Yeast glucan induces increase in lysozyme and complement-mediated haemolytic activity in Atlantic salmon blood

Abstract

The activities of lysozyme, alkaline and acid phosphatase, N-acetyl-glucosaminidase and complement (as spontaneous haemolytic activity) were measured in plasma of Atlantic salmon, Salmo salar L., after intraperitoneal injection of a β -1,3 and β -1,6 linked glucan from Saccharomyces cerevisiae . The glucan has previously been shown to induce resistance of Atlantic salmon to several bacterial pathogens. The glucan treatment resulted in increased activities of lysozyme 1–3 weeks and complement 2–4 weeks after injection. The activities of alkaline phosphatase and N-acetyl-glucosaminidase showed a decrease 1 week after injection and then slowly restored to normal levels, whereas acid phosphatase was only slightly altered during the experimental period. These results indicate that the glucan induces a selective increase in lysozyme rather than a general release of lysosomal enzymes. The time intervals of enhanced activities of lysozyme and complement partially overlapped with the time intervals of expected enhanced protection against pathogens. Thus, induction of increased activities of lysozyme and complement may, at least in part, explain the mechanisms by which glucan induces protection against bacterial pathogens in salmon.