Rational design of vaccination strategies for Atlantic cod (VACSACOD)

In this project, we investigate how cod are able to achieve immunological memory without these genes. We have established a vaccination protocol that demonstrates cod have protective immunological memory. We are working on mapping the expression of all genes in individual cells in the cod's immune system, in normal conditions, during vaccination, and during a severe infection. Using advanced bioinformatics tools, we will identify which cell types respond to the vaccine and the nature of the response. In humans and other animals, vaccines usually elicit strong antibody responses that are characteristic of immunological protection, but previously published results from other researchers have shown that cod do not have strong antibody responses to vaccines. Therefore, it is assumed that specific antibodies are not important in the cod's immune defense. We have shown that by using a vaccination method where B cells do not need help from T cells to make specific antibodies, the production of specific antibodies can be activated in cod. Furthermore, we have used this method to vaccinate cod against Vibrio anguillarum. We then purified antibodies from the serum of vaccinated fish and injected these antibodies into naive (unvaccinated) cod and demonstrated that this passive transfer of antibodies is sufficient to protect the recipients against the disease. Such knowledge is necessary for developing better vaccines for Atlantic cod, which is essential for the effective commercial farming of cod.

MHC class I and MHC class II genes for antigen presentation and antigen receptor genes and their mechanism of somatic diversification evolved 550-600 mya. Codfishes specifically lost MHC class II and function of the associated molecule CD4 100 mya, i.e. about 450-500 million years later. Immunologic research of non-model organisms have been difficult due to lack of specific antibodies. We will inject partially purified cod leukocytes into mice and generate hybridomas for monoclonal antibody production and make polyclonal antibodies to synthetic peptide sequences derived from cod proteins. With these novel tools and with established technologies, VACSACOD will characterize the unique immune system of cod. We will isolate and purify leukocytes from cod and characterize T-cell responses to establish signatures of protective immunity to monitor vaccination regimes. We will determine the role of T cells in graft rejection and antibody responses. Pathogen-specific antibodies derived from B cells are essential for immune protection in other teleosts and mammals, but their role in codfishes is questioned. We will investigate how these antibodies contribute to protection in the established vaccine against vibriosis. We will determine whether cod B cells can present foreign antigen to T cells in spite of the lack of MHC class II in this species. We will determine the location in tissues of other antigen-presenting cells and investigate their function in vivo. We will develop Atlantic cod immunologic research and vaccinology. Because of the unique immune system of cod, vaccinology based on research in model fish or other cold-water species is likely to come short in developing efficient vaccines for cod. Conversely, the immune system of cod could reveal novel mechanisms that also operate in other species but have escaped notice due to a minor role in MHC class II-positive organisms. Such mechanism may nevertheless be exploited for therapeutic benefit.