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

The immunoregulatory role of GH in sea bass (Dicentrarchus labrax), in relation to the intensity of infection by the myxosporean parasiteSphaerospora dicentrarchi, was investigated. Thein vitrodetection of superoxide anion (O2−) in head kidney phagocytes was optimised using the nitroblue tetrazolium (NBT) assay. O2−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 O2−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 byS. dicentrarchi, produced higher levels of O2−compared with non-parasitised fish. Overnight priming with 5 nMrecombinant 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 nMand 150 nMrtGH. LPS (20 μg ml−1) priming did not induce an increase in O2−production, but it significantly increased cell adherence in non-parasitised fish.