

These data suggest that the bulge of human anagen HFs represents a hitherto unrecognized site of relative IP in human skin. Simultaneously, we present the first evidence of IDO and HLA-E protein expression in normal human HFs. Bulge IP presumably protects the HF epithelial stem cell reservoir from autoaggressive immune attack whereas a loss of bulge IP may play a central role in the pathogenesis of cicatricial alopecias.

Human embryo immune escape mechanisms rediscovered by the tumor

Towards the end of the 1990s, the two opposing theories on immunosurveillance and immunostimulation were extensively studied by researchers in an attempt to understand the complex mechanisms that regulate the relation between tumors and the host's immune system. Both theories probably have elements that would help us to comprehend how the host can induce anti-tumor clinical responses through stimulation of the immune system and which could also give us a deeper insight into the mechanisms of tumor immunosuppression. The model that most resembles the behavior of tumor cells in terms of growth, infiltration and suppression of the immune system of the environment in which they live is undoubtedly that of the embryonic cell. The fetus behaves like an allogenic transplant within the mother's body, using every means it has to escape from and defend itself against the mother's immune system. The majority of these mechanisms are the same as those found in tumor cells: antigenic loss, lack of expression of classic HLA-I molecules, production of immunosuppressive cytokines, induction of lack of expression of co-stimulatory molecules in antigen presenting cells, and induction of apoptosis in infiltrating lymphocytes, with activation of a type Th2 regulatory lymphocyte response. A careful and comparative study of key mechanisms capable of triggering tolerance or cytotoxicity in both embryonic and tumor cells could prove immensely valuable in designing new strategies for anti-tumor immunotherapy.

Immune-refractory cancers and their little helpers--an extended role for immunetolerogenic MHC molecules HLA-G and HLA-E?

There is strong evidence to support a role for non-classical MHC class I (class Ib) molecules, most notably HLA-E and HLA-G in tumour immune escape. In this article, we summarize the current knowledge on their expression, regulation and functional relevance in various malignancies, particularly brain tumours. Special emphasis is devoted to the phenomenon that these tolerogenic molecules are expressed by non-transformed cells that are found in close neighborhood to tumour cells representing either parenchymal cells or immune cells attracted to the tumour microenvironment. Here they may act as "natural" or "inducible" suppressors of anti-tumoural immune responses. We thus speculate about the role of HLA-G expressing T cells, a novel population of natural regulatory cells that was identified recently. It is suggested that various cell types within a tumour cooperate in order to inhibit anti-tumour immunity-and that immunetolerogenic HLA-G may play a major role in this context.

HLA-E*0101 allele in homozygous state favors severe bacterial infections in sickle cell anemia

Severe bacterial infections are the major causes of morbidity and mortality in sickle cell anemia (SCA) but are poorly explained. The distribution of a bi-allelic polymorphism (Arg107Gly) of human leukocyte antigen-E (HLA-E) locus was investigated in 144 SCA patients, most of whom originated from from sub-Saharan Africa. Among them, 73 presented with at least one severe bacterial infection, whereas 71 did not. The HLA-E*0101/E*0101 genotype was more frequent among the group with infections than their counterparts (47% vs 21%; p corrected = 0.003). This genetic association is of relevance, given the emerging evidence for the involvement of HLA-E molecules in host response to pathogens.

Homozygous status for HLA-E*0103 confers protection from acute graft-versus-host disease and transplant-related mortality in HLA-matched sibling hematopoietic stem cell transplantation

BACKGROUND

The posttransplant period following hematopoietic stem cell transplantation (HSCT) is potentially high risk for developing survival-compromising complications, many of which are known to be under the control of immunogenetic factors. Given the dual role of human leukocyte antigen (HLA)-E molecules in innate and adaptive immune processes, we analyzed the impact of HLA-E polymorphism in genoidentical HSCT setting.

METHODS

We analyzed 187 HLA-genoidentical sibling pairs for HLA-E polymorphism. To explore its potential association with the incidence of acute and chronic graft versus host disease (aGVHD, cGVHD), severe infections, risk for transplant-related mortality (TRM), and overall survival, HLA-E locus was genotyped by a polymerase chain-reaction-sequence-specific primer (PCR-SSP) strategy.

RESULTS

Multivariate analysis, taking into account the patient-, donor- and transplant-related factors, showed that the incidence of aGVHD and TRM at day 180 were low when the genotype was HLA-E*0103/E*0103, either in the donor or in the recipient, the pairs being identical for HLA-E alleles (hazard ratio [HR]=0.71, P=0.009; and HR=0.42, P=0.04, respectively). We also found a trend towards association between E*0103 homozygosity and improved survival (P=0.05). There was no association between HLA-E polymorphism and incidence of severe infections.

CONCLUSIONS

These data suggest that the homozygous state for HLA-E*0103 allele behaves as a protective genetic factor against aGVHD and TRM and likely contributes to improved survival in HLA-genoidentical bone marrow transplantation.