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Abstract: Delayed development of virus-specific immune response has been observed in pigs infected with the porcine reproductive and respiratory syndrome virus (PRRSV). Several studies support the hypothesis that the PRRSV is capable of modulating porcine immune system, but the mechanisms involved are yet to be defined. In this study, we evaluated the induction of T regulatory cells by PRRSV-infected dendritic cells (DCs). Our results showed that PRRSV-infected DCs significantly increased Foxp3+CD25+ T cells, an effect that was reversible by IFN-α treatment, and this outcome was reproducible using two distinct PRRSV strains. Analysis of the expressed cytokines suggested that the induction of Foxp3+CD25+ T cells is dependent on TGF-β but not IL-10. In addition, a significant up-regulation of Foxp3 mRNA, but not TBX21 or GATA3, was detected. Importantly, our results showed that the induced Foxp3+CD25+ T cells were able to suppress the proliferation of PHA-stimulated PBMCs. The T cells induced by the PRRSV-infected DCs fit the Foxp3+CD25+ T helper 3 (Th3) regulatory cell phenotype described in the literature. The induction of this cell phenotype depended, at least in part, on PRRSV viability because IFN-α treatment or virus inactivation reversed these effects. In conclusion, this data supports the hypothesis that the PRRSV succeeds to establish and replicate in porcine cells early post-infection, in part, by inducing Th3 regulatory cells as a mechanism of modulating the porcine immune system. [Copyright &y& Elsevier]

Abstract: The aim of this study was to characterize the immune responses of DCs after infection with four different EU strains of PRRSV and whether they show any ability to immunomodulate T cells activation. Our results show that all EU strains can efficiently infect and replicate in DCs. Nevertheless, SLA-II levels remained unaltered in DC infected by all EU PRRSV strains, whereas SLA-I expression was only reduced when strain 2992 was used. IL-10 production was induced by three EU PRRSV strains, being strain 2992 the highest inducer. However, no induction of Treg cells, measured by CD25 and Foxp3 expression on lymphocytes co-cultured with infected DCs, was found. TGF-β induction was not detected in DC infected with any EU strain tested. In conclusion, DCs infected with EU PRRSV strains exhibited an unbalanced ability to stimulate T cell response and was strain dependent. However, Treg cells were not induced, at least in vitro. [Copyright &y& Elsevier]