Cytokines transcript levels in lung and lymphoid organs during genotype 1 Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) infection

Porcine Reproductive and Respiratory Syndrome (PRRS) is one of the most economically important diseases of swine. PRRS virus (PRRSV) infection in the pig is characterized by a weak or absent host innate immune response. The underlying mechanisms of PRRSV pathogenesis are still unclear. The analysis of transcript levels represents an alternative to immunoassays for the detection of cytokines that sometimes are difficult to detect due to their low amounts. This study sets out to determine the differences in pathogenesis and the immune response between lung, tonsil, tracheobronchial lymph node (Tb-LN) and retropharyngeal LN (Rf-LN) of PRRSV 2982 strain infected pigs. PRRSV strain 2982 avoided the onset of an effective innate immune response, especially in PRRSV main target (lung) and reservoir (tonsil) organs. PRRSV lead to an impaired expression of IFN-α and TNF-α gene expression, which finally induced a weak and delayed adaptive immune response through an inefficient IL-12 and IFN-γ expression. Finally, PRRSV replication favored the expression of the anti-inflammatory IL-10 cytokine in infected pigs.