Chronic inhaled ovalbumin exposure induces antigen-dependent but not antigen-specific inhalational tolerance in a murine model of allergic airway disease

Tolerance induced by chronic inhaled antigen in a murine asthma model is not mediated by endotoxin

Ovalbumin (OVA)-sensitized wildtype (WT) and endotoxin-resistant (ER) mice developed similar degrees of airways eosinophilia and serum OVA-specific IgE levels after acute aerosolized OVA challenge. WT mice demonstrated methacholine hyperreactivity, whereas ER mice showed no change in responsiveness. With chronic aerosolized OVA challenge, both WT and ER mice developed local tolerance, with resolution of airway eosinophilia but persistence of anti-OVA IgE in serum. Thus, the development of local tolerance with chronic aerosol exposure to OVA is independent of any potential effects of endotoxin in the OVA aerosol solution.

Interleukin-10 does not mediate inhalational tolerance in a chronic model of ovalbumin-induced allergic airway disease

OBJECTIVE

IL-10 is a potent anti-inflammatory cytokine, and IL-10-producing regulatory T cells are effective inhibitors of murine asthmatic responses. This study determined whether IL-10-dependent mechanisms mediated the local inhalational tolerance seen with chronic inhalational exposure to antigen.

METHODS

Wildtype and IL-10(-/-) mice were sensitized with ovalbumin (OVA) and then challenged with daily OVA inhalations for 10 days or 6 weeks.

RESULTS

The 10-day animals developed allergic airway disease, characterized by BAL eosinophilia, histologic airway inflammation and mucus secretion, methacholine hyperresponsiveness, and OVA-specific IgE production. These changes were more pronounced in IL-10(-/-) mice. The 6-week IL-10(-/-) and wildtype animals both developed inhalational tolerance, with resolution of airway inflammation but persistence of OVA-specific IgE production.

CONCLUSION

IL-10 may have anti-inflammatory effects in the acute stage of murine allergic airways disease, but the cytokine does not mediate the development of local inhalational tolerance with chronic antigen exposure.

Bromelain exerts anti-inflammatory effects in an ovalbumin-induced murine model of allergic airway disease

OBJECTIVE

Bromelain, a clinically used pineapple extract and natural product, has reported anti-inflammatory and immunomodulatory activities. The purpose of this study was to determine the effect of bromelain treatment in an ovalbumin (OVA)-induced murine model of allergic airway disease (AAD).

METHODS

To establish AAD, mice were sensitized with intraperitoneal (i.p.) OVA/alum and challenged with daily OVA aerosols. Mice were treated i.p. with either saline, 2 or 6 mg/kg bromelain, twice daily for four consecutive days. Bronchoalveolar lavage leukocytes and cytokines, lung histology, airway hyperresponsiveness, and lymphocyte populations via flow cytometry were compared between groups.

RESULTS

Bromelain treatment of AAD mice resulted in reduced total BAL leukocytes, eosinophils, CD4+ and CD8+ T lymphocytes, CD4+/CD8+ T cell ratio, and IL-13.

CONCLUSION

Bromelain attenuated development of AAD while altering CD4+ to CD8+ T lymphocyte populations. The reduction in AAD outcomes suggests that bromelain may have similar effects in the treatment of human asthma and hypersensitivity disorders.

Experimental approaches to evaluate respiratory allergy in animal models

Asthma is defined as a chronic disease of the entire lung and asthma attacks may either be immediate, delayed or dual in onset. Allergic asthma is a complex chronic inflammatory disease of the airways and its etiology is multifactorial. It involves the recruitment and activation of many inflammatory and structural cells, all of which release mediators that result in typical pathological changes of asthma. A wealth of clinical and experimental data suggests that allergic asthma is due to an aberrant lung immune response mediated through T-helper type 2 (Th2) cells and associated cytokine-signaling pathways. The pathology of asthma is associated with reversible narrowing of airways, associated with prominent features that involve structural changes in the airway walls and extracellular matrix remodeling including abnormalities of bronchial smooth muscle, eosinophilic inflammation of the bronchial wall, hyperplasia and hypertrophy of mucous glands. The primary objective of respiratory allergy tests is to determine whether a low-molecular-weight chemical (hapten) or high-molecular-weight compound (antigen) exhibits sensitizing properties to the respiratory tract. This may range from reactions occurring in the nose (allergic rhinitis), in the bronchial airways (i.e., allergic bronchitis, asthma) or alveoli (e.g., hypersensitivity pneumonitis). Current assays utilize several phases, viz. an induction phase, which includes multiple exposures to the test compound (sensitization) via the respiratory tract (e.g., by intranasal or intratracheal instillations), by inhalation exposures or by dermal contact, and a single or multiple challenge or elicitation phase. The challenge can either be with the chemical (hapten), the homologous protein conjugate of the hapten or the antigen. The choice depends both on the irritant potency and the physical form (vapor, aerosol) of the hapten. The appropriate selection of concentrations (dosages) both for the induction and elicitation of respiratory allergy appears to be paramount for the outcome of test. Endpoints to characterize positive response range from the induction of immunoglobulins, cytokine or lymphokine patterns in serum (or the lung) to (patho-)physiological reactions typifying asthma. None of the currently applied animal models duplicate all features of human asthma. Accordingly, the specific pros and cons of the selected animal model, including protocol variables, animal species and strain selected, must be interpreted cautiously in order to arrive at a meaningful extrapolation for humans.

Mismatched antigen prepares gamma delta T cells for suppression of airway hyperresponsiveness

Gammadelta T cells suppress airway hyperresponsiveness (AHR) induced in allergen-challenged mice but it is not clear whether the suppression is allergen specific. The AHR-suppressive cells express TCR-Vgamma4. To test whether the suppressive function must be induced, we adoptively transferred purified Vgamma4(+) cells into gammadelta T cell-deficient and OVA-sensitized and -challenged recipients (B6.TCR-Vgamma4(-/-)/6(-/-)) and measured the effect on AHR. Vgamma4(+) gammadelta T cells isolated from naive donors were not AHR-suppressive, but Vgamma4(+) cells from OVA-stimulated donors suppressed AHR. Suppressive Vgamma4(+) cells could be isolated from lung and spleen. Their induction in the spleen required sensitization and challenge. In the lung, their function was induced by airway challenge alone. Induction of the suppressors was associated with their activation but it did not alter their ability to accumulate in the lung. Vgamma4(+) gammadelta T cells preferentially express Vdelta4 and -5 but their AHR-suppressive function was not dependent on these Vdeltas. Donor sensitization and challenge not only with OVA but also with two unrelated allergens (ragweed and BSA) induced Vgamma4(+) cells capable of suppressing AHR in the OVA-hyperresponsive recipients, but the process of sensitization and challenge alone (adjuvant and saline only) was not sufficient to induce suppressor function, and LPS as a component of the allergen was not essential. We conclude that AHR-suppressive Vgamma4(+) gammadelta T cells require induction. They are induced by allergen stimulation, but AHR suppression by these cells does not require their restimulation with the same allergen.