Impact of porcine circovirus type 2 on porcine epidemic diarrhea virus replication in the IPI-FX cell line depends on the order of infection

Hao Zhang; Hongyan Shi; Yanwu Wei; Da Shi; Mengxiang Cao; Jianbo Liu; Jianhang Liu; Liang Li; Changming Liu; Li Feng; Liping Huang

doi:10.3389/fmicb.2023.1162104

Impact of porcine circovirus type 2 on porcine epidemic diarrhea virus replication in the IPI-FX cell line depends on the order of infection

Front Microbiol. 2023 Mar 30:14:1162104. doi: 10.3389/fmicb.2023.1162104. eCollection 2023.

Authors

Hao Zhang¹, Hongyan Shi¹, Yanwu Wei¹, Da Shi¹, Mengxiang Cao¹, Jianbo Liu¹, Jianhang Liu¹, Liang Li¹, Changming Liu¹, Li Feng¹, Liping Huang¹

Affiliation

¹ Division of Swine Digestive System Infectious Diseases, State Key Laboratory for Animal Disease Control and Prevention, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin, China.

Abstract

Introduction: A study in 2006 showed that the clinical course of PEDV disease was markedly aggravated by transplacental infection of PCV2. Therefore, we investigated whether the small intestine supports PCV2 replication and the effect of PCV2 infection on PEDV replication in epithelial cells in vitro.

Methods: To confirm the intestinal tropism of PCV2, the viral loads in the small-intestinal tissues after PCV2 infection were determined with virus titration, and the viral titers in the infected pig jejunum, ileum, ileocecal valve, and colon were 10^4.86, 10^4.09, 10^2.52, and 10^2.35 TCID₅₀/g, respectively. We then determined the propagation characteristics of PCV2 in ileal epithelial cells (IPI-FX) and jejunal epithelial cells (IPEC-J2) with an immunoperoxidase monolayer assay, virus titration, and an immunofluorescence assay. Both IPI-FX and IPEC-J2 cells supported the replication of PCV2, with titers of 10^5.5 and 10^5.0 TCID₅₀/ml, respectively. We established an infection model of PCV2 and PEDV in IPI-FX cells and found that PEDV and PCV2 infected the cells individually and together. The effects of PCV2 infection on PEDV replication were determined with reverse transcription-quantitative PCR (qPCR), western blotting, and virus titration. When PCV2 infected IPI-FX cells before PEDV, PCV2 significantly inhibited the replication of PEDV in a dose- and time-dependent manner and that the mRNAs of IFN-β, TNF-α, IL1β, and OASL were downregulated (detected with qPCR). Surprisingly, when IPI-FX cells were co-infected with PCV2 and PEDV, PCV2 promoted the replication of PEDV, the expression of the host IFN-β, TNF-α, IL1β, and OASL mRNAs was upregulated.

Discussion: These findings demonstrate that the co-infection of IPI-FX cells with PCV2 and PEDV represents an excellent in vitro model in which to investigate their combined pathogenic mechanisms.

Keywords: IPEC-J2 cells; IPI-FX cells; co-infection; porcine circovirus type 2; porcine epidemic diarrhea virus.