TNF and COVID-19: Indeed, Zheng and colleagues demonstrated an upregulation of the inhibitory receptor NKG2A expression on natural killer cells (NK) and cytotoxic lymphocytes (CTLs) in COVID-19 patients with a compromised degranulation capacity and a reduced production of IFN-γ, IL-2, granzyme B and tumor necrosis factor α (TNF-α) (7).