Evaluation of immune responses to porcine reproductive and respiratory syndrome virus in pigs during early stage of infection under farm conditions

Abstract

BackgroundPorcine reproductive and respiratory syndrome virus (PRRSV) causes chronic, economically devastating disease in pigs of all ages. Frequent mutations in the viral genome result in viruses with immune escape mutants. Irrespective of regular vaccination, control of PRRSV remains a challenge to swine farmers. In PRRSV-infected pigs, innate cytokine IFN-α is inhibited and the adaptive arm of the immunity is delayed. To elucidate both cellular and innate cytokine responses at very early stages of PRRSV infection, seven weeks old pigs maintained on a commercial pig farm were infected and analyzed.ResultsOne pig in a pen containing 25 pigs was PRRSV infected and responses from this pig and one penmate were assessed two days later. All the infected and a few of the contact neighbor pigs were viremic. At day 2 post-infection, approximately 50% of viremic pigs had greater than 50% reduction in NK cell-mediated cytotoxicity, and nearly a 1-fold increase in IFN-α production was detected in blood of a few pigs. Enhanced secretion of IL-4 (in ~90%), IL-12 (in ~40%), and IL-10 (in ~20%) (but not IFN-γ) in PRRSV infected pigs was observed. In addition, reduced frequency of myeloid cells, CD4-CD8+ T cells, and CD4+CD8+ T cells and upregulated frequency of lymphocytes bearing natural T regulatory cell phenotype were detected in viremic pigs. Interestingly, all viremic contact pigs also had comparable immune cell modulations.ConclusionReplicating PRRSV in both infected and contact pigs was found to be responsible for rapid modulation in NK cell-meditated cytotoxicity and alteration in the production of important immune cytokines. PRRSV-induced immunological changes observed simultaneously at both cellular and cytokine levels early post-infection appear to be responsible for the delay in generation of adaptive immunity. As the study was performed in pigs maintained under commercial environmental conditions, this study has practical implications in design of protective vaccines.

Pathogenicity of three type 2 porcine reproductive and respiratory syndrome virus strains in experimentally inoculated pregnant gilts

“…However, conflicting data on IFN␣ expression/production after PRRSV infection can be found in the literature. While some studies could not detect significant IFN␣ increases in serum of PRRSV inoculated pigs within one week of infection (Gomez-Laguna et al, 2009;Lawson et al, 2010), others did (Dwivedi et al, 2012;Guo et al, 2013). However, none of these experiments used pregnant sows or gilts.…”

Peptide nanofiber hydrogel adjuvanted live virus vaccine enhances cross-protective immunity to porcine reproductive and respiratory syndrome virus

“…IL-4 expression has been shown to control macrophage inflammatory activities in the pig [26]. While IL-4 expression levels in PRRSV-infected pigs can remain unaltered [27], recent studies suggest that natural PRRSV infection can significantly induce the expression of IL-4 [28], suggesting that PRRSV-mediated IL-4 induction may be strain dependent. In our hands, the increased IL-4 expression after VR-2332 challenge correlated well with enhanced protection of pigs vaccinated with MLV+H9e than that of pigs vaccinated with MLV-alone.…”

Emergency vaccination alleviates highly pathogenic porcine reproductive and respiratory syndrome virus infection after contact exposure

“…The infected pigs exhibited higher levels of viraemia at 3 DPI, thereby suggesting that the pigs transmitted the virus within 2 DPI, which may account for the rapid spread of the virus in herds [21]. PRRSV transmission is primarily via the respiratory route [22].…”