Ergosterol peroxide exhibits antiviral and immunomodulatory abilities against porcine deltacoronavirus (PDCoV) via suppression of NF-κB and p38/MAPK signaling pathways in vitro

•Porcine deltacoronavirus is an emerging virus posing economic and health burdens.•Now there are no effective antiviral agents against porcine deltacoronavirus (PDCoV).•Ergosterol peroxide downregulated the activation of the NF-κB and p38/MAPK pathways.•Ergosterol peroxide can inhibit PDCoV infection and regulate host immune responses.•Ergosterol peroxide is a potential antiviral agent against PDCoV. Porcine deltacoronavirus (PDCoV) is an emerging swine enteropathogenic coronavirus (CoV) that poses economic and public health burdens. Currently, there are no effective antiviral agents against PDCoV. Cryptoporus volvatus often serves as an antimicrobial agent in Traditional Chinese Medicines. This study aimed to evaluate the antiviral activities of ergosterol peroxide (EP) from C. volvatus against PDCoV infection. The inhibitory activity of EP against PDCoV was assessed by using virus titration and performing Quantitative Reverse transcription PCR (RT-qPCR), Western blotting and immunofluorescence assays in LLC-PK1 cells. The mechanism of EP against PDCoV was analyzed by flow cytometry, RT-qPCR and Western blotting. We found that EP treatment inhibited PDCoV infection in LLC-PK1 cells in a dose-dependent manner. Subsequently, we demonstrated that EP blocked virus attachment and entry using RT-qPCR. Time-of-addition assays indicated that EP mainly exerted its inhibitory effect at the early and middle stages in the PDCoV replication cycle. EP also inactivated PDCoV infectivity directly as well as suppressed PDCoV-induced apoptosis. Furthermore, EP treatment decreased the phosphorylation of IκBα and p38 MAPK induced by PDCoV infection as well as the mRNA levels of cytokines (IL-1β, IL-6, IL-12, TNF-α, IFN-α, IFN-β, Mx1 and PKR). These results imply that EP can inhibit PDCoV infection and regulate host immune responses by downregulating the activation of the NF-κB and p38/MAPK signaling pathways in vitro. EP can be used as a potential candidate for the development of a new anti-PDCoV therapy.