Of mice and men

Role of IL-18-transformed CD274-expressing eosinophils in promoting airway obstruction in experimental asthma

BACKGROUND

IL-5-dependent residential and IL-18-transformed pathogenic eosinophils have been reported; however, the role of IL-18-transformed CD274-expressing pathogenic eosinophils compared to IL-5-generated eosinophils in promoting airway obstruction in asthma has not yet been examined.

METHODS

Eosinophils are detected by tissue anti-MBP and anti-EPX immunostaining, CD274 expression by flow cytometry, and airway resistance using the Buxco FinePointe RC system.

RESULTS

We show that A. fumigatus-challenged wild-type mice, and different gene-deficient mice including naïve CC10-IL-18-transgenic mice, accumulate mostly peribronchial and perivascular CD274-expressing eosinophils except naïve CD2-IL-5-transgenic mice. Additionally, we show that CD2-IL-5 transgenic mice following rIL-18 treatment accumulate high number of CD274-expressing perivascular and peribronchial eosinophils with induced collagen, goblet cell hyperplasia and airway resistance compared to saline-challenged CD2-IL5 transgenic mice. Furthermore, we also show that even A. fumigatus-challenged IL-5 ^-/- mice and rIL-18 given ΔdblGATA mice accumulate CD274-expressing eosinophil-associated asthma pathogenesis including airway obstruction. Most importantly, we provide evidence that neutralization of CD274 and IL-18 in A. fumigatus-challenged mice ameliorate experimental asthma. Taken together, the data presented are clinically significant in establishing that anti-IL-18 neutralization is a novel immunotherapy to restrict asthma pathogenesis.

CONCLUSIONS

We demonstrate that IL-18 is critical for inducing asthma pathogenesis, and neutralization of CD274 is a potential immunotherapeutic strategy for asthma.

Murine asthma models

Immunotoxicity can take the form of an enhanced immune response or hypersensitivity. Asthma is one possible consequence of hypersensitivity in the lung, with characteristics that include reversible airway obstruction, eosinophil infiltration into the lung, and airway hyperresponsiveness to agonists such as methacholine. In toxicology, two primary areas of investigation prompt the measurement of the asthmatic response in an animal: (1) identification of chemicals or proteins that cause asthma, i.e., respiratory allergens, and (2) identification of exposures that will exacerbate existing asthma. An ovalbumin-induced asthma model can be used to identify exposures that exacerbate existing asthma. A protocol for the sensitization and challenge of mice with ovalbumin is described; it leads to the asthma symptoms of airway hyperresponsiveness and eosinophil infiltration. Assessment of airway hyperresponsiveness to methacholine uses whole body plethysmography in conscious unrestrained mice. Bronchoalveolar lavage of the mouse determines the extent of cellular infiltration into the airspace. Removal of lung lobes and assay of eosinophil peroxidase and myeloperoxidase provides a measure of the numbers of eosinophils and neutrophils, respectively, in the lung. Depending on the experimental goals, bronchoalveolar lavage fluid and lung tissue can also be used for isolation of RNA, and measurement of cytokines, chemokines, antibodies, and inflammatory mediators.

A Monoclonal Antibody to α1β1 Blocks Antigen-induced Airway Responses in Sheep

The integrin alpha1beta1 (very late antigen-1; CD49a/CD29) is a major adhesion receptor for collagen I, IV, and VI, and its induced expression on activated monocytes and lymphocytes plays a central role in their retention and activation at inflammatory sites in autoimmune pathologies. However, the role of alpha1beta1 in allergic settings has not been explored. In this study, we show that a single 45-mg dose of aerosolized monoclonal antibody AQC2 to the alpha1 chain of human and sheep very late antigen-1, given 30 minutes before challenge, blocks both the allergen-induced late response and the associated airway hyperresponsiveness, functional indicators of allergen-induced inflammation, in sheep. AQC2 does not affect the early response. Consistent with these effects, AQC2 tended to reduce the cell response associated with local antigen instillation. An isotype-matched control antibody had no protective effects. Two humanized versions of AQC2, a wild-type IgG1 and an aglycosyl form of the same monoclonal antibody, which has reduced Fc receptor-mediated effector functions, are equally effective in blocking the antigen-induced late response and airway hyperresponsiveness in the sheep model. These data suggest that mononuclear leukocyte adhesion-dependent pathologies contribute to allergic lung disease and provide proof-of-concept that antagonists of alpha1 integrins may be useful in preventing these events.