Background: With the popularity of heating, ventilation, and air conditioning (HVAC) and the growth of time that humans spend indoors, people have begun to think more about what kind of indoor air-conditioned environments are beneficial and sustainable for health, especially for preventing respiratory infectious diseases. This study aims to explore the role of airflow in mechanically ventilated environments in modulating airway immune and defense mechanisms.

Methods: Based on the self-developed mouse-applicable climate chamber system and the corresponding mouse model, this study investigated the health effects of exposure to thermal environments [(I) 20 ℃, 0 m/s; (II) 20 ℃, 1.5 m/s; and (III) 15 ℃, 1.5 m/s] on influenza-infected mice (female, 6-8 weeks), of which body and organ weight, and survival situation were measured and recorded. Lung histopathologic changes were analyzed by hematoxylin-eosin (H&E) staining. The messenger ribonucleic acid (mRNA) relative expression levels of interleukin-6 (IL-6) and interferon-γ (IFN-γ) in lung tissues were determined by quantitative real-time polymerase chain reaction (qRT-PCR). Lung tissue virus titer measurement was also conducted. We also collected peripheral blood samples for blood cell counts to assess the impact of environmental conditions on systemic inflammation.

Results: Prolonged mild exposure to cold airflow inhibited weight gain and significantly increased lung coefficient. The relative mRNA expression of inflammatory factors in lung tissues was elevated considerably and the area occupied proportion of the lung interstitium was significantly increased after cold airflow exposure. However, peripheral blood neutrophil and lymphocyte percentages were not significantly different from those of the control group. While there were remarkable differences in body weight changes, survival situations, lung coefficients, lung tissue viral titers, and peripheral blood neutrophil and lymphocyte percentages for mice with different environmental exposure experiences after viral infection.

Conclusions: Our findings suggest that the effects of airflow on health do not exist independently of temperature. Prolonged mild cold airflow in air-conditioned environments may induce respiratory injury and thus exacerbate respiratory virus infection outcomes, suggesting that the effect of airflow in air-conditioned environments should receive due attention in protecting public respiratory health.