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Fig. 1 | Stem Cell Research & Therapy

Fig. 1

From: Mesenchymal stem cells: current clinical progress in ARDS and COVID-19

Fig. 1

Schematic diagram of how SARS-CoV-2 causes COVID-19. The SARS-CoV-2 virus enters the respiratory tract. The S protein on the surface of the virus binds to the secretory cells of the nasal epithelium and the membrane protein ACE2, which is highly expressed in bronchoalveolar type II cells. Subsequently, SARS-CoV-2 enters the host cell through phagocytosis, thereby partially reducing or completely abrogating the enzymatic function of ACE2 and increasing the concentration of proinflammatory angiotensin II. A high concentration of angiotensin II in the lung interstitium promotes apoptosis, releases proinflammatory cytokines, and triggers an inflammatory response [9], leading to symptoms of a cytokine storm and pneumonia in COVID-19 patients and to ARDS in severe cases. Mar, macrophage; ACE2, angiotensin-converting enzyme 2; TMPRSS2, transmembrane protease serine 2; NK, natural killer cell; IFN, interferon; IL, interleukin; GM-CSF, granulocyte-macrophage colony-stimulating factor; TNF, tumor necrosis factor

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