Resolution of airway inflammation and hyperreactivity after in vivo transfer of CD4+CD25+ regulatory T cells is interleukin 10 dependent

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 18 acts on memory T helper cells type 1 to induce airway inflammation and hyperresponsiveness in a naive host mouse

Interleukin (IL)-18 was originally regarded to induce T helper cell (Th)1-related cytokines. In general, factors favoring interferon (IFN)-gamma production are believed to abolish allergic diseases. Thus, we tested the role of IL-18 in regulation of bronchial asthma. To avoid a background response of host-derived T cells, we administered memory type Th1 or Th2 cells into unsensitized mice and examined their role in induction of bronchial asthma. Administration of antigen (Ag) induced both airway inflammation and airway hyperresponsiveness (AHR) in mice receiving memory Th2 cells. In contrast, the same treatment induced only airway inflammation but not AHR in mice receiving memory Th1 cells. However, these mice developed striking AHR when they were coadministered with IL-18. Furthermore, mice having received IFN-gamma-expressing Th1 cells sorted from polarized Th1 cells developed severe airway inflammation and AHR after intranasal administration of Ag and IL-18. Thus, Th1 cells become harmful when they are stimulated with Ag and IL-18. Newly polarized Th1 cells and IFN-gamma-expressing Th1 cells, both of which express IL-18 receptor alpha chain strongly, produce IFN-gamma, IL-9, IL-13, granulocyte/macrophage colony-stimulating factor, tumor necrosis factor alpha, regulated on activation, normal T cell expressed and secreted, and macrophage inflammatory protein 1alpha upon stimulation with Ag, IL-2, and IL-18 in vitro. Thus, Ag and IL-18 stimulate memory Th1 cells to induce severe airway inflammation and AHR in the naive host.     

Construction of single-chain interleukin-12 DNA plasmid to treat airway hyperresponsiveness in an animal model of asthma.

Allergic asthma is strongly associated with the airway inflammation caused by the dysregulated production of cytokines secreted by the allergen-specific type-2 T helper (Th2) cells. Interleukin (IL)-12 is a heterodimeric cytokine, which strongly promotes the differentiation of naive CD4(+) T cells to the type-1 T helper (Th1) phenotype and suppresses the expression of Th2 cytokines. Therefore, immunotherapy with IL-12 has been suggested as a possible therapy for asthma. In previous studies, we developed a murine model of airway inflammation based on the purified, house dust-mite allergen Der p 1 (Dermatophagodies pteronyssinus) as a clinically relevant allergen. We hypothesized that the expression of IL-12 in the airway may represent an effective therapy for allergic airway diseases. In this study, we investigate whether the local transfer of the IL-12 gene to respiratory tissues modifies allergic inflammation and airway hyper-responsiveness (AHR) in our disease model. To enhance the in vivo delivery of the IL-12 gene, we expressed the murine single-chain IL-12 protein from a nonviral vector to which the two IL-12 subunits (p35 and p40) were linked by a 14- to 18-amino-acid linker. One of these single-chain IL-12s, containing an 18 amino-acid polypeptide linker, was stably expressed and had a high level of biological activity comparable to that of native IL-12 in vitro. In mice with Der p 1-induced asthma, the local administration of this IL-12 fusion gene into the lungs significantly prevented the development of AHR, abrogated airway eosinophilia, and inhibited type-2 cytokine production. These findings indicate that the local transfer of the single-chain IL-12 gene is effective in modulating pulmonary allergic responses and may be a convenient method for future applications of DNA vaccination.     

IL-31-IL-31R interactions negatively regulate type 2 inflammation in the lung

Interleukin (IL) 31Ralpha (glycoprotein 130-like monocyte receptor and glycoprotein 130-like receptor) heterodimerizes with oncostatin M receptor beta to bind IL-31, a cytokine expressed preferentially by CD4(+) T helper type 2 (Th2) cells. However, the functions of IL-31-IL-31R signaling in immune regulation remain unknown. Here, we identify a novel role for IL-31R in limiting type 2 inflammation in the lung. After intravenous injection of Schistosoma mansoni eggs, IL-31Ralpha(-/-) mice developed severe pulmonary inflammation, characterized by an increase in the area of granulomatous inflammation, increased numbers of resistin-like molecule alpha(+) cells, and enhanced collagen deposition compared to WT counterparts. In vitro, macrophages generated from IL-31Ralpha(-/-) mice promoted enhanced ovalbumin-specific CD4(+) T cell proliferation and purified naive CD4(+) T cells from IL-31Ralpha(-/-) mice exhibited enhanced proliferation and expression of Th2 cytokines, identifying a T cell- and macrophage-intrinsic regulatory function for IL-31R signaling. In contrast, the generation of CD4(+) T cell-mediated Th1 responses were normal in IL-31Ralpha(-/-) mice, suggesting that the regulatory role of IL-31R signaling is limited to type 2 responses. Together, these data implicate IL-31R signaling as a novel negative regulatory pathway that specifically limits type 2 inflammation.     

Allergen Uptake, Activation, and IL-23 Production by Pulmonary Myeloid DCs Drives Airway Hyperresponsiveness in Asthma-Susceptible Mice

Maladaptive, Th2-polarized inflammatory responses are integral to the pathogenesis of allergic asthma. As regulators of T cell activation, dendritic cells (DCs) are important mediators of allergic asthma, yet the precise signals which render endogenous DCs “pro-asthmatic”, and the extent to which these signals are regulated by the pulmonary environment and host genetics, remains unclear. Comparative phenotypic and functional analysis of pulmonary DC populations in mice susceptible (A/J), or resistant (C3H) to experimental asthma, revealed that susceptibility to airway hyperresponsiveness is associated with preferential myeloid DC (mDC) allergen uptake, and production of Th17-skewing cytokines (IL-6, IL-23), whereas resistance is associated with increased allergen uptake by plasmacytoid DCs. Surprisingly, adoptive transfer of syngeneic HDM-pulsed bone marrow derived mDCs (BMDCs) to the lungs of C3H mice markedly enhanced lung IL-17A production, and rendered them susceptible to allergen-driven airway hyperresponsiveness. Characterization of these BMDCs revealed levels of antigen uptake, and Th17 promoting cytokine production similar to that observed in pulmonary mDCs from susceptible A/J mice. Collectively these data demonstrate that the lung environment present in asthma-resistant mice promotes robust pDC allergen uptake, activation, and limits Th17-skewing cytokine production responsible for driving pathologic T cell responses central to the development of allergen-induced airway hyperresponsiveness.     

The absence of interleukin 9 does not affect the development of allergen-induced pulmonary inflammation nor airway hyperreactivity.

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.     

CD4+CD25+ T cells protect against experimentally induced asthma and alter pulmonary dendritic cell phenotype and function

The role of natural CD4+CD25+ regulatory T (T reg) cells in the control of allergic asthma remains poorly understood. We explore the impact of T reg cell depletion on the allergic response in mice susceptible (A/J) or comparatively resistant (C3H) to the development of allergen-induced airway hyperresponsiveness (AHR). In C3H mice, anti-CD25-mediated T reg cell depletion before house dust mite treatment increased several features of the allergic diathesis (AHR, eosinophilia, and IgE), which was concomitant with elevated T helper type 2 (Th2) cytokine production. In similarly T reg cell-depleted A/J mice, we observed a moderate increase in airway eosinophilia but no effects on AHR, IgE levels, or Th2 cytokine synthesis. As our experiments suggested that T reg cell depletion in C3H mice before sensitization was sufficient to enhance the allergic phenotype, we characterized dendritic cells (DCs) in T reg cell-depleted C3H mice. T reg cell-depleted mice had increased numbers of pulmonary myeloid DCs with elevated expression of major histocompatibility complex class II, CD80, and CD86. Moreover, DCs from T reg cell-depleted mice demonstrated an increased capacity to stimulate T cell proliferation and Th2 cytokine production, which was concomitant with reduced IL-12 expression. These data suggest that resistance to allergen-driven AHR is mediated in part by CD4+CD25+ T reg cell suppression of DC activation and that the absence of this regulatory pathway contributes to susceptibility.     

A regulatory role for the C5a anaphylatoxin in type 2 immunity in asthma

Complement component 5 (C5) has been described as either promoting or protecting against airway hyperresponsiveness (AHR) in experimental allergic asthma, suggesting pleomorphic effects of C5. Here we report that local pharmacological targeting of the C5a receptor (C5aR) prior to initial allergen sensitization in murine models of inhalation tolerance or allergic asthma resulted in either induction or marked enhancement of Th2-polarized immune responses, airway inflammation, and AHR. Importantly, C5aR-deficient mice exhibited a similar, increased allergic phenotype. Pulmonary allergen exposure in C5aR-targeted mice resulted in increased sensitization and accumulation of CD4+ CD69+ T cells associated with a marked increase in pulmonary myeloid, but not plasmacytoid, DC numbers. Pulmonary DCs from C5aR-targeted mice produced large amounts of CC chemokine ligand 17 (CCL17) and CCL22 ex vivo, suggesting a negative impact of C5aR signaling on pulmonary homing of Th2 cells. In contrast, C5aR targeting in sensitized mice led to suppressed airway inflammation and AHR but was still associated with enhanced production of Th2 effector cytokines. These data suggest a dual role for C5a in allergic asthma, i.e., protection from the development of maladaptive type 2 immune responses during allergen sensitization at the DC/T cell interface but enhancement of airway inflammation and AHR in an established inflammatory environment.     

Placenta growth factor augments airway hyperresponsiveness via leukotrienes and IL-13

Airway hyperresponsiveness (AHR) affects 55%–77% of children with sickle cell disease (SCD) and occurs even in the absence of asthma. While asthma increases SCD morbidity and mortality, the mechanisms underlying the high AHR prevalence in a hemoglobinopathy remain unknown. We hypothesized that placenta growth factor (PlGF), an erythroblast-secreted factor that is elevated in SCD, mediates AHR. In allergen-exposed mice, loss of Plgf dampened AHR, reduced inflammation and eosinophilia, and decreased expression of the Th2 cytokine IL-13 and the leukotriene-synthesizing enzymes 5-lipoxygenase and leukotriene-C4-synthase. Plgf^–/– mice treated with leukotrienes phenocopied the WT response to allergen exposure; conversely, anti-PlGF Ab administration in WT animals blunted the AHR. Notably, Th2-mediated STAT6 activation further increased PlGF expression from lung epithelium, eosinophils, and macrophages, creating a PlGF/leukotriene/Th2-response positive feedback loop. Similarly, we found that the Th2 response in asthma patients is associated with increased expression of PlGF and its downstream genes in respiratory epithelial cells. In an SCD mouse model, we observed increased AHR and higher leukotriene levels that were abrogated by anti-PlGF Ab or the 5-lipoxygenase inhibitor zileuton. Overall, our findings indicate that PlGF exacerbates AHR and uniquely links the leukotriene and Th2 pathways in asthma. These data also suggest that zileuton and anti-PlGF Ab could be promising therapies to reduce pulmonary morbidity in SCD.     

Critical role of IFN-alpha/beta and IFN-gamma in the regulation of airway inflammation

Immune balance, which is controlled by IFN-gamma-producing Th1 cells and IL-4-producing Th2 cells, plays a critical role in the regulation of airway inflammation. We have demonstrated that Th1 cells induced neutrophilia, airway hyperresponsiveness (AHR) but not mucus hypersecretion, while Th2 cells induced eosinophilia, AHR and mucus hypersecretion. Here, we indicated that IFN-gamma produced by Th1 cells accelerated neutrophilia and AHR but inhibited eosinophilia and mucus hypersecretion. We also demonstrated an important role of type 1 IFN-alpha/beta during inhibition of Th2-dependent airway inflammation by TLR-9-ligand, CpG-ODN. CpG-ODN-induced IFN-alpha/beta partially appeared to act against Th2 cells to inhibit the production of IL-4 and IL-13, which are key cytokines to regulate the activation and migration of Th2 cells in the lung.     

CCR3 is essential for skin eosinophilia and airway hyperresponsiveness in a murine model of allergic skin inflammation

The CC chemokine receptor 3 (CCR3) is expressed by eosinophils, mast cells, and Th2 cells. We used CCR3(-/-) mice to assess the role of CCR3 in a murine model of allergic skin inflammation induced by repeated epicutaneous sensitization with ovalbumin (OVA), and characterized by eosinophil skin infiltration, local expression of Th2 cytokines, and airway hyperresponsiveness (AHR) to inhaled antigen. Eosinophils and the eosinophil product major basic protein were absent from the skin of sham and OVA-sensitized CCR3(-/-) mice. Mast cell numbers and expression of IL-4 mRNA were normal in skin of CCR3(-/-) mice, suggesting that CCR3 is not important for infiltration of the skin by mast cells and Th2 cells. CCR3(-/-) mice produced normal levels of OVA-specific IgE, and their splenocytes secreted normal amounts of IL-4 and IL-5 following in vitro stimulation with OVA, indicating effective generation of systemic Th2 helper responses. Recruitment of eosinophils to lung parenchyma and bronchoalveolar lavage (BAL) fluid was severely impaired in CCR3(-/-) mice, which failed to develop AHR to methacholine following antigen inhalation. These results suggest that CCR3 plays an essential role in eosinophil recruitment to the skin and the lung and in the development of AHR.     

Interleukin 12 inhibits antigen-induced airway hyperresponsiveness, inflammation, and Th2 cytokine expression in mice

Allergic asthma is characterized by airway hyperresponsiveness and pulmonary eosinophilia, and may be mediated by T helper (Th) lymphocytes expressing a Th2 cytokine pattern. Interleukin (IL) 12 suppresses the expression of Th2 cytokines and their associated responses, including eosinophilia, serum immunoglobulin E, and mucosal mastocytosis. We have previously shown in a murine model that antigen- induced increases in airway hyperresponsiveness and pulmonary eosinophilia are CD4+ T cell dependent. We used this model to determine the ability of IL-12 to prevent antigen-induced increases in airway hyperresponsiveness, bronchoalveolar lavage (BAL) eosinophils, and lung Th2 cytokine expression. Sensitized A/J mice developed airway hyperresponsiveness and increased numbers of BAL eosinophils and other inflammatory cells after single or repeated intratracheal challenges with sheep red blood cell antigen. Pulmonary mRNA and protein levels of the Th2 cytokines IL-4 and IL-5 were increased after antigen challenge. Administration of IL-12 (1 microgram/d x 5 d) at the time of a single antigen challenge abolished the airway hyperresponsiveness and pulmonary eosinophilia and promoted an increase in interferon (IFN) gamma and decreases in IL-4 and IL-5 expression. The effects of IL-12 were partially dependent on IFN-gamma, because concurrent treatment with IL-12 and anti-IFN-gamma monoclonal antibody partially reversed the inhibition of airway hyperresponsiveness and eosinophilia by IL-12. Treatment of mice with IL-12 at the time of a second antigen challenge also prevented airway hyperresponsiveness and significantly reduced numbers of BAL inflammatory cells, reflecting the ability of IL-12 to inhibit responses associated with ongoing antigen-induced pulmonary inflammation. These data show that antigen-induced airway hyperresponsiveness and inflammation can be blocked by IL-12, which suppresses Th2 cytokine expression. Local administration of IL-12 may provide a novel immunotherapy for the treatment of pulmonary allergic disorders such as atopic asthma.     

Costimulation through B7-2 (CD86) Is Required for the Induction of a Lung Mucosal T Helper Cell 2 (TH2) Immune Response and Altered Airway Responsiveness

The recruitment of eosinophils into the airways after allergen exposure is dependent on interleukin (IL) 5 secreted from antigen-specific CD4⁺ T cells of the T helper cell (Th) 2 subset. However, while it is established that costimulation through CD28 is required for TCR-mediated activation and IL-2 production, the importance of this mechanism for the induction of a Th2 immune response is less clear. In the present study, we administered the fusion protein CTLA-4 immunoglobulin (Ig) into the lungs before allergen provocation to determine whether CD28/CTLA-4 ligands are required for allergen-induced eosinophil accumulation and the production of Th2 cytokines. Administration of CTLA-4 Ig inhibited the recruitment of eosinophils into the lungs by 75% and suppressed IgE in the bronchoalveolar lavage fluid. CTLA-4 Ig also inhibited the production of IL-4, IL-5, and IL-10 by 70–80% and enhanced interferon-γ production from CD3–T cell receptor–activated lung Thy1.2+ cells. Allergen exposure upregulated expression of B7-2, but not B7-1, on B cells from the lung within 24 h. Moreover, airway administration of an anti-B7-2 monoclonal antibody (mAb) inhibited eosinophil infiltration, IgE production, and Th2 cytokine secretion comparable in magnitude to that observed with CTLA-4 Ig. Treatment with an anti-B7-1 mAb had a small, but significant effect on eosinophil accumulation, although was less effective in inhibiting Th2 cytokine production. The anti-B7-2, but not anti-B7-1, mAb also inhibited antigen-induced airway hyperresponsiveness in vivo. In all of the parameters assessed, the combination of both the anti-B7-1 and anti-B7-2 mAb was no more effective than anti-B7-2 mAb treatment alone. We propose that strategies aimed at inhibition of CD28 interactions with B7-2 molecules may represent a novel therapeutic target for the treatment of lung mucosal allergic inflammation.     

Ozone exposure in a mouse model induces airway hyperreactivity that requires the presence of natural killer T cells and IL-17

Exposure to ozone, which is a major component of air pollution, induces a form of asthma that occurs in the absence of adaptive immunity. Although ozone-induced asthma is characterized by airway neutrophilia, and not eosinophilia, it is nevertheless associated with airway hyperreactivity (AHR), which is a cardinal feature of asthma. Because AHR induced by allergens requires the presence of natural killer T (NKT) cells, we asked whether ozone-induced AHR had similar requirements. We found that repeated exposure of wild-type (WT) mice to ozone induced severe AHR associated with an increase in airway NKT cells, neutrophils, and macrophages. Surprisingly, NKT cell-deficient (CD1d(-/-) and Jalpha18(-/-)) mice failed to develop ozone-induced AHR. Further, treatment of WT mice with an anti-CD1d mAb blocked NKT cell activation and prevented ozone-induced AHR. Moreover, ozone-induced, but not allergen-induced, AHR was associated with NKT cells producing interleukin (IL)-17, and failed to occur in IL-17(-/-) mice nor in WT mice treated with anti-IL-17 mAb. Thus, ozone exposure induces AHR that requires the presence of NKT cells and IL-17 production. Because NKT cells are required for the development of two very disparate forms of AHR (ozone- and allergen-induced), our results strongly suggest that NKT cells mediate a unifying pathogenic mechanism for several distinct forms of asthma, and represent a unique target for effective asthma therapy.     

Th2-driven, allergen-induced airway inflammation is reduced after treatment with anti-Tim-3 antibody in vivo

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-gamma 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.     

Essential role of TNF receptor superfamily 25 (TNFRSF25) in the development of allergic lung inflammation

We identify the tumor necrosis factor receptor superfamily 25 (TNFRSF25)/TNFSF15 pair as critical trigger for allergic lung inflammation, which is a cardinal feature of asthma. TNFRSF25 (TNFR25) signals are required to exert T helper cell 2 (Th2) effector function in Th2-polarized CD4 cells and co-stimulate interleukin (IL)-13 production by glycosphingolipid-activated NKT cells. In vivo, antibody blockade of TNFSF15 (TL1A), which is the ligand for TNFR25, inhibits lung inflammation and production of Th2 cytokines such as IL-13, even when administered days after airway antigen exposure. Similarly, blockade of TNFR25 by a dominant-negative (DN) transgene, DN TNFR25, confers resistance to lung inflammation in mice. Allergic lung inflammation-resistant, NKT-deficient mice become susceptible upon adoptive transfer of wild-type NKT cells, but not after transfer of DN TNFR25 transgenic NKT cells. The TNFR25/TL1A pair appears to provide an early signal for Th2 cytokine production in the lung, and therefore may be a drug target in attempts to attenuate lung inflammation in asthmatics.