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CYP1A2 IS NOT REQUIRED FOR 2, 3, 7, 8-TETRACHLORODIBENZO-P-DIOXIN-INDUCED IMMUNOSUPPRESSION
Citation:
Smialowicz, R J., D. E. Burgin, W C. Williams, J J. Diliberto, R W. Setzer, AND L S. Birnbaum. CYP1A2 IS NOT REQUIRED FOR 2, 3, 7, 8-TETRACHLORODIBENZO-P-DIOXIN-INDUCED IMMUNOSUPPRESSION. TOXICOLOGY. Elsevier Ireland Limited, Limerick, Ireland, 197:15-22, (2004).
Description:
ABSTRACT
One of the most sensitive and reproducible immunotoxic endpoints of 2,3,7,8-tetrachloro-dibenzo-p-dioxin (TCDD) exposure is suppression of the antibody response to sheep red blood cells (SRBCs) in mice. Immunosuppression occurs in concert with hepatomegaly and associated induction of several hepatic cytochrome P450 enzymes, including CYP1A2 which is responsible for the hepatic sequestration of TCDD. In this study, TCDD-induced immunosuppression was evaluated in C57BL/6N CYP1A2 (+/+) wild-type and compared with that of age-matched CYP1A2 (-/-) knockout and CYP1A2 (+/-) heterozygote female mice. Groups of mice were given a single gavage dose of 0, 0.03, 0.1, 0.3, 1.0, 3.0 or 10.0 g TCDD/kg, followed seven days later by immunization with SRBCs. Serum was obtained five days after immunization and body, spleen, thymus and liver weights were measured. SRBC antibody titers were determined by an enzyme-linked immunosorbent assay (ELISA). Anti-SRBC titers were suppressed at 1.0, 1.0 and 0.3 g TCDD/kg for CYP1A2 (+/+), CYP1A2 (+/-), and CYP1A2 (-/-) mice, respectively, which indicated a three fold increase in TCDD-induced immunosuppression for the CYP1A2 (-/-) mice. This increase in TCDD-induced immunosuppression may be due to the inability of CYP1A2 (-/-) mice to sequester TCDD in the liver leading to a higher dose to the immune system. In CYP1A2(+/+) mice, a dose of 0.3 g TCDD/kg was sufficient to increase the liver-to-body weight ratio, while in CYP1A2 (-/-) mice a dose of 10 g TCDD/kg was required. Application of analysis of variance and dose-response modeling approaches indicate that there is little evidence that the immunosuppression dose-response curves, for the three strains, differ in the lower part of the dose response range. Thus CYP1A2 is not required for TCDD-induced immunosuppression in the mouse.