(A) scRNA-seq analysis of ACE2 and MUC1 expression in different cell types in the respiratory mucosa. Dataset include samples from nasal cavity (N), upper, intermediate and lower respiratory tract [16]. (B) Expression of TM mucins MUC1, MUC4 and MUC16 and gel-forming mucins MUC5AC and MUC5B in ACE2 positive cells. MUC1 is the most highly expressed mucin in ACE2-positive cells. (C) Immunofluorescence confocal microscopy images showing expression of TM mucins MUC1 (214D4, green), MUC4 (8G7, green) and gel-forming mucin MUC5AC (MUC5AC, green) in permeabilized Calu-3 cells. Maximum projections and side views of Z-stacks are shown. (D) Immunofluorescence confocal microscopy without permeabilization showing expression of MUC1 on the surface of Calu-3 cells. MUC4 and MUC5AC could barely be detected suggesting intracellular localization. (E) Immunofluorescence confocal microscopy imaging for α-2,6 sialic acids (SNA, red), α-2,3 sialic acids (MALII, red) and fucose (UEAI, red) in combination with MUC1 (214D4 antibody, green) demonstrates high levels of sialic acid and fucose in Calu-3 cells. Nuclei were stained with DAPI (blue). White scale bars represent 20 μm.