The RDP system simulates SARS-CoV-2 infection. (A–C) Caco-2 cells were infected with SARS-CoV-2 at an MOI of 0.01 and Caco-2-SARS-CoV-2 N cells were infected with RDPs at an MOI of 0.01 for 24 and 48 h. RNA extracted from the cells was evaluated by RT-qPCR (A) and lysates were subjected to immunoblot analysis (B and C). (D) Caco-2 cells were infected with SARS-CoV-2 at an MOI of 0.05 and Caco-2-SARS-CoV-2 N cells were infected with RDPs at an MOI of 0.05 for 48 h. Nucleus marker DAPI (blue) and SARS-CoV-2 N (red) were then visualized with confocal microscopy. Scale bars, 10 μm. (E and F) Caco-2 cells were infected with SARS-CoV-2 at an MOI of 0.01 and Caco-2-SARS-CoV-2 N cells were infected with RDPs at an MOI of 0.01 for 24 and 48 h. RNA extracted from the cells was evaluated by RT-qPCR (E), and lysates were subjected to immunoblot analysis (F). Graphs show mean ± SEM (n = 3 in A and E). *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001, ns, not significant (unpaired, two-tailed Student’s t test). Data in B–D and F are expressed at least twice in independent experiments, and one representative is shown. Data in A and E are expressed in at least three independent experiments. Source data are available for this figure: SourceData FS2.