FACTORS INFLUENCING PHAGOCYTIC RESPONSE OF MACROPHAGES FROM THE SEA BASS (DICENTRARCHUS-LABRAX L) - AN ULTRASTRUCTURAL AND QUANTITATIVE STUDY

Background: Although phagocytosis is considered the main nonspecific d efense mechanism in fish, the significance of the influence of bacteri al properties and assay conditions on this mechanism has not been esta blished, We report the influence of leukocyte source, bacterial specie s, presence or absence of a bacterial wall, bacterial status (live or dead), and bacterial opsonization on in vitro phagocytosis by sea bass (Dicentrarchus Labrax L.) macrophages. Methods: Leukocytes were chall enged with bacteria under different conditions and ultrastructurally s tudied, The number of phagocytic macrophages and the number of bacteri a ingested per macrophage were quantified by microscopical counting, a nd the data obtained were statistically analyzed following general lin ear models. Results: Macrophages from sea bass peritoneal exudate show ed a greater capacity to engulf bacteria than did these isolated from blood, which, in turn, had greater engulfment properties than did thos e isolated from head-kidney, Greater phagocytic activity was observed in the assays carried out with Escherichia coli than in those carried out with Salmonella typhimurium, especially when the TA1950 S. typhimu rium strain (with wall) was used, Macrophages showed greater phagocyti c activity against live bacteria, Bacterial opsonization had a variabl e effect on phagocytosis. Sea bass macrophages did not always ingest t he same number of bacteria. Conclusions: Sea bass macrophages have str ong bacterial phagocytic activity, Significant differences were found that had been influenced by bacterial properties as well as by assay c onditions, Positive correlation between the number of phagocytic macro phages and the number of bacteria ingested per phagocyte was observed. (C) 1997 Wiley-Liss, Inc.