AN INVITRO TECHNIQUE FOR SURVEYING IMMUNOSTIMULANTS IN FISH

In vitro assays were developed to investigate the effects of immunosti mulants on leukocytes in spleen sections of rainbow trout (Oncorhynchu s mykiss). Fish spleens were divided, and individual sections were pla ced in 10 ml of tissue culture media and 0.1, 1, 10, or 100 mug/ml dil utions of Levamisole, QAC (quaternary ammonium compound), or ISK (a po lypeptide). After 4 days of incubation, cell suspensions were prepared to examine the effects of the immunostimulants on neutrophil oxidativ e activity using the nitroblue tetrazolium (NBT) assay and on phagocyt ic activity by engulfment of glutaraldehyde-fixed sheep red blood cell s. QAC induced a heightened activity in plates receiving 0.1 and 1.0 m ug/ml, but suppressed activity at 10 and 100 mug/ml levels. Sections i ncubated with ISK showed heightened responses at all doses except 100 mug/ml. Levamisole showed heightened responses at all doses in the NBT assay, and at the 1.0 and 10 mug/ml doses in the phagocytic assay.