FUNCTIONAL-CHARACTERIZATION OF A MACROPHAGE-ACTIVATING FACTOR PRODUCED BY LEUKOCYTES OF GILTHEAD SEABREAM (SPARUS-AURATA L.)

Relatively little is known about factors that modulate in vivo lower v ertebrate phagocyte responses, particularly in fish. In this study we report that head-kidney leucocytes from the marine fish gilthead seabr eam (Sparus aurata L.) release soluble macrophage-activating factor/s (MAF) after stimulation with concanavalin A (Con A) and phorbol myrist ate acetate (PMA). Migration, phagocytosis, reactive oxygen intermedia tes (ROI) production and bactericidal activity were enhanced after inc ubation of target phagocytes with the MAF-containing supernatants. In order to ascertain the effect of MAF and bacterial lipopolysaccharide (LPS) on ROI and reactive nitrogen intermediates (RNI) production in g ilthead seabream macrophages, macrophages were incubated with MAF in t he presence of LPS. The results revealed that co-stimulation of macrop hages with MAF and LPS inhibited O-2(-) production but synergistically induced release of nitric oxide. These data suggest that the main act ivities of fish phagocytes are regulated by cytokines, which can inter act positively or negatively with pathogen-derived molecules to determ ine the final activation state of the cells. (C) 1998 Academic Press L imited.