Immunological and Apoptic Studies of Dimethylbenzanthracene (DMBA)-Induced Toxicity as Possible Ecotoxicological Bioindicator in Tilapia (Oreochromis niloticus)

Polycyclic aromatic hydrocarbons (PAH) have become widespread environmental contaminants. The aquatic environment has been regionally contaminated, sometimes heavily, with a variety of immunotoxic pollutants. The aim of the present study is to evaluate the effects of DMBA (Dimethylbenzanthracene), on immune parameters in tilapia. Further, apoptic cells were also evaluated as an endpoint of immunotoxic substances. The data show that peripheral total blood cellularity was significantly reduced and differential leukocyte counts revealed a significant reduction in fish exposed to 5 and 15 mg DMBA /Kg dose groups. Spleen/body weight ratios for the 5 mg/Kg dose showed a non-significant increasing trend. This trend reached significance at the 15 mg/Kg dose. In addition to splenic size, total cellularity of the spleen increased significantly in fish exposed to 15 mg/Kg DMBA. Pronephric total cellularity was significantly reduced by DMBA at both the 5 mg/Kg and 15 mg/Kg doses. In addition, at 15 mg/ Kg DMBA, an increase in percentages of apoptotic cells was evident in cyto-centrifugation preparations stained with Giemsa. The Cyto-centrifugation of spleen leukocytes followed by staining with Acridine Orange showed that the 15 mg/Kg DMBA causes an increase in percentage cells. Pronephric leukocytes from the 15 mg/Kg dose group displayed significant morphological changes and decrease in total number. Cyto-centrifugation of pronephros lymphocytes stained with Acridine Orange showed a noticeable increase in apoptotic cells in this hematopoietic compartment when stained with Acridine Orange at dose 15 mg / Kg. The transformed lymphocytes in control group and after DMBA showed insignificant decrease of the transformed cells at dose 15 mg/Kg. Therefore, the present data suggest that fish are immunologically sensitive, and may represent a viable alternate species to mammals for evaluating chemical-induced immune toxicity.