TNF and COVID-19: Although elevated IL-6 is considered a key prognostic factor in severe COVID-19 [31], and inhibition of IL-6 reduces mortality [47,53]  in the present study, no differences were found in the circulating levels of this cytokine or IL-6 signaling receptors (IL-1β, IL-10, TNF, IL-6, sIL-6R, sgp130).