CYP1A2 is not required for 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced immunosuppression.
One of the most sensitive and reproducible immunotoxic endpoints of 2,3,7,8-tetrachlorodibenzo-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 (+/-) heterozygous female mice. Groups of mice were given a single gavage dose of 0, 0.03, 0.1, 0.3, 1.0, 3.0 or 10.0microg TCDD/kg, followed 7 days later by immunization with SRBCs. Serum was obtained 5 days after immunization and body, spleen, thymus and liver weights were measured. sheep red blood cell (SRBC) antibody titers were determined by an enzyme-linked immunosorbent assay (ELISA). Anti-SRBC titers were suppressed at 1.0, 1.0 and 0.3microg 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 3.0microg TCDD/kg was sufficient to increase the liver weight, while in CYP1A2 (-/-) mice no increase in liver weight was observed. 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.
Experimental Toxicology Division, National Health and Environmental Effects Research Laboratory, US Environmental Protection Agency, Research Triangle Park, NC 27711, USA. smialowicz.ralph@epa.gov
R J
RJ
Smialowicz
D E
DE
Burgin
W C
WC
Williams
J J
JJ
Diliberto
R W
RW
Setzer
L S
LS
Birnbaum
D000284:Administration, Oral; D000818:Animals; D000917:Antibody Formation / Q000187:drug effects* / Q000235:genetics; D019388:Cytochrome P-450 CYP1A2 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004785:Environmental Pollutants / Q000008:administration & dosage / Q000633:toxicity*; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D005838:Genotype; D006462:Hemolytic Plaque Technique; D016867:Immunocompromised Host / Q000235:genetics; D007165:Immunosuppression Therapy; D007166:Immunosuppressive Agents / Q000008:administration & dosage / Q000633:toxicity*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009929:Organ Size / Q000187:drug effects; D000072317:Polychlorinated Dibenzodioxins / Q000008:administration & dosage / Q000633:toxicity*; D013950:Thymus Gland / Q000187:drug effects / Q000473:pathology
D004785:Environmental Pollutants; D007166:Immunosuppressive Agents; D000072317:Polychlorinated Dibenzodioxins; D019388:Cytochrome P-450 CYP1A2