Furthermore, recently it was discovered that natural killer (NK) cells and CD8+ T cells of patients with COVID-19 have a higher expression of the NK cell inhibitory receptor, NKG2A, which is characterized by lower intracellular amounts of CD107, IFN-γ, IL-2, TNF-α, and granzyme B [139,140,141]. Here, GZMB is linked to COVID-19.