FIGURE 4.

A schematic representation of a mucosal gradient for the passage of SARS‐CoV‐2 from the upper respiratory tract mucosal airway intersection to the epithelial cell–bound ACE2 target. The polybasic cleavage site at the junction of S1 and S2 present in SARS‐CoV‐2 likely provides for efficient cell entry and removal from the mucosal layer, thus ensuring that the concentration of the virus will be minimal compared with that which may be present at the mucosal airway surface. The figure also highlights the importance of Gibbs free energy in both the diffusion of SARS‐CoV‐2 across the mucosal layers and the subsequent interaction with its ACE2 receptor