NONSPECIFIC IMMUNE-RESPONSE OF NILE TILAPIA, OREOCHROMIS-NILOTICA, TOTHE EXTRACELLULAR PRODUCTS OF MYCOBACTERIUM SPP. AND TO VARIOUS ADJUVANTS

Nile tilapia were immunized by injecting extracellular products (ECP) of Mycobacterium spp. (strain TB40, TB267 or the type strain Mycobacte rium marinum) into their swim bladders. A variety of adjuvants - Freun d's complete adjuvant (FCA), Freund's incomplete adjuvant (FIA) and Ti tremax - were similarly injected into additional groups of tilapia. Ph osphate-buffered saline (PBS) was used as a control. The number of nit roblue tetrazolium (NBT)-positive cells observed in the swim bladder o f the immunized fish had significantly increased by the fourth day pos t-immunization. By day 8, the number of NBT-positive cells in fish imm unized with ECP from mycobacteria strains TB40 or TB267 were fewer tha n in fish immunized with ECP from M. marinum or fish injected with FCA or FIA. The level of lysozyme activity detected in the serum of fish 4 days after being immunized with ECP from various Mycobacterium spp. was also significantly higher than that found in the serum of the cont rol fish. Head kidney macrophages showed an enhanced reduction of NET when cultured in vine with 1 mu g ml(-1) of ECP. Concentrations greate r than this (10 or 100 mu g ml(-1)) were found to suppress the reducti on of NBT by the macrophages.