PRF1 and COVID-19: Moreover, with in vitro studies having shown that exposure to IL-6 and TNF-α, two cytokines whose circulating levels are elevated in COVID-19 patients (3, 77, 146) impairs NKCC and reduces perforin, NKp30 and NKp46 expression (147–149), then the SARS-CoV-2-induced cytokine storm would exacerbate the abovementioned functional and phenotypical features of NK cell immunesenescence, which would be predicted to further reduce NK cell anti-viral activity.