EICOSANOIDS AND THEIR ROLE IN IMMUNE MODULATION IN FISH - A BRIEF OVERVIEW

Eicosanoids have been demonstrated to play a central role in immune re gulation in mammals brought about by their direct effects on cells suc h as macrophages and lymphocytes or by their indirect effects via cyto kines. Studies have shown that fish mononuclear phagocytes, granulocyt es and thrombocytes synthesize and release both cyclooxygenase- and li poxygenase-derived products such as prostaglandin E(2), leukotriene B- 4 and lipoxin A(4). Whether lymphocytes have the ability to generate l eukotrienes and lipoxins is still unclear but they do appear to have 1 2-lipoxygenase activity that leads to the generation of 12-hydroxy fat ty acid derivatives. As in mammals, leukotriene and lipoxin biosynthes is requires the presence of a 5-lipoxygenase activating protein-like m olecule that is sensitive to the action of the specific inhibitor, MK- 886. The prostaglandin-generating ability of trout macrophages can be altered by incubation with lipopolysaccharide suggesting the possible presence of an inducible cyclooxygenase activity. Prostaglandins have been found to suppress the mitogen-induced proliferation of trout leuc ocytes and the generation of humoral antibody and plasma cells both in vivo and in vitro. The lipoxygenase products, leukotriene B-4 and lip oxin A(2), have more variable effects ranging from inhibition to stimu lation depending on the assay system employed. Overall, there is clear evidence that eicosanoids play a role in immune regulation in fish in a similar way to that reported in mammals. (C) 1995 Academic Press Li mited