EFFECT OF INJECTED YEAST GLUCAN ON THE ACTIVITY OF MACROPHAGES IN ATLANTIC SALMON, SALMO-SALAR L, AS EVALUATED BY IN-VITRO HYDROGEN-PEROXIDE PRODUCTION AND PHAGOCYTIC CAPACITY

A prepared polysaccharide from the cell wall of yeast, M-Glucan, has p reviously been demonstrated to have immunostimulatory effects in salmo nids as observed by enhanced in vivo non-specific disease resistance i n Atlantic salmon, Salmo salar L., and increased in vitro bactericidal activity of rainbow trout, Oncorhynchus mykiss (Walbaum), macrophages . In the present study M-Glucan was injected intraperitoneally into At lantic salmon and the effect on core components in the non-specific pa rt of the immune system was observed. The hydrogen peroxide (H2O2) pro duction of isolated head kidney macrophages from glucan-injected fish was measured 3 and 6 weeks after M-Glucan treatment and was increased at both time-points upon phorbol myristate acetate- (PMA) triggering. Without PMA triggering the difference was only significant 3 weeks aft er glucan injection when compared to a control group injected with sal ine. In a phagocytic assay with macrophages and Vibrio salmonicida the initial uptake of bacteria was elevated at both 3 and 6 weeks after g lucan treatment. There was no significant difference when uptake of an other fish pathogenic bacteria, Renibacterium salmoninarum, was studie d. Treatment of Atlantic salmon with M-Glucan also resulted in enhance d serum lysozyme activity in week 3 of the experimental period. The re sults indicate that M-Glucan elevates the activity of the nonspecific part of the immune system and the use of M-Glucan as an immunostimulan t is discussed.