Modulación de la respuesta inmune en trucha arcoíris (Oncorhynchus mykiss) frente a distintas estrategias vacunales antivirales

Resumen

The aquaculture industry constitutes a very important animal-producing sector in the context of an increasing human population and a commercial fishing industry that is at or beyond its sustained yield. To achieve an optimal level of growth, the problem of fish infectious diseases in aquaculture must be urgently addressed. Viruses constitute one of the major threats for the aquaculture industry, and the great majority of fish diseases notifiable to the European Union (EU) or the world organization for animal health (OIE) are of viral nature. Among these notifiable diseases, two viruses of the family Rhabdoviridae: viral hemorrhagic septicaemia virus (VHSV) and infectious haematopoietic necrosis virus (IHNV) both belonging to the genus Novirhabdovirus have the potential to severely impact the EU trout aquaculture. Infectious pancreatic necrosis virus (IPNV) within the Birnaviridae family is also one of the main causes of mortality for worldwide salmonid juveniles, being especially destructive in salmonid eggs and fingerlings, in which a lifelong asymptomatic carrier state can be established. However while the control of these viruses constitutes a major concern for the aquaculture industry, to date, no cost-effective vaccines are available for any of them worldwide. Many previous efforts were made searching for efficient vaccines against rhabdoviruses with none or little success. In contrast, intramuscular administration of plasmid DNA encoding the viral glycoprotein proved to be highly effective against both VHSV and IHNV reaching protection levels of up to 95-100%. However, to date, different practical issues limit their commercialization in Europe such as concerns related to the viral regulatory sequences (promoters and terminators) present in plasmid constructs, relatively high vaccination costs and the lack of administration methods such as bath or oral delivery that require less manpower than injection. Moreover, not having identified the immune mechanisms responsible for protection strongly limits: the development of best possible vaccination strategies for other fish viruses; the development of new adjuvant and costimulation strategies and the development of in vitro immunoassays to predict vaccine efficacy. Concerning DNA vaccines against fish rhabdoviruses, in this work, we have tried to address several of these problems. Through the introduction of immune-stimulatory CpG sequences in the vaccine constructs we have been able to increase the immunogenicity of the VHSV DNA vaccine. We have also studied the local immune response in the muscle of vaccinated fish from a point of view not previously approached, the transcription of chemokines and the characterization of the infiltrating cells. Finally, the possibility of administering the DNA vaccines orally through encapsulation in alginate microspheres has also been evaluated, focusing on the mucosal immune responses triggered. Moreover, virus like particles (VLPs) against viral pathogens not only constitute a novel approach for the development of antiviral vaccines for an specific virus, but also for the creation of multivalent vaccines in which antigens from other pathogens may be expressed on the surface of these VLPs. Despite positive results on protection, not many studies have focused on the immune response triggered by VLPs; studies that may provide hints for the identification of immune mechanisms responsible for antiviral protection, which are mostly unknown in fish. Thus, in the current work, we have also studied some aspects of the immune response triggered by them. All these immunological studies performed with different antiviral vaccines in fish should contribute to a further understanding of the immune responses responsible for protection against viruses in fish, an essential point for a future rational design of antiviral vaccines.