Functional characterisation of a macrophage-activating factor produced by leucocytes of gilthead seabream (Sparus aurataL.)

Relatively little is known about factors that modulatein vivolower vertebrate phagocyte responses, particularly in fish. In this study we report that head-kidney leucocytes from the marine fish gilthead seabream (Sparus aurataL.) release soluble macrophage-activating factor/s (MAF) after stimulation with concanavalin A (Con A) and phorbol myristate acetate (PMA). Migration, phagocytosis, reactive oxygen intermediates (ROI) production and bactericidal activity were enhanced after incubation 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 gilthead seabream macrophages, macrophages were incubated with MAF in the presence of LPS. The results revealed that co-stimulation of macrophages with MAF and LPS inhibited O2−production but synergistically induced release of nitric oxide. These data suggest that the main activities of fish phagocytes are regulated by cytokines, which can interact positively or negatively with pathogen-derived molecules to determine the final activation state of the cells.