Thinking about how asthma and allergic diseases arise is undergoing several shifts. In ‘Bedside to Bench’, Clare M. Lloyd and Sejal Saglani examine how recent human studies are putting the focus on the epithelium as a major contributor to asthma. The findings shift the emphasis away from the T helper type 2 immune response, and call into question the utility of current animal models of the disease. Although asthma and other allergic disorders are known to have origins in infancy, some researchers are looking even earlier, to effects in utero and before conception. In ‘Bench to Bedside’, Catherine Hawrylowicz and Kimuli Ryanna highlight animal studies that outline some of the effects of the maternal environment, and they examine the potential implications for prevention of disease.
CD4+CD25+ regulatory T cells can inhibit excessive T-cell responses in vivo. We have previously demonstrated that prophylactic administration of CD4+CD25+ regulatory T cells suppresses the development of acute allergen-induced airway inflammation in vivo.
We sought to determine the effect of therapeutic transfer of CD4+CD25+ regulatory T cells on established pulmonary inflammation and the subsequent development of airway remodeling.
CD4+CD25+ cells were transferred after the onset of allergic inflammation, and airway challenges were continued to induce chronic inflammation and airway remodeling.
Administration of CD4+CD25+ regulatory T cells reduced established lung eosinophilia, TH2 infiltration, and expression of IL-5, IL-13, and TGF-β. Moreover, subsequent mucus hypersecretion and peribronchial collagen deposition were reduced after prolonged challenge. In contrast, transfer of CD4+CD25+ regulatory T cells had no effect on established airway hyperreactivity either 7 days or 4 weeks after transfer.
In this study we demonstrate for the first time that therapeutic transfer of CD4+CD25+ regulatory T cells can resolve features of chronic allergen-induced inflammation and prevent development of airway remodeling.
Regulatory T cells; TH2 cells; eosinophils; TGF-β; airway remodeling; allergic inflammation
Airway remodeling is a central feature of asthma and includes the formation of new peribronchial blood vessels, which is termed angiogenesis. In a number of disease models, bone marrow-derived endothelial progenitor cells (EPCs) have been shown to contribute to the angiogenic response. In this study we set out to determine whether EPCs were recruited into the lungs in a model of allergic airways disease and to identify the factors regulating EPC trafficking in this model. We observed a significant increase in the number of peribronchial blood vessels at day 24, during the acute inflammatory phase of the model. This angiogenic response was associated with an increase in the quantity of EPCs recoverable from the lung. These EPCs formed colonies after 21 days in culture and were shown to express CD31, von Willebrand factor, and vascular endothelial growth factor (VEGF) receptor 2, but were negative for CD45 and CD14. The influx in EPCs was associated with a significant increase in the proangiogenic factors VEGF-A and the CXCR2 ligands, CXCL1 and CXCL2. However, we show directly that, while the CXCL1 and CXCL2 chemokines can recruit EPCs into the lungs of allergen-sensitized mice, VEGF-A was ineffective in this respect. Further, the blockade of CXCR2 significantly reduced EPC numbers in the lungs after allergen exposure and led to a decrease in the numbers of peribronchial blood vessels after allergen challenge with no effect on inflammation. The data presented here provide in vivo evidence that CXCR2 is critical for both EPC recruitment and the angiogenic response in this model of allergic inflammation of the airways.
CXC chemokines; Progenitor cell; Asthma; Angiogenesis
IL-9-secreting (TH9) T cells are thought to represent a distinct T-cell subset. However, evidence for their functionality in disease is uncertain.
To define a functional phenotype for TH9-driven pathology in vivo.
We used fluorescence-activated cell sorting to identify circulating TH9 cells in atopic and nonatopic subjects. In mice we utilized a model of allergic airways disease induced by house dust mite to determine TH9 cell function in vivo and the role of activin A in TH9 generation.
Allergic patients have elevated TH9 cell numbers in comparison to nonatopic donors, which correlates with elevated IgE levels. In a murine model, allergen challenge with house dust mite leads to rapid TH9 differentiation and proliferation, with much faster kinetics than for TH2 cell differentiation, resulting in the specific recruitment and activation of mast cells. The TGF-β superfamily member activin A replicates the function of TGF-β1 in driving the in vitro generation of TH9 cells. Importantly, the in vivo inhibition of TH9 differentiation induced by allergen was achieved only when activin A and TGF-β were blocked in conjunction but not alone, resulting in reduced airway hyperreactivity and collagen deposition. Conversely, adoptive transfer of TH9 cells results in enhanced pathology.
Our data identify a distinct functional role for TH9 cells and outline a novel pathway for their generation in vitro and in vivo. Functionally, TH9 cells promote allergic responses resulting in enhanced pathology mediated by the specific recruitment and activation of mast cells in the lungs.
Activin A; TH9 cells; IL-9; asthma; allergy; mast cells; house dust mite; TGF-β
Allergic asthma is a complex disease that has been modeled extensively in small rodents. Airway eosinophilia and changes in lung function have been documented using a variety of protocols. However, recent efforts have improved these models by trying to replicate the structural remodeling that occurs in the lung as a consequence of chronic allergen-driven inflammation. This review documents the recent developments in protocols and systems designed to examine pathways leading to allergen-induced airway remodeling.
The discovery of IL-33 as the ligand for the orphan Th2 associated receptor ST2 has uncovered a whole range of different avenues for this pathway. Although the extracellular functions of ST2 as a marker for Th2 cell and mast cell activity were well defined, the complexities of IL-33 regulation, nuclear function and secretion are only just being realised. The well documented expression pattern of ST2 has identified a role for the IL-33/ST2 axis in the classical Th2 cell and mast cell driven pathogenesis of asthma and anaphylaxis. However, the induction of IL-33 expression by environmental or endogenous triggers now suggests a wider role for the pathway during infection, inflammation and tissue damage.
Rationale: Airway hyperreactivity and remodeling are characteristic features of asthma. Interactions between the airway epithelium and environmental allergens are believed to be important in driving development of pathology, particularly because altered epithelial gene expression is common in individuals with asthma.
Objectives: To investigate the interactions between a modified airway epithelium and a common aeroallergen in vivo.
Methods: We used an adenoviral vector to generate mice overexpressing the transforming growth factor-β signaling molecule, Smad2, in the airway epithelium and exposed them to house dust mite (HDM) extract intranasally.
Measurements and Main Results: Smad2 overexpression resulted in enhanced airway hyperreactivity after allergen challenge concomitant with changes in airway remodeling. Subepithelial collagen deposition was increased and smooth muscle hyperplasia was evident resulting in thickening of the airway smooth muscle layer. However, there was no increase in airway inflammation in mice given the Smad2 vector compared with the control vector. Enhanced airway hyperreactivity and remodeling did not correlate with elevated levels of Th2 cytokines, such as IL-13 or IL-4. However, mice overexpressing Smad2 in the airway epithelium showed significantly enhanced levels of IL-25 and activin A after HDM exposure. Blocking activin A with a neutralizing antibody prevented the increase in lung IL-25 and inhibited subsequent collagen deposition and also the enhanced airway hyperreactivity observed in the Smad2 overexpressing HDM-exposed mice.
Conclusions: Epithelial overexpression of Smad2 can specifically alter airway hyperreactivity and remodeling in response to an aeroallergen. Moreover, we have identified novel roles for IL-25 and activin A in driving airway hyperreactivity and remodeling.
asthma; lung; epithelium; smooth muscle; collagen
Background: Lipoxygenases (LOXs) generate eicosanoids in inflammation.
Results: Monocyte/macrophage LOXs generate novel phospholipid-esterified eicosanoids containing ketoeicosatetraenoic acid or hydroperoxyeicosatetraenoic acid. They activate peroxisome proliferator-activated receptor-γ transcriptional activity and are found in cystic fibrosis bronchoalveolar fluid.
Significance: LOXs generate esterified eicosanoids in vitro and in vivo.
Conclusion: These new lipids represent new families of bioactive mediators.
12/15-Lipoxygenases (LOXs) in monocytes and macrophages generate novel phospholipid-esterified eicosanoids. Here, we report the generation of two additional families of related lipids comprising 15-ketoeicosatetraenoic acid (KETE) attached to four phosphatidylethanolamines (PEs). The lipids are generated basally by 15-LOX in IL-4-stimulated monocytes, are elevated on calcium mobilization, and are detected at increased levels in bronchoalveolar lavage fluid from cystic fibrosis patients (3.6 ng/ml of lavage). Murine peritoneal macrophages generate 12-KETE-PEs, which are absent in 12/15-LOX-deficient mice. Inhibition of 15-prostaglandin dehydrogenase prevents their formation from exogenous 15-hydroxyeicosatetraenoic acid-PE in human monocytes. Both human and murine cells also generated analogous hydroperoxyeicosatetraenoic acid-PEs. The electrophilic reactivity of KETE-PEs is shown by their Michael addition to glutathione and cysteine. Lastly, both 15-hydroxyeicosatetraenoic acid-PE and 15-KETE-PE activated peroxisome proliferator-activated receptor-γ reporter activity in macrophages in a dose-dependent manner. In summary, we demonstrate novel peroxisome proliferator-activated receptor-γ-activating oxidized phospholipids generated enzymatically by LOX and 15-prostaglandin dehydrogenase in primary monocytic cells and in a human Th2-related lung disease. The lipids are a new family of bioactive mediators from the 12/15-LOX pathway that may contribute to its known anti-inflammatory actions in vivo.
Eicosanoid; Innate Immunity; Lipoxygenase Pathway; Macrophages; Mass Spectrometry (MS); Monocytes; Phospholipid
The CC chemokine receptor 4 (CCR4) shows selectivity for the recruitment of memory T cell subsets, including those of the T helper cell type 2 (Th2) phenotype. In humans, CCR4+ T cells are recruited to the asthmatic lung in response to allergen challenge; however, the contribution of this pathway to allergic disease remains uncertain. We therefore investigated the role of CCR4 in allergic airways inflammation in the guinea pig. Blockade of CCR4 with a specific antibody resulted in only minor changes in numbers of CCR4+ Th cells in the bronchoalveolar lavage fluid of allergen-challenged guinea pigs and failed to inhibit the generation of eotaxin/CC chemokine ligand (CCL)11 or macrophage-derived chemokine/CCL22 or the recruitment of inflammatory leukocytes to the lung. These data suggest that although CCR4 was originally proposed as a marker of Th2 status, antigen-specific Th2 cells are recruited to the lung predominantly by other pathways. This study casts doubts on the validity of CCR4 as a therapeutic target in the treatment of asthma.
T lymphocytes; chemokines; allergy
Expression of chemokine receptors on T helper 2 cells and eosinophils has been postulated to be the mechanism by which these cells are selectively recruited to the lung during allergic inflammatory reactions. Mouse models have provided evidence to show that blocking the ligands for these receptors is successful in abrogating the pathophysiological effects of allergen challenge. However, recent studies describing the effect of genetic deletions of these chemokine receptors have not confirmed the results obtained with ligand knockouts or neutralising antibodies. Coupled with the realisation that, because of a lack of species cross-reactivity, it is not possible to test small molecule antagonists against human receptors in the original in vivo animal models, the future of chemokine receptor therapeutics is in question. However, recent advances have been made regarding the therapeutic potential of blocking the chemokine receptors CCR3, CCR4 and CCR8 in allergic airway disease.
T cell immunoglobulin and mucin domain–containing molecule-3 (Tim-3) is a surface molecule that is preferentially expressed on activated Th1 cells in comparison to Th2 cells. Blockade of Tim-3 has been shown to enhance Th1-driven pathology in vivo, suggesting that blockade of Tim-3 may improve the development of Th2-associated responses such as allergy. To examine the effects of Tim-3 blockade on the Th2 response in vivo, we administered anti–Tim-3 antibody during pulmonary inflammation induced by transfer of ovalbumin (OVA)-reactive Th2 cells, and subsequent aerosol challenge with OVA. In this model, anti–Tim-3 antibody treatment before each airway challenge significantly reduced airway hyperreactivity, with a concomitant decrease in eosinophils and Th2 cells in the lung. We examined Th1 and Th2 cytokine levels in the lung after allergen challenge and found that pulmonary expression of the Th2 cytokine IL-5 was significantly reduced, whereas IFN-γ levels were significantly increased by anti–Tim-3 antibody treatment. Thus, blocking Tim-3 function has a beneficial effect during pulmonary inflammation by skewing the Th2 response toward that of a Th1 type, suggesting an important role for Tim-3 in the regulation of allergic disease.
CCRL2 is a heptahelic transmembrane receptor that shows the highest degree of homology with CCR1, an inflammatory chemokine receptor. CCRL2 mRNA was rapidly (30 min) and transiently (2-4 hrs) regulated during dendritic cell (DC) maturation. Protein expression paralleled RNA regulation. In vivo, CCRL2 was expressed by activated DC and macrophages, but not by eosinophils and T cells. CCRL2−/− mice showed normal recruitment of circulating DC into the lung but a defective trafficking of antigen-loaded lung DC to mediastinal lymph nodes. This defect was associated to a reduction in lymph node cellularity and reduced priming of Th2 response. CCRL2−/− mice were protected in a model of OVA-induced airway inflammation with reduced leukocyte recruitment in the BAL (eosinophils and mononuclear cells) and reduced production of the Th2 cytokines IL-4 and IL-5 and chemokines CCL11 and CCL17. The central role of CCRL2 deficiency in DC was supported by the fact that adoptive transfer of CCRL2−/− antigen-loaded DC in wild type animals recapitulated the phenotype observed in knock out mice. These data show a nonredundant role of CCRL2 in lung DC trafficking and propose a role for this receptor in the control of excessive airway inflammatory responses.
Infection or stimulation of the innate immune system by nonspecific microbial antigens is thought to educate the immune system to respond appropriately to allergens, preventing allergy.
To determine the immunologic pathways that might explain how infection/microbial exposure inhibits allergic sensitization.
Immunologic studies of non-antigen-specific functions of CD8 memory cells, their maturation in vivo, and their effects in a mouse asthma model, to test the hypothesis that CD8 memory is shaped by innate immunity in a way that can inhibit allergic disease.
We found that CD8 memory T-cell (CD8 Tm) populations bridge innate and adaptive immunity by responding to either antigen or cytokines alone. CD8 Tm populations partially subvert the clonal selection process by activating their neighbors through induction of dendritic cell IL-12. Stimulation of innate or acquired immunity in the lung or gut causes expansion/maturation of CD8 Tm populations, which provide an early source of cytokines, enhance TH1 immunity, and inhibit allergic sensitization and airway inflammation/hyperresponsiveness in a non-antigen-specific fashion.
CD8 T-cell–mediated immune memory is long-lived and can retain its capacity for rapid cytokine release in a nonantigen-specific fashion. This novel type of memory enhances TH1 over TH2 immunity and prevents allergic sensitization after exposure to environmental antigens or infection.
CD8 T cell; immunologic memory; innate immunity; allergy; TH1/TH2; dendritic cell; IL-12
Asthma is characterized by T helper cell 2 (Th2) type inflammation, leading to airway hyperresponsiveness and tissue remodeling. Th2 cell-driven inflammation is likely to represent an abnormal response to harmless airborne particles. These reactions are normally suppressed by regulatory T cells, which maintain airway tolerance. The anti-inflammatory cytokine IL-10 is likely to play a central role. The role of the cytokine transforming growth factor β (TGF-β) is more complex, with evidence for immune suppression and remodeling in the airways. In asthmatic individuals there is a breakdown in these regulatory mechanisms. There is emerging evidence that early life events, including exposure to allergen and infections, are critical in programming effective regulatory pathways to maintain pulmonary homeostasis. In this review we examine the clinical and experimental evidence for T regulatory cell function in the lung and discuss the events that might influence the functioning of these cells. Ultimately, the ability to enhance regulatory function in affected individuals may represent an effective treatment for asthma.
IL-9 is a pleiotropic cytokine that has multiple effects on structural as well as numerous hematopoietic cells, which are central to the pathogenesis of asthma.
The contribution of IL-9 to asthma pathogenesis has thus far been unclear, due to conflicting reports in the literature. These earlier studies focused on the role of IL-9 in acute inflammatory models; here we have investigated the effects of IL-9 blockade during chronic allergic inflammation.
Mice were exposed to either prolonged ovalbumin or house dust mite allergen challenge to induce chronic inflammation and airway remodeling.
Measurements and Main Results
We found that IL-9 governs allergen-induced mast cell (MC) numbers in the lung and has pronounced effects on chronic allergic inflammation. Anti–IL-9 antibody–treated mice were protected from airway remodeling with a concomitant reduction in mature MC numbers and activation, in addition to decreased expression of the profibrotic mediators transforming growth factor-β1, vascular endothelial growth factor, and fibroblast growth factor-2 in the lung. Airway remodeling was associated with impaired lung function in the peripheral airways and this was reversed by IL-9 neutralization. In human asthmatic lung tissue, we identified MCs as the main IL-9 receptor expressing population and found them to be sources of vascular endothelial growth factor and fibroblast growth factor-2.
Our data suggest an important role for an IL-9-MC axis in the pathology associated with chronic asthma and demonstrate that an impact on this axis could lead to a reduction in chronic inflammation and improved lung function in patients with asthma.
IL-9; mast cells; asthma; airway remodeling; AHR
Osteopontin (Opn) is important for T helper type 1 (TH1) immunity and autoimmunity. However, the role of this cytokine in TH2-mediated allergic disease as well as its effects on primary versus secondary antigenic encounters remain unclear. Here we demonstrate that OPN is expressed in the lungs of asthmatic individuals and that Opn-s, the secreted form of Opn, exerts opposing effects on mouse TH2 effector responses and subsequent allergic airway disease: pro-inflammatory at primary systemic sensitization, and anti-inflammatory during secondary pulmonary antigenic challenge. These effects of Opn-s are mainly mediated by the regulation of TH2-suppressing plasmacytoid dendritic cells (DCs) during primary sensitization and TH2-promoting conventional DCs during secondary antigenic challenge. Therapeutic administration of recombinant Opn during pulmonary secondary antigenic challenge decreased established TH2 responses and protected mice from allergic disease. These effects on TH2 allergic responses suggest that Opn-s is an important therapeutic target and provide new insight into its role in immunity.
The pathology of pediatric severe therapy-resistant asthma (STRA) is little understood.
We hypothesized that STRA in children is characterized by airway eosinophilia and mast cell inflammation and is driven by the TH2 cytokines IL-4, IL-5, and IL-13.
Sixty-nine children (mean age, 11.8 years; interquartile range, 5.6-17.3 years; patients with STRA, n = 53; control subjects, n = 16) underwent fiberoptic bronchoscopy, bronchoalveolar lavage (BAL), and endobronchial biopsy. Airway inflammation, remodeling, and BAL fluid and biopsy specimen TH2 cytokines were quantified. Children with STRA also underwent symptom assessment (Asthma Control Test), spirometry, exhaled nitric oxide and induced sputum evaluation.
Children with STRA had significantly increased BAL fluid and biopsy specimen eosinophil counts compared with those found in control subjects (BAL fluid, P < .001; biopsy specimen, P < .01); within the STRA group, there was marked between-patient variability in eosinophilia. Submucosal mast cell, neutrophil, and lymphocyte counts were similar in both groups. Reticular basement membrane thickness and airway smooth muscle were increased in patients with STRA compared with those found in control subjects (P < .0001 and P < .001, respectively). There was no increase in BAL fluid IL-4, IL-5, or IL-13 levels in patients with STRA compared with control subjects, and these cytokines were rarely detected in induced sputum. Biopsy IL-5+ and IL-13+ cell counts were also not higher in patients with STRA compared with those seen in control subjects. The subgroup (n = 15) of children with STRA with detectable BAL fluid TH2 cytokines had significantly lower lung function than those with undetectable BAL fluid TH2 cytokines.
STRA in children was characterized by remodeling and variable airway eosinophil counts. However, unlike in adults, there was no neutrophilia, and despite the wide range in eosinophil counts, the TH2 mediators that are thought to drive allergic asthma were mostly absent.
Pediatric asthma; eosinophilia; remodeling; severe therapy-resistant asthma; mediators
Cystic fibrosis (CF) is characterized by bronchoalveolar neutrophilia and submucosal lymphocytosis. We hypothesized that Th17 lymphocytes are part of this submucosal infiltrate.
Quantification and phenotyping of the lymphocytic infiltrate in the bronchial submucosa of patients with CF (n=53, of which 20 were newly diagnosed), non-CF bronchiectasis (n = 17), and healthy control subjects (n = 13).
We measured IL-17 levels in bronchoalveolar lavage and CD4+, CD8+, and IL-17+ cell counts in endobronchial biopsies. Correlations were made with infection status and other inflammatory markers. Potential cellular sources of IL-17 were determined by double staining.
Measurements and Main Results
IL-17+ cell counts (median [interquartile range] cells/mm2) were significantly higher in patients with established CF (205 [115–551]) and non-CF bronchiectasis (245 [183–436]) than in control subjects (53 [12–82]) (P<0.01 for both). Patients with newly diagnosed CF had intermediate counts (171 [91–252]). IL-17–positive CD4+ T cells, γδT cells, natural killer T cells, and neutrophils were identified. Bronchoalveolar lavage IL-17 levels (pg/ml) were highest in established CF (14.6 [2.2–38.4]), low in newly diagnosed CF and control subjects (1.7 [1.7–1.74]; 1.7 [1.7–3]), and intermediate in non-CF bronchiectasis (9.1 [1.7–34] pg/ml) (Kruskal-Wallis P = 0.001). There was a significant correlation between IL-17 and neutrophil counts (P < 0.001, R = 0.6) as well as IL-4 (P < 0.001, R = 0.84).
Th17 lymphocytes are present in the airway submucosa in CF, even in a young, newly diagnosed group. Other IL-17+ cells include neutrophils, γδ T cells, and natural killer T cells.
Th17 cells; cystic fibrosis; inflammation
House dust mites (HDM; Dermatophagoides sp.) are one of the commonest aeroallergens worldwide and up to 85% of asthmatics are typically HDM allergic. Allergenicity is associated both with the mites themselves and with ligands derived from mite-associated bacterial and fungal products. Murine models of allergic airways disease for asthma research have recently switched from the use of surrogate allergen ovalbumin together with adjuvant to use of the HDM extract. This has accelerated understanding of how adaptive and innate immunity generate downstream pathology. We review the myriad ways in which HDM allergic responses are orchestrated. Understanding the molecular pathways that elicit HDM-associated pathology is likely to reveal novel targets for therapeutic intervention.
Asthma frequently commences in early life during airway and immune development and exposure to new environmental challenges. Endobronchial biopsies from children with asthma are abnormal, and lung function is maximally reduced by 6 years of age. As longitudinal biopsy studies are unethical in children, the relationship between development of pathology and reduced lung function is unknown. We aimed to establish a novel neonatal mouse model of allergic airways disease to investigate the developmental sequence of the pathophysiologic features of asthma. Neonatal Balb/c mice were challenged three times weekly from Day 3 of life using intranasal house dust mite (HDM) or saline for up to 12 weeks. Weekly assessments of airway inflammation and remodeling were made. Airway hyperresponsiveness (AHR) to methacholine was assessed from Week 2 onward. Total and eosinophilic inflammation was significantly increased in the lungs of HDM-exposed neonates from Week 2 onwards, and a peak was seen at 3 weeks. Goblet cells and peribronchiolar reticulin deposition were significantly increased in HDM-exposed neonates from Week 3, and peribronchiolar collagen was significantly greater from Week 4. HDM-exposed neonates had increased AHR from Week 2 onward. Although inflammation and AHR had subsided after 4 weeks without allergen challenge, the increased reticulin and collagen deposition persisted in HDM-exposed mice. Neonatal mice exposed to intranasal HDM developed eosinophilic inflammation, airway remodeling, and AHR as reported in pediatric asthma. Importantly, all abnormalities developed in parallel, not sequentially, between 2 and 3 weeks of age.
pediatric; remodeling; asthma pathophysiology; mouse model; allergic airways disease
Deficient suppression of T cell responses to allergen by CD4+CD25+ regulatory T cells has been observed in patients with allergic disease. Our current experiments used a mouse model of airway inflammation to examine the suppressive activity of allergen-specific CD4+CD25+ T cells in vivo. Transfer of ovalbumin (OVA) peptide–specific CD4+CD25+ T cells to OVA-sensitized mice reduced airway hyperreactivity (AHR), recruitment of eosinophils, and T helper type 2 (Th2) cytokine expression in the lung after allergen challenge. This suppression was dependent on interleukin (IL) 10 because increased lung expression of IL-10 was detected after transfer of CD4+CD25+ T cells, and regulation was reversed by anti–IL-10R antibody. However, suppression of AHR, airway inflammation, and increased expression of IL-10 were still observed when CD4+CD25+ T cells from IL-10 gene–deficient mice were transferred. Intracellular cytokine staining confirmed that transfer of CD4+CD25+ T cells induced IL-10 expression in recipient CD4+ T cells, but no increase in IL-10 expression was detected in airway macrophages, dendritic cells, or B cells. These data suggest that CD4+CD25+ T cells can suppress the Th2 cell–driven response to allergen in vivo by an IL-10–dependent mechanism but that IL-10 production by the regulatory T cells themselves is not required for such suppression.
Deficient suppression of T cell responses to allergen by CD4+CD25+ regulatory T cells has been observed in patients with allergic disease. Our current experiments used a mouse model of airway inflammation to examine the suppressive activity of allergen-specific CD4+CD25+ T cells in vivo. Transfer of ovalbumin (OVA) peptide-specific CD4+CD25+ T cells to OVA-sensitized mice reduced airway hyperreactivity (AHR), recruitment of eosinophils, and T helper type 2 (Th2) cytokine expression in the lung after allergen challenge. This suppression was dependent on interleukin (IL) 10 because increased lung expression of IL-10 was detected after transfer of CD4+CD25+ T cells, and regulation was reversed by anti-IL-10R antibody. However, suppression of AHR, airway inflammation, and increased expression of IL-10 were still observed when CD4+CD25+ T cells from IL-10 gene-deficient mice were transferred. Intracellular cytokine staining confirmed that transfer of CD4+CD25+ T cells induced IL-10 expression in recipient CD4+ T cells, but no increase in IL-10 expression was detected in airway macrophages, dendritic cells, or B cells. These data suggest that CD4+CD25+ T cells can suppress the Th2 cell-driven response to allergen in vivo by an IL-10-dependent mechanism but that IL-10 production by the regulatory T cells themselves is not required for such suppression.
Interleukin (IL)-9 is a pleiotropic cytokine secreted by T helper (Th)2 cells and has been proposed as a candidate gene for asthma and allergy. We have used mice genetically deficient in IL-9 to determine the role of this cytokine in the pathophysiologic features of the allergic pulmonary response–airway hyperreactivity (AHR) and eosinophilia. We have demonstrated that IL-9 is not required for the development of a robust Th2 response to allergen in sensitized mice. IL-9 knockout mice developed a similar degree of eosinophilic inflammation and AHR to their wild-type littermates. Goblet cell hyperplasia and immunoglobulin (Ig) E production were also unaffected by the lack of IL-9. Moreover, levels of bronchoalveolar lavage (BAL) IL-4, IL-5, and IL-13 were comparable between wild-type and knockout mice. These findings indicate that IL-9 is not obligatory for the development of eosinophilia and AHR, and imply that other Th2 cytokines can act in a compensatory fashion.
Th2 cytokines; asthma; airway hyperreactivity; eosinophilia; mucus
Rationale: γδT lymphocytes are enriched within the epithelial microenvironment, where they are thought to maintain homeostasis and limit immunopathology. γδT cells are postulated to exert a regulatory influence during acute allergic airway disease, but the mechanism is unknown. Although regulation of allergic airway disease has been attributed to IL-17–producing T helper (Th) 17 cells, we have found that γδT cells represent the major source of IL-17 in the allergic lung.
Objectives: The aim of this study was to determine the contribution of these IL-17–producing γδT cells to regulation of allergic airway inflammation.
Methods: Flow cytometry revealed that IL-17–producing γδT cells are more prevalent than IL-17+αβT cells (Th17) in a murine model of ovalbumin-induced allergic inflammation.
Measurements and Main Results: Transfer of γδT cells at the peak of acute allergic responses ameliorated airway hyperresponsiveness with a corresponding acceleration in the resolution of eosinophilic and Th2-driven inflammation. Conversely, functional blockade of γδT cells led to exacerbation of injury. Neither treatment changed pulmonary Th17 cell numbers. Moreover, transfer of Th17 cells had no effect on disease outcome. Importantly, IL-17–deficient γδT cells were unable to promote resolution of injury. These data identify IL-17–producing γδT cells as key regulators of the allergic response in vivo.
Conclusions: This unfolds a new perspective for the understanding of γδT cell function with regard to innate regulation of the adaptive immune responses, emphasizing that resolution of responses are important in determining the outcome of acute inflammatory episodes as well as for maintenance of tissue integrity and homeostasis.
airway hyperresponsiveness; airway inflammation; inflammatory resolution; γδT cells; IL-17