If NK cells are present in sufficient number and are functioning correctly, we hardly will be affected by Covi-19. Currently, a growing body of data is emerging on the variation in the number and function of NK cells during SARS-COV-2 infection, correlating it with the severity of clinical presentation and outcome (ZHENG ET AL 2000) Weilh et al (2000) because NK cells are shown to be an efficient protective shield against viral infection.
Extensive evidence exists that the early innate function of NK cells is essential and beneficial in immune defense against respiratory viral infection. These activities include antiviral cytokine production (IFN-y) and lysis of virus-infected cells (1). In severe SARS cases, the parameter of NK cells was significantly lower than in middle cases of SARS cells. And apparently, the number of NK cells remained low for the entire disease and only began to recover after the 40th day of the disease. So it seems that SARS alters the function of NK cells.
However, we can also assume that many infected cases with SARS already have an exhausted NK cell function. Why are the NK cells in many people not functioning and why their immune systems so exhausted?
Figure 5: How NK Cells Kill Viruses in Infected Cells