Fig. 2.

Infectivity of SARS-CoV-2 in A549 cells under air-liquid interface culture condition

(A) Schematic representation of the ALI culture system. A549 cells were seeded onto a culture insert with growth medium (non-ALI condition). The medium at the apical chamber was then removed to start the ALI culture (ALI day 0). Cells were maintained for another 21 days by supplying ALI medium to the basal chamber (ALI day 21). (B and C) A549 cells in non-ALI and ALI day 21 were examined by hematoxylin and eosin (H&E) (B) and periodic acid-schiff (PAS) staining (C). Mucus in cells displayed purple color after PAS staining. Scale bars = 100 μm. (D and E) Relative levels of KI-67 (D) and SARS-CoV-2 N (E) were measured by qRT-PCR and normalized to the expression levels of β-actin. (F) Growth curves of SARS-CoV-2 in A549 cells in non-ALI and ALI culture conditions. The mucus fluids in the apical area were suspended in culture medium and subjected to viral titration using a plaque assay. The values in the graphs are expressed as the mean ± SD of triplicate samples. ∗p < 0.05, ∗∗∗p < 0.001, two-tailed Student's t-test. . (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)