Fig. 3: Cellular tropism of influenza virus and SARS-CoV-2.
From: Influenza virus and SARS-CoV-2: pathogenesis and host responses in the respiratory tract
a | The haemagglutinin (HA) protein of influenza viruses preferentially binds sialosaccharides on the surface of pulmonary epithelial cells. Whereas human influenza viruses prefer sialic acids (SAs) linked to galactose by α(2,6) linkage (SAα2,6Gal), avian influenza viruses prefer SAα2,3Gal. These are distributed in a gradient in the human respiratory tract. Immunohistochemistry staining demonstrates intracellular localization of influenza viruses in epithelial cells at three sites from mice challenged with influenza A virus. b | The spike (S) protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) binds angiotensin-converting enzyme 2 (ACE2) on the surface of certain olfactory and respiratory epithelial cells distributed along the human respiratory tract after activation by a cellular protease, such as transmembrane serine protease 2 (TMPRSS2) (other proteases, including cathepsin L, neuropilin 1 and furin are involved in activation). Histopathological images in part a courtesy of P. Vogel.
