Analysis of constitutive cytokine expression by pigs infected in-utero with porcine reproductive and respiratory syndrome virus
Introduction
Porcine reproductive and respiratory syndrome virus (PRRSV) is an enveloped, single-stranded, positive RNA virus of the Arteriviridae group (Benfield et al., 1992). When porcine reproductive and respiratory syndrome (PRRS) was first observed, it was characterized by excessive rates of late-term abortion, stillbirths and mummified fetuses (Dial et al., 1990). Live-born piglets were often born weak and displayed respiratory distress or clinical signs of secondary bacterial pathogens (Dial et al., 1990, Done and Paton, 1995, Keffaber et al., 1992, Stephenson et al., 1993). Once the reproductive disease outbreak subsides, a PRRSV and secondary bacterial disease complex of weaned pigs may continue for years (Stephenson et al., 1993), suggesting PRRSV infection might have immunosuppressive effects on pigs.
We have previously reported on a novel disease model that reproduces the immunosuppressive effects of PRRSV (Feng et al., 2001). Suckling piglets from sows infected at day 98 gestation were found to be highly susceptible to Streptococcus suis type 2 infection. Pathologically the most striking lesions were in the thymus, which displayed a severe depletion of cortical thymocytes. We also found that in-utero infection with PRRSV caused changes in thymocyte subpopulations and peripheral blood T-lymphocyte subsets highlighted by a significantly decreased CD4+/CD8+ ratio (Feng et al., 2002). These results suggest that in-utero infection with PRRSV can modulate immune functions in piglets.
The nature and role of the humoral and cell-mediated immune responses against PRRSV have not been fully characterized. Cytokines are integral components of the immune response and important for cell-mediated and humoral immunity. Information about the cytokine response during PRRSV infection may be crucial for us to understand the host immune response to the virus and potentially the pathogenesis of the disease. In the present study, we investigated constitutive cytokine patterns in peripheral blood mononuclear cells (PBMCs) of piglets infected in-utero with PRRSV. We demonstrated that IL-6, IL-10, and IFN-γ mRNA expressions were significantly increased at 0 and 14 days of age. We also showed that the IL-10/IL-12 ratio was significantly increased, suggesting an imbalance of IL-10 and IL-12 mRNA expression in PRRSV-infected pigs.
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Animals and experimental design
Eight PRRSV-free pregnant sows were purchased from a geographically isolated unvaccinated herd which had been free of clinical signs of PRRSV infection and had remained seronegative to PRRSV for the past 3 years. Five sows were inoculated with strain SD 23983 of PRRSV (gift from Dr. Benfield, South Dakota State University) by intranasal instillation of 2 ml inoculum containing 103.2 50% tissue culture infective doses (TCID50) virus as previously described (Kim et al., 1993) at 98 days gestation.
Clinical signs and virus isolation
Piglets born to PRRSV-infected sows were weak and had rough hair coats. Some exhibited fever, eyelid edema, forehead edema, conjunctivitis, inappetence, and dyspnea during the first 2 weeks of life. After 6 weeks, the pigs from PRRSV-infected sows were clinically normal. Control pigs showed no adverse clinical signs throughout the experimental period. PRRSV was isolated from the sera of all pigs born to PRRSV-infected sows at 0 and 14 days of age (Table 1). However, at 67 days of age PRRSV was
Discussion
The purpose of this study was to investigate the cytokine mRNA expression profiles produced by PBMC from piglets infected in-utero with PRRSV. This report extends our previous studies in which we demonstrated that in-utero infection with PRRSV increased piglet susceptibility to S. suis infection (Feng et al., 2001) and caused abnormal changes in thymocyte and T-lymphocyte subsets (Feng et al., 2002). We report herein that IL-6, IL-10, and INF-γ mRNA levels are significantly increased in
Acknowledgements
We thank Dr. Jack Britt for his critiques and Dr. Zuckermann for his generous gift of biotinylated porcine CD8 MAb. We also thank Mrs. Kimberly Ainge, Dr. Kristie Karli, Dr. Kelly Gambino, Dr. Stacy Jones, and Dr. Jan Shaw for taking care of the newborn piglets. This report was funded by North Carolina Pork Producers Association, College of Veterinary Medicine, and College of Agriculture and Life Sciences, North Carolina State University.
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Innate and adaptive immunity against Porcine Reproductive and Respiratory Syndrome Virus
2015, Veterinary Immunology and ImmunopathologyPlasmids expressing porcine interferon gamma up-regulate pro-inflammatory cytokine and co-stimulatory molecule expression which are suppressed by porcine reproductive and respiratory syndrome virus
2013, Veterinary Immunology and ImmunopathologyCitation Excerpt :In contrast to the reduced pro-inflammatory cytokine and co-stimulatory molecule expression, monocytes inoculated with PRRSV demonstrated significantly increased IL-10 and increased TGFβ expression in response to LPS stimulation (Table 2 and Fig. 4). PRRSV induction of IL-10 and TGFβ expression has been demonstrated in vitro in PBMC and myeloid APC inoculated with the virus (Chang et al., 2008; Charerntantanakul and Kasinrerk, 2010, 2012; Flores-Mendoza et al., 2008; Genini et al., 2008; Park et al., 2008; Royaee et al., 2004; Suradhat and Thanawongnuwech, 2003; Suradhat et al., 2003), and in vivo in serum, bronchoalveolar lavage fluid, and lymphoid tissues of PRRSV-infected pigs (Chung and Chae, 2003; Diaz et al., 2005, 2006; Feng et al., 2003; Johnsen et al., 2002; Labarque et al., 2003). PRRSV up-regulation of IL-10 expression has been demonstrated to contribute to the reduced expression of some pro-inflammatory immune parameters, e.g. IFNγ, TNFα, CD80, and CD86 as examined by IL-10 knockdown using porcine IL-10-specific antisense oligodeoxynucleotides and plasmids expressing porcine IL-10 short hairpin RNA (Charerntantanakul and Kasinrerk, 2010, 2012).
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Present address: Linberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, CB #7295, Chapel Hill, NC 27599, USA.