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

Amoebic gill disease (AGD) is a disease caused by the ectoparasite <i>Neoparamoeba perurans</i> which affects several cultured marine fish worldwide. The characterization 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. This method is a variant of traditional quantitative RT-PCR whereby RNA was extracted and reverse transcribed from gill samples obtained using a biopsy punch from designated areas of the gill from fish. In theory this method could be used to map the transcriptional responses throughout the entire gill with the resolution of the mapped changes dependent on the number and size of gill subsamples. In the present study we restricted our subsample area to eight 2 mm biopsy punches from the dorsal portion of the second left gill arch of each individual fish. 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. Furthermore, a correlation analysis between CD8-α and TCR-α showed that the mRNA expression of these two genes was strongly positively correlated (r = 0.9). Contrary to previous studies, our data suggest that the parasite, <i>N. perurans</i>, 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.