This increased arming of NK cells was very evident in the CD56bright subset, which in patients with severe COVID-19 expressed high levels of perforin and even higher of granzyme B. Interestingly, two populations (Pop14 and Pop15) that differed in the expression of perforin, granzyme B and CD16 were identified within the CD56bright NK cells. Here, GZMB is linked to COVID-19.