Evidence of immune and inflammatory processes in the gills of AGD-affected Atlantic salmon, Salmo salar L.

• 2D quantitative RT-PCR was used to map the transcriptional responses in AGD-affected gills of Atlantic salmon.
• Neoparamoeba perurans elicits a classical inflammatory response in the gills of AGD-affected A. salmon.
• Expression of immune genes within gill lesions misrepresents the cellular immune response in the gills during AGD.
• AGD elicited an increased expression of cellular markers, most notably antigen presenting cells, B-cells and T-cells.
• T-cells within the AGD-affected gills are mainly constituted of CD8+ cells and not CD4+ T-cells.

Amoebic gill disease (AGD) is a disease caused by the ectoparasite Neoparamoeba perurans which affects several cultured marine fish worldwide. The characterisation of pro-inflammatory and immune related genes at the mRNA level in AGD-affected Atlantic salmon gills was performed at 10 days post-inoculation using 2D quantitative RT-PCR, a method of mapping transcriptional responses in tissues. The genes of interest were IL-1β, TNF-α, TCR-α chain, CD8, CD4, MHC-IIα, MHC-I, IgM and IgT. A significant increase in expression of the mRNA of all the genes was observed in the gills of AGD-affected fish. Contrary to previous studies, our data suggest that the parasite, N. perurans, elicits a classical inflammatory response in the gills of AGD-affected fish and indicates that the mRNA expression of immune genes within gill lesions misrepresents the cellular immune response in the gills during AGD.