T cells and ILC2s are major effector cells in influenza‐induced exacerbation of allergic airway inflammation in mice

Influenza virus infection is an important cause of severe asthma exacerbations, but it remains unclear how a Th1‐mediated antiviral response triggers a prototypical Th2 disease. We investigated CD4⁺ T cells and group 2 innate lymphoid cells (ILC2s) in influenza virus‐infected mice. We found that ILC2s accumulated in the lung rapidly after influenza virus infection, but the induction of IL‐5 and IL‐13 secretion was delayed and concomitant with T cell activation. In an influenza‐induced exacerbation of allergic airway inflammation model we noticed an initial reduction of ILC2 numbers and cytokine production in broncho‐alveolar lavage compared to chronic house dust mite (HDM)‐mediated airway inflammation alone. ILC2s phenotype was characterized by low T1/ST2, ICOS, KLRG1, and CD25 expression, resembling naïve ILC2s. The contribution of ILC2s to type 2 cytokine production in the early stage of the influenza‐induced exacerbation was limited. In contrast, T cells showed increased IL‐4 and IL‐5 production when exposed to both HDM and influenza virus. Upon virus clearance, ILC2s regained an activated T1/ST2^highICOS^highKLRG1^highCD25^high phenotype paired with cytokine production and were major contributors to the type 2 cytokine milieu. Collectively, our data indicate that both T cells and ILC2s contribute to influenza‐induced exacerbation of allergic airway inflammation, but with different kinetics.     

Regulatory T cells and type 2 innate lymphoid cell‐dependent asthma

Group 2 innate lymphoid cells (ILC2s) are a recently identified group of cells with the potent capability to produce Th2‐type cytokines such as interleukin (IL)‐5 and IL‐13. Several studies suggest that ILC2s play an important role in the development of allergic diseases and asthma. Activation of pulmonary ILC2s in murine models lacking T and B cells induces eosinophilia and airway hyper‐reactivity (AHR), which are cardinal features of asthma. More importantly, numerous recent studies have highlighted the role of ILC2s in asthma persistence and exacerbation among human subjects, and thus, regulation of pulmonary ILC2s is a major area of investigation aimed at curbing allergic lung inflammation and exacerbation. Emerging evidence reveals that a group of regulatory T cells, induced Tregs (iTregs), effectively suppress the production of ILC2‐driven, pro‐inflammatory cytokines IL‐5 and IL‐13. The inhibitory effects of iTregs are blocked by preventing direct cellular contact or by inhibiting the ICOS‐ICOS‐ligand (ICOSL) pathway, suggesting that both direct contact and ICOS‐ICOSL interaction are important in the regulation of ILC2 function. Also, cytokines such as IL‐10 and TGF‐β1 significantly reduce cytokine secretion by ILC2s. Altogether, these new findings uncover iTregs as potent regulators of ILC2 activation and implicate their utility as a therapeutic approach for the treatment of ILC2‐mediated allergic asthma and respiratory disease.     

Group 2 innate lymphoid cells in lung inflammation

Although allergic asthma is a heterogeneous disease, allergen‐specific T helper 2 (Th2) cells producing the key cytokines involved in type 2 inflammation, interleukin‐4 (IL‐4), IL‐5 and IL‐13, are thought to play a major role in asthma pathogenesis. This model is challenged by the recent discovery of group 2 innate lymphoid cells (ILC2) that represent a critical innate source of type 2 cytokines. These ILC2 are activated by epithelial cell‐derived cytokines, including IL‐25 and IL‐33, which have been implicated in the initiation of asthma. In this review, we will discuss recent studies supporting a significant role for ILC2 in lung inflammation, with special attention to allergen‐induced asthma.     

A Potential Role of Group 2 Innate Lymphoid Cells in Eosinophilic Chronic Rhinosinusitis With Nasal Polyps

Chronic rhinosinusitis with nasal polyps (CRSwNP), a type 2-based upper airway disease, is mainly characterized by high asthma comorbidity and recurrence after surgery. It has been shown that type 2 cytokines, including interleukin (IL)-4, IL-5, and IL-13 released from T helper 2 (Th2) cells as well as group 2 innate lymphoid cells (ILC2s), contribute to chronic inflammation of CRSwNP. This review summarizes recent progresses made in our understanding of ILC2 activity, particularly ILC2 accumulation at airway inflammation sites, cooperation with Th2 cells in aggravating the CRSwNP inflammatory process and interactions with regulatory T cells (Tregs) in resisting Tregs-mediated suppressive function in allergic inflammation. A better understanding of the biology of ILC2s should lay a good foundation in elucidating the pathogenesis of CRSwNP, and subsequently may lead to the development of new therapeutic strategies for the management of CRSwNP.     

Cytotoxic T lymphocyte antigen 4 immunoglobulin modified dendritic cells attenuate allergic airway inflammation and hyperresponsiveness by regulating the development of T helper type 1 (Th1)/Th2 and Th2/regulatory T cell subsets in a murine model of asthma

T helper type 2 (Th2) and regulatory T cells (T(reg) ) have been postulated to have critical roles in the pathogenesis of allergic asthma. Cytotoxic T lymphocyte antigen 4 immunoglobulin (CTLA4Ig) gene-modified dendritic cells (DC-CTLA4Ig) have the potential to reduce Th2 cells and induce T(reg) cells. In the present study, we evaluated the therapeutic effects and potential mechanisms of the adoptive transfer of DC-CTLA4Ig into mice in an experimental model of asthma. BALB/c mice were sensitized with ovalbumin (OVA) and challenged with aerosolized OVA for 7 days. Just prior to the first challenge, DC-CTLA4Ig, DCs or DCs infected with DC-green fluorescent protein (GFP) were injected intravenously into mice. The administration of DC-CTLA4Ig reduced airway hyperresponsiveness, relieved asthmatic airway inflammation and decreased the numbers of esosinophils in the BALF in OVA-sensitized/challenged mice. In addition, DC-CTLA4Ig altered the balance of Th1/Th2 cytokine production in the lungs with increased interferon (IFN)-γ levels and decreased interleukin (IL)-4 levels, decreased the percentage of Th2 and increased both the percentage of Th1 and T(reg) cells in the lungs of OVA-sensitized/challenged mice. This research demonstrates that DC-CTL4Ig reduces airway hyperresponsiveness effectively and prevents airway inflammation in OVA-sensitized/challenged mice, which is due most probably to attenuated secretion of Th2 cytokines and increased secretion of Th1 cytokines in the local airway, and the correction of the pulmonary imbalance between Th1/Th2 cells and Th2/T(reg) cells.     

Pulmonary innate lymphoid cells are major producers of IL-5 and IL-13 in murine models of allergic asthma

Allergic asthma is characterized by chronic airway inflammation and hyperreactivity and is thought to be mediated by an adaptive T helper-2 (Th2) cell-type immune response. Here, we demonstrate that type 2 pulmonary innate lymphoid cells (ILC2s) significantly contribute to production of the key cytokines IL-5 and IL-13 in experimental asthma. In naive mice, lineage-marker negative ILC2s expressing IL-7Rα, CD25, Sca-1, and T1/ST2(IL-33R) were present in lungs and mediastinal lymph nodes (MedLNs), but not in broncho-alveolar lavage (BAL) fluid. Upon intranasal administration of IL-25 or IL-33, an asthma phenotype was induced, whereby ILC2s accumulated in lungs, MedLNs, and BAL fluid. After IL-25 and IL-33 administration, ILC2s constituted ～50 and ～80% of IL-5(+) /IL-13(+) cells in lung and BAL, respectively. Also in house dust mite-induced or ovalbumin-induced allergic asthma, the ILC2 population in lung and BAL fluid increased significantly in size and ILC2s were a major source of IL-5 or IL-13. Particularly in OVA-induced asthma, the contribution of ILC2s to the total population of intracellular IL-5(+) and IL-13(+) cells in the lung was in the same range as found for Th2 cells. We conclude that both ILC2s and Th2 cells produce large amounts of IL-5 and IL-13 that contribute to allergic airway inflammation.     

Polymorphonuclear myeloid-derived suppressor cells attenuate allergic airway inflammation by negatively regulating group 2 innate lymphoid cells

Hyperactivation of the type 2 immune response is the major mechanism of allergic asthma, in which both group 2 innate lymphoid cells (ILC2s) and type 2 helper T (Th2) cells participate. Myeloid-derived suppressor cells (MDSCs) alleviate asthma by suppressing Th2 cells. However, the potential effects of MDSCs on the biological functions of ILC2s remain largely unknown. Here, we examined the roles of MDSCs (MDSCs) in the modulation of ILC2 function. Our results showed that polymorphonuclear (PMN)-MDSCs, but not monocytic (M-) MDSCs, effectively suppressed the cytokine production of ILC2s both in vitro and in vivo, thereby alleviating airway inflammation. Further analyses showed that cyclo-oxygenase-1 may mediate the suppressive effects of PMN-MDSCs on ILC2 responses. Our findings demonstrated that PMN-MDSCs may serve as a potent therapeutic target for the treatment of ILC2-driven allergic asthma.     

Bone marrow type 2 innate lymphoid cells: a local source of interleukin‐5 in interleukin‐33‐driven eosinophilia

T helper type 2 (Th2) cells, type 2 innate lymphoid cells (ILC2s) and eosinophil progenitors have previously been described to produce interleukin‐5 (IL‐5) in the airways upon allergen provocation or by direct administration of IL‐33. Eosinophilic airway inflammation is known to be associated with IL‐5‐dependent eosinophil development in the bone marrow, however, the source of IL‐5 remains unclear. T helper cells, ILC2s and CD34⁺ progenitors have been proposed to be involved in this process, therefore, we investigated whether these cells are taking part in eosinophilopoiesis by producing IL‐5 locally in the bone marrow in IL‐33‐driven inflammation. Airway exposure with IL‐33 led to eosinophil infiltration in airways and elevated eotaxin‐2/CCL24. Importantly, IL‐5 production as well as expression of the IL‐33 receptor increased in ILC2s in the bone marrow under this treatment. A small but significant induction of IL‐5 was also found in CD34⁺ progenitors but not in T helper cells. Similar results were obtained by in vitro stimulation with IL‐33 where ILC2s rapidly produced large amounts of IL‐5, which coincided with the induction of eosinophil hematopoiesis. IL‐33‐mediated eosinophil production was indeed dependent on IL‐5 as both airway and bone marrow eosinophils decreased in mice treated with anti‐IL‐5 in combination with IL‐33. Interestingly, the responsiveness of ILC2s to IL‐33 as well as IL‐33‐induced eotaxin‐2/CCL24 were independent of the levels of IL‐5. In summary, we demonstrate for the first time that IL‐33 acts directly on bone marrow ILC2s, making them an early source of IL‐5 and part of a process that is central in IL‐33‐driven eosinophilia.     

OX40 blockade inhibits house dust mite driven allergic lung inflammation in mice and in vitro allergic responses in humans

The costimulatory receptor OX40 is expressed on activated T cells and regulates T‐cell responses. Here, we show the efficacy and mechanism of action of an OX40 blocking antibody using the chronic house dust mite (HDM) mouse model of lung inflammation and in vitro HDM stimulation of cells from HDM allergic human donors. We have demonstrated that OX40 blockade leads to a reduction in the number of eosinophils and neutrophils in the lavage fluid and lung tissue of HDM sensitized mice. This was accompanied by a decrease in activated and memory CD4⁺ T cells in the lungs and further analysis revealed that both the Th2 and Th17 populations were inhibited. Improved lung function and decreased HDM‐specific antibody responses were also noted. Significantly, efficacy was observed even when anti‐OX40 treatment was delayed until after inflammation was established. OX40 blockade also inhibited the release of the Th2 cytokines IL‐5 and IL‐13 from cells isolated from HDM allergic human donors. Altogether, our data provide evidence of a role of the OX40/OX40L pathway in ongoing allergic lung inflammation and support clinical studies of a blocking OX40 antibody in Th2 high severe asthma patients.     

ICOS regulates the pool of group 2 innate lymphoid cells under homeostatic and inflammatory conditions in mice

Group 2 innate lymphoid cells (ILC2s) are innate effectors playing an important role in the defense against helminthic infections and in the pathogenesis of allergic inflammation. Cytokines have been identified as the major stimuli driving ILC2 activation and expansion. Conversely, it is unclear whether costimulatory molecules contribute to regulation of ILC2 functions. ILC2s display high expression of inducible T‐cell costimulator (ICOS), which belongs to the CD28 superfamily, and which has been shown to control late effector T‐cell functions, and is of utmost importance for the humoral immune response. However, the biological function of ICOS expression on ILC2s is unknown. Here, we show that ICOS signaling in mice regulates ILC2 homeostasis independently of T cells and B cells, by promoting proliferation and accumulation of mature ILC2s in lung and intestine. In a model of IL‐33‐induced airway inflammation, ICOS controls ILC2 activation and eosinophil infiltration in the lung. Our data identify a role of ICOS in innate immunity and indicate that not only cytokines, but also costimulatory pathways such as those involving ICOS, can contribute to regulate the ILC2 pool. Thus, ICOS costimulation blockade, which is currently under clinical evaluation for inhibiting the humoral immune response, could also target innate inflammatory circuits.     

IL-33: biological properties,functions, and roles in airway disease

Interleukin (IL)-33 is a key cytokine involved in type 2 immunity and allergic airway diseases. Abundantly expressed in lung epithelial cells, IL-33 plays critical roles in both innate and adaptive immune responses in mucosal organs. In innate immunity, IL-33 and group 2 innate lymphoid cells (ILC2s) provide an essential axis for rapid immune responses and tissue homeostasis. In adaptive immunity, IL-33 interacts with dendritic cells, Th2 cells, follicular T cells, and regulatory T cells, where IL-33 influences the development of chronic airway inflammation and tissue remodeling. The clinical findings that both the IL-33 and ILC2 levels are elevated in patients with allergic airway diseases suggest that IL-33 plays an important role in the pathogenesis of these diseases. IL-33 and ILC2 may also serve as biomarkers for disease classification and to monitor the progression of diseases. In this article, we reviewed the current knowledge of the biology of IL-33 and discussed the roles of the IL-33 in regulating airway immune responses and allergic airway diseases.     

Innate lymphoid cells in asthma: Will they take your breath away?

Asthma is a complex and heterogeneous disease that is characterized by airway hyper‐reactivity (AHR) and airway inflammation. Although asthma was long thought to be driven by allergen‐reactive T_H2 cells, it has recently become clear that the pathogenesis of asthma is more complicated and associated with multiple pathways and cell types. A very exciting recent development was the discovery of innate lymphoid cells (ILCs) as key players in the pathogenesis of asthma. ILCs do not express antigen receptors but react promptly to “danger signals” from inflamed tissue and produce an array of cytokines that direct the ensuing immune response. The roles of ILCs may differ in distinct asthma phenotypes. ILC2s may be critical for initiation of adaptive immune responses in inhaled allergen‐driven AHR, but may also function independently of adaptive immunity, mediating influenza‐induced AHR. ILC2s also contribute to resolution of lung inflammation through their production of amphiregulin. Obesity‐induced asthma is associated with expansion of IL‐17A‐producing ILC3s in the lungs. Furthermore, ILCs may also contribute to steroid‐resistant asthma. Although the precise roles of ILCs in different types of asthma are still under investigation, it is clear that inhibition of ILC function represents a potential target that could provide novel treatments for asthma.     

IL-25 Promotes Th2 Immunity Responses in Airway Inflammation of Asthmatic Mice via Activation of Dendritic Cells

Allergic asthma occurs as a consequence of inappropriate immunologic inflammation to allergens and characterized by Th2 adaptive immune response. Recent studies indicated that interleukin (IL)-25, a member of the IL-17 cytokine family, had been implicated in inducing Th2 cell-dependent inflammation in airway epithelium and IL-25-deficient mice exhibit impaired Th2 immunity responses; however, how these cytokines influence innate immune responses remains poorly understood. In this study, we used ovalbumin (OVA) sensitization and challenge to induce the murine asthmatic model and confirmed by histological analysis of lung tissues and serum levels of total and OVA-specific immunoglobulin (Ig)-E. The expression of IL-25 was detected by quantitative real-time PCR and immunohistochemistry, respectively, and the dendritic cells (DCs) activation was detected by levels of CD80 and CD86 in bronchoalveolar lavage fluid (BALF) by flow cytometry. The mice sensitized and challenged with OVA showed high expression of IL-25 in both mRNA and protein levels in lungs. We detected the expression of CD80 and CD86 in BALF was also increased. A tight correlation between IL-25 mRNA and other Th2 cells producing cytokines such as IL-4, IL-5, and IL-13 in BALF was identified. Furthermore, when the asthmatic mice were treated with inhaled corticosteroids, the inflammatory cells infiltration and the inflammatory cytokines secretion were significantly decreased. In this study, we show that IL-25 promoted the accumulation of co-stimulatory molecules of CD80 and CD86 on DCs and then induced the differentiation of prime naive CD4⁺ T cells to become proinflammatory Th2 cells and promoted Th2 cytokine responses in OVA-induced airway inflammation. The ability of IL-25 to promote the activation and differentiation of DCs population was identified as a link between the IL-17 cytokine family and the innate immune response and suggested a previously unrecognized innate immune pathway that promotes Th2 cytokine responses in asthmatic airway inflammation. Inhaled corticosteroids might be capable of inhibiting the promotion of IL-25 and present a promising strategy for the treatment of asthma     

Type 2 innate lymphoid cells: at the cross-roads in allergic asthma

Allergic asthma is a chronic inflammatory disease of the lower airways that affects millions of people worldwide. Allergic asthma is a T helper 2 cell (Th2)-mediated disease, in which Th2 cytokines interleukin (IL)-4, IL-5, and IL-13 are closely associated with the symptoms. IL-4 is needed by B cells to switch toward an IgE response, IL-5 recruits and activates eosinophils while IL-13 increases mucus production. The identification of type 2 innate lymphoid cells (ILC2), which are able to rapidly produce large amounts of IL-5 and IL-13 in response to epithelial derived cytokines, implicated a new key player besides Th2 cells. ILCs constitute a family of innate lymphocytes distinct from T and B cells. ILC2s are located in various epithelial compartments in mice and human, including the lung. The recent finding of increased numbers of ILC2s in the airways of severe asthma patients prompts further research to clarify their immunological function. Murine studies have shown that ILC2s are an early innate source of IL-5 and IL-13 after allergen exposure, which induce airway eosinophilic infiltration, mucus hyperproduction, and airway hyperresponsiveness but not allergen-specific IgE production. ILC2s contribute to the initiation as well as to the maintenance of the adaptive type 2 immune response. Here, we review the recent progress on our understanding of the role of ILC2s in the immunopathology of allergic asthma, in particular by studies using murine models which have elucidated fundamental mechanisms by which ILC2s act.     

Post-allergen challenge inhibition of poly(ADP-ribose) polymerase harbors therapeutic potential for treatment of allergic airway inflammation

Background Identifying therapeutic drugs that block the release or effects of T‐helper type 2 (Th2) cytokines after allergen exposure is an important goal for the treatment of allergic inflammatory diseases including asthma. We recently showed, using a murine model of allergic airway inflammation, that poly(ADP‐ribose) polymerase (PARP) plays an important role in the pathogenesis of asthma‐related lung inflammation. PARP inhibition, by single injection of a novel inhibitor, thieno[2,3‐c]isoquinolin‐5‐one (TIQ‐A), before ovalbumin (OVA) challenge, prevented airway eosinophilia in C57BL/6 mice with concomitant suppression of Th2 cytokine production and mucus secretion. Objective To evaluate the efficacy of the drug when it is given after OVA challenge for its possible therapeutic potential. Methods This study was conducted using a murine model of allergic airway inflammation. Results A single injection of TIQ‐A (6 mg/kg) one or 6 h post‐allergen challenge conferred similar reduction in OVA challenge‐induced eosinophilia. More significantly, post‐allergen challenge administration of the drug exerted even better suppression on the production of IL‐4, IL‐5, IL‐13, and IgE and prevented airway hyperresponsiveness to inhaled‐methacholine. The significant decrease in IL‐13 was accompanied by a complete absence of airways mucus production indicating a potential protection against allergen‐induced airway remodelling. Conclusion The coincidence of the inflammation trigger and the time of drug administration appear to be important for the drug's more pronounced protection. The observed time window for efficacy, 1 or 6 h after allergen challenge may be of great clinical interest. These findings may provide a novel therapeutic strategy for the treatment of allergic airway inflammation, including asthma.     

Administration of polysaccharides from Antrodia camphorata modulates dendritic cell function and alleviates allergen‐induced T helper type 2 responses in a mouse model of asthma

Asthma is a chronic disease characterized by airway inflammation caused by the dysregulated production of cytokines secreted by allergen‐specific type 2 T helper (Th2) cells. Antrodia camphorata is a commonly used fungus in Asian folk medicine, and A. camphorata polysaccharides are reported to possess anti‐cancer activities. In this study, the immunomodulatory effects of purified fractionated polysaccharides (GF2) from A. camphorata on dendritic cells (DCs) and their potential preventive effects against ovalbumin (OVA) ‐induced asthma were investigated. In the presence of GF2, lipopolysaccharide (LPS) ‐activated DCs exhibited up‐regulated expression of major histocompatibility complex (MHC) class II and co‐stimulatory molecules, as well as enhanced interleukin‐10 (IL‐10) and IL‐12 production. GF2 treatment on LPS‐activated DCs suppressed naïve CD4⁺ T‐cell proliferation and Th2 cell polarization with IL‐10 production in an allogeneic mixed lymphocyte reaction. In animal experiments, a high dose of GF2 efficiently reduced expression levels of OVA‐specific immunoglobulin G1 (IgG1) and IgE. However, lower doses of GF2 significantly enhanced OVA‐specific IgG2a production. Our data also showed that administration of GF2 dose‐dependently inhibited the development of airway hyperresponsiveness, airway eosinophilia and Th2 responses. OVA‐specific CD4⁺ T cells from higher doses of GF2‐treated mice had significantly lower proliferative capacities compared with control mice. Moreover, treatment with GF2 significantly increased the high levels of IL‐10 and low levels of interferon‐γ produced by T cells. Taken together, these data indicate that administration of A. camphorata polysaccharides (GF2) may have therapeutic potential when used as an adjuvant for the immunomodulatory treatment of allergic asthma.     

Effects of 4 months of smoking in mice with ovalbumin-induced airway inflammation

Background The effects of smoking on asthma pathogenesis are complex and not well studied. We have shown recently that 3 weeks of smoking attenuates ovalbumin (OVA)‐induced airway inflammation in mice and that 4–6 months of smoking induces emphysema in mice without airway inflammation. Effects of combined long‐term smoking and OVA exposure have not been investigated so far. Objective To study whether long‐term smoking affects progression of allergic airway inflammation and/or enhances the development of emphysema in mice. Methods Mice were sensitized to OVA and challenged with saline or OVA aerosols for 6 months. From 2 months onwards, mice were also exposed to air or smoke. Lung tissue was analysed for extent of inflammation, emphysema, remodelling and for cytokine levels, and serum for OVA‐specific IgE levels. Results Chronic OVA exposure of 6 months resulted in a T helper type 2 (Th2)‐type inflammation with increased levels of IL‐4, IL‐5, IL‐6 and infiltration of eosinophils, CD4⁺ T cells, macrophages and plasma cells. Smoking induced a Th17‐type of airway inflammation, characterized by neutrophils, macrophages, B cells and increased levels of IL‐17, IL‐6, granulocyte‐macrophage colony‐stimulating factor, granulocyte colony‐stimulating factor and monocyte chemoattractant protein‐1. Concomittant smoking and OVA exposure resulted in inflammation similar to OVA exposure alone. OVA exposure increased IgE levels compared with saline exposure, and smoking did not further increase these levels. Conclusion We did not find evidence for increased inflammation, IgE levels or emphysema in mice with allergic airway inflammation after 4 months of smoking compared with non‐smoking. However, a 4‐month exposure to smoke alone did enhance neutrophilic airway inflammation characterized by high pulmonary IL‐17 levels. A Th2 inflammatory environment due to OVA exposure may be one explanation as to why no further detrimental effects of smoking on allergic airway inflammation were found.     

Toll‐like receptor 4 agonists adsorbed to aluminium hydroxide adjuvant attenuate ovalbumin‐specific allergic airway disease: role of MyD88 adaptor molecule and interleukin‐12/interferon‐γ axis

Background Epidemiological and experimental data suggest that bacterial lipopolysaccharides (LPS) can either protect from or exacerbate allergic asthma. Lipopolysaccharides trigger immune responses through toll‐like receptor 4 (TLR4) that in turn activates two major signalling pathways via either MyD88 or TRIF adaptor proteins. The LPS is a pro‐Type 1 T helper cells (Th1) adjuvant while aluminium hydroxide (alum) is a strong Type 2 T helper cells (Th2) adjuvant, but the effect of the mixing of both adjuvants on the development of lung allergy has not been investigated. Objective We determined whether natural (LPS) or synthetic (ER‐803022) TLR4 agonists adsorbed onto alum adjuvant affect allergen sensitization and development of airway allergic disease. To dissect LPS‐induced molecular pathways, we used TLR4‐, MyD88‐, TRIF‐, or IL‐12/IFN‐γ‐deficient mice. Methods Mice were sensitized with subcutaneous injections of ovalbumin (OVA) with or without TLR4 agonists co‐adsorbed onto alum and challenged with intranasally with OVA. The development of allergic lung disease was evaluated 24 h after last OVA challenge. Results Sensitization with OVA plus LPS co‐adsorbed onto alum impaired in dose‐dependent manner OVA‐induced Th2‐mediated allergic responses such as airway eosinophilia, type‐2 cytokines secretion, airway hyper‐reactivity, mucus hyper production and serum levels of IgE or IgG1 anaphylactic antibodies. Although the levels of IgG2a, Th1‐affiliated isotype increased, investigation into the lung‐specific effects revealed that LPS did not induce a Th1 pattern of inflammation. Lipopolysaccharides impaired the development of Th2 immunity, signaling via TLR4 and MyD88 molecules and via the IL‐12/IFN‐γ axis, but not through TRIF pathway. Moreover, the synthetic TLR4 agonists that proved to have a less systemic inflammatory response than LPS also protected against allergic asthma development. Conclusion Toll‐like receptor 4 agonists co‐adsorbed with allergen onto alum down‐modulate allergic lung disease and prevent the development of polarized T cell‐mediated airway inflammation.     

IgE-dependent enhancement of Th2 cell-mediated allergic inflammation in the airways

T helper 2 (Th2) cell-derived cytokines, including interleukin (IL)-4, IL-5 and IL-13, play important roles in causing allergic airway inflammation. In contrast to Th2 cells, however, the role of IgE and mast cells in inducing allergic airway inflammation is not understood fully. In the present study, we addressed this point using transgenic mice expressing trinitrophenyl (TNP)-specific IgE (TNP-IgE mice), which enable us to investigate the role of IgE without the influence of antigen-specific T cell activation and other immunoglobulins. When the corresponding antigen, TNP-BSA, was administered intranasally to TNP-IgE mice, a large number of CD4+ T cells were recruited into the airways. In contrast, TNP-BSA administration did not induce eosinophil recruitment into the airways or airway hyperreactivity. Furthermore, when ovalbumin (OVA)-specific Th2 cells were transferred to TNP-IgE mice and the mice were challenged with inhaled OVA, TNP-BSA administration increased OVA-specific T cell recruitment and then enhanced Th2 cell-mediated eosinophil recruitment into the airways. These results indicate that IgE-induced mast cell activation principally induces CD4+ T cell recruitment into the airways and thus plays an important role in enhancing Th2 cell-mediated eosinophilic airway inflammation by recruiting Th2 cells into the site of allergic inflammation.