Fig. 3: ACE2 and TMPRSS2 localises to the plasma membrane excluding cilia and this coincides with the sites of viral attachment.
From: Ultrastructural insight into SARS-CoV-2 entry and budding in human airway epithelium
a–c Immunofluorescence antibody labelling against ACE2 and TMPRSS2 using anti-tubulin as a marker for cilia and phalloidin for the actin enriched microvilli. Both ACE2 and TMPRSS2 were found to be localised to cell surface that included the microvilli. Although there is diffuse, likely nonspecific, staining everywhere with the TMPRSS2 antibody, it is clearly enriched on the apical plasma membrane. Grey scale images of the staining profiles of ACE2 and TMPRSS2 show that they only extend a short distance from the cell surface unlike the tubulin staining of cilia and overlap with the phalloidin staining. d A diagram of the staining pattern of the antibodies. e–g When looking by TEM, virions (red arrowheads) are seen attached to microvilli (black arrowheads) and not to cilia (white arrowheads). h Quantification of the number of viral particles attached (within 3 nm) to microvilli and cilia, there is a little affinity of the virus to cilia for all three isolates. Single samples were examined for each and the number of cells assessed N = 14. Mean and SEM shown and statistical significance was determine using paired, two-tailed Student’s t-tests (B.1.1.7 P = 5.3 × 10−13, B.1.258 P = 3.44 × 10−19, and B.1.117.19 P = 7.19 × 10−18). Scale bars a–c 10 μm and e–g 400 nm.
