Activation of immune mechanisms in Atlantic salmon (Salmo salar L.) by CpG oligonucleotides

Viral diseases cause severe problems for the aquaculture industry and development of efficient virus vaccines is a priority target. Cellular defence mechanisms, both innate and acquired, are especially important to combat viral infections. Therefore ident ification of adjuvants which promote stable induction of Th1 immunity, combined with minimal side effects, is requested. Unmethylated CpG oligodinucleotides (ODNs) within specific flanking bases are relatively abundant in bacterial DNA and are known to st imulate innate immune responses. CpG ODNs show promise as vaccine adjuvant in animal models, and are shown to give less side effects compared to other adjuvants. Studies by our group have shown that certain CpG ODNs induce cytokine expression, stimulate c ell proliferation and induce protection against IPN virus in Atlantic salmon. The innate immune system has evolved the ability to recognize CpG motifs in bacterial DNA via the Toll-like receptor (TLR) 9. In fish, the molecular mechanisms of pathogen-stimu lated TLR-mediated responses are largely unknown. Work by our group and others have demonstrated that fish leucocytes are activated by CpG DNA, indicating the existence of a TLR9 ortholog in salmon. The aim of this project is to clone full-length TLR9 gen e ortholog(s) in salmon, and to study function of CpG-stimulated innate immunity in fish. Knowledge about the various processes explaining how the immune system becomes activated by TLRs will be addressed.