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

TCDD and CH223191 Alter T Cell Balance but Fail to Induce Anti-Inflammatory Response in Adult Lupus Mice

Aryl hydrocarbon receptor (AhR) responds to endogenous and exogenous ligands as a cytosolic receptor, transcription factor, and E3 ubiquitin ligase. Several studies support an anti-inflammatory effect of AhR activation. However, exposure to the AhR agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) during early stages of development results in an autoimmune phenotype and exacerbates lupus. The effects of TCDD on lupus in adults with pre-existing autoimmunity have not been described. We present novel evidence that AhR stimulation by TCDD alters T cell responses but fails to impact lupus-like disease using an adult mouse model. Interestingly, AhR antagonist CH223191 also changed T cell balance in our model. We next developed a conceptual framework for identifying cellular and molecular factors that contribute to physiological outcomes in lupus and created models that describe cytokine dynamics that were fed into a system of differential equations to predict the kinetics of T follicular helper (Tfh) and regulatory T (Treg) cell populations. The model predicted that Tfh cells expanded to larger values following TCDD exposure compared with vehicle and CH223191. Following the initial elevation, both Tfh and Treg cell populations continuously decayed over time. A function based on the ratio of predicted Treg/Tfh cells showed that Treg cells exceed Tfh cells in all groups, with TCDD and CH223191 showing lower Treg/Tfh cell ratios than the vehicle and that the ratio is relatively constant over time. We conclude that AhR ligands did not induce an anti-inflammatory response to attenuate autoimmunity in adult lupus mice. This study challenges the dogma that TCDD supports an immunosuppressive phenotype.

Endocrine-disrupting chemicals and autoimmune diseases

Endocrine-disrupting chemicals (EDCs) widely exist in people's production and life which have great potential to damage human and animal health. Over the past few decades, growing attention has been paid to the impact of EDCs on human health, as well as immune system. So far, researchers have proved that EDCs (such as bisphenol A (BPA), phthalate, tetrachlorodibenzodioxin (TCDD), etc.) affect human immune function and promotes the occurrence and development of autoimmune diseases (ADs). Therefore, in order to better understand how EDCs affect ADs, we summarized the current knowledge about the impact of EDCs on ADs, and elaborated the potential mechanism of the impact of EDCs on ADs in this review.

The Ancestral Environment Shapes Antiviral CD8+ T cell Responses across Generations

Recent studies have linked health fates of children to environmental exposures of their great grandparents. However, few studies have considered whether ancestral exposures influence immune function across generations. Here, we report transgenerational inheritance of altered T cell responses resulting from maternal (F0) exposure to the aryl hydrocarbon receptor ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Since F0 exposure to TCDD has been linked to transgenerational transmission of reproductive problems, we asked whether maternal TCDD exposure also caused transgenerational changes in immune function. F0 exposure caused transgenerational effects on the CD8+ T cell response to influenza virus infection in females but not in males. Outcrosses showed changes were passed through both parental lineages. These data demonstrate that F0 exposure to an aryl hydrocarbon receptor (AHR) agonist causes durable changes to immune responses that can affect subsequent generations. This has broad implications for understanding how the environment of prior generations shapes susceptibility to pathogens and antiviral immunity in later generations.

Type 3 innate lymphoid cells are altered in colons of C57BL/6 mice with dioxin exposure

Type 3 innate lymphoid cells (ILC3s) are distributed in the gut and regulate inflammation by secreting cytokines, including interferon (IFN)-γ and interleukin (IL)-17. The maintenance and function of ILC3s involve the activity of aryl hydrocarbon receptor (AhR), a potent ligand of which is 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), one of the most toxic dioxin congeners. Thus, TCDD exposure might affect ILC3s. To obtain in vivo evidence supporting this notion, we exposed female C57BL/6 mice orally to TCDD (low/high doses: 0.1/10 μg/kg body weight) during pregnancy and lactation periods, and after the exposure, evaluated the mothers and offspring for alterations in ILC3 differentiation and function in the colon. ILC3 frequency among colonic lamina propria lymphocytes was preferentially diminished in the offspring, and, in parallel, the median fluorescence intensity (MFI) of retinoic acid receptor-related orphan receptor (ROR)γt, which is associated with ILC3 differentiation, was also decreased in ILC3s. Conversely, the percentages of two subsets of the cells, one positive for natural cytotoxicity receptor NKp46 and the other for IL-17a, were increased in TCDD-exposed mothers and offspring. Moreover, the percentage of IFN-γ⁺ ILC3s was increased specifically in the mothers, but this was in conjunction with a significant decrease in the MFI of IFN-γ, which suggests that the IFN-γ⁺ ILC3 subset was functionally altered. In conclusion, maternal exposure to TCDD suppresses ILC3 differentiation in the offspring and influences ILC3 function in distinct manners in the mother and offspring. Our study provides new insights into the intergenerational interference of dioxins in colonic ILC3s.

Epigenetic underpinnings of developmental immunotoxicity and autoimmune disease

The concordance rate for developing autoimmune disease in identical twins is around 50% demonstrating that gene and environmental interactions contribute to disease etiology. The environmental contribution to autoimmune disease is a wide-ranging concept including exposure to immunotoxic environmental chemicals. Because the immune system is immature during development suggests that adult-onset autoimmunity may originate when the immune system is particularly sensitive. Among the pollutants most closely associated with inflammation and/or autoimmunity include Bisphenol-A, mercury, TCDD, and trichloroethylene. These toxicants have been shown to impart epigenetic changes (e.g., DNA methylation) that may alter immune function and promote autoreactivity. Here we review these autoimmune-promoting toxicants and their relation to immune cell epigenetics both in terms of adult and developmental exposure.

Modulatory Influence of Segmented Filamentous Bacteria on Transcriptomic Response of Gnotobiotic Mice Exposed to TCDD

Environmental toxicants such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), an aryl hydrocarbon receptor (AhR), are known to induce host toxicity and structural shifts in the gut microbiota. Key bacterial populations with similar or opposing functional responses to AhR ligand exposure may potentially help regulate expression of genes associated with immune dysfunction. To examine this question and the mechanisms for AhR ligand-induced bacterial shifts, C57BL/6 gnotobiotic mice were colonized with and without segmented filamentous bacteria (SFB) – an immune activator. Mice were also colonized with polysaccharide A producing Bacteroides fragilis – an immune suppressor to serve as a commensal background. Following colonization, mice were administered TCDD (30 μg/kg) every 4 days for 28 days by oral gavage. Quantified with the nCounter^® mouse immunology panel, opposing responses in ileal gene expression (e.g., genes associated with T-cell differentiation via the class II major histocompatibility complex) as a result of TCDD dosing and SFB colonization were observed. Genes that responded to TCDD in the presence of SFB did not show a significant response in the absence of SFB, and vice versa. Regulatory T-cells examined in the mesenteric lymph-nodes, spleen, and blood were also less impacted by TCDD in mice colonized with SFB. TCDD-induced shifts in abundance of SFB and B. fragilis compared with previous studies in mice with a traditional gut microbiome. With regard to the mouse model colonized with individual populations, results indicate that TCDD-induced host response was significantly modulated by the presence of SFB in the gut microbiome, providing insight into therapeutic potential between AhR ligands and key commensals.

Fetal Hematopoietic Stem Cells Are the Canaries in the Coal Mine That Portend Later Life Immune Deficiency

Disorders of the blood system are a significant and growing global health concern and include a spectrum of diseases ranging from aplastic anemia and leukemias to immune suppression. This array of hematological disorders is attributed to the fact that the blood system undergoes a perpetual cycle of turn over with aged and exhausted red and white blood cells undergoing daily replacement. The foundational cells of this replenishment process are comprised of rare hematopoietic stem cells (HSCs) located in the bone marrow that possess the dual function of long-term self-renewal and multilineage differentiation. This constant turnover makes the hematopoietic system uniquely vulnerable to changes in the environment that impact multilineage differentiation, self-renewal, or both. Notably, environmental endocrine-disrupting exposures occurring during development, when HSCs are first emerging, can lead to alterations in HSC programming that impacts the blood and immune systems throughout life. In this review, we describe the process of fetal hematopoiesis and provide an overview of the intrauterine environmental and endocrine-disrupting compounds that disrupt this process. Finally, we describe research opportunities for fetal HSCs as potential sentinels of later-life blood and immune system disorders.

Developmental Activation of the AHR Increases Effector CD4+ T Cells and Exacerbates Symptoms in Autoimmune Disease-Prone Gnaq+/- Mice

Perinatal environmental exposures are potentially important contributors to the increase in autoimmune diseases. Yet, the mechanisms by which these exposures increase self-reactive immune responses later in life are poorly understood. Autoimmune diseases require CD4(+) T cells for initiation, progression, and/or clinical symptoms; thus, developmental exposures that cause durable changes in CD4(+) T cells may play a role. Early life activation of the aryl hydrocarbon receptor (AHR) causes persistent changes in the response of CD4(+) T cells to infection later in life but whether CD4(+) T cells are affected by developmental exposure in the context of an autoimmune disease is unknown. Gnaq(+/-) mice develop symptoms of autoimmune disease similar to those measured clinically, and therefore can be used to evaluate gene-environment interactions during development on disease progression. Herein, we examined the effect of AHR activation in utero and via lactation, or solely via lactation, on disease onset and severity in adult Gnaq(+/-) offspring. Developmental activation of the AHR-accelerated disease in Gnaq(+/-) mice, and this correlates with increases in effector CD4(+) T-cell populations. Increased symptom onset and cellular changes due to early life AHR activation were more evident in female Gnaq(+/-) mice compared with males. These observations suggest that developmental AHR activation by pollutants, and other exogenous ligands, may increase the likelihood that genetically predisposed individuals will develop clinical symptoms of autoimmune disease later in life.

Immunotoxicology and its application in risk assessment

Immunotoxicology is the study of undesired modulation of the immune system by extrinsic factors. Toxicological assessments have demonstrated that the immune system is a target following exposure to a diverse group of xenobiotics including ultraviolet radiation, chemical pollutants, therapeutics, and recreational drugs. There is a well-established cause and effect relationship between suppression of the immune response and reduced resistance to infections and certain types of neoplasia. In humans, mild-to-moderate suppression of the immune response is linked to reduced resistance to common community-acquired infections, whereas opportunistic infections, which are very rare in the general population, are common in individuals with severe suppression. Xenobiotic exposure may also result in unintended stimulation of immune function. Although a cause and effect relationship between unintended stimulation of the immune response and adverse consequences has yet to be established, evidence does suggest that hypersensitivity, autoimmunity, and pathological inflammation may be exacerbated in susceptible populations exposed to certain xenobiotics. Xenobiotics can act as allergens and elicit hypersensitivity responses, or they can modulate hypersensitivity responses to other allergens such as pollen or dust mite by acting as adjuvants, enhancing the development or expression of hypersensitivity. Allergic contact dermatitis, allergic rhinitis, and asthma are the most commonly encountered types of hypersensitivity reactions resulting from chemical exposure. The immunologic effectors and mechanisms involved in autoimmune reactions are the same as those associated with responses to foreign antigens; however, the reactions are directed against the host's own cells. Thus, chemicals that induce immune suppression, nonspecific immunostimulation, or hypersensitivity may also impact autoimmunity. Risk assessment for immunotoxicity should be performed using the same approaches and principles for other noncancer effects. However, since xenobiotics may have effects on more than one aspect of immune function, immunotoxicity data should be evaluated separately for evidence of suppression, stimulation, hypersensitivity, and autoimmunity.

Developmental exposure to 2,3,7,8 tetrachlorodibenzo-p-dioxin attenuates capacity of hematopoietic stem cells to undergo lymphocyte differentiation

The process of hematopoiesis, characterized by long-term self-renewal and multi-potent lineage differentiation, has been shown to be regulated in part by the ligand-activated transcription factor known as the aryl hydrocarbon receptor (AHR). 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), a ubiquitous contaminant and the most potent AHR agonist, also modulates regulation of adult hematopoietic stem and progenitor cell (HSC/HPC) homeostasis. However, the effect of developmental TCDD exposure on early life hematopoiesis has not been fully explored. Given the inhibitory effects of TCDD on hematopoiesis and lymphocyte development, we hypothesized that in utero exposure to TCDD would alter the functional capacity of fetal HSC/HPCs to complete lymphocyte differentiation. To test this hypothesis, we employed a co-culture system designed to facilitate the maturation of progenitor cells to either B or T lymphocytes. Furthermore, we utilized an innovative limiting dilution assay to precisely quantify differences in lymphocyte differentiation between HSC/HPCs obtained from fetuses of dams exposed to 3μg/kg TCDD or control. We found that the AHR is transcribed in yolk sac hematopoietic cells and is transcriptionally active as early as gestational day (GD) 7.5. Furthermore, the number of HSC/HPCs present in the fetal liver on GD 14.5 was significantly increased in fetuses whose mothers were exposed to TCDD throughout pregnancy. Despite this increase in HSC/HPC cell number, B and T lymphocyte differentiation is decreased by approximately 2.5 fold. These findings demonstrate that inappropriate developmental AHR activation in HSC/HPCs adversely impacts lymphocyte differentiation and may have consequences for lymphocyte development in the bone marrow and thymus later in life.

Parabens: potential impact of low-affinity estrogen receptor binding chemicals on human health

Parabens, alkyl esters of p-hydroxybenzoic acid, are widely used in cosmetics, pharmaceuticals, personal care products and as food additives to inhibit microbial growth and extend product shelf life. Consumers of these compounds are frequently exposed via the skin, lips, eyes, oral mucosa, nails, and hair. Parabens are estrogenic molecules but exert weaker activity than natural estrogens, which would imply a low risk. Consistent with this idea, a number of recent commission reports from different countries suggested that parabens pose a negligible endocrine-disrupting risk at the recommended doses. However, individuals are not routinely exposed to a single paraben, and most of the available paraben toxicity data, reviewed in these reports, are from single-exposure studies. Further, assessing the additive and cumulative risk of multiple paraben exposure from daily use of multiple cosmetic and/or personal care products is presently not possible based on current studies. In this review, current and recent studies of paraben exposure and public health policies as well as critical gaps in the knowledge are discussed and new research directions regarding multiple exposures and novel target cohorts are recommended.

Prenatal cadmium exposure alters postnatal immune cell development and function

Cadmium (Cd) is generally found in low concentrations in the environment due to its widespread and continual use, however, its concentration in some foods and cigarette smoke is high. Although evidence demonstrates that adult exposure to Cd causes changes in the immune system, there are limited reports of immunomodulatory effects of prenatal exposure to Cd. This study was designed to investigate the effects of prenatal exposure to Cd on the immune system of the offspring. Pregnant C57Bl/6 mice were exposed to an environmentally relevant dose of CdCl(2) (10ppm) and the effects on the immune system of the offspring were assessed at two time points following birth (2 and 7weeks of age). Thymocyte and splenocyte phenotypes were analyzed by flow cytometry. Prenatal Cd exposure did not affect thymocyte populations at 2 and 7weeks of age. In the spleen, the only significant effect on phenotype was a decrease in the number of macrophages in male offspring at both time points. Analysis of cytokine production by stimulated splenocytes demonstrated that prenatal Cd exposure decreased IL-2 and IL-4 production by cells from female offspring at 2weeks of age. At 7weeks of age, splenocyte IL-2 production was decreased in Cd-exposed males while IFN-γ production was decreased from both male and female Cd-exposed offspring. The ability of the Cd-exposed offspring to respond to immunization with a S. pneumoniae vaccine expressing T-dependent and T-independent streptococcal antigens showed marked increases in the levels of both T-dependent and T-independent serum antibody levels compared to control animals. CD4(+)FoxP3(+)CD25(+) (nTreg) cell percentages were increased in the spleen and thymus in all Cd-exposed offspring except in the female spleen where a decrease was seen. CD8(+)CD223(+) T cells were markedly decreased in the spleens in all offspring at 7weeks of age. These findings suggest that even very low levels of Cd exposure during gestation can result in long term detrimental effects on the immune system of the offspring and these effects are to some extent sex-specific.

Changes in fibrinopeptide A peptides in the sera of rats chronically exposed to low doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a ubiquitously distributed endocrine disruptors. To investigate peptide changes in the sera of rats chronically exposed to TCDD and to explore the association of these changes with liver morphology, TCDD was administrated to male rats at doses of 140, 350, and 875 ng/kg/week for 29 weeks. Serum was collected and proteomic analysis was performed using automated Bruker Daltonics ClinProt with matrix-assisted laser desorption/ionization time-of-flight mass spectrometer. One peptide at 1740.89 was found to be significantly decreased and further identified with nano LC-MS/MS system. The MS BLAST homology search engine reported the peptide to be a partial sequence of fibrinopeptide A. Liver fatty degeneration and necrosis were assessed by hematoxylin and eosin staining. Liver fatty degeneration and necrosis were both found to be significantly increased after TCDD exposure. Levels of fibrinopeptide A were significantly correlated with liver fatty degeneration and necrosis.

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.

Immunotoxic effects of environmental toxicants in fish - how to assess them?

Numerous environmental chemicals, both long-known toxicants such as persistent organic pollutants as well as emerging contaminants such as pharmaceuticals, are known to modulate immune parameters of wildlife species, what can have adverse consequences for the fitness of individuals including their capability to resist pathogen infections. Despite frequent field observations of impaired immunocompetence and increased disease incidence in contaminant-exposed wildlife populations, the potential relevance of immunotoxic effects for the ecological impact of chemicals is rarely considered in ecotoxicological risk assessment. A limiting factor in the assessment of immunotoxic effects might be the complexity of the immune system what makes it difficult (1) to select appropriate exposure and effect parameters out of the many immune parameters which could be measured, and (2) to evaluate the significance of the selected parameters for the overall fitness and immunocompetence of the organism. Here, we present - on the example of teleost fishes - a brief discussion of how to assess chemical impact on the immune system using parameters at different levels of complexity and integration: immune mediators, humoral immune effectors, cellular immune defenses, macroscopical and microscopical responses of lymphoid tissues and organs, and host resistance to pathogens. Importantly, adverse effects of chemicals on immunocompetence may be detectable only after immune system activation, e.g., after pathogen challenge, but not in the resting immune system of non-infected fish. Current limitations to further development and implementation of immunotoxicity assays and parameters in ecotoxicological risk assessment are not primarily due to technological constraints, but are related from insufficient knowledge of (1) possible modes of action in the immune system, (2) the importance of intra- and inter-species immune system variability for the response against chemical stressors, and (3) deficits in conceptual and mechanistic assessment of combination effects of chemicals and pathogens.

Prenatal TCDD causes persistent modulation of the postnatal immune response, and exacerbates inflammatory disease, in 36-week-old lupus-like autoimmune SNF1 mice

BACKGROUND

Prenatal exposure to the persistent environmental pollutant and model Ah receptor agonist, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), has been shown to permanently suppress postnatal cell-mediated immunity. More recently, skewing of select adult T and B cell responses toward enhanced inflammation has also been described in C57BL/6 mice after prenatal TCDD. This raises questions about adverse postnatal immune consequences of prenatal TCDD in animals genetically predisposed to inappropriate inflammatory responses.

METHODS

Lupus-prone SNF(1) mice were exposed to 0, 40, or 80 µg/kg TCDD on gestation day (gd) 12 and examined at 36 weeks-of-age for immunomodulatory effects that correlated with worsened lupus pathology.

RESULTS

Bone marrow pro- and large pre-B cells were decreased by prenatal TCDD, in both adult male and female mice, as were pre- and immature B cells. Splenic CD23(-) CD1(hi) and CD19(+) CD5(+) B cells were increased in males, as were B220(hi) B cells in females, further suggesting persistent disruption of B cell lymphopoiesis by prenatal TCDD. Female mice displayed decreased IL-10 production by ConA-activated splenocytes, while males underproduced IL-4. Autoreactive CD4(+) Vβ17a(+) spleen T cells were increased in both sexes by 80 µg/kg TCDD. Male mice but not females showed increased anti-ds DNA and cardiolipin autoantibody levels.

CONCLUSIONS

Prenatal TCDD augmented the hallmark indicators of SLE progression in the lupus-prone SNF(1) mice, including renal immune complex deposition, glomerulonephritis, and mesangial proliferation. Prenatal TCDD therefore caused persistent modulation of the postnatal immune response, and exacerbated inflammatory disease, in lupus-like autoimmune SNF(1) mice.

Aryl hydrocarbon receptor activation in hematopoietic stem/progenitor cells alters cell function and pathway-specific gene modulation reflecting changes in cellular trafficking and migration

The aryl hydrocarbon receptor (AhR) is a transcription factor belonging to the Per-ARNT-Sim family of proteins. These proteins sense molecules and stimuli from the cellular/tissue environment and initiate signaling cascades to elicit appropriate cellular responses. Recent literature reports suggest an important function of AhR in hematopoietic stem cell (HSC) biology. However, the molecular mechanisms by which AhR signaling regulates HSC functions are unknown. In previous studies, we and others reported that treatment of mice with the AhR agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) compromises the competitive reconstitution of bone marrow (BM) cells into irradiated host animals. Additional studies indicated a requirement for AhR in hematopoietic cells and not marrow microenvironment cells. In this study, we tested the hypothesis that TCDD-mediated phenotypic and functional changes of HSCs are a result of changes in gene expression that disrupt stem cell numbers and/or their migration. TCDD treatment to mice increased the numbers of phenotypically defined HSCs in BM. These cells showed compromised migration to the BM in vivo and to the chemokine CXCL12 in vitro, as well as increased expression of the leukemia-associated receptors CD184 (CXCR4) and CD44. Gene expression profiles at 6 and 12 h after exposure were consistent with the phenotypic and functional changes observed. The expressions of Scin, Nqo1, Flnb, Mmp8, Ilf9, and Slamf7 were consistently altered. TCDD also disrupted expression of other genes involved in hematological system development and function including Fos, JunB, Egr1, Ptgs2 (Cox2), and Cxcl2. These data support a molecular mechanism for an AhR ligand to disrupt the homeostatic cell signaling of HSCs that may promote altered HSC function.

Reproductive immunology: a focus on the role of female sex hormones and other gender-related factors

Reproductive immunology has attracted the attention of researchers interested in fertility and pregnancy as well as those interested in immunity and autoimmunity. Over the past couple of decades, a wealth of data on the immune-reproductive interactions has been generated. This issue of the Journal will examine several topics including the role of immune factors in the induction of anti-Ro antibody-mediated autoimmunity in neonates and the immunological effects of gender and sex hormones. The possible implications of the research reviewed here for the development of novel therapeutic approaches are also addressed.

Prenatal TCDD in mice increases adult autoimmunity

Two immunologically different mouse strains, C57BL/6 and SNF(1), were exposed to a mid-gestation dose of TCDD. The C57BL/6 mouse has a high-affinity aryl hydrocarbon receptor (AhR) and is sensitive to TCDD. The SNF(1) mouse has a low-affinity AhR but spontaneously develops autoimmune nephritis. Autoreactive Vβ(+)CD4(+)17a and Vβ(+)CD3(+) T cells were increased at 24-weeks-of-age in offspring of C57BL/6 mice, more so in females than males. The cytokine IFN-γ was elevated in the females, while IL-10 was elevated in males. Phenotypic changes in B-lineage cells were present in bone marrow and spleen, and circulating autoantibodies were increased after prenatal TCDD. Kidneys of males showed significant anti-IgG and anti-C3 deposition, suggesting early-stage autoimmune disease. The SNF(1) offspring similarly showed increased peripheral Vβ(+) cells in the females, increased autoantibody production in both sexes, and increased IFN-γ production in females. Male SNF(1) mice had increased anti-IgG and anti-C3 deposition in kidneys. Both mouse models therefore showed clear signatures of enhanced autoimmunity after prenatal TCDD.

Perinatal exposure of mice to TCDD decreases allergic sensitisation through inhibition of IL-4 production rather than T regulatory cell-mediated suppression

OBJECTIVE

The 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a widespread, man-made, persistent organic pollutant with high immunotoxic potentials. It suppresses cell-mediated and humoral immune responses through mechanisms dependent on aryl-hydrocarbon receptor expression and immunosuppressive activity of the cells. Most sensitive to TCDD are organisms during fetal and infant life, mostly due to the developmental stage of many biological systems of the host, including immune system. Recent data show that T regulatory cells that have the potential to suppress immune reactions and which develop after TCDD exposure are also responsible for protection from allergy development. Our goal was to investigate if perinatal exposure to TCDD can affect allergic sensitisation and if T reg cells participate in this phenomenon.

MATERIALS AND METHODS

Mice, Balb/c, were perinatally exposed to TCDD or to the carrier. Six weeks old control or exposed mice were sensitised with ovalbumin. Spleen cells of the animals were used to assess the content of T reg cells by means of flow cytometry. Levels of cytokines were assessed by ELISA technique in supernatants of the cells stimulated with anti-CD3 antibody. As a measure of sensitisation, total IgE and anti-OVA IgE were measured in serum of mice by ELISA method. To assess the function of T reg cells isolated from OVA-sensitised control or TCDD exposed animals we performed transfer studies.

RESULTS

Here we show that perinatal exposure to TCDD decreases allergic sensitisation and that this process is related to inhibition of IL-4 synthesis rather than suppression mediated by T regulatory cells.

CONCLUSION

We hypothesise that dioxin exposure can be an important environmental modulator of immunological responses that participate in allergic reactions.

Identifying patterns of immune-related disease: use in disease prevention and management

BACKGROUND

Childhood susceptibility to diseases linked with immune dysfunction affects over a quarter of the pediatric population in some countries. While this alone is a significant health issue, the actual impact of immune-related diseases extends over a lifetime and involves additional secondary conditions. Some comorbidities are well known (e.g., allergic rhinitis and asthma). However, no systematic approach has been used to identify life-long patterns of immune-based disease where the primary condition arises in childhood. Such information is useful for both disease prevention and treatment approaches.

DATA SOURCES

Recent primary research papers as well as review articles were obtained from PubMed, Chem Abstracts, Biosis and from the personal files of the authors. Search words used were: the diseases and conditions shown Figs. 1 and 2 in conjunction with comorbid, comorbidities, pediatric, childhood, adult, immune, immune dysfunction, allergy, autoimmune, inflammatory, infectious, health risks, environment, risk factors.

RESULTS

Childhood diseases such as asthma, type-1 diabetes, inflammatory bowel disease, respiratory infections /rhinitis, recurrent otitis media, pediatric celiac, juvenile arthritis and Kawasaki disease are examples of significant childhood health problems where immune dysfunction plays a significant role. Each of these pediatric diseases is associated with increased risk of several secondary conditions, many of which appear only later in life. To illustrate, four prototypes of immune-related disease patterns (i.e., allergy, autoimmunity, inflammation and infectious disease) are shown as tools for: 1) enhanced disease prevention; 2) improved management of immune-based pediatric diseases; and 3) better recognition of underlying pediatric immune dysfunction.

CONCLUSIONS

Identification of immune-related disease patterns beginning in childhood provides the framework for examining the underlying immune dysfunctions that can contribute to additional diseases in later life. Many pediatric diseases associated with dysfunctional immune responses have been linked with an elevated risk of other diseases or conditions as the child ages. Diseases within a pattern may be interlinked based on underlying immune dysfunctions and/or current therapeutic approaches for managing the entryway diseases. It may be beneficial to consider treatment options for the earliest presenting diseases that will concomitantly reduce the risk of immune-linked secondary conditions. Additionally, improved disease prevention is possible with more relevant and age-specific immune safety testing.

The aryl hydrocarbon receptor: regulation of hematopoiesis and involvement in the progression of blood diseases

The aryl hydrocarbon receptor (AhR) is a basic helix-loop-helix protein that belongs to the superfamily of environment-sensing PAS (Per-ARNT-Sim) proteins. A large number of ligands have been described to bind AhR and promote its nuclear translocation. In the nucleus, the AhR and its dimerization partner the AhR nuclear translocator (ARNT) form a DNA-binding complex that acts as a transcriptional regulator. Animal and human data suggest that, beyond its mediating responses to xenobiotic and/or unknown endogenous ligands, the AhR has a role, although as yet undefined, in the regulation of cell cycle and inflammation. The AhR also appears to regulate the hematopoietic and immune systems during development and adult life in a cell-specific manner. While accidental exposure to xenobiotic AhR ligands has been associated with leukemia in humans, the specific mechanisms of AhR involvement are still not completely understood. However, recent data are consistent with a functional role of the AhR in the maintenance of hematopoietic stem and/or progenitor cells (HSCs/HPCs). Studies highlighting AhR regulation of HSCs/HPCs provide a rational framework to understand their biology, a role of the AhR in hematopoietic diseases, and a means to develop interventions for these diseases.

Risk of autoimmune disease: challenges for immunotoxicity testing

Autoimmunity represents a potentially diverse and complex category among the range of adverse outcomes for detection with immunotoxicity testing. For this reason, the risk of autoimmune disease is discussed in this overview chapter with additional mention among the later specific protocol chapters. Improvements in clinical diagnostic capabilities and disease recognition have led to a more accurate picture of the extent of autoimmune diseases across different human populations. While the risk of any single autoimmune disease remains modest when compared with that of lung or heart disease, the cumulative prevalence of autoimmune diseases is both significant and increasing. Autoimmune diseases are usually viewed in the context of the damaged tissue or organ (e.g., as a thyroid, gastrointestinal, cardiovascular or neurological disease). But improved recognition that underlying immune dysfunction can connect the risks for these as well as other diseases is critical for optimizing risk assessment. Since autoimmune diseases are chronic in nature with many first appearing in children or in young adults, these diseases exert a serious impact on both health care costs and quality of life. This chapter provides a discussion of the issues that should be considered with immunotoxicity testing for risk of autoimmunity.

Developmental exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin alters postnatal T cell phenotypes and T cell function and exacerbates autoimmune lupus in 24-week-old SNF1 mice

BACKGROUND

Untreated, more than 95% of female SWR x NZB: F(1) (SNF(1)) mice spontaneously develop a fatal lupus-like glomerulonephritis by 8 months-of-age, while disease onset in males is much slower.

METHODS

: Timed-pregnant SNF(1) mice (10 per treatment) were exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on gestational day (GD) 12 by oral maternal gavage with 0, 40, or 80 microg/kg TCDD.

RESULTS

Offspring of the TCDD-exposed dams showed numerous alterations in T lineage cells at 24 weeks-of-age. Females but not males showed decreased CD4(+)8(+) and increased CD4(-)8(-) thymocytes. Females also showed increased autoreactive CD4(+)Vbeta17(a+) axillary and inguinal lymph node T cells. Concanavalin A-stimulated splenocytes from prenatal TCDD-treated mice produced decreased interleukin 17 (IL-17) in the females while males showed increased IL-2 and IFN-gamma, and diminished IL-4. Mitogen-stimulated pan-lymphoproliferative responses were significantly increased across sex by TCDD. Anti-IgG and anti-C3 immune complex deposition in kidneys was present in the males after TCDD, and visibly worsened in females.

CONCLUSIONS

Developmental TCDD exposure can permanently alter T lymphopoiesis in autoimmune-prone SNF1 mice. The alteration profile is beyond the classic immune suppression response, to also include exacerbation and induction of a lupuslike autoimmune disease.

Gestational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin disrupts B-cell lymphopoiesis and exacerbates autoimmune disease in 24-week-old SNF1 mice

Female SNF(1) hybrid mice spontaneously develop an immune complex-mediated glomerulonephritis as early as 24 weeks of age, whereas the disease onset in males is much slower. Further, a rise in concentration of glomerulus-specific autoantibodies via autoreactive B cells is critical to progression of the disease in this strain. Environmental factors contributing to the onset or degree of such autoimmunity are of interest yet poorly understood. In the present study, time-pregnant SWR x NZB dams (10/treatment) were gavaged on gestational 12 with 40 or 80 mg/kg 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and the SNF(1) offspring were evaluated at 24 weeks of age. Bone marrow B220(low)CD24(-)AA4.1(+) committed B lineage progenitors were increased in female offspring by TCDD, however, committed progenitors and pro-B cells were decreased in males. Splenic marginal zone B cells (CD21(hi)CD24(low-int)) were decreased and follicular B cells (CD21(int)CD24(low)) were increased across sex by prenatal TCDD, whereas transitional-2 B cells (CD21(int)CD24(hi)) and (CD23(low-int) CD1(low-int)) were decreased in males only. Antibodies to double-stranded DNA were significantly increased across sex by TCDD. Anti-IgG and anti-C3 immune complex renal deposition was visibly worsened in females, and present in TCDD-treated males. These data suggest that developmental exposure to TCDD permanently and differentially alters humoral immune function by sex, and exacerbates a type III hypersensitivity lupus-like autoimmune disease in genetically predisposed mice.

Assessment of trichloroethylene (TCE) exposure in murine strains genetically-prone and non-prone to develop autoimmune disease

There is increasing laboratory and epidemiologic evidence relating exposure to trichloroethylene (TCE) with autoimmune disease including scleroderma and lupus. New Zealand Black/New Zealand White (NZBWF1) and B6C3F1 mice were exposed to TCE (0, 1, 400 or 14,000 ppb) via drinking water for 27 or 30 weeks, respectively. NZBWF1 mice spontaneously develop autoimmune disease while B6C3F1 mice, a standard strain used in immunotoxicology testing, are not genetically prone to develop autoimmune disease. During the TCE exposure period, serum levels of total IgG, and autoantibodies (anti-ssDNA, -dsDNA, and -glomerular antigen [GA]) were monitored. At the termination of the study, renal pathology, natural killer (NK) cell activity, total IgG levels, autoantibody production, T-cell activation, and lymphocytic proliferative responses were evaluated. TCE did not alter NK cell activity, or T- and B-cell proliferation in either strain. Numbers of activated T-cells (CD4+/CD44+) were increased in the B6C3F1 mice but not in the NZBWF1 mice. Renal pathology, as indicated by renal score, was significantly increased in the B6C3F1, but not in the NZBWF1 mice. Serum levels of autoantibodies to dsDNA and ssDNA were increased at more time points in B6C3F1, as compared to the NZBWF1 mice. Anti-GA autoantibodies were increased by TCE treatment in early stages of the study in NZBWF1 mice, but by 23 weeks of age, control levels were comparable to those of TCE-exposed animals. Serum levels anti-GA autoantibodies in B6C3F1 were not affected by TCE exposure. Overall, these data suggest that TCE did not contribute to the progression of autoimmune disease in autoimmune-prone mice during the period of 11-36 weeks of age, but rather lead to increased expression of markers associated with autoimmune disease in a non-genetically prone mouse strain.

Early-life environment, developmental immunotoxicology, and the risk of pediatric allergic disease including asthma

Incidence of childhood allergic disease including asthma (AD-A) has risen since the mid-20th century with much of the increase linked to changes in environment affecting the immune system. Childhood allergy is an early life disease where predisposing environmental exposures, sensitization, and onset of symptoms all occur before adulthood. Predisposition toward allergic disease (AD) is among the constellation of adverse outcomes following developmental immunotoxicity (DIT; problematic exposure of the developing immune system to xenobiotics and physical environmental factors). Because novel immune maturation events occur in early life, and the pregnancy state itself imposes certain restrictions on immune functional development, the period from mid-gestation until 2 years after birth is one of particular concern relative to DIT and AD-A. Several prenatal-perinatal risk factors have been identified as contributing to a DIT-mediated immune dysfunction and increased risk of AD. These include maternal smoking, environmental tobacco smoke, diesel exhaust and traffic-related particles, heavy metals, antibiotics, environmental estrogens and other endocrine disruptors, and alcohol. Diet and microbial exposure also significantly influence immune maturation and risk of allergy. This review considers (1) the critical developmental windows of vulnerability for the immune system that appear to be targets for risk of AD, (2) a model in which the immune system of the DIT-affected infant exhibits immune dysfunction skewed toward AD, and (3) the lack of allergy-relevant safety testing of drugs and chemicals that could identify DIT hazards and minimize problematic exposure of pregnant women and children.