Humoral and cell-mediated immune status in mice exposed to trichloroethylene in the drinking water

An Animal Model of Trichloroethylene-Induced Skin Sensitization in BALB/c Mice

Trichloroethylene (TCE) is a major occupational hazard and environmental contaminant that can cause multisystem disorders in the form of occupational medicamentosa-like dermatitis. Development of dermatitis involves several proinflammatory cytokines, but their role in TCE-mediated dermatitis has not been examined in a well-defined experimental model. In addition, few animal models of TCE sensitization are available, and the current guinea pig model has apparent limitations. This study aimed to establish a model of TCE-induced skin sensitization in BALB/c mice and to examine the role of several key inflammatory cytokines on TCE sensitization. The sensitization rate of dorsal painted group was 38.3%. Skin edema and erythema occurred in TCE-sensitized groups, as seen in 2,4-dinitrochlorobenzene (DNCB) positive control. Trichloroethylene sensitization-positive (dermatitis [+]) group exhibited increased thickness of epidermis, inflammatory cell infiltration, swelling, and necrosis in dermis and around hair follicle, but ear painted group did not show these histological changes. The concentrations of serum proinflammatory cytokines including tumor necrosis factor (TNF)-α, interferon (IFN)-γ, and interleukin (IL)-2 were significantly increased in 24, 48, and 72 hours dermatitis [+] groups treated with TCE and peaked at 72 hours. Deposition of TNF-α, IFN-γ, and IL-2 into the skin tissue was also revealed by immunohistochemistry. We have established a new animal model of skin sensitization induced by repeated TCE stimulations, and we provide the first evidence that key proinflammatory cytokines including TNF-α, IFN-γ, and IL-2 play an important role in the process of TCE sensitization.

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.

Trichloroethylene Does Not Accelerate Autoimmune Diabetes in NOD Mice

Pre-existing or contributing risk factors, including genetic predisposition and environmental influences, are largely thought to play a crucial (though ill-elucidated) role in the development of autoimmunity. Trichloroethylene (TCE) is a widely used organic solvent, which has been suspected of increasing the prevalence of autoimmune diseases, e.g., lupus, following environmental contamination. Although few epidemiological data are available, several studies reported an accelerated and more severe disease in TCE-exposed autoimmunity-prone MRL(+/+) mice. To test whether TCE can exert similar deleterious effects on organ-specific autoimmune diseases, non obese diabetic (NOD) mice were given 5 mg/ml TCE via the drinking water for 12 weeks. TCE administration induced a decrease in CD44(+) splenic T-cells and CD45RB(high), CD54(+) blood and splenic T-cells. Conversely, the number of CD45RB(low) splenocytes was increased. Interestingly, the progressive increase in serum TNF-alpha and IFN-gamma levels normally seen with age in these mice was inhibited by TCE. There was also a relative lower incidence of histological changes in the pancreas of TCE-exposed NOD mice than in unexposed mice. Contrary to what has been found in systemic models of autoimmunity, TCE did not accelerate the diabetes of NOD mice and may have a protective effect. This finding suggests that comparative studies using different genetically related autoimmune-prone models are needed to investigate the role of xenobiotics in the precipitation of autoimmunity, particularly in sensitive populations.

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.

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.

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.

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

This study assessed the developmental immunotoxicity of trichloroethylene (TCE) in B6C3F1 mice exposed via drinking water (0, 1,400, 14,000 ppb) from gestation day 0 (GD0) to either 3 or 8 weeks of age. Lymphocyte proliferation, NK cell activity, SRBC-specific IgM production (PFC response), splenic B220+ cells, and thymic and splenic T-cell immunophenotypes were assessed at 3 and 8 weeks of age. Delayed type hypersensitivity (DTH) and autoantibodies to ds-DNA were assessed in 8-week old animals only. Proliferation and NK cell activity were not affected at either age. Decreased PFC responses were noted in male offspring at both ages and both TCE treatment levels. PFC responses in female offspring were suppressed by treatment with 14,000 ppb TCE at both ages assessed and at 1,400 ppb TCE at 8 weeks of age. Splenic numbers of B220 cells were only decreased in 3-week old pups exposed to 14,000 ppb TCE. The most pronounced alteration in T-cell subpopulations were increases in all thymic (CD4+, CD8+, CD4+/CD8+, and CD4-/CD8-) T-cell types in 8-week old animals. DTH was increased in females at both TCE levels and in males at the high dose only. These results indicate that TCE may be an effective developmental immunotoxicant and suggests that additional studies are required to determine the health risks associated with developmental exposure to TCE.

Effects of occupational trichloroethylene exposure on cytokine levels in workers

OBJECTIVE

We sought to investigate trichloroethylene-induced alterations of the immune system in humans.

METHODS

The levels of interleukin-2, interleukin-4, and interferon-gamma in sera obtained from workers exposed to trichloroethylene were determined and compared with those of internal and external control subjects.

RESULTS

In workers with a mean urinary trichloroacetic acid concentration of 13.3 +/- 5.9 mg/g creatinine, exposed to a mean environmental trichloroethylene level of 35 +/- 14 mg/m, we observed a significant increase in sera interleukin-2 and interferon-gamma levels and a reduction in interleukin-4 concentrations compared with those of workers from the internal and external control groups.

CONCLUSIONS

This study provides the first report on quantitative immune changes induced by occupational exposure to low levels of trichloroethylene and strongly suggests that exposure to this substance alters immunohomeostasis in humans with possible effects on health.

Immunotoxicity of trichloroethylene: a study with MRL-lpr/lpr mice

In recent immunological studies, it has been suggested that trichloroethylene (TCE) participates in the onset of pneumatosis cystoides intestinalis (PCI) through a certain mechanism; however, the mechanism by which it develops remains unknown. Based on findings that secondary PCI is often linked with autoimmune disease, the possibility that some genetic or immunological mechanisms are involved in the development of PCI has been proposed. Pneumatosis cystoides intestinalis is not a type of disease where a dose-response relationship with TCE exposure can be recognized and it is difficult to reproduce its physiopathology through TCE exposure in ordinary experimental animals. In the present study, immunological changes caused by TCE exposure were investigated by employing MRL-lpr/lpr mice that are genetically labile to autoimmune diseases. To observe changes in B cell functions, serum antibody titres were measured; and for the T cell function, T cell subsets were examined. The animals were exposed to TCE at dosages of 0, 500, 1000 and 2000 ppm through inhalation 4 h a day, 6 days a week, for 8 weeks. It was found that only IgG production capacity was suppressed and there were no changes in T cell subsets with TCE concentrations up to 1000 ppm. At a concentration of 2000 ppm, changes were noted in both T and B cell functions. Typical organs that are responsible for immunological functions were examined for their morphological changes under a light microscope: the spleen and liver exhibited dose-response changes at a concentration of 500 ppm or greater. The development of immunoblastoid cells at a concentration of 1000 ppm indicated a possibility that a change has occurred in the immunological system. These findings show that exposure to TCE at high concentrations affects the immune system, but the study failed to induce PCI in the experimental animals. Further studies on TCE exposure at lower concentrations for longer periods are needed.

Trichloroethylene accelerates an autoimmune response by Th1 T cell activation in MRL +/+ mice

Trichloroethylene (1,1,2-trichloroethene) is a major environmental contaminant. There is increasing evidence relating exposure to trichloroethylene with autoimmunity. To investigate potential mechanisms, we treated the autoimmune-prone MRL +/+ mice with trichloroethylene in the drinking water at 0, 2.5 or 5.0 mg/ml and sacrificed them at 4, 8 and 22 weeks. As early as 4 weeks of treatment, Western blot analysis showed a dose-dependent increase in the level of trichloroethylene-modified proteins, indicating that a reactive metabolite of trichloroethylene was formed. Significant increases in antinuclear antibodies (ANA) and total serum immunoglobulins were found following 4-8 weeks of trichloroethylene treatment, indicating that trichloroethylene was accelerating an autoimmune response. Investigation into possible mechanisms of this autoimmune response revealed that trichloroethylene treatment dramatically increased the expression of the activation marker CD44 on splenic CD4+ T cells at 4 weeks. In addition, splenic T cells from mice treated for 4 weeks with trichloroethylene secreted more IFN-gamma and less IL-4 than control T cells, consistent of a T-helper type 1 (Th1) type immune or inflammatory response. A specific immune response directed against dichloroacetylated proteins was found at 22 weeks of trichloroethylene treatment. Taken collectively, the results suggest that trichloroethylene treatment accelerated an autoimmune response characteristic of MRL +/+ mice in association with nonspecific activation of Th1 cells. In addition, long-term treatment with trichloroethylene led to the initiation of a trichloroethylene-specific immune response.

Is occupational organic solvent exposure a risk factor for scleroderma?

OBJECTIVE

The primary objective was to determine whether occupational exposure to organic solvents is related to an increased risk of systemic sclerosis (SSc; scleroderma).

METHODS

Occupational histories were obtained from 178 SSc patients and 200 controls. Exposure scores were computed for each individual using job exposure matrices, which were validated by an industrial expert.

RESULTS

Among men, those with SSc were more likely than controls to have a high cumulative intensity score (odds ratio [OR] 2.9, 95% confidence interval [95% CI] 1.1-7.6) and a high maximum intensity score (OR 2.9, 95% CI 1.2-7.1) for any solvent exposure. They were also more likely than controls to have a high maximum intensity score for trichloroethylene exposure (OR 3.3, 95% CI 1.0-10.3). Among men and women, significant solvent-disease associations were observed among SSc patients who tested positive for the anti-Scl-70 autoantibody; these trends were not observed among the men and women who tested negative for anti-Scl-70.

CONCLUSION

These results provide evidence that occupational solvent exposure may be associated with an increased risk of SSc.

Trichloroethylene--a review of the literature from a health effects perspective

This report reviews the literature on the impact of exposure to trichloroethylene (TCE) on human health. Special emphasis is given to the health effects reported in excess of national norms by participants in the TCE Subregistry of the Volatile Organic Compounds Registry of the National Exposure Registries--persons with documented exposure to TCE through drinking and use of contaminated water. The health effects reported in excess by some or all of the sex and age groups studied were speech and hearing impairments, effects of stroke, liver problems, anemia and other blood disorders, diabetes, kidney disease, urinary tract disorders, and skin rashes.

Light- and electron microscopical studies on the prolonged toxicity of trichloroethylene on rainbow trout (Oncorhynchus mykiss)

Trichloroethylene, an organochlorine compound used as solvent in numerous industrial processes, was studied with regard to its effects on rainbow trout Oncorhynchus mykiss. Fish were exposed to trichloroethylene via the surrounding water in sublethal concentrations (0.5; 2.5 mg/l) for a period of 21 or 28 days. Three different commercial products of trichloroethylene, all highly purified but varying in quality and amount of stabilizing agents were used. Subchronic exposure resulted in forced apoptosis as well as adaptive and degenerative changes at the subcellular and cellular level in gills, liver, spleen, head- and trunk kidney at the lower concentration. At the higher concentration, necrotic lesions mainly in liver, spleen and head-kidney were found. Trichloroethylene showed particular affinity to the haematopoietic tissue with proliferation and elevated phagocytic activity of reticulo-endothelial cells. Moreover, an increase in phagocytosis of red blood cells which showed abnormalities in ultrastructure was striking. The histopathologic changes after exposure to three different commercial products of trichloroethylene varying in content of stabilizing agents did not show distinct variations.

Effects of trichloroethylene on hepatic and splenic lymphocytotoxic activities in rodents

The effects of trichloroethylene (TRI), a widely used industrial solvent, on various immunological and toxicological parameters have been examined in Sprague-Dawley rats and B6C3F1 mice. Rats were administered TRI in vivo at 0.05, 0.5 and 5.0 mmol/kg per day intraperitoneally (i.p.) for 3 days. Mice were similarly treated with TRI at 10.0 mmol/kg. The highest TRI dose resulted in decreased splenocyte count and relative spleen weights, in rats and mice respectively and inhibition of hepatic natural killer cell (NK), natural cytotoxic cell (NC) and NPK cell (a newly described immune cell killing) activities in both rats and mice. High dose TRI in vitro resulted in minor decreases (less than 10%) in splenocyte viability, inhibition of LPS-stimulated mitogenesis in rat cells and marked inhibitions of NK and NC activities in all groups of effector cells. At the lowest in vitro dose mouse hepatic NK activity was still inhibited. Overall the data show that TRI is able to inhibit the activity of lymphocytotoxic cells which are involved in the immune surveillance of cancerous cells. This inhibition is particularly evident in the liver after in vivo administration and both liver and spleen cells after in vitro exposure. This suggests the possibility that compromised immune function may play a role in the carcinogenic responses in experimental animals on exposure to TRI.

Consideration of the target organ toxicity of trichloroethylene in terms of metabolite toxicity and pharmacokinetics

Trichloroethylene (TRI) is readily absorbed into the body through the lungs and gastrointestinal mucosa. Exposure to TRI can occur from contamination of air, water, and food; and this contamination may be sufficient to produce adverse effects in the exposed populations. Elimination of TRI involves two major processes: pulmonary excretion of unchanged TRI and relatively rapid hepatic biotransformation to urinary metabolites. The principal site of metabolism of TRI is the liver, but the lung and possibly other tissues also metabolize TRI, and dichlorovinyl-cysteine (DCVC) is formed in the kidney. Humans appear to metabolize TRI extensively. Both rats and mice also have a considerable capacity to metabolize TRI, and the maximal capacities of the rat versus the mouse appear to be more closely related to relative body surface areas than to body weights. Metabolism is almost linearly related to dose at lower doses, becoming dose dependent at higher doses, and is probably best described overall by Michaelis-Menten kinetics. Major end metabolites are trichloroethanol (TCE), trichloroethanol-glucuronide, and trichloroacetic acid (TCA). Metabolism also produces several possibly reactive intermediate metabolites, including chloral, TRI-epoxide, dichlorovinyl-cysteine (DCVC), dichloroacetyl chloride, dichloroacetic acid (DCA), and chloroform, which is further metabolized to phosgene that may covalently bind extensively to cellular lipids and proteins, and, to a much lesser degree, to DNA. The toxicities associated with TRI exposure are considered to reside in its reactive metabolites. The mutagenic and carcinogenic potential of TRI is also generally thought to be due to reactive intermediate biotransformation products rather than the parent molecule itself, although the biological mechanisms by which specific TRI metabolites exert their toxic activity observed in experimental animals and, in some cases, humans are not known. The binding intensity of TRI metabolites is greater in the liver than in the kidney. Comparative studies of biotransformation of TRI in rats and mice failed to detect any major species or strain differences in metabolism. Quantitative differences in metabolism across species probably result from differences in metabolic rate and enterohepatic recirculation of metabolites. Aging rats have less capacity for microsomal metabolism, as reflected by covalent binding of TRI, than either adult or young rats. This is likely to be the same in other species, including humans. The experimental evidence is consistent with the metabolic pathways for TRI being qualitatively similar in mice, rats, and humans. The formation of the major metabolites--TCE, TCE-glucuronide, and TCA--may be explained by the production of chloral as an intermediate after the initial oxidation of TRI to TRI-epoxide.(ABSTRACT TRUNCATED AT 400 WORDS)

Immunotoxicological investigations in the mouse: general approach and methods

The adverse effects of chemicals on the lymphoreticular system have generated considerable toxicological interest. In this series of papers, the effects of selected environmentally relevant compounds are reported. This first paper describes the methods and general approach used in judging a chemical's potential risk to the immune system. Risk evaluation was approached utilizing acute, 14- and 90-day studies. Both sexes of the CD-1 random-bred mouse were employed. The immune system was evaluated against a background of more standard toxicological parameters, which included fluid consumption, body and organ weights, hematology, serum and liver chemistries, hepatic microsomal enzyme activities and blood coagulation. Bone marrow status was evaluated by assessing DNA synthesis. Humoral immunity was evaluated by determining the number of IgM spleen antibody-forming cells (AFC) to sheep erythrocytes (sRBC), the serum antibody level to sRBC, and spleen lymphocyte response to the B cell mitogen, lipopolysaccharide (LPS). The status of cell-mediated immunity was assessed by quantitating the delayed type hypersensitivity (DTH) response to sRBC, proliferation of the popliteal lymph node, and the spleen cell response to the T lymphocyte mitogen, Concanavalin A (Con A). Macrophage function was evaluated by measurement of the vascular clearance rate and distribution of radiolabeled sRBC in the liver, spleen, lungs, and thymus, and recruitability, adherence, chemotaxis, and phagocytic activity of peritoneal exudate cells (PEC). Historical control data from six 14- and 90-day studies conducted over a one year period are given. The data resulting from these types of studies can provide a basis for the initial evaluation of a chemical's adverse effect on the immune system.

Trichloroethylene: an update

The toxicity of tricholoroethylene (TCE) has been summarized in a number of reviews. In this particular update, only the more recent studies that deal with metabolism and carcinogenicity have been examined. In reviewing the more recent publications on metabolism of TCE, we determined that differences exist in its metabolism if low doses are compared with high doses in animals. There may also be a difference in the metabolism of TCE between different species--namely mice, rats, and humans. TCE has not been shown to be a potent carcinogen in rats and it only seems to be a potent carcinogen in one specific strain of mice, namely the B6C3F1 mouse. Epidemiology studies have been rather limited. The number of persons examined so far for chronic toxic effects is small, compared with the enormous size of the work force that is exposed to TCE over prolonged periods. On an empirical basis, the occupational experience with TCE does not suggest that this compound is a potent carcinogen. The risk associated with exposure to trace amount (ppb) concentrations of TCE in water appear to be minimal or perhaps negligible. Because there are differences in metabolism of TCE, it is important that theoretical risks attributed to TCE in the past be reexamined. It is highly possible that in humans, the metabolic pathway leading to the formation of the proximate carcinogen is not activated at low doses, where TCE is excreted by first-order kinetics.

Effects of oral exposure to trichloroethylene on female reproductive function

The present study was conducted to determine if subchronic oral exposure to trichloroethylene (TCE) influenced female reproductive performance, and if TCE or major metabolites trichloroacetic acid (TCA) and trichloroethanol (TCOH) preferentially accumulated in female reproductive organs or neonatal tissues. Female Long-Evans hooded rats were exposed to vehicle (corn-oil), 10, 100 or 1000 mg/kg/day by gavage for 2 weeks before mating and throughout mating to day 21 of pregnancy. Gas chromatography analysis of tissues from females at the end of premating exposure indicated that TCE levels were uniformly high in fat, adrenals and ovaries across treatment groups, while uterine tissue had relatively high levels of TCA. Female fertility, however, was not influenced in any treatment group. In the 1000 mg/kg/day group, 5 out of 23 females died and weight gain was significantly depressed throughout the treatment period. Neonatal survival was significantly depressed in this group alone, with the majority of deaths occurring among female offspring at the time of birth. TCA levels in blood, liver, and milk contents of the stomach in female but not male neonates increased across treatment groups. These results indicate that oral exposure to TCE at levels below those causing limiting maternal toxicity had no influence on pregnancy outcome, and that the accumulation of TCE and TCA in ovaries, adrenals and uteri had no influence on mating success.