Susceptibility of cell lines from different animal species to porcine deltacoronavirus

Abstract:

[Objective] To explore whether porcine deltacoronavirus (PDCoV) can infect and proliferate in different animal species-derived cell lines. [Methods] The Sichuan isolate CHN-SC2015 of PDCoV was inoculated in twelve cell lines derived from hamster, poultry, monkey, human and swine. After at least five blindly passages in each cell line, the virus was identified by RT-PCR, RT-qPCR, indirect immunofluorescence assay (IFA), and sequencing. [Results] PDCoV caused distinct cytopathic effect (CPE) in Vero, PAM, PK15, ST, and LLC-PK1 cells at the 1st passage (P1) and proliferated to various degrees in PAM, PK15, ST, and LLC-PK1 cells, while the CPE gradually disappeared during subsequent passages in Vero and PAM cells. Except that in the three susceptible cell lines (PK15, LLC-PK1, and ST), the viral copies of the infected cell lines gradually decreased with the increase in passages, and PDCoV could not be detected at P4 or P5 of DEF, Marc-145, HEK-293, ZYM-SIEC02, and PAM cells. PCR results showed that PDCoV could be detected only in CEF and Vero cells at P5. The IFA results showed that PDCoV could infect other cell lines except BHK-21 and ZYM-SIEC02, and specific immunofluorescence was observed in PK15, LLC-PK1, and ST cells at P1, P3, and P9. Therefore, only three cell lines (PK15, LLC-PK1, and ST) were suitable for serial passage, with the virus titers up to 10^7.11, 10^7.00, and 10^7.37 TCID₅₀/mL at P9, respectively. After passage in different cell lines, CHN-SC2015 accumulated 14 nucleotide mutations corresponding to 12 amino acid mutations. [Conclusion] This study indicates that PDCoV can infect a variety of cells in vitro, suggesting that it may have the potential of cross-species transmission.