Upregulation of IL-10 gene expression in porcine peripheral blood mononuclear cells by porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome (PRRS) virus-specific interferon-gamma(+) T-cell responses after PRRS virus infection or vaccination with an inactivated PRRS vaccine

Although field studies have found porcine reproductive and respiratory syndrome (PRRSV) inactivated vaccines to be beneficial in reducing losses linked to PRRSV infection, immune mechanisms induced by these vaccines need better understanding. In the study reported here, we examined the interferon-gamma(+) (IFNgamma(+)) PRRS-specific T cell responses induced after infection and vaccination with an inactivated PRRS vaccine. Autologous monocyte-derived dendritic cells loaded with the PRRSV P120 strain were used to re-stimulate ex vivo T cells that had been primed in vivo by either the virus or the vaccine, or both. Virus-specific IFNgamma(+) T cells were quantified by using a porcine IFNgamma- ELISpot assay. A specific but low live virus-induced response was observed between days 35 and 70 for most of the pigs tested, while a significant inactivated vaccine-induced PRRSV-specific IFNgamma(+) T-cell response was measured soon after vaccination. Moreover, we observed that vaccination of pre-challenged pigs clearly favoured the PRRSV-specific cell-mediated immunity primed by the live virus. To characterize further the nature of the PRRSV-specific T cells, the different T-cell subsets involved in PRRSV immunity were analyzed by flow cytometry. We showed that the inactivated vaccine was able to prime both CD4(+)CD8(int+) and CD8(high) virus-specific T cells and that CD4(+)CD8(int+) were preferentially recalled by the live virus.

Interleukin-12 (IL-12) ameliorates the effects of porcine respiratory and reproductive syndrome virus (PRRSV) infection

Porcine respiratory and reproductive syndrome virus (PRRSV) disease, one of the most economically significant viral diseases in the swine industry, is characterized by miscarriages, premature farrowing, stillborn pigs, and respiratory disease associated with death and chronic poor performance of nursing and weaned pigs. Interleukin-12 (IL-12) is a key component in driving the development of cell-mediated immunity as well as stimulating interferon-gamma (IFN-gamma) production from T cells and natural killer cells. Although some studies have investigated the use of IL-12 as a vaccine adjuvant in swine, little is known about its effectiveness as a treatment against viral diseases in swine. The present study investigated whether recombinant porcine IL-12 (rpIL-12) enhances the immune response and thereby diminishes the effects of PRRSV infection in young pigs. Interestingly, in vitro experiments demonstrated that rpIL-12 is capable of inducing swine pulmonary alveolar macrophages (PAMs), the target cells of PRRSV, to produce IFN-gamma in a dose and time dependent manner. In addition, in vitro studies also revealed that rpIL-12 treatment was capable of significantly reducing PRRSV viral titers in PAMs. In vivo administration of rpIL-12 significantly decreased PRRSV titers in the lungs and blood of infected animals. Furthermore, treatment with rpIL-12 prevented significant growth retardation in PRRSV-infected animals. Finally, in response to viral antigen recall challenge, PAMs isolated from rpIL-12-treated/PRRSV-infected animals produced greater amounts of IFN-gamma and lesser amounts of interleukin-10 than PAMs isolated from non-rpIL-12-treated/PRRSV-infected animals. Taken together our data indicate that treatment with rpIL-12 may provide an effective approach to control or ameliorate PRRSV-induced disease in swine.

Immune responses of pigs after experimental infection with a European strain of Porcine reproductive and respiratory syndrome virus

The purpose of this experiment was to study the immune response of pigs during an experimental infection with a European strain of Porcine reproductive and respiratory syndrome virus (PRRSV). Five pigs were challenged intranasally with PRRSV strain VP21 and another five were kept as controls. Clinical course and humoral and cell-mediated responses were monitored for 70 days post-infection (p.i.). Infected pigs developed mild signs at 24 h p.i. Viraemia was detectable by nested RT-PCR until day 14 p.i. Earliest seroconversions (ELISA) were seen by day 7 p.i. (three of five animals) and, by day 14, all inoculated pigs had seroconverted (ELISA and immunoperoxidase monolayer assay). Virus-neutralizing antibodies were undetectable until day 56 p.i. and, by day 70 p.i., two inoculated pigs still were negative. Flow-cytometry assays using peripheral blood mononuclear cells (PBMC) showed an upshift in CD8+ cells (day 7 p.i.) and a downshift of CD21+ cells (days 7 and 28 p.i.). Regarding cell-mediated responses, development of PRRSV-specific gamma interferon-secreting cells (IFN-γ-SC) and interleukin 4-secreting cells (IL4-SC) in PBMC was examined by ELISPOT assay. IFN-γ-SC were not detected significantly until day 14 p.i., whereas, for IL4-SC, no differences between groups were seen. Concurrently with the onset of viraemia and the development of clinical signs, serum haptoglobin levels and interleukin 10 (IL10) in PRRSV-stimulated PBMC-culture supernatants increased significantly. These differences disappeared later on. For IL2, IL4, IL8 or transforming growth factor beta, no differences were seen among groups. These results are compatible with a model in which the immune response does not fully control the outcome of the infection.

Deciphering the involvement of innate immune factors in the development of the host response to PRRSV vaccination

The natural response of pigs to porcine reproductive and respiratory syndrome virus (PRRSV) infections and vaccinations needs to be altered so that better protection is afforded against both homologous and heterologous challenges by this pathogen. To address this problem, real-time gene expression assays were coupled with cytokine Elispot and protein analyses to assess the nature of the anti-PRRSV response of pigs immunized with modified live virus (MLV) vaccine. Although T helper 1 (Th1) immunity was elicited in all vaccinated animals, as evidenced by the genesis of PRRSV-specific interferon-gamma secreting cells (IFNG SC), the overall extent of the memory response was variable and generally weak. Peripheral blood mononuclear cells (PBMC) isolated from these pigs responded to PRRSV exposure with a limited increase in their expression of the Th1 immune markers, IFNG, tumor necrosis factor-alpha and interleukin-15 (IL15), and a reduction in the quantity of mRNAs encoding the innate and inflammatory proteins, IL1B, IL8 and IFNA. Efforts to enhance Th1 immunity, by utilizing an expression plasmid encoding porcine IFNA (pINA) as an adjuvant, resulted in a temporary increase in the frequency of PRRSV-specific IFNG SC but only minor changes overall in the expression of Th1 associated cytokine or innate immune marker mRNA by virus-stimulated PBMC. Administration of pINA, however, did correlate with decreased IL1B secretion by cultured, unstimulated PBMC but had no effect on their ability to release IFNG. Thus, while exogenous addition of IFNA during PRRSV vaccination has an impact on the development of a Th1 immune response, other alterations will be required for substantial boosting of virus-specific protection.

Upregulation of interleukin-10 gene expression in the leukocytes of pigs infected with porcine reproductive and respiratory syndrome virus

Recent studies suggest that porcine reproductive and respiratory syndrome virus (PRRSV) may have immunomodulatory effects on the host immune system by upregulating interleukin (IL)-10 gene expression. To determine the effect of PRRSV on porcine cytokine gene expression in vivo, we infected pigs with either the European or North American strain of PRRSV and monitored cytokine gene expression in peripheral blood mononuclear cells (PBMC) and bronchoalveolar lavage cells (BALC) using a multiplex PCR assay. Our results showed that both European and North American strains of PRRSV significantly upregulated IL-10 gene expression in PBMC of infected pigs from 5 days post-infection (p.i.). In addition, upregulation of IL-10 and interferon (IFN)-gamma gene expression was observed in BALC starting from 9 days p.i. The upregulation of cytokine gene expression in BALC was observed concurrent with an increased percentage of lymphocytes in the BALC population, suggesting a role for peripheral leukocytes in cytokine production in lungs. Our results showed that PRRSV infection resulted in an upregulation of IL-10 gene expression in vivo and that both European and North American strains induced comparable levels of IL-10 gene expression in the infected pigs, despite differences in the clinical signs. Our data support the notion that induction of IL-10 production may be one of the strategies used by PRRSV to modulate the host's immune responses, and this may contribute to the unique clinical picture observed following PRRSV infection.

Infection of porcine reproductive and respiratory syndrome virus suppresses the antibody response to classical swine fever virus vaccination

The effects of porcine reproductive and respiratory syndrome virus (PRRSV) infection on the antibody response to vaccination with classical swine fever (CSF) vaccine in piglets were investigated. Piglets were inoculated intranasally with the PRRSV BJ-4 strain, and then vaccinated intramuscularly with CSF vaccine 2 days later. Control animals were either vaccinated with CSF vaccine or infected with PRRSV alone. Time course of the antibody response against either PRRSV or CSF vaccine was measured. In animals infected with PRRSV prior to CSF vaccination, the antibody response to CSF vaccine was significantly lower than that observed in animals treated with CSF vaccination alone, especially during 3-5 weeks after vaccination. At the same time, no significant difference in serum PRRSV antibody level was observed between the animals treated with both PRRSV and CSF vaccine and the animals treated with PRRSV alone. These results suggested that the reduced antibody response against CSF vaccine observed in PRRSV-infected animals might be related to the higher prevalence of CSF in PRRSV prevalent farms in China.