Several studies (immunohistochemistry and transcriptomic analysis) show that the following relationship exists between ACE2 expression and smokers:

smokers with chronic obstruction pulmonary disease (COPD) > healthy smokers > nonsmokers

Increased expression was noticed in alveolar type 2 progenitor cells (AT 2), alveolar macrophages, and the small airway epithelium. This phenomenon is thought to play a role in the metabolic changes that lead to the replication of SARS-CoV-2. Additionally, cigarette smoke is a common risk factor for many other respiratory diseases.