ARS | Publication request: Immune responses induced by DNA vaccines bearing Spike gene of PEDV combined with porcine IL-18

Submitted to: Virus Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 10, 2012
Publication Date: June 5, 2012
Citation: Suo, S., Li, X., Li, P., Li, G., Ren, Y., Zarlenga, D.S., Ren, X. 2012. Immune responses induced by DNA vaccines bearing Spike gene of PEDV combined with porcine IL-18. Virus Research. DOI: 10.1016/j.virusres.2012.05.007.

Interpretive Summary: Porcine epidemic diarrhea virus (PEDV) causes porcine epidemic diarrhea (PED) which in turn can result in very high mortality in newborn piglets. The disease was first reported in England in 1971 and has since been reported worldwide. Although conventional inactivated and attenuated vaccines have been used in some areas, such vaccines have drawbacks such as recovery of virulence, spread of viruses and high cost or poor protection efficacy. Therefore, development of novel and effective vaccines is necessary for the control of PED. In this study, eukaryotic expression plasmids encoding the full-length S protein and truncated fragments thereof were synthesized along with the swine cytokine gene, IL-18. Using a mouse model, we compared host immune responses triggered by directly injecting these DNAs into mice to determine if DNA injection would elicit a protective response and if IL-18 could enhance that response. Our results showed that the cloned S gene induces a strong immune response and that the IL-18 gene product enhanced that response but not synergistically. Eventually, these data may facilitate the development of efficacious viral gene vaccines and broad use by the veterinary community.

Technical Abstract: Porcine epidemic diarrhea virus (PEDV) is the causative agent of porcine epidemic diarrhea, a highly contagious enteric disease of swine. The Spike (S) protein is one of the main structural proteins of PEDV capable of inducing neutralizing antibodies in vivo. Herein, we generated three distinct DNA constructs in the eukaryotic expression plasmid pVAX1; one encoding the S protein [pVAX1-(PEDV-S)], the second encoding the N-terminal fragment (S1) [pVAX1-(PEDV-S1)] containing potent antigenic sites, and the third expressing the porcine interleukin-18 (pIL-18) [pVAX1-(IL-18)]. Immunofluorescence assays in BHK-21 cells demonstrated successful protein expression from all 3 constructs. Kunming mice were injected separately with each of these constructs or with a pVAX1-(PEDV-S1)/pVAX1-(IL-18) combination, an attenuated PEDV vaccine, or vector only control. Animals were examined for T lymphocyte proliferation, anti-PEDV antibodies, IFN-' and IL-4 protein levels, and cytotoxic T cell function in mouse spleens and peripheral blood. In all cases, results showed that pVAX1-(PEDV-S) and the combination of pVAX1-(PEDV-S1) with pVAX1-(IL-18) induced the strongest responses but that pIL-18 had no adjuvant effects when given in combination with pVAX1-(PEDV-S1).