Porcine epidemic diarrhea virus infection induces NF-κB activation through the TLR2, TLR3 and TLR9 pathways in porcine intestinal epithelial cells.

Porcine epidemic diarrhea virus (PEDV) is a coronavirus that induces persistent diarrhoea in swine, resulting in severe economic losses in swine-producing countries. Insights into the interplay between PEDV infection and the innate immune system are necessary for understanding the associated mechanism of pathogenesis. The transcription factor NF-κB plays an important role in regulating host immune responses. Here, we elucidated for the first time to our knowledge the potential mechanism of PEDV-mediated NF-κB activation in porcine small intestinal epithelial cells (IECs). During PEDV infection, NF-κB p65 was found to translocate from the cytoplasm to the nucleus, and PEDV-dependent NF-κB activity was associated with viral dose and active replication. Using small interfering RNAs to screen different mRNA components of the Toll-like receptor (TLR) or RIG-I-like receptor signalling pathways, we demonstrated that TLR2, TLR3 and TLR9 contribute to NF-κB activation in response to PEDV infection, but not RIG-I. By screening PEDV structural proteins for their ability to induce NF-κB activities, we found that PEDV nucleocapsid protein (N) could activate NF-κB and that the central region of N was essential for NF-κB activation. Furthermore, TLR2 was involved in PEDV N-induced NF-κB activation in IECs. Collectively, these findings provide new avenues of investigation into the molecular mechanisms of NF-κB activation induced by PEDV infection.

Porcine epidemic diarrhea virus inhibits dsRNA-induced interferon-ß production in porcine intestinal epithelial cells by blockade of the RIG-I-mediated pathway.

BACKGROUND: The lack of optimal porcine cell lines has severely impeded the study and progress in elucidation of porcine epidemic diarrhea virus (PEDV) pathogenesis. Vero cell, an African green monkey kidney cell line, was often used to isolate and propagate PEDV. Nonetheless, the target cells of PEDV in vivo are intestinal epithelial cells, during infection, intestinal epithelia would be damaged and resulted in digestive disorders. The immune functions of porcine epithelial cells and interactions with other immune cell populations display a number of differences compared to other species. Type I interferon (IFN) plays an important role in antiviral immune response. Limited reports showed that PEDV could inhibit type I interferon production. In this study, porcine small intestinal epithelial cells (IECs), the target cells of PEDV, were used as the infection model in vitro to identify the possible molecular mechanisms of PEDV-inhibition IFN-ß production. RESULTS: PEDV not only failed to induce IFN-ß expression, but also inhibited dsRNA-mediated IFN-ß production in IECs. As the key IFN-ß transcription factors, we found that dsRNA-induced activation of IFN regulatory factor 3 (IRF-3) was inhibited after PEDV infection, but not nuclear factor-kappaB (NF-κB). To identify the mechanism of PEDV intervention with dsRNA-mediated IFN-ß expression more accurately, the role of individual molecules of RIG-I signaling pathway were investigated. In the upstream of IRF-3, TANK-binding kinase 1 (TBK1)-or inhibitor of κB kinase-ε (IKKε)-mediated IFN-ß production was not blocked by PEDV, while RIG-I-and its adapter molecule IFN-ß promoter stimulator 1 (IPS-1)-mediated IFN-ß production were completely inhibited after PEDV infection. CONCLUSION: Taken together, our data demonstrated for the first time that PEDV infection of its target cell line, IECs, inhibited dsRNA-mediated IFN-ß production by blocking the activation of IPS-1 in RIG-I-mediated pathway. Our studies offered new visions in understanding of the interaction between PEDV and host innate immune system.

Putative phage-display epitopes of the porcine epidemic diarrhea virus S1 protein and their anti-viral activity.

Porcine epidemic diarrhea virus (PEDV) is a pathogen of swine that causes severe diarrhea and dehydration resulting in substantial morbidity and mortality in newborn piglets. Phage display is a technique with wide application, in particular, the identification of key antigen epitopes for the development of therapeutic and diagnostic reagents and vaccines. To identify antigen epitopes with specificity for PEDV, a monoclonal antibody (MAb-5E12) against the immunodominant region of the PEDV Spike protein (S1) was used as the target for biopanning a 12-mer phage display, random peptide library. After multiple rounds of biopanning and stringent washing, three phage-displayed peptides, designated L, W and H, were identified that recognize MAb-5E12. Sequence analysis showed that the one or more of the peptides exhibited partial sequence similarity to the native S1 sequence 'MQYVYTPTYYML' (designated peptide M) at position 201-212. In combination with software analysis for the prediction of B cell epitopes, aa 201-212 exhibited characteristics of a linear epitope on the PEDV S1 protein. In contrast to peptide M, a consensus motif 'PxxY' was identified on both peptides L and W, and on the S1 protein, but not on peptide H. Peptide M and the MAb-5E12-recognizing peptides L and W significantly inhibited the adsorption of PEDV on the cell surface as monitored through plaque-reduction assays. Furthermore, data from real-time PCR and indirect immunofluorescence assays were consistent with the ability of peptides M, L and W to block viral protein expression and thereby function as antiviral agents for PEDV.

Generation of a monoclonal antibody to S1 protein of porcine epidemic diarrhea virus.

Gene encoding the N-terminal half of spike protein (S1) of porcine epidemic diarrhea virus (PEDV) was cloned and expressed as a recombinant protein in Escherichia coli BL21 (DE3). Then, female BALB/c mice were immunized with the purified recombinant S1 protein (rS1), and a monoclonal antibody (MAb designated as 5E12) against the rS1 protein was achieved by hybridoma technique. MAb 5E12 not only reacted with rS1 protein indirect ELISA and Western blot, but also recognized PEDV transiently expressed in Vero E6 cells in indirect immunofluorescence examinations. This work suggests that 5E12 would be a useful tool as a specific diagnostic reagent for detecting PEDV S protein.