Pcdna3.1a plasmid

The pcDNA3.1A plasmid was from Invitrogen (Carlsbad, CA, USA). The pcDNA-chIL7, pcDNA-chIL7/H, pcDNA-VP2 (VP2 is an epitope in IBDV VP2 consisted of 122 amino acids) and pcDNA-VP2/H-IRES-chIL7/H and pcDNA-VP2-IRES-chIL7 plasmids were previously constructed in our laboratory [17 (link)]. Human embryonic kidney (HEK) 293T cells (ATCC CRL-11268) and UMNSAH/DF-1 chicken embryonic fibroblast cells (DF-1 cells) (ATCC CRL-12203) were purchased from ATCC (Manassas, VA, USA). A virulent IBDV strain (Harbin-1 strain) was kindly provided by Zandong Li of China Agricultural University. Specific pathogen–free (SPF) chickens were purchased from Jinan Sais Poultry Company (Jinan, China) and raised in an isolator in an environmental control room with a 12/12 h light/dark cycle. Animal experiments were approved by the Animal Ethics Committee of the Hebei Agricultural University (No. DW20170016)

The pcDNA3.1A plasmid used to construct eukaryotic expression vectors for PPV-encoded genes was purchased from Invitrogen (Carlsbad, CA, USA). A virulent PPV strain was a generous gift from Professor Weiquan Liu (College of Biology, China Agricultural University). Porcine kidney (PK)-15 cells used for PPV amplification and apoptosis assay were purchased from the Center for Type Culture Collection of China in Beijing (Beijing, China), cultured in Dulbecco’s Modified Eagle’s Medium (DMEM) supplemented with 10 % (v/v) fetal bovine serum (FBS), 100 U/mL penicillin, 100 μg/mL streptomycin, and 2 mM L-glutamine at 37 ℃ in a 5 % CO₂ atmosphere incubator. The placental tissue collected from PPV-induced aborted and normal labored sows was provided by the local pig farms.