Infection induces the production of proinflammatory cytokines and chemokines such as interleukin-8 (IL-8) and interleukin-6 (IL-6). Although they facilitate local antiviral immunity, their excessive release leads to life-threatening cytokine release syndrome, exemplified by the severe cases of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. In the present study, we found that interleukin-8 (IL-8) was upregulated by PDCoV infection. We then demonstrated that PDCoV E protein induced IL-8 production and that the TM domain and the C-terminal domain of the E protein were important for IL-8 production. Subsequently, we showed here that deleting the AP-1 and NF-κB binding motif in porcine IL-8 promoter abrogated its activation, suggesting that IL-8 expression was dependent on AP-1 and NF-κB. Furthermore, PDCoV E induced IL-8 production, which was also dependent on the NF-κB pathway through activating nuclear factor p65 phosphorylation and NF-κB inhibitor alpha (IκBα) protein phosphorylation, as well as inducing the nuclear translocation of p65, eventually resulting in the promotion of IL-8 production. PDCoV E also activated c-fos and c-jun, both of which are members of the AP-1 family. These findings provide new insights into the molecular mechanisms of PDCoV-induced IL-8 production and help us further understand the pathogenesis of PDCoV infection.

In recent years, a novel, highly virulent variant of porcine epidemic diarrhea virus (PEDV) has emerged, causing substantial economic losses to the pork industry worldwide. In this study, a PEDV strain named LNsy was successfully isolated in China. Phylogenetic analysis based on the whole genome revealed that PEDV LNsy belonged to the G2 subtype. For the first time, a unique four amino acids (4-aa) insertion was identified in the COE region of the spike (S) protein (residues 499-640), resulting in an extra alpha helix in the spatial structure of the COE region. To determine changes in virus-neutralization (VN) antibody reactivity of the virus, polyclonal antibodies (PAbs) against the S protein of different subtypes were used in a VN test. Both PAbs against the S protein of the G1 and G2 subtype showed reduced VN reactivity to PEDV LNsy. Further, recombination analyses revealed that PEDV LNsy was the result of recombination between PEDV GDS13 and GDS46 strains at the genomic breakpoints (nt 17,959-20,594 in the alignment) in the ORF1b gene of the genomes. Pathological examination showed gross morphological pathological changes in the gut, including significant villus atrophy and shedding of the infected piglets. These results indicated that a 4-aa insertion in the COE region of the S protein may have partly altered the profiles of VN antibodies and thus it will be important to develop vaccine candidates to resist wild virus infection and to monitor the genetic diversity of PEDV.