Immune Gene Expression Profliing in Atlantic Salmon during Amoebic Gill Disease

Immune gene expression profiling can provide valuable information about pathogenesis of a disease and mechanisms of protection. Amoebic gill disease (AGD) is a condition affecting some species of farm-reared marine fish caused by Neoparamoeba perurans. This disease has been reported from Australia, USA, Norway, Ireland, Spain, Scotland, Chile, Canada and New Zealand and in all these countries it has been associated with the presence of N. perurans.  Amoebic gill disease (AGD) is the most serious health problem of farmed Atlantic salmon in Tasmania. We have used functional genomics and proteomics to improve our understanding of this disease. A significant increase in expression of the mRNA of IL-1b, TNF-a, TCR-a chain, CD8, CD4, MHC-IIa, MHC-I, IgM and IgT was observed in the gills of AGD-affected fish on day 10 post-infection. A long term AGD challenge trial showed very minor changes in immune gene expression with the exception of MHC-II, CD4 and CD8 downregulated in the AGD lesions and MHC-I close to AGD lesions. In another study C-reactive protein, apolipoprotein 1, granulin, cathepsin, angiogenin-1 were upregulated in gill mucus of fish affected by AGD for 18 weeks. As our understanding of the fish immune response increases and new tools become available our interpretation of the immune response in AGD and other amoebic infections of fish will improve leading to practical solutions for this disease.