Tonsil and buccal mucosal expression of SARS-CoV and influenza virus activating proteases and receptors.

<p>Tonsil (A–D) and buccal mucosa (E–H) immunostained for TMPRSS2 (A&E), ACE2 (B&F) and HAT (C&G), or stained for 2,6-linked sialic acid (D&H; detected with elderberry (<i>Sambucus nigra</i>) lectin). All positive reactions are detected with the peroxidase technique (brown) and the tissue is counterstained with haematoxylin (blue). (A) There is strong positive anti-TMPRSS2 immunostaining of tonsillar epithelium (Ep) and lymphocytes (Ly). (B) There is weakly positive anti-ACE2 immunostaining of tonsillar epithelium (Ep), but little obvious positive immunostaining of lymphocytes (Ly). (C) There is strongly positive anti-HAT immunostaining of the basal and superficial, but not the middle, layers of tonsillar epithelium (Ep), but little obvious positive immunostaining of lymphocytes (Ly). (D) All structures are strongly stained for 2,6-sialic acid except for a few areas of cells within the tonsillar epithelium (Ep). (E) There is strong positive anti-TMPRSS2 immunostaining of buccal epithelium (Ep) and of a blood vessel (BV) in the underlying connective tissue (CT). (F) There is strong positive anti-ACE2 immunostaining of buccal epithelium (Ep) and weaker positive immunostaining of a blood vessel (BV) in the underlying connective tissue (CT). (G) There is strong positive anti-HAT immunostaining of buccal epithelium (Ep), but a blood vessel (BV) in the underlying connective tissue (CT) appears negative. (H) All structures are strongly stained for 2,6-sialic acid. Scale bar = 50 microns (shown in panels D and H and also pertaining to 3 preceding panels in each case).