Cytokine profiles in pregnant gilts experimentally infected with porcine reproductive and respiratory syndrome virus and relationships with viral load and fetal outcome

Authors: LADINIG, ANDREA - University Of Saskatoon; Lunney, Joan; SOUZA, CARLOS - Embrapa; ASLEY, CAROLYN - University Of Saskatoon; PLASTOW, GRAHAM - University Of Alberta; HARDING, JOHN - University Of Saskatoon

Submitted to: Veterinary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/24/2014
Publication Date: 10/20/2014
Publication URL: http://handle.nal.usda.gov/10113/61240
Citation: Ladinig, A., Lunney, J.K., Souza, C., Asley, C., Plastow, G., Harding, J. 2014. Cytokine profiles in pregnant gilts experimentally infected with porcine reproductive and respiratory syndrome virus and relationships with viral load and fetal outcome. Veterinary Research. 45:113.

Interpretive Summary: Porcine Reproductive and Respiratory Syndrome (PRRS) causes major losses to the pig industry, $642,000/year in the US alone. In spite of extensive research, immunologic control mechanisms against PRRS virus (PRRSv) remain poorly understood, e.g., the role of certain immune proteins, known as cytokines and chemokines, in controlling or preventing PRRSv infection have been exhaustively studied in nursery pigs but show contradictory results.. There have been no detailed reports on cytokine responses to PRRSv infection in pregnant females (gilts). The objectives of this study were to compare host responses between PRRSv-infected and non-infected pregnant gilts, and to investigate whether cytokine levels could be predictive of serum viral load or fetal mortality rate. To address this question gilt blood samples were collected after PRRSv infection started during the third trimester (gestation days 86 to 107). Additionally, blood cells were prepared, cultured and their supernatants collected after stimulation either with PRRSv or an immune cell mitogen. Sera and supernatants were then analysed for protein levels of a panel of cytokines and one chemokines using a bead based multiplex assay. Our results showed that in gilt sera 3 immune proteins, interferon alpha (IFNa), interferon gamma (IFNg) and chemokine ligand 2 (CCL2), differed significantly in PRRSv inoculated versus control gilts. In supernatants of PRRSv stimulated cells from infected gilts, levels of innate cytokines were changed: IFNa was significantly decreased, while interleukin-8 (IL8) was significantly increased. Overall, only IFNa in supernatants of PRRSv stimulated cells was significantly associated with fetal mortality rate. Based on these results we concluded that IFNa was the best indicator of susceptibility to reproductive PRRSv infection and should be pursued as a biomarker for this viral infection.

Technical Abstract: In spite of extensive research, immunologic control mechanisms against Porcine Reproductive and Respiratory Syndrome virus (PRRSv) remain poorly understood. Cytokine responses have been exhaustively studied in nursery pigs and show contradictory results. Since no detailed reports on cytokine responses to PRRSv in pregnant females exist, the objectives of this study were to compare host cytokine responses between PRRSv-infected and non-infected pregnant gilts, and to investigate relationships between cytokine levels in infected gilts and viral load or fetal mortality rate. Serum samples and supernatants of peripheral blood mononuclear cells (PBMC) either stimulated with PRRSv or phorbol myristate acetate/Ionomycin (PMA/Iono) were analysed for cytokines/chemokines: interleukins (IL) 1-beta (IL1ß), IL4, IL8, IL10, IL12, chemokine ligand 2 (CCL2), interferon alpha (IFNa) and interferon gamma (IFN'). Three cytokines (IFNa, CCL2, IFN') in gilt serum differed significantly in inoculated versus control gilts over time. In supernatants of PRRSv stimulated PBMC from PRRSv-infected gilts, levels of IFNa were significantly decreased, while IL8 secretion was significantly increased. PRRSv infection altered the secretion of all measured cytokines, with the exception of IFNa, from PBMC after mitogen stimulation, indicating a possible immunomodulatory effect of PRRSv. IFNa, CCL2, and IFN' in serum, and IFN' in supernatants of PMA/Iono stimulated PBMC were significantly associated with viral load in tissues, serum or both. However, only IFNa in supernatants of PRRSv stimulated PBMC was significantly associated with fetal mortality rate. We conclude that of the eight cytokines tested in this study IFNa was the best indicator of susceptibility to reproductive PRRSv infection.