STIMULATION OF RESPIRATORY BURST AND PHAGOCYTIC-ACTIVITY IN ATLANTIC SALMON (SALMO-SALAR L) MACROPHAGES BY LIPOPOLYSACCHARIDE

The present paper describes the effect of lipopolysaccharides (LPS) fr om Aeromonas salmonicida and other Gram-negative bacteria on the respi ratory burst, phagocytosis and bactericidal activity of head kidney ma crophages from Atlantic salmon (Salmo salar L.) in vitro. Macrophages were first cultured in the presence of various concentrations of LPS f rom A. salmonicida for 1, 2 and 5 days and then tested for respiratory burst activity (reduction of nitroblue tetrazolium) after exposure to phorbol myristate acetate (PMA). The most marked increase in respirat ory burst activity of LPS-treated macrophages was observed after 5 day s of incubation with 1, 10 and 100 mu g LPS ml(-1). The increase appea red to be dose-dependent with a maximal response at 10 mu g ml(-1). At this LPS-concentration and incubation time the respiratory burst acti vity was 3.9 times larger in the treated macrophages than in the contr ol macrophages. LPS from three other Gram-negative bacterial; salmon p athogens and two non-fish pathogens also enhanced the respiratory burs t activity of salmon macrophages. Macrophages incubated with 10 and 50 mu g LPS ml(-1) also showed a significant increase in PMA-stimulated H2O2-production after 5 days of incubation. LPS also stimulated the ph agocytic activity of Atlantic salmon macrophages against opsonized and nonopsonized glucan particles, and glutaraldehyde-fixed sheep red blo od cells. LPS-treated macrophages showed an increased ability to kill an avirulent A-layer lacking strain of A. salmonicida, but not a virul ent A-layer positive strain. (C) 1995 Academic Press Limited