Effects of high doses of cortisol on innate cellular immune response of seabream (Sparus aurata L.)

The effects of high doses of cortisol, biologically the most active corticosteroid in the circulating blood of teleost fish, on gilthead seabream (Sparus aurata L.) leucocytes were determined. Leucocytes isolated from the head-kidney (the principal haemopoietic organ of this fish species) were incubated with five different concentrations (ranging from 0 to 10(-1) mM) of cortisol for 30, 120, 240, 360, and 480 min and their effects on leucocyte viability and some of the main innate cellular immune responses were evaluated. The viability and the cytotoxic activity of leucocytes against tumor cells were not significantly affected by in vitro incubation with cortisol, at any of the assayed concentration or incubation times. With cortisol concentrations of 10(-9), 10(-7) or 10(-5) mM, the respiratory burst activity of head-kidney leucocytes were significantly depressed after 30 min of incubation. On the other hand, with cortisol concentrations of 10(-1) mM, the phagocytosis of yeast cells and the total peroxidase content of leucocytes were significantly depressed at incubation times longer than 240 min. To corroborate that the observed effects were due to the cortisol treatment, assays were developed using both cortisol and cycloheximide, which blocked the inhibitory effects of cortisol. The present results demonstrate that cortisol plays an important role in the down-regulation of phagocytic but not of cytotoxic activity in seabream leucocytes. (C) 2004 Elsevier Inc. All rights reserved.