HLA-G: an asthma gene on chromosome 6p

HLA-G in asthma and its potential as an effective therapeutic agent

OBJECTIVE

Asthma is a heterogeneous disease. Severity of asthma and sensitivity to medications vary across asthma subtypes. Human leukocyte antigen (HLA)-G has a wide range of functions in normal and pathological physiology. Due to its powerful immune function, HLA-G participates in the pathogenesis of different asthma phenotypes by regulating the activity and function of various immune cells. The mechanism of HLA-G in asthma is not fully clear, and there is no consensus on its mechanism in asthma. Further studies are needed to explore the role of HLA-G in different phenotypes of human asthma.

METHODS

Observational study.

RESULTS

HLA-G is an important immunomodulatory factor in asthma. Studies have found different levels of HLA-G in patients with different asthma subtypes and healthy controls, but other studies have come to the opposite conclusion.

CONCLUSION

We speculate that further study on the mechanism of HLA-G in asthma pheno-types may explain some of the contradictions in current studies. Findings should provide information regarding the potential of HLA-G as a novel target for asthma diagnosis and treatment.

HLA-G in Allergy: Does It Play an Immunoregulatory Role?

Allergy is an inflammatory process determined by a cascade of immune events characterized by T-helper 2 lymphocytes polarization leading to interleukin-4 upregulation, IgE secretion, and mast cell and eosinophil activation. HLA-G molecules, both in membrane-bound and in soluble forms, are known to play a key immunoregulatory role and their involvement in allergic diseases is supported by increasing literature data. HLA-G expression and secretion is specifically induced in peripheral blood mononuclear cells of allergic patients after in vitro incubation with the causal allergen. Elevated levels of soluble HLA-G molecules are detected in serum of patients with allergic rhinitis correlating with allergen-specific IgE levels, clinical severity, drug consumption and response to allergen-specific immunotherapy. HLA-G genetic polymorphisms confer susceptibility to allergic asthma development and high levels of soluble HLA-G molecules are found in plasma and bronchoalveolar lavage fluid of patients with allergic asthma correlating with allergen-specific IgE levels. Interestingly, allergic pregnant women have lower plasma sHLA-G levels than non-allergic women during the 3^rd trimester of pregnancy and at delivery. Finally, in allergic patients with atopic dermatitis HLA-G molecules are expressed by T cells, monocytes-macrophages and Langerhans cells infiltrating the dermis. Although at present is difficult to completely define the role of HLA-G molecules in allergic diseases, it may be suggested that they are specifically expressed and secreted by immune cells during the allergic reaction in an attempt to suppress allergic inflammation.

Future prospect of faecal microbiota transplantation as a potential therapy in asthma

There is convincing evidence from both human and animal studies suggesting that the gut microbiota plays an important role in regulating immune responses associated with the development of asthma. Certain intestinal microbial strains have been demonstrated to suppress or impair immune responsiveness in asthma experimental models, suggesting that specific species among gut commensal microbiota may play either a morbific or phylactic role in the progression of asthma. Evidence to date suggests that the intestinal microbiota represent fertile targets for prevention or management of asthma. The faecal microbiota transplantation (FMT) is a rather straightforward therapy that manipulates the human gastrointestinal (GI) microbiota, by which a healthy donor microbiota is transferred into an existing but disturbed microbial ecosystem. The FMT may therefore represent a therapeutic approach for asthma treatment in the foreseeable future. At present, FMT therapy for asthma is very limited and should be actively studied. Considerable efforts are needed to increase our knowledge in the field of FMT therapy for asthma. In this review, we aimed to provide several insights into the development of FMT therapy for asthma.

HLA-G Haplotypes Are Differentially Associated with Asthmatic Features

Human leukocyte antigen (HLA)-G, a HLA class Ib molecule, interacts with receptors on lymphocytes such as T cells, B cells, and natural killer cells to influence immune responses. Unlike classical HLA molecules, HLA-G expression is not found on all somatic cells, but restricted to tissue sites, including human bronchial epithelium cells (HBEC). Individual variation in HLA-G expression is linked to its genetic polymorphism and has been associated with many pathological situations such as asthma, which is characterized by epithelium abnormalities and inflammatory cell activation. Studies reported both higher and equivalent soluble HLA-G (sHLA-G) expression in different cohorts of asthmatic patients. In particular, we recently described impaired local expression of HLA-G and abnormal profiles for alternatively spliced isoforms in HBEC from asthmatic patients. sHLA-G dosage is challenging because of its many levels of polymorphism (dimerization, association with β2-microglobulin, and alternative splicing), thus many clinical studies focused on HLA-G single-nucleotide polymorphisms as predictive biomarkers, but few analyzed HLA-G haplotypes. Here, we aimed to characterize HLA-G haplotypes and describe their association with asthmatic clinical features and sHLA-G peripheral expression and to describe variations in transcription factor (TF) binding sites and alternative splicing sites. HLA-G haplotypes were differentially distributed in 330 healthy and 580 asthmatic individuals. Furthermore, HLA-G haplotypes were associated with asthmatic clinical features showed. However, we did not confirm an association between sHLA-G and genetic, biological, or clinical parameters. HLA-G haplotypes were phylogenetically split into distinct groups, with each group displaying particular variations in TF binding or RNA splicing sites that could reflect differential HLA-G qualitative or quantitative expression, with tissue-dependent specificities. Our results, based on a multicenter cohort, thus support the pertinence of HLA-G haplotypes as predictive genetic markers for asthma.

A polymorphism in HLA-G modifies statin benefit in asthma

Several reports have shown that statin treatment benefits patients with asthma, however inconsistent effects have been observed. The mir-152 family (148a, 148b and 152) has been implicated in asthma. These microRNAs suppress HLA-G expression, and rs1063320, a common SNP in the HLA-G 3’UTR which is associated with asthma risk, modulates miRNA binding. We report that statins up-regulate mir-148b and 152, and affect HLA-G expression in an rs1063320 dependent fashion. In addition, we found that individuals who carried the G minor allele of rs1063320 had reduced asthma related exacerbations (emergency department visits, hospitalizations or oral steroid use) compared to non-carriers (p=0.03) in statin users ascertained in the Personalized Medicine Research Project at the Marshfield Clinic (n=421). These findings support the hypothesis that rs1063320 modifies the effect of statin benefit in asthma, and thus may contribute to variation in statin efficacy for the management of this disease.

Maternal fecundity and asthma among offspring-is the risk programmed preconceptionally? Retrospective observational study

OBJECTIVE

To evaluate the association between maternal fecundity factors and time to pregnancy and risk of asthma in offspring.

DESIGN

Retrospective observational hospital-based birth cohort study.

SETTING

A university-based obstetrics and gynecology department.

PATIENT(S)

A total of 40,914 women, who delivered between 1989 and 2007, were linked with the register for asthma reimbursement (n = 2,577) for their offspring. Fecundity factors were recorded during pregnancy. Logistic regression analyses were used.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Asthma among offspring.

RESULT(S)

The risk of asthma was significantly increased if the mother had any infertility problems (adjusted odds ratio [adjusted OR] 1.39, 95% confidence interval [CI] 1.19-1.63), medical infertility treatment (aOR 1.43, 95% CI 1.13-1.80), or any infertility treatment (aOR 1.50, 95% CI 1.26-1.79). The risk of asthma among offspring was also higher among mothers who had more than two miscarriages (aOR 1.25, 95% CI 1.04-1.51) and time to pregnancy over 3 months (aOR 1.25, 95% CI 1.07-1.45).

CONCLUSION(S)

These findings suggest that maternal subfertility exposes offspring to an increased risk of asthma.

CLINICAL TRIAL REGISTRATION NUMBER

The study is registered in Kuopio University Hospital register (TUTKI): ID 5302448.

Perinatal gene-gene and gene-environment interactions on IgE production and asthma development

Atopic asthma is a complex disease associated with IgE-mediated immune reactions. Numerous genome-wide studies identified more than 100 genes in 22 chromosomes associated with atopic asthma, and different genetic backgrounds in different environments could modulate susceptibility to atopic asthma. Current knowledge emphasizes the effect of tobacco smoke on the development of childhood asthma. This suggests that asthma, although heritable, is significantly affected by gene-gene and gene-environment interactions. Evidence has recently shown that molecular mechanism of a complex disease may be limited to not only DNA sequence differences, but also gene-environmental interactions for epigenetic difference. This paper reviews and summarizes how gene-gene and gene-environment interactions affect IgE production and the development of atopic asthma in prenatal and childhood stages. Based on the mechanisms responsible for perinatal gene-environment interactions on IgE production and development of asthma, we formulate several potential strategies to prevent the development of asthma in the perinatal stage.

Different implications of paternal and maternal atopy for perinatal IgE production and asthma development

Asthma is a hereditary disease associated with IgE-mediated reaction. Whether maternal atopy and paternal atopy have different impacts on perinatal IgE production and asthma development remains unclear. This paper reviews and summarizes the effects of maternal and paternal atopy on the developmental aspects of IgE production and asthma. Maternal atopy affects both pre- and postnatal IgE production, whereas paternal atopy mainly affects the latter. Maternally transmitted genes GSTP1 and FceRI-beta are associated with lung function and allergic sensitization, respectively. In IgE production and asthma development, the maternal influence on gene-environment interaction is greater than paternal influence. Maternal, paternal, and/or postnatal environmental modulation of allergic responses have been linked to epigenetic mechanisms, which may be good targets for early prevention of asthma.

Allele frequencies of human leukocyte antigen-G in a Korean population

The human leukocyte antigen (HLA)-G is a nonclassical major histocompatibility complex class I molecule with relatively limited polymorphism. The differences in allele frequency according to ethnicity and country have not been studied enough, so far. Therefore, fundamental data including allele frequencies and polymorphism are needed for studies on immunological function of HLA-G in each population. We investigated allele frequencies and 14-bp polymorphism of the HLA-G in Koreans. HLA-G alleles and 14-bp polymorphisms were determined by sequence-based typing analysis of exons 2-4 and polymerase chain reaction of exon 8 in 200 unrelated individuals. Genotyping analysis identified eight different HLA-G alleles, which indicates that the Korean population presents limited HLA-G allelic polymorphism. HLA-G*01:01:01:01 and G*01:04:01 were frequent alleles (42.5% and 34.0%), and allelic frequencies were similar to those of other Asian populations. The 14-bp deletion alleles are higher (78%) in Koreans, although the frequencies of the 14-bp insertion/deletion polymorphism have been known to be nearly equal in many Caucasian populations. HLA-G*01:01:08 was reported strong linkage disequilibrium with the 14-bp deletion in a previous report; the same allele was accompanied with 14-bp insertion in our study. There are a few studies investigating allele frequencies, and most of them were studied before high-resolution method era. This is the first study regarding HLA-G genotypes in Korean, which were identified by high-resolution method. From this study, we identified HLA-G frequencies of a Korean population and expect this study could help further investigations for immunological and clinical implications of HLA-G.

Amniotic fluid soluble human leukocyte antigen-G in term and preterm parturition, and intra-amniotic infection/inflammation

OBJECTIVE

Circulating soluble human leukocyte antigen-G (sHLA-G) has been associated with pregnancy complications, and determination of sHLA-G concentrations in amniotic fluid (AF) has been reported in normal pregnancies. Our aim was to determine if the AF concentrations of sHLA-G change with advancing gestation, spontaneous labor at term, and in patients with spontaneous preterm labor (PTL) with intact membranes, as well as in those with preterm prelabor rupture of membranes (PROM), in the presence or absence of intra-amniotic infection/inflammation (IAI).

STUDY DESIGN

This cross-sectional study included the following groups: (1) mid-trimester (n = 55); (2) normal pregnancy at term with (n = 50) and without (n = 50) labor; (3) spontaneous PTL with intact membranes divided into: (a) PTL who delivered at term (n = 153); (b) PTL who delivered preterm without IAI (n = 108); and (c) PTL with IAI (n = 84); and (4) preterm PROM with (n = 46) and without (n = 44) IAI. sHLA-G concentrations were determined by ELISA. Non-parametric statistics were used for analysis.

RESULTS

(1) Among patients with PTL, the median AF sHLA-G concentration was higher in patients with IAI than in those without IAI or women that delivered at term (p < 0.001 for both comparisons); (2) Similarly, patients with preterm PROM and IAI had higher median AF sHLA-G concentrations than those without IAI (p = 0.004); (3) Among patients with PTL and delivery, those with histologic chorioamnionitis and/or funisitis had a higher median AF sHLA-G concentration than those without histologic inflammation (p < 0.001); and (4) The median AF sHLA-G concentration did not change with advancing gestational age.

CONCLUSIONS

AF sHLA-G concentrations are elevated in preterm parturition associated to IAI as well as in histologic chorioamnionitis. We propose that sHLA-G may participate in the regulation of the host immune response against intra-amniotic infection.

Significant evidence for linkage to chromosome 5q13 in a genome-wide scan for asthma in an extended pedigree resource

Asthma is a multifactorial disease with undetermined genetic factors. We performed a genome-wide scan to identify predisposition loci for asthma. The asthma phenotype consisted of physician-confirmed presence or absence of asthma symptoms. We analyzed 81 extended Utah pedigrees ranging from three to six generations, including 742 affected individuals, ranging from 2 to 40 per pedigree. We performed parametric multipoint linkage analyses with dominant and recessive models. Our analysis revealed genome-wide significant evidence of linkage to region 5q13 (log of the odds ratio (LOD)=3.8, recessive model), and suggestive evidence for linkage to region 6p21 (LOD=2.1, dominant model). Both the 5q13 and 6p21 regions indicated in these analyses have been previously identified as regions of interest in other genome-wide scans for asthma-related phenotypes. The evidence of linkage at the 5q13 region represents the first significant evidence for linkage on a genome-wide basis for this locus. Linked pedigrees localize the region to approximately between 92.3-105.5 Mb.

MicroRNA target site polymorphisms and human disease

MicroRNAs (miRNAs) are important regulators of eukaryotic gene expression. They have been implicated in a broad range of biological processes, and miRNA-related genetic alterations probably underlie more human diseases than currently appreciated. Several studies have identified genetic variants in miRNA target sites that are claimed to be associated with disorders ranging from Parkinson's disease to cancer. However, careful assessment of these studies indicates that very few provide a combination of rigorous genetic and functional evidence. We therefore suggest a set of concrete recommendations to guide future investigations. Specifically, we highlight the importance of unbiased association studies and follow-up functional experiments for providing a clearer picture of the extent to which microRNA target site variations are relevant in various human diseases.

Gene expression profiling of nasal polyps associated with chronic sinusitis and aspirin-sensitive asthma

OBJECTIVE

To identify genes whose expression is most characteristic of chronic rhinosinusitis and aspirin-sensitive asthma through genome-wide transcriptional profiling of nasal polyp tissue.

STUDY DESIGN

Prospective, controlled study conducted at a tertiary care institution.

METHODS

Thirty genome-wide expression microarrays were used to compare nasal polyp tissue from patients with chronic rhinosinusitis alone (CRS, n = 10) or chronic rhinosinusitis and a history of aspirin-sensitive asthma (ASA, n = 10) to normal sinonasal mucosa from patients who underwent surgery for non-sinus related conditions (controls, n = 10). Genes found to be most characteristic of each polyp phenotype, as determined from bioinformatic analyses, were validated using real-time quantitative polymerase chain reaction (RT-PCR) and immunohistochemistry in different patient sets.

RESULTS

The transcriptional signature of the control mucosa was distinctly different from that of either polyp phenotype. Genes most characteristic of the CRS phenotype included two upregulated genes--met proto-oncogene (MET) and protein phosphatase 1 regulatory subunit 9B (PPP1R9B)-and two downregulated genes--prolactin-induced protein (PIP) and zinc alpha2-glycoprotein (AZGP1). The gene most characteristic of the ASA phenotype was periostin (POSTN), which was upregulated relative to controls. Differences between the CRS and ASA phenotypes were associated with alterations in the 6p22, 22q13, and 1q23 chromosomal regions.

CONCLUSIONS

Nasal polyps appear to have characteristic transcriptional signatures compared to normal sinonasal mucosa. The five genes identified in this study likely play roles in the pathogenesis of polyps associated with CRS and ASA, and are therefore attractive targets for novel medical therapies for these common debilitating diseases.

HLA-G in the skin--friend or foe?

Skin is the largest organ of the human body that harbors a robust and versatile immune surveillance system. Whereas impaired immune function of the skin enables tumor growth, excessive immune activation results in different inflammatory diseases of the skin. HLA-G is a non-classical MHC class I molecule that was initially described to provide immunotolerogenic signals. In this context, HLA-G was mainly investigated as a mechanism that tumor cells employ to evade and inhibit host immune response. Expression of HLA-G in several inflammatory conditions in the skin implicated that the (dys)function of this molecule may also underlie excessive immune stimulation observed in these disorders. This review focuses on the functionality of HLA-G in the skin and summarizes available data obtained from studies performed in skin cancer and inflammatory dermatoses.

14 bp deletion polymorphism in the HLA-G gene is a risk factor for idiopathic dilated cardiomyopathy in a Chinese Han population

Human leukocyte antigen (HLA) has been reported to be associated with the pathogenesis of autoimmune-associated idiopathic dilated cardiomyopathy (IDC). However, the HLA-G in this context is limited. In the current study, a total of 117 IDC patients and age and sex matched 401 unrelated healthy controls in a Chinese Han population were HLA-G genotyped for the 14 bp insertion and deletion polymorphism. IDC patients showed markedly increased frequencies of -14 bp/-14 bp genotype [Pc = 0.00049, odds ratio (OR) = 2.17] and -14 bp alleles (Pc = 4.1 x 10(-5), OR = 1.97) when compared with healthy controls. Whereas the frequencies of +14 bp/+14 bp genotype (Pc = 0.0036, OR = 0.35) and +14 bp alleles (Pc = 4.1 x 10(-5), OR = 0.51) were significantly lower in IDC. These data, for the first time, indicated that 14 bp insertion/deletion polymorphism in HLA-G gene could be a genetic risk factor for the susceptibility to IDC.

HLA-G alleles and HLA-G 14 bp polymorphisms in a Brazilian population

Brazilians represent one of the most heterogeneous populations in the world as the result of five centuries of interethnic crosses. We investigated the polymorphism of the HLA-G locus in a Brazilian urban sample. HLA-G alleles were determined by SBT analysis of exons 2-4 and 8 in 103 unrelated individuals. The genotyping analysis identified 11 different HLA-G alleles, including the recently described G*010110 allele, and four new variants in this population. These data indicate that this Brazilian population presents high HLA-G allelic polymorphism, suggesting increased levels of intrapopulational genetic diversity that may be because of the admixed nature of the sample. This is the first study regarding HLA-G genotyping that was performed at such refined resolution level in this heterogeneous population.

New insights into the pathophysiology of gestational diabetes mellitus: possible role of human leukocyte antigen-G

Diabetes can develop in up to 10% of pregnant women who have not previously had the condition. This condition which usually begins in the second half of the pregnancy is called gestational diabetes mellitus (GDM). In most cases, all diabetic symptoms disappear following delivery. However, women with GDM have an increased risk of developing type 2 diabetes mellitus (DM) later in life, especially if they were overweight before the pregnancy. The cause of GDM is unknown. Although hormones present in the pregnancy, especially human placental lactogen, are thought to be responsible for the development of this condition, many questions remain to be answered. It is still not known why GDM develops in a subgroup of pregnant women. It may be possible that events leading to the development of GDM are triggered by an antigenic load which is the fetus itself. Human leukocyte antigen-G (HLA-G) expression that functions to protect the fetus from immune attack by down-regulating cytotoxic T cell responses to fetal trophoblast antigens is postulated to protect the islet cells of the pancreatic tissue also. HLA-G and nuclear factor-kappaB (NF-kappaB) interaction is suggested to be central in the events leading to GDM development. An analogy between the development of DM in some transplant patients and GDM development in a proportion of pregnancies is postulated, so that an antigenic load triggers the diabetogenic process. Further support of this hypothesis with new studies may lead to the possibility that recombinant HLA-G can be used for the prevention of diabetes in high risk patients.

The early-life origins of asthma

PURPOSE OF REVIEW

Inflammatory mediators produced from activated mast cells and T helper type 2 cells drive allergic inflammation. The pathways required for mast and T helper type 2 cell activation and the effects of their products are being defined in order to identify new therapeutics. We focus on recent findings on the chief inducer of mast cell activation, the IgE receptor-signaling cascade, and the development of new inhibitors of this pathway. We also summarize work that examines the molecular mechanisms utilized by the interleukin IL-4/13 receptors and characterizes therapeutic compounds that target these pathways.

RECENT FINDINGS

The tyrosine kinases Lyn, Fyn and Syk have complex roles in IgE receptor signaling. Biochemical analysis and gene expression profiling have shed light on both the positive and negative functions of these proteins and establish additional connections with downstream pathways. Syk inhibitors were identified that may prove useful as antiinflammatory agents. Progress has been made in characterizing how IL-4/13 interact with their cognate receptors that will aid in the design of inhibitors of these interactions.

SUMMARY

Recent studies have advanced our understanding of how the IgE receptor and IL-4/13 receptors function. This new knowledge may lead to the development of novel and highly specific inhibitors of allergic inflammation.

Asthma genetics 2006: the long and winding road to gene discovery

Asthma and atopy are complex phenotypes that are influenced by both genetic and environmental factors. A review of nearly 500 papers on disease association studies identified 25 genes that have been associated with an asthma or atopy phenotype in six or more populations. An additional 54 genes have been associated in 2-5 populations. Here, we discuss the methods that have been used to identify susceptibility genes for common diseases and overview the status of asthma genetic research. Finally, current challenges and future directions are discussed.

Genetic segregation of airway disease traits despite redundancy of calcium-activated chloride channel family members

Complex airway diseases such as asthma and chronic obstructive pulmonary disease exhibit stereotyped traits (especially airway hyperreactivity and mucous cell metaplasia) that are variably expressed in each patient. Here, we used a mouse model for virus-induced long-term expression of these traits to determine whether individual traits can be genetically segregated and thereby linked to separate determinants. We showed that an F2 intercross population derived from susceptible and nonsusceptible mouse strains can manifest individual phenotypic extremes that exhibit one or the other disease trait. Functional genomic analysis of these extremes further indicated that a member of the calcium-activated chloride channel (CLCA) gene family designated mClca3 was inducible with mucous cell metaplasia but not airway hyperreactivity. In confirmation of this finding, we found that mClca3 gene transfer to mouse airway epithelium was sufficient to induce mucous cell metaplasia but not airway hyperreactivity. However, newly developed mClca3(-/-) mice exhibited the same degree of mucous cell metaplasia and airway hyperreactivity as wild-type mice. Bioinformatic analysis of the Clca locus led to the identification of mClca5, and gene transfer indicated that mClca5 also selectively drives mucous cell metaplasia. Thus, in addition to the capacity of CLCA family members to exhibit diverse functional activities, there is also preserved function so that more than one family member mediates mucous cell metaplasia. Nonetheless, Clca expression appears to be a selective determinant of mucous cell metaplasia so that shared homologies between CLCA family members may still represent a useful target for focused therapeutic intervention in hypersecretory airway disease.