Subacute immunotoxic effects of the polycyclic aromatic hydrocarbon 7,12-dimethylbenzanthracene (DMBA) on spleen and pronephros leukocytic cell counts and phagocytic cell activity in tilapia (Oreochromis niloticus)

Abstract

Tilapia (Oreochromis niloticus) were exposed by intraperitoneal injection of the polycyclic aromatic hydrocarbon (PAH) 7,12-dimethylbenzanthracene (DMBA). The relative effects of this carcinogenic PAH on total cellularity and histology of the spleen and pronephros, as well as on the functional capacity of phagocytic cells isolated from both spleen and pronephros, were evaluated as possible indicators of chemical-induced immunotoxicity. Spleen and pronephros total white blood cell counts were reduced, in most cases, in a dose-related manner by DMBA. Marked hypocellularity was also observed histologically in the lymphoid regions of the spleen of DMBA-exposed fish. However, the ability of pronephros and spleen phagocytic cells to phagocytize foreign particles (fluorescent micro- spheres) was not altered by exposure to DMBA unless dose levels associated with signs of chemical toxicity (reduced swimming and feeding activity, increased cutaneous pigmentation, and increased mortality) were used. When the phagocyte chemiluminescent response was evaluated, there was again no depression of superoxide radical (hydrogen peroxide) produc- tion unless other signs of chemical toxicity were apparent. These data suggest that total leukocyte counts in tilapia hematopoietic organs may represent more sensitive indicators of environmental PAH exposure than does phagocytic activity or chemiluminescent response of phagocytes isolated from these organs. © 1998 Elsevier Science B.V. All rights reserved