Allergic airway sensitization induces T cell activation but not airway hyperresponsiveness in B cell-deficient mice

CD4+ T cell responses in mice lacking MHC class II molecules specifically on B cells

The role of B lymphocytes in initiating and maintaining a CD4+ T cell response has been examined using a variety of strategies, but remains controversial because of weaknesses inherent to each of the approaches. Here, we address this issue by measuring CD4+ T cell priming both in mutant mice devoid of B cells and in chimeric animals lacking major histocompatibility complex class II molecules specifically on B cells. We find that peptide and some protein antigens do not require B cells expressing class II molecules, nor B cells themselves, to efficiently prime. This could be demonstrated by the usual lymph node proliferation assay, a rather indirect in vitro measure of priming, and by a direct ex vivo assay of population expansion and activation marker expression. Interestingly, one protein antigen, conalbumin, could not prime in the absence of B cells, but could in the presence of B cells devoid of class II molecules. This finding constrains the possible mechanisms whereby B lymphocytes contribute to the initiation of a CD4+ T cell response, arguing against the importance of surface immunoglobulin-mediated antigen presentation by B cells.

Th2-Induced Eotaxin Expression and Eosinophilia Coexist with Th1 Responses at the Effector Stage of Lung Inflammation

The T cell-mediated lung inflammation that is associated with allergic asthma is characterized mainly by massive eosinophil infiltration, which induces airway injury and the subsequent late-phase reactivity. Because Th2 cells are often isolated from asthmatic subjects, these cells are postulated to play a role in asthma pathogenesis. We report that adoptively transferred, influenza hemagglutinin-specific Th1 and Th2 cells induced different patterns of chemokines leading to different types of cellular infiltration. Th2 cells were sufficient to induce dramatic Ag-dependent lung eosinophilia and eotaxin expression; by contrast, Th1 transfer primarily induced neutrophil recruitment with little eotaxin production. To determine whether Th1 cells show inhibitory effects on Th2 cell-mediated responses, Th1 and Th2 cells were cotransferred. Hemagglutinin-specific Th1 cells did not inhibit Ag-induced lung eosinophilia, nor did they inhibit eotaxin expression. Furthermore, influenza virus infection of the lung in mice receiving hemagglutinin-specific Th2 cells also induced eotaxin expression and eosinophilia that could not be inhibited by the cotransfer of Th1 cells. Our results show that Th2-mediated allergic lung inflammation coexists with the Th1-mediated responses that are stimulated by diverse forms of Ags.

A Novel T Cell-Regulated Mechanism Modulating Allergen-Induced Airways Hyperreactivity in BALB/c Mice Independently of IL-4 and IL-5

The immunoregulatory functions of IL-4 and IL-5 have identified these cytokines as primary targets for the resolution of airways inflammation and bronchial hyperreactivity in asthma. However, the individual contribution of each of these cytokines and of IL-5-regulated eosinophilia to the induction of airways hyperreactivity in mouse models of asthma remains highly controversial. In this investigation, we have used IL-4- and IL-5-deficient mice of the same genetic background in combination with inhibitory mAbs to these cytokines to identify unequivocally the contribution of these factors to the induction of airways hyperreactivity. Sensitization and aeroallergen challenge of wild-type mice with OVA induced pathological changes to the respiratory epithelium, airways eosinophilia, and hyperreactivity to β-methacholine. Inhibition of the actions of IL-4 and/or IL-5 did not abolish airways hyperreactivity, and in the case of IL-4-deficient mice pretreated with anti-IL-5 mAb, airways hyperreactivity persisted in the absence of pronounced airways inflammation. Airways hyperreactivity was abolished only by anti-CD4+ mAb treatment. However, aeroallergen challenge of IL-5−/− mice showed that morphologic changes to the airways were critically linked to IL-5 and eosinophilia. This investigation demonstrates the existence in BALB/c mice of a novel CD4+ T cell pathway for modulating airways hyperreactivity. These findings may provide an explanation for the dissociation of airways eosinophilia from the development of airways hyperreactivity observed in some cases of asthma and in animal models of this disease.

Evidence that cyclosporin A and dexamethasone inhibit allergic airway eosinophilic inflammation via suppression of interleukin-5 synthesis by T cells

1. We have recently demonstrated that airway eosinophilic inflammation can be transferred to unprimed mice by infusing interleukin (IL)-5-producing T cell clones. Using that murine model, we performed this study to delineate the mechanism of cyclosporin A and dexamethasone to inhibit allergic airway eosinophilic inflammation. 2. The ovalbumin-reactive murine T cell clones, FJ17, produced IL-2, IL-4 and IL-5 upon stimulation with relevant antigen. In FJ17-transferred mice, messenger RNA (mRNA) of IL-2 and IL-5 expressed in the lungs, the number of eosinophils in bronchoalveolar lavage fluid (BALF) was increased and the bronchial responsiveness to acetylcholine was enhanced after antigen provocation. 3. Cyclosporin A (10, 100 ng ml(-1)) and dexamethasone (10, 100 ng ml(-1) suppressed the production of IL-5 as well as IL-2 and IL-4 by FJ17 in vitro. 4. Subcutaneously administered cyclosporin A (30 mg kg(-1)) and dexamethasone (10 mg kg(-1)) inhibited antigen-induced mRNA expression of IL-2 and IL-5, increase of BALF eosinophils and bronchial hyperresponsiveness of FJ17-transferred mice in vivo. The number of BALF eosinophils was correlated with the bronchial responsiveness to acetylcholine (r=0.672). 5. The results clearly indicated that the suppression of IL-5 synthesis by T cells is involved in the effects of cyclosporin A and dexamethasone to inhibit allergic airway eosinophilic inflammation.

Requirements for allergen-induced airway hyperreactivity in T and B cell-deficient mice

BACKGROUND

The pathogenesis of asthma is believed to reflect antigen-induced airway inflammation leading to the recruitment of eosinophils and activation of mast cells through cell-associated IgE. Controversies persist however, regarding the relative importance of different pathogenic cells and effector molecules.

MATERIALS AND METHODS

A variety of gene-targeted mice were examined for the induction of cholinergic airway hyperresponsiveness (AH), allergic airway inflammation, mucus production, and serum IgE reactivity following intratracheal challenge with a potent allergen. AH was determined using whole-body plethysmography following acetylcholine challenge. Where possible, results were confirmed using neutralizing antibodies and cell-specific reconstitution of immune deficient mice.

RESULTS

T and B cell-deficient, recombinase-activating-gene-deficient mice (RAG -/-) failed to develop significant allergic inflammation and AH following allergen challenge. Reconstitution of RAG -/- mice with CD4+ T cells alone was sufficient to restore allergen-induced AH, allergic inflammation, and goblet cell hyperplasia, but not IgE reactivity. Sensitized B cell-deficient mice also developed airway hyperreactivity and lung inflammation comparable to that of wild-type animals, confirming that antibodies were dispensable. Treatment with neutralizing anti-IL-4 antibody or sensitization of IL-4-deficient mice resulted in loss of airway hyperreactivity, whereas treatment with anti-IL-5 antibody or sensitization of IL-5-deficient mice had no effect.

CONCLUSIONS

In mice, CD4+ T cells are alone sufficient to mediate many of the pathognomonic changes that occur in human asthma by a mechanism dependent upon IL-4, but independent of IL-5, IgE, or both. Clarification of the role played by CD4+ T cells is likely to stimulate important therapeutic advances in treatment of asthma.

Epicutaneous sensitization with protein antigen induces localized allergic dermatitis and hyperresponsiveness to methacholine after single exposure to aerosolized antigen in mice

Our understanding of the pathogenesis of atopic dermatitis (AD) and its relationship to asthma remains incomplete. Herein, we describe a murine model of epicutaneous (EC) sensitization to the protein allergen, chicken egg albumin, ovalbumin (OVA), which results in a rise in total and OVA-specific serum IgE and leads to the development of a dermatitis characterized by infiltration of CD3(+) T cells, eosinophils, and neutrophils and by local expression of mRNA for the cytokines IL-4, IL-5, and interferon-gamma. A single exposure of the EC sensitized mice to aerosolized OVA induced eosinophilia in the bronchoalveolar lavage fluid and airway hyperresponsiveness to intravenous methacholine as assessed by measurement of pulmonary dynamic compliance (Cdyn). These results suggest a possible role for EC exposure to antigen in atopic dermatitis and in the development of allergic asthma.

CD23 deficient mice develop allergic airway hyperresponsiveness following sensitization with ovalbumin

The low affinity receptor for IgE (CD23) is reported to regulate immune and inflammatory events and as a result, it may have a role in the development of allergic airway inflammation and hyperresponsiveness (AHR). To test this hypothesis CD23-deficient mice were studied following different modes of allergic sensitization. Mice were actively sensitized either intraperitoneally with ovalbumin (OA)/alum or via the airways (10 days exposure to OA aerosol with no adjuvant). Passive sensitization was performed by intravenous injections of OA-specific IgE. Airway responsiveness, serum IgE and IgG levels were assessed together with airway inflammation. Passive sensitization followed by airway challenges resulted in increased OA-specific lgG and IgE in the serum of wild-type mice only, while both the CD23+/+ and CD23-/- groups developed tracheal smooth muscle hyperresponsiveness to electrical field stimulation, indicating that IgE/CD23-mediated immune functions may not be necessary for the development of allergic changes. Active sensitization of both CD23-/- and CD23+/+ mice resulted in increased serum levels of OA-specific IgE and lgG, airway eosinophilia and significant AHR when compared with nonsensitized mice. The genetic deficiency of CD23-/- mice not only failed to prevent but was associated with a significant increase of these responses. These results indicate that CD23 may not be essential for the development of allergen-induced AHR and further, that its presence may have some inhibitory effects on the allergic response.

The mouse trap

Mouse models of asthma are now being used extensively in drug research. However, the successful unravelling of combinatorial interplays of cells and molecules in the murine airways may not be matched by equally successful demonstrations of an asthma-like pathophysiology. Here, Carl Persson, Jonas Erjefält, Magnus Korsgren and Frank Sundler discuss the fact that major features of asthma may still need to be demonstrated in the airways of allergic mice.

Development of eosinophilic airway inflammation and airway hyperresponsiveness in mast cell-deficient mice

Mast cells are the main effector cells of immediate hypersensitivity and anaphylaxis. Their role in the development of allergen-induced airway hyperresponsiveness (AHR) is controversial and based on indirect evidence. To address these issues, mast cell-deficient mice (W/W v) and their congenic littermates were sensitized to ovalbumin (OVA) by intraperitoneal injection and subsequently challenged with OVA via the airways. Comparison of OVA-specific immunoglobulin E (IgE) levels in the serum and numbers of eosinophils in bronchoalveolar lavage fluid or lung digests showed no differences between the two groups of mice. Further, measurements of airway resistance and dynamic compliance at baseline and after inhalation of methacholine were similar. These data indicate that mast cells or IgE-mast cell activation is not required for the development of eosinophilic inflammation and AHR in mice sensitized to allergen via the intraperitoneal route and challenged via the airways.