Structure and function of the human MHC class Ib molecules HLA-E, HLA-F and HLA-G

Diversity in the HLA-I Recognition of HLA-F Monoclonal Antibodies: HLA-F or HLA-Ib Monospecific, HLA-E or HLA-G Bispecific Antibodies with or without HLA-Ia Reactivity

Previous investigators have used various anti-HLA-F monoclonal antibodies (mAbs) to demonstrate that the tissue distribution of HLA-F is highly restricted. Notably, these mAbs differed in their immunodiagnostic capabilities. Specifically, mAbs Fpep1.1 and FG1 detected HLA-F intracellularly in B cells but not on the cell surface, whereas mAb 3D11 detected HLA-F on the cell surface. The presence of HLA-F on T cells was recognized by mAb FG1 but not by mAb Fpep1.1. mAb 3D11 detected HLA-F on the cell surface of activated B cells and on peripheral blood lymphocytes, but not on the normal cells. Importantly, mAb 3D11 revealed that HLA-F exists as a heavy chain (HC) monomer, rather than as an HC associated with B2m. Although these mAbs are believed to be specific to HLA-F, their monospecificity has not been formally established, which is critical for immunodiagnostic and therapeutic purposes. Previously, we investigated the diversity of HLA class I reactivities of anti-HLA-E mAbs using HLA-I coated multiplex bead assays on a Luminex platform. We reported that more than 80% of the HLA-E mAbs were cross-reactive with other HLA-I molecules, with exceptionally few truly HLA-E-monospecific mAbs. In the present investigation, we generated IgG mAbs against HCs of HLA-F in Balb/C mice and examined the cross-reactivity of anti-HLA-F mAbs with other HLA-I alleles using a multiplex bead assay on the Luminex platform. Beads coated with an array of HLA homo- and heterodimers of different HLA-Ia (HLA-A, HLA-B, and HLA-C) and Ib (HLA-E, HLA-F, and HLA-G) alleles were used to examine the binding of the anti-HLA-F mAbs. Only two mAbs were HLA-F monospecific, and five were HLA-Ib restricted. Several anti-HLA-F mAbs cross-reacted with HLA-E (n = 4), HLA-G (n = 3), HLA-Ia alleles (n = 9), HLA-G and HLA-Ia (n = 2), and HLA-Ib and HLA-Ia (n = 6). This monospecificity and polyreactivity were corroborated by the presence of HLA-F monospecific and HLA-I-shared sequences. This study emphasizes the need to monitor the mono-specificity of HLA-F for reliable immunodiagnostics and passive immunotherapy.

Role of MHC class I pathways in Mycobacterium tuberculosis antigen presentation

MHC class I antigen processing is an underappreciated area of nonviral host–pathogen interactions, bridging both immunology and cell biology, where the pathogen’s natural life cycle involves little presence in the cytoplasm. The effective response to MHC-I foreign antigen presentation is not only cell death but also phenotypic changes in other cells and stimulation of the memory cells ready for the next antigen reoccurrence. This review looks at the MHC-I antigen processing pathway and potential alternative sources of the antigens, focusing on Mycobacterium tuberculosis (Mtb) as an intracellular pathogen that co-evolved with humans and developed an array of decoy strategies to survive in a hostile environment by manipulating host immunity to its own advantage. As that happens via the selective antigen presentation process, reinforcement of the effective antigen recognition on MHC-I molecules may stimulate subsets of effector cells that act earlier and more locally. Vaccines against tuberculosis (TB) could potentially eliminate this disease, yet their development has been slow, and success is limited in the context of this global disease’s spread. This review’s conclusions set out potential directions for MHC-I-focused approaches for the next generation of vaccines.

Lower HLA-G levels in extravillous trophoblasts of human term placenta in gestational diabetes mellitus than in normal controls

The non-classical human leucocyte antigen (HLA) class I molecule HLA-G is widely known to play a major role in feto-maternal tolerance. We tested the hypothesis that HLA-G expression is altered in placentas of women with gestational diabetes mellitus (GDM) in a specific pattern that depends on fetal sex. HLA-G expression was analysed in a total of 80 placentas (40 placentas from women with GDM and 40 healthy controls) by immunohistochemistry using the semi-quantitative immunoreactive score (IRS). Double immunofluorescence staining identified the cells expressing HLA-G in the decidua and allowed evaluation of the expression pattern. We found a significant (p < 0.001) reduction of HLA-G expression in extravillous cytotrophoblasts (EVTs) in the placentas of women with GDM as compared to the healthy controls and were able to demonstrate that this downregulation was not due to a loss of cell number, but to a loss of expression intensity. A special change in the cell pattern of EVTs was observed, with these cells showing an obvious decrease in HLA-G expression on their cell surface. No significant differences according to fetal sex were found. These data show a possible association between decreased HLA-G expression and presence of GDM and provide new insights into altered placental function in women with GDM.

Evolution and molecular interactions of major histocompatibility complex (MHC)-G, -E and -F genes

Classical HLA (Human Leukocyte Antigen) is the Major Histocompatibility Complex (MHC) in man. HLA genes and disease association has been studied at least since 1967 and no firm pathogenic mechanisms have been established yet. HLA-G immune modulation gene (and also -E and -F) are starting the same arduous way: statistics and allele association are the trending subjects with the same few results obtained by HLA classical genes, i.e., no pathogenesis may be discovered after many years of a great amount of researchers’ effort. Thus, we believe that it is necessary to follow different research methodologies: (1) to approach this problem, based on how evolution has worked maintaining together a cluster of immune-related genes (the MHC) in a relatively short chromosome area since amniotes to human at least, i.e., immune regulatory genes (MHC-G, -E and -F), adaptive immune classical class I and II genes, non-adaptive immune genes like (C2, C4 and Bf) (2); in addition to using new in vitro models which explain pathogenetics of HLA and disease associations. In fact, this evolution may be quite reliably studied during about 40 million years by analyzing the evolution of MHC-G, -E, -F, and their receptors (KIR—killer-cell immunoglobulin-like receptor, NKG2—natural killer group 2-, or TCR-T-cell receptor—among others) in the primate evolutionary lineage, where orthology of these molecules is apparently established, although cladistic studies show that MHC-G and MHC-B genes are the ancestral class I genes, and that New World apes MHC-G is paralogous and not orthologous to all other apes and man MHC-G genes. In the present review, we outline past and possible future research topics: co-evolution of adaptive MHC classical (class I and II), non-adaptive (i.e., complement) and modulation (i.e., non-classical class I) immune genes may imply that the study of full or part of MHC haplotypes involving several loci/alleles instead of single alleles is important for uncovering HLA and disease pathogenesis. It would mainly apply to starting research on HLA-G extended haplotypes and disease association and not only using single HLA-G genetic markers.

Increased sHLA-G Is Associated with Improved COVID-19 Outcome and Reduced Neutrophil Adhesion

Human leukocyte antigen (HLA) is a group of molecules involved in inflammatory and infective responses. We evaluated blood sHLA-E and sHLA-G levels in hospitalized COVID-19 patients with respiratory failure and their relationship with clinical evolution, changes in endothelial activation biomarker profile, and neutrophil adhesion. sHLA-E, sHLA-G, and endothelial activation biomarkers were quantified by ELISA assay in plasma samples. Neutrophil adhesion to endothelium was assessed in the presence/absence of patients’ plasma samples. At admission, plasma levels of sHLA-G and sHLA-E were significantly higher in COVID-19 patients with respiratory failure compared to controls. COVID-19 clinical improvement was associated with increased sHLA-G plasma levels. In COVID-19, but not in control patients, an inverse correlation was found between serum sICAM-1 and E-selectin levels and plasma sHLA-G values. The in vitro analysis of activated endothelial cells confirmed the ability of HLA-G molecules to control sICAM-1 and sE-selectin expression via CD160 interaction and FGF2 induction and consequently neutrophil adhesion. We suggest a potential role for sHLA-G in improving COVID-19 patients’ clinical condition related to the control of neutrophil adhesion to activated endothelium.

HLA-G1+ Expression in GGTA1KO Pigs Suppresses Human and Monkey Anti-Pig T, B and NK Cell Responses

The human leukocyte antigen G1 (HLA-G1), a non-classical class I major histocompatibility complex (MHC-I) protein, is a potent immunomodulatory molecule at the maternal/fetal interface and other environments to regulate the cellular immune response. We created GGTA1-/HLAG1+ pigs to explore their use as organ and cell donors that may extend xenograft survival and function in both preclinical nonhuman primate (NHP) models and future clinical trials. In the present study, HLA-G1 was expressed from the porcine ROSA26 locus by homology directed repair (HDR) mediated knock-in (KI) with simultaneous deletion of α-1-3-galactotransferase gene (GGTA1; GTKO) using the clustered regularly interspersed palindromic repeats (CRISPR)/CRISPR associated protein 9 (Cas9) (CRISPR/Cas9) gene-editing system. GTKO/HLAG1+ pigs showing immune inhibitory functions were generated through somatic cell nuclear transfer (SCNT). The presence of HLA-G1 at the ROSA26 locus and the deletion of GGTA1 were confirmed by next generation sequencing (NGS) and Sanger's sequencing. Fibroblasts from piglets, biopsies from transplantable organs, and islets were positive for HLA-G1 expression by confocal microscopy, flow cytometry, or q-PCR. The expression of cell surface HLA-G1 molecule associated with endogenous β2-microglobulin (β2m) was confirmed by staining genetically engineered cells with fluorescently labeled recombinant ILT2 protein. Fibroblasts obtained from GTKO/HLAG1+ pigs were shown to modulate the immune response by lowering IFN-γ production by T cells and proliferation of CD4+ and CD8+ T cells, B cells and natural killer (NK) cells, as well as by augmenting phosphorylation of Src homology region 2 domain-containing phosphatase-2 (SHP-2), which plays a central role in immune suppression. Islets isolated from GTKO/HLA-G1+ genetically engineered pigs and transplanted into streptozotocin-diabetic nude mice restored normoglycemia, suggesting that the expression of HLA-G1 did not interfere with their ability to reverse diabetes. The findings presented here suggest that the HLA-G1+ transgene can be stably expressed from the ROSA26 locus of non-fetal maternal tissue at the cell surface. By providing an immunomodulatory signal, expression of HLA-G1+ may extend survival of porcine pancreatic islet and organ xenografts.

A novel and efficient approach to high-throughput production of HLA-E/peptide monomer for T-cell epitope screening

Over the past two decades, there has been a great interest in the study of HLA-E-restricted αβ T cells during bacterial and viral infections, including recently SARS-CoV-2 infection. Phenotyping of these specific HLA-E-restricted T cells requires new tools such as tetramers for rapid cell staining or sorting, as well as for the identification of new peptides capable to bind to the HLA-E pocket. To this aim, we have developed an optimal photosensitive peptide to generate stable HLA-E/pUV complexes allowing high-throughput production of new HLA-E/peptide complexes by peptide exchange. We characterized the UV exchange by ELISA and improved the peptide exchange readout using size exclusion chromatography. This novel approach for complex quantification is indeed very important to perform tetramerization of MHC/peptide complexes with the high quality required for detection of specific T cells. Our approach allows the rapid screening of peptides capable of binding to the non-classical human HLA-E allele, paving the way for the development of new therapeutic approaches based on the detection of HLA-E-restricted T cells.

Beyond the HLA polymorphism: A complex pattern of genetic susceptibility to pemphigus

Pemphigus is a group of autoimmune bullous skin diseases that result in significant morbidity. As for other multifactorial autoimmune disorders, environmental factors may trigger the disease in genetically susceptible individuals. The goals of this review are to summarize the state of knowledge about the genetic variation that may affect the susceptibility and pathogenesis of pemphigus vulgaris and pemphigus foliaceus – both the endemic and the sporadic forms –, to compare and discuss the possible meaning of the associations reported, and to propose recommendations for new research initiatives. Understanding how genetic variants translate into pathogenic mechanisms and phenotypes remains a mystery for most of the polymorphisms that contribute to disease susceptibility. However, genetic studies provide a strong foundation for further developments in this field by generating testable hypotheses. Currently, results still have limited influence on disease prevention and prognosis, drug development, and clinical practice, although the perspectives for future applications for the benefit of patients are encouraging. Recommendations for the continued advancement of our understanding as to the impact of genetic variation on pemphigus include these partially overlapping goals: (1) Querying the functional effect of genetic variants on the regulation of gene expression through their impact on the nucleotide sequence of cis regulatory DNA elements such as promoters and enhancers, the splicing of RNA, the structure of regulatory RNAs and proteins, binding of these regulatory molecules to regulatory DNA elements, and alteration of epigenetic marks; (2) identifying key cell types and cell states that are implicated in pemphigus pathogenesis and explore their functional genomes; (3) integrating structural and functional genomics data; (4) performing disease-progression longitudinal studies to disclose the causal relationships between genetic and epigenetic variation and intermediate disease phenotypes; (5) understanding the influence of genetic and epigenetic variation in the response to treatment and the severity of the disease; (6) exploring gene-gene and genotype-environment interactions; (7) developing improved pemphigus-prone and non-prone animal models that are appropriate for research about the mechanisms that link genotypes to pemphigus. Achieving these goals will demand larger samples of patients and controls and multisite collaborations.

Is there a role played by HLA-E, if any, in HPV immune evasion?

Cervical cancer incidence worldwide exceeds half a million new cases per year. The human papillomavirus (HPV) being the major causative agent of CC uses a variety of strategies to evade immune surveillance, where the immune status varies amongst individuals. This immune evasion altered by HPV is reflected in persistent infections, causing the evolution of cervical neoplasia. The role of the immune system in viral recognition and elimination is of extreme relevance in the development of CC. The interactions of the HLA-E ligand in the target cell along with CD94/NKG2 receptors, which are expressed predominantly, but not exclusively, on NK cells' surface, are responsible for activating or inhibiting cytotoxic activity according to their function. The engagement between HLA-E and CD94/NKG2 molecules is one of the fundamental surveillance mechanisms in patients with CIN I, II and III, where HLA-E expression increases significantly, especially in HPV 16 and 18 infections. Higher HLA-E expression was observed in most histopathological types of CC, and at the same time was correlated to best survival of the patient. This review aims to summarize and discuss the immunological role of HLA-E in the context of HPV infection and immune system evasion, and the oncogenic process of cervical cancer.

Constitutively expressed MHC class Ib molecules regulate macrophage M2b polarization and sepsis severity in irradiated mice

Macrophages can change their physiology in response to microenvironmental signals. This differentiation into classically activated M1 or alternatively activated M2 macrophages is known as polarization. In this study, we isolated bone marrow-derived macrophages from β2m-deficient (deficient in both MHC class Ia and Ib) and K^b D^b -deficient (deficient only in MHC class Ia) mice and found that β2m-deficient macrophages showed a significantly lower M2b polarization efficiency. In addition, the absence of constitutive MHC class Ib expression decreased the stability of the Notch-1 intracellular domain. Finally, we found that β2m-deficient mice exposed to irradiation showed reduced bacterial translocation and sepsis severity. Overall, our study demonstrates that MHC class Ib molecules are essential for M2b macrophage polarization and suggests that MHC class Ib molecules play an important role during infection-induced innate immunity.

Avian MHC Evolution in the Era of Genomics: Phase 1.0

Birds are a wonderfully diverse and accessible clade with an exceptional range of ecologies and behaviors, making the study of the avian major histocompatibility complex (MHC) of great interest. In the last 20 years, particularly with the advent of high-throughput sequencing, the avian MHC has been explored in great depth in several dimensions: its ability to explain ecological patterns in nature, such as mating preferences; its correlation with parasite resistance; and its structural evolution across the avian tree of life. Here, we review the latest pulse of avian MHC studies spurred by high-throughput sequencing. Despite high-throughput approaches to MHC studies, substantial areas remain in need of improvement with regard to our understanding of MHC structure, diversity, and evolution. Recent studies of the avian MHC have nonetheless revealed intriguing connections between MHC structure and life history traits, and highlight the advantages of long-term ecological studies for understanding the patterns of MHC variation in the wild. Given the exceptional diversity of birds, their accessibility, and the ease of sequencing their genomes, studies of avian MHC promise to improve our understanding of the many dimensions and consequences of MHC variation in nature. However, significant improvements in assembling complete MHC regions with long-read sequencing will be required for truly transformative studies.

Single-cell RNA-seq variant analysis for exploration of genetic heterogeneity in cancer

Inter- and intra-tumour heterogeneity is caused by genetic and non-genetic factors, leading to severe clinical implications. High-throughput sequencing technologies provide unprecedented tools to analyse DNA and RNA in single cells and explore both genetic heterogeneity and phenotypic variation between cells in tissues and tumours. Simultaneous analysis of both DNA and RNA in the same cell is, however, still in its infancy. We have thus developed a method to extract and analyse information regarding genetic heterogeneity that affects cellular biology from single-cell RNA-seq data. The method enables both comparisons and clustering of cells based on genetic variation in single nucleotide variants, revealing cellular subpopulations corroborated by gene expression-based methods. Furthermore, the results show that lymph node metastases have lower levels of genetic heterogeneity compared to their original tumours with respect to variants affecting protein function. The analysis also revealed three previously unknown variants common across cancer cells in glioblastoma patients. These results demonstrate the power and versatility of scRNA-seq variant analysis and highlight it as a useful complement to already existing methods, enabling simultaneous investigations of both gene expression and genetic variation.

Multiple receptors converge on H2-Q10 to regulate NK and γδT-cell development

Class Ib major histocompatibility complex (MHC) is an extended family of molecules, which demonstrate tissue-specific expression and presentation of monomorphic antigens. These characteristics tend to imbue class Ib MHC with unique functions. H2-Q10 is potentially one such molecule that is overexpressed in the liver but its immunological function is not known. We have previously shown that H2-Q10 is a ligand for the natural killer cell receptor Ly49C and now, using H2-Q10-deficient mice, we demonstrate that H2-Q10 can also stabilize the expression of Qa-1b. In the absence of H2-Q10, the development and maturation of conventional hepatic natural killer cells is disrupted. We also provide evidence that H2-Q10 is a new high affinity ligand for CD8αα and controls the development of liver-resident CD8αα γδT cells. These data demonstrate that H2-Q10 has multiple roles in the development of immune subsets and identify an overlap of recognition within the class Ib MHC that is likely to be relevant to the regulation of immunity.

MHC Molecules, T cell Receptors, Natural Killer Cell Receptors, and Viral Immunoevasins-Key Elements of Adaptive and Innate Immunity

Molecules encoded by the Major Histocompatibility Complex (MHC) bind self or foreign peptides and display these at the cell surface for recognition by receptors on T lymphocytes (designated T cell receptors-TCR) or on natural killer (NK) cells. These ligand/receptor interactions govern T cell and NK cell development as well as activation of T memory and effector cells. Such cells participate in immunological processes that regulate immunity to various pathogens, resistance and susceptibility to cancer, and autoimmunity. The past few decades have witnessed the accumulation of a huge knowledge base of the molecular structures of MHC molecules bound to numerous peptides, of TCRs with specificity for many different peptide/MHC (pMHC) complexes, of NK cell receptors (NKR), of MHC-like viral immunoevasins, and of pMHC/TCR and pMHC/NKR complexes. This chapter reviews the structural principles that govern peptide/MHC (pMHC), pMHC/TCR, and pMHC/NKR interactions, for both MHC class I (MHC-I) and MHC class II (MHC-II) molecules. In addition, we discuss the structures of several representative MHC-like molecules. These include host molecules that have distinct biological functions, as well as virus-encoded molecules that contribute to the evasion of the immune response.

The expanding role of murine class Ib MHC in the development and activation of Natural Killer cells

Major Histocompatibility Complex-I (MHC-I) molecules can be divided into class Ia and class Ib, with three distinct class Ib families found in the mouse. These families are designated as Q, T and M and are largely unexplored in terms of their immunological function. Among the class Ib MHC, H2-T23 (Qa-1b) has been a significant target for Natural Killer (NK) cell research, owing to its homology with the human class Ib human leukocyte antigen (HLA)-E. However, recent data has indicated that members of the Q and M family of class Ib MHC also play a critical role in the development and regulation NK cells. Here we discuss the recent advances in the control of NK cells by murine class Ib MHC as a means to stimulate further exploration of these molecules.

Genetic and epigenetic regulation of major histocompatibility complex class I gene expression in bovine trophoblast cells

Problem

The regulatory mechanisms governing differential expression of classical major histocompatibility complex (MHC) class I (MHC‐Ia) and non‐classical MHC class I (MHC‐Ib) genes are poorly understood.

Method of study

Quantitative reverse transcription‐ polymerase chain reaction (PCR) was used to compare the abundance of MHC‐I transcripts and related transcription factors in peripheral blood mononuclear cells (PBMC) and placental trophoblast cells (PTC). Methylation of MHC‐I CpG islands was detected by bisulfite treatment and next‐generation sequencing. Demethylation of PBMC and PTC with 5′‐aza‐deoxycytidine was used to assess the role of methylation in gene regulation.

Results

MHC‐I expression was higher in PBMC than PTC and was correlated with expression of IRF1, class II MHC transactivator (CIITA), and STAT1. The MHC‐Ia genes and BoLA‐NC1 were devoid of CpG methylation in PBMC and PTC. In contrast, CpG sites in the gene body of BoLA‐NC2, ‐NC3, and ‐NC4 were highly methylated in PBMC but largely unmethylated in normal PTC and moderately methylated in somatic cell nuclear transfer PTC. In PBMC, demethylation resulted in upregulation of MHC‐Ib by 2.8‐ to 6‐fold, whereas MHC‐Ia transcripts were elevated less than 2‐fold.

Conclusion

DNA methylation regulates bovine MHC‐Ib expression and is likely responsible for the different relative levels of MHC‐Ib to MHC‐Ia transcripts in PBMC and PTC.

Human Leukocyte Antigen F Presents Peptides and Regulates Immunity through Interactions with NK Cell Receptors

Evidence is mounting that the major histocompatibility complex (MHC) molecule HLA-F (human leukocyte antigen F) regulates the immune system in pregnancy, infection, and autoimmunity by signaling through NK cell receptors (NKRs). We present structural, biochemical, and evolutionary analyses demonstrating that HLA-F presents peptides of unconventional length dictated by a newly arisen mutation (R62W) that has produced an open-ended groove accommodating particularly long peptides. Compared to empty HLA-F open conformers (OCs), HLA-F tetramers bound with human-derived peptides differentially stained leukocytes, suggesting peptide-dependent engagement. Our in vitro studies confirm that NKRs differentiate between peptide-bound and peptide-free HLA-F. The complex structure of peptide-loaded β₂m-HLA-F bound to the inhibitory LIR1 revealed similarities to high-affinity recognition of the viral MHC-I mimic UL18 and a docking strategy that relies on contacts with HLA-F as well as β₂m, thus precluding binding to HLA-F OCs. These findings provide a biochemical framework to understand how HLA-F could regulate immunity via interactions with NKRs.

β2-microglobulin gene duplication in cetartiodactyla remains intact only in pigs and possibly confers selective advantage to the species

Several β2-microglobulin (B2M) -bound protein complexes undertake key roles in various immune system pathways, including the neonatal Fc receptor (FcRn), cluster of differentiation 1 (CD1) protein, non-classical major histocompatibility complex (MHC), and well-known MHC class I molecules. Therefore, the duplication of B2M may lead to an increase in the biological competence of organisms to the environment. Based on the pig genome assembly SSC10.2, a segmental duplication of ~45.5 kb, encoding the entire B2M protein, was identified in pig chromosome 1. Through experimental validation, we confirmed the functional duplication of the B2M gene with a completely identical coding sequence between two copies in pigs. Considering the importance of B2M in the immune system, we performed the phylogenetic analysis of B2M duplication in ten mammalian species, confirming the presence of B2M duplication in cetartioldactyls, like cattle, sheep, goats, pigs and whales, but non-cetartiodactyl species, like mice, cats, dogs, horses, and humans. The density of long interspersed nuclear element (LINE) at the edges of duplicated blocks (39 to 66%) was found to be 2 to 3-fold higher than the average (20.12%) of the pig genome, suggesting its role in the duplication event. The B2M mRNA expression level in pigs was 12.71 and 7.57 times (2-ΔΔCt values) higher than humans and mice, respectively. However, we were unable to experimentally demonstrate the difference in the level of B2M protein because species specific anti-B2M antibodies are not available. We reported, for the first time, the functional duplication of the B2M gene in animals. The identification of partially remaining duplicated B2M sequences in the genomes of only cetartiodactyls indicates that the event was lineage specific. B2M duplication could be beneficial to the immune system of pigs by increasing the availability of MHC class I light chain protein, B2M, to complex with the proteins encoded by the relatively large number of MHC class I heavy chain genes in pigs. Further studies are necessary to address the biological meaning of increased expression of B2M.

HLA-F coding and regulatory segments variability determined by massively parallel sequencing procedures in a Brazilian population sample

Human Leucocyte Antigen F (HLA-F) is a non-classical HLA class I gene distinguished from its classical counterparts by low allelic polymorphism and distinctive expression patterns. Its exact function remains unknown. It is believed that HLA-F has tolerogenic and immune modulatory properties. Currently, there is little information regarding the HLA-F allelic variation among human populations and the available studies have evaluated only a fraction of the HLA-F gene segment and/or have searched for known alleles only. Here we present a strategy to evaluate the complete HLA-F variability including its 5' upstream, coding and 3' downstream segments by using massively parallel sequencing procedures. HLA-F variability was surveyed on 196 individuals from the Brazilian Southeast. The results indicate that the HLA-F gene is indeed conserved at the protein level, where thirty coding haplotypes or coding alleles were detected, encoding only four different HLA-F full-length protein molecules. Moreover, a same protein molecule is encoded by 82.45% of all coding alleles detected in this Brazilian population sample. However, the HLA-F nucleotide and haplotype variability is much higher than our current knowledge both in Brazilians and considering the 1000 Genomes Project data. This protein conservation is probably a consequence of the key role of HLA-F in the immune system physiology.

Immunoregulatory Role of HLA-G in Allergic Diseases

Allergic diseases are sustained by a T-helper 2 polarization leading to interleukin-4 secretion, IgE-dependent inflammation, and mast cell and eosinophil activation. HLA-G molecules, both in membrane-bound and in soluble forms, play a central role in modulation of immune responses. Elevated levels of soluble HLA-G (sHLA-G) molecules are detected in serum of patients with allergic rhinitis to seasonal and perennial allergens and correlate with allergen-specific IgE levels, clinical severity, drug consumption, and response to allergen-specific immunotherapy. sHLA-G molecules are also found in airway epithelium of patients with allergic asthma and high levels of sHLA-G molecules are detectable in plasma and bronchoalveolar lavage of asthmatic patients correlating with allergen-specific IgE levels. Finally, HLA-G molecules are expressed by T cells, monocytes-macrophages, and Langerhans cells infiltrating the dermis of atopic dermatitis patients. Collectively, although at present it is difficult to completely define the role of HLA-G molecules in allergic diseases, it may be suggested that they are expressed and secreted by immune cells during the allergic reaction in an attempt to suppress allergic inflammation.

Natural Killer Lymphocytes Are Dysfunctional in Kidney Transplant Recipients on Diagnosis of Cancer

BACKGROUND

The incidence of cancer is increased after solid organ transplantation. Natural killer (NK) cells are key effectors of the tumor immune response.

METHODS

We conducted a cross sectional multicentre matched case-control study including 42 kidney transplant recipients (KTRs) on diagnosis of cancer and 41 KTRs without cancer. Extensive phenotyping of NK cells populations and functional tests of NK cells were performed.

RESULTS

Kidney transplant recipients with cancer had a higher incidence of acute rejection (P = 0.02) and cytomegalovirus (CMV) infection (P = 0.03) than controls. They had more lymphopenia than control KTRs (1020/mm3 +/- 32 vs 1218/mm3 +/- 34; P = 0.001) including a CD4+ lymphopenia (P = 0.01). Total CD3-/CD56+ NK cell counts were similar in both groups. However, KTRs with cancer had a lower frequency of the cytokine-enriched CD56bright NK cell subset (P = 0.001). The percentage of NK cells expressing NKp46 was decreased in KTRs with cancer (45% vs 53 %, P = 0.001). Furthermore, the ability of NK cells to degranulate CD107a+ cytolytic vesicles was reduced (11% vs 22%; P = 0.02), and the percentage of NK cells secreting IFN[gamma] was decreased (7.5% vs 28.8%; P = 0.01) in KTRs with cancer.

CONCLUSIONS

These results reveal an imbalance between NK cell subpopulations and functional NK cell defects in KTRs at the diagnosis of malignancy, including a decreased expression of NKp46 and decreased numbers of NK cells producing INF[gamma]. This study highlights the role of NKp46, a major activating NK cell receptor, which could be considered as a potential marker during immunological follow-up of KTRs.

Association of HLA-G*01:01:02:01/G*01:04:01 polymorphism with gastric adenocarcinoma

Human leukocyte antigen-G (HLA-G) plays an important role in tumor cell escape from immune surveillance and HLA-G polymorphisms might service as a potential risk factor for clinical outcomes in GAC (gastric adenocarcinoma). We investigated the association between HLA-G polymorphisms as well as soluble HLA-G level and accordance of GAC. This case-control study included 100 GAC patients and 102 unrelated Iranian individual's samples as control. The clinical stages ranged from I to IV. PCR-RFLP method was carried out in order to specify the genotypes of the HLA-G gene. Concentrations of sHLA-G in serum were determined with the sHLA-G-specific enzyme linked immunosorbent assay (ELISA) kit. The G*01:04:01 and G*01:01:02:01 alleles were the predominant alleles in GAC patients and healthy controls. The G*01:01:03:01 and G*01:01:08 allele distributions are significantly higher among controls comparing to cases and seem to have protective effect (P value=0.026 and 0.007 respectively). There is a substantial differences in G*01:01:02:01/G*01:04:01 genotype frequencies between cases and controls (OR=2.8, P value<0.001). The G*01:01:03:01/G*01:04:01 and G*01:01:02:01/G*01:01:08 genotypes frequency are higher among controls in comparison to patients (P value=0.028 and 0.007 respectively). The polymorphisms in HLA-G could affect GAC induction and its outcome. Also, increased sHLA-G levels in serum might be a useful biomarker for diagnosis.

Behavior of soluble HLA-A, -B, -C and HLA-G molecules in patients with chronic hepatitis C virus infection undergoing pegylated interferon-α and ribavirin treatment: potential role as markers of response to antiviral therapy

The serum levels of soluble HLA class I antigens (sHLA-A, -B, -C and sHLA-G) were determined in 40 HCV genotype 1-infected patients before (T ₀), after 3, 6, and 12 months (T ₃, T ₆, and T ₁₂) of pegylated-IFN-α plus ribavirin therapy and 6 months (T ₁₈) after the end of treatment. Twenty patients were sustained virological responders (SVR), and 20 were non-responders (NR). sHLA-A, -B, -C levels at T ₀ were significantly higher in both SVR (mean 10.48 μg/ml) and NR (mean 11.87 μg/ml) patients as compared to healthy controls (mean 0.34 μg/ml, p < 0.0001) and HIV-infected subjects (mean 1.22 μg/ml, p < 0.0001). sHLA-G levels at T ₀ were significantly higher in SVR (mean 24.78 ng/ml) and NR (mean 24.93 ng/ml) patients as compared to healthy controls (mean 10.34 ng/ml, p = 0.015 and p = 0.014, respectively) but were lower as compared to HIV-infected subjects (mean 48.00 ng/ml, p < 0.0001). The levels of sHLA-A, -B, -C and sHLA-G significantly decreased in SVR from T ₀ to T ₁₈ (mean 1.64 and 1.43 ng/ml, respectively, p < 0.0001) and correlated with HCV-RNA, AST, ALT, γGT, and ALP levels. The determination of soluble HLA class I levels could be proposed as a surrogate marker to discriminate SVR and NR HCV-infected patients during PEG-IFN-α plus ribavirin therapy.

The Attenuated Live Yellow Fever Virus 17D Infects the Thymus and Induces Thymic Transcriptional Modifications of Immunomodulatory Genes in C57BL/6 and BALB/C Mice

Thymus is involved in induction of self-tolerance in T lymphocytes, particularly due to Aire activity. In peripheral tissues, Treg cells and immunomodulatory molecules, like the major histocompatibility complex (MHC) class Ib molecules, are essential for maintenance of autotolerance during immune responses. Viral infections can trigger autoimmunity and modify thymic function, and YFV17D immunization has been associated with the onset of autoimmunity, being contraindicated in patients with thymic disorders. Aiming to study the influence of YFV17D immunization on the transcriptional profiles of immunomodulatory genes in thymus, we evaluated the gene expression of AIRE, FOXP3, H2-Q7 (Qa-2/HLA-G), H2-T23 (Qa-1/HLA-E), H2-Q10, and H2-K1 following immunization with 10,000 LD50 of YFV17D in C57BL/6 and BALB/c mice. The YFV17D virus replicated in thymus and induced the expression of H2-Q7 (Qa-2/HLA-G) and H2-T23 (Qa-1/HLA-E) transcripts and repressed the expression of AIRE and FOXP3. Transcriptional expression varied according to tissue and mouse strain analyzed. Expression of H2-T23 (Qa-1/HLA-E) and FOXP3 was induced in thymus and liver of C57BL/6 mice, which exhibited defective control of viral load, suggesting a higher susceptibility to YFV17D infection. Since the immunization with YFV17D modulated thymus gene expression in genetically predisposed individuals, the vaccine may be related to the onset of autoimmunity disorders.

Predictive value of HLA-G and HLA-E in the prognosis of colorectal cancer patients

HLA-G and HLA-E are non-classical HLA Ib molecules. Recently, increasingly more reports have shown that HLA-G is highly expressed in different malignancies. In this article, we detected the expression levels of HLA-G and HLA-E in primary colorectal cancer patients. Our results showed that 70.6% and 65.7% of the colorectal cancer tissues had positive HLA-G or HLA-E expression, respectively, and that 46.1% positively expressed both molecules. We also analyzed the correlations between the expression levels of HLA-G, HLA-E or both combined and the clinical outcomes of the patients. Kaplan-Meier analysis results showed that the expression levels of HLA-G or HLA-E alone and the combined expression of both molecules were all statistically correlated with the overall survival of colorectal cancer patients. Cox multivariate analysis showed that only HLA-G expression can serve as independent factor for OS. Our results also showed that the expression of HLA-E was significantly correlated with tumor metastasis.

Impact of human leukocyte antigen molecules E, F, and G on the outcome of transplantation

BACKGROUND

HLA class I molecules are divided into classic (Ia) and nonclassic (Ib). Nonclassic HLA molecules (E, F, and G) have acquired relevance owing to their immunomodulatory properties and possible repercussions for induction of tolerance in organ transplantation. The objective of this study was to identify the impact of these molecules on transplant success or failure.

METHODS

A systematic review of literature was performed with the use of MeSH terms in Pubmed. Clinical trials, randomized clinical trials, case-control studies, and reviews from the past 15 years were included.

RESULTS

HLA-E*0103/E*0103 genotype is associated with lower risk of graft-versus-host disease, decreased mortality, and greater disease-free survival after bone marrow transplantation. There were no significant associations between HLA-F and clinical outcomes in any of the studies. Elevated serum levels of HLA-G were associated with a lower incidence of rejection in hepatic and renal transplantation during the 1st year and lower T-cell response after bone marrow, liver, and kidney transplantation. Detection of mRNA of HLA-G1 was also associated with less graft rejection.

CONCLUSIONS

Current literature suggests that nonclassic HLA Ib molecules play an important role in immunotolerance in organ transplantation; however, more studies are required to predict outcomes related to specific genotypes.

The use of microRNA by human viruses: lessons from NK cells and HCMV infection

Depending on ethnicity and on social conditions, between 40 and 90 % of the population is infected with human cytomegalovirus (HCMV). In immunocompetent patients, the virus may cause an acute disease and then revert to a state of latency, which enables its coexistence with the human host. However, in cases of immunosuppression or in neonatal infections, HCMV can cause serious long-lasting illnesses. HCMV has developed multiple mechanisms in order to escape its elimination by the immune system, specifically by two killer cell types of the adaptive and the innate immune systems; cytotoxic T lymphocytes (CTL) and natural killer (NK) cells, respectively. Another fascinating aspect of HCMV is that like other highly developed herpesviruses, it expresses its own unique set of microRNAs. Here, we initially describe how the activity of NK cells is regulated under normal conditions and during infection. Then, we discuss what is currently known about HCMV microRNA-mediated interactions, with special emphasis on immune modulation and NK cell evasion. We further illustrate the significant modulation of cellular microRNAs during HCMV infection. Although, the full target spectrum of HCMV microRNAs is far from being completely elucidated, it can already be concluded that HCMV uses its "multitasking" microRNAs to globally affect its own life cycle, as well as important cellular and immune-related pathways.

Temporal HLA profiling and immunomodulatory effects of human adult bone marrow- and adipose-derived mesenchymal stem cells

AIM

To investigate the temporal HLA expression profile and immunomodulatory function of mesenchymal stem cells (MSCs) during in vitro expansion.

MATERIALS & METHODS

Adult bone marrow-derived MSCs (BMSCs) and adipose-derived MSCs (AMSCs) were cultured and HLA class I and II mRNA expression were investigated during serial expansion using semiquantitative reverse-transcription PCR. The immunomodulatory properties of MSCs were monitored using peripheral blood mononuclear cell (PBMC) proliferation and cytotoxicity assays.

RESULTS

Semiquantitative reverse-transcription PCR revealed that classical HLA class I molecules were highly expressed in MSCs and remained relatively stable during extended culture. Variable expression levels of HLA class II molecules were detected in both BMSCs and AMSCs across passages. AMSCs were more resistant to PBMC-mediated cytotoxicity and suppressed PBMC proliferation more than BMSCs, although the effect was diminished with increasing passage.

CONCLUSION

These findings provide insight regarding the relationship between MSC passage number and MSC immunosuppressive properties and suggest that AMSCs hold advantages over BMSCs for immunomodulatory therapeutic purposes.

Soluble HLA-I/peptide monomers mediate antigen-specific CD8 T cell activation through passive peptide exchange with cell-bound HLA-I molecules

Accumulating evidence that serum levels of soluble class I HLA molecules (sHLA-I) can, under various pathological conditions, correlate with disease stage and/or patient survival, has stimulated interest in defining whether sHLA-I can exert immunological functions. However, despite a mounting number of publications suggesting the ability of sHLA-I to affect immune effectors in vitro, the precise underlying mechanism still remains controversial. In this article, we address potential functions of both classical and nonclassical sHLA-I, using soluble recombinant HLA-I/peptide monomers, and clearly demonstrate their ability to trigger Ag-specific activation of CD8 T cells in vitro. Furthermore, we provide strong evidence that this behavior results from the passive transfer of peptides from monomers to T cell-bound HLA-I molecules, allowing for fratricide representation and activation. Hence, we proposed a unifying model of T cell activation by HLA-I/peptide monomers, reappraising the potential involvement of sHLA-I molecules in the immune response.

IL-27 driven upregulation of surface HLA-E expression on monocytes inhibits IFN-γ release by autologous NK cells

HLA-G and HLA-E are HLA-Ib molecules with several immunoregulatory properties. Their cell surface expression can be modulated by different cytokines. Since IL-27 and IL-30 may either stimulate or regulate immune responses, we have here tested whether these cytokines may modulate HLA-G and -E expression and function on human monocytes. Monocytes expressed gp130 and WSX-1, the two chains of IL27 receptor (R), and IL6Rα (that serves as IL-30R, in combination with gp130). However, only IL27R appeared to be functional, as witnessed by IL-27 driven STAT1/ STAT3 phosphorylation. IL-27, but not IL-30, significantly upregulated HLA-E (but not HLA-G) expression on monocytes. IFN-γ; secretion by activated NK cells was dampened when the latter cells were cocultured with IL-27 pretreated autologous monocytes. Such effect was not achieved using untreated or IL-30 pretreated monocytes, thus indicating that IL-27 driven HLA-E upregulation might be involved, possibly through the interaction of this molecule with CD94/NKG2A inhibitory receptor on NK cells. In contrast, cytotoxic granules release by NK cell in response to K562 cells was unaffected in the presence of IL-27 pretreated monocytes. In conclusion, we delineated a novel immunoregulatory function of IL-27 involving HLA-E upregulation on monocytes that might in turn indirectly impair some NK cell functions.

Human leukocyte antigen-G and regulatory T cells during specific immunotherapy for pollen allergy

BACKGROUND

TH2-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 TH1-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 TH1 during SIT.

Intrathecal soluble HLA-E correlates with disease activity in patients with multiple sclerosis and may cooperate with soluble HLA-G in the resolution of neuroinflammation

Expression and function of the immunoregulatory molecule HLA-E was investigated in patients with relapsing-remitting (RR) multiple sclerosis (MS). Serum and cerebrospinal fluid (CSF) soluble (s)HLA-E and -G levels were measured by ELISA in 80 RRMS patients. Controls were patients with other inflammatory neurological disorders (OIND, n = 81) and noninflammatory neurological disorders (NIND, n = 86). Serum sHLA-E concentrations were higher in RRMS than in NIND patients only. CSF sHLA-E concentrations were higher in RRMS than controls. Increased CSF sHLA-E levels were detected in MRI inactive and clinically stable RRMS patients. sHLA-E intrathecal synthesis (ITS) was higher in RRMS than controls, and the number of patients with sHLA-E ITS above cut-off was higher i) in MS than controls, and ii) in clinically stable than clinically active MS patients. sHLA-E CSF levels and ITS correlated with i) the same sHLA-G parameters, and ii) disease duration. HLA-E expression and co-expression with CD markers were investigated in MS plaques from three different cases by immunohistochemistry and confocal microscopy, respectively. Infiltrating T lymphocytes and macrophages, as well as resident microglial cells and astrocytes expressed HLA-E. CSF samples from MS patients were finally tested for inhibitory activity of in vitro CTL and NK cell mediated cytotoxicity. sHLA-E⁺ were more effective than sHLA-E⁻ CSF samples in such inhibition. Maximum inhibition was achieved with sHLA-E⁺/sHLA-G⁺ CSF samples In conclusion, increased sHLA-E CSF levels may play an immunomodulatory role in MS, contributing to the inhibition of intrathecal inflammatory response. The potential of sHLA-E as biomarker of MS activity warrants further investigation.

Impact of HLA-E gene polymorphism on HLA-E expression in tumor cells and prognosis in patients with stage III colorectal cancer

Human leukocyte antigen (HLA)-E can contribute to the escape of cancer cells from host immune mechanisms. However, it is unknown whether HLA-E gene polymorphisms might play a role in cancer immune escape. This study aimed to evaluate the correlation between HLA-E gene polymorphisms and HLA-E expression in tumor tissue and determine the effects on clinical outcome of patients with stage III colorectal cancer. Two hundred thirty patients with stage III colorectal cancer were enrolled. HLA-E expression was detected in patient-derived tumor tissues with immunohistochemistry. HLA-E gene alleles in tumor tissues were detected with the polymerase chain reaction-sequence-specific primer method. In colorectal cancer tissue and in the normal tissue adjacent to the tumor, the HLA-E expression rates were 72.2 and 15.1 %, respectively (P < 0.05). Patients with overexpression, low expression, and no expression of HLA-E exhibited disease-free survival of 55.3, 72.9, and 72.1 %, respectively. Patients with HLA-E overexpression exhibited the lowest long-term survival rate. No relationship was observed between the type of HLA-E gene polymorphism and its expression level in tumor tissues; moreover, no polymorphisms appeared to affect the long-term survival of patients with colorectal cancer. The type of HLA-E polymorphism did not have an impact on HLA-E expression in tumors or the prognosis in patients with stage III colorectal cancer. However, the level of HLA-E expression in tumor tissue strongly predicted long-term survival in these patients.

Increased HLA-E expression in white matter lesions in multiple sclerosis

The molecular mechanisms underpinning central nervous system damage in multiple sclerosis (MS) are complex and it is widely accepted that there is an autoimmune component. Both adaptive and innate immune effector mechanisms are believed to contribute to tissue disease aetiology. HLA-E is a non-classical MHC class Ib molecule that acts as the ligand for the NKG2A inhibitory receptor present on natural killer (NK) and CD8+ cells. Peptide binding and stabilization of HLA-E is often considered to signal infection or cell stress. Here we examine the up-regulation of HLA-E in MS brain tissue. Expression is significantly increased in white matter lesions in the brain of MS patients compared with white matter of neurologically healthy controls. Furthermore, using quantitative immunohistochemistry and confocal microscopy, we show increased HLA-E protein expression in endothelial cells of active MS lesions. Non-inflammatory chronic lesions express significantly less HLA-E protein, comparable to levels found in white matter from controls. Increased HLA-E protein levels were associated with higher scores of inflammation. These results suggest the potential for an effect in central nervous system pathogenesis from HLA-E modulation in stressed tissue. Co-localization with infiltrating CD8+ cells implicates a possible role for HLA-E-restricted regulatory CD8+ cells, as has been proposed in other autoimmune diseases.

HIV-1 dynamics: a reappraisal of host and viral factors, as well as methodological issues

The dynamics of HIV-1 viremia is a complex and evolving landscape with clinical and epidemiological (public health) implications. Most studies have relied on the use of set-point viral load (VL) as a readily available proxy of viral dynamics to assess host and viral correlates. This review highlights recent findings from population-based studies of set-point VL, focusing primarily on robust data related to host genetics. A comprehensive understanding of viral dynamics will clearly need to consider both host and viral characteristics, with close attention to (i) the timing of VL measurements, (ii) the biology of viral evolution, (iii) compartments of active viral replication, (iv) the transmission source partner as the immediate past microenvironment, and (v) proper application of statistical models.

Defects in NKG2D ligand expression result in failed tolerance induction at the maternal-fetal interface: a possible cause for recurrent miscarriage

Certain maternal immune responses against the fetus at the maternal-fetal interface may contribute to recurrent miscarriage (RM). Trophoblast cells involve in forming of maternal-fetal interface and interact with many immune cells, including NK cells. NK cells accumulate at the maternal-fetal interface and play a critical role during pregnancy. NKG2D ligands can activate NK cells through engaging with corresponding receptors. The 5'-end flanking regions of DNA sequence of some NKG2D ligands contain heat shock elements. It is very possible that oxidative stress, produced in pathological process of RM, induces abnormal NKG2D ligand expression in the trophoblast cells, which stimulate cytotoxicity of NK cells. Moreover, in normal pregnancy, soluble NKG2D ligands are secreted into sera by syncytiotrophoblast cells, which disturb NKG2D-mediated maternal anti-fetus immunity. Reduction of soluble NKG2D ligand levels in association with upregulation of NKG2D on immune cells may also contribute to pathogenesis of RM.

The Père David's deer MHC class I genes show unexpected diversity patterns, with monomorphic classical genes but polymorphic nonclassical genes and pseudogenes

Père David's deer (Elaphurus davidianus) is a highly inbred species that arose from 11 founders but now comprises a population of about 3,000 individuals, making it interesting to investigate the adaptive variation of this species from the major histocompatibility complex (MHC) perspective. In this study, we isolated Elda-MHC class I loci using magnetic bead-based cDNA hybridization, and examined the molecular variations of these loci using single-strand conformation polymorphism (SSCP) and sequence analysis. We obtained seven MHC class I genes, which we designated F1, F12, G2, I7, AF, I8, and C1. Our analyses of stop codons, phylogenetic trees, amino acid conservation, and G+C content revealed that F1, F12, G2, and I7 were classical genes, AF was a nonclassical gene, and I8 and C1 were pseudogenes. Our subsequent molecular examinations showed that the diversity pattern in the Père David's deer was unusual. Most mammals have more polymorphic classical class I loci vs. the nonclassical and neutral genes. In contrast, the Père David's deer was found to be monomorphic at classical genes F1, F12, G2, and I7, dimorphic at the nonclassical AF gene, dimorphic at pseudogene I8, and tetramorphic at pseudogene C1. The adverse polymorphism patterns of Elda-I genes might provide evidence for selection too faster deplete MHC variation than drift in the bottlenecked populations, while the postbottleneck tetramorphism of the C1 pseudogene appears to be evidence of strong historical balancing selection.

Soluble HLA-G dampens CD94/NKG2A expression and function and differentially modulates chemotaxis and cytokine and chemokine secretion in CD56bright and CD56dim NK cells

Soluble HLA-G (sHLA-G) inhibits natural killer (NK) cell functions. Here, we investigated sHLA-G-mediated modulation of (1) chemokine receptor and NK receptor expression and function and (2) cytokine and chemokine secretion in CD56bright and CD56dim NK cells. sHLA-G-treated or untreated peripheral blood (PB) and tonsil NK cells were analyzed for chemokine receptor and NK receptor expression by flow cytometry. sHLA-G down-modulated (1) CXCR3 on PB and tonsil CD56bright and CD56dim, (2) CCR2 on PB and tonsil CD56bright, (3) CX3CR1 on PB CD56dim, (4) CXCR5 on tonsil CD56dim, and (5) CD94/NKG2A on PB and tonsil CD56brigh) and CD56dim NK cells. Such sHLA-G-mediated down-modulations were reverted by adding anti-HLA-G or anti-ILT2 mAbs. sHLA-G inhibited chemotaxis of (1) PB NK cells toward CXCL10, CXCL11, and CX3CL1 and (2) PB CD56bright NK cells toward CCL2 and CXCL10. IFN-γ secretion induced by NKp46 engagement was inhibited by NKG2A engagement in untreated but not in sHLA-G-treated NK cells. sHLA-G up-regulated secretion of (1) CCL22 in CD56bright and CD56dim and (2) CCL2, CCL8, and CXCL2-CXCL3 in CD56dim PB NK cells. Signal transduction experiments showed sHLA-G-mediated down-modulation of Stat5 phosphorylation in PB NK cells. In conclusion, our data delineated novel mechanisms of sHLA-G-mediated inhibition of NK-cell functions.

Recent advances in understanding immunology of reproductive failure

Aspects of the immunological relationship between mother and conceptus still remain a mystery, although the recent advances in molecular biology have enlightened some of the parameters that participate in fetomaternal cross-talk during implantation. The atypical expression of major histocompatibility complex (MHC), the specific role of some hormones and cytokines, as well as the temporal and spatial distributions of uterine natural killer cells, represent substantive parameters of fetomaternal immunotolerance during implantation. Although human maternal and fetal immunology is difficult to investigate, aberrant immune responses and an imbalanced cytokine network may be related to infertility, implantation failures after IVF and recurrent pregnancy losses. In this review, immunological and interacting factors involved in human reproductive failure are summarized and critically evaluated.

Soluble human leukocyte antigen-G serum levels in patients with acquired immune deficiency syndrome affected by different disease-defining conditions before and after antiretroviral treatment

We have previously reported that the serum levels of soluble human leukocyte antigen (HLA)-A, -B, -C, and -G antigens are elevated in human immunodeficiency virus (HIV)-infected subjects and decrease after antiretroviral therapy. In this study, we measured soluble HLA-G serum levels in patients with acquired immune deficiency syndrome (AIDS) affected by different AIDS-defining conditions before and during antiretroviral therapy and correlated them with virologic and immunologic parameters of response to treatment. Soluble HLA-G levels were significantly higher in AIDS patients before treatment as compared with healthy controls and significantly decreased after 36 months of therapy. The decrease of soluble HLA-G correlated with the decrease of plasma HIV-RNA level and CD8(+) T-lymphocytes number and with the increase of CD4(+) T-lymphocytes number. Soluble HLA-G levels were significantly higher in patients with opportunistic infections and Kaposi's sarcoma compared with patients with the wasting syndrome. These data suggest that infections and neoplasms may trigger the shedding of soluble HLA-G molecules, and confirm that the level of soluble HLA-G in serum might represent a surrogate marker to monitor virologic response and immune reconstitution in HIV-positive individuals.

HLA-F is a surface marker on activated lymphocytes

Of the three nonclassical class I antigens expressed in humans, HLA-F has been least characterized with regard to expression or function. In this study, we examined HLA-F expression focusing on lymphoid cells, where our previous work with homologous cell lines had demonstrated surface HLA-F expression. HLA-F protein expression was observed by Western blot analysis in all resting lymphocytes, including B cells, T cells, NK cells, and monocytes, all of which lacked surface expression in the resting state. Upon activation, using a variety of methods to activate different lymphocyte subpopulations, all cell types that expressed HLA-F intracellularly showed an induction of surface HLA-F protein. An examination of peripheral blood from individuals genetically deficient for TAP and tapasin expression demonstrated the same activation expression profiles for HLA-F,but with altered kinetics post-activation. Further analysis of CD41+CD25+1 Treg showed that HLA-F was not upregulated on the major fraction of these cells when they were activated,whereas CD41+CD25- T cells showed strong expression of surface HLA-F when activated under identical conditions. These findings are discussed with regard to possible functions for HLA-F and its potential clinical use as a marker of an activated immune response.

Renal transplant immunosuppression impairs natural killer cell function in vitro and in vivo

Background

Despite an increasing awareness of the importance of innate immunity, the roles of natural killer (NK) cells in transplant rejection and antiviral and cancer immunity during immunosuppression have not been clearly defined.

Methods

To address this issue we have developed a quantitative assay of NK cell function that can be used on clinical samples and have studied the influence of immunosuppression on NK cell function. NK cell degranulation and intracellular interferon (IFN)-γ production were determined by flow cytometry of peripheral blood samples.

Results

Overnight ex vivo treatment of peripheral blood cells from healthy controls with ciclosporin or tacrolimus inhibited NK cell degranulation and IFN-γ production in a dose-dependent manner. A similar impairment of function was seen in NK cells from patients treated in vivo with calcineurin inhibitors. In the early post-transplant period, there was a variable reduction of NK cell counts after treatment with alemtuzumab and basiliximab.

Conclusions

The functional inhibition of NK cells in early transplant patients coincides with the period of maximum susceptibility to viral infections. The ability to assay NK cell function in clinical samples allows assessment of the impact of immunosuppression on these effector cells. This information may be helpful in guiding the titration of immunosuppression in the clinical setting.

Effects of Salmonella on spatial-temporal processes of jejunal development in chickens

To study effects of Salmonella enteritidis on morphological and functional changes in chicken jejunal development, we analysed gene expression profiles at seven points post-infection in 1-21 day-old broiler chickens. Nine clusters with different gene expression patterns were identified, and the genes in each cluster were further analyzed by a functional annotation clustering method (DAVID). Functional and morphological developmental processes dominated in all the nine clusters. Salmonella infection caused delays in several intestinal-morphological processes, whereas functional metabolic processes occurred in a similar spatial-temporal frame compared to normal jejunum development. A clear difference between normal developing- and Salmonella disturbed jejunum was the higher expression of genes involved in cell turn-over at early stages in the infected jejunum. Surprisingly, we found no clustered immune related processes in the infected birds. To compare the immunological processes between control and Salmonella infected chickens, the gene expression data was superimposed on known immunological KEGG pathways. Furthermore an in-depth analysis on the immune gene level was performed. As expected, we did find immunological processes in the Salmonella infected jejunum. Several of these processes could be verified by immunohistochemistry measurements of different immunological cell types. However, the well-ordered spatial-temporal development of the immune system, as observed in control non-infected animals, was completely abolished in the infected animals. Several immunological processes started much earlier in time, whereas other processes are disorganised. These data indicate that normal morphological and immunological development of jejunum is changed dramatically by a disturbance due to Salmonella infection. Due to the disturbance, the well-organized spatial-temporal development of morphological processes are delayed, those of the immunological development are scattered, whereas metabolic functional processes are almost not affected. This demonstrates the flexibility of developmental processes in the broiler chicken intestine.

HLA-F complex without peptide binds to MHC class I protein in the open conformer form

HLA-F has low levels of polymorphism in humans and is highly conserved among primates, suggesting a conserved function in the immune response. In this study, we probed the structure of HLA-F on the surface of B lymphoblastoid cell lines and activated lymphocytes by direct measurement of peptide binding to native HLA-F. Our findings suggested that HLA-F is expressed independently of bound peptide, at least in regard to peptide complexity profiles similar to those of either HLA-E or classical MHC class I (MHC-I). As a further probe of native HLA-F structure, we used a number of complementary approaches to explore the interactions of HLA-F with other molecules, at the cell surface, intracellularly, and in direct physical biochemical measurements. This analysis demonstrated that HLA-F surface expression was coincident with MHC-I H chain (HC) expression and was downregulated upon perturbation of MHC-I HC structure. It was further possible to directly demonstrate that MHC-I would interact with HLA-F only when in the form of an open conformer free of peptide and not as a trimeric complex. This interaction was directly observed by coimmunoprecipitation and by surface plasmon resonance and indirectly on the surface of cells through coincident tetramer and MHC-I HC colocalization. These data suggest that HLA-F is expressed independently of peptide and that a physical interaction specific to MHC-I HC plays a role in the function of MHC-I HC expression in activated lymphocytes.