In vitro effect of levamisole on the neutrophil activity in rainbow trout (Oncorhynchus mykiss).

An in vitro immunization and cultivation method for fish spleen organ section was used to investigate the effects of levamisole on the neutrophil activity. After 10 days of culture with either 50 micrograms/ml, 25 micrograms/ml, 5 micrograms/ml or no levamisole in the media, the nonspecific defense reactions were measured by determining the metabolic activity of neutrophils by using the nitroblue tetrazolium test, and phagocytic and adherence indexes by incubating the fish cells with suspensions of formalin-killed Staphylococcus aureus. Elevations were found in nonspecific cellular defense in the 5 micrograms/ml levels of levamisole. The 25 micrograms/ml levels instigated a slight elevation in nonspecific cellular defense and the 50 micrograms/ml levels suppressed all indicators, whether levamisole was given alone or combined with Yersinia ruckeri O-antigen or DNP-Ficoll. These antigens are themselves nonspecific cellular defense stimulators, and a synergistic effect was evident when combined with 25 micrograms/ml and 5 micrograms/ml levels of levamisole.