Effect of an immunopotentiator on Aeromonas salmonicida infection in rainbow trout (Salmo gairdneri).

The immunoactive peptide FK-565 (heptanoyl-y-D-glutamyl-(L)-mesodiaminopimelyl-(D)-alanine) was found to induce protection against intraperitoneal Aeromonas salmonicida infection in rainbow trout (Salmo gairdneri Richardson). The survival rate was as high as 60% when FK-565 was given intraperitoneally as a single dose (1mg/kg) one day before bacterial challenge. A non-specific stimulation of phagocytic cells by FK-565 at an early stage of the bacterial infection may contribute to the resistance observed. The phagocytic activity of peritoneal phagocytic cells as well as phagocytic cells of the pronephros were stimulated by FK-565 in vivo and in vitro, respectively, as compared to untreated control fish. Furthermore, decreased activity of phagocytic cells previously immunosuppressed with cyclophosphamide was rapidly restored by application of FK-565.