B cells have been identified as sensitive cellular targets responsible for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-mediated suppression of humoral immunity. In previous studies, TCDD was shown to produce a significant inhibition of IgM secretion and mu gene expression in LPS-activated CH12.LX B cells (AhR expressing) but not in BCL-1 B cells (AhR deficient). The present studies extend these previous findings by investigating the effect of TCDD on AP-1 and nuclear factor (NF)-κB, both of which play an important role in B-cell activation, differentiation, and immunoglobulin (Ig) gene expression. Electrophoretic mobility shift assays and chloramphenicol acetyl transferase reporter gene experiments demonstrated that lipopolysaccharide (LPS)-induced DNA binding and transcriptional activity of AP-1 was markedly inhibited by TCDD at 24, 48, and 72 h after cellular activation of CH12.LX cells. Conversely, TCDD treatment produced no significant change on the activity of NF-κB. Two AhR antagonists, α-naphthoflavone and 2,2′,5,5′-tetrachlorobiphenyl, attenuated TCDD-induced inhibition of AP-1 binding in CH12.LX cells. Concordant with this result, TCDD did not inhibit LPS-induced AP-1 activity in BCL-1 B cells. Moreover, supershift analysis revealed the major component of the AP-1 complex in LPS-activated CH12.LX cells was c-Jun. Additional studies revealed that the nuclear c-jun and c-jun steady-state mRNA expression was inhibited by TCDD treatment. Collectively, these results suggest that TCDD-induced inhibition of IgM expression by B cells may be mediated, at least in part, through a down-regulation of AP-1 activity in an AhR-dependent manner.
Bibliographical noteFunding Information:
The authors are thankful to Drs. M. Lee at KRICT and S. H. Han at KRIBB for their critical review of the manuscript. This work was supported by funds from the G7 project of the Ministry of Environment, Korea. Dr. Jeon is supported by the Korea Ministry of Science and Technology and the KOSEF through the Research Center for Proteineous Materials. Dr. Kaminski is supported by NIH Grant ES02520.
- B cell