YEAST BETA-GLUCAN STIMULATES RESPIRATORY BURST ACTIVITY OF ATLANTIC SALMON (SALMO-SALAR L) MACROPHAGES

Previous studies have shown that head kidney macrophages isolated from glucan injected rainbow trout (Oncorhychus mykiss) and Atlantic salmo n (Salmo salar L.) have increased ability to kill Aeromonas salmonicid a. The present work was aimed at investigating the in vitro effects of glucan on the respiratory burst and bactericidal potential of Atlanti c salmon head kidney macrophages. Salmon macrophages were incubated fo r 1-7 days with various concentrations of yeast beta-glucan (MacroGard (R)) and tested for respiratory burst activity by the reduction of nit roblue-tetrazolium (NBT) after exposure to phorbol myristate acetate ( PMA) or opsonized zymosan. The macrophages showed a marked increase in respiratory burst activity 4 to 7 days after addition of glucan. Macr ophages treated with 0.1-1 mu g mL(-1) gave a maximum respiratory burs t response, whereas 10 mu g mL(-1) had no effect and 50 mu g mL(-1) wa s inhibitory, The glucan also triggered respiratory burst activity dir ectly, but this occurred only at relative high concentrations with a m aximal effect at greater than or equal to 200 mu g mL(-1). The validit y of using the NET-assay as a measure of respiratory burst activity wa s confirmed by using inhibitors of O-2(-) production (superoxide dismu tase, trifluoperazine and diphenylene iodonium). Despite the stimulato ry effect of glucan on the respiratory burst activity of salmon macrop hages, these cells did not show Introduction increased bactericidal ac tivity against the avirulent and virulent strain of A. salmonicida. Up regulation of burst activity alone is thus apparently not sufficient t o enhance bactericidal activity against this pathogen by Atlantic salm on macrophages.