ACE2 and TMPRSS2 are expressed in the gastrointestinal tract and in PSC-HIOs. (A) Paraffin-embedded sections of indicated gastrointestinal tissues and embedded Caco-2 cells were stained for ACE2 and TMPRSS2 protein. Strong luminal expression is found in epithelia of duodenum, colon, and gallbladder, with weaker expression in the stomach and the mucosal lining of the esophagus. Representative images are shown. Scale bars = 20 μm. (B) Duodenum biopsy was stained for ACE2 and TMPRSS2 using primary antibodies and fluorophore-conjugated secondary antibodies and imaged by fluorescence microscopy. Scale bar = 50 μM. (C) ACE2 and TMPRSS2 expression from panel A was graded according to signal intensity (relative to the positive control, Caco-2 cells). (D) Microscopy of PSC-HIOs. Scale bar = 50 μM. (E) PSC-HIOs were stained for ACE2 (left panels) and TMPRSS2 (right panels). Nuclei are stained with DAPI in blue. (F–H) PSC-HIOs were costained for ACE2 and (F) enteroendocrine cell marker CHGA, (G) Paneth cell marker LYZ, or (H) goblet cell marker MUC2 showing coexpression with CHGA and LYZ but not with MUC2. Nuclei are stained with DAPI in blue. Arrows indicate co-expression. Left panels show representative images, right panels magnifications.