Modulation of the respiratory burst activity of Mediterranean sea bass (Dicentrarchus labraxL.) phagocytes by growth hormone and parasitic status

Abstract The immunoregulatory role of GH in sea bass ( Dicentrarchus labrax ), in relation to the intensity of infection by the myxosporean parasite Sphaerospora dicentrarchi , was investigated. The in vitro detection of superoxide anion (O 2 − ) in head kidney phagocytes was optimised using the nitroblue tetrazolium (NBT) assay. O 2 − production was proportional to the quantity of total protein per well, and 15 and 30 min of PMA triggering gave the highest stimulation index. Cells adhered overnight produced more O 2 − than cells adhered for 3 h. Trifluoperazine abolished the reduction of NBT almost completely, whereas superoxide dismutase only caused 37·4% inhibition. Cells from fish parasitised by S. dicentrarchi , produced higher levels of O 2 − compared with non-parasitised fish. Overnight priming with 5 n M recombinant rainbow trout growth hormone (rtGH) produced a significant increase in the respiratory burst of phagocytes from non-parasitised fish. Phagocytes from fish with medium intensity of infection attained the maximum response at 50 n M and 150 n M rtGH. LPS (20 μg ml −1 ) priming did not induce an increase in O 2 − production, but it significantly increased cell adherence in non-parasitised fish.