Figure 7.

PDCoV infection spread is more efficient in a cell-to-cell manner. (A) Experimental design: PDCoV pre-infected LLC-PK cells were set as effector cells, whereas cell tracker pre-labelled non-infected LLC-PK cells were set as target cells. At 24 h post-infection, the effector cells (0.3 × 10⁵ cells) were collected and added to the target cells (1.0 × 10⁵ cells) directly (contact cell model). Or the effector cells were seeded on trans-well filters and incubated with target cells as same cell number as mentioned above (uncontact cell model). In both infection models, medium supplemented (or not) with 5 μg/ml trypsin was added. (B) After 48 h of interaction between effector cells and target cells, the expression of viral N protein in target cells were detected by immunofluorescence assay. The cell nuclei were labelled by DAPI; scale bar = 20 μm. (C) PDCoV RNA copies were quantified by qPCR in cells; error bars represent the SEM. *** stands for p < 0.001; experiments were repeated at least three times.