Extended tumour necrosis factor/HLA-DR haplotypes and asthma in an Australian population sample

Study of HLA class II loci reveals DQB1*03:03:02 as a risk factor for asthma in a Pakistani population

Asthma, a chronic inflammatory disorder of the lungs and airways, typically results from a combination of multiple environmental and genetic factors. Human leucocyte antigen (HLA) region on chromosome 6p21 encodes the most highly polymorphic loci in the human genome, encoding genes with central roles in the immune function where HLA loci are strongly associated with various immune-mediated diseases such as autoimmunity, allergies and infection. The alleles of HLA class II genes such as DRB1 and DQB1 are the key genetic markers in the development of asthma and have been extensively studied in different ethnicities of the world population. However, the genetic screening of HLA class II alleles and haplotypes in Pakistani asthmatics has not been studied so far. The aim of the present study was to screen the HLA class II DRB1 and DQB1 alleles in asthma cases and controls in a Pakistani population. Seven hundred and two healthy controls and asthma patients were genotyped for HLA class II by sequence-specific polymerase chain reaction assays. The HLA-DRB1 and HLA-DQB1 allele and haplotype frequencies were calculated, and their risk or protective association with asthma was determined. Two-locus haplotypes of DRB1 and DQB1 alleles were imputed using Arlequin version 3.1 software. The signals of association with asthma were stronger at the DQB1 locus as compared to DRB1. HLA DQB1*03:03:02 (odds ratio [OR] = 2.42, 95% confidence interval [CI] = 1.34-4.25) was significantly associated with an increased risk of asthma, as was the haplotype comprised allele DRB1*07:01-DQB1*03:03:02 (OR = 2.40, 95% CI = 1.25-4.62). In contrast, DQB1*06 (OR = 0.39, 95% CI = 0.22-0.70) and DQB1*06:02 (OR = 0.27, 95% CI = 0.10-0.71) emerged as protective alleles for asthma. Our data concludes that the HLA DQB1*03:03:02 allele was a risk allele for asthma, whereas two DQB1 alleles, DQB1*06 and DQB1*06:02, were associated with asthma protection. Our findings highlight a prominent role for HLA-DQB1 alleles in asthma pathogenesis in studied Pakistani cases. More studies, especially with a larger study cohort are needed to confirm the utility of HLA DQB1*03:03:02 as a predictive marker.

Association Between TNF-α-308, +489, -238 Polymorphism, and COPD Susceptibility: An Updated Meta-Analysis and Trial Sequential Analysis

The tumor necrosis factor alpha (TNF-α) polymorphism may play an important role in chronic obstructive pulmonary disease (COPD) susceptibility. However, the results are still inconclusive. Eligible studies were searched in Cochrane Library database, EMBASE, Pudmed, Web of science, China National Knowledge Infrastructure, and Wanfang database. Finally, a total of 27 case-control studies with 3473 COPD cases and 4935 controls were included in the present analysis. We also performed trial sequential analysis (TSA) to confirm our results. Overall, association between TNF-α-308G/A polymorphism and COPD susceptibility was identified in allelic model (A vs. G, OR = 1.21, 95%CI: 1.01-1.45, p = 0.04) when smoking status was not adjusted. In ethnicity subgroup analysis, we found that the TNF-α -308G/A polymorphism was associated to COPD among Asians (GA vs. GG, OR = 1.35, 95%CI: 1.04-1.77, p = 0.02) when smoking status was not adjusted. However, no significant association was found in Asian smokers or Caucasian smokers. In conclusion, our study suggest that TNF-α-308 GA genotype is related to COPD in the Asian population. In addition, the TNF-α+489G/A, - 238G/A variants do not increase the risk of COPD. Systematic Review Registration: https://www.crd.york.ac.uk/PROSPERO/, identifier CRD42021273980.

Potential Metabolic Biomarkers in Adult Asthmatics

Asthma is the most common chronic airway inflammation, with multiple phenotypes caused by complicated interactions of genetic, epigenetic, and environmental factors. To date, various determinants have been suggested for asthma pathogenesis by a new technology termed omics, including genomics, transcriptomics, proteomics, and metabolomics. In particular, the systematic analysis of all metabolites in a biological system, such as carbohydrates, amino acids, and lipids, has helped identify a novel pathway related to complex diseases. These metabolites are involved in the regulation of hypermethylation, response to hypoxia, and immune reactions in the pathogenesis of asthma. Among them, lipid metabolism has been suggested to be related to lung dysfunction in mild-to-moderate asthma. Sphingolipid metabolites are an important mediator contributing to airway inflammation in obese asthma and aspirin-exacerbated respiratory disease. Although how these molecular variants impact the disease has not been completely determined, identification of new causative factors may possibly lead to more-personalized and precise pathway-specific approaches for better diagnosis and treatment of asthma. In this review, perspectives of metabolites related to asthma and clinical implications have been highlighted according to various phenotypes.

Single Nucleotide and Copy-Number Variants in IL4 and IL13 Are Not Associated with Asthma Susceptibility or Inflammatory Markers: A Case-Control Study in a Mexican-Mestizo Population

BACKGROUND

Asthma is a complex and chronic inflammatory airway disease. Asthma's etiology is unknown; however, genetic and environmental factors could affect disease susceptibility. We designed a case-control study aimed to evaluate the role of single-nucleotide polymorphisms (SNP), and copy-number variants (CNV) in the IL4 and IL13 genes in asthma susceptibility and their participation in plasma cytokine levels depending on genotypes Methods: We include 486 subjects, divided into asthma patients (AP, n = 141) and clinically healthy subjects (CHS, n = 345). We genotyped three SNP, two in the IL4 and two in the IL13 gene; also, two CNVs in IL4. The IL-4, IL-13 and IgE plasma levels were quantified.

RESULTS

Biomass-burning smoke exposure was higher in the AP group compared to CHS (47.5% vs. 20.9%; p < 0.01, OR = 3.4). No statistical differences were found in the genetic association analysis. In both CNV, we only found the common allele. For the analysis of IL-4, IL-13, and IgE measures stratified by genotypes, no significant association or correlation was found.

CONCLUSION

In the Mexican-mestizo population, SNPs neither CNVs in IL4 nor IL13 are associated with asthma susceptibility or involved serum cytokine levels. Biomass-burning smoke is a risk factor in asthma susceptibility.

HLA and asthma phenotypes/endotypes: a review

Asthma is a complex chronic inflammatory disease of the airways caused by the interaction of genetic susceptibility with environmental influences. Genome-wide association studies (GWAS) represent the most powerful approach for asthma, that have identified several genes (e.g., IL18R1, IL33, SMAD3, ORMDL3, HLA-DQ and IL2RB loci). HLA super-locus is a genomic region in the chromosomal position 6p21. Since no gene can be considered as an asthma gene, able to reflect the complex etiology and the heterogeneity of the disease the terms 'phenotype' and more recently 'endotype' have been used. This review, according to literature availability, focuses on the relationship between human leukocyte antigens (HLA) region specifically the HLA class II genes and different asthma phenotypes/endotypes, such as allergic asthma/Th2 associated, occupational and aspirin-sensitive asthma. The most common HLA haplotypes in the different asthma phenotypes are HLA-DRB1in allergic asthma, HLA-DQB1in occupational asthma and HLA-DPB1 in aspirin-sensitive asthma. However, it is difficult to study the role of class II genes in vivo because of the heterogeneity of human population, the complexity of MHC, and the strong linkage disequilibrium among different class II genes. Despite the variation and the inconsistency of the HLA haplotypes and alleles in different types of asthma, the association between HLA class II genes and asthma has been demonstrated in the majority of studies.

Thymic stromal lymphopoietin: a promising therapeutic target for allergic diseases

Thymic stromal lymphopoietin (TSLP), an interleukin 7-like cytokine, can trigger dendritic cell (DC)-mediated T-helper type 2 (Th2) inflammatory responses. Recent evidence demonstrates that cytokines TSLP and OX40 (CD134)/OX40 ligand seem to be important players in the maintenance of Th2 memory pool in the pathogenesis of asthma. Accumulating data reveal that the pathogenic T cells involved in asthma are likely to be inflammatory Th2 cells. TSLP is involved in the development of asthma through crosstalk with nuclear factor NF-ĸB. Progression of skin fibrosis in atopic dermatitis occurs via TSLP/TSLP receptor. TSLP-mediated dermal inflammation aggravates experimental allergic asthma. Also, TSLP polymorphisms are associated with susceptibility to asthma, atopic dermatitis, and eczema herpeticum. These findings suggest a master switch of TSLP in the initiation of allergic and adaptive inflammation through innate pathways at the epithelial cell-DC interface. The TSLP pathway is therefore a promising target for immunotherapy of allergic diseases.

An assessment of the association between childhood asthma and HLA DRB1*03 using extended haplotype analysis

Ancestral haplotypes between human leukocyte antigen (HLA) class I and class II alleles are well-recognized in the literature. We previously published a positive association between the class II HLA allele DRB1*03 and the subsequent development of asthma in a retrospective cohort of 383 children. To refine this association, we investigated whether DRB1*03-specific haplotypes extending across the HLA are associated with asthma incidence. We found evidence of strong HLA DRB1*03-dependent linkage disequilibrium across the region, but no association between DRB1*03 ancestral haplotypes and childhood asthma. We did, however, observe a trend toward a positive association between HLA DRB1*03 and asthma by adding non-ancestral DRB1*03 positive haplotypes. Our results suggest that the role of the HLA DRB1*03 in asthma susceptibility is independent of ancestral-haplotype-mediated linkage disequilibrium.

A study of the TNF/LTA/LTB locus and susceptibility to severe malaria in highland papuan children and adults

BACKGROUND

Severe malaria (SM) syndromes caused by Plasmodium falciparum infection result in major morbidity and mortality each year. However, only a fraction of P. falciparum infections develop into SM, implicating host genetic factors as important determinants of disease outcome. Previous studies indicate that tumour necrosis factor (TNF) and lymphotoxin alpha (LTα) may be important for the development of cerebral malaria (CM) and other SM syndromes.

METHODS

An extensive analysis was conducted of single nucleotide polymorphisms (SNPs) in the TNF, LTA and LTB genes in highland Papuan children and adults, a population historically unexposed to malaria that has migrated to a malaria endemic region. Generated P-values for SNPs spanning the LTA/TNF/LTB locus were corrected for multiple testing of all the SNPs and haplotype blocks within the region tested through 10,000 permutations. A global P-value of < 0.05 was considered statistically significant.

RESULTS

No associations between SNPs in the TNF/LTA/LTB locus and susceptibility to SM in highland Papuan children and adults were found.

CONCLUSIONS

These results support the notion that unique selective pressure on the TNF/LTA/LTB locus in different populations has influenced the contribution of the gene products from this region to SM susceptibility.

Tumor necrosis factor-alpha in severe corticosteroid-refractory asthma

Tumor necrosis factor (TNF)-alpha is a proinflammatory cytokine. Blocking TNF-alpha has been demonstrated to be effective in various diseases, including both rheumatoid and psoriatic arthritis. There is evidence to show that levels of TNF-alpha are elevated in patients with severe asthma. TNF-alpha is involved in the initiation and perpetuation of the inflammatory process, epithelial damage and remodeling, and mucin hypersecretion. Furthermore, TNF-alpha polymorphism has also been reported in the asthmatic population. Based on the necessity for alternative treatments for asthmatics with severe disease and those who are particularly resistant to conventional asthma therapy, it has been shown that molecules targeted at blocking the effects of TNF-alpha probably constitute a considerable advance in the management of these difficult patients. This review focuses on the evidence of TNF-alpha axis upregulation in severe corticosteroid-refractory asthma, as well as the role of TNF-alpha inhibition and the adverse effects of treatment.

Obesity and asthma

Population-based studies have defined a significant, bidirectional, dose-dependent association between obesity and asthma. Obesity does not cause airflow obstruction, but can result in pulmonary restriction and a reduction in airway diameter, and that could contribute to airway hyper-responsiveness. Mouse models of asthma have demonstrated that obesity and adipokines can enhance airway hyper-responsiveness, airway inflammation, and allergic responses, but it is unclear whether obesity-associated inflammatory mechanisms are relevant in human asthma. Shared environmental and genetic factors are incompletely understood, but very likely to be relevant. Obese asthma appears to be a distinct and novel phenotype of asthma, associated with a reduction in lung volumes, lack of eosinophilic inflammation, altered response to asthma controller therapy, glucocorticoid resistance, and poor asthma control.

Tumor necrosis factor alpha -308 gene locus promoter polymorphism: an analysis of association with health and disease

Tumor necrosis factor-alpha (TNF-alpha) is a potent immunomediator and proinflammatory cytokine that has been implicated in the pathogenesis of a large number of human diseases. The location of its gene within major histocompatibility complex and biological activities has raised the possibility that polymorphisms within this locus may contribute to the pathogenesis of wide range of autoimmune and infectious diseases. For example, a bi-allelic single nucleotide substitution of G (TNFA1 allele) with A (TNFA2 allele) polymorphism at -308 nucleotides upstream from the transcription initiation site in the TNF-alpha promoter is associated with elevated TNF-alpha levels and disease susceptibilities. However, it is still unclear whether TNF-alpha -308 polymorphism plays a part in the disease process, in particular whether it could affect transcription factor binding and in turn influence TNF-alpha transcription and synthesis. Several studies have suggested that TNFA2 allele is significantly linked with the high TNF-alpha-producing autoimmune MHC haplotype HLA-A1, B8, DR3, with elevated serum TNF-alpha levels and a more severe outcome in diseases. This review discusses the genetics of the TNF-alpha -308 polymorphism in selected major diseases and evaluates its common role in health and disease.

Allergy and autoimmunity: parallels and dissimilarity: the yin and yang of immunopathology

The etiopathogenesis of allergy and autoimmune diseases is caused by genetic and acquired (environmental) factors, which might be common to both immunopathologies. Genetic factors play an important role in the development and process of immunopathological diseases. Several studies suggest a close relation between gene polymorphism of HLA and cytokines and development of autoimmunity and allergy. Certain gene polymorphisms act as risk or as protective factors. The infection also plays an important role in the induction of allergy and autoimmunity--as a trigger or as a protective factor. Moreover, similar clinical manifestations of both immunopathologies could result in diagnostic problems. This review summarizes the linkage of mechanisms of etiopathogenesis, clinical manifestations and therapeutic strategy between allergic and autoimmune diseases.

Asthma genetics: from linear to multifactorial approaches

Asthma risk has a clear hereditary component but, unexpectedly, the majority of reported associations between genetic variants and asthma have not been consistently replicated across studies. Methodological flaws have been indicated as a possible explanation for these inconsistencies. However, an alternative explanation is that the effects of genetic variants depend on other factors whose frequency and distribution vary, both across individuals and across populations. Within this framework, we review recent advances in asthma genetics and conclude that a paradigm shift is needed, because a static model in which the DNA sequence is associated with disease risk in a linear fashion fails to consider the interdependence of the diverse components of asthma risk. We propose an integrated approach, linking sequence variation to specific phenotypic manifestations of the disease by taking into account concurrent influences from biological systems and environmental factors that interact within specific developmental windows of opportunity.

Combined effect of tumour necrosis factor-alpha and interleukin-13 polymorphisms on bronchial hyperresponsiveness in Korean children with asthma

BACKGROUND

TNF-alpha and IL-13, two pivotal pro-inflammatory cytokines, are increased in asthmatic airways and may be linked to asthma susceptibility and/or bronchial hyperresponsiveness (BHR).

OBJECTIVE

We investigated the association between the TNF-alpha-308G/A polymorphism and asthma susceptibility or asthma-related phenotypes in Korean children with asthma, and tested for a combined effect with IL-13 polymorphisms.

METHODS

Asthmatic children (n=719) and non-atopic healthy control children (n=243) were evaluated for asthma phenotypes including total serum IgE and BHR to methacholine. Genotypes were determined by PCR-restriction fragment length polymorphism analysis.

RESULTS

The allele frequency of TNF-alpha-308A in asthmatics (14.1%) was higher than that in control children [8.7%, odds ratio (OR) 1.72, 95% confidence interval (CI) 1.05-2.82]. Significantly lower PC(20) values were found in asthmatic children carrying one or two copies of the TNF-alpha risk allele (-308A) vs. those homozygous for the common allele (P=0.026). Combined analysis revealed that atopic asthmatic children co-inherited the risk alleles of TNF-alpha-308G/A and IL-13 +2044G/A more frequently than control children (aOR 1.91, 95% CI 1.00-3.65), and asthmatic children co-inheriting both risk alleles had significantly lower PC(20) values vs. asthmatic children homozygous for the common alleles (P=0.024).

CONCLUSION

The TNF-alpha promoter polymorphism (-308G/A) may be associated with asthma susceptibility and BHR in Korean children with asthma. In addition, there appears to be a synergistic effect between the TNF-alpha promoter polymorphism and an IL-13 coding region polymorphism in terms of asthma susceptibility and BHR in this population.

The asthma-obesity link in childhood: open questions, complex evidence, a few answers only

Obesity and asthma are public health priorities in developed countries. Genes which may contribute to the control of both conditions include those encoding for the beta2-adrenergic receptor, tumour necrosis factor-alpha (TNF-alpha) and the insulin-like growth factor 1 (IGF-1). Prospective studies consistently supported a link between obesity and reported wheezing or asthma diagnosis in children. However, there are still no clear explanations for such a link. On one hand, overweight asthmatic children may perceive their asthma as worse. On the other hand, atopic sensitization and bronchial hyper-reactivity do not explain the observed associations. After puberty, the association between asthma and obesity tends to be stronger in girls than in boys. It is conceivable that severe obesity in adolescent females may aggravate asthma through mechanisms different from those linking prepubertal obesity to unremitting asthma in males. Future studies should therefore address multiple age- and gender-specific hypotheses about the mechanisms that link obesity to asthma throughout childhood.

HLA Dr-Dq haplotypes and the TNFA-308 polymorphism: associations with asthma and allergy

BACKGROUND

The HLA (human leukocyte antigen) class II genes DQB1 and DRB1 and the Tumor Necrosis Factor alpha gene (TNFA) within the HLA complex (chromosome 6p21) have been associated with asthma and allergy. Due to the strong linkage disequilibrium characterizing this complex and the multiple asthma/allergy expressions, we aimed to determine which of these genes were primarily involved in specific asthma/allergy traits.

METHODS

The DRB1-DQB1 alleles and TNFA-308 polymorphism were genotyped in 959 children from the Environment and Childhood Asthma study and analyzed for possible associations with allergic and non-allergic asthma (with/without at least one positive skin prick test for allergens) and specific allergic sensitization, as well as bronchial hyperresponsiveness and total IgE, using both allele and extended haplotype analyses.

RESULTS

Different genes within the HLA complex were associated with separate asthma and allergy traits. Nonallergic asthma was associated with both the TNFA-308A allele [Odds ratio (OR) 1.7 (1.3-2.3)] and DRB1 03 allele [OR 1.6(1-2.6)], but extended DRB1 03-TNFA-308 haplotype analysis suggested that the DRB1-DQB1 association was secondary to linkage disequilibrium with the TNFA-308 polymorphism. Allergies were associated with HLA class II alleles only; birch sensitization with DQB1 0603-DRB1 13 [OR 2.3 (1.4-4.0)] and mugwort sensitization with DQB1 0609-DRB1 13 [OR 7.1 (1.9-27.0)] and DQB1 0501-DRB1 01 [OR 2.0 (1.0-4.0)].

CONCLUSIONS

Our data suggests that asthma is not associated with DRB1 or DQB1 but rather TNFA or a gene(s) in linkage disequilibrium, while sensitization to specific allergens is associated with particular alleles at the DQ and/or DR loci. A novel association between DQB1 0603-DRB1 13 and birch allergy is identified.

[Asthma genetic factors]

Asthma is a chronic inflammatory airways disease, with a rising prevalence, particularly in childhood, and is considered an important public health problem. Its familial transmission is recognised, while the description and identification of the genes implicated in this disease are a challenge. In this revision paper the authors give a comprehensive explanation of the associated genes as well as the laboratorial methods that allow their identification.

Polymorphisms in the IL-4, IL-4 receptor alpha chain, TNF-alpha, and lymphotoxin-alpha genes and risk of asthma in Hong Kong Chinese adults

BACKGROUND

Susceptibility to the development of asthma and other atopic diseases is known to be associated with genetic components. However, association studies with interleukin-4 (IL-4), IL-4 receptor alpha subunit (IL-4R alpha), tumor necrosis factor-alpha (TNF-alpha) and lymphotoxin-alpha (LT-alpha) genes were inconclusive, as both positive and negative results were obtained in several populations studied. We aimed to investigate the association of the polymorphisms for IL-4 (C-589T), IL-4R alpha (Gln576Arg), TNF-alpha (G-308A) and LT-alpha (A252G) genes as candidates and asthma in adult Hong Kong Chinese population.

METHODS

The association study was conducted in an age- and smoking status-matched case-control design in asthma patients (n = 292) and healthy controls (n = 292) using polymerase chain reaction and restriction fragment length polymorphism.

RESULTS

No significant differences were found in allele and genotype frequencies of all four genes between patients and controls. After stratification by atopic status, the heterozygous AG genotype of LT-alpha (A252G) was found to increase risk of asthma in atopic population [odds ratio (OR) = 2.00, 95% CI 1.09-3.67, p = 0.024]. When stratified by smoking status, we found increased risk of asthma with subjects carrying the heterozygous AG and homozygous GG genotypes of LT-alpha in ever-smokers (OR = 2.73, 95% CI 1.11-6.69, p = 0.028 for heterozygotes; OR = 3.34, 95% CI 1.16-9.62, p = 0.026 for homozygotes).

CONCLUSION

Our results suggest that the variability of LT-alpha genotypes may have potential implications for individual susceptibility to asthma in atopic or in ever-smoking Chinese adults in Hong Kong.

Association of TNF-alpha genetic polymorphism with HLA DPB1*0301

BACKGROUND

We speculated TNF-alpha can be one of candidate gene for aspirin-intolerant asthma (AIA) because TNF-alpha is pro-inflammatory cytokine and known to be increased level in asthmatic airways. In addition, genetic interaction between TNF-alpha and human antigen leucocyte (HLA) DPB1*0301, which is a strong genetic marker for AIA, was examined for its close location within chromosome 6.

METHOD

To investigate genetic association of TNF-alpha with an AIA phenotype, three study groups (163 patients with AIA, 197 patients with aspirin-tolerant asthma (ATA), 257 normal control subjects) were enrolled. Single nucleotide polymorphisms (SNPs) were genotyped using a single-base extension method and HLA DPB1 genotyping was determined by high-throughput sequencing method.

RESULTS

All five SNPs of TNF-alpha were tested; there were no significant differences in allele and genotype frequencies among the three groups. However, significant association between TNF-alpha-308G>A polymorphism and atopy status was noted (P<0.05). Gene to gene interaction between TNF-alpha-1031T>C (or -863C>A or -857C>A) and HLA DPB1*0301could synergistically increase the susceptibility to AIA with odds ratio (OR) to 7.738 (or OR=8.184 for -863C>A, OR=7.500 for -857C>T, P<0.001, respectively).

CONCLUSION

TNF-alpha promoter polymorphism may significantly increase susceptibility to AIA by gene-to-gene interaction with HLA DPB1*0301.

Association of tumor necrosis factor-alpha -308G>A polymorphism with IgE-mediated allergy to betalactams in an Italian population

Tumor necrosis factor-alpha (TNF-alpha) is released from mast cells via an immunoglobulin E (IgE)-dependent mechanism. The variant G>A at -308 of TNFA is part of an extended haplotype HLA-A1-B8-DR3-DQ2 and influences the gene expression. We evaluated this variant in relation to IgE-mediated reactions to betalactams, in 427 subjects, including 167 cases and 260 age- and gender-paired controls. TNFA GG genotype was a significant independent predictor of the primary risk of betalactam allergy, concurrently with total IgE level, with an age- and sex-adjusted odds ratio estimated at 2.45 (95% confidence interval: 1.18-5.08, P=0.0163). Cases with -308AA genotype had a higher serum level of specific IgE than those with -308GA/GG genotype, with median levels (relative units) of 4.6 (inter-quartiles: 3.9-10.6) and 2.2 (1.4-4.3), respectively (P=0.0046). In conclusion, our results suggest an ambivalent influence of a genetic determinant of pro-inflammatory pathways on IgE-mediated hypersensitivity to betalactams.

Parental smoking modifies the relation between genetic variation in tumor necrosis factor-alpha (TNF) and childhood asthma

BACKGROUND

Polymorphisms in the proinflammatory cytokine genes tumor necrosis factor-alpha (TNF) and lymphotoxin-alpha (LTA, also called TNF-beta) have been associated with asthma and atopy in some studies. Parental smoking is a consistent risk factor for childhood asthma. Secondhand smoke and ozone both stimulate TNF production.

OBJECTIVES

Our goal was to investigate whether genetic variation in TNF and LTA is associated with asthma and atopy and whether the association is modified by parental smoking in a Mexican population with high ozone exposure.

METHODS

We genotyped six tagging single nucleotide polymorphisms (SNPs) in TNF and LTA, including functional variants, in 596 nuclear families consisting of asthmatics 4-17 years of age and their parents in Mexico City. Atopy was determined by skin prick tests.

RESULTS

The A allele of the TNF-308 SNP was associated with increased risk of asthma [relative risk (RR) = 1.54; 95% confidence interval (CI), 1.04-2.28], especially among children of non-smoking parents (RR = 2.06; 95% CI, 1.19-3.55; p for interaction = 0.09). Similarly, the A allele of the TNF-238 SNP was associated with increased asthma risk among children of nonsmoking parents (RR = 2.21; 95% CI, 1.14-4.30; p for interaction = 0.01). LTA SNPs were not associated with asthma. Haplotype analyses reflected the single SNP findings in magnitude and direction. TNF and LTA SNPs were not associated with the degree of atopy.

CONCLUSIONS

Our results suggest that genetic variation in TNF may contribute to childhood asthma and that associations may be modified by parental smoking.

TNF-alpha (-308 G/A) and CD14 (-159T/C) polymorphisms in the bronchial responsiveness of Korean children with asthma

BACKGROUND

TNF-alpha is a pivotal proinflammatory cytokine increased in asthmatic airways. The TNF-alpha gene family might be linked to asthma or bronchial hyperresponsiveness (BHR), and TNF-alpha production might be modulated by CD14(+) cells.

OBJECTIVE

We investigated the association between asthma susceptibility or asthma-related phenotypes and TNF-alpha (-308G/A) polymorphism and examined the combined effect with CD14 (-159T/C) polymorphism in Korean children.

METHODS

Asthmatic (n = 788) and control (n = 153) children were evaluated for asthma phenotypes. Genotypes were determined by using the single-base extension method and PCR-restriction fragment length polymorphism.

RESULTS

There was no difference between asthmatic children and control subjects in terms of the allele frequencies of TNF-alpha (-308G/A) and CD14 (-159T/C). Significantly lower PC(20) values were seen in asthmatic (P = .016) children with the TNF-alpha risk allele (-308A). Higher frequencies of 1 or 2 copies of the risk allele were found in asthmatic children with moderate-to-severe BHR to methacholine and exercise compared with control children (adjusted odds ratio of 2.57 [95% CI, 1.30-5.08] and adjusted odds ratio of 2.04 [95% CI 0.99-4.20], respectively). In addition, asthmatic children with risk alleles at both loci had significantly greater BHR than those homozygous for the common alleles (P = .018).

CONCLUSION

The TNF-alpha promoter polymorphism (-308G/A) might be associated with severe BHR in Korean children with asthma. In addition, these children show a synergistic effect between the TNF-alpha promoter (-308A) and CD14 promoter (-159C) polymorphisms in terms of BHR.

CLINICAL IMPLICATIONS

The TNF-alpha polymorphism might be a disease-modifying gene in asthma and modulated by the CD14 gene.

Haplotype analysis of a 100 kb region spanning TNF-LTA identifies a polymorphism in the LTA promoter region that is associated with atopic asthma susceptibility in Japan

BACKGROUND

The tumour necrosis factor (TNF) gene family, which includes TNF, LTA, and LTB, is located consecutively on human chromosome 6p21 region, which has been linked to asthma by several genome-wide screens. (LTA, lymphotoxin-alpha; LTB, lymphotoxin-beta).

OBJECTIVE

The aim of the present study was to determine whether genes on 6q21 are related to development of atopic asthma. Methods We screened for mutations in the coding and promoter regions of genes in the TNF-LTA region, including BAT1, NFKBIL1, LTA, TNF, LTB, AIF, and BAT2, and conducted a transmission disequilibrium test of 41 polymorphisms in 137 families identified through pro-bands with childhood-onset atopic asthma. (BAT1, HLA-B-associated transcript 1; NFKBIL1, nuclear factor of kappa light polypeptide gene enhancer in B cells inhibitor-like 1; AIF, allograft inflammatory factor 1).

RESULTS

Haplotypes of the LTA/TNF linkage disequilibrium block were associated significantly with asthma (global P=0.0097). Transmission patterns of the common haplotypes to asthmatic offspring were predicted by a single-nucleotide polymorphism in the LTA promoter region. The G allele of the LTA-753G/A polymorphism was transmitted preferentially to asthma-affected individuals (P=0.001). Luciferase reporter assays with constructs containing the 5' and 3' flanking regions of the LTA gene showed 30-50% lower transcriptional activity when the -753A allele was present than that of other haplotypes.

CONCLUSION

Our results suggest that LTA is one of the genes that contributes to susceptibility to atopic asthma, and that the association of the TNF/LTA haplotypes to asthma may be defined by the polymorphism in the LTA promoter region in the Japanese population.

Obesity and asthma

Asthma and obesity are prevalent disorders, each with a significant public health impact, and a large and growing body of literature suggests an association between the two. The systemic inflammatory milieu in obesity leads to metabolic and cardiovascular complications, but whether this environment alters asthma risk or phenotype is not yet known. Animal experiments have evaluated the effects of leptin and obesity on airway inflammation in response to both allergic and nonallergic exposures and suggest that airway inflammatory response is enhanced by both endogenous and exogenous leptin. Cross-sectional and prospective cohort studies of humans have shown a modest overall increase in asthma incidence and prevalence in the obese, although body mass index does not appear be a significant modifier of asthma severity. Studying the obesity-asthma relationship in large cohorts, in which self-reports are frequently used to ascertain the diagnosis of asthma, has been complicated by alterations in pulmonary physiology caused by obesity, which may lead to dyspnea or other respiratory symptoms but do not fulfill accepted physiologic criteria for asthma. Recent investigations toward elucidating a shared genetic basis for these two disorders have identified polymorphisms in specific regions of chromosomes 5q, 6p, 11q13, and 12q, each of which contains one or more genes encoding receptors relevant to asthma, inflammation, and metabolic disorders, including the beta(2)-adrenergic receptor gene ADRB2 and the glucocorticoid receptor gene NR3C1. Further research is warranted to synthesize these disparate observations into a cohesive understanding of the relationship between obesity and asthma.

Association between polymorphism of tumour necrosis factor alpha-308 gene promoter and asthma: a meta-analysis

BACKGROUND

Asthma is a complex polygenic disease in which gene-environment interactions are important. The gene encoding tumour necrosis factor alpha (TNFalpha) is one of several candidate loci for asthma pathogenesis and is highly polymorphic. A number of studies have investigated the polymorphism of TNFalpha-308 gene promoter (substitution G-->A, designated as TNF1 and TNF2) in relation to asthma susceptibility in different populations. However, the results of individual studies have been inconsistent.

METHODS

To address the inconsistent findings in studies of the association of the polymorphism of TNFalpha-308 gene promoter with susceptibility to asthma, a systematic review was undertaken of the published data and a meta-analysis was performed. The MEDLINE database was searched for case-control studies published in English language journals from 1966 to October 2005. Data were extracted using standardised forms and pooled odds ratios (ORs) with 95% confidence intervals (CIs) were calculated.

RESULTS

Fifteen eligible studies, comprising 2409 patients with asthma and 3266 controls, were included in the meta-analysis. Using the random effects model, the pooled result showed that the TNF2 allele is associated with overall susceptibility to asthma (OR 1.37, 95% CI 1.02 to 1.84, p=0.04). The ORs for asthma susceptibility in TNF2 homozygote individuals were significantly increased at 2.01 (95% CI 1.26 to 3.20, p=0.009) and 1.51 (95% CI 1.02 to 2.22, p=0.041) compared with TNF1 homozygotes and TNF2/1 heterozygotes, respectively. In addition, the pooled OR for asthma risk in TNF2/1 heterozygotes was also significantly higher than that in TNF1/1 homozygotes (OR 1.47, 95% CI 1.01 to 2.13, p=0.045).

CONCLUSIONS

The TNF2 allele confers a significant risk for developing asthma. A large scale case-control study is needed to clarify the functional effect of the polymorphism of the TNFalpha gene in the pathogenesis of asthma.

Associations of tumor necrosis factor G-308A with childhood asthma and wheezing

RATIONALE

Tumor necrosis factor (TNF) mediates a spectrum of airway inflammatory responses, including those to air pollutants, and is an asthma candidate gene. One TNF promoter variant (G-308A) affects expression of TNF and has been associated with inflammatory diseases; however, studies of asthma have been inconsistent. Because ozone produces oxidative stress, increased airway TNF, and inflammation, the associations of the -308 TNF polymorphism with asthma may vary by ozone exposure and variants of oxidant defense genes glutathione-S-transferase (GST) M1 and GSTP1.

OBJECTIVES

To investigate the association of TNF G-308A with asthma and wheezing and to determine whether these associations vary with ozone exposure and GSTM1 and GSTP1 genotype.

METHODS

We studied associations of TNF-308 genotype with lifetime and current wheezing and asthma among 3,699 children in the Children's Health Study. We examined differences in associations with community ozone and by GSTM1 null and GSTP1 105 Ile/Val (A105G) genotype.

RESULTS

Children with TNF-308 GG had decreased risk of asthma (odds ratio, 0.8; 95% confidence interval, 0.7-0.9) and lifetime wheezing (odds ratio, 0.8; 95% confidence interval, 0.7-0.9). The protective effects of GG genotype on wheezing outcomes were of greater magnitude in lower compared with higher ozone communities. These findings were replicated in the two cohorts of fourth-grade children recruited in 1993 and 1996. The reduction of the protective effect from the -308 GG genotype with higher ozone exposure was most marked in the GSTM1 null and GSTP1 Ile/Ile groups.

CONCLUSIONS

The TNF-308 GG genotype may have a protective role in asthma pathogenesis, depending on airway oxidative stress levels.

TNF-alpha as a promising therapeutic target in chronic asthma: a lesson from rheumatoid arthritis

TNF-alpha (tumour necrosis factor-alpha) is known to play a critical role in the pathogenic mechanisms of a number of chronic inflammatory diseases, including RA (rheumatoid arthritis), Crohn's disease and psoriasis. The notion that TNF-alpha is released in allergic responses from both mast cells and macrophages via IgE-dependent mechanisms, the demonstration that elevated levels of TNF-alpha are frequently observed in bronchoalveolar fluid of asthmatic subjects undergoing allergen challenge and the results from exposure studies of TNF-alpha in vivo showing increases in airway responsiveness in both normal and asthmatic subjects emphasize the importance of TNF-alpha in the initiation of allergic asthmatic airway inflammation and the generation of airway hyper-responsiveness. Drugs targeting TNF-alpha have been developed to neutralize the deleterious effects of this inflammatory cytokine and have proved to be safe and effective in the treatment of patients with RA, Crohn's disease and psoriasis refractory to conventional treatments. Biological therapies blocking TNF-alpha are likely to constitute a considerable advance in the management of those difficult cases of asthma that are particularly resistant to typical treatment modalities. In this review article, we intend to address the potential role of TNF-alpha in asthma and to put forward the idea that drugs that have been developed to neutralize the deleterious effects of TNF-alpha may also be useful in the management of chronic severe asthma.

Extended haplotype in the tumor necrosis factor gene cluster is associated with asthma and asthma-related phenotypes

RATIONALE

Tumor necrosis factor is a proinflammatory cytokine found in increased concentrations in asthmatic airways. The TNF-alpha (TNF) and lymphotoxin-alpha (LTA) genes belong to the TNF gene superfamily located within the human major histocompatibility complex on chromosome 6p in a region repeatedly linked to asthma. The TNF position -308 and LTA NcoI polymorphisms are believed to influence TNF transcription and secretion, respectively.

OBJECTIVES

This study sought to determine whether polymorphisms in TNF or LTA, or in TNF-LTA haplotypes, are associated with asthma and asthma phenotypes.

METHODS

We genotyped the TNF -308 and LTA NcoI polymorphisms, and two other haplotype-tagging polymorphisms in the TNF and LTA genes, in 708 children with mild to moderate asthma enrolled in the Childhood Asthma Management Program and in their parents. Using an extension of the family-based association tests in the PBAT program, each polymorphism was tested for association with asthma, age at onset of asthma, and time series data on baseline FEV(1) % predicted, postbronchodilator FEV(1) % predicted, body mass index, and log of PC(20).

MEASUREMENTS AND MAIN RESULTS

Although no associations were found for the individual single-nucleotide polymorphisms, the haplotype analysis found the LTA NcoI_G/LTA 4371T/TNF -308G/TNF 1078G haplotype to be associated with asthma and with all five phenotype groups.

CONCLUSIONS

We conclude that it is unlikely that the TNF -308 or LTA NcoI polymorphisms influence asthma susceptibility individually, but that this haplotype of variants may be functional or may be in linkage disequilibrium with other functional single-nucleotide polymorphisms.

Effect of tumor necrosis factor antagonism on allergen-mediated asthmatic airway inflammation

OBJECTIVE

To assess whether tumor necrosis factor (TNF) antagonism can attenuate eosinophilic airway inflammation in patients with mild-to-moderate allergic asthma.

DESIGN

Randomized, double-blind, placebo-controlled trial.

SETTING

National Institutes of Health (NIH) Clinical Center.

PATIENTS

Twenty-six patients with mild-to-moderate allergic asthma, receiving only inhaled beta-2-agonists, who demonstrated both an early and late phase response to inhalational allergen challenge.

INTERVENTION

Injection of a soluble TNF receptor (TNFR:Fc, etanercept, Enbrel) or placebo, 25mg subcutaneously, twice weekly for 2 weeks, followed by a bronchoscopic segmental allergen challenge.

MEASUREMENTS

The primary outcome measure was whether TNFR:Fc can access the lung and inhibit TNF bioactivity. Secondary outcome measures included pulmonary eosinophilia, Th2-type cytokines, and airway hyperresponsiveness.

RESULTS

Anti-TNF therapy was associated with transient hemiplegia in one patient, which resulted in suspension of the study. Data from the 21 participants who completed the study were analyzed. Following treatment, patients receiving anti-TNF therapy had significantly increased TNFR2 levels in epithelial lining fluid (ELF) (P<0.001), consistent with delivery of TNFR:Fc to the lung. TNF antagonism did not attenuate pulmonary eosinophilia and was associated with an increase in ELF IL-4 levels (P=0.033) at 24h following segmental allergen challenge. TNF antagonism was not associated with a change in airway hyperresponsiveness to methacholine.

CONCLUSIONS

TNF antagonism may not be effective for preventing allergen-mediated eosinophilic airway inflammation in mild-to-moderate asthmatics. Transient hemiplegia, which may mimic an evolving stroke, may be a potential toxicity of anti-TNF therapy.

Ole e 2 and Ole e 10: new clinical aspects and genetic restrictions in olive pollen allergy

BACKGROUND

The clinical characteristics in olive pollen allergy are dependent on the antigenic load, the allergens profile, and the genetic restrictions. Our objective was to determine specific response pattern in Ole e 2 and Ole e 10 sensitization at those levels.

METHODS

We studied 146 patients with seasonal rhinitis and/or asthma and positive prick test to Olea europaea pollen. IgE against Ole e 2 and Ole e 10 were detected by skin prick test and ELISA. HLA-DRB1 and HLA-DQB1 loci were typed by polymerase chain reaction sequence-specific primers method.

RESULTS

A total of 102 (69.9%) and 79 (54.0%) patients showed significant IgE antibody response against Ole e 2 and Ole e 10, respectively. There was a significant association between Ole e 2 (OR 2.2, P = 0.04) and Ole e 10 reactivities (OR 2.8, P = 0.007) with asthma. In addition, total and specific IgE antibody levels significantly correlated with asthma (P < 0.05). Patients who reacted to both allergens reached the highest asthma risk factor (OR 4.3, P = 0.002). Phenotypic frequency of DR7 (OR 5.4, Pc = 0.003) and DQ2 (OR 3.6, Pc = 0.02) were increased in positive Ole e 2 patients compared with control subjects. DR2(15) phenotypic frequency was significantly increased (OR 5.6, Pc = 0.02) in positive Ole e 10 patients compared with control subjects.

CONCLUSIONS

Our data suggest an association of Ole e 2 and Ole e 10 with bronchial asthma. Also, we found a genetic control of Ole e 2 and Ole e 10 IgE-specific responses that could be relevant to clinical disease in olive pollen allergy.

Is there a future for TNF promoter polymorphisms?

The in vitro study of TNF promoter polymorphism (SNP) function was stimulated by the numerous case-control (association) studies of the polymorphisms in relation to human disease and the appearance of several studies claiming to show a functional role for these SNPs provided a further impetus to researchers interested in the role of TNF in their disease of interest. In this review we consider case-control studies, concentrating on the autoimmune and inflammatory diseases rheumatoid arthritis, multiple sclerosis, ankylosing spondylitis, and asthma, and on infectious diseases including malaria, hepatitis B and C infection, leprosy and sepsis/septic shock. We also review the available evidence on the functional role of the various TNF promoter polymorphisms. In general, case-control studies have produced mixed results, with little consensus in most cases on whether any TNF polymorphisms are actually associated with disease, although results have been more consistent in the case of infectious diseases, particularly malaria. Functional studies have also produced mixed results but recent work suggests that the much studied -308G/A polymorphism is not functional, while the function of other TNF polymorphisms remains controversial. Studies of the TNF region are increasingly using extended haplotypes that can better capture the variation of the MHC region.

Gene-gene synergistic effect on atopic asthma: tumour necrosis factor-alpha-308 and lymphotoxin-alpha-NcoI in Taiwan's children

BACKGROUND

Asthma is now known to be an inflammatory response caused by the release of inflammatory mediators and cytokines. Tumour necrosis factor (TNF) is a potent cytokine in the inflammation response of the airway, and the polymorphisms of TNF genes have been associated with asthma.

OBJECTIVE

This study investigated two variants, TNF-alpha-308*2 and lymphotoxin (LT)-alpha-NcoI*1, which may predispose individuals to asthma and atopy pathogenesis.

METHODS

PCR-based assays were performed to determine LT-alpha-NcoI*1 and TNF-alpha-308*2 genotypes among our subjects, with 128 atopic asthmatics and 51 non-atopic asthmatics, 55 atopic controls, and 78 non-atopic controls in this genetic case-control study.

RESULTS

The TNF-alpha-308*2 polymorphism increased in subjects with atopic asthma vs. non-atopic controls after adjusting for age distribution (adjusted odds ratios, AOR=2.73, 95% confidence interval, CI=1.16-6.64), but was not associated with non-atopic asthma (AOR=2.40, 95% CI=0.81-7.09). LT-alpha-NcoI*1 did not show an independent association with either atopic asthma or any one phenotype of specific IgE. The synergistic effect between these two genes was conducted, and the interaction between TNF-alpha-308*2 and LT-alpha-NcoI*1 polymorphisms was seen for atopic asthma (OR=2.59, 95% CI=1.10-6.10) when compared with all controls.

CONCLUSION

We have concluded that TNF-alpha-308 may be a risk factor for atopic asthma, whereas the LT-alpha-NcoI polymorphism may modify risk to atopic asthma with TNF-alpha-308.

Association studies for asthma and atopic diseases: a comprehensive review of the literature

Hundreds of genetic association studies on asthma-related phenotypes have been conducted in different populations. To date, variants in 64 genes have been reported to be associated with asthma or related traits in at least one study. Of these, 33 associations were replicated in a second study, 9 associations were not replicated either in a second study or a second sample in the same study, and 22 associations were reported in just a single published study. These results suggest the potential for a great amount of heterogeneity underlying asthma. However, many of these studies are methodologically limited and their interpretation hampered by small sample sizes.

Atopic asthma and TNF-308 alleles: linkage disequilibrium and association analyses

The association of a tumor necrosis factor -308 allele (TNF2) to asthma has been reported in some studies but not in others. The aim of this study was to test this association in a population recruited on the basis of allergy to Parietaria. In the study population, asthma was positively associated to HLA-DRB1*03 (p = 0.01) and to the haplotype TNF2/DRB1*03 (p = 0.02). In the parent subgroup, the proportion of asthmatics was increased in patients with TNF2 (p = 0.01), but the primary association of asthma was to the haplotype TNF2/DRB1*1104 (p = 0.005). The study population was subdivided according to prick skin test (ST) positivity to Lolium, Parietaria, and D. pteronyssinus. Asthma was associated to HLA-DRB1*03 and to the haplotype TNF2/DRB1*03 (p = 0.0015 and 0.0001, respectively) in patients ST positive to Lolium, and to the haplotype TNF2/DRB1*1104 (p = 0.025) in patients ST positive to Parietaria. The transmission disequilibrium test detected excess transmission of HLA-DRB1*03 and of the haplotype TNF2/DRB1*03 (p = 0.03 and 0.04, respectively) to siblings with asthma and ST positivity to Lolium and of HLA-DRB1*1104 and of the haplotype TNF2/DRB1*1104 (p = 0.04 and 0.015, respectively) to siblings with asthma and ST positivity to Parietaria. Taken together, these observations indicate that the haplotypes TNF2/DRB1*03 and TNF2/*B1*1104 contain alleles controlling atopic asthma in patients with sensitization to Lolium and Parietaria, respectively. This suggests that the association of asthma to TNF2 reflects linkage disequilibrium with genes influencing specific immune response.

The association between tumor necrosis factor, HLA-DR alleles, and IgE-mediated asthma in Taiwanese adolescents

BACKGROUND

Human leukocyte antigen (HLA) DR genes and the tumor necrosis factor (TNF) gene locus are associated with asthma and IgE production. TNFalpha-308G/A frequencies between Japanese and Caucasians in the UK have been found to be different. The roles of HLA-DRB1 and TNF genotypes are unknown in Taiwanese adolescents with IgE-mediated asthma (I-asthma).

METHODS

From the population of a 1996 nation-wide survey, we recruited a random sample for a physical examination, determination of total serum IgE (sIgE), dust-mite-specific IgE, and HLA-DRB1, TNFalpha-308, and LTalphaNcoI polymorphisms by polymerase chain reaction.

RESULTS

A total of 80 I-asthmatics and 69 non-asthmatics completed the study. We suggested that I-asthmatics had a higher frequency of the DR13 gene (OR = 8.6, 95% CI = [1.6-161]). The DR13 gene was associated with high sIgE and high dust-mite-specific IgE, especially Dermatophagoides farinae. No TNF haplotype or genotype was associated with I-asthma. The DR13 gene was linked to the LTalphaNcoI*1 allele. When sIgE was adjusted by multiple logistic regression, the risk of I-asthma was much higher for the DR13(+)/LTalphaNcoI*1 haplotype (OR = 25.6, 95% CI = [2.2-1378]) than for the others.

CONCLUSIONS

In Taiwanese children sensitized to Der f, the DR13(+)/LTalphaNcoI*1 haplotype was associated with a much higher risk of having clinical asthma than any other DR13/LTalphaNcoI haplotype.

Relation between tumour necrosis factor polymorphism TNFalpha-308 and risk of asthma

Tumour necrosis factor (TNF) alpha affects immune response and airway inflammation, which are characteristics of asthma. Genetic factors may impact TNFalpha levels, and several polymorphisms in the TNF gene cluster on chromosome 6p21 have been associated with TNFalpha production and potential increased risk of asthma. The present paper evaluates the relation between two single nucleotide polymorphisms (SNPs) in the TNF gene cluster and asthma risk. The SNPs investigated here are guanine (G) to adenosine (A) substitutions in the TNFalpha and lymphotoxin alpha (LTalpha) genes. The TNFalpha SNP is at position -308 in the promoter region (TNFalpha-308), while the LTalpha SNP is in the first intron NcoI recognition sequence (LTalpha-NcoI). (For both SNPs the G allele is denoted as 1, and the A allele 2.) We determined TNFalpha-308 and LTalpha-NcoI genotypes in 511 individuals: 236 asthma cases and 275 non-asthmatic controls. Data were analysed by logistic regression of asthma status on the genotypes and potential confounders. TNFalpha-308*2 was positively associated with asthma, and this relation was strengthened when restricting cases to individuals reporting acute asthma: the adjusted odds ratio (OR) comparing carriers of one or two TNFalpha-308*2 alleles versus none was 1.86 (95% confidence interval (CI)=1.03-3.34, P=0.04). Further restricting the subjects to those with a family history of asthma, and those of European-American ancestry strengthened the association even more: adjusted OR=3.16 (95% CI=1.04-9.66; P=0.04). LTalpha-NcoI*1 was weakly associated with asthma, and analysis of both genes suggests that only the TNFalpha-308*2 allele increases risk of asthma.

The interaction of the polymorphisms in transporter of antigen peptides (TAP) and lymphotoxin alpha (LT-alpha) genes and atopic diseases in the Czech population

BACKGROUND

Transporter antigen peptide gene (TAP) products are involved in antigen processing. These genes, inducible by interferon gamma, as well as lymphotoxin alpha (LT-alpha), are located in the HLA region. Their involvement in immune response regulation makes them candidate atopy susceptibility genes.

OBJECTIVE

This study investigates a possible association between previously identified polymorphisms within the TAP-1 and LT-alpha genes and clinically manifested atopic diseases in the Czech population.

METHODS

Caucasian subjects of Czech nationality (n = 427) were included in our study. We examined 184 healthy controls and 243 patients with histories of atopic asthma, allergic rhinitis and atopic dermatitis or their combinations. We used the amplification refractory mutation system polymerase chain reaction to determine TAP-1 gene polymorphisms. LT-alpha genotypes were determined by PCR and restriction analysis by NcoI.

RESULTS

No significant differences were found in allele or genotype frequencies of the LT-alpha gene, as well as in polymorphisms for Val-->Ile at codon 333 and Gly-->Asp at codon 637 in the TAP-1 gene between controls and patients. However, analysis of the concurrence of the double genotypes of the TAP-1 polymorphism at codon 333 and the LT-alpha genes showed differences between controls and atopic patients (P < 0.02).

CONCLUSION

Several reports have indicated that different HLA products and genes may be risk factors for or protective factors against the development of atopy. We report no association between polymorphisms in the LT-alpha and TAP-1 genes alone and atopic diseases in the central Europe Caucasian (Czech) population, but there was an interesting interaction between the TAP333 and LT-alpha polymorphisms.

Tumour necrosis factor-alpha: the role of this multifunctional cytokine in asthma

Tumour necrosis factor-alpha (TNF-alpha) is recognized as an important mediator in many cytokine- dependent inflammatory events. It is known that TNF-alpha is released in allergic responses from both mast cells and macrophages via IgE-dependent mechanisms, and elevated levels have been demonstrated in the bronchoalveolar fluid (BALF) of asthmatic subjects undergoing allergen challenge. Inhaled TNF-alpha increases airway responsiveness to methacholine in normal and asthmatic subjects associated with a sputum neutrophilia. Additional data indicate that TNF-alpha can upregulate adhesion molecules, facilitate the immigration of inflammatory cells into the airway wall and activate pro-fibrotic mechanisms in the subepithelium. These data suggest that TNF-alpha plays a role in the initiation of allergic asthmatic airway inflammation and the generation of airway hyper-reactivity. In addition, polymorphisms of the TNF-alpha gene 5' untranslated region, particularly at -308 bp, have been described as being associated with asthma. This polymorphism is associated with increased levels of TNF-alpha, but as yet, no asthma studies have demonstrated a phenotypic difference between those individuals with the polymorphism and those with the wild type gene. The TNF receptors (TNF-R p55 and p75), also known as CD120a and b, have also been shown to be present in the lung, but their functional importance is only just emerging. In asthma, TNF may function as a pro-inflammatory cytokine that causes the recruitment of neutrophils and eosinophils. Treatment directed specifically at a reduction in TNF-alpha activity may conceivably be useful as a glucocorticosteroid-sparing asthma therapy.

Susceptibility genes in asthma and allergy

Genome-wide screens for asthma and atopy susceptibility loci have been completed in six population samples. Despite the extensive clinical heterogeneity associated with these phenotypes, 20 chromosomal regions show evidence of linkage (P < 0.01) in three or more population samples. Thus, this survey suggests that at least 20 independent loci influence susceptibility to asthma, atopy, or associated phenotypes and indicates that the genetics of these phenotypes are truly complex. Ongoing studies are aimed at identifying the specific gene or genes in these regions that confer susceptibility to asthma or atopy.

Association of the TNF-alpha-308 (G-->A) polymorphism with self-reported history of childhood asthma

Asthma is a complex disease involving genetic and environmental aetiology. The tumour necrosis factor-alpha (TNF-alpha) and angiotensin-converting enzyme (ACE) genes have been implicated in asthma pathogenesis. This study investigated the association of a G-308A variant of TNF-alpha and an insertion/deletion (I/D) variant of ACE with a self-reported history of childhood asthma, in two population groups. At Northwick Park Hospital, London, 1,811 pregnant women attending for antenatal care were recruited. Participants with a self-reported history of childhood asthma, determined by a researcher-administered questionnaire, and controls with no personal or family history of asthma, of UK/Irish (cases n=20; controls n=416) and South Asian (cases n=6; controls n=275) origin were used in this study. Participants were genotyped for the TNF-alpha-308 and ACE I/D variants by a PCR-RFLP and PCR approach. The TNF-alpha-308 allele 2 (-308A) was significantly associated with self-reported childhood asthma in the UK/Irish (Odds ratios (OR): 2.6; 95% confidence intervals (CI): 1.1-6.2; P=0.03) but not in the South Asian population. The ACE DD genotype was not associated with childhood asthma in either population group. Gametic phase disequilibrium between the TNF-alpha-308 and ACE I/D variants was significantly different from zero in UK/Irish cases (delta=0.09; P=0.034). The TNF-alpha308 allele 2 or a linked major histocompatibility complex (MHC) variant may be a genetic risk factor for childhood asthma in the UK/Irish sample.

A European study on the genetics of mite sensitization

BACKGROUND

Sensitization to mite allergens represents a prominent feature of atopy and an important predictor of bronchial asthma.

OBJECTIVE

It was the intention of this study to define genetic loci linked to mite sensitization because these could represent the genetic basis of the important atopic component of asthma.

METHODS

We studied a multiethnic white population of 99 families, including 224 sib pairs sensitized to Dermatophagoides pteronyssinus. A genome-wide candidate-region search was performed that covered potential asthma and atopy regions.

RESULTS

As for nonparametric linkage (NPL) analysis, 14 of the candidate regions showed evidence for linkage (NPL > 2.0), and 4 of them showed prominent linkage (NPL > 3.0). However, there were substantial ethnic differences. Maximizing the LOD score analysis identified candidate regions with suspected dominant and recessive mode of inheritance. Furthermore, genetic imprinting models provided significant evidence for linkage in the 8p23 region and revealed potential maternal imprinting. The regions found are distinct to those in asthma searches that have been found to be linked to asthma, as well to other inflammatory diseases. In addition, we could not find linkage to the HLA region. By different cutoff points of the phenotype definition, the IL cluster showed evidence of being linked to the degree of sensitization rather than to sensitization per se.

CONCLUSION

The results indicate that the genetic basis of the atopic component of asthma is different from that of the inflammatory component. Furthermore, it seems reasonable to assume that specific sensitizations are influenced by distinct genetic variants leading to their initiation versus those leading to their enhancement.

Contributing factors to the pathobiology. The genetics of asthma

Markers in 19 chromosomal regions have shown some evidence of linkage to asthma, atopy, or related phenotypes in multiple independent genome-wide searches. Linkages to five of these regions (5q, 6p, 11q, 12q, and 13q) have also been reported in non-genome-wide screens. In addition, at least two independent studies have reported linkages to markers on 16p. Numerous candidate genes in these regions have shown varying levels of association to asthma or atopic phenotypes, potentially implicating them as disease susceptibility loci. These include the IL4, CD14, and B2ADR genes on 5q, the HLA-DRB1 and TNF genes on 6p, the FCERB1 and CC16 genes on 11q, and the IL4RA gene on 16p. It still remains to be determined whether polymorphisms in these genes account for the reported linkages in these regions. Studies are underway in laboratories around the world to identify the disease-causing variations in these genes that account for the linkages just discussed. Identifying specific genetic polymorphisms that influence asthma and atopic phenotypes will shed light on the molecular pathways involved in these complex disorders and provide a better understanding of the pathophysiology of asthma and atopy.