T helper 1 cells and interferon gamma regulate allergic airway inflammation and mucus production.

CD4 T helper (Th) type 1 and Th2 cells have been identified in the airways of asthmatic patients. Th2 cells are believed to contribute to pathogenesis of the disease, but the role of Th1 cells is not well defined. In a mouse model, we previously reported that transferred T cell receptor–transgenic Th2 cells activated in the respiratory tract led to airway inflammation with many of the pathologic features of asthma, including airway eosinophilia and mucus production. Th1 cells caused inflammation with none of the pathology associated with asthma. In this report, we investigate the role of Th1 cells in regulating airway inflammation. When Th1 and Th2 cells are transferred together into recipient mice, there is a marked reduction in airway eosinophilia and mucus staining. To address the precise role of Th1 cells, we asked (i), Are Th2-induced responses inhibited by interferon (IFN)-γ? and (ii) Can Th1 cells induce eosinophilia and mucus in the absence of IFN-γ? In IFN-γ receptor^−/− recipient mice exposed to inhaled antigen, the inhibitory effects of Th1 cells on both airway eosinophilia and mucus production were abolished. In the absence of IFN-γ receptor signaling, Th1 cells induced mucus but not eosinophilia. Thus, we have identified new regulatory pathways for mucus production; mucus can be induced by Th2 and non-Th2 inflammatory responses in the lung, both of which are inhibited by IFN-γ. The blockade of eosinophilia and mucus production by IFN-γ likely occurs through different inhibitory pathways that are activated downstream of Th2 cytokine secretion and require IFN-γ signaling in tissue of recipient mice.     

IL-13Ralpha2 and IL-10 coordinately suppress airway inflammation, airway-hyperreactivity, and fibrosis in mice

Development of persistent Th2 responses in asthma and chronic helminth infections are a major health concern. IL-10 has been identified as a critical regulator of Th2 immunity, but mechanisms for controlling Th2 effector function remain unclear. IL-10 also has paradoxical effects on Th2-associated pathology, with IL-10 deficiency resulting in increased Th2-driven inflammation but also reduced airway hyperreactivity (AHR), mucus hypersecretion, and fibrosis. We demonstrate that increased IL-13 receptor alpha 2 (IL-13Ralpha2) expression is responsible for the reduced AHR, mucus production, and fibrosis in BALB/c IL-10(-/-) mice. Using models of allergic asthma and chronic helminth infection, we demonstrate that IL-10 and IL-13Ralpha2 coordinately suppress Th2-mediated inflammation and pathology, respectively. Although IL-10 was identified as the dominant antiinflammatory mediator, studies with double IL-10/IL-13Ralpha2-deficient mice illustrate an indispensable role for IL-13Ralpha2 in the suppression of AHR, mucus production, and fibrosis. Thus, IL-10 and IL-13Ralpha2 are both required to control chronic Th2-driven pathological responses.     

Induction of Airway Mucus Production By T Helper 2 (Th2) Cells: A Critical Role For Interleukin 4 In Cell Recruitment But Not Mucus Production

Airway inflammation is believed to stimulate mucus production in asthmatic patients. Increased mucus secretion is an important clinical symptom and contributes to airway obstruction in asthma. Activated CD4 Th1 and Th2 cells have both been identified in airway biopsies of asthmatics but their role in mucus production is not clear. Using CD4 T cells from mice transgenic for the OVA-specific TCR, we studied the role of Th1 and Th2 cells in airway inflammation and mucus production. Airway inflammation induced by Th2 cells was comprised of eosinophils and lymphocytes; features found in asthmatic patients. Additionally, there was a marked increase in mucus production in mice that received Th2 cells and inhaled OVA, but not in mice that received Th1 cells. However, OVA-specific Th2 cells from IL-4–deficient mice were not recruited to the lung and did not induce mucus production. When this defect in homing was overcome by administration of TNF-α, IL-4 −/− Th2 cells induced mucus as effectively as IL-4 +/+ Th2 cells. These studies establish a role for Th2 cells in mucus production and dissect the effector functions of IL-4 in these processes. These data suggest that IL-4 is crucial for Th2 cell recruitment to the lung and for induction of inflammation, but has no direct role in mucus production.     

Treatment of experimental asthma by long-term gene therapy directed against IL-4 and IL-13

The clinical manifestations of allergic asthma are believed to result from a dysregulated, T helper 2 lymphocyte (Th2)-biased response to antigen. Although asthma symptoms can be controlled acutely, there is a need for a therapy that will address the underlying immune dysfunction and provide continuous control of chronic airway inflammation. The Th2-type cytokines, IL-13 and IL-4, have been demonstrated to play a crucial role in asthma pathogenesis and their selective neutralization results in the alleviation of asthmatic symptoms in mouse models. The activity of both of these cytokines can be inhibited by a mutant IL-4 protein, IL-4 receptor antagonist (IL-4RA), and thus, continual IL-4RA therapy might be beneficial in treatment of chronic asthma. To explore the potential utility of long-term gene therapy for the treatment of asthma we used a recombinant adeno-associated virus (AAV) vector to deliver and provide sustained expression of IL-4RA in vivo. We show that AAV-mediated delivery of IL-4RA to the airways of mice reduces airway hyperresponsiveness (AHR) and airway eosinophilia triggered by either IL-13 or IL-4. Furthermore, AAV-delivered IL-4RA, expressed either systemically or in the airways of mice following allergen sensitization, significantly inhibited development of airway eosinophilia and mucus production and reduced the levels of asthma-associated Th2 cytokines and AHR in the experimental mouse model of allergic asthma. Thus, gene therapy can be a potential therapeutic option to treat and control chronic airway inflammation and asthmatic symptoms.     

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.     

The H1 histamine receptor regulates allergic lung responses

Histamine, signaling via the type 1 receptor (H1R), has been shown to suppress Th2 cytokine production by in vitro cultured T cells. We examined the role of H1R in allergic inflammation in vivo using a murine asthma model. Allergen-stimulated splenic T cells from sensitized H1R-/- mice exhibited enhanced Th2 cytokine production. Despite this Th2 bias, allergen-challenged H1R-/- mice exhibited diminished lung Th2 cytokine mRNA levels, airway inflammation, goblet cell metaplasia, and airway hyperresponsiveness (AHR). Restoration of pulmonary Th2 cytokines in H1R-/- mice by intranasal IL-4 or IL-13 restored inflammatory lung responses and AHR. Further investigation revealed that histamine acts as a T cell chemotactic factor and defective T cell trafficking was responsible for the absence of lung inflammation. Cultured T cells migrated in response to histamine in vitro, but this was ablated by blockade of H1R but not H2R. In vivo, allergen-specific WT but not H1R-/- CD4+ T cells were recruited to the lungs of naive recipients following inhaled allergen challenge. H1R-/- T cells failed to confer airway inflammation or AHR observed after transfer of WT T cells. Our data establish a role for histamine and H1R in promoting the migration of Th2 cells into sites of allergen exposure.     

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.     

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.     

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.     

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.     

Blockade of CD49d (alpha4 integrin) on intrapulmonary but not circulating leukocytes inhibits airway inflammation and hyperresponsiveness in a mouse model of asthma.

Immunized mice after inhalation of specific antigen have the following characteristic features of human asthma: airway eosinophilia, mucus and Th2 cytokine release, and hyperresponsiveness to methacholine. A model of late-phase allergic pulmonary inflammation in ovalbumin-sensitized mice was used to address the role of the alpha4 integrin (CD49d) in mediating the airway inflammation and hyperresponsiveness. Local, intrapulmonary blockade of CD49d by intranasal administration of CD49d mAb inhibited all signs of lung inflammation, IL-4 and IL-5 release, and hyperresponsiveness to methacholine. In contrast, CD49d blockade on circulating leukocytes by intraperitoneal CD49d mAb treatment only prevented the airway eosinophilia. In this asthma model, a CD49d-positive intrapulmonary leukocyte distinct from the eosinophil is the key effector cell of allergen-induced pulmonary inflammation and hyperresponsiveness.     

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.     

Adenovirus expressing Fas ligand gene decreases airway hyper-responsiveness and eosinophilia in a murine model of asthma

Allergic asthma is characterized by airway hyper-responsiveness (AHR) and cellular infiltration of the airway with predominantly eosinophils and Th2 cells. The normal resolution of inflammation in the lung occurs through the regulated removal of unneeded cells by Fas-Fas ligand-mediated apoptosis. Fas ligand (FasL) is a member of the tumor necrosis factor family, and when bound to Fas, it induces apoptosis of the cells. To examine the effect of the FasL gene on airway inflammation and immune effector cells in allergic asthma, recombinant adenovirus expressing murine FasL (Ad-FasL) was delivered intratracheally into ovalbumin (OVA)-immunized mice. We found that a single administration of Ad-FasL in OVA-immunized mice significantly alleviated AHR and eosinophilia by inducing the apoptosis of eosinophils and/or reducing eosinophil attractant factors, such as IL-5 and eotaxin levels. The number of infiltrated lymphocytes and Th2 cytokines, including IL-5 and IL-13, decreased in OVA-immunized mice by administration of Ad-FasL. KC and TNF-alpha production also decreased in Ad-FasL-treated OVA-immunized mice. These findings indicated that the administration of Ad-FasL to OVA-sensitized mice significantly suppressed pulmonary allergic responses. Although more studies are needed, these results suggested that Ad-FasL might be applied as an alternative therapy for allergic asthma.     

New insights into the relationship between airway inflammation and asthma

Asthma is a condition characterized by variable airflow obstruction, airway hyper-responsiveness (AHR) and airway inflammation which is usually, but not invariably, eosinophilic. Current thoughts on the pathogenesis of asthma are focused on the idea that it is caused by an inappropriate response of the specific immune system to harmless antigens, particularly allergens such as cat dander and house dust mite, that result in Th2-mediated chronic inflammation. However, the relationship between inflammation and asthma is complex, with no good correlation between the severity of inflammation, at least as measured by the number of eosinophils, and the severity of asthma. In addition, there are a number of conditions, such as eosinophilic bronchitis and allergic rhinitis, in which there is a Th2-mediated inflammatory response, but no asthma, as measured by variable airflow obstruction or AHR. Bronchoconstriction can also occur without obvious airway inflammation, and neutrophilic inflammation can in some cases be associated with asthma. When we compared the immunopathology of eosinophilic bronchitis and asthma, the only difference we observed was that, in asthma, the airway smooth muscle (ASM) was infiltrated by mast cells, suggesting that airway obstruction and AHR are due to an ASM mast cell myositis. This observation emphasizes that the features that characterize asthma, as opposed to bronchitis, are due to abnormalities in smooth muscle responsiveness, which could be intrinsic or acquired, and that inflammation is only relevant in that it leads to these abnormalities. It also emphasizes the importance of micro-localization as an organizing principle in physiological responses to airway inflammation. Thus, if inflammation is localized to the epithelium and lamina propria, then the symptoms of bronchitis (cough and mucus hypersecretion) result, and it is only if the ASM is involved -- for reasons that remain to be established -- that asthma occurs.     

src homology 2 domain-containing tyrosine phosphatase SHP-1 controls the development of allergic airway inflammation

Th2 cells are generated from naive CD4 T cells upon T cell receptor (TCR) recognition of antigen and IL-4 stimulation and play crucial roles in humoral immunity against infectious microorganisms and the pathogenesis of allergic and autoimmune diseases. A tyrosine phosphatase, SHP-1, that contains src homology 2 (SH2) domains is recognized as a negative regulator for various intracellular signaling molecules, including those downstream of the TCR and the IL-4 receptor. Here we assessed the role of SHP-1 in Th1/Th2 cell differentiation and in the development of Th2-dependent allergic airway inflammation by using a natural SHP-1 mutant, the motheaten mouse. CD4 T cells appear to develop normally in the heterozygous motheaten (me/+) thymus even though they express decreased amounts of SHP-1 (about one-third the level of wild-type thymus). The me/+ naive splenic CD4 T cells showed enhanced activation by IL-4 receptor-mediated signaling but only marginal enhancement of TCR-mediated signaling. Interestingly, the generation of Th2 cells was increased and specific cytokine production of mast cells was enhanced in me/+ mice. In an OVA-induced allergic airway inflammation model, eosinophilic inflammation, mucus hyperproduction, and airway hyperresponsiveness were enhanced in me/+ mice. Thus, SHP-1 may have a role as a negative regulator in the development of allergic responses, such as allergic asthma.     

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.     

Systemic and local interferon gamma gene delivery to the lungs for treatment of allergen-induced airway hyperresponsiveness in mice.

Allergen-induced airway hyperresponsiveness, an animal model of asthma in humans, may respond to immunotherapy with Th1 cytokines. For example, local administration of recombinant IL-12 or IFN-gamma, or intratracheal delivery of the genes for these cytokines, has been shown to reduce the severity of allergen-induced airway hyperresponsiveness (AHR) in rodent models. We reasoned that systemic cytokine gene delivery to the lungs by intravenous injection of lipid-DNA complexes might also be an effective approach to treatment of allergen-induced AHR. Therefore, the effects of either systemic or local pulmonary IFN-gamma gene delivery were evaluated in mice with allergen-induced AHR. The effects of treatment on AHR, airway eosinophilia and cytokine production, and serum IgE concentrations were evaluated in mice that were first sensitized to ovalbumin and then subjected to aerosol ovalbumin challenge. Intravenous IFN-gamma gene delivery significantly inhibited development of AHR and airway eosinophilia and decreased serum IgE levels, compared with control mice or mice treated with noncoding DNA. Intratracheal IFN-gamma gene delivery also significantly inhibited AHR and airway eosinophilia, but did not affect serum IgE levels. Treatment with recombinant IFN-gamma was much less effective than IFN-gamma gene delivery by either route. We conclude that either systemic or local pulmonary delivery of a Th1 cytokine gene such as IFN-gamma may be an effective approach for treatment of allergen-induced asthma.     

Targeted inactivation of the IL-4 receptor alpha chain I4R motif promotes allergic airway inflammation

The insulin/interleukin-4 (IL-4) receptor (I4R) motif mediates the association of insulin receptor substrate (IRS)-2 with the interleukin-4 (IL-4)Ralpha chain and transduces mitogenic signals in response to IL-4. Its physiological functions were analyzed in mice with a germline point mutation that changed the motif's effector tyrosine residue into phenylalanine (Y500F). The Y500F mutation abrogated IRS-2 phosphorylation and impaired IL-4-induced CD4+ T lymphocyte proliferation but left unperturbed Stat6 activation, up-regulation of IL-4-responsive gene products, and Th cell differentiation under Th2 polarizing conditions. However, in vivo the Y500F mutation was associated with increased allergen-induced IgE production, airway responsiveness, tissue eosinophilia, and mucus production. These results define an important role for the I4R motif in regulating allergic inflammation.     

SLAT regulates Th1 and Th2 inflammatory responses by controlling Ca2+/NFAT signaling

SWAP-70-like adapter of T cells (SLAT) is a novel guanine nucleotide exchange factor for Rho GTPases that is upregulated in Th2 cells, but whose physiological function is unclear. We show that SLAT(-/-) mice displayed a developmental defect at one of the earliest stages of thymocyte differentiation, the double-negative 1 (DN1) stage, leading to decreased peripheral T cell numbers. SLAT(-/-) peripheral CD4(+) T cells demonstrated impaired TCR/CD28-induced proliferation and IL-2 production, which was rescued by the addition of exogenous IL-2. Importantly, SLAT(-/-) mice were grossly impaired in their ability to mount not only Th2, but also Th1-mediated lung inflammatory responses, as evidenced by reduced airway neutrophilia and eosinophilia, respectively. Levels of Th1 and Th2 cytokine in the lungs were also markedly reduced, paralleling the reduction in pulmonary inflammation. This defect in mounting Th1/Th2 responses, which was also evident in vitro, was traced to a severe reduction in Ca(2+) mobilization from ER stores, which consequently led to defective TCR/CD28-induced translocation of nuclear factor of activated T cells 1/2 (NFATc1/2). Thus, SLAT is required for thymic DN1 cell expansion, T cell activation, and Th1 and Th2 inflammatory responses.