Effects of creosote exposure on rainbow trout pronephros phagocyte activity and the percentage of lymphoid B cells

An outdoor microcosm study was conducted in order to evaluate the kinetics of immunomodulation in rainbow trout (Oncorhynchus mykiss) exposed to liqui d creosote. Fish were sampled on d 7, 14, 21, and 28 from microcosms dosed initially with 0, 3, and 10 mul/L of creosote. Pronephros leukocytes were m onitored for phagocytic activity, oxidative burst, and surface immunoglobul in-positive (Slg*) B-cell counts. Oxidative burst was inhibited by creosote exposure; however, by sampling d 28, the burst response returned to near c ontrol levels. Phagocytic activity, on the other hand, was stimulated, peak ing on sampling d 7, then returning to near control levels by d 28. Althoug h control Slg(+) B-cell counts were quite variable across sampling days, Sl g(+) B-cell counts were also elevated in creosote-exposed fish after seven days of exposure. Slg(+) B-cell numbers decreased significantly to near con trol levels during the remainder of the study. The overall results from thi s study confirm that creosote has the potential to alter certain immune par ameters, and emphasize the importance of monitoring changes in the immune s ystem during exposure. Polycyclic aromatic hydrocarbons (PAHs), a major con stituent of liquid creosote, are the suspected immune-altering agents.