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.