FURTHER EVALUATION OF THE INCORPORATION OF AN IMMUNOTOXICOLOGICAL FUNCTIONAL ASSAY FOR ASSESSING HUMORAL IMMUNITY FOR HAZARD IDENTIFICATIONPURPOSES IN RATS IN A STANDARD TOXICOLOGY STUDY

A previous study (Ladics et al., 1995) conducted in our laboratory usi ng the known immunosuppressant agent, cyclophosphamide, indicated that a functional assay for assessment of humoral immunity may be conducte d in rats in a standard toxicology study. The objective of this study was to further examine the feasibility of conducting an immunotoxicolo gical assay for assessing humoral immunity in rats in a standard toxic ology study using a chemical, carbon tetrachloride (CCl4), whose princ ipal target organ of toxicity is not the immune system. Specifically, the previous study and this study were done to determine whether the c onduct of an assay for assessing humoral immune function would affect standard toxicological endpoints. Male CD rats were untreated or dosed orally for 30 or 90 days, excluding weekends, with vehicle or 12.5 or 25 mg/kg CCl4. Six days prior to sacrifice, selected rats were inject ed intravenously with sheep red blood cells (SRBC) for assessment of h umoral immune function. One day prior to necropsy, blood for hematolog ical and clinical chemical measurements was collected from each rat. O n the day of necropsy standard protocol tissues were collected, weighe d, processed to slides, and later examined microscopically. One-half o f each spleen was used to assess spleen cell numbers and quantitate ly mphocyte subsets (T-helper; T-cyt/sup; total T- and B-cells) by flow c ytometry. Serum was analyzed for anti-SRBC IgM antibody by using an en zyme-linked immunosorbent assay. Administration of 12.5 and 25 mg/kg C Cl4 for 30 days decreased SRBC-specific serum IgM levels 42 and 45%, r espectively, while 25 mg/kg CCl4 for 90 days increased SRBC-specific I gM levels by 50%. CCl4 did not alter splenic lymphocyte subset numbers nor the weight nor morphology of lymphoid organs. Exposure to 25 mg/k g CCl4 did increase liver weight and serum sorbitol dehydrogenase leve ls, as well as produce centrilobular fatty change. SRBC administration did not alter any hematological or clinical chemistry parameters, nor lymphocyte subset numbers. With the expected exception of the spleen (slight increase in number and size of germinal centers), administrati on of SRBC did not significantly alter the weights or morphology of ro utine protocol tissues. Furthermore, administration of SRBC did not ma sk the rather mild hepatotoxic effects of CCl4 exposure observed in th is study. Based on these and previous findings, it appears that a func tional assay for assessing humoral immunity may be conducted in animal s on standard toxicology study without altering standard toxicological endpoints. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved .