Figure 3.

Schematic of SARS-CoV-2 infection of host tissue and disease pathogenesis. SARS-CoV-2 infects host cells (primarily epithelial cells) that express the host receptor, ACE2 and TMPRSS2, resulting in phase I of infection. In phase II, viral proliferation occurs in infected cells and this results in a local immune response, release of cytokines and chemokines (black circles), attraction of macrophages (green cell) and T cells (orange cell) to infected cells, and activation of further adaptive immune responses. In most cases, there is a healthy immune response, and infected cells are eliminated and further viral infection can be blocked by neutralizing antibodies (green). In this phase III of infection, there is a reduction of virus spread, resolution of infection, suppression of inflammation with limited tissue injury, and eventual recovery. However, in some cases of phase III of infection, the viral infection may lead to increased production of proinflammatory cytokines, resulting in a cytokine storm, causing multiorgan damage and acute respiratory distress syndrome (ARDS).