In vitro immunostimulation of rainbow trout (Oncorhynchus mykiss) spleen cells with levamisole.

An in vitro immunization and cultivation method for fish spleen organ sections was used to investigate the effects of levamisole on the immune response. 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. The specific immune system activity was shown by the passive hemolytic plaque assay demonstrating the numbers of antibody-producing cells. Elevations were found in nonspecific defense and specific immune response in the 5 micrograms/ml levels of levamisole. The 25 micrograms/ml levels instigated a slight elevation in some nonspecific levels but showed suppression in the specific immune response. 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 defense stimulators, and a synergistic effect was evident when combined with 25 micrograms/ml and 5 micrograms/ml levels of levamisole.