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 niloticu s) as an alternative experimental model to mammals for preliminary chemical immunotoxicity risk assessment is being evaluated by examining the Nationa l Toxicology Program's standard battery of rodent immunotoxicity assays in chemical-treated 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[alpha]p yrene (B[alpha]P). Reduced antibody production against sheep red blood cell (SRBC) antigen in response to B[alpha]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, art effec t also reported in rodents. Although the normal teleost immune responsivene ss was weaker than seen with mice under comparable conditions (presumably d ue to differences in antibody structure of teleosts), tilapia were found to exhibit well-defined primary and secondary humoral responses to SRBC, and an immunotoxic response to B[alpha]P comparable to the rodent model.