Thymic stromal lymphopoietin rather than IL-33 drives food allergy after epicutaneous sensitization to food allergen.

BACKGROUND: A major route of sensitization to food allergen is through an impaired skin barrier. IL-33 and thymic stromal lymphopoietin (TSLP) have both been implicated in epicutaneous sensitization and food allergy, albeit in different murine models. OBJECTIVE: We assessed the respective contributions of TSLP and IL-33 to the development of atopic dermatitis (AD) and subsequent food allergy in TSLP and IL-33 receptor (ST2)-deficient mice using an AD model that does not require tape stripping. METHOD: TSLP receptor (TSLPR)-/-, ST2-/-, and BALB/cJ control mice were exposed to 3 weekly epicutaneous skin patches of one of saline, ovalbumin (OVA), or a combination of OVA and Aspergillus fumigatus (ASP), followed by repeated intragastric OVA challenges and development of food allergy. RESULTS: ASP and/or OVA patched, but not OVA-alone patched, BALB/cJ mice developed an AD-like skin phenotype. However, epicutaneous OVA sensitization occurred in OVA patched mice and was decreased in ST2-/- mice, resulting in lower intestinal mast cell degranulation and accumulation, as well as OVA-induced diarrhea occurrences on intragastric OVA challenges. In TSLPR-/- mice, intestinal mast cell accumulation was abrogated, and no diarrhea was observed. AD was significantly milder in OVA + ASP patched TSLPR-/- mice compared to wild type and ST2-/- mice. Accordingly, intestinal mast cell accumulation and degranulation were impaired in OVA + ASP patched TSLPR-/- mice compared to wild type and ST2-/- mice, protecting TSLPR-/- mice from developing allergic diarrhea. CONCLUSION: Epicutaneous sensitization to food allergen and development of food allergy can occur without skin inflammation and is partly mediated by TSLP, suggesting that prophylactic targeting of TSLP may be useful in mitigating the development of AD and food allergy early in life in at-risk infants.

Disease-associated KIF3A variants alter gene methylation and expression impacting skin barrier and atopic dermatitis risk.

Single nucleotide polymorphisms (SNPs) in the gene encoding kinesin family member 3A, KIF3A, have been associated with atopic dermatitis (AD), a chronic inflammatory skin disorder. We find that KIF3A SNP rs11740584 and rs2299007 risk alleles create cytosine-phosphate-guanine sites, which are highly methylated and result in lower KIF3A expression, and this methylation is associated with increased transepidermal water loss (TEWL) in risk allele carriers. Kif3aK14∆/∆ mice have increased TEWL, disrupted junctional proteins, and increased susceptibility to develop AD. Thus, KIF3A is required for skin barrier homeostasis whereby decreased KIF3A skin expression causes disrupted skin barrier function and promotes development of AD.

IL33 contributes to diesel pollution-mediated increase in experimental asthma severity.

BACKGROUND: Exposure to traffic pollution, notably diesel exhaust particles (DEP), increases risk for asthma and asthma exacerbations. The contribution of cytokines generated by stressed lung epithelial cells (IL25, IL33, TSLP) to DEP-induced asthma severity remains poorly understood. METHODS: BALB/c mice were exposed intratracheally once to DEP or 9 times over 3-weeks to either saline, DEP, and/or house dust mite extract (HDM). Airway hyper-responsiveness (AHR), pulmonary inflammation, and T-cell subsets were assessed 24 hours after the last exposure in mice sufficient and deficient for the IL33 receptor ST2. RESULTS: DEP exposure induces oxidative stress, IL6, neutrophils and pulmonary accumulation of IL33, but not IL25 or TSLP or other features of allergic disease. When mice are co-exposed to DEP and low doses of HDM, DEP increases IL33 lung levels and Th2 responses. ST2 deficiency partially protected mice from HDM + DEP induced AHR in association with decreased type 2 inflammation and lung levels of IL5+ IL17A+ co-producing T-cells. Upon in vitro HDM challenge of lung cells from HDM ± DEP exposed ST2-/- mice, secretion of IL5, IL13, IL6 and IL17A was abrogated by a mechanism involving IL33 signaling in both dendritic cells and T-cells. HDM + DEP exposed bone marrow derived dendritic cells and IL33 pulsed BMDC promote a mixed Th2/Th17 response that was dependent on ST2 expression by CD4+ T-cells. CONCLUSION: IL33 contributes to DEP mediated increase in allergen-induced Th2 inflammation and AHR in a mouse model of severe steroid resistant asthma, potentially through the accumulation of pathogenic IL5+ IL17A+ CD4+ effector T-cells.

TET1 contributes to allergic airway inflammation and regulates interferon and aryl hydrocarbon receptor signaling pathways in bronchial epithelial cells.

Previous studies have suggested a role for Tet1 in the pathogenesis of childhood asthma. However, how Tet1 contributes to asthma remains unknown. Here we used mice deficient for Tet1 in a well-established model of allergic airway inflammation and demonstrated that loss of Tet1 increased disease severity including airway hyperresponsiveness and lung eosinophilia. Increased expression of Muc5ac, Il13, Il33, Il17a, Egfr, and Tff2 were observed in HDM-challenged Tet1-deficient mice compared to Tet1+/+ littermates. Further, transcriptomic analysis of lung RNA followed by pathway and protein network analysis showed that the IFN signaling pathway was significantly upregulated and the aryl hydrocarbon receptor (AhR) pathway was significantly downregulated in HDM-challenged Tet1-/- mice. This transcriptional regulation of the IFN and AhR pathways by Tet1 was also present in human bronchial epithelial cells at base line and following HDM challenges. Genes in these pathways were further associated with changes in DNA methylation, predicted binding of transcriptional factors with relevant functions in their promoters, and the presence of histone marks generated by histone enzymes that are known to interact with Tet1. Collectively, our data suggest that Tet1 inhibits HDM-induced allergic airway inflammation by direct regulation of the IFN and AhR pathways.

Commensal Candida albicans Positively Calibrates Systemic Th17 Immunological Responses.

Mucosal barriers are densely colonized by pathobiont microbes such as Candida albicans, capable of invasive disseminated infection. However, systemic infections occur infrequently in healthy individuals, suggesting that pathobiont commensalism may elicit host benefits. We show that intestinal colonization with C. albicans drives systemic expansion of fungal-specific Th17 CD4+ T cells and IL-17 responsiveness by circulating neutrophils, which synergistically protect against C. albicans invasive infection. Protection conferred by commensal C. albicans requires persistent fungal colonization and extends to other extracellular invasive pathogens such as Staphylococcus aureus. However, commensal C. albicans does not protect against intracellular influenza virus infection and exacerbates allergic airway inflammation susceptibility, indicating that positively calibrating systemic Th17 responses is not uniformly beneficial. Thus, systemic Th17 inflammation driven by CD4+ T cells responsive to tonic stimulation by commensal C. albicans improves host defense against extracellular pathogens, but with potentially harmful immunological consequences.

Loss of GTPase of immunity-associated protein 5 (Gimap5) promotes pathogenic CD4+ T-cell development and allergic airway disease.

BACKGROUND: GTPase of immunity-associated protein 5 (GIMAP5) is essential for lymphocyte homeostasis and survival. Recently, human GIMAP5 single nucleotide polymorphisms have been linked to an increased risk for asthma, whereas loss of Gimap5 in mice has been associated with severe CD4+ T cell-driven immune pathology. OBJECTIVE: We sought to identify the molecular and cellular mechanisms by which Gimap5 deficiency predisposes to allergic airway disease. METHODS: CD4+ T-cell polarization and development of pathogenic CD4+ T cells were assessed in Gimap5-deficient mice and a human patient with a GIMAP5 loss-of-function (LOF) mutation. House dust mite-induced airway inflammation was assessed by using a complete Gimap5 LOF (Gimap5sph/sph) and conditional Gimap5fl/flCd4Cre/ert2 mice. RESULTS: GIMAP5 LOF mutations in both mice and human subjects are associated with spontaneous polarization toward pathogenic TH17 and TH2 cells in vivo. Mechanistic studies in vitro reveal that impairment of Gimap5-deficient TH cell differentiation is associated with increased DNA damage, particularly during TH1-polarizing conditions. DNA damage in Gimap5-deficient CD4+ T cells could be controlled by TGF-ß, thereby promoting TH17 polarization. When challenged with house dust mite in vivo, Gimap5-deficient mice displayed an exacerbated asthma phenotype (inflammation and airway hyperresponsiveness), with increased development of TH2, TH17, and pathogenic TH17/TH2 cells. CONCLUSION: Activation of Gimap5-deficient CD4+ T cells is associated with increased DNA damage and reduced survival that can be overcome by TGF-ß. This leads to selective survival of pathogenic TH17 cells but also TH2 cells in human subjects and mice, ultimately promoting allergic airway disease.

Rational targeting Cdc42 restrains Th2 cell differentiation and prevents allergic airway inflammation.

BACKGROUND: Asthma is an allergic airway inflammation-driven disease that affects more than 300 million people world-wide. Targeted therapies for asthma are largely lacking. Although asthma symptoms can be prevented from worsening, asthma development cannot be prevented. Cdc42 GTPase has been shown to regulate actin cytoskeleton, cell proliferation and survival. OBJECTIVES: To investigate the role and targeting of Cdc42 in Th2 cell differentiation and Th2-mediated allergic airway inflammation. METHODS: Post-thymic Cdc42-deficient mice were generated by crossing Cdc42flox/flox mice with dLckicre transgenic mice in which Cre expression is driven by distal Lck promoter. Effects of post-thymic Cdc42 deletion and pharmacological targeting Cdc42 on Th2 cell differentiation were evaluated in vitro under Th2-polarized culture conditions. Effects of post-thymic Cdc42 deletion and pharmacological targeting Cdc42 on allergic airway inflammation were evaluated in ovalbumin- and/or house dust mite-induced mouse models of asthma. RESULTS: Post-thymic deletion of Cdc42 led to reduced peripheral CD8+ T cells and attenuated Th2 cell differentiation, with no effect on closely related Th1, Th17 and induced regulatory T (iTreg) cells. Post-thymic Cdc42 deficiency ameliorated allergic airway inflammation. The selective inhibition of Th2 cell differentiation by post-thymic deletion of Cdc42 was recapitulated by pharmacological targeting of Cdc42 with CASIN, a Cdc42 activity-specific chemical inhibitor. CASIN also alleviated allergic airway inflammation. CASIN-treated Cdc42-deficient mice showed comparable allergic airway inflammation to vehicle-treated Cdc42-deficient mice, indicative of negligible off-target effect of CASIN. CASIN had no effect on established allergic airway inflammation. CONCLUSION AND CLINICAL RELEVANCE: Cdc42 is required for Th2 cell differentiation and allergic airway inflammation, and rational targeting Cdc42 may serve as a preventive but not therapeutic approach for asthma control.

Vitamin D supplementation attenuates asthma development following traffic-related particulate matter exposure.

BACKGROUND: Recent literature suggests that children who are vitamin D deficient are uniquely susceptible to the effects of traffic-related air pollution (TRAP) exposure. This is highly significant because large segments of the population reside in zones of high TRAP exposure. OBJECTIVE: We sought to determine whether vitamin D supplementation mitigates the effect of TRAP exposure on asthma development, asthma exacerbation, and/or airway inflammation and to determine the timing of vitamin D supplementation that confers maximal health benefit. METHODS: Using established mouse models of asthma, we examined the effect of prenatal and postnatal vitamin D supplementation on asthma development, as well as the utility of vitamin D as a treatment for established asthma in the context of diesel exhaust particle (DEP) exposure. RESULTS: DEP and allergen coexposure resulted in increased airway hyperresponsiveness (AHR) and accumulation of pathogenic TH2/TH17 cells in the lungs of vitamin D-deficient mice compared with control mice. Prenatal and postnatal vitamin D supplementation significantly attenuated the development of AHR and decreased pulmonary accumulation of TH2/TH17 cells after coexposure to TRAP and allergen but not to allergen alone. Restoration of normal vitamin D status had no effect on AHR once asthma was already established. CONCLUSIONS: Our data establish that vitamin D confers protection against asthma development specifically in the context of TRAP exposure. Although vitamin D replacement did not reverse established asthma, restoration of normal vitamin D status in early life significantly attenuated the development of AHR in the setting of DEP-exacerbated allergic asthma and reduced numbers of lung TH2/TH17 cells, which portend the development of severe asthma.

ß-Glucan exacerbates allergic asthma independent of fungal sensitization and promotes steroid-resistant TH2/TH17 responses.

BACKGROUND: Allergic sensitization to fungi has been associated with asthma severity. As a result, it has been largely assumed that the contribution of fungi to allergic disease is mediated through their potent antigenicity. OBJECTIVE: We sought to determine the mechanism by which fungi affect asthma development and severity. METHODS: We integrated epidemiologic and experimental asthma models to explore the effect of fungal exposure on asthma development and severity. RESULTS: We report that fungal exposure enhances allergen-driven TH2 responses, promoting severe allergic asthma. This effect is independent of fungal sensitization and can be reconstituted with ß-glucan and abrogated by neutralization of IL-17A. Furthermore, this severe asthma is resistant to steroids and characterized by mixed TH2 and TH17 responses, including IL-13+IL-17+CD4+ double-producing effector T cells. Steroid resistance is dependent on fungus-induced TH17 responses because steroid sensitivity was restored in IL-17rc-/- mice. Similarly, in children with asthma, fungal exposure was associated with increased serum IL-17A levels and asthma severity. CONCLUSION: Our data demonstrate that fungi are potent immunomodulators and have powerful effects on asthma independent of their potential to act as antigens. Furthermore, our results provide a strong rationale for combination treatment strategies targeting IL-17A for this subgroup of fungus-exposed patients with difficult-to-treat asthma.

Vanin-1 expression and methylation discriminate pediatric asthma corticosteroid treatment response.

BACKGROUND: There is considerable heterogeneity in asthma treatment response. OBJECTIVE: We sought to identify biomarkers of corticosteroid treatment response in children with asthma and evaluate the utility and mechanistic basis of these biomarkers. METHODS: Children (5-18 years) presenting to the emergency department with an acute asthma exacerbation were recruited and followed during hospitalization. Nasal epithelial cells were collected on presentation to the emergency department (T0) and 18 to 24 hours later (T1), and T1/T0 gene expression ratios were analyzed to identify genes associated with good and poor corticosteroid treatment response phenotypes. The utility of these genes in discriminating between systemic corticosteroid treatment response groups was then tested prospectively in a new cohort of patients. A gene candidate (vanin-1 [VNN1]) that consistently distinguished good versus poor response phenotypes was further studied in an experimental asthma model, and VNN1 promoter methylation was measured by means of bisulfite pyrosequencing in patients. RESULTS: VNN1 mRNA expression changes were associated with systemic corticosteroid treatment response in children with acute asthma, and VNN1 was required for optimal response to corticosteroid treatment in an experimental asthma model. A CpG site within the VNN1 promoter was differentially methylated between good versus poor treatment response groups, and methylation at this site correlated with VNN1 mRNA expression. CONCLUSIONS: We have identified a biological basis for poor corticosteroid treatment response that can be used to distinguish a subgroup of asthmatic children who respond poorly to systemic corticosteroid treatment. VNN1 contributes to corticosteroid responsiveness, and changes in VNN1 nasal epithelial mRNA expression and VNN1 promoter methylation might be clinically useful biomarkers of treatment response in asthmatic children.

Exposure to allergen and diesel exhaust particles potentiates secondary allergen-specific memory responses, promoting asthma susceptibility.

BACKGROUND: Exposure to traffic pollution particulate matter, predominantly diesel exhaust particles (DEPs), increases the risk of asthma and asthma exacerbation; however, the underlying mechanisms remain poorly understood. OBJECTIVE: We sought to examine the effect of DEP exposure on the generation and persistence of allergen-specific memory T cells in asthmatic patients and translate these findings by determining the effect of early DEP exposure on the prevalence of allergic asthma in children. METHODS: The effect of DEPs on house dust mite (HDM)-specific memory responses was determined by using an asthma model. Data from children enrolled in the Cincinnati Childhood Allergy and Air Pollution Study birth cohort were analyzed to determine the effect of DEP exposure on asthma outcomes. RESULTS: DEP coexposure with HDM resulted in persistent TH2/TH17 CD127(+) effector/memory cells in the lungs, spleen, and lymph nodes of adult and neonatal mice. After 7 weeks of rest, a single exposure to HDM resulted in airway hyperresponsiveness and increased TH2 cytokine levels in mice that had been previously exposed to both HDM and DEPs versus those exposed to HDM alone. On the basis of these data, we examined whether DEP exposure was similarly associated with increased asthma prevalence in children in the presence or absence of allergen exposure/sensitization in the Cincinnati Childhood Allergy and Air Pollution Study birth cohort. Early-life exposure to high DEP levels was associated with significantly increased asthma prevalence among allergic children but not among nonallergic children. CONCLUSION: These findings suggest that DEP exposure results in accumulation of allergen-specific TH2/TH17 cells in the lungs, potentiating secondary allergen recall responses and promoting the development of allergic asthma.