The concept of maintaining animal health through the best possible nutrition is well-accepted in modern animal farming. A large number of additives or feed ingredients (e.g. probiotics and glucans) are available for inclusion in functional feeds. However, little attention has been paid to the role of individual amino acids (AA) as potential immunomodulators. The new concept of functional AA is arising in the nutritional immunology field, and are defined as those AA that participate in and regulate key metabolic pathways to improve, for instance, health and survival of the organisms. For instance, methionine and tryptophan have known roles in the improvement of the immune response to infection and recent evidence indicate that mucosal immune defences appear to be influenced by their availability in fish. Still, the role of methionine and tryptophan on mucosal immune mechanisms and particularly in response to bacterial pathogens still needs further attention. This is particularly true for the aquaculture industry, where few therapeutic possibilities are available against infectious episodes. Moreover, methionine presents a pivotal role in the regulation of many cellular events with crucial impact on the immune system, such as in processes involved in the control of inflammation and polyamines synthesis, a fact that could be of advantage to develop and improve vaccination strategies.

The present project mainly aims: i) to provide a better understanding of the underpinning mechanisms of mucosal immune defences of fish fed methionine and tryptophan supplements; and ii) to study the synergistic effects of dietary methionine and vaccination using the rainbow trout (Oncorhynchus mykiss) as a model.

IMMUNAA project will firstly explore in Task1 how an acute bacterial infection as well as methionine and tryptophan nutrition can modulate the European seabass mucosal immune responses and disease resistance. Blood, plasma and mucosal immune parameters as well as oxidative stress biomarkers will give some insights on the role of methionine and tryptophan from a functional approach. The mechanisms behind those responses will be further explored through gene expression (Task1) and shot-gun proteomics (Task2) approaches. The IMMUNAA team will use an innovative multidisciplinary approach that aims to explore the links between methionine nutrition and immune plasticity. Considering the role of methionine on enhancing immune cells trafficking and proliferation, its putative synergistic effect on improving vaccine efficiency will be assessed in Task3. Finally, Task4 aims to deepen our knowledge on the role of methionine nutrition against bacterial and viral diseases and how its interaction with vaccination can improve disease resistance. Functional studies with flow cytometry will allow the identification and assessment of IgM+ B cells populations and to what extent IgM+ B cells differentiate to plasmablasts/plasma cells.

The IMMUNAA project assembled an innovative research strategy to include methionine and tryptophan supplements in functional feeds in order to improve mucosal immunity in European seabass. The functional role of methionine on improving vaccine efficiency will also be explored in seabass and its effectiveness demonstrated in rainbow trout. Through a practical point of view, the outcome of this project is to design dietary therapeutic interventions in order to increase disease resistance against fastidious pathogens such as Tenacibaculum maritimum and reduce the use of chemicals as prophylactic strategies. The expected impact of the IMMUNAA project is to deepen our knowledge on the interactions of methionine and tryptophan nutrition, immune response to infection and disease resistance. Nowadays, few studies have demonstrated clear links between AA nutrition and immune function/disease resistance or other key welfare aspects in fish. Ultimately, the synergistic effects between methionine and vaccine efficiency will also be suited for the development of more effective protocols in fish hatcheries and on-growing facilities and will open a new window of nutritional immunology research in aquaculture.