THE HEMOLYTIC PLAQUE-FORMING CELL ASSAY IN TILAPIA (OREOCHROMIS NILOTICUS) EXPOSED TO BENZO[a]PYRENE: ENHANCED OR DEPRESSED PLAQUE FORMATION DEPENDS ON DOSING SCHEDULE

The prospect of utilizing the cichlid teleost tilapia (Oreochromis niloticus) as an alternative experimental model to mammals for preliminary chemical immunotoxicity risk assessment is being evaluated by examining the National Toxicology Program's standard battery of rodent immunotoxicity assays in chemicaltreated tilapia. The present report examines the hemolytic plaque forming cell assay (PFC), a quantitative indicator of antibody production, in tilapia exposed to the polycyclic aromatic hydrocarbon (PAH) benzo[a]pyrene (B[a]P). Reduced antibody production against sheep red blood cell (SRBC) antigen in response to B\[a]P was observed using the PFC assay, via reduction in plaque number. Under specific immunization circumstances, increased plaque formation was observed in chemical-exposed fish, an effect also reported in rodents. Although the normal teleost immune responsiveness was weaker than seen with mice under comparable conditions (presumably due to differences in antibody structure of teleosts), tilapia werefound toexhibit well-defined primary and secondary humoral responses to SRBC, and an immunotoxic response to B[a]P comparable to the rodent model.