Sensitivity of rainbow trout leucocytes to aflatoxin B1

In vitroexposure of rainbow trout (Oncorhynchus mykiss) peripheral blood leucocytes to aflatoxin B1(AFB1) leads to a dramatic suppression of immunological function as indicated by decreased lymphocyte proliferation and immunoglobulin production in response to the mitogen lipopolysaccharide. These leucocytes were up to 1000-fold more sensitive to this carcinogen than were murine leucocytes. Additionally, leucocytes procured from trout during July–December were significantly (P=0·01) more sensitive to AFB1than those obtained during January–June. Immunosuppression was observed with AFB1concentrations that were not toxic as measured by cell viability. This decrease in AFB1sensitivity appears to occur subsequent to a generalised winter-associated period of decreased immune reactivity that has been observed in a number of ectothermic species and in this study.