To identify the DEPs following viral infection, the total cellular proteins extracted from PDCoV- and mock-infected IPEC-J2 cells were processed for quantitative proteomics research using iTRAQ-coupled LC-MS/MS technique. In all, 5502 cellular proteins were identified in both PDCoV- and mock-infected IPEC-J2 cells at 24 hpi (Supplementary File S1). On the basis of the widely used criteria for judging DEPs (fold changes >1.2 or <0.83 and with p < 0.05),28,29 23 proteins were significantly upregulated and 55 proteins were markedly downregulated in PDCoV-infected IPEC-J2 cells in comparison with the mock-infected cells (Table 1). Meanwhile, six viral proteins, including the nucleocapsid protein, spike protein, membrane protein, 3C-like proteinase Nsp5, accessory proteins NS6 and NS7 (Supplementary File S2), were also identified in PDCoV-infected IPEC-J2 cells by searching against the porcine deltacoronavirus Uniprot database. In order to ensure the reliability of the obtained proteomic data, three biological replicates of PDCoV- or mock-infected cell samples were collected and three technical replicates were performed during the proteomic analysis. The difference was plotted against the percentage of the identified proteins, which suggested that the proteomic data had high credibility (Supplementary Figure S1). Notably, due to the fact that the current genome database of pigs is inadequately annotated in comparison to the human genome database, we found six uncharacterized or unassigned proteins among the 78 DEPs (Table 1). Therefore, a functional analysis of these proteins warrants further investigation.