POSSIBLE INCORPORATION OF AN IMMUNOTOXICOLOGICAL FUNCTIONAL ASSAY FORASSESSING HUMORAL IMMUNITY FOR HAZARD IDENTIFICATION PURPOSES IN RATSON STANDARD TOXICOLOGY STUDY

The objective of this study was to examine the feasibility of conducti ng an immunotoxicological assay for assessing humoral immunity in rats on standard toxicology study. Male CD rats were untreated or dosed in traperitoneally daily for 30 or 90 days, excluding weekends, with vehi cle or 2 mg/kg cyclophosphamide (CY). Six days prior to sacrifice, sel ected rats were injected intravenously with sheep red blood cells (SRB C). One day prior to necropsy, blood samples for hematological and cli nical chemical measurements were collected from each rat. On the day o f necropsy standard protocol tissues were collected, weighed, processe d to slides, and examined microscopically. One-half of each spleen was . used to prepare a single cell suspension in order to assess spleen c ell numbers. Serum was analyzed for anti-SRBC IgM antibody using an en zyme-linked immunosorbent assay. A second set of studies was performed to examine further the effect of SRBC administration on lymphoid orga n weights using 30- and 90-day study age-equivalent naive male CD rats . Exposure of animals to 2 mg/kg CY for 30 or 90 days resulted in a 28 % and 61% decrease, respectively, in SRBC-specific serum IgM levels. C Y treatment also caused mild alterations in some leukocytic parameters , with significant decreases of 35% and 33% in white blood cell and ly mphocyte counts, respectively, observed in 30-day CY-treated animals r eceiving SRBC. Injection of SRBC alone did not alter hematological or clinical chemistry parameters. With the expected exception of the sple en (increased number and size of germinal centers), administration of SRBC did not significantly alter the weights or morphology of routine protocol tissues. Furthermore, administration of SRBC did not mask the immunosuppressive effects of CY treatment under the conditions of thi s study. Based on our preliminary findings, a functional assay for ass essing humoral immunity may be conducted in animals on standard toxico logy study.