A review of 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced changes in immunocompetence: 1991 update

Potential pathway and mechanisms underlining the immunotoxicity of benzo[a]pyrene to Chlamys farreri

The long-distance migration of polycyclic aromatic hydrocarbons (PAHs) promotes their release into the marine environment, posing a serious threat to marine life. Studies have shown that PAHs have significant immunotoxicity effects on bivalves, but the exact mechanism of immunotoxicity remains unclear. This paper aims to investigate the effects of exposure to 0.4, 2, and 10 μg/L of benzo(a)pyrene (B[a]P) on the immunity of Chlamys farreri under environmental conditions, as well as the potential molecular mechanism. Multiple biomarkers, including phagocytosis rate, metabolites, neurotoxicity, oxidative stress, DNA damage, and apoptosis, were adopted to assess these effects. After exposure to 0.4, 2, and 10 μg/L B[a]P, obvious concentration-dependent immunotoxicity was observed, indicated by a decrease in the hemocyte index (total hemocyte count, phagocytosis rate, antibacterial and bacteriolytic activity). Analysis of the detoxification metabolic system in C. farreri revealed that B[a]P produced B[a]P-7,8-diol-9,10-epoxide (BPDE) through metabolism, which led to an increase in the expression of protein tyrosine kinase (PTK). In addition, the increased content of neurotransmitters (including acetylcholine, γ -aminobutyric acid, enkephalin, norepinephrine, dopamine, and serotonin) and related receptors implied that B[a]P might affect immunity through neuroendocrine system. The changes in signal pathway factors involved in immune regulation indicated that B[a]P interfered with Ca2+ and cAMP signal transduction via the BPDE-PTK pathway or neuroendocrine pathway, resulting in immunosuppression. Additionally, B[a]P induced the increase in reactive oxygen species (ROS) content and DNA damage, as well as an upregulation of key genes in the mitochondrial pathway and death receptor pathway, leading to the increase of apoptosis rate. Taken together, this study comprehensively investigated the detoxification metabolic system, neuroendocrine system, and cell apoptosis to explore the toxic mechanism of bivalves under B[a]P stress.

Pesticide use and risk of systemic autoimmune diseases in the Agricultural Health Study

BACKGROUND

Systemic lupus erythematosus (SLE) risk has been associated with pesticide use, but evidence on specific pesticides or other agricultural exposures is lacking. We investigated history of pesticide use and risk of SLE and a related disease, Sjögren's syndrome (SS), in the Agricultural Health Study.

METHODS

The study sample (N = 54,419, 52% male, enrolled in 1993-1997) included licensed pesticide applicators from North Carolina and Iowa and spouses who completed any of the follow-up questionnaires (1999-2003, 2005-2010, 2013-2015). Self-reported cases were confirmed by medical records or medication use (total: 107 incident SLE or SS, 79% female). We examined ever use of 31 pesticides and farm tasks and exposures reported at enrollment in association with SLE/SS, using Cox regression to estimate hazard ratios (HR) and 95% confidence intervals (CI), with age as the timescale and adjusting for gender, state, and correlated pesticides.

RESULTS

In older participants (>62 years), SLE/SS was associated with ever use of the herbicide metribuzin (HR 5.33; 95%CI 2.19, 12.96) and applying pesticides 20+ days per year (2.97; 1.20, 7.33). Inverse associations were seen for petroleum oil/distillates (0.39; 0.18, 0.87) and the insecticide carbaryl (0.56; 0.36, 0.87). SLE/SS was inversely associated with having a childhood farm residence (0.59; 0.39, 0.91), but was not associated with other farm tasks/exposures (except welding, HR 2.65; 95%CI 0.96, 7.35).

CONCLUSIONS

These findings suggest that some agricultural pesticides may be associated with higher or lower risk of SLE/SS. However, the overall risk associated with farming appears complex, involving other factors and childhood exposures.

Immunotoxicity of Xenobiotics in Fish: A Role for the Aryl Hydrocarbon Receptor (AhR)?

The impact of anthropogenic contaminants on the immune system of fishes is an issue of growing concern. An important xenobiotic receptor that mediates effects of chemicals, such as halogenated aromatic hydrocarbons (HAHs) and polyaromatic hydrocarbons (PAHs), is the aryl hydrocarbon receptor (AhR). Fish toxicological research has focused on the role of this receptor in xenobiotic biotransformation as well as in causing developmental, cardiac, and reproductive toxicity. However, biomedical research has unraveled an important physiological role of the AhR in the immune system, what suggests that this receptor could be involved in immunotoxic effects of environmental contaminants. The aims of the present review are to critically discuss the available knowledge on (i) the expression and possible function of the AhR in the immune systems of teleost fishes; and (ii) the impact of AhR-activating xenobiotics on the immune systems of fish at the levels of immune gene expression, immune cell proliferation and immune cell function, immune pathology, and resistance to infectious disease. The existing information indicates that the AhR is expressed in the fish immune system, but currently, we have little understanding of its physiological role. Exposure to AhR-activating contaminants results in the modulation of numerous immune structural and functional parameters of fish. Despite the diversity of fish species studied and the experimental conditions investigated, the published findings rather uniformly point to immunosuppressive actions of xenobiotic AhR ligands in fish. These effects are often associated with increased disease susceptibility. The fact that fish populations from HAH- and PAH-contaminated environments suffer immune disturbances and elevated disease susceptibility highlights that the immunotoxic effects of AhR-activating xenobiotics bear environmental relevance.

Rapamycin Alleviates 2,3,7,8-Tetrachlorodibenzo-p-dioxin-Induced Aggravated Dermatitis in Mice with Imiquimod-Induced Psoriasis-Like Dermatitis by Inducing Autophagy

Recently, the mTOR signaling has emerged as an important player in the pathogenesis of psoriasis. We previously found that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced psoriatic skin inflammation was related to the inhibition of autophagy in keratinocytes. However, the effects and detailed molecular mechanisms of the mTOR inhibitor rapamycin and TCDD on psoriasis in vivo remain to be elucidated. In this study, we aimed to evaluate the effects of rapamycin and TCDD on skin lesions in imiquimod (IMQ)-induced psoriasis using a mouse model. TCDD aggravated skin inflammation in an IMQ-induced psoriatic mouse model. Furthermore, TCDD increased the expression of aryl hydrocarbon receptor (AHR), CYP1A1, proinflammatory cytokines, oxidative stress markers (NADPH oxidase (Nox) 2, Nox4), and phosphorylated P65NF-ĸB, whereas the expression of autophagy-related factors and the antioxidant marker nuclear factor-erythroid 2-related factor 2 (NRF2) decreased. Rapamycin reduced the aggravated skin inflammation induced by TCDD and restored TCDD-induced autophagy suppression and the increase of AHR expression, oxidative stress, and inflammatory response in the skin lesions of a psoriatic mouse model. In conclusion, we demonstrated that rapamycin alleviates TCDD-induced aggravated dermatitis in mice with imiquimod-induced psoriasis-like dermatitis through AHR and autophagy modulation.

From Suppressor T cells to Regulatory T cells: How the Journey That Began with the Discovery of the Toxic Effects of TCDD Led to Better Understanding of the Role of AhR in Immunoregulation

Aryl hydrocarbon receptor (AhR) was identified in the early 1970s as a receptor for the ubiquitous environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, dioxin), which is a member of halogenated aromatic hydrocarbons (HAHs). TCDD was found to be highly toxic to the immune system, causing thymic involution and suppression of a variety of T and B cell responses. The fact that environmental chemicals cause immunosuppression led to the emergence of a new field, immunotoxicology. While studies carried out in early 1980s demonstrated that TCDD induces suppressor T cells that attenuate the immune response to antigens, further studies on these cells were abandoned due to a lack of specific markers to identify such cells. Thus, it was not until 2001 when FoxP3 was identified as a master regulator of Regulatory T cells (Tregs) that the effect of AhR activation on immunoregulation was rekindled. The more recent research on AhR has led to the emergence of AhR as not only an environmental sensor but also as a key regulator of immune response, especially the differentiation of Tregs vs. Th17 cells, by a variety of endogenous, microbial, dietary, and environmental ligands. This review not only discusses how the role of AhR emerged from it being an environmental sensor to become a key immunoregulator, but also confers the identification of new AhR ligands, which are providing novel insights into the mechanisms of Treg vs. Th17 differentiation. Lastly, we discuss how AhR ligands can trigger epigenetic pathways, which may provide new opportunities to regulate inflammation and treat autoimmune diseases.

Analysis of global trends and gaps for studies about 2,4-D herbicide toxicity: A scientometric review

2,4-dichlorophenoxyacetic acid (2,4-D) is a herbicide that is used worldwide in agricultural and urban activities to control pests, reaching natural environments directly or indirectly. The research on 2,4-D toxicology and mutagenicity has advanced rapidly, and for this reason, this review summarizes the available data in Web of Science (WoS) to provide insights into the specific characteristics of 2,4-D toxicity and mutagenicity. Contrary to traditional reviews, this study uses a new method to quantitatively visualize and summarize information about the development of this field. Among all countries, the USA was the most active contributor with the largest publication and centrality, followed by Canada and China. The WoS categories 'Toxicology' and 'Biochemical and Molecular Biology' were the areas of greatest influence. 2,4-D research was strongly related to the keywords glyphosate, atrazine, water and gene expression. The studies trended to be focused on occupational risk, neurotoxicity, resistance or tolerance to herbicides, and to non-target species (especially aquatic ones) and molecular imprinting. In general, the authors have worked collaboratively, with concentrated efforts, allowing important advances in this field. Future research on 2,4-D toxicology and mutagenicity should probably focus on molecular biology, especially gene expression, assessment of exposure in human or other vertebrate bioindicators, and pesticide degradation studies. In summary, this scientometric analysis allowed us to make inferences about global trends in 2,4-D toxicology and mutagenicity, in order to identify tendencies and gaps and thus contribute to future research efforts.

Can contamination of the environment by dioxins cause craniofacial defects?

Cleft lip and cleft palate also known as orofacial cleft is a congenital malformation involving the partial or total lack of anatomical continuity of craniofacial tissue. The most common environmental factors that may cause orofacial clefts include pharmaceuticals, alcohol, addictive drugs, and tobacco smoke. Living in the area of industrial factories, garbage, ironworks, crematoria, wastewater treatment plants, and plastic waste landfills also has a significant impact on the development of the craniofacial defects. Some of the main factors causing the formation of congenital craniofacial defects are dioxins, of which emission to the environment is an important environmental and health problem. Dioxins are a diverse group of organic chemical compounds, derivatives of oxanthrene and fumarates, which are organoleptically imperceptible. Acting mainly through induction of inflammation, they influence a number of metabolic processes, including the process of bone mineralization and embryonic development. In this work, we highlight the problem of orofacial cleft including the impact of dioxin on development of this defect and the recommended prevention.

Immune response induced by major environmental pollutants through altering neutrophils in zebrafish larvae

Environmental pollutants may cause adverse effects on the immune system of aquatic organisms. However, the cellular effects of pollutants on fish immune system are largely unknown. Here, we exploited the transgenic zebrafish Tg(lysC:DsRed2) larva as a preliminary screening system to evaluate the potential inflammatory effects of environmental pollutants. Tg(lysC:DsRED2) larvae aged 7-day-postfertilization (7 dpf) were treated with selected environmental chemicals for 24 h (24 h) and the number of neutrophils were quantified using both image analysis and fluorescence activated cell sorting (FACS). We found that the numbers of neutrophils in the Tg(lysC:DsRED2) larvae were significantly increased by most of the organic chemicals tested, including E2 (17β-estradiol), BPA (Bisphenol-A), NDEA (N-nitrosodiethylamine), 4-NP (4-Nitrophenol) and Lindane (γ-hexachlorocyclohexane). Neutrophil numbers were also increased by all the metals tested (Na2HAsO4· 7H2O, Pb(NO3)2, HgCl₂, CdCl2, CuSO₄·5H₂O, ZnSO4, and K2Cr2O7). The only exception was TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin), which significantly reduced the number of neutrophils after exposure. Additionally, the transcription of genes (lyz, mpo, tnfα and il8) related to fish immune system were significantly modulated upon exposure to some of the selected chemicals such as E2, TCDD, Cu and Cd. This study revealed that representatives of major categories of environmental pollutants could cause an acute inflammatory response in zebrafish larvae as shown by alterations in the neutrophils, which may imply a common immunotoxicity mechanism for most environmental pollutants. This study has also demonstrated that Tg(lyz:DsRed2) transgenic zebrafish is an excellent tool for screening environmental chemicals with potential inflammatory effects through FACS-facilitated neutrophil counting.

The Influence of α-Tocopherol on Serum Biochemical Markers During Experimentally Induced Pleuritis in Rats Exposed to Dioxin

Toxicity of dioxins is wide ranging. Amongst the organs, the liver is the most susceptible to damage by dioxins. Damage caused to liver cells results in promoting inflammatory processes. The aim of this work was to evaluate whether high doses of tocopherol will change the inflammatory response, monitored by biochemical indicators, by improving liver function in rats exposed to tetrachlorodibenzo-p-dioxin (TCDD). The study was conducted on a population of female Buffalo rats. The animals were divided into the following groups: Control Group A—representing physiological norms for the studied diagnostic indicators; Control Group B—subjects were administered a 1% ceragenin solution to induce pleuritis; Study Group 1—where rats were administered α-tocopherol acetate for 3 weeks, after which pleuritis was induced; Study Group 2—rats were administered a single dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), while 3 weeks later, pleuritis was induced; and Study Group 3—rats were administered a single dose of TCDD and next, were administered α-tocopherol acetate for 3 weeks, followed by pleuritis induction. The results clearly show that administering tocopherol in the course of inflammation causes changes to the distribution and ratio of in the serum protein fractions, including acute phase proteins. The latter proteins are indicative to the improvement in liver function and linked to protein synthesis and stimulation of the antibody-mediated immunity. Moreover, in the course of inflammation caused by exposure of rats to TCDD, tocopherol significantly affected the acute phase protein concentration.

Biochemical and physiological effects from exhaust emissions. A review of the relevant literature

Exhaust emissions are to date ranked among the most frequent causes of premature deaths worldwide. The combustion of fuels such as diesel, gasoline, and bio-blends provokes a series of pathophysiological responses in exposed subjects, which are associated with biochemical and immunological triggering. It is critical to understand these mechanisms, which are directly related to the levels of aerosol, liquid and gaseous components in fuel exhaust (e.g. nanoparticles, particulate matter, volatile compounds), so to cast attention on their toxicity and gradually minimize their use. This review reports findings in the recent literature concerning the biochemical and cellular pathways triggered during intoxication by exhaust emissions, and links these findings to pathophysiological responses such as inflammation and vasoconstriction. This study provides critical in vitro and in vivo data for the reduction of emissions in urban centers, with an emphasis on the prevention of exposure of groups such as children, the elderly, and other affected groups, and shows how the exposure to exhaust emissions induces mechanisms of pathogenesis related to cardiopulmonary pathologies and long-term diseases such as asthma, allergies, and cancer. This review summarizes the cellular and physiological responses of humans to exhaust emissions in a comprehensive fashion, and is important for legislative developments in fuel politics.

The Aryl Hydrocarbon Receptor in Immunity: Tools and Potential

The signaling pathway of the evolutionary old transcription factor AhR is inducible by a number of small molecular weight chemicals, including toxicants such as polycyclic aromatic hydrocarbons, bacterial toxic pigments, and physiological compounds such as tryptophan derivatives or dietary indoles. AhR activation is of immunological importance, but at the same time mediates toxicity of environmental pollutants, such as immunosuppression by dioxins. Measuring AhR activity and identification of ligands is thus of great interest for a variety of research fields. In this chapter, I briefly introduce the AhR signaling pathway, its role in immunology, and the tools and assays needed to analyze AhR signaling. Both are also needed when therapeutic applications are envisioned.

Can exposure to environmental chemicals increase the risk of diabetes type 1 development?

Type 1 diabetes mellitus (T1DM) is an autoimmune disease, where destruction of beta-cells causes insulin deficiency. The incidence of T1DM has increased in the last decades and cannot entirely be explained by genetic predisposition. Several environmental factors are suggested to promote T1DM, like early childhood enteroviral infections and nutritional factors, but the evidence is inconclusive. Prenatal and early life exposure to environmental pollutants like phthalates, bisphenol A, perfluorinated compounds, PCBs, dioxins, toxicants, and air pollutants can have negative effects on the developing immune system, resulting in asthma-like symptoms and increased susceptibility to childhood infections. In this review the associations between environmental chemical exposure and T1DM development is summarized. Although information on environmental chemicals as possible triggers for T1DM is sparse, we conclude that it is plausible that environmental chemicals can contribute to T1DM development via impaired pancreatic beta-cell and immune-cell functions and immunomodulation. Several environmental factors and chemicals could act together to trigger T1DM development in genetically susceptible individuals, possibly via hormonal or epigenetic alterations. Further observational T1DM cohort studies and animal exposure experiments are encouraged.

Breakdown of mucosal immunity in gut by 2,3,7,8-tetraclorodibenzo-p-dioxin (TCDD)

OBJECTIVES

Mucosal immunity plays a pivotal role for body defense against infection and allergy. The aim of this study was to clarify the effects of 2,3,7,8-tetraclorodibenzo-p-dioxin (TCDD) on mucosal immunity in the gut.

METHODS

Fecal IgA level and oral tolerance induction were examined in TCDD-treated mice. Flow cytometric and histological analyses were also performed.

RESULTS

Single oral administration of low dose 2,3,7,8-TCDD resulted in a marked decrease in IgA secretion in the gut without any effects on the cellular components of gut-associated lymphoid tissues (GALT) including Peyer's patches (PPs) and mesenteric lymph nodes (LNs). Decressed IgA secretion by TCDD was not observed in aryl hydrocarbon receptor (AhR)-deficient mice. Flow cytometric analysis revealed that IgA B cells in PPs and the mesenteric LNs remained unchanged in the TCDD-treated mice. An immunofluorescence study also demonstrated that a significant number of cytoplasmic IgA cells were present in the lamina propria of the gut in the TCDD-treated mice. Furthermore, oral tolerance induction by ovalbumin (OVA) was impaired in the TCDD-treated mice and OVA-specific T cell proliferation occurred in the peripheral lymphoid tissues including the spleen and LNs.

CONCLUSIONS

These results suggest that a relatively low dose of TCDD impairs mucosal immunity in the gut and induces systemic sensitization by oral antigens.

A single mid-gestation exposure to TCDD yields a postnatal autoimmune signature, differing by sex, in early geriatric C57BL/6 mice

We recently observed an autoimmune profile in 24-week-old C57BL/6 mice that received a 2.5 or 5.0μg/kg mid-gestation dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (Mustafa et al., 2008). The clinical signs were consistent with a lupus-like syndrome and included: increased autoantibody levels, renal IgG and C3 immune complex deposition with associated inflammation, and increased peripheral Vβ(+) T cells. No studies currently exist following the progression of such disease into middle or advanced ages, when human autoimmune diseases may manifest. Therefore in the present study, littermates of mice from the previous 24 week prenatal TCDD study were allowed to age to 48 weeks, considered early geriatric in mice. Similarities and differences in the disease profile based on age and sex were observed. Peripheral autoreactive Vβ(+) T cells were increased in both sexes at 48 weeks, in contrast to males only at 24 weeks. Activated T cells from 48-week-old prenatal TCDD females over-produced the pro-inflammatory cytokine IFN-γ while males over-produced IL-10, effects again not seen at 24 weeks. Splenic transitional-2 B cells (CD21(int)CD24(hi)) were increased in males while transitional-1 B cells (CD23(neg) CD1(neg)) were increased in females at 48 weeks. Autoantibodies to cardiolipin and CD138(+) spleen plasma cells were significantly increased in the aged males but not females. Anti-IgG and anti-C3 immune complex renal deposition were also significantly increased in the prenatal TCDD males but not females. These selective changes in the aged male mice may be noteworthy, in that the prevalence of SLE in humans shifts dramatically toward males with aging. The collective findings in aged mice suggest that prenatal TCDD permanently biases the postnatal immune response in C57BL/6 mice toward autoimmunity, and support a significant B cell component to the induced renal autoimmune disease.

In vitro cytokine release from human peripheral blood mononuclear cells in the assessment of the immunotoxic potential of chemicals

Alternative methods to the use of animals in testing of chemicals are needed. We investigated if the immunotoxic potential of 12 dietary toxicants could be predicted from effects on cytokine release from human peripheral blood mononuclear cells (PBMC) after in vitro exposure. Nine cytokines were selected to reflect different types of immune responses. The toxicants were classified as immunotoxic or non-immunotoxic substances according to the published in vivo data. Isolated human PBMC were exposed for 20 h to three concentrations of each of the 12 substances in the presence of human liver S9 fraction. After further incubation of PBMC in fresh medium containing the mitogen phytohemagglutinin (PHA, 10 μg/ml) for 48 h, release of the nine selected cytokines into the supernatant as well as cell proliferation were measured by Luminex technology™ and the BrdU incorporation assay, respectively. All 12 substances investigated affected the release of one or more cytokines, and each of the substances showed different cytokine release patterns. Within the limitations of the study design, the present study suggests that the effect of the substances on mitogen-induced cytokine release from PBMC cannot predict their immunotoxic potential, but may be useful in mechanistic studies.

The long winding road toward understanding the molecular mechanisms for B-cell suppression by 2,3,7,8-tetrachlorodibenzo-p-dioxin

Suppression of humoral immune responses by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was first reported in the mid-1970s. Since this initial observation, much effort has been devoted by many laboratories toward elucidation of the cellular and molecular mechanisms responsible for the profound impairment of humoral immune responses by TCDD, which is characterized by decreased B cell to plasma cell differentiation and suppression of immunoglobulin production. These efforts have led to a significant body of research demonstrating a direct effect of TCDD on B-cell maturation and function as well as a requisite but as yet undefined role of the aryl hydrocarbon receptor (AhR) in these effects. Likewise, a number of molecular targets putatively involved in mediating B-cell dysfunction by TCDD, and other AhR ligands, have been identified. However, our current understanding has primarily relied on findings from mouse models, and the translation of this knowledge to effects on human B cells and humoral immunity in humans is less clear. Therefore, a current challenge is to determine how TCDD and the AhR affect human B cells. Efforts have been made in this direction but continued progress in developing adequate human models is needed. An in-depth discussion of these advances and limitations in elucidating the cellular and molecular mechanisms putatively involved in the suppression of B-cell function by TCDD as well as the implications on human diseases associated in epidemiological studies with exposure to TCDD and dioxin-like compounds is the primary focus of this review.

An integrated genomic analysis of aryl hydrocarbon receptor-mediated inhibition of B-cell differentiation

The aryl hydrocarbon receptor (AHR) agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) alters differentiation of B cells and suppresses antibody production. A combination of whole-genome, microarray-based chromatin immunoprecipitation (ChIP-on-chip), and time course gene expression microarray analysis was performed on the mouse B-cell line CH12.LX following exposure to lipopolysaccharide (LPS) or LPS and TCDD to identify the primary and downstream transcriptional elements of B-cell differentiation that are altered by the AHR. ChIP-on-chip analysis identified 1893 regions with a significant increase in AHR binding with TCDD treatment. Transcription factor binding site analysis on the ChIP-on-chip data showed enrichment in AHR response elements. Other transcription factors showed significant coenrichment with AHR response elements. When ChIP-on-chip regions were compared with gene expression changes at the early time points, 78 genes were identified as potential direct targets of the AHR. AHR binding and expression changes were confirmed for a subset of genes in primary mouse B cells. Network analysis examining connections between the 78 potential AHR target genes and three transcription factors known to regulate B-cell differentiation indicated multiple paths for potential regulation by the AHR. Enrichment analysis on the differentially expressed genes at each time point evaluated the downstream impact of AHR-regulated gene expression changes on B-cell-related processes. AHR-mediated impairment of B-cell differentiation occurred at multiple nodes of the B-cell differentiation network and potentially through multiple mechanisms including direct cis-acting effects on key regulators of B-cell differentiation, indirect regulation of B-cell differentiation-related pathways, and transcriptional coregulation of target genes by AHR and other transcription factors.

Transcriptomic profile indicative of immunotoxic exposure: in vitro studies in peripheral blood mononuclear cells

Investigating the immunotoxic effects of exposure to chemicals usually comprises evaluation of weight and histopathology of lymphoid tissues, various lymphocyte parameters in the circulation, and immune function. Immunotoxicity assessment is time consuming in humans or requires a high number of animals, making it expensive. Furthermore, reducing the use of animals in research is an important ethical and political issue. Immunotoxicogenomics represents a novel approach to investigate immunotoxicity able of overcoming these limitations. The current research, embedded in the European Union project NewGeneris, aimed to retrieve gene expression profiles that are indicative of exposure to immunotoxicants. To this end, whole-genome gene expression was investigated in human peripheral blood mononuclear cells in response to in vitro exposure to a range of immunotoxic chemicals (4-hydroxy-2-nonenal, aflatoxin B1, benzo[a]pyrene, deoxynivalenol, ethanol, malondialdehyde, polychlorinated biphenyl 153, and 2,3,7,8-tetrachlorodibenzo-p-dioxin) and nonimmunotoxic chemicals (acrylamide, dimethylnitrosamine, 2-amino-3-methyl-3H-imidazo[4,5-F]quinoline, and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine). Using Agilent oligonucleotide microarrays, whole-genome gene expression profiles were generated, which were analyzed using Genedata's Expressionist software. Using Recursive Feature Elimination and Support Vector Machine, a set of 48 genes was identified that distinguishes the immunotoxic from the nonimmunotoxic compounds. Analysis for enrichment of biological processes showed the gene set to be highly biologically and immunologically relevant. We conclude that we have identified a promising transcriptomic profile indicative of immunotoxic exposure.

2,3,7,8-tetrachlorodibenzo-p-dioxin-mediated suppression of toll-like receptor stimulated B-lymphocyte activation and initiation of plasmacytic differentiation

2,3,7,8-Tetrachlordibenzo-p-dioxin (TCDD) is a potent suppressor of humoral immunity, disrupting antibody production in response to both T cell-dependent and T cell-independent antigens. Among the cell types required for humoral responses, the B cell is highly, and directly, sensitive to TCDD. B cells become antibody-secreting cells via plasmacytic differentiation, a process regulated by several transcription factors, including activator protein-1, B-cell CLL/lymphoma 6 (BCL-6), and B lymphocyte-induced maturation protein 1 (Blimp-1). The overarching conceptual framework guiding experimentation is that TCDD disrupts plasmacytic differentiation by altering the expression or activity for upstream regulators of Blimp-1. Multiparametric flow cytometry was used to investigate TCDD-induced alterations in both activation marker and transcription factor expression following lipopolysaccharide (LPS) activation of purified B cells. TCDD significantly impaired LPS-activated expression of major histocompatibility complex class II, cluster of differentiation (CD)69, CD80, and CD86. Immunosuppressive concentrations of TCDD also suppressed LPS-activated Blimp-1 and phosphorylated c-Jun expression, whereas elevating BCL-6 expression. Because BCL-6 and c-Jun are directly and indirectly regulated by the kinases AKT, extracellular signal-regulated kinase (ERK), and Jun N-terminal kinase (JNK), it was hypothesized that TCDD alters toll-like receptor-activated kinase phosphorylation. TCDD at 0.03 and 0.3 nM significantly impaired phosphorylation of AKT, ERK, and JNK in CH12.LX B cells activated with LPS, CpG oligonucleotides, or resiquimod (R848). In primary B cells, R848-activated phosphorylation of AKT, ERK, and JNK was also impaired by TCDD at 30 nM. These results suggest that impairment of plasmacytic differentiation by TCDD involves altered transcription factor expression, in part, by suppressed kinase phosphorylation.

Expression of constitutively-active aryl hydrocarbon receptor in T-cells enhances the down-regulation of CD62L, but does not alter expression of CD25 or suppress the allogeneic CTL response

Activation of aryl hydrocarbon receptor (AhR) by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in T-cells is required for TCDD-induced suppression of the allogeneic CTL response and for induction of CD25(hi)CD62L(low) adaptive regulatory T-cells. Here, the ability of a constitutively-active AhR (CA-AhR) expressed in T-cells alone to replicate the effects of TCDD was examined. The response of CA-AhR-expressing B6 donor T-cells in B6xD2F1 mice was compared to the response of wild-type B6 donor T-cells in B6xD2F1 mice given a single dose of TCDD. Expression of CA-AhR in donor T-cells enhanced the down-regulation of CD62L on Day 2 after injection, similar to a single oral dose of TCDD, but did not induce up-regulation of CD25 on Day 2 or affect CTL activity on Day 10. This suggests that activation of AhR in T-cells alone may not be sufficient to alter T-cell responses in this acute graft-versus-host (GvH) model. Since host APC are responsible for activating the donor T-cells, we examined the influence of the F1 host's AhR on donor T-cell responses by creating an AhR(-/-) B6xD2F1 host that had a greatly diminished AhR response to TCDD compared to wild-type F1 mice. As in AhR(+/+) B6xD2F1 mice, the CTL response in AhR(-/-) B6xD2F1 mice was completely suppressed by TCDD. This suggests that either CA-AhR dose not fully replicate the function of TCDD-activated AhR in suppression of the CTL response, or that minimal activation of AhR in host cells is required to combine with activation of AhR in T-cells to elicit the immunosuppressive effects of TCDD.

A bistable switch underlying B-cell differentiation and its disruption by the environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin

The differentiation of B cells into antibody-secreting plasma cells upon antigen stimulation, a crucial step in the humoral immune response, is disrupted by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Several key regulatory proteins in the B-cell transcriptional network have been identified, with two coupled mutually repressive feedback loops among the three transcription factors B-cell lymphoma 6 (Bcl-6), B lymphocyte-induced maturation protein 1(Blimp-1), and paired box 5 (Pax5) forming the core of the network. However, the precise mechanisms underlying B-cell differentiation and its disruption by TCDD are not fully understood. Here we show with a computational systems biology model that coupling of the two feedback loops at the Blimp-1 node, through parallel inhibition of Blimp-1 gene activation by Bcl-6 and repression of Blimp-1 gene deactivation by Pax5, can generate a bistable switch capable of directing B cells to differentiate into plasma cells. We also use bifurcation analysis to propose that TCDD may suppress the B-cell to plasma cell differentiation process by raising the threshold dose of antigens such as lipopolysaccharide required to trigger the bistable switch. Our model further predicts that high doses of TCDD may render the switch reversible, thus causing plasma cells to lose immune function and dedifferentiate to a B cell-like state. The immunotoxic implications of these predictions are twofold. First, TCDD and related compounds would disrupt the initiation of the humoral immune response by reducing the proportion of B cells that respond to antigen and differentiate into antibody-secreting plasma cells. Second, TCDD may also disrupt the maintenance of the immune response by depleting the pool of available plasma cells through dedifferentiation.

Simultaneous in vivo time course and dose response evaluation for TCDD-induced impairment of the LPS-stimulated primary IgM response

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a potent suppressor of humoral immunity but the specific molecular mechanisms responsible for immunosuppression by TCDD are poorly understood. In vivo and in vitro studies of the primary humoral IgM response demonstrated that the B cell is a sensitive cell type to modulation by TCDD. We hypothesized that in vivo administration of TCDD disrupts expression of transcription factors controlling B cell to plasma cell differentiation. Female C57BL6 mice were treated with a single dose of TCDD (3, 10, or 30 microg/kg) and/or vehicle (sesame oil). On day 4 post-TCDD administration mice were sensitized with 25 microg lipopolysacchride (LPS) by intraperitioneal injection to stimulate an immune response. Splenocytes were isolated on subsequent days following LPS, up to 3 days post-LPS, and the expression of IgM, XBP-1, PAX5, BCL-6, and Blimp-1 was assessed. TCDD treatment dose-dependently suppressed LPS-induced IgM antibody-forming cell number, which was correlated with decreased frequency of CD19+ CD138+ cells. Gene expression analysis revealed that TCDD caused a dose-dependent suppression of Igmicro chain, Igkappa chain, IgJ chain, XBP-1, and Blimp-1. TCDD also dose-dependently suppressed LPS-stimulated increases in Blimp-1 protein expression in CD19+ B cells. The deregulation of Blimp-1 expression by TCDD provides a partial explanation for the concomitant suppression of the IgM response and confirms previous observations established in vitro.

Children's immunology, what can we learn from animal studies (3): Impaired mucosal immunity in the gut by 2,3,7,8-tetraclorodibenzo-p-dioxin (TCDD): a possible role for allergic sensitization

We have recently reported breakdown of mucosal immunity in the gut by tetraclorodibenzo-p-dioxin (TCDD). That is, single oral administration of low dose 2,3,7,8-TCDD resulted in a marked decrease in IgA secretion in AhR-dependent manner and impaired oral tolerance in the gut. In the present study, we found TCDD exposure by breast feeding also resulted in decreased level of IgA in the gut. Ig production by B cells by LPS stimulation was not affected by TCDD administration. Instead, particular chemokine receptor expression on B1 cells, a major cell source for intestinal IgA antibody, was decreased in mice treated with TCDD. In consistence with this observation, B1, but not B2 cells from TCDD treated mice showed impaired chemotaxis towards B lymphocyte chemokine (BLC)/CXCL13. In contrast, chemotaxis of intestinal dendritic cells (DCs) towards secondary lymphoid-tissue chemokine (SLC)/CXCL19 was not impaired in mice treated with TCDD. Furthermore, there was no change in the number and profile of intestinal microflora in TCDD-treated mice. These results indicate that TCDD exposure by breast feeding results in breakdown of intestinal mucosal immunity of pups and that it may be attributed in part to impaired B1 cell migration from the peritoneal cavity to intestinal mucosa.

Perinatal TCDD exposure and the adult onset of autoimmune disease

Modulation of the developing immune system can occur following perinatal exposure to a number of immunotoxic compounds, including polyhalogenated hydrocarbons like 2,3,7,8-tetra-chlorodibenzo-p-dioxin (TCDD; dioxin), the most toxic of the congeners. Studies in rodents have shown immunologic effects from perinatal TCDD exposure are more severe and persistent than following exposure in the adult, and include what appears to be life-long immunosuppression. Whether prenatal TCDD exposure may predispose an individual to postnatal autoimmune disease remains largely unknown. TCDD crosses the placenta and alters normal prenatal thymocyte maturation, T-cell receptor expression and expression of thymic major histocompatability complex Class II molecules. During the juvenile stage, mice exposed to TCDD prenatally show increased peripheral T-cells possessing "autoreactive" variable-beta receptors. These data suggest that gestational exposure to TCDD may interfere with normal development of central tolerance in the thymus. In possible support of this theory, when autoimmune disease-prone mice were treated with TCDD during gestation, postnatal autoimmunity had an accelerated onset and was exacerbated. This review provides an overview of the currently available information, which appears to support a hypothesis for increased risk of postnatal autoimmune responses as a result of TCDD exposure during the sensitive time of immune system establishment.

Constitutively active aryl hydrocarbon receptor expressed in T cells increases immunization-induced IFN-gamma production in mice but does not suppress T(h)2-cytokine production or antibody production

The ligand-dependent transcription factor aryl hydrocarbon receptor (AhR) has been implicated in various immune functions. Our previous studies have shown that AhR activation by exposure of ovalbumin (OVA)-immunized mice to the potent ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) increases immunization-induced IFN-gamma production in the spleen and suppresses the production of T(h)2 cytokines and OVA-specific antibodies. In the present study, we used transgenic (Tg) mice that express a constitutively active mutant of aryl hydrocarbon receptor (CA-AhR) specifically in T-lineage cells to clarify the role of AhR activation in T cells in these reactions. The results of this study clearly demonstrated that AhR activation only in the T cells augments IFN-gamma production upon OVA immunization. By contrast, production of T(h)2 cytokines and antibodies were not significantly suppressed by CA-AhR in the T cells. These results suggest that suppression of T(h)2 cytokines and antibodies production require AhR activation not only in T cells but also in other cell types as caused by TCDD exposure. Alternatively, these results may indicate that IFN-gamma augmentation and T(h)2 cytokines and antibodies suppression depend on different ways of functions of AhR in the T cells and that CA-AhR does not replicate the suppressive effect of TCDD-activated AhR on T(h)2 cytokines and antibodies. Expression of CA-AhR in the T cells was also shown to increase the percentage of CD25(+) cells among CD4(+) cells in the thymus and spleen. Thus, studies using T-cell-specific CA-AhR Tg mice provide a way to dissect the role of AhR in individual cell types and how the AhR functions.

TCDD-mediated suppression of the in vitro anti-sheep erythrocyte IgM antibody forming cell response is reversed by interferon-gamma

Suppression of humoral immune responses by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) has been well established to require the aryl hydrocarbon receptor; however, the downstream mechanisms for this immunotoxic response remain poorly understood. Based on evidence demonstrating that primary hepatocytes pretreated with interferon-gamma (IFN-gamma) exhibited decreased induction of cytochrome P450 1A1 (CYP1A1) by TCDD, and that serum factors alter the sensitivity of the in vitro T-cell-dependent IgM antibody forming cell (AFC) response, it was hypothesized that IFN-gamma attenuates suppression of humoral immune responses by TCDD. In fact, concomitant addition of IFN-gamma (100 U/ml) produced a concentration-related attenuation of TCDD-mediated suppression of the anti-sheep erythrocyte (anti-sRBC) IgM AFC response. Time-of-addition studies performed by adding 100 U/ml IFN-gamma at 0, 1, 2, 4, 12, 24, 48, and 72 h post-TCDD showed that suppression of the AFC response was prevented only when IFN-gamma was added within 2 h of TCDD treatment. mRNA levels of the IgM components, immunoglobulin kappa light chain, immunoglobulin mu heavy chain, and immunoglobulin J-chain were significantly decreased by TCDD treatment, an effect that was completely reversed by IFN-gamma (100 U/ml) cotreatment. Further studies showed that IFN-alpha, IFN-beta, and IFN-gamma significantly attenuate TCDD-induced increases in CYP1A1 mRNA levels to varying degrees, but concentrations as high as 1000 U/ml of type I IFNs did not reverse the effect of TCDD on the anti-sRBC IgM AFC response. In summary, IFN-gamma prevents TCDD-mediated suppression of the IgM AFC response in a concentration- and time-related manner by altering transcriptional effects associated with TCDD treatment.

An enhanced postnatal autoimmune profile in 24 week-old C57BL/6 mice developmentally exposed to TCDD

Developmental exposure of mice to the environmental contaminant and AhR agonist, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), causes persistent postnatal suppression of T cell-mediated immune responses. The extent to which prenatal TCDD may induce or exacerbate postnatal autoimmune disease remains unknown. In the present study, time-pregnant high affinity AhR C57BL/6 mice received a single oral administration of 0, 2.5, or 5 microg/kg TCDD on gestation day (gd) 12. Offspring of these mice (n=5/gender/treatment) were evaluated at 24 weeks-of-age and showed considerable immune dysregulation that was often gender-specific. Decreased thymic weight and percentages of CD4(+)CD8(+) thymocytes, and increased CD4(+)CD8(-) thymocytes, were present in the female but not male offspring. Males but not females showed decreased CD4(-)CD8(+) T cells, and increased Vbeta3(+) and Vbeta17a(+) T cells, in the spleen. Males but not females also showed increased percentages of bone marrow CD24(-)B220(+) B cell progenitors. Antibody titers to dsDNA, ssDNA and cardiolipin displayed increasing trends in both male and female mice, reaching significance for anti-dsDNA in both genders and for ssDNA in males at 5 microg/kg TCDD. Immunofluorescent staining of IgG and C3 deposition in kidney glomeruli increased in both genders of prenatal TCDD-exposed mice, suggestive of early stages of autoimmune glomerulonephritis. Collectively, these results show that exposure to TCDD during immune system development causes persistent humoral immune dysregulation as well as altered cell-mediated responses, and induces an adult profile of changes suggestive of increased risk for autoimmune disease.

Effects of organochlorines, individually and in mixtures, on B-cell proliferation in marine mammals and mice

Organochlorines (OC) are lipophilic and stable, and therefore accumulate in tissues of top predators, such as marine mammals. While the immunomodulatory effects of individual OC have been studied in lab animals, their effects in other species (such as marine mammals) and the possible interactions between chemicals in mixtures are not well understood. This study investigated the immunomodulatory effects of four polychlorinated biphenyls (PCB, IUPAC numbers 138, 153, 169, and 180), as well as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), individually and in mixtures, in marine mammals and mice. Mitogen-induced B lymphocyte proliferation was mostly modulated by non-coplanar PCBs, for which general mechanisms underlying toxicity are poorly understood. Simple additive effects of OC in mixtures were found only in mice, while both synergistic and antagonistic interactions between OC were found in marine mammals. The toxic equivalency (TEQ) approach, which is currently used to assess the dioxin-like toxicity of OC mixtures, failed to predict immunotoxicity in mice and marine mammals, likely due to the complexity of interactions between OC and effects via dioxin-independent pathways. The commonly used mouse model failed to predict the immunotoxicity due to OC in the marine mammals tested. In addition, clustering data suggested that phylogeny might not help predict the toxicity of OC. Lymphoproliferative response was modulated in most species tested suggesting the possibility of increased susceptibility to infectious diseases in these animals. These findings may be helpful in more accurately characterizing the immunotoxic potential of OC in different target species and help in more relevant risk assessment.

Relative potency based on hepatic enzyme induction predicts immunosuppressive effects of a mixture of PCDDS/PCDFS and PCBS

The toxic equivalency factor (TEF) approach was employed to compare immunotoxic potency of mixtures containing polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans and polychlorinated biphenyls relative to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), using the antibody response to sheep erythrocytes (SRBC). Mixture-1 (MIX-1) contained TCDD, 1,2,3,7,8-pentachlorodibenzo-p-dioxin (PeCDD), 2,3,7,8-tetrachlorodibenzofuran (TCDF), 1,2,3,7,8-pentachlorodibenzofuran (1-PeCDF), 2,3,4,7,8-pentachlorodibenzofuran (4-PeCDF), and 1,2,3,4,6,7,8,9-octachlorodibenzofuran (OCDF). Mixture-2 (MIX-2) contained MIX-1 and the following PCBs, 3,3',4,4'-tetrachlorobiphenyl (IUPAC No. 77), 3,3',4,4',5-pentachlorobiphenyl (126), 3,3',4,4',5,5N-hexachlorobiphenyl (169), 2,3,3',4,4'-pentachlorobiphenyl (105), 2,3',4,4',5-pentachlorobiphenyl (118), and 2,3,3',4,4',5-hexachlorobiphenyl (156). The mixture compositions were based on relative chemical concentrations in food and human tissues. TCDD equivalents (TEQ) of the mixture were estimated using relative potency factors from hepatic enzyme induction in mice [DeVito, M.J., Diliberto, J.J., Ross, D.G., Menache, M.G., Birnbaum, L.S., 1997. Dose-response relationships for polyhalogenated dioxins and dibenzofurans following subchronic treatment in mice. I .CYP1A1 and CYP1A2 enzyme activity in liver, lung and skin. Toxicol. Appl. Pharmacol. 130, 197-208; DeVito, M.J., Menache, G., Diliberto, J.J., Ross, D.G., Birnbaum L.S., 2000. Dose-response relationships for induction of CYP1A1 and CYP1A2 enzyme activity in liver, lung, and skin in female mice following subchronic exposure to polychlorinated biphenyls. Toxicol. Appl. Pharmacol. 167, 157-172] Female mice received 0, 1.5, 15, 150 or 450 ng TCDD/kg/day or approximately 0, 1.5, 15, 150 or 450 ng TEQ/kg/day of MIX-1 or MIX-2 by gavage 5 days per week for 13 weeks. Mice were immunized 3 days after the last exposure and 4 days later, body, spleen, thymus, and liver weights were measured, and antibody response to SRBCs was observed. Exposure to TCDD, MIX-1, and MIX-2 suppressed the antibody response in a dose-dependent manner. Two-way ANOVA indicated no differences in the response between TCDD and the mixtures for body weight, spleen/body weight and decreased antibody responses. The results support the use of the TEF methodology and suggest that immune suppression by dioxin-like chemicals may be of concern at or near background human exposures.

Cigarette smoke as a trigger for the dioxin receptor-mediated signaling pathway

Dioxins and dioxin-like chemicals cause a wide range of pathologies including carcinogenesis, immune dysfunction, and developmental/reproductive abnormalities. Most of these toxic effects are mediated by aryl hydrocarbon receptor (AhR; also called the dioxin receptor), a ligand-activated transcription factor. Constitutive activation of AhR via genetic manipulation causes development of cancers, inflammation and immune abnormality in mice even without exposure to xenobiotic ligands. Recent investigation disclosed that cigarette smoke contains high levels of agonists for AhR and strongly activates the dioxin signaling pathway. In this review, we describe and discuss possible roles of AhR activation in cigarette smoke-related pathologies, especially focusing on carcinogenesis, inflammation, atherosclerosis, immune dysfunction and teratogenesis.

Concentration of polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans and dioxin-like PCBs in human adipose tissue from Turkish men

There is no previous report from Turkey on chemically determined polychlorinated dibenzo-para-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and dioxin-like polychlorinated biphenyls (PCBs) in human tissues expressed as World Health Organization (WHO) toxic equivalents (TEQs). The objective of this study was to determine the occurrence of PCDDs/Fs, and dioxin-like PCBs in the general adult Turkish population. For this reason we measured adipose tissue concentrations of PCDDs/Fs and dioxin-like PCBs in 23 Turkish men living in Ankara,Turkey in 2004. PCDD/F concentrations ranged between 3.2 and 19.7 pg WHO-TEQ/g fat (5.34 and 42.7 WHO-TEQ/g fat, respectively, including dioxin-like PCBs). The mean concentrations of WHO(PCDD/F)-TEQ and WHO(PCB)-TEQ were 9.2 and 6.67 pg/g on a lipid basis , respectively. Samples were analyzed for PCDD/F and twelve dioxin-like PCB congeners using high resolution gas chromatography/high resolution mass spectrometry (HRGC/HRMS). This study is very important since it is the first report on PCDDs/Fs and dioxin-like PCB contamination in human adipose tissue from Turkey.

Diagnostic relevance of the determination of lymphocyte subpopulations in environmental medicine

Earlier hopes that determination of lymphocyte subpopulations might become a strong diagnostic tool in environmental medicine have not been fulfilled in recent years. Analysis of the scientific literature rather shows that there are only few examples for environmental exposures causing reproducible shifts of lymphocyte subpopulations. Moreover, current knowledge suggests that "environmental diseases" are not associated with characteristic changes of subpopulation patterns. If lymphocyte subpopulations are analyzed, each diagnostic step, including indication, sample handling, analytic procedure and data-interpretation, should adhere to good quality criteria. Taking all together, the determination of lymphocyte subpopulations in the context of environmental medicine comes under category IV of the criteria of the Commission for Methods and Quality Assurance in Environmental Medicine of the German federal health authority (Robert Koch-Institute; RKI): "A procedure cannot be recommended because there is not sufficient information to justify it" (here: no solid trends in epidemiological examinations), "and because theoretical considerations speak against an application" (here: high physiological variability and missing exposure or substance specificity).

The early embryo loss caused by 2,3,7,8-tetrachlorodibenzo-p-dioxin may be related to the accumulation of this compound in the uterus

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a reproductive and developmental toxicant that can alter endocrine status, leading to decreased fertility and altered embryonic development; however, there are limited reports on TCDD toxicity during early pregnancy. In the present study, pregnant and pseudopregnant NIH mice were exposed to TCDD orally (2, 50 and 100 ng/kg body weight) during early gestation (days 1-8), pre-implantation stages (days 1-3), and peri-implantation to early post-implantation stages (days 4-8). TCDD concentration in uterus, liver, kidney, brain and fat on day 9 of pregnancy was monitored by an aryl hydrocarbon receptor (Ah receptor, AhR)-mediated LacZ reporter system in yeast. Results showed that the number of implanted embryos was significantly reduced on day 9 of gestation by 50 and 100 ng/kg TCDD exposure. The number of implantation sites was lower for animals exposed to TCDD on days 1-3 versus those exposed during days 4-8. Decidualization in pseudopregnant mice was also inhibited by TCDD exposure. TCDD concentrations as low as 2 ng/kg significantly decreased serum progesterone levels but had no effect on serum estradiol. TCDD level in the uterus was equal to levels in the liver, but lower than the fat tissue. These results suggest that TCDD sensitivity might be attributed its local accumulation in the uterus.

Effect of a singlein ovo injection of 2,3,7,8-tetrachlorodibenzo-p-dioxin on protein expression in liver and ovary of the one-day-old chick analyzed by fluorescent two-dimensional difference gel electrophoresis and mass spectrometry

The polyhalogenated aromatic hydrocarbon 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is an ubiquitously distributed environmental pollutant which can induce a broad spectrum of toxic responses in animals, including birds. In this study, we investigated the impact of 0 or 20 ng TCDD injections into the yolk of chicken eggs before start of development, on liver and ovarian protein expression in hatchlings using fluorescent two-dimensional difference gel electrophoresis (2-D-DIGE) under a pH range of 4-7, combined with MS. Despite considerable interindividual variability, exposure to TCDD prior to the start of embryonic development resulted in significant changes in expression of a small set of proteins. Expression of fibrinogen gamma chain precursor in the liver and 60 kDa heat shock protein in the ovary were significantly higher as a result of the very early exposure to TCDD. NADH ubiquinone oxidoreductase (42 kDa subunit) and regucalcin expression was decreased by early TCDD treatment in the liver and ovary, respectively. These proteins could not be directly linked with drug metabolism per se but are involved in blood clotting, oxidative stress, electron transport, and calcium regulation. It remains to be elucidated how these changes in the hatchling might be linked to the observed long-term consequences during posthatch life of the chicken.

CYP1A1 in polycyclic aromatic hydrocarbon-induced B lymphocyte growth suppression

The AhR is a ligand-activated transcription factor that mediates immunosuppression by environmental PAH. Previous studies demonstrated that activation of mature human B cells up-regulates AhR expression, suggesting that human B cells are direct PAH targets. To test this hypothesis and to determine the metabolic requirements for PAH toxicity in a human model, the effects of a prototypic PAH, B[a]P, on B cell growth were evaluated. B[a]P and its proximal (B[a]P-7,8-dihydrodiol) and terminal (B[a]P-7,8-dihydrodiol-9,10-epoxide) metabolites inhibited growth in a dose-dependent manner. A poorly metabolized AhR ligand had no effect, suggesting that biotransformation is required for growth inhibition. Inhibition of the CYP1A1 monooxygenase completely blocked growth inhibition induced by B[a]P or B[a]P-7,8-dihydrodiol, but not by B[a]P-dihydrodiol-9,10-epoxide, indicating that CYP1A1-dependent metabolism of B[a]P into the terminal B[a]P-7,8-dihydrodiol-9,10-epoxide metabolite is required for growth inhibition. These studies show for the first time the metabolic requirements for PAH-mediated suppression of human B cell growth.

Immunomodulatory effects of in vitro exposure to organochlorines on T-cell proliferation in marine mammals and mice

Marine mammals bioaccumulate various environmental contaminants such as organochlorines (OCs), which biomagnify via the food web. While the immunomodulatory effects of individual OCs have been studied, the effects of mixtures are not well understood. The immunomodulatory effects of polychlorinated biphenyl (PCB) 138, 153, 169, and 180 as well as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and all possible mixtures were examined in marine mammals and mice. Lymphocyte proliferation was significantly modulated by OCs in all species tested, mostly by non-coplanar PCBs, as shown using regression analyses. Correlation analyses showed significant correlations (interpreted as additive effects) between OCs in mice, killer whales, and Steller sea lions. Nonadditive synergistic and antagonistic interactions between OCs were detected in most of the species tested. Toxic equivalency (TEQ) values used for OC toxicity assessment failed to predict the immunomodulatory effects measured in mice and marine mammals. The commonly used mouse model failed to predict immunomodulatory effects in other species. Clustering data suggested that phylogeny does not predict toxicity of OCs. Overall, our data suggest the presence of species-specific sensitivities to different mixtures, in which OCs interactions may be complex and that may exert their effects through dioxinlike or dioxin-independent pathways. Lastly, lymphocyte proliferation, an important part of adaptive immunity, was significantly modulated in mice and marine mammals, suggesting the possibility of increased susceptibility to diseases. These findings will be useful to better characterize the risk associated with OC exposure and possibly lead to new conservation and management strategies.

Perinatal exposure to low doses of PCB 153 and PCB 126 affects maternal and neonatal immunity in goat kids

Pregnant does (10 goats/group) were dosed orally either with polychlorinated biphenyl (PCB) 153 (98 microg/kg body weight/d) or PCB 126 (ng/kg body weight/d) dissolved in corn oil or with corn oil only (control group) from gestation day (GD) 60 until delivery. An additional group (n = 5) of pregnant does received the synthetic estrogen diethylstilbestrol (DES; 0.4 microg/kg body weight/d) by intramuscular injection using the same treatment schedule as for the PCB groups. Blood samples for immune analysis were collected at wk 0, 1, 2, 4, 6, and 8 of age. The effects of perinatal PCB exposure on postnatal humoral immune responses were examined by assessing the levels of total immunoglobulin G (IgG) and immunoglobulins to specific microbes at wk 0, 1, 2, 4, 6, and 8 of age, and immune responses following immunization of kids at 2 wk of age. PCB 153 exposure suppressed maternal and neonatal immunity, as demonstrated by reduced transfer of maternal IgG and specific antibodies to the environmental microbes Arcanobacterium pyogenes, Mannheimia haemolytica, and reovirus (REO-1). Furthermore, PCB 153 reduced the level of maternal antibodies to Mycobacterium avium paratuberculosis and equine influenza virus (EIV-1) in the newborn kids. The antibody response against EIV-1 was significantly higher in PCB 153-exposed kids 2 wk following immunization. PCB 126 exposure reduced the levels of maternal antibodies to REO-1. In contrast, gestational exposure to PCB 126 increased the concentrations of maternal antibodies to tetanus toxoid. No differences from controls in plasma total IgG levels at birth or colostrum IgG concentrations were observed in the PCB 126-treated does. However, a significant reduction in IgG levels from GD 60 until delivery was found in this group. Gestational exposure to DES reduced the concentrations of maternal antibodies against A. pyogenes, M. haemolytica, M. avium Paratuberculosis, and REO-1. These results suggest that perinatal exposure to low doses of PCB 126 and PCB 153 affects the maternal immunity in kids. The difference in responses between PCB 126 and PCB 153 treatment groups may strengthen the hypothesis that PCBs mediate immunotoxic effects through both AhR-dependent and -independent mechanisms. The observation that the effects produced by PCB 153 resembled those produced by DES raises the question of whether this congener may modulate immunity by estrogenic mechanisms.

The comparative immunotoxicity of five selected compounds following developmental or adult exposure

It is well established that human diseases associated with abnormal immune function, including some common infectious diseases and asthma, are considerably more prevalent at younger ages. Although not established absolutely, it is generally believed that development constitutes a period of increased immune system susceptibility to xenobiotics, since adverse effects may occur at lower doses and/or immunomodulation may be more persistent, thus increasing the relative risk of xenobiotic exposure to the immunologically immature organism. To address this issue, a brief overview of immune maturation in humans is provided to demonstrate that functional immaturity alone predisposes the young to infection. Age-dependent differences in the immunotoxic effects of five diverse compounds, diethylstilbestrol (DES), diazepam (DZP), lead (Pb), 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and tributyltin oxide (TBTO), which have undergone adult and developmental immunotoxicity testing in rodents, are then reviewed, as are human data when available. For all five chemicals, the developing immune system was found to be at greater risk than that of the adult, either because lower doses produced immunotoxicity, adverse effects were more persistent, or both.

Constitutive activation of the aryl hydrocarbon receptor in T-lineage cells induces thymus involution independently of the Fas/Fas ligand signaling pathway

Thymus involution is one of the most prominent consequences of exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The characteristic features of TCDD-induced thymic changes include reductions in the number of the thymocytes and in the ratio of CD4 to CD8 T cells in the thymus. While these changes have been shown to be caused by activation of a transcription factor, the aryl hydrocarbon receptor (AhR), the down-stream biological events that induce the thymic changes have not been determined. In the present study, we examined the involvement of Fas/Fas ligand (FasL)-dependent apoptosis, a likely mechanism suggested by previous studies, in the thymocyte loss by AhR activation of thymocytes. We recently generated transgenic (Tg) mice expressing a constitutively active AhR (CA-AhR) mutant specifically in T-lineage cells. These Tg mice reproduced the thymus involution caused by TCDD at relatively high doses. In this study, we crossed the T-cell-specific CA-AhR Tg mice with Faslpr mice, which have the homozygous defective fas (lpr) gene, or with FasLgld mice, which have the homozygous mutated fas ligand (gld) gene, to generate mice that are defective in Fas/FasL signaling and express the CA-AhR in T lineage cells. Faslpr and FasLgld CA-AhR Tg mice showed the same extent of thymocyte reduction as Faswt and FasLwt CA-AhR Tg mice. The ratio of CD4 to CD8 T cells in thymocytes was also not affected by the absence of Fas or FasL in the CA-AhR Tg mice. These results show that strong activation of the AhR in thymocytes induces thymus involution independently of Fas/FasL signaling.

T cell-derived IL-5 production is a sensitive target of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

The immune system is one of the organs most vulnerable to the toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Among the various immunotoxic effects of TCDD, the thymus involution and suppression of IgM antibody production are well known sensitive reactions of the thymocytes and B cells affected by TCDD. Recently, we reported that TCDD greatly inhibits the production of type-2 helper T (Th2) cell-derived cytokines, especially IL-5, by the splenocytes in mice immunized with ovalbumin (OVA). In the present study, we investigated the dose-dependency of these TCDD immunotoxic effects in OVA-immunized mice to identify the most sensitive target. Mice of two age groups, 6 weeks old and 3 weeks old, were dosed with 0.3, 1.0, or 3.0 microg TCDD/kg and immunized with OVA using alum as an adjuvant. Seven days later, the thymus weight, thymocyte population, antigen-specific IgM in the plasma, and IL-5 production by the splenocytes were examined. Among them, IL-5 production was significantly suppressed by all three doses of TCDD and reduced to about 30% by even a small dose of 0.3 microg TCDD/kg in both age groups. The thymus weight was significantly reduced by 1.0 microg or 3.0 microg TCDD/kg, but IgM production was not affected by up to 3.0 microg/kg of TCDD in both age groups. Taken together, the Th2 cell-derived IL-5 production was the most sensitive endpoint detecting TCDD toxicity among those examined. Our results also suggest that effector T cells are targets more vulnerable to TCDD toxicity than thymocytes or antibody-producing B cells in the OVA-immunized mice.

Effects of a single dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin, given at post-puberty, in senescent mice

2,3,7,8-Tetrachlorodibenzo-p-dioxin is a well-known immunosuppressive environmental pollutant. TCDD interferes with physiological signaling of the arylhydrocarbon receptor, leading to cell-specific changes in gene transcription and cell differentiation. With respect to the immune system, the T-cell lineage and B-cell lineages are particularly affected. Although a single dose given to mice is excreted within weeks, these changes in differentiation may have long-term consequences for immune competence. We studied the effects of a single dose of TCDD given to young mice on some parameters of their immune system after they had aged almost to the end of their lifespan. Groups of 15 mice were given either 2.5 microg TCDD/kg b.w. or 25 microg TCDD/kg b.w. at the age of 8-12 weeks, and were analyzed between 16 and 21 months of age. Survival was equal in all groups. Blood glucose levels did not differ, and glucose tolerance after oral challenge was normal in old control mice and TCDD-exposed mice. No differences in the frequencies of B-cells, T-cells, or NK-cells were detectable. TCDD-exposed mice at both doses had a significantly higher titer of IgM compared to controls. Histological examination of pancreas, liver, kidney, spleen, and lungs yielded no differences, except for the lungs, where a significantly higher number of animals displayed activated BALT. In conclusion, our data suggest that a single dose of TCDD in young mice is correlated to activated secondary lymphoid tissues and high IgM titers. Both findings are congruent with a weakened immune system.

Evaluation of relative potencies of PCB126 and PCB169 for the immunotoxicities in ovalbumin (OVA)-immunized mice

Dioxin-like polychlorinated biphenyls (PCBs) exert their toxicities by activating the arylhydrocarbon receptor (AhR), a ligand-dependent transcription factor, in a similar manner to the most toxic dioxin, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). In the present study, we re-evaluated the relative potency (REP) of the toxic members of dioxin-like PCBs, PCB126 (toxic equivalency factor, TEF 0.1) and PCB169 (TEF 0.01) relative to TCDD, focusing our attention on their effects on the immune reactions of mice immunized with ovalbumin (OVA). Thymus involution, IgM production, and IL-5 produced by the splenocytes were examined in addition to CYP1A1 induction, the established index of AhR-activation, in the spleen. PCB126 had an REP value of 0.1 because of its effects on thymus, IgM, IL-5, and CYP1A1 induction in the spleen, although its effect on IgG1 production was weaker. On the other hand, PCB169 had a smaller REP value estimated at less than 0.01 with regard to CYP1A1 induction in the spleen and all examined immunological effects, except for IgM production. The tissue concentrations of PCB169 and TCDD could not explain the reason for the smaller potency of PCB169, since the spleen contained a higher proportion of PCB169 to TCDD than dosed. These results indicate that dioxin-like PCBs, especially PCB169, shows deviating REPs against immune reactions, and also suggest that PCB169-liganded AhR behaves differently from TCDD-liganded AhR in immune cells.

Protective Effects of Vitamin A and Vitamin E Succinate against 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD)-Induced Body Wasting, Hepatomegaly, Thymic Atrophy, Production of Reactive Oxygen Species and DNA Damage in C57BL/6J Mice

The protective effect of vitamin A and vitamin E succinate against 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced acute toxicity and measures of oxidative stress was studied. Ten mice were treated with either vitamin A (50 mg/kg every other day for eight days) or vitamin E succiante (150 mg/kg/day followed by a dose of 40 mg/kg/day for five additional days). Half of each of the above groups of animals received TCDD on day 4. Five mice received corn oil or TCDD alone. After five days of TCDD treatment, antioxidant combination treatment with vitamin A and TCDD or vitamin E succinate and TCDD resulted in a significant reduction in indicators of acute toxicity including the decrease in total body and thymus weight as compared to TCDD alone (P<0.05). The combination treatment produced also a significant reduction in the increase in liver weight as compared to TCDD only (P<0.05). Following one day of treatment with 50 microg TCDD/kg, vitamin A and vitamin E succinate produced a significant decrease in the production of superoxide anion by peritoneal lavage cells (P<0.05) and in DNA-single strand breaks in the same cells (P<0.05) as assessed by the reduction of cytochrome c and the alkaline elution technique, respectively. A significant decrease in DNA-single strand breaks in peritoneal lavage cells was observed following 5 days treatment with 50 microg TCDD/kg (P<0.05). The results indicate a potential role for oxidative stress in the acute toxicity of TCDD and a protective effect for vitamin A and vitamin E succinate in the overall toxicity of TCDD including measures of oxidative stress.

Interactions at a dioxin responsive element (DRE) and an overlapping kappaB site within the hs4 domain of the 3'alpha immunoglobulin heavy chain enhancer

Our previous results describing the CH12.LX (AhR-expressing) and BCL-1 (AhR-deficient) B cell lines have supported an AhR/dioxin-responsive element (DRE)-mediated mechanism for TCDD-induced inhibition of micro heavy chain expression and thus of IgM secretion. Transcriptional regulation of the Ig heavy chain genes involves several regulatory elements including the 3'alpha Ig heavy chain enhancer, which is composed of four regulatory domains that span approximately 40 kb. One of these domains, hs4, contains a DRE-like site that overlaps a kappaB motif. We have previously demonstrated TCDD-inducible binding of both the AhR nuclear complex and NF-kappaB/Rel proteins to the DRE and kappaB motifs, respectively, as well as TCDD and LPS-induced transcriptional activity through the hs4 domain. The objective of the present study was to determine if the AhR nuclear complex and NF-kappaB/Rel proteins converge at these two overlapping cis-elements and act cooperatively to influence enhancer activity. To eliminate the potential influence of other transcription factors which bind to the hs4 domain, the approach was to construct a series of luciferase reporters containing a variable heavy chain (VH) promoter and a 42 bp fragment of the 1.4 kb hs4 regulatory domain, that included only the overlapping DRE and kappaB motif or mutations of these motifs for transient transfection experiments in CH12.LX and BCL-1 cells. In the CH12.LX cells, TCDD activated the hs4 fragment; however, co-treatment with LPS led to a marked and synergistic activation as previously observed with the wild type 1.4 kb hs4 domain. Mutation of either or both of the DRE and kappaB motifs diminished the effect of TCDD and LPS on the luciferase reporters possessing the 42 bp portion of hs4, and resembled the effect of these treatments on the promoter alone. In the BCL-1 cells, activity of the hs4 fragment was not induced by TCDD and/or LPS treatment. These results suggest that the AhR nuclear complex and NF-kappaB/Rel proteins converge at the DRE and kappaB motif to influence transcriptional activity of the hs4 enhancer fragment.

A Constitutively Active Arylhydrocarbon Receptor Induces Growth Inhibition of Jurkat T Cells through Changes in the Expression of Genes Related to Apoptosis and Cell Cycle Arrest

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is known to suppress T cell-dependent immune reactions through the activation of the arylhydrocarbon receptor (AhR). Our previous findings suggest that TCDD inhibits the activation and subsequent expansion of T cells following antigen stimulation in mice, leading to a decreased level of T cell-derived cytokines involved in antibody production. In the present study, we investigated the effects of activated AhR on T cells by transiently expressing a constitutively active AhR (CA-AhR) mutant in AhR-null Jurkat T cells. In agreement with our previous findings, CA-AhR markedly inhibited the growth of Jurkat T cells. The inhibited cell growth was found to be concomitant with both an increase in the annexin V-positive apoptotic cells and the accumulation of cells in the G(1) phase. The growth inhibition was also shown to be mediated by both xenobiotic response element (XRE)-dependent and -independent mechanisms, because an A78D mutant of the CA-AhR, which lacks the ability of XRE-dependent transcription, partially inhibited the growth of Jurkat T cells. Furthermore, we demonstrated that CA-AhR induces expression changes in genes related to apoptosis and cell cycle arrest. These expression changes were shown to be solely mediated in an XRE-dependent manner, because the A78D mutant of the CA-AhR did not induce them. To summarize, these results suggest that AhR activation causes apoptosis and cell cycle arrest, especially through expression changes in genes related to apoptosis and cell cycle arrest by the XRE-dependent mechanism, leading to the inhibition of T cell growth.