Figure 1.
Coronavirus pathogenesis. The viral spike protein becomes activated by TMPRSS2 (a cell protease). The spike then binds to the ACE2 receptor in the host cell. 55 Infection with COVID-19 causes intracellular components and virus particles and released to the extracellular space, which results in the attraction of immune cells and massive inflammatory responses. 56 The total count of some lymphocytes, including CD4 + T cells, CD + 8 T cells, Treg cells, NK cells, and B cells, decreases. However, the count of neutrophils and leukocytes increases. In COVID-19, the dendritic cells present the antigens. 57 Besides, the macrophages' vast release of cytokines, which can contribute to the cytokine storm and its followed tissue damages. 58 The figure was created by BioRender.com