Developmental immunotoxicity of trichloroethylene (TCE): studies in B6C3F1 mice

Reanalysis of Trichloroethylene and Tetrachloroethylene Metabolism to Glutathione Conjugates Using Human, Rat, and Mouse Liver in Vitro Models to Improve Precision in Risk Characterization

BACKGROUND

Both trichloroethylene (TCE) and tetrachloroethylene (PCE) are high-priority chemicals subject to numerous human health risk evaluations by a range of agencies. Metabolism of TCE and PCE determines their ultimate toxicity; important uncertainties exist in quantitative characterization of metabolism to genotoxic moieties through glutathione (GSH) conjugation and species differences therein.

OBJECTIVES

This study aimed to address these uncertainties using novel in vitro liver models, interspecies comparison, and a sensitive assay for quantification of GSH conjugates of TCE and PCE, S-(1,2-dichlorovinyl)glutathione (DCVG) and S-(1,2,2-trichlorovinyl) glutathione (TCVG), respectively.

METHODS

Liver in vitro models used herein were suspension, 2-D culture, and micropatterned coculture (MPCC) with primary human, rat, and mouse hepatocytes, as well as human induced pluripotent stem cell (iPSC)-derived hepatocytes (iHep).

RESULTS

We found that, although efficiency of metabolism varied among models, consistent with known differences in their metabolic capacity, formation rates of DCVG and TCVG generally followed the patterns human ≥ rat ≥ mouse , and primary hepatocytes > iHep . Data derived from MPCC were most consistent with estimates from physiologically based pharmacokinetic models calibrated to in vivo data.

DISCUSSION

For TCE, the new data provided additional empirical support for inclusion of GSH conjugation-mediated kidney effects as critical for the derivation of noncancer toxicity values. For PCE, the data reduced previous uncertainties regarding the extent of TCVG formation in humans; this information was used to update several candidate kidney-specific noncancer toxicity values. Overall, MPCC-derived data provided physiologically relevant estimates of GSH-mediated metabolism of TCE and PCE to reduce uncertainties in interspecies extrapolation that constrained previous risk evaluations, thereby increasing the precision of risk characterizations of these high-priority toxicants. https://doi.org/10.1289/EHP12006.

Volatile organic compounds: A proinflammatory activator in autoimmune diseases

The etiopathogenesis of inflammatory and autoimmune diseases, including pulmonary disease, atherosclerosis, and rheumatoid arthritis, has been linked to human exposure to volatile organic compounds (VOC) present in the environment. Chronic inflammation due to immune breakdown and malfunctioning of the immune system has been projected to play a major role in the initiation and progression of autoimmune disorders. Macrophages, major phagocytes involved in the regulation of chronic inflammation, are a major target of VOC. Excessive and prolonged activation of immune cells (T and B lymphocytes) and overexpression of the master pro-inflammatory constituents [cytokine and tumor necrosis factor-alpha, together with other mediators (interleukin-6, interleukin-1, and interferon-gamma)] have been shown to play a central role in the pathogenesis of autoimmune inflammatory responses. The function and efficiency of the immune system resulting in immunostimulation and immunosuppression are a result of exogenous and endogenous factors. An autoimmune disorder is a by-product of the overproduction of these inflammatory mediators. Additionally, an excess of these toxicants helps in promoting autoimmunity through alterations in DNA methylation in CD4 T cells. The purpose of this review is to shed light on the possible role of VOC exposure in the onset and progression of autoimmune diseases.

Irreversible effects of trichloroethylene on the gut microbial community and gut-associated immune responses in autoimmune-prone mice

The developing immune system is particularly sensitive to immunotoxicants. This study assessed trichloroethylene (TCE)-induced effects on the gut microbiome and cytokine production during the development in mice. Mice were exposed to TCE (0.05 or 500 μg/mL) at the levels that approximate to environmental or occupational exposure, respectively. Mice were subjected to a continuous developmental exposure to these doses encompassing gestation, lactation and continuing directly in the drinking water postnatally for 154 days (PND154) or PND259. To observe persistence of the effect TCE was removed from the drinking water in a subset of mice on PND154 and were provided regular drinking water until the study terminus (PND259). Abundance of total tissue-associated bacteria reduced only in mice exposed to TCE until PND259. The ratio of Firmicutes/Bacteroidetes did not alter during this continuos exposure; however, cessation of high-dose TCE at PND154 resulted in the increased abundance Bacteroidetes at PND259. Furthermore, high-dose TCE exposure until PND259 resulted in a lower abundance of the genera Bacteroides and Lactobaccilus and increased abundance of genus Bifidobactrium and bacterial family Enterobacteriaceae. TCE exposure until PND154 showed significant changes in the production of interleukin-33; that might play a dual role in maintaining the balance and homeostasis between commensal microbiota and mucosal health. At PND259, interleukin-3, granulocyte-macrophage colony-stimulating factor and Eotaxin were altered in both, the continuous exposure and cessation groups, whereas only a cessation group had a higher level of KC that may facilitate infiltration of neutrophils. The irreversible effects of TCE after a period of exposure cessation suggested a unique programming and potential toxicity of TCE even at the environmental level exposure.

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.

A single dose of trichloroethylene given during development does not substantially alter markers of neuroinflammation in brains of adult mice

Trichloroethylene (TCE) is a widespread environmental contaminant associated with developmental immunotoxicity and neurotoxicity. Previous studies have shown that MRL^+/+ mice exposed to TCE from gestation through early-life demonstrate robust increases in inflammatory markers in peripheral CD4⁺ T-cells, as well as glutathione depletion and increased oxidative stress in cerebellum-associated with alterations in behavior. Since increased oxidative stress is associated with neuroinflammation, we hypothesized that neuroinflammatory markers could be altered relative to unexposed mice. MRL^+/+ mice were given 0.5 mg/ml of TCE in vehicle or vehicle (water with 1% Alkamuls EL-620) from conception through early adulthood via drinking water to dams and then directly to post-weaning offspring. Animals were euthanized at 49 days of age and levels of pro- and anti-inflammatory cytokines, density of T-cell staining, and micro-glial morphology were evaluated in brains to begin to ascertain a neuroinflammatory profile. Levels of IL-6 were decreased in female animals and while not statistically significant, and levels of IL-10 were higher in brains of exposed male and female animals. Supportive of this observation, although not statistically significant, the number of ameboid microglia was higher in exposed relative to unexposed animals. This overall profile suggests the emergence of an anti-inflammatory/neuroprotective phenotype in exposed animals, possibly as a compensatory response to neuroinflammation that is known to be induced by developmental exposure to TCE.

Toxicological effects of trichloroethylene exposure on immune disorders

Trichloroethylene (TCE) is one of the most common ground water contaminants in USA. Even though recent regulation mandates restricted utilization of TCE, its use is not completely prohibited, especially in industrial and manufacturing processes. The risk of TCE on human health is an ongoing field of study and its implications on certain diseases such as cancer has been recognized and well-documented. However, the link between TCE and immune disorders is still an under-studied area. Studies on the risk of TCE on the immune system is usually focused on certain immune class disorders, but consensus on the impact of TCE on the immune system has not been established. This review presents representative work that investigates the effect of TCE on immune disorders and highlights future opportunities. We attempt to provide a broader perspective of the risks of TCE on the immune system and human health.

Inflammatory and oxidative stress-related effects associated with neurotoxicity are maintained after exclusively prenatal trichloroethylene exposure

Trichloroethylene (TCE) is a widespread environmental toxicant with immunotoxic and neurotoxic potential. Previous studies have shown that continuous developmental exposure to TCE encompassing gestation and early life as well as postnatal only exposure in the drinking water of MRL+/+ mice promoted CD4⁺ T cell immunotoxicity, glutathione depletion and oxidative stress in the cerebellum, as well increased locomotor activity in male offspring. The purpose of this study was to characterize the effects of exclusively prenatal exposure on these parameters. Another goal was to investigate potential plasma oxidative stress/inflammatory biomarkers to possibly be used as predictors of TCE-mediated neurotoxicity. In the current study, 6 week old male offspring of dams exposed gestationally to 0, 0.01, and 0.1mg/ml TCE in the drinking water were evaluated. Our results confirmed that the oxidized phenotype in plasma and cerebellum was maintained after exclusively prenatal exposure. A Phenotypic analysis by flow cytometry revealed that TCE exposure expanded the effector/memory subset of peripheral CD4⁺ T cells in association with increased production of pro-inflammatory cytokines IFN-γ and IL-17. Serum biomarkers of oxidative stress and inflammation were also elevated in plasma suggesting that systemic effects are important and may be used to predict neurotoxicity in our model. These results suggested that the prenatal period is a critical stage of life by which the developing CNS and immune system are susceptible to long-lasting changes mediated by TCE.

The trichloroethylene metabolite S-(1,2-dichlorovinyl)-l-cysteine but not trichloroacetate inhibits pathogen-stimulated TNF-α in human extraplacental membranes in vitro

Extraplacental membranes define the gestational compartment and provide a barrier to infectious microorganisms ascending the gravid female reproductive tract. We tested the hypothesis that bioactive metabolites of trichloroethylene (TCE) decrease pathogen-stimulated innate immune response of extraplacental membranes. Extraplacental membranes were cultured for 4, 8, and 24h with the TCE metabolites trichloroacetate (TCA) or S-(1,2-dichlorovinyl)-l-cysteine (DCVC) in the absence or presence of lipoteichoic acid (LTA) or lipopolysaccharide (LPS) to simulate infection. In addition, membranes were cocultured with DCVC and Group B Streptococcus (GBS). DCVC (5-50μM) significantly inhibited LTA-, LPS-, and GBS-stimulated cytokine release from tissue cultures as early as 4h (P≤0.05). In contrast, TCA (up to 500μM) did not inhibit LTA-stimulated cytokine release from tissue punches. Because cytokines are important mediators for host response to infectious microorganisms these findings suggest that TCE exposure could potentially modify susceptibility to infection during pregnancy.

Trichloroethylene: Mechanistic, epidemiologic and other supporting evidence of carcinogenic hazard

The chlorinated solvent trichloroethylene (TCE) is a ubiquitous environmental pollutant. The carcinogenic hazard of TCE was the subject of a 2012 evaluation by a Working Group of the International Agency for Research on Cancer (IARC). Information on exposures, relevant data from epidemiologic studies, bioassays in experimental animals, and toxicity and mechanism of action studies was used to conclude that TCE is carcinogenic to humans (Group 1). This article summarizes the key evidence forming the scientific bases for the IARC classification. Exposure to TCE from environmental sources (including hazardous waste sites and contaminated water) is common throughout the world. While workplace use of TCE has been declining, occupational exposures remain of concern, especially in developing countries. The strongest human evidence is from studies of occupational TCE exposure and kidney cancer. Positive, although less consistent, associations were reported for liver cancer and non-Hodgkin lymphoma. TCE is carcinogenic at multiple sites in multiple species and strains of experimental animals. The mechanistic evidence includes extensive data on the toxicokinetics and genotoxicity of TCE and its metabolites. Together, available evidence provided a cohesive database supporting the human cancer hazard of TCE, particularly in the kidney. For other target sites of carcinogenicity, mechanistic and other data were found to be more limited. Important sources of susceptibility to TCE toxicity and carcinogenicity were also reviewed by the Working Group. In all, consideration of the multiple evidence streams presented herein informed the IARC conclusions regarding the carcinogenicity of TCE.

Human health effects of trichloroethylene: key findings and scientific issues

BACKGROUND

In support of the Integrated Risk Information System (IRIS), the U.S. Environmental Protection Agency (EPA) completed a toxicological review of trichloroethylene (TCE) in September 2011, which was the result of an effort spanning > 20 years.

OBJECTIVES

We summarized the key findings and scientific issues regarding the human health effects of TCE in the U.S. EPA's toxicological review.

METHODS

In this assessment we synthesized and characterized thousands of epidemiologic, experimental animal, and mechanistic studies, and addressed several key scientific issues through modeling of TCE toxicokinetics, meta-analyses of epidemiologic studies, and analyses of mechanistic data.

DISCUSSION

Toxicokinetic modeling aided in characterizing the toxicological role of the complex metabolism and multiple metabolites of TCE. Meta-analyses of the epidemiologic data strongly supported the conclusions that TCE causes kidney cancer in humans and that TCE may also cause liver cancer and non-Hodgkin lymphoma. Mechanistic analyses support a key role for mutagenicity in TCE-induced kidney carcinogenicity. Recent evidence from studies in both humans and experimental animals point to the involvement of TCE exposure in autoimmune disease and hypersensitivity. Recent avian and in vitro mechanistic studies provided biological plausibility that TCE plays a role in developmental cardiac toxicity, the subject of substantial debate due to mixed results from epidemiologic and rodent studies.

CONCLUSIONS

TCE is carcinogenic to humans by all routes of exposure and poses a potential human health hazard for noncancer toxicity to the central nervous system, kidney, liver, immune system, male reproductive system, and the developing embryo/fetus.

Organic solvents as risk factor for autoimmune diseases: a systematic review and meta-analysis

BACKGROUND

Genetic and epigenetic factors interacting with the environment over time are the main causes of complex diseases such as autoimmune diseases (ADs). Among the environmental factors are organic solvents (OSs), which are chemical compounds used routinely in commercial industries. Since controversy exists over whether ADs are caused by OSs, a systematic review and meta-analysis were performed to assess the association between OSs and ADs.

METHODS AND FINDINGS

The systematic search was done in the PubMed, SCOPUS, SciELO and LILACS databases up to February 2012. Any type of study that used accepted classification criteria for ADs and had information about exposure to OSs was selected. Out of a total of 103 articles retrieved, 33 were finally included in the meta-analysis. The final odds ratios (ORs) and 95% confidence intervals (CIs) were obtained by the random effect model. A sensitivity analysis confirmed results were not sensitive to restrictions on the data included. Publication bias was trivial. Exposure to OSs was associated to systemic sclerosis, primary systemic vasculitis and multiple sclerosis individually and also to all the ADs evaluated and taken together as a single trait (OR: 1.54; 95% CI: 1.25-1.92; p-value<0.001).

CONCLUSION

Exposure to OSs is a risk factor for developing ADs. As a corollary, individuals with non-modifiable risk factors (i.e., familial autoimmunity or carrying genetic factors) should avoid any exposure to OSs in order to avoid increasing their risk of ADs.

Assessment of the immunotoxic potential of trichloroethylene and perchloroethylene in rats following inhalation exposure

The immunotoxic potential of trichloroethylene (TCE) and perchloroethylene (PERC) was assessed after inhalation exposure through the evaluation of the antibody forming cell (AFC) response to sheep red blood cells (SRBC). Female Sprague-Dawley rats were exposed to TCE or PERC vapor at 0, 100, 300, or 1000 ppm for 6 h/day, 5 days/week for 4 weeks (20 exposure days). Additional 0 ppm control groups were included and were dosed with cyclophosphamide via intraperitoneal injection to serve as positive immunosuppressive controls in the SRBC assay. Additional end-points evaluated included liver, kidney, spleen, and thymus weights, hematology, cellular differentials in bronchoalveolar lavage fluid, histopathology of select tissues, and assessment of the phagocytic activity of pulmonary alveolar macrophage (PERC only). Exposure to the high concentration of TCE (1000 ppm) resulted in increases in relative liver and kidney weights and suppression of AFC responses (AFC/spleen and AFC/10(6) spleen cells) by ≈ 70%, while no treatment-related effects were noted at 100 and 300 ppm. Animals exposed to PERC at levels of 300 or 1000 ppm had statistically significant increases in relative liver weights that were accompanied by very slight hypertrophy of the centrilobular hepatocytes. Animals exposed to PERC did not demonstrate a treatment-related effect on the AFC response and no effect was noted on the phagocytic activity of pulmonary alveolar macrophages. The results of these studies indicate that TCE had immunotoxic potential only at high exposure concentrations (1000 ppm), while PERC, at similar exposure concentrations, did not display any evidence of immunotoxicity.

Environmental toxicants and the developing immune system: a missing link in the global battle against infectious disease?

There is now compelling evidence that developmental exposure to chemicals from our environment contributes to disease later in life, with animal models supporting this concept in reproductive, metabolic, and neurodegenerative diseases. In contrast, data regarding how developmental exposures impact the susceptibility of the immune system to functional alterations later in life are surprisingly scant. Given that the immune system forms an integrated network that detects and destroys invading pathogens and cancer cells, it provides the body's first line of defense. Thus, the consequences of early life exposures that reduce immune function are profound. This review summarizes available data for pollutants such as cigarette smoke and dioxin-like compounds, which consistently support the idea that developmental exposures critically impact the immune system. These findings suggest that exposure to common chemicals from our daily environment represent overlooked contributors to the fact that infectious diseases remain among the top five causes of death worldwide.

Fractal immunology and immune patterning: potential tools for immune protection and optimization

Fractals are self-similar geometric patterns that are inherently embedded throughout nature. Their discovery and application have produced significant benefits across a wide variety of biomedical applications. Recently, complex physiological systems (e.g., neurological, respiratory, cardiovascular) have been shown to exhibit fractal dimensions that are capable of distinguishing among physiologic function versus dysfunction and, in turn, health versus disease. Additionally, fractal data suggest that the immune system operates under similar patterned relationships, and this is in keeping with the recent findings that immune-based diseases are organized according to specific patterns. This review considers the potential benefits of using fractal analysis along with considerations of nonlinearity, scaling, and chaos as calibration tools to obtain holistic information on immune-environment interactions. The potential uses of both synthetic and artificial immune systems for improved protection of the biological immune system are also discussed. The addition of holistic measures of immune status to currently collected biomarkers of immunotoxicity has the potential to increase the effectiveness of health risk assessment. The objective of extending fractal physiology analyses to the immune system would be to promote immune optimization as a public health benefit, which would include improved: (1) immunotoxicity testing and effective health risk reduction and (2) measures of effective immune management for children, adults, and aged individuals.

Enhancement of immediate allergic reactions by trichloroethylene ingestion via drinking water in mice

The prevalence of allergic disorders is increasing in industrial areas and countries. Recent reports suggest that some environmental pollutants are related to the increase in allergic diseases, and we reported that trichloroethylene (TCE) is a candidate chemical for causing the increase of allergic diseases, as TCE ingestion is associated with allergic reaction enhancement. TCE is widely used in many industries, and it is commonly detected as an environmental contaminant. This study aimed to clarify the immunotoxicity of TCE in detail. BALB/c mice were treated with TCE dissolved in drinking water for 2 and 4 weeks, and the mice were immunized with ovalbumin (OVA)/aluminum hydroxide (alum) twice. On the final day of the TCE exposure period, we measured the active cutaneous anaphylaxis (ACA) reaction and the antigen- specific IgE level in serum as well as the histamine level at the allergic reaction site and assayed the proliferation rates of splenocytes collected from the animals. The ACA reaction was enhanced by TCE ingestion. The OVA specific IgE level in mice was enhanced by TCE exposure for 4 weeks. The proliferation rate of the splenocytes was enhanced by TCE ingestion for 2 and 4 weeks. The enhancement of the ACA reaction by TCE ingestion via drinking water may be related to the increase in splenocyte proliferation. On the other hand, it may be weakly related to antigen-specific IgE production.

Suppression of pulmonary host defenses and enhanced susceptibility to respiratory bacterial infection in mice following inhalation exposure to trichloroethylene and chloroform

Numerous epidemiological studies have associated episodes of increased air pollution with increased incidence of respiratory disease, including pneumonia, croup, and bronchitis. Trichloroethylene (TCE) and chloroform are among 33 hazardous air pollutants identified by the U.S. Environmental Protection Agency as presenting the greatest threat to public health in the largest number of urban areas. Also, both are common indoor air pollutants. Here, we assessed the potential effects of TCE and chloroform on resistance to pulmonary bacterial infection and related alveolar macrophage (AM) function. CD-1 mice were exposed by inhalation to filtered air (control) or concentrations of TCE ranging from 5 to 200 ppm, or concentrations of chloroform ranging from 100 to 2000 ppm. Immediately following exposure, mice were challenged with an aerosol of Streptococcus zooepidemicus and monitored for clearance of bacteria from the lung and mortality. In separate experiments, exposed mice were injected intratracheally with viable bacteria and phagocytic function was evaluated in macrophages obtained from lung washes 30 min later. The NOEL for enhanced mortality to infection was 25 ppm for TCE and 500 ppm for chloroform. Relative to the air controls, differences in clearance of bacteria from the lung were noted in mice exposed to TCE (NOEL = 50 ppm) and to chloroform (NOEL 100 ppm), and differences in AM phagocytic index were noted for TCE (NOEL = 100 ppm) and for chloroform (NOEL < 100 ppm). The data support the utility of the S. zooepidemicus infectivity model in assessing potential increased risk of respiratory infection and suggest that delayed clearance of bacteria from the lung or decreased phagocytosis are viable alternatives to mortality as an endpoint. Collectively, these endpoints are among the most sensitive health effects reported for TCE.

The delayed type hypersensitivity assay using protein and xenogeneic cell antigens

The delayed-type hypersensitivity (DTH) assay has a lengthy history in immunotoxicity testing since it was one of the original functional assays included in the National Toxicology Program (NTP) immunotoxicology test panel. Based on NTP data analysis, the DTH assay is among the most predictive immunotoxicity tests when included with at least two other immune parameters. The DTH assay has the advantage of being: (1) a useful measure of cell-mediated immunity, (2) an in vivo assay where there is less opportunity for ex vivo confounders and (3) a clinically significant human correlate to the tuberculin test. Disadvantages of the DTH assay are that it is potentially labor-intensive to perform, it is somewhat resistant to automation and, when compared with the cyctotoxic T lymphocyte (CTL) assay, it is a relatively crude measurement. However, some groups have been attempting to address the limitations of the DTH assays (see Note 1).The assay is related to the contact hypersensitivity response (CHR), which is covered in another chapter. The DTH response has been used as an indicator of cell-mediated immune status and is dependent upon both T helper 1(Th1)-driven responses as well as cell recruitment and chemotaxis to a local site. As a result, the DTH functional response may be influenced by disruption of either Th1-driven, antigen-dependent T cell development or mobilization of sensitized T cells to a local site. The present chapter describes four common protocols with consideration restricted to protein and xenogeneic cell immunogens.

Trichloroethylene alters central and peripheral immune function in autoimmune-prone MRL(+/+) mice following continuous developmental and early life exposure

Trichloroethylene (TCE) is a widespread environmental toxicant known to promote CD4(+) T-lymphocyte activation, IFNgamma production, and autoimmunity in adult MRL(+/+) mice. Because developing tissues may be more sensitive to toxicant exposure, it was hypothesized that continuous TCE exposure beginning at conception might induce even more pronounced CD4(+) T-lymphocyte effects and exacerbate the development of autoimmunity in MRL(+/+) mice. In the current study, MRL(+/+) mice were exposed to occupationally-relevant doses of TCE from conception until adulthood (i.e., 7-8 wk-of-age). The CD4(+) T-lymphocyte effects in the thymus and periphery were evaluated, as well as serum antibody levels. TCE exposure altered the number of thymocyte subsets, and reduced the capacity of the most immature CD4-/CD8- thymocytes to undergo apoptosis in vitro. In the periphery, T-lymphocyte IFN(gamma) production was monitored in the blood prior to sacrifice by intracellular cytokine staining and flow cytometry. TCE induced a dose-dependent increase in T-lymphocyte IFN(gamma) as early as 4-5-week-of-age. However, these effects were transient, and not observed in splenic T-lymphocytes in 7-8-week-old mice. In contrast, the serum levels of anti-histone autoantibodies and total IgG(2a) were significantly elevated in the TCE-exposed offspring. The data illustrated that occupationally-relevant doses of TCE administered throughout development until adulthood affected central and peripheral immune function in association with early signs of autoimmunity. Future studies will address the possibility that early-life exposure to TCE may alter some aspect of self tolerance in the thymus, leading to autoimmune disease later in life.

Developmental immunotoxicology (DIT): windows of vulnerability, immune dysfunction and safety assessment

Developmental immunotoxicity (DIT) is an increasing health concern since DIT outcomes predispose children to those diseases that have been on the rise in recent decades (e.g., childhood asthma, allergic diseases, autoimmune conditions, childhood infections). The enhanced vulnerability of the developing immune system for environmental insult is based on unique immune maturational events that occur during critical windows of vulnerability in early life. The semi-allogeneic pregnancy state, with suppression of graft rejection and associated skewing of the fetal and neonatal immune system, also influences the specific nature of DIT outcomes. In the exposed offspring, targeted immunosuppression can co-exist with an increased risk of allergic and/or autoimmune disease. Because with DIT immune dysfunction rather than profound immunosuppression is the greater concern, testing approaches should emphasize multi-functional assessment. Beyond T-cells, dendritic cells and macrophages are sensitive targets. The last-trimester fetus and the neonate are normally depressed in T(H)1-dependent functions and postnatal acquisition of needed T(H)1 capacity is a major concern with DIT. With this in mind, assessment should include a measure of T(H)1-dependent cell-mediated immunity [cytotoxic T-lymphocyte (CTL) activity or delayed-type hypersensitivity (DTH) response] in conjunction with a multi-isotype T-dependent antibody response (TDAR) and evaluation of innate immunity (e.g., NK activity). Other parameters such as immune histology, immunophenotyping, cytokine responses, and organ weights can be useful when included with immune functional evaluation. A multifunctional DIT protocol using influenza challenge is presented as one example of an approach that permits dysfunction and misregulation to be evaluated.

Evidence of autoimmune-related effects of trichloroethylene exposure from studies in mice and humans

OBJECTIVE

Our objective was to examine experimental and epidemiologic studies pertaining to immune-related, and specifically autoimmune-related, effects of trichloroethylene (TCE).

DATA SOURCES AND EXTRACTION

We performed a literature search of PubMed and reviewed bibliographies in identified articles. We then systematically reviewed immune-related data, focusing on clinical and immunologic features and mechanistic studies.

DATA SYNTHESIS

Studies conducted in MRL+/+ lupus mice report an accelerated autoimmune response in relation to exposure to TCE or some metabolites. Effects have been reported after 4 weeks of exposure to TCE at doses as low as 0.1 mg/kg/day in drinking water and have included increased antinuclear antibodies and interferon-gamma (IFN-gamma) and decreased secretion of interleukin-4 (IL-4), consistent with an inflammatory response. Autoimmune hepatitis, inflammatory skin lesions, and alopecia have been found after exposures of 32-48 weeks. Recent mechanistic experiments in mice examined oxidative stress and, specifically, effects on lipid-peroxidation-derived aldehydes in TCE-induced autoimmune disease. Two studies in humans reported an increase in IL-2 or IFN-gamma and a decrease in IL-4 in relation to occupational or environmental TCE exposure. Occupational exposure to TCE has also been associated with a severe, generalized hypersensitivity skin disorder accompanied by systemic effects, including hepatitis. In three case-control studies of scleroderma with a measure of occupational TCE exposure, the combined odds ratio was 2.5 [95% confidence interval (CI), 1.1-5.4] in men and 1.2 (95% CI, 0.58-2.6) in women.

CONCLUSION

The consistency among the studies and the concordance between the studies in mice and humans support an etiologic role of TCE in autoimmune disease. Multisite collaborations and studies of preclinical immune markers are needed to further develop this field of research.

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.

Integrated approach to immunotoxicity: electron transfer, reactive oxygen species, antioxidants, cell signaling, and receptors

As with all body organs, the immune system is subjected to attack by a variety of toxins. Serious consequences can result because the immune organs serve as a defense against infective agents. The toxins, both organic and inorganic, fall into a large variety of classes, such as metals, therapeutic drugs, industrial chemicals, pollutants, pesticides, fuels, herbicides and abused drugs. Although the mode of action is multifaceted, our focus is on electron transfer (ET), reactive oxygen species (ROS), antioxidants (AOs), cell signaling, and receptors. It is significant that the toxins or their metabolites incorporate ET functionalities capable of redox cycling with resultant generation of ROS and accompanying oxidative stress.

Lifetime exposure to trichloroethylene (TCE) does not accelerate autoimmune disease in MRL +/+ mice

A genetically-prone murine lupus model was used to assess the developmental effects of trichloroethylene (TCE) exposure on disease symptom onset (e.g., autoantibody production and proteinuria), lymphocyte proliferation, splenic B-cell populations, and thymic and splenic T-cell populations. MRL +/+ mice were exposed to TCE (0, 1,400 or 14,000 ppb) via drinking water beginning on gestation day (GD) 0 and continuing until 12 months of age. With the exception of splenic CD4-/CD8-cells in female mice only, no alterations were observed in splenic T-cell populations, numbers of splenic B220+ cells, or in lymphocyte proliferation at 12 months of age. Furthermore, populations of all thymic T-cell subpopulations were decreased in male but not female mice following exposure to 14,000 ppb TCE. Autoantibody levels (anti-dsDNA and anti-GA) were assessed periodically from 4 to 12 months of age. Over this period, no increase in autoantibody levels as compared to control was detected, suggesting that TCE did not contribute to or accelerate the development of autoimmune disease markers following lifetime exposure. Not only does this study offer encouraging results, but it is the first study to approach the development of autoimmunity in a novel lifetime exposure paradigm, using an autoimmune prone model, at environmentally relevant exposure levels.

Gestational exposure to perfluorooctane sulfonate suppresses immune function in B6C3F1 mice

Perfluorinated alkyl acids (PFAAs) are used in a multitude of applications and are categorized as high-production volume chemicals produced in quantities exceeding 10,000 lbs/year. As a result, widespread exposure has been documented in adults, children, and infants. It is generally accepted that children are more sensitive to the effects of xenobiotic exposures during fetal and postnatal periods of development; therefore, considerable efforts are required to investigate the potential impact of a model PFAA, perfluorooctane sulfonate (PFOS) on children's immunological health. Using the pairing of female C57BL/6N mice with male C3H/HeJ, developmental immunotoxicity was evaluated in B6C3F1 pups following oral maternal exposure to PFOS on gestations days 1-17. Exposure levels included 0.1, 1, and 5 mg/kg/day PFOS. Natural killer (NK) cell activity, SRBC IgM plaque assay, CD4/8 lymphocytic subpopulations, nitrite production in peritoneal macrophages, and body/organ weights were evaluated at 4 and 8 weeks of age in F1 pups. No significant dose-responsive changes in maternal or pup body weights, flow cytometry, or macrophage function were observed, yet hepatomegaly was indicated in F1 male pups at 4 weeks of age. Functional deficits were not evident until 8 weeks of age when NK cell function and IgM production were significantly decreased. When compared with females, male pups were more sensitive to the effects of PFOS thereby establishing a no observed adverse effect level and low observed adverse effect level of 0.1 and 1.0 mg/kg/day (males only) following maternal PFOS exposure level, respectively. This study establishes that the developing immune system is sensitive to the effects of PFOS and results in functional deficits in innate and humoral immunity detectable at adulthood.

A new assay system for evaluation of developmental immunotoxicity of chemical compounds using respiratory syncytial virus infection to offspring mice

We evaluated the effect of 6-propyl-2-thiouracil (PTU), an anti-thyroid agent, on developmental immunity using respiratory syncytial virus (RSV) infection to offspring mice as a new risk assessment for brominated flame retardants (BFRs), because some BFRs are suspected of affecting the thyroid system. Pregnant mice were exposed to PTU in drinking water from gestation day 10 to weaning on postnatal day 21. Their offspring mice were infected intranasally with RSV. Exposure of 100ppm PTU significantly increased virus titers in the lungs of RSV-infected offspring compared with the control, and the 10ppm also elevated levels of interferon-γ, a marker of pneumonia, in the bronchoalveolar lavage fluids of offspring. Histopathological analysis revealed that PTU-exposure exacerbated pneumonia in RSV-infected offspring. Thus, exacerbation of RSV infection suggested PTU-exposure of dams elicited developmental immune disorder in the offspring. The murine RSV infection model may be useful to evaluate the developmental immunotoxicity of BFRs.