IL17A and COVID-19: Two possible mechanisms which could explain the association between periodontitis and the COVID-19 disease are: (1) the direct contact of virus with the periodontal tissues, also due to the high expression of ACEII and CD147, as mentioned above; and/or (2) the similar overexpression of several cytokines, a COVID-19 ‘cytokine storm’, with elevated serum levels of IL-1 beta, IL-6, IL-7, IL-10, IL-17, IL-2, IL-8, IL-9, GM-CSF, G-CSF, IFN-gamma, TNF alpha, MIP1A, MIP1B, MCP1 and IP10 [27, 28].