TMPRSS2 and chronic obstructive pulmonary disease: Further, studies have found elevated expression of ACE2 and TMPRSS2 in several groups of patients with chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis (IPF) [51], [56], [57], [58], [59], [60]; both expressions significantly correlated with previous cigarette exposure [56], [61], [62]; COPD is considered a major risk factor for COVID-19 [63], [44].