Age-dependent pulmonary reactivity to house dust mite allergen: a model of adult-onset asthma?

Asthma is a heterogeneous disease differentiated by factors like allergen sensitivity, inflammation, sex, and age at onset. The mouse model is widely used to study the early-life development of allergic asthma. However, age-dependent allergen responses later in life remain relatively understudied and lack a widely accepted model. To differentiate age-dependent responses to the ubiquitous house dust mite (HDM), 3- and 9-mo-old female C57BL/6 mice were randomized into two groups each and exposed to HDM or phosphate-buffered saline (control) via intranasal instillation for sensitization and challenge phases. At 24 h after challenge, all mice underwent pulmonary function testing and methacholine challenge. Bronchoalveolar lavage fluid (BALF) was collected for assessment of cell differentials, and right lung lobes were fixed, sectioned, and stained for histopathology and immunohistochemistry. Both age groups demonstrated strong inflammatory/allergic responses to HDM exposure. However, only 9-mo-old HDM-exposed mice demonstrated significant airway hyperresponsiveness compared with age-matched controls. These HDM-exposed mice also had 1) statistically significant increases in tissue bronchiolitis, perivasculitis, and BALF neutrophilia relative to their younger counterparts and 2) significantly increased extent of immunostaining compared with all other groups. This study presents a potential model for adult-onset asthma, focusing specifically on the atopic, perimenopausal female phenotype. Our findings suggest that lung function declines with age and that the inflammatory profile of this adult subgroup is a mixed, rather than a simple, atopic, Th2 response. This model may enhance our understanding of how age influences the development of asthmic-like symptoms in older subgroups.