Inhibition of macrophage activity by mitogen-induced goldfish leukocyte deactivating factor

Macrophage activating and deactivating cytokines have been characterized in mammalian systems but little is known about these immunoregulatory molecul es in fish. Using gel permeation and chromatofocusing fast performance liqu id chromatography (GP-FPLC and C-FPLC) we partially purified a macrophage d eactivating factor (MDF) from mitogen-induced goldfish kidney leukocytes. I nhibition of the macrophage-derived nitric or;ide (NO) response induced by this MDF was time-, dose- and temperature-dependent. Macrophages pre-treate d for 6 or 24 h with MDF before activation with macrophage activating facto rs (MAF) and/or bacterial lipopolysaccharide (LPS) exhibited a down-regulat ion in their NO response, while those treated with MDF 24 h after activatio n with MAF and LPS did not. MDF treatment also impaired the NO response of goldfish macrophages infected with the mammalian protozoan parasite Leishma nia major. These results suggest that MDF exhibits its inhibitory effect do wnstream of the converging intracellular pathways induced by LPS and/or L. major. The novel teleost MDF has an approximate M-r of 15 kD and a pI < 4, and is the first endogenous molecule of teleosts known to down regulate mac rophage antimicrobial responses. (C) 1999 Elsevier Science Ltd. All rights reserved.