Caracterización de la respuesta inmune de lechones durante la infección y tras la vacunación con el virus del Síndrome Reproductivo y Respiratorio Porcino
Since it was described in 1987, Porcine Reproductive and Respiratory Syndrome (PRRS) has become one of the most important diseases in the swine worldwide. A recent study estimates that the economic losses caused by PRRS in the US amount to more than US$ 560 millions annually.
Regarding the commercialized vaccines, as of today, there is no convincing evidence indicating that they confer an acceptable and universal protection against the infection. One of the reasons for the lack of development of newer and more efficacious vaccines is the scarce knowledge on the immune response (IR) of pigs after infection by field strains.
The etiologic agent for this disease is known as PRRS virus (PRRSV) or Porcine Arterivirus. Two genotypes are recognized (American and European). In addition, genetic diversity of strains within a given genotype is high. To date, the majority of the studies regarding the IR of pigs after the PRRSV infection or vaccination have been done using the American strains.
The aim of this thesis is to characterize the IR against the European genotype. Firstly, during the infection of piglets with a wild-type Spanish strain and secondly after the vaccination with two attenuated virus (commercialized vaccines), evaluating their efficacy after a challenge with a homologous or a heterologous strain.
First study: The most significant results in the IR of the piglets experimental infected with a Spanish strain are: lack of IL-2 and IL-4 production, early production of non-neutralizing antibodies, inconstant and late humoral neutralizing response and slow and irregular development of PRRSV-specific IFN-gamma-secreting cells (IFN-gamma-SC) measured by ELISPOT. Nevertheless, this last parameter would be associated with the disappearance of the virus from the blood. The IL-10 and haptoglobin production in the first phases of the infection could explain the anomalous cell response observed. We postulate that the IR maybe plays a secondary role in the resolution of the infection, as it has already been demonstrated with other Arterivirus as lactate dehydrogenase-elevating virus of the mice.
Second study: After vaccination, some pigs remain viremic as late as 42 days post-vaccination. This extended period of viremia could significantly contribute to the spread of vaccine virus and, potentially, this phenomenon could facilitate the reversion to virulence. Surprisingly, after the challenge, only pigs vaccinated with the homologous strain (V1) become viremic (4/5). Vaccinated pigs do not develop neutralizing antibodies before the challenge. Therefore, this parameter cannot be related to the protection conferred by the vaccines. Our results suggest that IFN-gamma-SC play an important role in protection against the PRRSV infection in piglets. Regardless of the vaccine used, the pigs are protected if IFN-gamma-SC reach a minimum frequency at time of the infection. In fact, heterologous vaccine (V3) confers the best protection because it induces the highest IFN-gamma-SC frequency. The lowest protection conferred by the homologous vaccine (V1) could be explained by its intrinsic ability to induce a high IL-10 production even in naïve cells. Our results suggest that the protection afforded by a vaccine against PRRSV cannot be forecasted only by a global view of the genetic similarity between the strains but, maybe, can be forecasted by the time passed after the vaccination and the inherent immune properties of each strain.
In summary, our studies show that the IR of the piglets after the infection with a wild-type strain is similar to the IR developed after the immunization with attenuated strains, both in European and American genotypes, in spite of the genetic diversity. The second study proves that the frequency of PRRSV-specific IFN-gamma-SC plays a significant role in the protection of vaccinated pigs against a PRRSV infection.
Document Full Text
Advisor:Mateu de Antonio, Enric M.
School:Universitat Autónoma de Barcelona
Source Type:Master's Thesis
Keywords:457 departament de salut i anatomia animals
Date of Publication:09/12/2006