Effect of different beta-glucans on the respiratory burst of turbot (Psetta maxima) and gilthead seabream (Sparus aurata) phagocytes

The in vitro effect of several beta-glucans on the respiratory burst of tur bot and gilthead seabream phagocytes was examined. Three particulated beta- glucans from yeast, Saccharomyces cerevisiae and a particulate glucan from the fungus Schizophyllum commune were used. In some experiments, cells were incubated for 1 or 2 h with a mixture of glucan (0-500 mu g ml(-1)) and ni troblue tetrazolium (NBT). In others, cells were preincubated with glucans for 1, 3 and 6 h and then incubated for Ih with NET with or without PMA. Ce lls from gilthead seabream and turbot responded similarly to glucans, and d ifferences in activity depended mainly on the concentration of glucans, the length of incubation period of cells and glucan, and on the glucan used. I ncubation of cells with glucans for 1 h directly induced a respiratory burs t which increased with the concentration of glucan. However, after 2 h incu bation a decrease in NET reduction occurred at the highest glucan concentra tions. An enhancement of the respiratory burst, which increased with the co ncentration of glucan, was also seen when cells were preincubated with gluc ans and then incubated with NET without PMA. However, when PMA was added to the NET solution, the highest NET reduction was found at low glucan concen trations whereas with higher concentrations of glucan the NET reduction dec reased significantly. Thus high concentrations of glucan directly induced r espiratory burst and led to exhaustion. Low concentrations of glucan primed the phagocytes to be capable of enhanced production of reactive oxygen spe cies on subsequent activation of the respiratory burst. The former may incr ease disease susceptibility, the latter increase resistance. (C) 1999 Acade mic Press.