TGFB1 and COVID-19: While an increased frequency of activated NKG2C+CD57+ CD56dim NK cell phenotypes may be seen in severe COVID-19 (121), severe infection is associated with peripheral NK cell depletion and an exhausted phenotype based on LAG3, PDCD1, and HAVCR2 expression, which may be mediated by aberrant TGF-β production and homing to lung tissue (121, 122).