KLRK1 and COVID-19: In peripheral NK cells, a dramatic decrease in the expression of the activating receptor NKG2D was observed between COVID negative and positive groups as evidenced by a 35% percent decrease in expression for all three COVID-19 positive severity groups (p=0.03 negative vs. asymptomatic, p=0.0018 negative vs. MM, p=0.0088 negative vs. SC) (Figure 2A).