SARS-CoV-2 is a highly contagious virus, but most people who contract SARS-CoV-2 have asymptomatic or mild Covid-19 disease. But what molecular and/or physiologic features discriminate severe/life-threatening Covid-19 from mild/asymptomatic cases? To thoroughly answer this question, one would need to know how the infection evolves and what cell types are involved.

This study details the exact cells in our airway/respiratory system that are most susceptible to SARS-CoV-19 infection, and correlates infection with the expression of ACE2 and TMPRSS2, which are normal cellular proteins that the virus uses to infect airway/respiratory cells. Not surprisingly, viral infection strongly correlated with the level of ACE2/TMPRSS2 expression in these specific cell types. However, there were notable exceptions: 1. specialized airway cells known as club cells express high levels of ACE2/TMPRSS2, but did not get infected with the virus, and 2. there were substantial differences in the level of infection between different people who expressed equivalent levels of ACE2/TMPRSS2. So, what additional factors govern SARS-CoV-2 infection, and how does the extent of SARS-CoV-2 infection in the respiratory system (and other systems), determine the course of the disease? The answer to this question may reveal new and exciting drug targets in the long-term and help identify high-risk individuals who should be vigilant about social distancing in the short-term.
SARS-CoV-2 Infection Dynamics
The actual paper