Abstract
The persistent environmental contaminant and immunotoxicant, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), markedly suppresses humoral immune responses. We recently reported impaired down-regulation of paired box 5 (Pax5), a repressor of B cell differentiation and concomitant suppression of the IgM response by TCDD in the murine CH12.LX B cell line. The objectives of the current study were to determine the impact of TCDD treatment on molecular outcomes characteristic of terminal B cell differentiation and to assess the role that Pax5 isoforms plays in the suppression of B cell differentiation by TCDD. In this study, we show that the highly abundant full-length Pax5 isoform, Pax5a, and at least two additional modestly expressed Pax5 isoforms were expressed in CH12.LX and splenic B cells. In lipopolysaccharide (LPS)-activated B cells, all of the identified Pax5 isoforms were synchronously down-regulated, and in the presence of TCDD cotreatment they were abnormally and synchronously elevated, suggesting a common mechanism of regulation. Furthermore, B cell differentiation markers X-box protein-1 and major histocompatibility complex class II showed that the levels to which Pax5 was derepressed by TCDD were sufficient to impair B cell differentiation and immunoglobulin gene expression. Confirming the involvement of Pax5, ectopic expression of Pax5a in the LPS-activated CH12.LX cells closely mimicked the suppression of the IgM response by TCDD. In summary, our results demonstrate that Pax5a has a critical role in both the TCDD-mediated impairment of B cell differentiation and the suppression of the humoral immune response.
Footnotes
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This work was supported by National Institutes of Health Grants R01ES2520-22, T32ES07255-17, and P42ES04911.
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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doi:10.1124/jpet.108.139857.
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ABBREVIATIONS: TCDD, 2,3,7,8-tetrachlorodibenzo-p-dioxin; AHR, aryl hydrocarbon receptor; LPS, lipopolysaccharide; MHC, major histocompatibility complex; IgH, Ig heavy chain; Igκ, Igκ light chain; IgJ, Ig-joining chain; XBP-1, X-box protein-1; Pax5, paired box 5; DMSO, dimethyl sulfoxide; CD, cluster of differentiation; FITC, fluorescein isothiocyanate; 7-AAD, 7-aminoactinomycin D; AFC, antibody-forming cell; PCR, polymerase chain reaction; RT, reverse transcription; GFP, green fluorescent protein; ELISA, enzyme-linked immunosorbent assay; ANOVA, analysis of variance; XBP-1u, unspliced XBP-1 isoform; XBP-1s, spliced isoforms of XBP-1; ARNT, AHR nuclear translocator.
- Received April 8, 2008.
- Accepted May 14, 2008.
- The American Society for Pharmacology and Experimental Therapeutics
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