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In fish, like in mammals, professional antigen presenting cells like dendritic cells, macrophages and B cells are phagocytic cells that ingest, process and present antigens for T cells via MHCII. Neutrophils are professional phagocytic cells with an oxygen-dependent degradation mechanism. By use of a monoclonal antibody against neutrophils in Atlantic salmon, we have shown that the neutrophil granulocytes are MHCII-positive cells. The neutrophils were isolated by magnetic cell sorting and morphological characterization and phenotypic analyses were performed. After in vitro challenge with bacteria, IL12p40, which is essential for proliferation of naive T cells, were upregulated. Further, Atlantic salmon was bath challenge with the same bacteria as the in vitro challenge experiment and the fraction of neutrophil granulocytes, B cells and MHCII positive cells in primary and secondary immune organs were measured by flow cytometry. Antigen-presentation in fish will be discussed.

Lumpfish (Cyclopterus lumpus L.) has shown to be an efficient biological tool in the fight against salmon lice (Lepeophtheirus salmonis) and are chosen by many fish farmers in Norway as an alternative to medicinal treatment. However, to improve the fish health and increase the overall efficiency of the cleaner fish strategy, more knowledge about its immune system and protective vaccines are required. We will present the current knowledge of its immune cells and its innate and adaptive immune responses upon bacteria challenge.