MODULATION OF THE RESPIRATORY BURST ACTIVITY OF MEDITERRANEAN SEA BASS (DICENTRARCHUS-LABRAX L.) PHAGOCYTES BY GROWTH-HORMONE AND PARASITICSTATUS

The immunoregulatory role of GH in sea bass (Dicentrarchus labrax), in relation to the intensity of infection by the myxosporean parasite Sp haerospora dicentrarchi, was investigated. The in vitro detection of s uperoxide anion (O-2(-)) in head kidney phagocytes was optimised using the nitroblue tetrazolium (NBT) assay. O-2(-) production was proporti onal to the quantity of total protein per well, and 15 and 30 min of P MA triggering gave the highest stimulation index. Cells adhered overni ght produced more O-2(-) than cells adhered for 3 h. Trifluoperazine a bolished the reduction of NBT almost completely, whereas superoxide di smutase only caused 37.4% inhibition. Cells from fish parasitised by S . dicentrarchi, produced higher levels of O-2(-) compared with non-par asitised fish. Overnight priming with 5 nM recombinant rainbow trout g rowth hormone (rtGH) produced a significant increase in the respirator y burst of phagocytes from non-parasitised fish. Phagocytes from fish with medium intensity of infection attained the maximum response at 50 nM and 150 nM rtGH. LPS (20 mu g ml(-1)) priming did not induce an in crease in O-2(-) production, but it significantly increased cell adher ence in non-parasitised fish. (C) 1998 Academic Press Limited.