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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., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) infection is characterized by persisting in lungs and lymphoid tissue, resulting in systemic lymphoid depletion. The aim of this study was to correlate the histological changes, viral antigen expression and apoptosis phenomena in tonsil, medial retropharyngeal and mediastinal lymph nodes of 12 pigs inoculated with a type 2 PRRSV isolate (Chilean strain 2402). Apoptosis phenomena were observed mainly in lymphocytes and secondly in macrophages of lymph nodes and tonsils of inoculated animals, showing a peak of both apoptotic cells and viral antigen expression at the end of the study (21 dpi). However, the number of apoptotic cells was higher than the number of PRRSV-positive cells at the end of the study. This finding together with the location of apoptotic cells and PRRSV-positive cells in different structures of lymphoid organs supports the hypothesis that PRRSV-positive macrophages might modulate the apoptosis phenomena in other cells, mainly lymphocytes, by means of an indirect mechanism. Furthermore, apoptotic cells were detected both in B- and T-cell areas of lymphoid organs, suggesting that apoptosis phenomena may play a role in the impairment of the host immune response during PRRS., (© 2012 Blackwell Verlag GmbH.)

Despite the numerous studies carried out, the mechanisms used by porcine reproductive and respiratory syndrome (PRRS) virus (PRRSV) to impair the host immune response are not yet clear. The aim of this study was to determine the expression of IL-12, IL-10, IFN-α and IFN-γ in lymphoid organs of PRRSV experimentally-infected pigs. Twenty eight piglets were inoculated with PRRSV field isolate 2982 and killed in batches of four at 3, 7, 10, 14, 17, 21 and 24 days post-inoculation (dpi). Control animals were mock-inoculated and killed at the end of the study. Samples from mediastinal and retropharyngeal lymph nodes and tonsil were collected and fixed for histopathological and immunohistochemical analyses. PRRSV antigen was mainly detected in the cytoplasm of macrophages, displaying a bimodal expression with a first peak at 3-7 dpi and a second peak at 14 dpi. The expression of IFN-α showed an early enhancement at 3 dpi, and both IL-12 and IFN-γ displayed a similar trend in all the lymphoid organs analysed, showing an increase at 3-7 dpi and at 14-17 dpi. On the other hand, the expression of IL-10 was lower than the one observed for the other cytokines. The expression of IL-10 compared with the higher expression of IL-12, IFN-α and IFN-γ detected in this study, indicates that other mechanisms besides the expression of IL-10 play a role in the inducement of an erratic host immune response. Taking into account the enhanced expression of IFNs together with the detection of PRRSV antigen until the end of the study in the examined lymphoid organs, further studies are being conducted to rule out a down-regulation in IFN signalling pathway., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Porcine reproductive and respiratory syndrome (PRRS) is considered one of the most important diseases in the swine industry. Although several studies have been carried out to elucidate the host immune response evoked against PRRS virus (PRRSV), there are several aspects that still remain unclear. The aim of this study was to determine the expression of IL-1α, IL-6 and TNF-α in the lymphoid organs (mediastinal and retropharyngeal lymph nodes and tonsil) of PRRSV-infected pigs and to determine their correlation with the expression of PRRSV antigen. Proinflammatory cytokine expression was different depending on the body compartment examined. Thus, whereas IL-1α and TNF-α were the main cytokines expressed in the mediastinal lymph node, IL-6 was the most highly expressed cytokine in the retropharyngeal lymph node, and no expression of proinflammatory cytokines was observed in the tonsil. These findings may be related to the impairment of the host immune response evoked after PRRSV infection. Therefore, lymphoid organs and proinflammatory cytokines represent an important target of study for clarifying the immunopathogenesis of PRRS., (© 2011 Blackwell Verlag GmbH.)