DEVELOPMENT AND VALIDATION OF THE ANTIBODY-FORMING CELL RESPONSE AS AN IMMUNOTOXICOLOGICAL END-POINT IN THE GUINEA-PIG

The mouse and rat are often the species of choice in standard toxicolo gical testing. However, due to potential differences in chemical metab olism between these species and humans, they may in some instances be inappropriate models for chemical safety assessment. Because the guine a pig is a well-known model for chemical sensitization and hypersensit ivity testing, the objective of the present study was to develop the h emolytic plaque assay in the guinea pig for use as an immunotoxicologi cal endpoint in toxicology studies where metabolic differences between this and other rodent species may affect risk characterization. The p resent study encompassed six experiments designed to address route of administration, appropriate number of sheep red blood cells (sRBC) for immunization, time course after immunization, and a validation experi ment to test the ability to detect suppression produced by a known imm unosuppressant. Animals were observed daily for morbidity, mortality, and any signs of distress, Animals were weighed and euthanized and spl eens were collected and weighed. The plaque assay was performed and th e number of antibody-forming cells (AFC)/spleen, AFC/10(6) splenocytes , and total spleen cellularity was determined. The data indicate that retroorbital injection of 2 x 10(9) sRBC in a volume of 0.5 mt 5 days prior to euthanasia produces the peak AFC response in the guinea pig. In addition, IP injection of cyclophosphamide (30 mg/kg day(-1)) for 6 days prior to euthanasia produces profound immunosuppression in the a bsence of any observed overt toxicity. The peak serum anti-sRBC enzyme -linked immunosorbant assay (ELISA) response is delayed in comparison to the AFC response, and occurred on day 8 after retroorbital immuniza tion in the guinea pig.