Enhanced lysozyme production in Atlantic salmon (Salmo salar L.) macrophages treated with yeast beta-glucan and bacterial lipopolysaccharide

Atlantic salmon head kidney macrophages grown in the presence of particulat e yeast beta -glucan and bacterial lipopolysaccharide (LPS) showed increase d production of lysozyme in the culture supernatants compared to non-treate d controls. The increased lysozyme production started at day 3 and was five - to six-fold higher compared to controls at day 6 in culture. beta -Glucan showed an approximate linear dose-response curve between 1 and 250 mug ml( -1) whereas LPS showed a dose-response curve with a well-defined optimum co ncentration (10 mug ml(-1)). The increase in lysozyme activity was accompan ied by an accumulation of lysozyme gene transcript in the stimulated cells. Recombinant human tumor necrosis factor alpha, known for its ability to st imulate lysozyme in human macrophages and to elevate respiratory burst acti vity of rainbow trout macrophages, failed to stimulate lysozyme production of Atlantic salmon macrophages. Macrophages isolated from fish suffering fr om a non-lethal Ichthyobodo necator infection displayed a highly increased ability to produce lysozyme in response to both beta -glucan and LPS. As in higher vertebrates, lysozyme production may reflect the differentiation st age of the Atlantic salmon macrophages as well as a direct activation of ly sozyme gene transcription by biological response modifiers. The rather late increase in lysozyme production induced by beta -glucan and LPS may thus b e explained by stimulation of differentiation of the macrophages in culture eventually combined with direct activation of transcription of the lysozym e gene. (C) 2001 Academic Press.