LEUKOCYTE HYPOCELLULARITY IN THE SPLEEN AND PRONEPHROS OF TILAPIA (OREOCHROMIS NILOTICUS) EXPOSED TO 2,3,7,8-TETRACHLORODIBENZO-p-DIOXIN (TCDD) MAY RESULT FROM ANTIPROLIFERATIVE EFFECTS AND ENHANCED APOPTOSIS

Abstract

Tilapia (Oreochromis niloticus) were subacutely exposed to the environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) by intraperitoneal injection of 1 or 5 mug/kg/day for five consecutive days. Cellularity and morphology of the spleen and pronephros were evaluated two days following dosing. Total cell counts in both the spleen and pronephros were significantly reduced by the 5-mug/kg but not the 1-mug/kg dose of TCDD. Cellular depletion was evident histologically at the higher dose level, particularly within lymphoid regions of the fish spleen and pronephros. Increased numbers of apoptotic cells were observed in the histologic preparations. Light microscopic analysis of cytospin samples from the pronephros of chemical-treated fish verified the increased incidence of cells displaying features typical of apoptosis (condensed nuclei and cytoplasmic fragmentation). Subsequent flow cytom etric evaluation using the DNA-binding dye, 7-aminoactinomycin D (7-AAD), demonstrated a population of apopto...