Cold air and air pollution induce bronchial hyperresponsiveness and inflammation in a murine model

Bronchial hyperresponsiveness is a key feature in different respiratory diseases, including exercise-induced bronchoconstriction (EIB). Often, harmful environmental conditions such as air pollution [diesel exhaust particles (DEP)] or cold dry air contribute to the development of symptoms. In this study, we aimed to evaluate the effects of cold air, DEP and exercise, both separately and combined, on the respiratory system.

Immediately before performing a submaximal exercise protocol or resting period, BALB/c mice were oropharyngeally challenged 5 days per week for 3 weeks with saline or 0.1 mg/ml DEP. Animals were divided into 8 groups based on exercise/no exercise, room temperature or 4 °C and saline or DEP. All animals were sacrificed to determine lung function, lung inflammation, including cellular and biochemical levels in bronchioalveolar lavage fluid, and immune mediated response.

BALB/c mice exhibit more pronounced bronchial hyperresponsiveness and neutrophilic inflammation compared to C57BL/6 mice. Submaximal exercise of BALB/c mice at 4 °C induced acute changed breathing patterns early in the exercise protocol. 24 h after the last running session, bronchial hyperresponsiveness to increasing concentrations of methacholine (with both saline and DEP exposure) was observed. When DEP exposure was added to exercise at 4 °C, small airway resistance was significantly increased, neutrophilic airway inflammation was induced and type 2 dendritic cells were more abundantly present in the lungs. Proinflammatory cytokines (TNF-α, MCP-1, KC and GM-CSF) in bronchoalveolar lavage were significantly increased and leakage of surfactant protein D to serum was enhanced in DEP-exposed animals, exercising at 4 °C. In DEP-exposed mice, macrophages were more loaded with DEP at 4 °C, exercise or both.