Cytokine Gene Expression during Ontogeny in Murine Thymus on Activation of the Aryl Hydrocarbon Receptor by 2,3,7,8-Tetrachlorodibenzo-p-dioxin
Abstract
2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) binds and activates the aryl hydrocarbon receptor (Ah-R), an endogenous transcription factor that is expressed in the thymus. TCDD exposure leads, among other effects, to thymus atrophy and immunosuppression. We previously analyzed the interference of TCDD with differentiation processes in fetal thymus organ cultures and found that in the presence of TCDD, the proliferation rate of immature (CD4−CD8− and CD4−CD8+ HSA+) thymocytes is inhibited, whereas the maturation along the CD4/CD8 path is accelerated. Moreover, the differentiation of thymocytes is skewed by TCDD at ≤40% (compared with ∼15% without TCDD) of the CD8 single-positive subset of future cytotoxic T cells, and apparently more cells audition for and pass positive selection. The fetal murine thymus expresses functional Ah-R mRNA, as shown by reverse transcription-polymerase chain reaction and TCDD-inducible CYP1A1 and CYP1B1 expression. Because the differentiation of thymocytes is to a considerable extent controlled by cytokines and many cytokine genes are potential targets of the Ah-R due to Ah-R-binding elements (xenobiotic response elements) in their promoters, we analyzed the cytokine expression in fetal thymus organ culture exposed to TCDD. Fetal thymi were cultured from gestation day 15 for ≤8 days, thus coveringex vivo the period after population of the thymus anlage until birth. We show with semiquantitative reverse transcription-polymerase chain reaction that more interleukin (IL)-1β, IL-2, IL-6, tumor growth factor (TGF)-β3, and tumor necrosis factor-α are produced in TCDD-exposed thymi, whereas other cytokines (e.g., TGF-β1, PAI-2, or IL-4) are only slightly up- and down-modulated during the culture period or not modulated at all (e.g., IL-1β, IL-7, interferon-γ, and TGF-β2).
Footnotes
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Send reprint requests to: Dr. Charlotte Esser, Medical Institute of Environmental Hygiene, Auf’m Hennekamp 50, 40225 Düsseldorf, Germany. E-mail:chesser{at}uni-duesseldorf.de
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↵1 Current affiliation: SUNY Health Science Center, Syracuse, New York 13210.
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↵2 Myung-Shin Jeon, personal communication.
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This work was supported financially through Sonderforschungsbereich 503, Molecular and Cellular Mediators of Exogenous Noxes (Heinrich-Heine-University of Düsseldorf, Düsseldorf, Germany).
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↵3 Myung-Shin Jeon, personal communication.
- Abbreviations:
- Ah-R
- aryl hydrocarbon receptor
- ARNT
- aryl hydrocarbon receptor nuclear transporter
- DRE
- dioxin-responsive element
- FTOC
- fetal thymus organ culture
- RT
- reverse transcription
- PCR
- polymerase chain reaction
- TCDD
- 2,3,7,8-tetrachlorodibenzo-p-dioxin
- TCR
- T cell receptor
- IL
- interleukin
- TNF-α
- tumor necrosis factor-α
- TGF-β
- tumor growth factor-β
- IFN-γ
- interferon-γ
- PAI-2
- plasminogen activator inhibitory factor
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- Received February 10, 1997.
- Accepted March 27, 1997.
- The American Society for Pharmacology and Experimental Therapeutics
