To protect host tissue, they secrete immune-suppressive cytokines such as IL-10 and TGF-β which antagonize the effects of the proinflammatory IL-6 and IL-17 that are implicated in COVID-19 (Ponnappan and Ponnappan, 2011; Schmitt et al., 2013; Ye et al., 2020). Here, IL17A is linked to COVID-19.