EXPOSURE OF TILAPIAN FISH TO THE PESTICIDE LINDANE RESULTS IN HYPOCELLULARITY OF THE PRIMARY HEMATOPOIETIC ORGAN (PRONEPHROS) AND THE SPLEEN WITHOUT ALTERING ACTIVITY OF PHAGOCYTIC-CELLS IN THESE ORGANS

Tilapia were dosed by intraperitoneal injection for 5 consecutive days with either 20 or 40 mg/kg of the environmental contaminant hexachlor ocyclohexane (lindane). The effects of this organochlorine pesticide o n morphology and total cellularity of the spleen and pronephros were e xamined on the second day following termination of dosing. The functio nal capacity of phagocytic cells isolated from both spleen and proneph ros was also evaluated as possible additional indicators of chemical-i nduced immunotoxicity. A dose-related reduction was found in spleen an d pronephros total white blood cell counts in the fish exposed to lind ane. In addition, hypocellularity of lymphoid regions in the spleen an d pronephros was evident in chemical-exposed animals upon histopatholo gical examination. However, phagocytosis of fluorescent microspheres b y phagocytic cells isolated from the spleen and pronephros was not inh ibited by the exposure to lindane. Similarly, no decrease in phorbolmy ristate acetate (PMA)-stimulated hydrogen peroxide production was obse rved in phagocytic cells collected from lindane-exposed fish. These re sults suggest that cellular depletion in tilapia spleen and pronephros may represent a more sensitive indicator of lindane exposure than doe s the functional capacity of phagocytic cells isolated from these hema topoietic organs. Ultrastructural observations support this hypothesis and, further, suggest that lymphocytic cells may be targeted at the p resent exposure levels. (C) 1997 Elsevier Science Ireland Ltd.