ACE2 and chronic obstructive pulmonary disease: The lung airway expression of both TMPRSS2 and ACE2 was found to be significantly upregulated in smokers compared with non-smokers, and in patients with chronic obstructive pulmonary disease compared with healthy subjects [70]; instead, children were found to have significantly lower expression of COVID-19 receptors in the upper and lower airways (nasal and bronchial) [70].