SERPINA1 and viral infectious disease: Consequently, the AAT treatment may limit the SARS-CoV-2 entry into host cells, which represents the first step of the viral infection; (ii) despite AAT increase in COVID-19 patients, according to its role as an inflammatory acute phase protein, it has been shown that the IL6:AAT ratio is higher in patients with the severe/critical disease than in mild/stable disease (McElvaney et al., 2020).