Transient contribution of mast cells to pulmonary eosinophilia but not to hyper-responsiveness

Therapeutic Potential for Intractable Asthma by Targeting L-Type Amino Acid Transporter 1

Bronchial asthma is a chronic disease characterized by airway inflammation, obstruction, and hyperresponsiveness. CD4⁺ T cells, particularly T helper (Th) 2 cells, and their specific cytokines are important mediators in asthma pathogenesis. However, it has been established that Th subsets, other than Th2, as well as various cell types, including innate lymphoid cells (ILCs), significantly contribute to the development of allergic inflammation. These cells require facilitated amino acid uptake to ensure their full function upon activation. Emerging studies have suggested the potential of pharmacological inhibition of amino acid transporters to inhibit T cell activation and the application of this strategy for treating immunological and inflammatory disorders. In the present review, we explore the possibility of targeting L-type amino acid transporter (LAT) as a novel therapeutic approach for bronchial asthma, including its steroid-resistant endotypes.

[Possible therapeutic use of L-type amino acid transporter 1 (LAT1)-specific inhibitor for intractable asthma treatment]

Bronchial asthma (asthma) is characterized by chronic airway inflammation, reversible obstruction, and hyperresponsive conditions. Although most asthma patients have been becoming controllable by virtue of inhaled corticosteroid (ICS), substantial number of patients still do not respond to the steroid-based therapy. Mast cells, eosinophils, and helper T (Th) 2 cells have been considered as key players in asthma pathogenesis. However, emerging studies have revealed that Th subsets other than Th2, as well as various other immune cells, significantly contribute to the development of steroid-resistant intractable asthma. T cells and other inflammatory cells require incorporating a large amount of nutrients such as amino acids and glucose to exhibit their full function following activation. Based on this remarkable character, it has recently been suggested that the pharmacological inhibition of amino acid transporters is promising for treating immunological and inflammatory disorders through the suppression of inflammatory cell activation. In this review, we explore the possible management of intractable asthma by developing a selective inhibitor for L-type amino acid transporter (LAT) 1.

L-type amino acid transporter 1 inhibitor suppresses murine Th2 cell-mediated bronchial hyperresponsiveness independently of eosinophil accumulation

Background

The activation of Th2 cells that play a pivotal role in the development of allergic eosinophilic inflammation is regulated by an L-type amino acid transporter (LAT) 1. However, the contribution of LAT1 to the pathogenesis of Th2 cell-mediated airway inflammation has not been investigated.

Objective

In this study, we investigated the effect of a LAT1 inhibitor, JPH203, on Th2 cell-mediated airway eosinophilic inflammation.

Methods

BALB/c mice were transferred with ovalbumin (OVA)-specific Th2 cell and challenged by corresponding allergen with or without administration of JPH203. Then, the infiltration of inflammatory cells including eosinophils and allergen-specific Th2 cells in the lungs and bronchial hyperresponsiveness (BHR) was assessed.

Results

Inflammatory responses in the lungs with massive accumulation of eosinophils and BHR were induced in Th2 cell-transferred mice upon challenge with OVA. The treatment with JPH203 significantly suppressed the allergen-induced BHR but not eosinophil infiltration. The infused Th2 cells were also accumulated in the lungs upon allergen challenge, though the response was not affected by JPH203 treatment.

Conclusion

JPH203 suppressed Th2 cell-mediated BHR through the mechanisms independently of the lung accumulation of eosinophils and Th2 cells.

T Cell-Mediated Nasal Hyperresponsiveness in Allergic Rhinitis

Allergic rhinitis patients suffer various symptoms such as sneezing, runny nose, and nasal congestion. As disease severity and chronicity progress, nasal hyperresponsiveness (NHR) develops in those patients. During the generation of a mouse allergic rhinitis model, we discovered that immunized mice developed NHR upon repeated nasal antigen challenge. Using genetically modified mice and an originally developed T cell-transferred mouse model, we confirmed the critical role of CD4⁺ T cells after differentiation into several helper subsets in NHR. On the other hand, immunoglobulin E/mast cell-dependent responses that are critical for evoking nasal symptoms and eosinophils that accumulate in allergic inflammation sites were dispensable. A steroid, but not drugs targeting mast cell-derived mediators, was effective in alleviating NHR. The possible generation of a new means to treat allergic rhinitis by targeting T cell-derived NHR-inducing factors is suggested.

Role of CD4+ T Cells in Allergic Airway Diseases: Learning from Murine Models

The essential contribution of CD4⁺ T cells in allergic airway diseases has been demonstrated, especially by using various murine models of antigen-induced airway inflammation. In addition to antigen-immunized mouse models employing mast cell-deficient mice and CD4⁺ T cell-depleting procedure, antigen-specific CD4⁺ T cell transfer models have revealed the possible development of allergic inflammation solely dependent on CD4⁺ T cells. Regardless of the classical Th1/Th2 theory, various helper T cell subsets have the potential to induce different types of allergic inflammation. T cell receptor (TCR)-transgenic (Tg) mice have been used for investigating T cell-mediated immune responses. Besides, we have recently generated cloned mice from antigen-specific CD4⁺ T cells through somatic cell nuclear transfer. In contrast to TCR-Tg mice that express artificially introduced TCR, the cloned mice express endogenously regulated antigen-specific TCR. Upon antigen exposure, the mite antigen-reactive T cell-cloned mice displayed strong airway inflammation accompanied by bronchial hyperresponsiveness in a short time period. Antigen-specific CD4⁺ T cell-cloned mice are expected to be useful for investigating the detailed role of CD4⁺ T cells in various allergic diseases and for evaluating novel anti-allergic drugs.

Effects of anti-allergic drugs on T cell-mediated nasal hyperresponsiveness in a murine model of allergic rhinitis

BACKGROUND

We have recently demonstrated that T cell-mediated nasal hyperresponsiveness (NHR) is a representative pathophysiological feature of allergic rhinitis (AR). Although several anti-allergic drugs are used for the treatment of AR, the efficacy of these drugs on T cell-mediated NHR have not been elucidated. In these studies we investigated the effects of dexamethasone (Dex), montelukast (Mk), and chlorpheniramine (Chl) on NHR in antigen-immunized and antigen-specific Th2 cell-transferred mice.

METHODS

OVA-immunized BALB/c mice were treated with Dex, Mk, or Chl and challenged intranasally with OVA. We then assessed NHR, the number of inflammatory cells in the nasal lavage fluid (NALF), mRNA expression of Th2 cytokines in the nasal tissue, the population of CD3⁺CD4⁺ cells in the nasal lymphoid tissue (NALT), and antigen-specific serum IgE and IgG levels. Antigen-induced NHR and changes in antigen-specific T cells in the NALT were investigated in OVA-specific Th2 cell-transferred mice.

RESULTS

Dex significantly suppressed antigen-induced NHR, inflammatory cell infiltration, and IL-4, IL-5, IL-6, and IL-13 expression in immunized mice. Chl was completely ineffective, and only IL-13 expression was suppressed by Mk. None of these drugs affected IgE and IgG production. Antigen-induced NHR and the increase in antigen-specific T cells in the NALT of Th2 cell-transferred mice were inhibited by Dex, but not by Mk or Chl.

CONCLUSIONS

Steroids are effective for the reduction of NHR in AR by suppressing the accumulation of inflammatory cells, especially antigen-specific T cells.

Essential Contribution of CD4+ T Cells to Antigen-Induced Nasal Hyperresponsiveness in Experimental Allergic Rhinitis

Nasal hyperresponsiveness (NHR) is a characteristic feature of allergic rhinitis (AR); however, the pathogenesis of NHR is not fully understood. In this study, during the establishment of an experimental AR model using ovalbumin-immunized and -challenged mice, augmentation of the sneezing reaction in response to nonspecific proteins as well as a chemical stimulant was detected. Whether NHR is independent of mast cells and eosinophils was determined by using mast cell- and eosinophil-deficient mice. NHR was suppressed by treatment with anti-CD4 antibody, suggesting the pivotal contribution of CD4+ T cells. Furthermore, antigen challenge to mice to which in vitro-differentiated Th1, Th2, and Th17 cells but not naïve CD4+ T cells had been adoptively transferred led to the development of equivalent NHR. Since antigen-specific IgE and IgG were not produced in these mice and since antigen-specific IgE-transgenic mice did not develop NHR even upon antigen challenge, humoral immunity would be dispensable for NHR. CD4+ T cells play a crucial role in the pathogenesis of AR via induction of NHR, independent of IgE-, mast cell-, and eosinophil-mediated responses.

Existence of antigen-specific immunoglobulin E is not sufficient for allergic nasal eosinophil infiltration in mice

BACKGROUND

Immunoglobulin E (IgE) is important for the development of allergic rhinitis (AR), though the contribution of IgE to the infiltration of eosinophils in the nasal mucosa has not been fully elucidated. In this study, antigen-induced sneezing and nasal eosinophil accumulation were comparatively investigated in anti-ovalbumin (OVA)-IgE transgenic (Tg) and wild-type (WT) mice.

METHODS

Tg and OVA-immunized WT mice were intranasally challenged with OVA. Antigen-specific serum IgE level, sneezing and infiltration of eosinophil into the nasal cavity were then examined.

RESULTS

The level of serum OVA-specific IgE in Tg mice was significantly higher than that in antigen-immunized WT mice. Compared to saline challenge, intranasal challenge with OVA significantly induced sneezing in both Tg and immunized WT mice. However, antigen-induced nasal eosinophil infiltration was observed in immunized WT mice but not in Tg mice.

CONCLUSIONS

IgE-mediated responses might not play a crucial role in antigen-induced eosinophil infiltration in AR.

Insights into mast cell functions in asthma using mouse models

Therapeutics targeting specific mechanisms of asthma have shown promising results in mouse models of asthma. However, these successes have not transferred well to the clinic or to the treatment of asthma sufferers. We suggest a reason for this incongruity is that mast cell-dependent responses, which may play an important role in the pathogenesis of both atopic and non-atopic asthma, are not a key component in most of the current asthma mouse models. Two reasons for this are that wild type mice have, in contrast to humans, a negligible number of mast cells localized in the smaller airways and in the parenchyma, and that only specific protocols show mast cell-dependent reactions. The development of mast cell-deficient mice and the reconstitution of mast cells within these mice have opened up the possibility to generate mouse models of asthma with a marked role of mast cells. In addition, mast cell-deficient mice engrafted with mast cells have a distribution of mast cells more similar to humans. In this article we review and highlight the mast cell-dependent and -independent responses with respect to airway hyperresponsiveness and inflammation in asthma models using mast cell-deficient and mast cell-engrafted mice.

Genetic factors in the treatment of bronchial asthma

Owing to the recent vast progress in analytical tools and procedures to elucidate the relationship between genes and diseases, many candidate genes leading to the development of bronchial asthma have been reported. However, the quantitative phenotypes of asthma, such as decrease in forced expiratory volume in the first second, serum hyper-IgE, bronchial hyperresponsiveness and blood hyper-eosinophilia, do not represent this disease completely. On the other hand, eosinophilic inflammation of the bronchial mucosa represents accurately the feature of bronchial asthma, although accurate quantification of its status is difficult. While the production of interleukin (IL)-5 in peripheral CD4(+) T cells probably correlates with eosinophilic inflammation of the airway, the effectiveness of anti-IL-5 antibody for the treatment of bronchial asthma is controversial. Since intervention with asthma-causing gene products may not be sufficient for the treatment of this disease, identification of therapy-responsive genes should become more important in the near future.

IgE regulates T helper cell differentiation through FcgammaRIII mediated dendritic cell cytokine modulation

Asthma and allergy are characterized by dysregulation of inflammatory responses toward Th2 responses and high serum levels of IgE. IgE plays a role in the effector phase by triggering the degranulation of mast cells after antigen-crosslinking but its role in the induction of helper T cell differentiation is unknown. We have previously shown lymphotoxin is required for maintaining physiological levels of serum IgE which minimize spontaneous Th1-mediated airway inflammation, suggesting a physiological role for IgE in the regulation of T helper cell differentiation. We describe the mechanism in which IgE modulates inflammation by regulating dendritic cell cytokine production. Physiological levels of IgE suppress IL-12 production in the spleen and lung, suggesting IgE limits Th1 responses in vivo. IgE directly stimulates dendritic cells through FcgammaRIII to suppress IL-12 in vitro and influences APC to skew CD4+ T cells toward Th2 differentiation. We demonstrate a novel role for IgE in regulating differentiation of adaptive inflammatory responses through direct interaction with FcgammaRIII on dendritic cells.

United airways: circulating Th2 effector cells in an allergic rhinitis model are responsible for promoting lower airways inflammation

BACKGROUND

Allergic rhinitis (AR) and asthma often coexist and are referred to as 'united airways' disease. However, the molecular and cellular pathways that are crucially involved in the interaction between upper and lower airways remain to be identified.

OBJECTIVE

We sought to assess whether and how AR exacerbates lower airway inflammation upon allergen challenge in mice.

METHODS

We previously developed an intranasal ovalbumin (OVA)-driven AR model, characterized by nasal eosinophilic inflammation, enhanced serum levels of OVA-specific IgE and Th2 cytokine production in cervical lymph nodes. In OVA-sensitized mice with or without AR, a lower airway challenge was given, and after 24 h, lower airway inflammation was analysed.

RESULTS

We found that AR mice were more susceptible to eosinophilic inflammation following a lower airway OVA challenge than OVA-sensitized controls. AR mice manifested increased numbers of eosinophils in bronchoalveolar lavage fluid and increased inter-cellular adhesion molecule-1 (ICAM-1) expression on lung endothelium, when compared with OVA-sensitized controls. Depletion of T cells in OVA-challenged AR mice completely abrogated all hallmarks of lower airway inflammation, including enhanced IL-5 and tissue eosinophilia. Conversely, adoptive transfer of Th2 effector cells in naïve animals induced lower airway eosinophilic inflammation after challenge with OVA. Blocking T cell recirculation during AR development by the spingosine-1 analogue FTY720 also prevented lower airway inflammation including ICAM-1 expression in AR mice upon a single lower airway challenge.

CONCLUSION

Our mouse model of 'united airways' disease supports epidemiological and clinical data that AR has a significant impact on lower airway inflammation. Circulating Th2 effector cells are responsible for lung priming in AR mice, most likely through up-regulation of ICAM-1.

Role of human mast cells and basophils in bronchial asthma

Mast cells and basophils are the only cells expressing the tetrameric (alphabetagamma2) structure of the high affinity receptor for IgE (FcepsilonRI) and synthesizing histamine in humans. Human FcepsilonRI+ cells are conventionally considered primary effector cells of bronchial asthma. There is now compelling evidence that these cells differ immunologically, biochemically, and pharmacologically, which suggests that they might play distinct roles in the appearance and fluctuation of the asthma phenotype. Recent data have revealed the complexity of the involvement of human mast cells and basophils in asthma and have shed light on the control of recruitment and activation of these cells in different lung compartments. Preliminary evidence suggests that these cells might not always be detrimental in asthma but, under some circumstances, they might exert a protective effect by modulating certain aspects of innate and acquired immunity and allergic inflammation.