Airway epithelial cells form a barrier to the outside world and are at the front line of mucosal immunity. Epithelial apical junctional complexes are multiprotein subunits that promote cell-cell ...adhesion and barrier integrity. Recent studies in the skin and gastrointestinal tract suggest that disruption of cell-cell junctions is required to initiate epithelial immune responses, but how this applies to mucosal immunity in the lung is not clear. Increasing evidence indicates that defective epithelial barrier function is a feature of airway inflammation in asthmatic patients. One challenge in this area is that barrier function and junctional integrity are difficult to study in the intact lung, but innovative approaches should provide new knowledge in this area in the near future. In this article we review the structure and function of epithelial apical junctional complexes, emphasizing how regulation of the epithelial barrier affects innate and adaptive immunity. We discuss why defective epithelial barrier function might be linked to TH 2 polarization in asthmatic patients and propose a rheostat model of barrier dysfunction that implicates the size of inhaled allergen particles as an important factor influencing adaptive immunity.
Background Atopic dermatitis (AD) is characterized by dry skin and a hyperactive immune response to allergens, 2 cardinal features that are caused in part by epidermal barrier defects. Tight ...junctions (TJs) reside immediately below the stratum corneum and regulate the selective permeability of the paracellular pathway. Objective We evaluated the expression/function of the TJ protein claudin-1 in epithelium from AD and nonatopic subjects and screened 2 American populations for single nucleotide polymorphisms in the claudin-1 gene (CLDN1). Methods Expression profiles of nonlesional epithelium from patients with extrinsic AD, nonatopic subjects, and patients with psoriasis were generated using Illumina's BeadChips. Dysregulated intercellular proteins were validated by means of tissue staining and quantitative PCR. Bioelectric properties of epithelium were measured in Ussing chambers. Functional relevance of claudin-1 was assessed by using a knockdown approach in primary human keratinocytes. Twenty-seven haplotype-tagging SNPs in CLDN1 were screened in 2 independent populations with AD. Results We observed strikingly reduced expression of the TJ proteins claudin-1 and claudin-23 only in patients with AD, which were validated at the mRNA and protein levels. Claudin-1 expression inversely correlated with TH 2 biomarkers. We observed a remarkable impairment of the bioelectric barrier function in AD epidermis. In vitro we confirmed that silencing claudin-1 expression in human keratinocytes diminishes TJ function while enhancing keratinocyte proliferation. Finally, CLDN1 haplotype-tagging SNPs revealed associations with AD in 2 North American populations. Conclusion Collectively, these data suggest that an impairment in tight junctions contributes to the barrier dysfunction and immune dysregulation observed in AD subjects and that this may be mediated in part by reductions in claudin-1.
To the Editor: Atopic dermatitis (AD) is the most common inflammatory skin disease, affecting up to 20% of children in the United States, and is characterized by an increased susceptibility to ...cutaneous infections.1,2 One in 10 subjects with AD has difficulty clearing cutaneous infections with a host of viruses including herpes simplex, vaccinia, human papilloma, and/or molluscum contagiosum.1 This typically manifests as more extensive cutaneous and sometimes systemic disease and/or resistance to standard therapies.
Background Disruption of the epithelial barrier might be a risk factor for allergen sensitization and asthma. Viral respiratory tract infections are strongly associated with asthma exacerbation, but ...the effects of respiratory viruses on airway epithelial barrier function are not well understood. Many viruses generate double-stranded RNA, which can lead to airway inflammation and initiate an antiviral immune response. Objectives We investigated the effects of the synthetic double-stranded RNA polyinosinic:polycytidylic acid (polyI:C) on the structure and function of the airway epithelial barrier in vitro. Methods 16HBE14o- human bronchial epithelial cells and primary airway epithelial cells at an air-liquid interface were grown to confluence on Transwell inserts and exposed to polyI:C. We studied epithelial barrier function by measuring transepithelial electrical resistance and paracellular flux of fluorescent markers and structure of epithelial apical junctions by means of immunofluorescence microscopy. Results PolyI:C induced a profound decrease in transepithelial electrical resistance and increase in paracellular permeability. Immunofluorescence microscopy revealed markedly reduced junctional localization of zonula occludens-1, occludin, E-cadherin, β-catenin, and disorganization of junction-associated actin filaments. PolyI:C induced protein kinase D (PKD) phosphorylation, and a PKD antagonist attenuated polyI:C-induced disassembly of apical junctions and barrier dysfunction. Conclusions PolyI:C has a powerful and previously unsuspected disruptive effect on the airway epithelial barrier. PolyI:C-dependent barrier disruption is mediated by disassembly of epithelial apical junctions, which is dependent on PKD signaling. These findings suggest a new mechanism potentially underlying the associations between viral respiratory tract infections, airway inflammation, and allergen sensitization.
Abstract Background Chronic schistosomiasis and its severe complication, periportal fibrosis, are characterized by a predominant Th2 response. To date, specific SNPs in ST2 have been some of the most ...consistently associated genetic variants for asthma. Objectives We investigated the role of ST2 (a receptor for the Th2 cytokine IL-33) in chronic and late-stage schistosomiasis caused by S. japonicum , and the potential effect of ST2 genetic variants on stage of disease and ST2 expression. Methods 947 adult participants (339 with end-stage schistosomiasis and liver cirrhosis, 307 with chronic infections without liver fibrosis, and 301 health controls) were recruited from a S. japonicum -endemic area (Hubei, China). Six ST2 SNPs were genotyped. Serum sST2 was measured by ELISA, and ST2 expression in normal liver tissues, HBV-induced fibrotic liver tissues and S. japonicum -induced fibrotic liver tissues was measured by immunohistochemistry. Results: sST2 levels were significantly higher in the end-stage group (36.04 95 %CI 33.85;38.37) compared to chronic cases and controls (22.7 95% CI 22.0;23.4, p-value < 1E-10). In addition, S. japonicum -induced fibrotic liver tissues showed increased ST2 staining compared to normal liver tissues (p-value=0.0001). Markers rs12712135, rs1420101 and rs6543119 were strongly associated with sST2 levels (p-values 2E-10, 5E-05 and 6E-05 respectively), and these results were replicated in an independent cohort from Brazil living in a S. mansoni endemic region. Conclusion We demonstrate for the first time that end-stage schistosomiasis is associated with elevated sST2 levels, and show that ST2 genetic variants are associated with sST2 levels in patients with schistosomiasis.
Background Amphiregulin, a member of the epidermal growth factor family, is expressed by activated mouse TH 2 cells. Amphiregulin produced by mouse hematopoietic cells contributes to the elimination ...of a nematode infection by a type 2 effector response. Objective To identify the human peripheral blood cell population expressing amphiregulin. Methods Amphiregulin-expressing cells were identified by flow cytometry of cell surface markers and histologic staining. Histamine and amphiregulin in supernatants were measured by enzyme immunoassay. Quantitative real-time PCR was used to measure mRNA expression. Results Stimulation of human PBMCs by anti-CD3 + anti-CD28 antibodies induced expression of amphiregulin mRNA and protein by a non–T-cell population. The amphiregulin-producing cells were basophils, as judged by morphology and expression of CD203c and CD123 (IL-3 receptor α chain). Activated mouse basophils also produced amphiregulin. Amphiregulin expression by basophils in response to anti-TCR stimulation required IL-3 produced by T cells, and IL-3 alone induced high levels of amphiregulin expression by purified basophils. Amphiregulin was expressed at much higher levels when human basophils were stimulated by IL-3 than by IgE cross-linking, whereas the opposite was true for IL-4 expression and histamine release. Heparin-binding epidermal growth factor–like growth factor was also expressed by IL-3–stimulated human basophils. PBMCs from human subjects with asthma contained significantly higher numbers of basophils able to produce amphiregulin compared with controls with or without allergy. Conclusion IL-3 can induce basophils to express high levels of amphiregulin, which may contribute to tissue remodeling during type 2 immune responses such as asthma.
Future studies to determine the therapeutic potential of elevating intra-epithelial cAMP levels in RSV bronchiolitis and respiratory infection should be worthwhile.
Background The transcription factor Yin-Yang 1 (YY-1) binds to the promoter regions of several T-cell cytokine genes, but the expression and contribution of this factor to cytokine gene expression ...and T-cell activation in vivo is not clear. Objective We sought to better define the role of YY-1 in T-cell gene regulation and allergic immune responses. Methods We studied cytokine gene expression in T lymphocytes isolated from wild-type mice and heterozygous littermates bearing 1 targeted yy-1 allele ( yy-1+/− mice). T cells were stimulated with anti-T-cell receptor (anti-TCR) plus CD28 antibodies or with peptide antigen plus antigen-presenting cells by using newly generated yy-1+/− TCR transgenic mice. We also studied ovalbumin-driven allergic immune responses in a mouse model of asthma and YY-1 expression in lung tissue from human asthmatic subjects. Results CD4+ T cells from yy-1+/− mice secreted significantly less IL-4 and IFN-γ compared with wild-type littermates after TCR-dependent activation, whereas IL-2 production was not significantly affected. Both airway inflammation and recall splenocyte IL-4 production were inhibited in yy-1+/− mice, as was antigen-driven T-cell proliferation. YY-1 expression was higher in airway biopsy specimens from asthmatic compared with control subjects. Conclusion These data indicate that YY-1 regulates T-cell cytokine gene expression and allergic immune responses in a gene dose-dependent manner.
Background Dendritic cells (DCs) translate environmental cues into T-cell activating signals, and are centrally involved in allergic airway inflammation. Ambient particulate matter (APM) is ...ubiquitous and associated with allergic diseases, but it is unknown whether APM directly activates DCs. Objective To study comprehensively the effects of APM on myeloid DC phenotype and function. Methods Development of DC was modeled using human CD34+ progenitor cells. APM was collected from ambient outdoor air in Baltimore city. We studied the effects of APM on DC activation in vitro , compared with LPS. Results Ambient particulate matter enhanced DC expression of costimulatory receptors but suppressed the expression of both the endocytosis receptor CD206 and uptake of fluorescein isothiocyanate–conjugated dextran. The expression of the Toll-like pattern-recognition receptors Toll-like receptor 2 and Toll-like receptor 4 was also blunted. APM-exposed DCs secreted less IL-12 and IL-6 but exhibited increased secretion of IL-18 and IL-10 compared with LPS stimulation. A TH 2-like pattern of cytokine production was seen in cocultures of APM-stimulated DCs and alloreactive naive CD4+ T cells where the IL-13 to IFN-γ ratio was reversed. This contrasted with the TH 1 polarizing effects of LPS on DCs. Conclusion We report for the first time that APM-exposed DCs direct a complex TH 1/TH 2-like pattern of T-cell activation by mechanisms that involve nonclassic activation of DCs. Clinical implications Inhaled APM can act directly on DCs as a danger signal to direct a proallergic pattern of innate immune activation.
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