The production of a macrophage-activating factor from rainbow trout Salmo gairdneri leucocytes

Rainbow trout head kidney and blood leucocytes are shown to be capable of secreting a soluble macrophage-activating factor (MAF) after stimulation with concanavalin A (Con A). The presence of phorbol myristate acetate (PMA) as a co-stimulant increased the production of MAF. Both respiratory burst activity (nitroblue tetrazolium, NBT, reduction and H2O2 production) and bactericidal activity were enhanced after incubation of resident or elicited macrophages with the MAF-containing supernatants for 48-72 hr. The target culture period before the addition of MAF did not affect their responsiveness, but a continuous presence of MAF was necessary for maximal stimulation.