IN-VITRO EFFECTS OF THE EXTRACELLULAR PROTEIN OF RENIBACTERIUM-SALMONINARUM ON PHAGOCYTE FUNCTION IN BROOK TROUT (SALVELINUS-FONTINALIS)

Renibacterium salmoninarum is a facultative intracellular pathogen oft en found in host phagocytes where it appears to successfully avoid the host fish's immunological defenses. The objective of this investigati on was to determine if soluble extracellular protein (ECP) produced by R. salmoninarum may contribute to the immunomodulation in bacterial k idney disease (BKD) via inhibition of phagocyte respiratory burst and/ or phagocytosis mechanisms. Splenic cells from adult brook trout (Salv elinus fontinalis) were incubated with two different concentrations of ECP(0.1 mg/ml and 1.0 mg/ml) and viable R. salmoninarum. Splenic cell cultures were evaluated for respiratory burst activity via flow cytom etry with the dichlorofluorescin diacetate (DCF-DA) assay and for phag ocytosis via light microscopic assessment of microsphere engulfment. R espiratory burst activity was significantly inhibited in all treatment groups as compared to untreated fish, while no differences were noted in phagocytic activity. (C) 1998 Elsevier Science B.V.