B cell differentiation and humoral immune responses are markedly suppressed by the persistent environmental contaminant, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The suppression of humoral immune responses by TCDD occurs by direct actions on the B cell and involves activation of the aryl hydrocarbon receptor. Transcriptional regulation of paired box gene 5 (Pax5), an important regulator of B cell differentiation, is altered by TCDD in concordance with the suppression of B cell differentiation and humoral immunoglobulin M response. We hypothesized that TCDD treatment leads to dysregulation of Pax5 transcription by interfering with the basic B cell differentiation mechanisms and aimed to determine the effects of TCDD on upstream regulators of Pax5. A critical regulator of B cell differentiation, B lymphocyte-induced maturation protein-1 (Blimp-1) acts as a transcriptional repressor of Pax5. In lipopolysaccharide (LPS)-activated murine B cell lymphoma, CH12.LX, Blimp-1 messenger RNA, and DNA-binding activity within the Pax5 promoter were suppressed by TCDD. Furthermore, LPS activation of CH12.LX cells upregulated DNA-binding activity of activator protein 1 (AP-1) at three responsive element-like motifs within the Blimp-1 promoter. TCDD treatment of LPS-activated CH12.LX cells suppressed AP-1 binding to these motifs between 24 and 72 h, in concordance with the suppression of Blimp-1 by TCDD. A more comprehensive analysis at 72 h demonstrated that the suppression of AP-1 binding within the Blimp-1 promoter by TCDD was concentration dependent. In summary, our findings link the TCDD-mediated suppression of Blimp-1 through AP-1 to the dysregulation of Pax5, which ultimately leads to the suppression of B cell differentiation and humoral immune responses.

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 fulllength 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.Suppression of primary humoral immune responses is one of the most sensitive sequela associated with exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a ubiquitous environmental contaminant. This suppression is characterized by a striking reduction in plasma cell formation and IgM secretion, and it is mediated through a direct effect by TCDD on B cells (Holsapple et al., 1986;Sulentic et al., 1998). TCDD serves as a ligand for the basic-helix-loop-helix/periodicity/ aryl hydrocarbon receptor (AHR) nuclear translocator (ARNT)/simple-minded family protein, AHR (Hankinson, 1995). Previous studies in mice and B cell lines that differ in AHR expression demonstrated the involvement of AHR in the suppression of humoral immune responses (Vecchi et al., 1983;Kerkvliet et al., 1990;Sulentic et al., 1998;Sulentic et al., 2000). The AHR is a 95 to 110-kDa cytoplasmic receptor (Burbach et al., 1992) that exists as part of a multimeric complex composed of dimers of heat shock protein 90 and the AHR-interactive protein (Bell and Poland, 2000;Petrulis and Perdew, 2002). Binding of TCDD to the AHR results in both the dissociation of AHR from the cytosolic complex and the nuclear translocation of the receptor where it releases heat shock protein 90 subunits and undergoes dimerization with ARNT (Whitelaw et al., 1995;Rowlands and Gustafsson, 1997). The interaction of the AHR/ARNT dimers with dioxinresponse e...

Previous studies have demonstrated that most of the intraspecies variation in sensitivity to the toxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), including suppression of antibody responses, in murine models is due to single nucleotide polymorphisms (SNPs) within the aryl hydrocarbon receptor (AhR) gene. The underlying reason for variation in sensitivity to TCDD-induced suppression of IgM responses among humans is not well understood, but is thought, in part, to be a result of different polymorphic forms of the AhR expressed by different individuals. In this study, the functional properties of six (P517S, R554K, V570I, V570I+P517S, R554K+V570I and P517S+R554K+V570I) human AhR variants were examined in the human B cell line, SKW 6.4. TCDD-induced Cyp1B1 and Cyp1A2 mRNA expression levels and Cyp1B1-regulated reporter gene activity, used for comparative purposes, were markedly lower in SKW cells containing the R554K SNP than in SKW-AHR+ (control AhR) cells. Furthermore, all AhR variants were able to mediate TCDD-induced suppression of the IgM response; however, a combined P517S+R554K+V570I variant partially reduced sensitivity to TCDD-mediated suppression of IgM secretion. Collectively, our findings show that the R554K human AhR SNP alone altered sensitivity of human B cells to TCDD-mediated induction of Cyp1B1 and Cyp1A2. By contrast, attenuation of TCDD-induced IgM suppression required a combination of all three SNPs P517S, R554K, and V570I.

A specific multiplex PCR was developed for the rapid and highly sensitive quality control of the viral DNA during Epinotia aporema granulovirus (EpapGV) production. At the beginning of this work only 2.3% of the EpapGV genomic sequence was known. In order to increase the availability of specific information, the terminal sequences of the inserts of several selected clones of EpapGV genomic libraries were determined. These data comprised 8.4% of the total DNA sequence and corresponded to regions distributed throughout the genome. Based on the small fraction of known sequence available a set of 32 primers was designed, using information theory to set the basis for this study. Each pair of designed primers was initially tested in individual PCRs to assess the correct size of the expected product and the sensitivity of the amplification. The specificity was verified in multiplex PCRs, using alternatively 1-3 sets of selected 5-6 primer pairs and EpapGV DNA preparations from different sources and degrees of purity. The results indicate that the multiplex PCR could be used for quality control in the bioinsecticide production, as well as in other applications such as the detection of latent infections in E. aporema colonies, and studies related to virus distribution, vertical transmission, host range, or persistence in the field.