An essential role of mast cells in the development of airway hyperresponsiveness in a murine asthma model

TLR3-, TLR7-, and TLR9-mediated production of proinflammatory cytokines and chemokines from murine connective tissue type skin-derived mast cells but not from bone marrow-derived mast cells

Recent studies have revealed that murine bone marrow-derived cultured mast cells (BMMC), which are phenotypically immature mast cells, express functional TLR2 and TLR4 that recognize distinct pathogen-associated molecules. However, it remains relatively uncertain whether mast cells express other TLR. We recently established a method to obtain large numbers of murine fetal skin-derived cultured mast cells (FSMC); these cells exhibit important features of connective tissue type mast cells. Working with FSMC and BMMC, the TLR mRNA expression profiles were compared between both cell types. Although TLR2 and TLR4 mRNA were detected in both cells at comparable levels, TLR3, TLR7, and TLR9 mRNA were expressed by FSMC at higher levels than by BMMC, suggesting distinct TLR expression profiles among different mast cell populations. With respect to their functional aspects, FSMC, but not BMMC, dose dependently produced proinflammatory cytokines (TNF-alpha and IL-6) and chemokines (RANTES, MIP-1alpha, and MIP-2) in response to poly(I:C), R-848, and CpG oligodeoxynucleotide, which are TLR3, TLR7, and TLR9 activators, respectively. Interestingly, these TLR activators failed to induce degranulation and IL-13 production by both mast cells, although peptidoglycan and LPS (TLR2 and TLR4 activators, respectively) induced IL-13 production by both cells. Mast cells, thus, may have potential to recruit other immune cells to the infected sites by responding to various bacterial and viral components through TLR signaling pathways, presumably being involved in initiating innate immunity and subsequently linking innate and acquired immune responses.

Platelet-activating factor receptor develops airway hyperresponsiveness independently of airway inflammation in a murine asthma model

Lipid mediators play an important role in modulating inflammatory responses. Platelet-activating factor (PAF) is a potent proinflammatory phospholipid with eosinophil chemotactic activity in vitro and in vivo. We show in this study that mice deficient in PAF receptor exhibited significantly reduced airway hyperresponsiveness to muscarinic cholinergic stimulation in an asthma model. However, PAF receptor-deficient mice developed an eosinophilic inflammatory response at a comparable level to that of wild-type mice. These results indicate an important role for PAF receptor, downstream of the eosinophilic inflammatory cascade, in regulating airway responsiveness after sensitization and aeroallergen challenge.

Increased airway responsiveness, allergy-type-I skin responses and systemic anaphylaxis in a humanized-severe combined immuno-deficiency mouse model

BACKGROUND

In patients with allergic bronchial asthma, a strong relationship between elevated serum IgE antibody titres and the development of increased airway responsiveness (AR) has been demonstrated. To further elucidate the relationship between human (hu) IgE and development of increased AR, we developed an in vivo model utilizing immuno-compromised severe combined immuno-deficiency (SCID) mice.

METHODS

SCID mice were either reconstituted with peripheral blood mononuclear cells (PBMC) from non-atopic, healthy or atopic individuals sensitized against house dust mite allergen (Der p), or passively sensitized with plasma from non-atopic, healthy or atopic individuals.

RESULTS

In both systems, atopic hu-SCID mice developed increased AR. The following results suggest that these responses were mediated via IgE antibodies: increased AR did not occur after transfer of either PBMC or IgE-negative plasma from non-atopic individuals; increased AR occurred simultaneous with increased serotonin release detected 15 min after allergen-aerosol challenge in bronchoalveolar lavage fluid; and increased AR required at least two allergen-aerosol challenges. SCID mice reconstituted with serum containing anti-Der p IgE antibodies developed positive immediate-type skin test responses to intradermal injection of Der p as well as anti-hu-IgE antibody. In addition, IgE binding to skin mast cells was demonstrated by immunohistochemistry. Furthermore, intravenous challenge of hu anti-Der p positive SCID mice with Der p resulted in systemic anaphylaxis.

CONCLUSION

These data provide evidence that passive immunization of SCID mice with hu IgE alters AR and that T cells and eosinophils were not a requirement for the development of increased AR in this model.

Mast Cells, FcεRI, and IL-13 Are Required for Development of Airway Hyperresponsiveness after Aerosolized Allergen Exposure in the Absence of Adjuvant

In certain models of allergic airway disease, mast cells facilitate the development of inflammation and airway hyper-responsiveness (AHR). To define the role of the high affinity IgE receptor (FcepsilonRI) in the development of AHR, mice with a disruption of the alpha subunit of the high affinity IgE receptor (FcepsilonRI(-/-)) were exposed on 10 consecutive days to nebulized OVA. Forty-eight hours after the last nebulization, airway responsiveness was monitored by the contractile response of tracheal smooth muscle to electrical field stimulation (EFS). After the 10-day OVA challenge protocol, wild-type mice demonstrated increased responsiveness to EFS, whereas similarly challenged FcepsilonRI(-/-) mice showed a low response to EFS, similar to nonexposed animals. Further, allergen-challenged FcepsilonRI(-/-) mice showed less airway inflammation, goblet cell hyperplasia, and lower levels of IL-13 in lung homogenates compared with the controls. IL-13-deficient mice failed to develop an increased response to EFS or goblet cell hyperplasia after the 10-day OVA challenge. We transferred bone marrow-derived mast cells from wild-type mice to FcepsilonRI(-/-) mice 1 day before initiating the challenge protocol. After the 10-day OVA challenge, recipient FcepsilonRI(-/-) mice demonstrated EFS-induced responses similar to those of challenged wild-type mice. Transferred mast cells could be detected in tracheal preparations. These results show that FcepsilonRI is important for the development of AHR after an aerosolized allergen sensitization protocol and that this effect is mediated through FcepsilonRI on mast cells and production of IL-13 in the lung.

Mast Cell-Independent Mechanisms of Immediate Hypersensitivity: A Role for Platelets

Mast cells have been implicated as the central effectors in allergic responses, yet a fatal anaphylactic response can be induced in mast cell-deficient mice. In this study, we examined the immediate hypersensitivity response in wild-type (WT) and mast cell-deficient mice (W/W(v)) in two different tissues (skin and skeletal muscle). Vascular permeability and leukocyte recruitment were studied after immediate challenge or 4 h postchallenge in OVA-sensitized mice. In skin, immediate challenge induced a significant increase in vascular permeability (75%) within 30 min and was accompanied by increased leukocyte adhesion 4 h postchallenge. In the absence of mast cells, no changes in vascular permeability or leukocyte recruitment were observed in skin. In WT skeletal muscle, immediate challenge induced a rapid increase (80%) in vascular permeability within 5 min and significant leukocyte recruitment after 4 h. Surprisingly, in W/W(v), a gradual increase in vascular permeability was observed, reaching a maximum (50%) within 30 min. Despite the absence of mast cells, subsequent leukocyte emigration was similar to that observed in WT mice. Pretreatment with anti-platelet serum in W/W(v) returned Ag-induced vascular permeability and leukocyte recruitment to baseline. Platelets were shown to interact with endothelium in skeletal muscle, but not dermal microvasculature. These data illustrate that mast cells play a prominent role in vascular permeability and leukocyte recruitment in skin in response to Ag, however, in skeletal muscle; these changes can occur in the absence of mast cells, and are mediated, in part, by the presence of platelets.

IgE crosslinkage of Fcε receptor I induces both production and activation of matrix metalloproteinase-9 in mast cells

Since mast cells play pivotal roles in allergic inflammations, we investigated how IgE-mediated stimulation modulated mast cell matrix metalloproteinase (MMP)-9 production, and its enzymatic activation. In this study, we clearly demonstrated that proMMP-9 released from murine bone marrow-derived cultured mast cells (BMCMC) was activated to its valid form after crosslinking of surface immunoglobulin (Ig)E. Serine protease inhibitors sensitive to chymases inhibited the phenomenon, indicating that certain chymases may be responsible for activation of proMMP-9. Although binding of IgE to its specific receptors did not alter MMP-9 production, the IgE crosslinkage increased both expression of mRNA, and production of MMP-9 in mast cells. Glucocorticoid declined extra cellular processing of proMMP-9 without affecting mRNA expression. These findings give rise to the possibility that production and activation of mast cell MMP-9 may be increased in the affected sites, thereby resulting in an exacerbation of tissue degradation in inflammatory conditions.

Role of interleukin-5 and eosinophils in allergen-induced airway remodeling in mice

Asthma is a chronic inflammatory disease characterized by variable bronchial obstruction, hyperresponsiveness, and by tissue damage known as airway remodeling. In the present study we demonstrate that interleukin (IL)-5 plays an obligatory role in the airway remodeling observed in experimental asthma. BALB/c mice sensitized by intraperitoneal injections of ovalbumin and exposed daily to aerosol of ovalbumin for up to 3 wk, develop eosinophilic infiltration of the bronchi and subepithelial and peribronchial fibrosis. The lesions are associated with increased amounts of hydroxyproline in the lungs and elevated levels of eosinophils and transforming growth factor (TGF)-beta1 in the bronchoalveolar lavage fluid. After 1 wk of allergen challenge, TGF-beta is mainly produced by eosinophils accumulated in the peribronchial and perivascular lesions. At a later stage of the disease, the main source of TGF-beta is myofibroblasts, identified by alpha-smooth muscle actin mAb. We show that all these lesions, including fibrosis, are abolished in sensitized and allergen-exposed IL-5 receptor-null mice, whereas they are markedly accentuated in IL-5 transgenic animals. More importantly, treatment of wild-type mice with neutralizing anti-IL-5 antibody, administered before each allergen challenge, almost completely prevented subepithelial and peribronchial fibrosis. These findings demonstrated that eosinophils are involved in allergen-induced subepithelial and peribronchial fibrosis probably by producing a fibrogenic factor, TGF-beta1.

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.

Activation of mast cells is essential for development of house dust mite Dermatophagoides farinae-induced allergic airway inflammation in mice

In this study, we demonstrate that Dermatophagoides farinae (Der f), a major source of airborne allergens, but not OVA, could rapidly activate mast cells in mice. This was indicated by an elevation of serum mouse mast cell protease 1, a mast cell-specific proteinase, as early as 30 min after intratracheal challenge. Administration of sodium cromoglycate (40 mg/kg, i.p., 1 h before Der f instillation), a mast cell stabilizer, not only suppressed acute mouse mast cell protease 1 production but also attenuated the allergic airway inflammation provoked by repetitive Der f challenge in mice (five times at 1-wk interval). Der f induced the expression of mRNA for TNF-alpha, IL-1beta, IL-4, IL-6, IL-9, and IL-13 in mastocytoma P815 cells and stimulated both P815 cells and bone marrow-derived mast cells to produce IL-4, IL-6, and TNF-alpha in a dose- and time-dependent manner. Cycloheximide as well as sodium cromoglycate blocked the Der f-induced IL-4 production, indicating a de novo protein synthesis process. Supernatants of Der f-stimulated mast cells chemoattracted monocytes and T lymphocytes; they up-regulated the expression of costimulatory B7 molecules, eotaxin, RANTES, monocyte chemoattractant protein 1, and IFN-inducible protein 10 mRNA of alveolar macrophages; they supported PHA-induced T cell proliferation; and they promoted Th2 cell development. Our data indicate that mast cells may be an important cell type during the initiation of Der f sensitization in the airway by modulating the function of alveolar macrophages and T cells.

Recall helper T cell response: T helper 1 cell-resistant allergic susceptibility without biasing uncommitted CD4 T cells

Effector and memory T lymphocytes differ significantly, and there is no experimental evidence that memory cells are sufficient to render an otherwise normal individual susceptible to localized allergic inflammation. Furthermore, nothing is known about the kinetics of memory responses after inhalation of antigen or interplay between an allergen-specific memory helper T (Th) cell Th2 population and uncommitted or competing Th1 cells. To study these processes, T cell receptor-transgenic CD4(+) effector cells were generated in vitro, transferred into naive recipients, and allowed to resume a quiescent state. Inhalation of protein antigen reactivated these Ag-specific Th2 donor cells, leading to allergic pulmonary inflammation and airway hyperreactivity. Susceptibility was correlated with the size of the input Th2 population, but Th1 cells neither enhanced nor reduced inflammation in this model. Importantly, the reactivation of these antigen-experienced cells by inhaled antigen did not skew the cytokine balance of recipient-derived T cells recruited to the lung nor did it inhibit the development of donor-derived Th1 cells from uncommitted antigen-experienced cells that form a normal part of immune responses. These data indicate that a quiescent memory Th2-cell population can create susceptibility to allergic pulmonary inflammation in a manner refractory to inhibition by Th1 cells or endogenous inhibitory mechanisms.

Accumulation of Peribronchial Mast Cells in a Mouse Model of Ovalbumin Allergen Induced Chronic Airway Inflammation: Modulation by Immunostimulatory DNA Sequences

Few peribronchial mast cells are noted either in the lungs of naive mice or in the lungs of OVA-sensitized mice challenged acutely with OVA by inhalation. In this study, we demonstrate that OVA-sensitized mice exposed to repetitive OVA inhalation for 1-6 mo have a significant accumulation of peribronchial mast cells. This accumulation of peribronchial mast cells is associated with increased expression of the Th2 cell-derived mast cell growth factors, including IL-4 and IL-9, but not with the non-Th2 cell-derived mast cell growth factor, stem cell factor. Pretreating mice with immunostimulatory sequences (ISS) of DNA containing a CpG motif significantly inhibited the accumulation of peribronchial mast cells and the expression of IL-4 and IL-9. To determine whether mast cells express Toll-like receptor-9 (TLR-9; the receptor for ISS), TLR-9 expression by mouse bone marrow-derived mast cells (MBMMCs) was assessed by RT-PCR. MBMMCs strongly expressed TLR-9 and bound rhodamine-labeled ISS. However, incubation of MBMMCs with ISS in vitro neither inhibited MBMMC proliferation nor inhibited Ag/IgE-mediated MBMMC degranulation, but they did induce IL-6. Overall these studies demonstrate that mice exposed to repetitive OVA challenge, but not acute OVA challenge, have an accumulation of peribronchial mast cells and express increased levels of mast cell growth factors in the lung. Although mast cells express TLR-9, ISS does not directly inhibit mast cell proliferation in vitro, suggesting that ISS inhibits accumulation of peribronchial mast cells in vivo by indirect mechanism(s), which include inhibiting the lung expression of Th2 cell-derived mast cell growth factors.

The orally available spleen tyrosine kinase inhibitor 2-[7-(3,4-dimethoxyphenyl)-imidazo[1,2-c]pyrimidin-5-ylamino]nicotinamide dihydrochloride (BAY 61-3606) blocks antigen-induced airway inflammation in rodents

Spleen tyrosine kinase (Syk) tyrosine kinase plays essential roles in receptors for Fc portion of immunoglobulins and B cell receptor complex signaling in various inflammatory cells; therefore, inhibitors of Syk kinase may show potential as antiasthmatic/allergic therapeutics. We identified 2-[7-(3,4-dimethoxyphenyl)-imidazo[1,2-c]pyrimidin-5-ylamino]-nicotinamide dihydrochloride (BAY 61-3606), a potent (Ki = 7.5 nM) and selective inhibitor of Syk kinase. BAY 61-3606 inhibited not only degranulation (IC50 values between 5 and 46 nM) but also lipid mediator and cytokine synthesis in mast cells. BAY 61-3606 was highly efficacious in basophils obtained from healthy human subjects (IC50 = 10 nM) and seems to be at least as potent in basophils obtained from atopic (high serum IgE) subjects (IC50 = 8.1 nM). B cell receptor activation and receptors for Fc portion of IgG signaling in eosinophils and monocytes were also potently suppressed by BAY 61-3606. Oral administration of BAY 61-3606 to rats significantly suppressed antigen-induced passive cutaneous anaphylactic reaction, bronchoconstriction, and bronchial edema at 3 mg/kg. Furthermore, BAY 61-3606 attenuated antigen-induced airway inflammation in rats. Based on these anti-inflammatory effects of BAY 61-3606 both in vitro and in vivo, it was demonstrated that Syk may play a very critical role in the pathogenesis of allergic reactions.

IgE alone stimulates mast cell adhesion to fibronectin via pathways similar to those used by IgE + antigen but distinct from those used by Steel factor

We recently demonstrated that immunoglobulin E (IgE), in the absence of cross-linking agents, activates signaling pathways in healthy murine bone marrow-derived mast cells (BMMCs) and that this activation enhances BMMC survival, at least in part, via secretion of autocrine-acting cytokines. We report herein that IgE alone also triggers the adhesion of both BMMCs and connective tissue mast cells (CTMCs) to the connective tissue component, fibronectin (FN). This adhesion occurs to the same extent as that triggered by optimal levels of Steel factor (SF) or IgE + antigen (IgE + Ag) and is mediated by an increased avidity of the integrin very late antigen 5 (VLA-5). Moreover, this IgE-induced adhesion, which is prolonged compared with that elicited by SF or IgE + Ag, requires phosphatidylinositol 3-kinase (PI3K), phospholipase C gamma (PLCgamma), and extracellular calcium but not extracellular-regulated kinase (Erk) or p38. Interestingly, we found, using the calcium channel blocker, 2-APB (2-aminoethoxydiphenyl borate) and Lyn-/- BMMCs that both IgE- and IgE + Ag-induced adhesion to FN require extracellular calcium entry, whereas SF does not. Furthermore, our data suggest that FN acts synergistically with IgE to prolong intracellular phosphorylation events and to enhance IgE-induced inflammatory cytokine production and BMMC survival.

Beta-arrestin-2 regulates the development of allergic asthma

Asthma is a chronic inflammatory disorder of the airways that is coordinated by Th2 cells in both human asthmatics and animal models of allergic asthma. Migration of Th2 cells to the lung is key to their inflammatory function and is regulated in large part by chemokine receptors, members of the seven-membrane-spanning receptor family. It has been reported recently that T cells lacking beta-arrestin-2, a G protein-coupled receptor regulatory protein, demonstrate impaired migration in vitro. Here we show that allergen-sensitized mice having a targeted deletion of the beta-arrestin-2 gene do not accumulate T lymphocytes in their airways, nor do they demonstrate other physiological and inflammatory features characteristic of asthma. In contrast, the airway inflammatory response to LPS, an event not coordinated by Th2 cells, is fully functional in mice lacking beta-arrestin-2. beta-arrestin-2-deficient mice demonstrate OVA-specific IgE responses, but have defective macrophage-derived chemokine-mediated CD4+ T cell migration to the lung. This report provides the first evidence that beta-arrestin-2 is required for the manifestation of allergic asthma. Because beta-arrestin-2 regulates the development of allergic inflammation at a proximal step in the inflammatory cascade, novel therapies focused on this protein may prove useful in the treatment of asthma.

The role of mast cells in asthma

While the role of mast cells in allergic reactions is unequivocal, their precise functions in asthma remain controversial. Mast cells uniquely populate all vascularized organs and tissues, including the upper and lower respiratory tree, even in healthy individuals. Histologic evidence suggests that asthma is accompanied by a mast cell hyperplasia in the inflamed mucosal epithelium and the adjacent smooth muscle. The mechanisms responsible for constitutive mast cell development have been partly elucidated. Moreover, both in vitro studies and in vivo disease models indicate that mast cells have a remarkably flexible program of gene expression, and this program can be drastically altered by the T-cell-derived Th2 cytokines relevant to asthma. Moreover, the role of mast cells in innate immunity is now firmly established, and the capacity for numerous microbial pathogens to initiate their activation in vitro and in vivo suggest mechanisms by which microbes could initiate disease exacerbations.

Role of immunoglobulin E and mast cells in murine models of asthma

Immunoglobulin E (IgE) and mast cells are believed to play important roles in allergic inflammation. However, their contributions to the pathogenesis of human asthma have not been clearly established. Significant progress has been made recently in our understanding of airway inflammation and airway hyperresponsiveness through studies of murine models of asthma and genetically engineered mice. Some of the studies have provided significant insights into the role of IgE and mast cells in the allergic airway response. In these models mice are immunized systemically with soluble protein antigens and then receive an antigen challenge through the airways. Bronchoalveolar lavage fluid from mice with allergic airway inflammation contains significant amounts of IgE. The IgE can capture the antigen presented to the airways and the immune complexes so formed can augment allergic airway response in a high-affinity IgE receptor (FcepsilonRI)-dependent manner. Previously, there were conflicting reports regarding the role of mast cells in murine models of asthma, based on studies of mast cell-deficient mice. More recent studies have suggested that the extent to which mast cells contribute to murine models of asthma depends on the experimental conditions employed to generate the airway response. This conclusion was further supported by studies using FcepsilonRI-deficient mice. Therefore, IgE-dependent activation of mast cells plays an important role in the development of allergic airway inflammation and airway hyperresponsiveness in mice under specific conditions. The murine models used should be of value for testing inhibitors of IgE or mast cells for the development of therapeutic agents for human asthma.

Mast cells play a partial role in allergen-induced subepithelial fibrosis in a murine model of allergic asthma

BACKGROUND

Role of mast cells in the development of allergen-induced airway remodelling has not been fully investigated in vivo.

OBJECTIVE

To clarify the possible role of mast cells in the development of allergen-induced airway remodelling, we compared their responses of genetically mast cell-deficient mice, WBB6F1-W/Wv (c-kit mutant) and Sl/Sld (c-kit ligand mutant) mice with those of congenic normal mice in a murine model of allergic asthma.

METHODS

Mice were sensitized to ovalbumin (OA) with alum, and exposed daily for 3 weeks to aerosolized OA. Twenty-four hours after the last inhalation, bronchial responsiveness to acetylcholine (Ach) was measured, and bronchoalveolar lavage (BAL), and biochemical and histological examinations were performed.

RESULTS

In both sensitized mast cell-deficient mice, the degree of bronchial hyper-responsiveness to Ach, the number of inflammatory cells and the level of transforming growth factor-beta1 in BAL fluid, IgE response and goblet cell hyperplasia in the epithelium after repeated allergen provocation were not significantly different from those of congenic mice. In contrast, subepithelial fibrosis, evaluated in the fibrotic area around the airways, observed in congenic mice after repeated allergen challenge was partially attenuated in both mast cell-deficient mice. In addition, the amount of hydroxyproline in the lung of mast cell-deficient mice was significantly lower than that of congenic mice. Furthermore, the decreased fibrotic area and amount of hydroxyproline in W/Wv mice was completely recovered by reconstitution of tissue mast cells with bone marrow-derived mast cells of congenic mice.

CONCLUSION

These findings suggest that mast cells play a partial role in the development of allergen-induced subepithelial fibrosis, although airway inflammation, epithelial remodelling and BHR caused by repeated allergen challenge are independent of mast cells, at least in this model.

Mast-cell activation augments the late phase reaction in experimental immune-mediated blepharoconjunctivitis

BACKGROUND

How the early phase allergic reaction affects the late phase reaction remains unclear. We examined this issue with an experimental model of allergic conjunctivitis that permits the two reactions to be disconnected from each other.

METHODS

Experimental immune-mediated blepharoconjunctivitis (EC) was initiated in Brown Norway rats by transferring ovalbumin (OVA)-specific T cells and then challenging with OVA-containing eye drops. To induce early phase reaction, a mast-cell activator, C48/80, was challenged together with or without OVA. Rats were evaluated clinically and eyes were harvested for histologic examination and for evaluation of chemokine expression by reverse-transcriptase PCR.

RESULTS

The rats challenged with OVA alone developed the T-cell-mediated late phase reaction histologically, but not clinically, in the absence of early phase reaction. While rats challenged with C48/80 with or without OVA exhibited clinical signs of the early phase reaction, the clinical late phase reaction was observed only in the OVA+C48/80 group. Eosinophilic infiltration into the conjunctiva during the late phase reaction of the OVA+C48/80 group markedly exceeded that of rats challenged with either OVA or C48/80 alone. RANTES (regulated on activation, normal T-cell expressed and secreted), an eosinophil attractant, was expressed both in the OVA+C48/80 and OVA groups, while eotaxin was expressed at equivalent levels in all three groups.

CONCLUSION

The mast-cell-mediated early phase reaction potentiates the T-cell-mediated late phase reaction, and RANTES is involved in eosinophilic infiltration induced by antigen-specific T cells. Other molecules induced by allergen-specific T cells activated in an as yet unknown manner by the mast cells may be responsible for the infiltration of eosinophils.

Role of Th2 responses in the development of allergen-induced airway remodelling in a murine model of allergic asthma

(1) To clarify the involvement of Th2 responses in the development of allergen-induced airway remodelling, we investigated the effect of anti-CD4 monoclonal antibody (mAb) and anti-CD8 mAb, and the responses of IL-4 gene-knockout (KO) mice in a murine model of allergic asthma. (2) Mice were immunized twice by intraperitoneal injections of ovalbumin (OA), and exposed to aeroallergen (OA, 1% w v(-1)) for 3 weeks. Twenty-four hours after the final challenge, airway responsiveness to acetylcholine was measured, and bronchoalveolar lavage (BAL) and histological examinations were carried out. (3) Anti-CD4 mAb (1 mg kg(-1)) clearly inhibited allergen-induced increases in airway responsiveness to acetylcholine, the number of eosinophils in BAL fluid, serum OA-specific IgE levels, IL-13 and transforming growth factor-beta1 levels in BAL fluid, and amount of hydroxyproline in the lung by 100, 99, 100, 100, 84, and 60%, respectively. Furthermore, the antibody (1 mg kg(-1)) also attenuated allergen-induced goblet cell hyperplasia in the epithelium and subepithelial fibrosis by 72 and 83%, respectively. In contrast, anti-CD8 mAb (1 mg kg(-1)) showed no effect on each parameter. Furthermore, all these parameters were attenuated in IL-4KO mice by 57, 93, 100, 45, 84 and 60%, and also 72 and 83%, respectively. (4) These findings suggest that Th2 responses play a critical role for the development of allergen-induced airway remodelling, and that the inhibition of Th2 responses, e.g. using anti-CD4 mAb, is a therapeutic approach for the treatment of airway remodelling in asthma.

Absence of immunoglobulin E synthesis and airway eosinophilia by vaccination with plasmid DNA encoding ProDer p 1

BACKGROUND

Various studies have shown that immunization with naked DNA encoding allergens induces T helper 1(Th1)-biased non-allergic responses.

OBJECTIVE

To evaluate the polarization of the immune responses induced by vaccinations with plasmid DNA encoding the major mite allergen precursor ProDer p 1.

METHODS

A DNA vaccine was constructed on the basis of a synthetic cDNA encoding ProDer p 1 with optimized codon usage. The immunogenicity of ProDer p 1 DNA in CBA/J mice was compared with that of purified natural Der p 1 or recombinant ProDer p 1 adjuvanted with alum. Vaccinated mice were subsequently exposed to aerosolized house dust mite extracts to provoke airway inflammation. The presence of inflammatory cells was examined in bronchoalveolar lavage (BAL) fluids and allergen-specific T cell reactivity was measured.

RESULTS

Naive mice immunized with ProDer p 1 DNA developed Th1 immune responses characterized by high titres of specific IgG2a antibodies, low titres of specific IgG1 and, remarkably, the absence of anti-ProDer p 1 IgE. No specific responses were observed in animals vaccinated with the blank DNA vector. By contrast, natural Der p 1 or recombinant ProDer p 1 adsorbed to alum induced pronounced Th2 allergic responses with strong specific IgG1 and IgE titres. Spleen cells from DNA ProDer p 1-vaccinated mice secreted high levels of IFN-gamma and low production of IL-5. Conversely, both adjuvanted allergens stimulated typical Th2-type cytokine profile characterized by high and low levels of IL-5 and IFN-gamma, respectively. Whereas BAL eosinophilia was clearly observed in Der p 1-immunized animals, ProDer p 1 DNA as well as ProDer p 1 vaccinations prevented airway eosinophil infiltrations.

CONCLUSIONS

These results suggest that vaccination with DNA encoding ProDer p 1 effectively fails to induce the allergen-induced IgE synthesis and airway cell infiltration. Plasmid DNA encoding ProDer p 1 may provide a novel approach for the treatment of house dust mite allergy.

Dissociation by steroids of eosinophilic inflammation from airway hyperresponsiveness in murine airways

BACKGROUND

The link between eosinophils and the development of airway hyperresponsiveness (AHR) in asthma is still controversial. This question was assessed in a murine model of asthma in which we performed a dose ranging study to establish whether the dose of steroid needed to inhibit the eosinophil infiltration correlated with that needed to block AHR.

METHODS

The sensitised BALB/c mice were dosed with vehicle or dexamethasone (0.01-3 mg/kg) 2 hours before and 6 hours after each challenge (once daily for 6 days) and 2 hours before AHR determination by whole-body plethysmography. At 30 minutes after the AHR to aerosolised methacholine the mice were lavaged and differential white cell counts were determined. Challenging with antigen caused a significant increase in eosinophils in the bronchoalveolar lavage (BAL) fluid and lung tissue, and increased AHR.

RESULTS

Dexamethasone reduced BAL and lung tissue eosinophilia (ED50 values of 0.06 and 0.08 mg/kg, respectively), whereas a higher dose was needed to block AHR (ED50 of 0.32 mg/kg at 3 mg/ml methacholine. Dissociation was observed between the dose of steroid needed to affect AHR in comparison with eosinophilia and suggests that AHR is not a direct consequence of eosinophilia.

CONCLUSION

This novel pharmacological approach has revealed a clear dissociation between eosinophilia and AHR by using steroids that are the mainstay of asthma therapy. These data suggest that eosinophilia is not associated with AHR and questions the rationale that many pharmaceutical companies are adopting in developing low-molecular-mass compounds that target eosinophil activation/recruitment for the treatment of asthma.

CCR8 is not essential for the development of inflammation in a mouse model of allergic airway disease

Chemokine receptors play an important role in the trafficking of various immune cell types to sites of inflammation. Several chemokine receptors are differentially expressed in Th1 and Th2 effector populations. Th2 cells selectively express CCR3, CCR4, and CCR8, which could direct their trafficking to sites of allergic inflammation. Additionally, increased expression of the CCR8 ligand, TCA-3, has been detected in affected lungs in a mouse model of asthma. In this study, CCR8-deficient mice were generated to address the biological role of CCR8 in a model of allergic airway disease. Using two different protocols of allergen challenge, we demonstrate that absence of CCR8 does not affect the development of pulmonary eosinophilia and Th2 cytokine responses. In addition, administration of anti-TCA-3-neutralizing Ab during allergen sensitization and rechallenge failed to inhibit airway allergic inflammation. These results suggest that CCR8 does not play an essential role in the pathogenesis of inflammation in this mouse model of allergic airway disease.

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.

Site-specific sensitization in a murine model of allergic rhinitis: role of the upper airway in lower airways disease

BACKGROUND

Allergic rhinitis (AR) is the most common atopic disease with strong links to asthma. We have developed a murine model of AR to study nasal, bronchial, and systemic immune response to local allergen stimulation.

OBJECTIVES

The purpose of this study was to develop and characterize a murine model of AR.

METHODS

Six- to 8-week-old BALB/c mice were sensitized by means of intranasal (local) application of ovalbumin (OVA) or systemic intraperitoneal injection. They were then challenged with intranasal OVA, and allergic response was assessed.

RESULTS

Intranasal particle deposition was found to be exclusively in the nares. All sensitized animals showed increased levels of OVA-specific serum IgE and IgG after challenge, although the timing to maximal response varied with the route and dose of allergen used. Histology of the upper and lower airways showed marked eosinophilic infiltration, and analysis of bronchoalveolar lavage fluid showed increased IL-5 and PMN infiltrates after challenge.

CONCLUSION

Using exclusive local sensitization and challenge of mouse nares, we were able to demonstrate inflammatory changes in both the upper and lower airways, even though distribution of allergen particles appeared to be only in the nares of these animals. This provides further evidence for the importance of the upper airway in lower airways disease. We have shown that the route of administration greatly affects the characteristics of the subsequent immune responses.

Absence of the complement anaphylatoxin C3a receptor suppresses Th2 effector functions in a murine model of pulmonary allergy

Asthma is a chronic inflammatory disease of the lung resulting in airway obstruction. The airway inflammation of asthma is strongly linked to Th2 lymphocytes and their cytokines, particularly IL-4, IL-5, and IL-13, which regulate airway hyperresponsiveness, eosinophil activation, mucus production, and IgE secretion. Historically, complement was not thought to contribute to the pathogenesis of asthma. However, our previous reports have demonstrated that complement contributes to bronchial hyperreactivity, recruitment of airway eosinophils, IL-4 production, and IgE responses in a mouse model of pulmonary allergy. To define the complement activation fragments that mediate these effects, we assessed the role of the complement anaphylatoxin C3a in a mouse model of pulmonary allergy by challenging C3aR-deficient mice intranasally with a mixed Ag preparation of Aspergillus fumigatus cell culture filtrate and OVA. Analysis by plethysmography after challenge revealed an attenuation in airway hyperresponsiveness in C3aR-deficient mice relative to wild-type mice. C3aR-deficient mice also had an 88% decrease in airway eosinophils and a 59% reduction in lung IL-4-producing cells. Consistent with the reduced numbers of IL-4-producing cells, C3aR-deficient mice had diminished bronchoalveolar lavage levels of the Th2 cytokines, IL-5 and IL-13. C3aR knockout mice also exhibited decreases in IgE titers as well as reduced mucus production. Collectively, these data highlight the importance of complement activation, the C3a anaphylatoxin, and its receptor during Th2 development in this experimental model and implicate these molecules as possible therapeutic targets in diseases such as asthma.

Th2 cytokine production from mast cells is directly induced by lipopolysaccharide and distinctly regulated by c-Jun N-terminal kinase and p38 pathways

Mast cells secrete multiple cytokines and play an important role in allergic inflammation. Although it is widely accepted that bacteria infection occasionally worsens allergic airway inflammation, the mechanism has not been defined. In this study, we show that LPS induced Th2-associated cytokine production such as IL-5, IL-10, and IL-13 from mast cells and also synergistically enhanced production of these cytokines induced by IgE cross-linking. LPS-mediated Th2-type cytokine production was abolished in mouse bone marrow-derived mast cells derived from C3H/HeJ mice, suggesting that Toll-like receptor 4 is essential for the cytokine production. Furthermore, we found that mitogen-activated protein kinases including extracellular signal-regulated kinase 1/2, c-Jun N-terminal kinase, and p38 kinase were activated by LPS stimulation in bone marrow-derived mast cells. Inhibition of extracellular signal-regulated kinase activation has little effect on LPS-mediated cytokine production. In contrast, inhibition of c-Jun N-terminal kinase activation significantly suppressed both IL-10 and IL-13 expression at both mRNA and protein levels. Interestingly, although inhibition of p38 did not down-regulate the mRNA induction, it moderately decreased all three cytokine productions by LPS. These results indicate that LPS-mediated production of IL-5, IL-10, and IL-13 was distinctly regulated by mitogen-activated protein kinases. Our findings may indicate a clue to understanding the mechanisms of how bacteria infection worsens the clinical features of asthma.

Regulation of mast-cell and basophil function and survival by IgE

Mast cells and basophils are important effector cells in T helper 2 (T(H)2)-cell-dependent, immunoglobulin-E-associated allergic disorders and immune responses to parasites. The crosslinking of IgE that is bound to the high-affinity receptor Fc epsilon RI with multivalent antigen results in the aggregation of Fc epsilon RI and the secretion of products that can have effector, immunoregulatory or autocrine effects. This response can be enhanced markedly in cells that have been exposed to high levels of IgE, which results in the increased surface expression of Fc epsilon RI. Moreover, recent work indicates that monomeric IgE (in the absence of crosslinking) can render mast cells resistant to apoptosis induced by growth-factor deprivation in vitro and, under certain circumstances, can induce the release of cytokines. So, the binding of IgE to Fc epsilon RI might influence mast-cell and basophil survival directly or indirectly, and can also regulate cellular function.

Augmentation of allergic early-phase reaction by nerve growth factor

The allergic early-phase reaction, a hallmark of allergic bronchial asthma, is caused by allergen and immunoglobulin E-dependent mediator release from mast cells. It was previously shown that nerve growth factor (NGF) contributes to acute airway inflammation. This study further investigates the role of NGF in the allergic early-phase reaction using a well-established mouse model of ovalbumin-induced allergic airway inflammation. Treatment of sensitized and aerosol challenged BALB/c mice with blocking anti-NGF antibodies inhibited allergen-induced early-phase reaction and suppressed airway inflammation. Transgenic mice constitutively overexpressing NGF in the airways (Clara-cell secretory protein promoter [CCSP]-NGF-tg) were employed and compared with wild-type animals. In sensitized and challenged CCSP-NGF-tg mice, early-phase reaction, airway inflammation, as well as percental relative increases in serotonin levels were augmented compared with wild-type mice. These effects were paralleled by increased serotonin levels in the airways, whereas immunoglobulin E levels remained unaffected. Furthermore, CCSP-NGF-tg mice developed an increased reactivity of sensory neurons in response to inhaled capsaicin demonstrating NGF-mediated neuronal plasticity. These data provide evidence for the functional role of NGF in the development of allergic early phase responses in the airways and the lung.

[Functional molecules in allergic bronchial asthma]

Bronchial asthma is considered to be a chronic airway inflammatory disease, characterized by airway obstruction, airway eosinophilic inflammation, and airway hyperresponsiveness (AHR) to a variety of stimuli. AHR is thought to be an important symptom, because the severity of the disease is generally correlated with the degree of AHR. Recent clinical studies have demonstrated the involvement of airway inflammation in the development of allergen-induced AHR, although, the mechanism of allergen-induced AHR has not been fully elucidated and remains controversial. In vivo animal models might provide important information on this point. We have established a mouse model of allergic asthma, which is characterized by airway eosinophilia, IgE production, T helper type 2 (Th2) cytokine production in the airway, and AHR, and investigated the role of inflammatory cells and functional molecules. Results from gene-knockout and mutant mice demonstrated the involvement of T cells, mast cells, prostanoids, and Th2 cytokines including interleukin (IL)-4 and IL-5 in the development of allergen-induced airway inflammation and AHR. In contrast, treatment with anti-IL-4 monoclonal antibody (mAb) or anti-IL-5 mAb during allergen inhalation did not inhibit allergen-induced AHR, although the combination of these mAbs clearly inhibited the enhanced responsiveness. These data indicate that it is a better strategy for control of the disease to inhibit or suppress multifunctional molecules like corticosteroids rather than to inhibit a single factor, because bronchial asthma is a multifactorial disease.

IgE-dependent mast cell activation potentiates airway responses in murine asthma models

We have studied murine models of asthma using FcepsilonRIalpha-chain-deficient (FcepsilonRIalpha(-/-)) mice to investigate the role of IgE-dependent mast cell activation in these models. When mice were either 1) immunized once with OVA in alum i.p. and then challenged with OVA intranasally, or 2) repeatedly immunized with OVA in the absence of adjuvant and subsequently challenged with nebulized OVA, FcepsilonRalpha(-/-) mice had significantly fewer eosinophils and lower IL-4 levels in their bronchoalveolar lavage fluid compared with wild-type mice. When mice were given anti-IL-5 antibody before OVA challenge in protocol 1, eosinophilic infiltration into the airways was significantly suppressed in both genotypes, but only FcepsilonRIalpha(-/-) mice showed significantly reduced airway hyperresponsiveness (AHR). In addition, when mice immunized and challenged with OVA also received a late OVA provocation at a higher concentration and were then exposed to methacholine, only wild-type mice developed a substantial increase in AHR. Since FcepsilonRI is expressed mainly on mast cells in mouse airways, we conclude that IgE-dependent activation of this cell type plays an important role in the development of allergic airway inflammation and AHR in mice. The models used may be of value for testing inhibitors of IgE or mast cells for development of therapeutic agents for human asthma.

Analyzing the roles of mast cells and basophils in host defense and other biological responses

The sudden and systemic activation of mediator release from mast cells and basophils that can occur when some sensitized subjects are challenged by minute amounts of specific antigen (eg, from an insect sting or peanuts) can result in fatal anaphylaxis, a reaction that arguably represents the most grotesque imbalance between the cost and benefit of an immune response. Why then do mast cells and basophils continue to exist and, in the case of mast cells, populate almost all vascularized tissues? This review will consider the roles of mast cells and basophils in health and disease, emphasizing particularly their proven or potential functions in host defense. We will also describe briefly some approaches to investigate mast cell and basophil functions in vivo, including the use of mast cells generated directly from embryonic stem cells in vitro.

Early phase bronchoconstriction in the mouse requires allergen-specific IgG

Allergen provocation of allergic asthma patients is often characterized by an initial period of bronchoconstriction, or early phase reaction (EPR), that leads to maximal airway narrowing within 15-30 min, followed by a recovery period returning airway function to baseline within 1-2 h. In this study, we used a defined OVA provocation model and mice deficient for specific leukocyte populations to investigate the cellular/molecular origins of the EPR. OVA-sensitized/challenged wild-type (C57BL/6J) mice displayed an EPR following OVA provocation. However, this response was absent in gene knockout animals deficient of either B or T cells. Moreover, transfer of OVA-specific IgG, but not IgE, before the OVA provocation, was capable of inducing the EPR in both strains of lymphocyte-deficient mice. Interestingly, an EPR was also observed in sensitized/challenged mast cell-deficient mice following an OVA provocation. These data show that the EPR in the mouse is an immunologically based pathophysiological response that requires allergen-specific IgG but occurs independent of mast cell activities. Thus, in the mouse the initial period of bronchoconstriction following allergen exposure may involve neither mast cells nor IgE-mediated events.

Mycoplasma pneumoniae-induced activation and cytokine production in rodent mast cells

BACKGROUND

Mycoplasma pneumoniae is a respiratory tract pathogen that has been associated with severe exacerbations in patients with chronic asthma. Murine models of infection have recently been established, with disease manifestations similar to those observed in human subjects. Previous studies have suggested that this organism is capable of producing activation of a wide range of immunologic cell types.

OBJECTIVE

We sought to determine whether M pneumoniae can induce mast cell activation in the rodent mast cell line RBL-2H3.

RESULTS

After 4 hours of coculture, morphologic changes indicative of activation were observed by means of electron microscopy, and M pneumoniae was identified, by means of immunoelectron microscopy, adhering to mast cell membranes. Coculture of rat basophilic leukemia cells with viable M pneumoniae for 4 hours resulted in net release of beta-hexosaminidase and serotonin into the supernatant. Live, but not heat-killed, organisms induced the release of IL-4 protein into the culture supernatant, with a peak at 4 hours. During coculture with M pneumoniae, production of mRNA for IL-4, IL-6, and TNF-alpha was upregulated after 2 hours and had returned to near baseline by 24 hours after infection.

CONCLUSIONS

We conclude that viable M pneumoniae induces activation of mast cells with release of granule contents, as well as cytokine production.

The murine CCR3 receptor regulates both the role of eosinophils and mast cells in allergen-induced airway inflammation and hyperresponsiveness

CCR3 is a chemokine receptor initially thought specific to eosinophils but subsequently identified on TH2 cell subsets, basophils, mast cells, neural tissue, and some epithelia. Because of the prominent role of these cells in allergic disease, including asthma, we generated mice deficient in CCR3 to determine its contribution in a model of allergic airway disease. Here we show that CCR3 is important for the basal trafficking of eosinophils to the intestinal mucosa but not the lung. In contrast, CCR3 disruption significantly curtails eosinophil recruitment to the lung after allergen challenge, with the majority of the eosinophils being arrested in the subendothelial space. Further, a role for CCR3 in mast cell homing has been identified; after sensitization and allergen challenge, we find increased numbers of intraepithelial mast cells in the trachea of knockout mice. Physiologically, we find that the net result of these complex cell fates after sensitization and allergen challenge is a paradoxical increase in airway responsiveness to cholinergic stimulation. These data underscore a more complex role for CCR3 in allergic disease than was anticipated.

The Th2 lymphocyte products IL-4 and IL-13 rapidly induce airway hyperresponsiveness through direct effects on resident airway cells

Airway inflammation and airway hyperresponsiveness (AHR) are hallmarks of asthma. Cytokines produced by T helper type 2 (Th2) lymphocytes have been implicated in both processes. There is strong support for the idea that Th2 cytokines can produce AHR indirectly by promoting the recruitment of inflammatory cells. Less attention has been given to the possibility that Th2 cytokines might induce AHR by acting directly on resident airway cells. To investigate this, we polarized and activated CD4(+) T cells in vitro and analyzed airway function after administration of lymphocyte-conditioned media to the airways of naive mice. Th2-lymphocyte-conditioned medium induced AHR within 6 h. This finding was reproduced in mast-cell-deficient and in T- and B-lymphocyte-deficient mice. AHR did not occur when Th2-lymphocyte-conditioned medium was administered to mice lacking the IL-4 receptor alpha subunit or Stat6, suggesting a critical role for interleukin (IL)-4 and/or IL-13. This was confirmed by the finding that recombinant IL-4 and IL-13 both induced AHR within 6 h. The induction of AHR occurred in the absence of inflammatory cell recruitment or mucus production. These results strongly suggest that products of activated Th2 lymphocytes can rapidly perturb airway function through direct effects on resident airway cells.

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

BACKGROUND

We have recently demonstrated that the transfer of interleukin (IL)-5-producing CD4+ T cell clones into unprimed mice is sufficient for the development ofeosinophilic inflammation in the bronchial mucosa upon antigen inhalation.

OBJECTIVE

The aim of this study was to elucidate the possible contribution of mast cells in eosinophilic inflammation and bronchial hyper-responsiveness (BHR), and to discriminate between the roles of CD4+ T cells and mast cells.

METHODS

Mast cell-deficient mice (WBB6F1-W/Wv) and their congenic normal littermates (WBB6F1-+/+) were immunized with ovalbumin and challenged by inhalation with the relevant antigen.

RESULTS

Airway eosinophilia was induced with equivalent intensity in +/+ and W/Wv mice 6, 24, 96 and 216 h after antigen inhalation. In contrast, 48 h after antigen challenge, eosinophilic infiltration into the bronchial mucosa was significantly less pronounced in W/Wv mice than in +/+ mice. Anti-CD4 monoclonal antibody (mAb), anti-IL-5 mAb, and cyclosporin A were administered next, demonstrating that the airway eosinophilia of W/Wv mice induced 48 h after antigen challenge was almost completely inhibited by each of these three treatments, but that of +/+ mice was significantly less susceptible. Bronchial responsiveness to acetylcholine was increased 48 h after antigen challenge and was not significantly different between +/+ and W/Wv mice. Administration of anti-IL-5 mAb completely inhibited the development of BHR in both +/+ and W/Wv mice.

CONCLUSION

These results indicate that, in mice, mast cells do have a supplemental role in the development of pulmonary eosinophilia but not BHR. CD4+ T cells totally regulate these responses by producing IL-5.

Mast cells regulate IFN-gamma expression in the skin and circulating IgE levels in allergen-induced skin inflammation

BACKGROUND

Mast cells are important effector cells in IgE-mediated allergic reactions. They are present in normal skin and increased in skin lesions of patients with atopic dermatitis (AD).

OBJECTIVE

We used mice deficient in mast cells (W/W(v)) to assess the role of these cells in a murine model of allergen-induced skin inflammation induced by repeated epicutaneous sensitization with ovalbumin (OVA); the model exhibits many of the characteristics of AD.

METHODS

Mice deficient in mast cells were sensitized with OVA. Histologic and immunohistochemical examinations, as well as measurements of IL-4 and IFN-gamma mRNA, were performed on OVA-sensitized skin. Total and antigen-specific serum IgE levels were determined.

RESULTS

Infiltration in W/W(v) mice by mononuclear cells, T cells, and eosinophils in OVA-sensitized skin was comparable to that in wild-type (WT) controls. Expression of IL-4 mRNA in sensitized skin sites was similarly increased in WT and W/W(v) mice. However, IFN-gamma mRNA expression was significantly increased in sensitized skin of W/W(v) mice but not in that of WT controls. IL-4 mRNA was readily detectable in unsensitized skin of WT controls but not in that of W/W,(v) mice, whereas expression of IL-12 p40 mRNA was significantly increased in unsensitized skin of W/W(v) mice in comparison with WT controls. Total serum IgE levels were significantly increased after epicutaneous sensitization in W/W(v) mice in comparison with WT controls.

CONCLUSION

These results suggest that mast cells regulate IFN-gamma expression in the skin and IgE levels in the circulation in a model of allergen-induced skin inflammation with similarities to AD. This is important, given the role of IFN-gamma in keratinocyte injury in AD and the role of IgE-mediated reactions in exacerbating AD.

CTLA4-IgG reverses asthma manifestations in a mild but not in a more "severe" ongoing murine model

We investigated whether CTLA4-Ig can reverse established asthma manifestations in a novel murine model of ongoing disease. In BALB/c mice, sensitized to ovalbumin (OVA) without adjuvant, airway inflammation was induced by a first series of OVA aerosol challenges. Murine CTLA4-IgG was then administered, followed by a second series of OVA inhalations. In control-treated mice, two series of OVA challenges induced upregulation of OVA-specific IgE in serum, eosinophils in the bronchoalveolar lavage fluid (BALF), and IL-5 production by lung lymphocytes upon OVA restimulation in vitro, compared with saline-challenged mice. CTLA4-IgG significantly inhibited all of these parameters in OVA-challenged mice. Importantly, mCTLA4-IgG performed better than the gold-standard dexamethasone because this corticosteroid did not inhibit the upregulation of OVA-specific IgE in serum. In a more "severe" ongoing model, induced by sensitization to OVA emulsified in aluminum hydroxide, resulting in airway hyperresponsiveness to methacholine and stronger inflammatory responses, mCTLA4-IgG was less effective in that only the number of eosinophils in the BALF was reduced (P = 0.053), whereas dexamethasone inhibited both BALF eosinophilia and cytokine production by lung lymphocytes. Thus, CTLA4-Ig might be an effective alternative therapy in established allergic asthma, especially in situations of mild disease.

Human mast cell and airway smooth muscle cell interactions: implications for asthma

Asthma is characterized by inflammation, hyperresponsiveness, and remodeling of the airway. Human mast cells (HMCs) play a central role in all of these changes by releasing mediators that cause exaggerated bronchoconstriction, induce human airway smooth muscle (HASM) cell proliferation, and recruit and activate inflammatory cells. Moreover, the number of HMCs present on asthmatic HASM is increased compared with that on nonasthmatic HASM. HASM cells also have the potential to actively participate in the inflammatory process by synthesizing cytokines and chemokines and expressing surface molecules, which have the capacity to perpetuate the inflammatory mechanisms present in asthma. This review specifically examines how the mediators of HMCs have the capacity to modulate many functions of HASM; how the synthetic function of HASM, particularly through the release and expression of stem cell factor, has the potential to influence HMC number and activation in an extraordinarily potent and proinflammatory manner; and how these interactions between HMCs and HASM have potential consequences for airway structure and inflammation relevant to the disease process of asthma.

Requirements for allergen-induced airway inflammation and hyperreactivity in CD4-deficient and CD4-sufficient HLA-DQ transgenic mice

BACKGROUND

Airway inflammation is central to the pathogenesis of allergic asthma, and molecules that mediate this process obviously represent targets for therapy.

OBJECTIVE

To study the role of CD4(+) T cells and/or HLA-DQ molecules in allergic asthma, we have generated and characterized models of short ragweed allergen (SRW)-induced inflammation using transgenic mice with HLA-DQ (DQ6 or DQ8), human CD4 (hCD4), or both on a genetic background that lacks mouse MHC II and CD4 (Abeta(0)/mCD4(0)).

METHODS

Mice were actively sensitized and later challenged intranasally with SRW allergenic extract. Bronchoalveolar lavage fluid composition, airway inflammation and hyperresponsiveness, blood eosinophil levels, and cell proliferation were examined.

RESULTS

In response to SRW treatment, both DQ6 and DQ8 transgenic mice expressing hCD4 developed pulmonary eosinophilia and associated lung tissue damage with increase in eosinophil peroxidase and T(H)2 cytokines in bronchoalveolar lavage fluid, strong airway hyperreactivity, and persistent blood eosinophilia. The response was independent of mast cells/histamine pathway and was mediated by DQ-restricted hCD4(+) T cells. Interestingly, lungs of CD4-deficient DQ6 transgenic mice showed an eosinophilic inflammation without local increase in cytokines and eosinophil peroxidase. The allergic reaction was absent in double-knockout mice and mice expressing either DQ8 or hCD4 alone.

CONCLUSIONS

DQ6 molecules are critical to SRW-induced allergy and can operate in the presence or absence of CD4. However, both DQ antigens and CD4 molecules are critical for full manifestation of allergen-induced asthma in transgenic mice.

Early interleukin 4-dependent response can induce airway hyperreactivity before development of airway inflammation in a mouse model of asthma

In experimental models of bronchial asthma with mice, airway inflammation and increase in airway hyperreactivity (AHR) are induced by a combination of systemic sensitization and airway challenge with allergens. In this report, we present another possibility: that systemic antigen-specific sensitization alone can induce AHR before the development of inflammation in the airway. Male BALB/c mice were sensitized with ovalbumin (OVA) by a combination of intraperitoneal injection and aerosol inhalation, and various parameters for airway inflammation and hyperreactivity were sequentially analyzed. Bronchial response measured by a noninvasive method (enhanced pause) and the eosinophil count and interleukin (IL)-5 concentration in bronchoalveolar lavage fluid (BALF) gradually increased following the sensitization, and significant increase was achieved after repeated OVA aerosol inhalation along with development of histologic changes of the airway. In contrast, AHR was already significantly increased by systemic sensitization alone, although airway inflammation hardly developed at that time point. BALF IL-4 concentration and the expression of IL-4 mRNA in the lung reached maximal values after the systemic sensitization, then subsequently decreased. Treatment of mice with anti-IL-4 neutralizing antibody during systemic sensitization significantly suppressed this early increase in AHR. In addition, IL-4 gene-targeted mice did not reveal this early increase in AHR by systemic sensitization. These results suggest that an immune response in the lung in an early stage of sensitization can induce airway hyperreactivity before development of an eosinophilic airway inflammation in BALB/c mice and that IL-4 plays an essential role in this process. If this early increase in AHR does occur in sensitized human infants, it could be another therapeutic target for early prevention of the future onset of asthma.

Induction of pulmonary allergen-specific IgA responses or airway hyperresponsiveness in the absence of allergic lung disease following sensitization with limiting doses of ovalbumin-alum

Respiratory allergies represent a failure to generate nonpathogenic responses to innocuous foreign materials. Herein we assessed the role of the sensitizing dose of allergen in this response/nonresponse paradigm, sensitizing BALB/c mice with 5 ng-2 microg of OVA-alum and assessing their responses to repeated OVA aerosol challenge. Mice sensitized with < or = 25 ng of OVA-alum did not develop atopic antibodies, airway hyperresponsiveness (AHR), eosinophilia, or pulmonary Th2 responses, but the 25-ng group animals did develop significant IgA responses. The mice sensitized with 100 ng of OVA-alum developed AHR in the absence of detectable allergic disease, while the mice sensitized with 250 ng-2 microg of OVA/alum developed full-spectrum allergic disease (i.e., eosinophilia, IgE, IgG1, pulmonary Th2 cytokine responses, and AHR). These data indicate that limiting doses of allergen can differentially induce IgA or AHR in the absence of atopic disease in mice.

Role of dendritic cells and Th2 lymphocytes in asthma: lessons from eosinophilic airway inflammation in the mouse

Asthma is a chronic disorder of the airways characterized by variable airway narrowing, mucus hypersecretion, and infiltration of the airway wall with eosinophils. It is now believed that asthma is controlled by Th2 lymphocytes producing cytokines such as IL-4, IL-5, IL-9, and IL-13. Animal models of eosinophilic airway inflammation and airway hyperreactivity have been developed to study the contribution of cells or mediators in the pathogenesis of asthma. In this review, we discuss the role of antigen presenting cells, CD4(+) and CD8(+) T lymphocytes, B lymphocytes, NK cells, and mast cells in the induction and maintenance of eosinophilic airway inflammation, mucus hypersecretion, and airway hyperreactivity.

Role of mast cells in antigen-induced airway inflammation and bronchial hyperresponsiveness in rats

The participation of mast cells in the induction of antigen-induced airway inflammation and bronchial hyperresponsiveness (BHR) to acetylcholine (ACh) was investigated using pharmacological agents and mast cell-deficient rats (Ws/Ws). A significant increase in the number of leukocytes in bronchoalveolar lavage fluid (BALF) and bronchial responsiveness to ACh were observed 24 h after antigen (ovalbumin) challenge in sensitized Brown-Norway (BN) rats. Disodium cromoglycate and terfenadine did not inhibit antigen-induced airway inflammation and BHR in sensitized BN rats. In contrast, cyclosporin A (CyA), FK-506 and prednisolone significantly inhibited antigen-induced airway inflammation and BHR in sensitized BN rats. In addition, disodium cromoglycate, terfenadine and prednisolone, but not CyA and FK-506, inhibited homologous passive cutaneous anaphylaxis in rats. Furthermore, a significant increase in the number of leukocytes in BALF and BHR was also observed in Ws/Ws rats 24 h after inhalation of antigen; however, the magnitude of BHR in Ws/Ws rats was lower than that in the congenic rats. These findings suggest that mast cells play a partial role in the development of antigen-induced BHR in rats and that the induction of BHR is barely suppressed by mast cell stabilizing agents.

IgE regulation and roles in asthma pathogenesis

Asthma and the predisposition to produce IgE are inherited as linked traits in families. In patients IgE levels correlate with asthma severity and bronchial hyperresponsiveness. The concept that IgE plays a critical role in asthma pathogenesis has driven the development of IgE blockers, which are currently being introduced into clinical use. This review focuses on the mechanisms whereby IgE participates both in immediate hypersensitivity responses in the airways and in the induction of chronic allergic bronchial inflammation. The molecular genetic events that give rise to IgE production by B cells and the cellular and cytokine factors that support IgE production in the bronchial mucosal microenvironment are discussed. It is clear that much remains to be learned regarding the roles of IgE in asthma and the genetic and environmental influences that lead to its production. Over the next few years, the emerging experience with anti-IgE in patients will provide a more complete understanding of the mechanisms whereby IgE contributes to disease, as well as the therapeutic potential of its inhibition.