Eosinophilic granule cells of salmonids: potential targets for anti-inflammatory therapy in fish

Eosinophilic granule cells (EGCs) have been likened to mammalian mast cells. Intraperitoneal injection of Aeromonas salmonicida and Vibrio anguillarum extracellular products induces migration and degranulation of intestinal EGCs in rainbow trout (Oncorhynchus mykiss ). Similarly EGC necrosis in the gut is commonly observed with Infectious Haemopoeitic Necrosis Virus (IHNV) infections. Pharmacological agents such as compound 48/80 which induce degranulation in mammalian mast cells cause time-dependent morphological changes and degranulation in EGCs both in vivo and in vitro. The combined evidence to date suggests striking similarities between EGCs and mammalian mast cells, suggesting that EGCs may be involved in the nonspecific defence mechanisms or inflammatory responses in fish. The potential therefore exists for the development of therapies which target EGCs and their responses in order to modulate inflammatory responses in fish.