Fig 4.
Unbiased apical and basoalteral expression of CD26/DPP4 enables bilateral MERS-CoV entry and release from polarized Calu-3 cells. (A) Confluent Calu-3 cells grown in the chamber slides were subjected to staining for CD26/DPP4 expression. The images of CD26/DPP4 surface expression (green) and nuclear staining (DAPI; blue) were captured by z-stack scanning from the bottom (A1), the middle (A2), and the top (A3) by using an inverted confocal microscope (Zeiss LSM 710). It is clear that CD26/DPP4 is uniformly expressed on the cell membrane of Calu-3 cells. (B and C) Highly polarized Calu-3 cells grown on filter inserts were inoculated with SARS-CoV (B) or MERS-CoV/EMC-2012 (C), at an MOI of 0.1, through either the apical or basolateral surface. At 24 h after infection, the culture supernatants collected from the apical and basolateral chambers were assessed for the contents of infectious viral particles by the TCID50 assay. *, P < 0.05; ***, P < 0.001 (Student's t test). The results are derived from representative findings for two independently conducted experiments.