Early Interleukin 4–Dependent Response Can Induce Airway Hyperreactivity before Development of Airway Inflammation in a Mouse Model of Asthma

Abstract

In experimental models of bronchial asthma with mice, airway inflammation and increase in airway hyperreactivity (AHR) are induced by a combination of systemic sensitization and airway challenge with allergens. In this report, we present another possibility: that systemic antigen-specific sensitization alone can induce AHR before the development of inflammation in the airway. Male BALB/c mice were sensitized with ovalbumin (OVA) by a combination of intraperitoneal injection and aerosol inhalation, and various parameters for airway inflammation and hyperreactivity were sequentially analyzed. Bronchial response measured by a noninvasive method (enhanced pause) and the eosinophil count and interleukin (IL)-5 concentration in bronchoalveolar lavage fluid (BALF) gradually increased following the sensitization, and significant increase was achieved after repeated OVA aerosol inhalation along with development of histologic changes of the airway. In contrast, AHR was already significantly increased by systemic sensitization alone, although airway inflammation hardly developed at that time point. BALF IL-4 concentration and the expression of IL-4 mRNA in the lung reached maximal values after the systemic sensitization, then subsequently decreased. Treatment of mice with anti–IL-4 neutralizing antibody during systemic sensitization significantly suppressed this early increase in AHR. In addition, IL-4 gene-targeted mice did not reveal this early increase in AHR by systemic sensitization. These results suggest that an immune response in the lung in an early stage of sensitization can induce airway hyperreactivity before development of an eosinophilic airway inflammation in BALB/c mice and that IL-4 plays an essential role in this process. If this early increase in AHR does occur in sensitized human infants, it could be another therapeutic target for early prevention of the future onset of asthma.