The Temporal Evolution of Airways Hyperresponsiveness and Inflammation

Airways hyperresponsiveness (AHR) is usually produced within days of first antigen exposure in mouse models of asthma. Furthermore, continual antigen challenge eventually results in the resolution of the AHR phenotype. Human asthma also waxes and wanes with time, suggesting that studying the time course of AHR in the allergic mouse would offer insights into the variation in symptoms seen in asthmatics. Mice were sensitized with ovalbumin (OVA) on days 0 and 14. As assessed by airway resistance (R ), lung elastance (H) and tissue damping (G), AHR was measured post an OVA inhalation on day 21 (Short Challenge group), after three days of OVA inhalation on day 25 (Standard Challenge group) and following an OVA inhalation on day 55 in mice previously challenged on days 21-23 (Recall Challenge group). Bronchoalveolar lavage was analyzed for inflammatory cells, cytokines and protein. AHR in the Short Challenge group was characterized by an increase in R and neutrophil accumulation in the lavage. AHR in the Standard Challenge group was characterized by increases in H and G but by only a modest response in R , while inflammation was eosinophilic. In the Standard Challenge protocol, mice lacking fibrinogen were no different from control in their AHR response. AHR in the Recall Challenge group was characterized by increases only in G and H and elevated numbers of both neutrophils and eosinophils. Lavage cytokines were only elevated in the Recall Challenge group. Lavage protein was significantly elevated in all groups. The phenotype in allergically inflamed mice evolves distinctly over time, both in terms of the nature of the inflammation and the location of the AHR response. The study of mouse models of AHR might be better served by focusing on this variation rather than simply on a single time point at which AHR is maximal.