MUC5AC and viral infectious disease: Third, cold exposure may suppress the immune response and increase susceptibility to viral infections in humans.38 Meanwhile, the transmission efficiency of the influenza virus is inversely correlated with ambient temperature.39 Fourth, cold temperature may provoke airway inflammation and mucin hypersecretion in airway epithelium, which results in COPD morbidity and mortality by blocking airways and causing recurrent infections.40 41