IFNG and COVID-19: Furthermore, the expression of CD94/NK group 2 member A (NKG2A) was increased on cytotoxic T lymphocytes (CTLs) and NK cells in COVID-19 patients, accompanied by low levels of CD107a, IFN-γ, IL-2, TNF-α, and granzyme B (Zheng M. et al., 2020).