Effects of methyl mercury exposure on spleen and blood natural killer (NK) cell activity in the mouse

Guardians under Siege: Exploring Pollution's Effects on Human Immunity

Chemical pollution poses a significant threat to human health, with detrimental effects on various physiological systems, including the respiratory, cardiovascular, mental, and perinatal domains. While the impact of pollution on these systems has been extensively studied, the intricate relationship between chemical pollution and immunity remains a critical area of investigation. The focus of this study is to elucidate the relationship between chemical pollution and human immunity. To accomplish this task, this study presents a comprehensive review that encompasses in vitro, ex vivo, and in vivo studies, shedding light on the ways in which chemical pollution can modulate human immunity. Our aim is to unveil the complex mechanisms by which environmental contaminants compromise the delicate balance of the body's defense systems going beyond the well-established associations with defense systems and delving into the less-explored link between chemical exposure and various immune disorders, adding urgency to our understanding of the underlying mechanisms and their implications for public health.

Histological analysis of the effects of cadmium, chromium and mercury alone and in combination on the spleen of male Sprague-Dawley rats

The mining sector in South Africa is expected to be the fifth largest in the world. Both mining and transport are the most common reasons for an increased risk of human exposure to heavy metal contamination in South Africa. Due to increasing amounts of metals in the environment, this study identified three metals cadmium, chromium and mercury based on the risk of exposure in South Africa. The aim of this study was to investigate the changes in the morphology of the spleen tissue of male Sprague-Dawley rats exposed to these metals alone and in combination by using light microscopy. Forty eight animals in eight experimental groups were exposed, via oral gavage, to these metals at 1000× the World Health Organization's acceptable water limits of each respective metal, alone and in combination, for 28 days. Changes in the histological structure of the spleen were observed using haematoxylin and eosin and picrosirius red staining. Necrosis was observed in all the groups, with the severity varying between the different exposure groups, alone or in combination. Fibrosis in the spleen tissue was only seen in the experimental groups exposed to cadmium and mercury respectively, as well as in the combination of cadmium and mercury.

Methylmercury, cadmium and arsenic(III)-induced toxicity, oxidative stress and apoptosis in Pacific red snapper leukocytes

Methylmercury (MeHg), cadmium (Cd) and arsenic (As(III)) are among the most toxic metals in aquatic systems that have been associated with multiple animal and human health problems. This study investigated cytotoxic, oxidative stress, and apoptosis effects on fish leukocytes following their exposure to metals. A preliminary study indicated that leukocytes exposed to MeHg at a concentration of 0.01 mM, Cd at 0.05 mM, and As(III) at 2 mM showed a time-dependent cell viability reduction (around 40%), so they were selected for further experiments. To evaluate the effect of MeHg, Cd and As(III) on Pacific red snapper Lutjanus peru, we measured cytotoxicity, reactive oxygen species, antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT)), nitric oxide production, apoptosis-related and immune-related genes on head-kidney and spleen leukocytes following exposure to MeHg (0.01 mM), Cd (0.05 mM) and As(III) (2 mM) for 30 min and 2 h. Reactive oxygen species (ROS) generation highly increased in time-dependent doses in head-kidney leukocytes compared with the control group. Regarding antioxidant activity, SOD increased significantly in leukocytes exposed to any heavy metals after two h. Expressly, CAT activity decreased in those leukocytes exposed to Cd and As(III). Apoptotic function genes (Casp-2, Casp-3, and Casp-7) strongly up-regulated after heavy metal exposure, but Cd was more toxic. Finally, granzyme A and perforin 1 strongly up-regulated in leukocytes exposed to MeHg and As(III) compared with the control group. Our data showed that MeHg, Cd, and As(III) might have been cytotoxic and induced oxidative stress and apoptosis with possible biological consequences in fish.

High-precision isotopic analysis sheds new light on mercury metabolism in long-finned pilot whales (Globicephala melas)

Whales accumulate mercury (Hg), but do not seem to show immediate evidence of toxic effects. Analysis of different tissues (liver, kidney, muscle) and biofluids (blood, milk) from a pod of stranded long-finned pilot whales (Globicephala melas) showed accumulation of Hg as a function of age, with a significant decrease in the MeHg fraction. Isotopic analysis revealed remarkable differences between juvenile and adult whales. During the first period of life, Hg in the liver became isotopically lighter (δ²⁰²Hg decreased) with a strongly decreasing methylmercury (MeHg) fraction. We suggest this is due to preferential demethylation of MeHg with the lighter Hg isotopes and transport of MeHg to less sensitive organs, such as the muscles. Also changes in diet, with high MeHg intake in utero and during lactation, followed by increasing consumption of solid food contribute to this behavior. Interestingly, this trend in δ²⁰²Hg is reversed for livers of adult whales (increasing δ²⁰²Hg value), accompanied by a progressive decrease of δ²⁰²Hg in muscle at older ages. These total Hg (THg) isotopic trends suggest changes in the Hg metabolism of the long-finned pilot whales, development of (a) detoxification mechanism(s) (e.g., though the formation of HgSe particles), and Hg redistribution across the different organs.

Immunotoxicity of mercury: Pathological and toxicological effects

Mercury (Hg) is toxic and hazardous metal that causes natural disasters in the earth's crust. Exposure to Hg occurs via various routes; like oral (fish), inhalation, dental amalgams, and skin from cosmetics. In this review, we have discussed the sources of Hg and its potential for causing toxicity in humans. In addition, we also review its bio-chemical cycling in the environment; its systemic, immunotoxic, genotoxic/carcinogenic, and teratogenic health effects; and the dietary influences; as well as the important considerations in risk assessment and management of Hg poisoning have been discussed in detail. Many harmful outcomes have been reported, which will provide more awareness.

Reversibility of Thymulin Production Impairment by L-Arginine Supplementation in Mice Exposed to Inorganic Mercury

Immunotoxicological effects of mercury on peripheral immune system are known. We had previously in vitro found that mercuric chloride inhibits thymulin production in mouse thymus cultures at concentrations as low as 10−8 M. In this study, thymus efficiency, assessed as production of active and total thymulin, was evaluated in vivo using young mice that were injected sc every 3 days for 4 weeks with saline containing mercuric chloride at different concentrations (0 -controls-, 0.001 or 1.0 mg HgCl2/kg body weight). The results show that both the doses are able to cause a significant reduction in active and total thymulin production. Since arginine enhances immune efficiency some of the animals also received a diet supplemented with arginine in order to evaluate a possible role of arginine during mercury intoxication. The data show that arginine has a protective effect on thymic endocrine efficiency. Mice, treated with the lowest dose of mercury and receiving an arginine supplemented diet, produced active and total thymulin like mercury untreated mice. Arginine is an aminoacid which may be found in various amounts in different foods, some foods are particularly rich in arginine i.e. peanuts, stock fish. We suggest that the daily arginine intake may account for an individual susceptibility to the mercury-induced immunological effects which are found in mercury occupationally exposed workers.

Mercury levels in maternal and cord blood and attained weight through the 24 months of life

Birth weight is a strong determinant of attained weight at early ages. Until now, many studies have reported that low birth weight corresponds with high mercury levels. However, the relationship between mercury exposure and attained weight of infant has not been well studied. Therefore, the aim of the present study was to assess the degree of prenatal exposure to mercury by measuring the total mercury levels in maternal and cord blood, and examine the relationship between the mercury level during pregnancy and the attained weight of infant during the first 24 months of life. The prospective cohort study of Mothers and Children's Environmental Health (MOCEH) was built up in 2006, and 921 mother-infant pairs were recruited. Information on the socio-demographic characteristics, health behavior and environmental exposure were collected from an interview with trained nurses. After delivery, infants and mothers were followed up at 6, 12 and 24 months and the weights of the infants were measured. The mercury concentrations in the late maternal blood (β=-0.19. p=0.05) and cord blood (β=-0.36. p=0.01) were negatively associated with the infants' attained weight over the first 24 months of age. The infants' attained weight in the small for their gestational age (SGA) group was lower than the normal birth weight group at the highest quartile of the mercury level. Therefore, efforts should be made to reduce the mercury level in the maternal blood at late pregnancy and cord blood. Further research on the possible harmful effects of prenatal mercury exposure on postnatal growth is recommended.

The impact of methylmercury on 1,25-dihydroxyvitamin D3-induced transcriptomic responses in dolphin skin cells

The Atlantic bottlenose dolphin has been the focus of much attention owing to the considerable impact of environmental stress on its health and the associated implications for human health. Here, we used skin cells from the dolphin to investigate the protective role of the vitamin D pathway against environmental stressors. We previously reported that dolphin skin cells respond to 1,25-dihydroxyvitamin D3 (1,25D3), the bioactive metabolite of vitamin D3, by upregulation of the vitamin D receptor (VDR) and expression of several genes. Methylmercury is a highly bioaccumulative environmental stressor of relevance to the dolphin. We currently report that in dolphin cells sublethal concentrations of methylmercury compromise the ability of 1,25D3 to upregulate VDR, to transactivate a vitamin D-sensitive promoter, and to express specific target genes. These results help elucidate the effects of vitamin D and methylmercury on innate immunity in dolphin skin and potentially in human skin as well, considering similarities in the vitamin D pathway between the two species.

Immunology of mercury

The heavy metal mercury is ubiquitously distributed in the environment resulting in permanent low-level exposure in human populations. Mercury can be encountered in three main chemical forms (elemental, inorganic, and organic) which can affect the immune system in different ways. In this review, we describe the effects of these various forms of mercury exposure on immune cells in humans and animals. In genetically susceptible mice or rats, subtoxic doses of mercury induce the production of highly specific autoantibodies as well as a generalized activation of the immune system. We review studies performed in this model and discuss their implications for the role of environmental chemicals in human autoimmunity.

Gene expression changes in bottlenose dolphin, Tursiops truncatus, skin cells following exposure to methylmercury (MeHg) or perfluorooctane sulfonate (PFOS)

Methylmercury (MeHg) and perfluorooctane sulfonate (PFOS) bioaccumulate and biomagnify in the environment and increasing concentrations of these pollutants have been found in wildlife and humans. Both chemicals are worldwide contaminants with wide ranging biological effects and have been identified in relatively high concentrations in apex level marine mammals such as bottlenose dolphins. The primary objective of this study was to determine if exposure to MeHg or PFOS would alter the gene expression in primary bottlenose dolphin epidermal cell cultures. Primary skin cells were isolated and cultured from skin samples collected from wild bottlenose dolphins. The cells were subsequently exposed to 13ppm PFOS or 1ppm MeHg and changes in gene expression were analyzed by suppressive subtractive hybridization (SSH) and quantitative real-time PCR (QPCR). 116 genes were positively identified in the dolphin skin cells by SSH. Of these, 16 total genes were analyzed by QPCR (9 and 11 genes following PFOS or MeHg exposure, respectively, with four overlapping genes). Results indicate MeHg significantly alters gene expression patterns following 24h exposure, but has no measurable effect after only 1h. PFOS exposure, however, caused significant alterations following both 1 and 25h. Overall, the changes in gene expression observed indicate these concentrations of MeHg and PFOS significantly alter normal gene expression patterns. The changes in gene expression following exposure to these contaminants not only indicate a cellular stress response, but also decreased cell cycle progression and cellular proliferation and reduced protein translation. Alterations in normal cellular biology, like those observed, may lead to changes in health in marine mammals exposed to contaminants; however, this warrants further investigation.

Methylmercury exposure assessment using dietary and biomarker data among frequent seafood consumers in France CALIPSO study

BACKGROUND

Seafood is considered by toxicologists as the main source of methylmercury (MeHg), but little data is available concerning contamination of seafood and MeHg status of French frequent consumers.

OBJECTIVES

The objectives were to assess food exposure and biomarker of exposure of MeHg from a group of frequent consumers of seafood.

METHODS

Two approaches to exposure assessment were used: the currently used food intake and the biomarker of exposure. A validated food frequency questionnaire (FFQ) was used to assess seafood consumptions for 80 products of 385 frequent consumers aged 18 and over in four French coastal areas. Seafood samples were collected in each region considering preservation methods and supply habits according to a total diet study sampling. Food samples were analyzed for MeHg. Exposure was assessed by combining consumptions with contamination data. Whole blood samples were collected from the volunteers and analyzed for MeHg.

RESULTS

The mean dietary exposure to MeHg or weekly intake (WI FFQ) was 1.51+/-1.17 microg/kg bw/wk. Thirty-five percent of the subjects exceed the Joint Expert Committee on Food Additives (JECFA) provisional tolerable weekly intake (PTWI), whereas the use of the biological results with the JECFA/Environmental Protection Agency (EPA) one-compartment pharmacokinetic model to calculate weekly intake (WI PKM) shows that only 2% of subjects exceed the PTWI. The mean of the individual ratios WI FFQ/WI PKM is 4.3 and the higher the WI FFQ and the blood MeHg level, the lower is the ratio, close to 1-2.

CONCLUSIONS

These analyses support the assumption that the calculated dose of methylmercury is overestimated with the FFQ-based method used in this study. Since FFQ are commonly used in risk assessments, the overestimate of dose is public health protective and this finding is somewhat reassuring from a public health point of view, especially since the JECFA or EPA have applied uncertainty factors of 3.2 or 3, respectively, to take into account the inter-individual pharmacokinetic variability.

Interactions among infections, nutrients and xenobiotics

During recent years there have been several incidents in which symptoms of disease have been linked to consumption of food contaminated by chemical substances (e.g., 2,3,7,8-tetrachlorodibenzo-p-dioxin, TCDD). Furthermore, outbreaks of infections in food-producing animals have attracted major attention regarding the safety of consumers, e.g., Bovine Spongiform Encephalitis (BSE) and influenza in chicken. As shown for several xenobiotics in an increasing number of experimental studies, even low-dose xenobiotic exposure may impair immune function over time, as well as microorganism virulence, resulting in more severe infectious diseases and associated complications. Moreover, during ongoing infection, xenobiotic uptake and distribution are often changed resulting in increased toxic insult to the host. The interactions among infectious agents, nutrients, and xenobiotics have thus become a developing concern and new avenue of research in food toxicology as well as in food-borne diseases. From a health perspective, in the risk assessment of xenobiotics in our food and environment, synergistic effects among microorganisms, nutrients, and xenobiotics will have to be considered. Otherwise, such effects may gradually change the disease panorama in society.

Modulating effects of dietary fats on methylmercury toxicity and distribution in rats

Fish consumption is the most important source of human exposure to methylmercury (MeHg). Since fish is also a rich source of n-3 polyunsaturated fatty acids, this study was conducted to examine the effects of dietary fats on MeHg-induced acute toxicity in rats. Weanling male Sprague Dawley rats were administered semi-purified casein-based isocaloric diet containing soy oil, seal oil, docosahexaenoic acid (DHA), fish oil, or lard for 28 days. Rats were then gavaged with 0, 1, or 3 mg MeHg/kg body weight (BW) per day and fed the same diet for 14 consecutive days. On 43rd day of the experiment, rats were sacrificed and blood samples were collected and analyzed for hematology. Liver and spleen were removed, fixed, and examined for pathological changes. Blood, feces, liver, and brain were analyzed for total mercury and/or MeHg contents. Serum samples were analyzed for clinical markers of hepatic injury and immunoglobulin. Total mercury contents in all tissues measured increased with dose. Mercury excretion in feces increased with dose and duration of MeHg treatment. Both diets and MeHg showed significant effects and interacted significantly on many of the toxicological endpoints measured. Many of the effects of MeHg were diet-dependent. For example, in the rats fed the lard diet, 3mg MeHg/kg BW significantly increased relative liver and spleen weight as compared with vehicle control; whereas in rats fed the fish oil, soy oil, seal oil, or DHA, this effect of MeHg was less obvious or absent, suggesting a protective effect of these diets. MeHg at 3mg/kg BW significantly decreased serum albumin level in all except DHA dietary groups, implying a protection by the DHA diet on this parameter. Only in the lard dietary group, did 3mg MeHg/kg BW significantly increase serum bilirubin level, indicating an enhancing effect of this diet on MeHg toxicity. MeHg suppressed the adaptive immune system and stimulated the innate immune system in rats in a diet-dependent fashion. The seal oil diet provided more resistance, while the fish oil diet rendered greater sensitivity to these effects of MeHg on the immune system. These results imply significant modulating effects of dietary fats on MeHg toxicity which may translate into more severe or protective clinical outcomes. Therefore, dietary fats are important factors to be considered in the risk assessment of MeHg exposure.

Organic mercury compounds and autoimmunity

Based on in vitro studies and short-term in vivo studies, all mercurials were for a long time considered as prototypic immunosuppressive substances. Recent studies have confirmed that organic mercurials such as methyl mercury (MeHg) and ethyl mercury (EtHg) are much more potent immunosuppressors than inorganic mercury (Hg). However, Hg interacts with the immune system in the presence of a susceptible genotype to cause immunostimulation, antinucleolar antibodies targeting fibrillarin, and systemic immune-complex (IC) deposits, a syndrome called Hg-induced autoimmunity (HgIA). Recent studies in mice with a susceptible genotype has revealed that the immunosuppressive effect of MeHg and EtHg will within 1-3 weeks be superseded by immunostimulation causing an HgIA-like syndrome. At equimolar doses of Hg, MeHg has the weakest immunostimulating, autoimmunogen, and IC-inducing effect, while the effect of thimerosal is similar to that of inorganic mercury. The immunosuppression is caused by the organic mercurials per se. Since they undergo rapid transformation to inorganic Hg, studies are being undertaken to delineate the importance of the organic substances per se and the newly formed inorganic Hg for induction of autoimmunity.

Immunosuppressive and autoimmune effects of thimerosal in mice

The possible health effects of the organic mercury compound thimerosal (ethylmercurithiosalicylate), which is rapidly metabolized to ethylmercury (EtHg), have recently been much debated and the effect of this compound on the immune system is largely unknown. We therefore studied the effect of thimerosal by treating A.SW (H-2s) mice, susceptible to induction of autoimmunity by heavy metals, with 10 mg thimerosal/L drinking water (internal dose ca 590 microg Hg/kg body weight/day) for up to 30 days. The lymph node expression of IL-2 and IL-15 mRNA was increased after 2 days, and of IL-4 and IFN-gamma mRNA after 6 and 14 days. During the first 14 days treatment, the number of splenocytes, including T and B cells as well as Ig-secreting cells decreased. A strong immunostimulation superseded after 30 days treatment with increase in splenic weight, number of splenocytes including T and B cells and Ig-secreting cells, and Th2- as well as Th-1-dependent serum immunoglobulins. Antinucleolar antibodies (ANoA) targeting the 34-kDa nucleolar protein fibrillarin, and systemic immune-complex deposits developed. The H-2s strains SJL and B10.S also responded to thimerosal treatment with ANoA. The A.TL and B10.TL strain, sharing background genes with the A.SW and B10.S strain, respectively, but with a different H-2 haplotype (t1), did not develop ANoA, linking the susceptibility to H-2. Thimerosal-treated H-2s mice homozygous for the nu mutation (SJL-nu/nu), or lacking the T-cell co-stimulatory molecule CD28 (B10.S-CD28-/-), did not develop ANoA, which showed that the autoimmune response is T-cell dependent. Using H-2s strains with targeted mutations, we found that IFN-gamma and IL-6, but not IL-4, is important for induction of ANoA by thimerosal. The maximum added renal concentration of thimerosal (EtHg) and inorganic mercury occurred after 14 days treatment and was 81 microg Hg/g. EtHg made up 59% and inorganic mercury 41% of the renal mercury. In conclusion, the organic mercury compound thimerosal (EtHg) has initial immunosuppressive effects similar to those of MeHg. However, in contrast to MeHg, thimerosal treatment leads in genetically susceptible mice to a second phase with strong immunostimulation and autoimmunity, which is T-cell dependent, H-2 linked and may at least partly be due to the inorganic mercury derived from the metabolism of ethyl mercury.

The immunosuppressive effect of methylmercury does not preclude development of autoimmunity in genetically susceptible mice

Methylmercury (MeHg) is a common environmental pollutant due to both natural and anthropogenic sources. Although the central nervous system (CNS) is considered the critical organ for the toxic effect of MeHg, it has recently been suggested that the immune system might be at least as sensitive as the CNS. We have examined the effects of MeHg on the immune system in genetically metal-susceptible mice. Subcutaneous (sc) injections of 2 mg MeHg/kg body weight (bw) every third day (internal dose ca. 540 microg Hg/kg bw/day) to A.SW mice of the H-2(s) haplotype, caused during the first week a 47 and 9% reduction of B- and T-cells, respectively, which indicates immunosuppression. Subsequently, an autoimmune syndrome developed which shared certain features with the syndrome induced by inorganic mercury in H-2(s) mice, including antibodies targeting the 34 kDa nucleolar protein fibrillarin, increased expression of IL-4 mRNA, increase of Th2-type of immunoglobulins (IgE and IgG1), and increased MHC class II expression on B-cells. However, the response using MeHg was attenuated compared with even lower doses of Hg in the form of inorganic mercury, and specifically lacked the increased expression of IL-2 and IFN-gamma mRNA, the polyclonal B-cell activation (PBA), and the systemic immune-complex (IC) deposits which are induced by inorganic mercury. Increasing the dose of MeHg increased the titre of anti-nucleolar antibodies and shortened the induction time, but did not lead to stronger immunostimulation or systemic IC-deposits. The kidney and liver selectively accumulated MeHg, while the blood, spleen and lymph nodes showed lower levels of MeHg. The accumulation of MeHg and Hg(2+) increased throughout the 30-day period. The fraction of Hg(2+) in the kidney varied between 4 and 22%, and the lymph nodes showed a maximum of 30% Hg(2+). We conclude first that MeHg has quantitatively different effect on the immune system compared with inorganic mercury, and secondly that an initial immunosuppression induced by a xenobiotic does not preclude subsequent immunostimulation and autoimmunity.

The Children's Amalgam Trial: design and methods

The safety of silver amalgam as a dental restorative material has been controversial since its introduction 150 years ago, but until recently it has been assumed that the exposure to mercury from dental amalgam is limited to the acute placement phase. However, some recent studies have raised safety concerns by demonstrating chronic release of mercury vapor from amalgam fillings during chewing and brushing. The Children's Amalgam Trial is a two-arm randomized trial of safety, comparing amalgam with a mercury-free restorative material. A single masking procedure is used to ensure that all investigators and staff measuring outcomes are unaware of assigned trial arm. The study follows 534 New England children, aged 6-10 years at enrollment, for 5 years. The children were recruited from two northeastern U.S. communities, one in rural Maine and one in urban Massachusetts. No trial subjects received prior amalgam restorations, and all were in need of at least two posterior occlusal fillings. Participants were randomized to receive either amalgam or composite material for all posterior restorations at baseline and at subsequent visits. The primary endpoint will be 5-year change in IQ scores. Secondary endpoints will include measures of other neuropsychological assessments and renal functioning. This paper describes the design of the Children's Amalgam Trial and includes data on baseline characteristics of the subjects.

Contrasting changes of sensitivity by lymphocytes and neutrophils to mercury in developing grey seals

Mercury is the principal metal contaminant in the St Lawrence Estuary. It impairs humoral, cellular and non-specific immune responses in many species. Since the immune system of juvenile seals is immature, it should react differently to the effects of contamination compared to that of mature animals. Phagocytosis and lymphoblastic transformation responses have been evaluated in the peripheral blood leukocytes of eight juvenile grey seals at different intervals of time over 11 weeks. Dose-response curves of 10(-9)-10(-3)M of methylmercury chloride have also been performed in vitro for evaluation of these two immune functions. The immune response of grey seals differs during their development. The phagocytosis response increased from the 2nd to 5th week post-weaning and then reached a plateau. As for the lymphoblastic transformation response, it was stable from the 2nd to the 3rd week post-weaning, increased significantly at week 4 post-weaning and then reached a plateau. These data suggest that these animals should be particularly vulnerable to infections, diseases and parasites before the 5th week post-weaning. Furthermore, mercury decreased the immune response, and age of seals had an effect on cell sensitivity to mercury. Concentrations of 10(-5)M of methylmercury chloride decreased phagocytosis and lymphoblastic transformation responses. Phagocytosis is more affected by MeHgCl contamination before this immune function reaches complete development which occurs at week 5 post-weaning. On the other hand, lymphoblastic transformation is more affected by this contaminant after its complete development which occurs at week 4 post-weaning.

Sensitivity to methylmercury-induced autoimmune disease in mice correlates with resistance to apoptosis of activated CD4+ lymphocytes

The sensitivity of splenic lymphoid cells to apoptosis induced by low concentrations of methylmercury (MeHgCl) has been examined in C57BL/6 and SJL mice, which are, respectively, resistant and sensitive to a genetically determined autoimmune disease induced by subtoxic doses of MeHgCl. To determine the implications of subtoxic doses of MeHgCl in the susceptibility of SJL mice to autoimmune disease, Concanavalin A (ConA) stimulated spleen cells from both mouse strains were treated in vitro with MeHgCl concentrations varying between 0.001 and 1.0 microM for 48h. Results have shown that ConA-activated splenic lymphoid cells from SJL mice increased in the presence of low concentrations of MeHgCl while the number of lymphoid cells from C57BL/6 mice rather decreased. Flow cytometric analysis of the cells showing a typical lymphoid forward scatter (FSC)/side scatter (SSC) pattern (region R1), and those characterized by a lower FSC and a higher SSC parameters (region R2), morphologically corresponding to apoptotic cells, revealed that lymphoid cells from C57BL/6 mice suffered a dose-dependent shift from region R1 toward region R2 when treated with concentrations ranging between 0.01 and 1 microM of MeHgCl. However, SJL splenic lymphoid cells cultured in the presence of low concentrations of MeHgCl proved more resistant to apoptosis. The level of apoptosis induced by MeHgCl in both regions was verified by AnnexinV-propidium iodide (PI) and TdT-mediated dUTP nick end labeling (TUNEL) immunolabelings. Phenotyping of lymphoid cells from both mouse strains cultured in the presence of low concentrations of MeHgCl and stimulated with ConA, indicated that CD4+ T cells from SJL mice increased while the corresponding cell subset from C57BL/6 mice became apoptotic. The resistance to apoptosis of ConA-activated lymphoid cells from SJL mice seemed related to an increase of CD4+ cells induced by the lower concentrations of MeHgCl (0.001 and 0.01 microM). However, these SJL cells were sensitive to anti-Fas-mediated apoptosis while residual anti-Fas-resistant cells from C57BL/6 mice were, themselves, sensitive to MeHgCl-induced apoptosis. The in vivo significance of these results has been confirmed by an observed increase in splenic cellularity and in the percentage of activated CD4+ cells from SJL mice. These increases were not observed in C57BL/6 mice.

Biochemical and molecular basis of thimerosal-induced apoptosis in T cells: a major role of mitochondrial pathway

The major source of thimerosal (ethyl mercury thiosalicylate) exposure is childhood vaccines. It is believed that the children are exposed to significant accumulative dosage of thimerosal during the first 2 years of life via immunization. Because of health-related concerns for exposure to mercury, we examined the effects of thimerosal on the biochemical and molecular steps of mitochondrial pathway of apoptosis in Jurkat T cells. Thimerosal and not thiosalcylic acid (non-mercury component of thimerosal), in a concentration-dependent manner, induced apoptosis in T cells as determined by TUNEL and propidium iodide assays, suggesting a role of mercury in T cell apoptosis. Apoptosis was associated with depolarization of mitochondrial membrane, release of cytochrome c and apoptosis inducing factor (AIF) from the mitochondria, and activation of caspase-9 and caspase-3, but not of caspase-8. In addition, thimerosal in a concentration-dependent manner inhibited the expression of XIAP, cIAP-1 but did not influence cIAP-2 expression. Furthermore, thimerosal enhanced intracellular reactive oxygen species and reduced intracellular glutathione (GSH). Finally, exogenous glutathione protected T cells from thimerosal-induced apoptosis by upregulation of XIAP and cIAP1 and by inhibiting activation of both caspase-9 and caspase-3. These data suggest that thimerosal induces apoptosis in T cells via mitochondrial pathway by inducing oxidative stress and depletion of GSH.

Organic mercury compounds: human exposure and its relevance to public health

Humans may be exposed to organic forms of mercury by either inhalation, oral, or dermal routes, and the effects of such exposure depend upon both the type of mercury to which exposed and the magnitude of the exposure. In general, the effects of exposure to organic mercury are primarily neurologic, while a host of other organ systems may also be involved, including gastrointestinal, respiratory, hepatic, immune, dermal, and renal. While the primary source of exposure to organic mercury for most populations is the consumption of methylmercury-contaminated fish and shellfish, there are a number of other organomercurials to which humans might be exposed. The antibacterial and antifungal properties of organomercurials have resulted in their long use as topical disinfectants (thimerosal and merbromin) and preservatives in medical preparations (thimerosal) and grain products (both methyl and ethyl mercurials). Phenylmercury has been used in the past in paints, and dialkyl mercurials are still used in some industrial processes and in the calibration of certain analytical laboratory equipment. The effects of exposure to different organic mercurials by different routes of exposure are summarized in this article.

In vitro inhibition of thymulin production in mercury-exposed thymus of young mice

Lymphocyte differentiation, maturation and peripheral functions are affected by the thymic protein hormone thymulin. Mercury at very low concentrations has been seen to impair some lymphocytic functions causing subclinical manifestations in exposed workers. The present study was performed to test in vitro the effect of mercury on the production kinetics of thymulin using cultures of whole thymuses from young mice. Exposure to mercury (10(-8) M and 10(-6) M) added to the cultures, reduced kinetic thymulin production at all time intervals considered (1, 2, 4, 5 and 6 h) as compared to kinetic thymulin production of thymuses from young control mice. After the first hour the inhibition is more evident at the highest mercury concentration. Thymulin production decreased by 70, 74, 82 and 86% and by 55, 66, 73 and 81% for mercury concentrations of 10(-6) M and 10(-8) M, respectively, after 2, 4, 5 and 6 h. Mercury toxic effect on thymulin kinetics may be directly exerted to thymulin synthesis in epithelial cells, although it is less dramatic than that of cycloheximide (CHX), known as a potent inhibitor of protein synthesis in such cells. The toxic effect of mercury on thymic endocrine activity might cause the subclinical effects on cell-mediated immunological status observed in mercury exposed workers.

Autism: a novel form of mercury poisoning

Autism is a syndrome characterized by impairments in social relatedness and communication, repetitive behaviors, abnormal movements, and sensory dysfunction. Recent epidemiological studies suggest that autism may affect 1 in 150 US children. Exposure to mercury can cause immune, sensory, neurological, motor, and behavioral dysfunctions similar to traits defining or associated with autism, and the similarities extend to neuroanatomy, neurotransmitters, and biochemistry. Thimerosal, a preservative added to many vaccines, has become a major source of mercury in children who, within their first two years, may have received a quantity of mercury that exceeds safety guidelines. A review of medical literature and US government data suggests that: (i) many cases of idiopathic autism are induced by early mercury exposure from thimerosal; (ii) this type of autism represents an unrecognized mercurial syndrome; and (iii) genetic and non-genetic factors establish a predisposition whereby thimerosal's adverse effects occur only in some children.

Dose-dependent apoptosis induced by low concentrations of methylmercury in murine splenic Fas+ T cell subsets

Methylmercury chloride (MeHgCl) is known to induce cellular and humoral immunodeficiencies in mice. In this study, the involvement of lymphoid subset disorders due to low concentrations of methylmercury (0.001-1.0 microM) has been examined. Cytofluorometric analysis of splenic cells exposed in vitro to low concentrations of MeHgCl for 48 h revealed two distinct populations: the first expressed a typical lymphoid forward light scatter (FSC)/side light scatter (SSC) pattern (R1 region), and the second was characterized by a lower FSC and a higher SSC (R2 region). A dose-dependent shift of cells from R1 region toward R2 region was observed in splenic cells treated with MeHgCl. The apoptotic state of cells in the R2 region was confirmed by the TdT-mediated dUTP nick end labeling (TUNEL) assay. Analysis of DNA content in splenic lymphoid cells showed that low concentrations of MeHgCl increased both hypoploid cells and cells in G0-G1/S phase, both in the R1 and R2 regions. However, the numbers of cells in G0-G1/S and G2/M phases were decreased, but hypoploid cells increased in both regions due to exposure to 1 microM MeHgCl. MeHgCl-induced apoptosis disappeared when splenic cells were pretreated with anti-Fas antibodies, indicating that Fas expressing cells were the target cells for MeHgCl-mediated apoptosis. Furthermore, T cells from the V beta 8 family were found to be more sensitive to apoptosis induced by low concentrations of MeHgCl. Taken together, these results suggest that MeHgCl at low concentrations mediates the development of apoptosis in peripheral T cell via the Fas/FasL pathway.

Immune function of bovine leukocytes after in vitro exposure to selected heavy metals

OBJECTIVE

To study effects of in vitro exposure of bovine leukocytes to mercury, cadmium, and lead on phagocytosis, natural killer cell activity, and lymphocyte proliferation.

SAMPLE POPULATION

Leukocytes from 6 nonpregnant Holstein heifers.

PROCEDURE

Leukocytes were exposed in vitro to the aforementioned metals, and leukocyte functions were assessed.

RESULTS

Phagocytosis was suppressed by 10(-5) to 10(-7) M CdCl2 and by 10(-5) and 10(-6) M HgCl2, but not 10(-7) M HgCl2 nor 10(-4) to 10(-6) M PbCl2. Spontaneous and concanavalin A- or phytohemagglutinin-stimulated proliferation of metal-treated bovine blood mononuclear cells was not significantly different from that of nontreated control cells, except for enhanced spontaneous proliferation in response to 10(-5) M HgCl2. When proliferation was expressed as a stimulation index, a dose-dependent increase of spontaneous proliferation was observed in response to exposure to HgCl2 and PbCl2. Compared with response to 10(-6) or 10(-7) M CdCl2, reduction of mitogen-induced and spontaneous proliferation was observed on exposure to 10(-5) M CdCl2. Natural killer cell activity against YAC-1 target cells, evaluated by flow cytometry, was decreased only in cells exposed to 10 M HgCl2.

CONCLUSION AND CLINICAL RELEVANCE

Bovine leukocytes are susceptible to the immunomodulatory effects of in vitro exposure to heavy metals at concentrations equal to or higher than those at which similar effects are seen for leukocytes from most other animal species for which data are available for comparison. Exception is phagocytosis, which is severely affected by low concentrations of CdCl2 and HgCl2 in cattle. Reduction of defense mechanisms on exposure to metals could lead to increased susceptibility to potential pathogens.

Flow cytometry as a tool to monitor the disturbance of phagocytosis in the clam Mya arenaria hemocytes following in vitro exposure to heavy metals

The effectiveness of toxicology biomonitoring programs could be improved by the addition of sensitive biomarkers. In this study the cell viability and sensitivity of phagocytic function of phagocytes from bivalves (Mya arenaria) to selected heavy metals were measured by flow cytometry, a novel approach. Hemocytes (phagocytes) collected from bivalves by puncture of the posterior adductor muscle were incubated in vitro for 18 h in hemolymph containing 10(-9)-10(-3)M of cadmium chloride, zinc chloride, mercuric chloride, methylmercury chloride or silver nitrate, before determining their capacity to phagocytose fluorescent latex beads by flow cytometry. Heterogeneity of the hemocyte cell population was determined by forward scatter (FSC) and side scatter (SSC) cytometric profile which showed two distinct cell populations. At low doses (10(-9), 10(-8) M), all the metal compounds studied stimulated phagocytic activity except silver nitrate. At higher levels of exposure (10(-6), 10(7) M), all metals caused a significant concentration-related decrease in hemocyte phagocytosis activity. From the concentration of each metal inducing 50% suppression (IC50) of the phagocytic activity, the immunotoxic potential of metals with respect to phagocytic function can be ranked in the following increasing order: ZnCl2 < CdCl2 < AgNO3 < HgCl2 < CH3HgCl. Parallel analysis of hemocyte viability showed that suppression of phagocytosis by heavy metals was not solely related to a decreased cell viability. These results reveal the high but different degree of sensitivity of the phagocytosis activity of bivalves with respect to heavy metals, as measured by flow cytometry, and demonstrate that flow cytometry is a potentially useful tool in ecotoxicological monitoring.

Methyl mercury-induced autoimmunity in mice

Female SJL/N, A.SW, B10.S (H-2s), BALB/C, DBA/2 (H-2d), A.TL and B10. TL (H-2t1) mice were treated with sc injections of 1.0 mg CH3HgCl/kg body weight every third day for 4 weeks. Controls were given sterile, isotonic NaCl. CH3HgCl (MeHg) induced in SJL, A.SW and B10.S mice antinucleolar antibodies (ANoA) targeting the nucleolar 34-kDa protein fibrillarin. The susceptibility to develop ANoA in response to MeHg was linked to the mouse major histocompatibility complex (H-2), since H-2s but not H-2t1 mice sharing background (non-H-2) genes developed ANoA. However, the background genes decided the strength of the ANoA response in the susceptible H-2s mice, and the ANoA titer was in the order: A.SW > SJL > B10.S. Although MeHg as well as inorganic mercury induced ANoA, the two forms of mercury differed both quantitatively and qualitatively in their effect on the immune system. MeHg induced in H-2s mice a weaker general (polyclonal) and specific (ANoA) B-cell response than HgCl2, probably due to weaker activation of Th2 cells with lower IL-4 production, as indicated by the minimal increase in serum IgE. The A. TL strain with a susceptible genetic background, but a H-2 haplotype resistant to HgCl2, responded to MeHg with a modest polyclonal B-cell response dominated by Th1-associated Ig isotypes. H-2s mice treated with MeHg showed in contrast to HgCl2-treated mice no systemic immune-complex (IC) deposits, which may be due to the weaker immune activation after MeHg treatment. The increase in serum IgE concentration and ANoA titer 2-6 weeks after stopping treatment with MeHg is identical to reactions during the first 2-3 weeks of HgCl2 treatment. Therefore, demethylation of MeHg probably increased the concentration of inorganic mercury in the body sufficiently to reactivate the immune system. This reactivation indicated that genetically susceptible mice are not resistant to challenge with mercury, making them distinctly different from rats.

The lichen rock tripe (Lasallia pustulata) as survival food: effects on growth, metabolism and immune function in Balb/c mice

The present study was performed to investigate whether the lichen rock tripe (Lasallia pustulata) can be used as food during survival situations. The effects of 30% lichen supplementation given to female Balb/c mice were studied on growth rate, metabolism and immune functions. After 3 weeks on this diet, it was found that the lichen supplementation did not affect the growth rate or the well-being of the animals. The growth rate tended to be higher in the lichen group when compared to control mice. Food consumption was similar in both groups, but with a trend towards slightly higher intake (12%) in the lichen group. The heart, liver, kidney and lymphoid organ (spleen and thymus) weights were not affected by the lichen. Histological hematoxylin eosin staining showed that all these organs were normal. Plasma glucose levels were unchanged, but plasma urea levels decreased by 24% (p < 0.05) with the lichen diet. Red and white blood cells and the number of lymphoid cells in the thymus and spleen were normal. The activity of thymocytes and spleen T-lymphocytes were not affected by the lichen diet, but spontaneous cell-mediated cytotoxicity (NK cells) tended (n.s.) to increase and spleen B-lymphocyte activity increased by 40% (p < 0.05). This study shows that the lichen rock tripe has immune stimulating effects important for host defence reactions and can be used as food in survival situations without any adverse effects on the metabolism.

Effects of selenium supplementation on virus-induced inflammatory heart disease

The effects of 10 wk of selenium (Se) supplementation (5 ppm) in drinking water on immune responses and resistance to a myocarditic Coxsackie virus B3 (CB3) infection were studied in female Balb/c mice. Se supplementation reduced CB3-induced mortality: at day 14 postinoculation, survival was 58% in the Se-treated group as compared to 25% in the untreated group. Whole-blood glutathione peroxidase (GSH-Px) activity was elevated by 68% (p < 0.001) and Se content in the liver by 24% (p < 0.001). Red (RBC) and white blood cell (WBC) counts, as well as the number of cells in the spleen and thymus, were unaffected. The cellular counts of T-lymphocytes (CD4+, CD8+) and natural killer (NK+) cells in the blood were not affected. However, the CD4+/CD8+ ratio (5.2) tended to increase after Se supplementation (5.9). The spleen lymphoproliferative response to T- and B-cell mitogens were increased by 9 and 43%, respectively (ns), in the Se-supplemented group. The total NK cell activity in blood and spleen showed minor increases, but when the activity in the blood was expressed per cell, the increase amounted to 35% (ns) with Se supplementation. The inflammatory and necrotic lesions in the ventricular myocardium at 7 and 14 d postinoculation were not significantly reduced by Se treatment, probably owing to the increased survival with Se even of mice with the most pronounced heart damage; comparable untreated mice were estimated to have died at day 14. Results indicate that modest doses of Se can improve immune function, which may increase the general resistance to this viral infection.

Alterations in immune parameters associated with low level methylmercury exposure in mice

Methylmercury (MeHg) is a known toxicant and continues to be a significant environmental contaminant. While the neurotoxicity and developmental toxicity of MeHg are well established, the immunotoxic effects of MeHg are just now being studied and described. This study evaluated strain and gender specific effects of low level, prolonged MeHg exposure in mice. Mice were exposed to MeHg in the drinking water (0, 3 or 10 ppm) for 4 weeks. Splenocytes and thymocytes were evaluated for alterations in immunophenotype, GSH levels, and intracellular Ca2+ flux after mitogen stimulation. MeHg exposure resulted in alterations in splenocyte and thymocyte subsets and a dose dependent decrease in GSH levels (as measured by monochlorobimane fluorescence and flow cytometry) of all splenocyte subsets. This decrease in GSH was further confirmed by biochemical assay in splenocytes. In addition, there was a dose response related decrease in mitogen stimulated Ca2+ flux and in the percentages of CD4+ splenocytes and CD8+ splenocytes from mice exposed to 10 ppm of MeHg. These results suggest that low-level chronic MeHg exposure may cause immune disfunction by disturbing thiol redox balance, transmembrane signaling and splenic cellularity.

Immunomodulating effects after perinatal exposure to methylmercury in mice

The influence of methylmercury on the developing immune system was studied in offspring from Balb/c mice exposed to 0, 0.5 or 5 mg Hg/kg as methylmercury in the diet. Dams were exposed for 10 weeks prior to mating, during gestation and lactation. Pups were exposed to mercury until day 15 of lactation, thereafter the pups were given control milk and control diet. Samples for mercury analysis were collected from the pups on days 22 and 50, and for immunological studies on days 10, 22 and 50. The exposure resulted in significantly increased total Hg concentrations in whole blood on day 22 and 50 in offspring from the 5 mg Hg/kg group, and in offspring from the 0.5 mg Hg/kg group on day 22. On day 50, blood mercury levels had decreased to background levels in the 0.5 mg Hg/kg group. Increased numbers of splenocytes and thymocytes were found in offspring from the 0.5 mg Hg/kg group. Flow cytometry analysis of thymocytes revealed increased numbers and altered proportions of lymphocyte subpopulations within the thymus in offspring from both of the exposed groups. The proliferative response of splenocytes to the B-cell mitogen LPS was increased in offspring from dams exposed to 5 mg Hg/kg, and the primary antibody response to a viral antigen was stimulated in pups from dams exposed to 0.5 mg Hg/kg. The present results indicate that placental and lactational transfer of mercury affects thymocyte development and stimulates certain mitogen- or antigen-induced lymphocyte activities in mice.

Effects of methyl mercury on cytokines, inflammation and virus clearance in a common infection (coxsackie B3 myocarditis)

A myocarditic coxsackievirus B3 (CB3) infection in Balb/c mice was used to investigate the effects of 12 weeks of methyl mercury (MeHg) exposure (3.69 mg/g diet) on inflammatory heart lesions, virus in the heart, the cytokine response, i.e. cachectin/TNF-alpha and gamma-interferon (IFN-gamma) levels in plasma, and on disease complications and mortality. This dose of MeHg did not influence mortality in this infection model. The inflammatory and necrotic lesions in the ventricular myocardium 7 days after the inoculation covered 2.2% of the tissue section area in infected control mice. This damage was increased (n.s.) by 50% (to 3.3% of the tissue section area) in MeHg-treated mice. The response pattern of lymphocyte subsets in situ in myocardial inflammatory lesions was corroborated using an immune histological technique. MeHg treatment tended to increase (2.2-fold, n.s.) the number of Mac 2+ cells (macrophages) in the heart muscle in this infection. Plasma levels of both TNF-alpha and IFN-gamma increased on day 3 of the infection in MeHg-treated as well as in non-MeHg-treated mice, but the mean IFN-gamma response was more pronounced in the MeHg-treated mice. On day 7 of the infection, when most animals still showed clinical signs of disease, cytokine levels were back to normal. MeHg-exposure in non-infected mice did not affect cytokine levels. In situ hybridization of virus RNA in myocardial tissue showed remaining virus in those mice who had the lowest plasma IFN-gamma levels. A 20% increased (P < 0.05) lymphoproliferative response to the T cell mitogen Con A was observed as a result of the MeHg treatment. Even heart tissue lesions and virus persistence tended to be influenced by MeHg in a direction compatible with the development of chronic disease.

Methylmercury induces Ca(2+)-dependent hyperpolarization of mouse thymocytes: a flow cytometric study using fluorescent dyes

The effect of methylmercury on mouse thymocytes was examined using fluorescent dyes for membrane potential and intracellular Ca2+. Methylmercury at concentrations of 1 microM or higher (up to 30 microM) produced hyperpolarization in a dose-dependent fashion. Charybdotoxin and quinine, but not 4-aminopyridine and tetraethylammonium, greatly suppressed methylmercury-induced hyperpolarization. Removal of external Ca2+ reduced the degree of hyperpolarization. Pretreatment of thymocytes with A23187 under Ca(2+)-free conditions abolished the hyperpolarization induced by methylmercury. Under both normal and Ca(2+)-free conditions methylmercury increased the intracellular concentration of Ca2+. The results suggest that the increase in intracellular Ca2+ is mediated through a Ca2+ release from intracellular stores as well as through influx of external Ca2+. Therefore, it is likely that methylmercury increases the intracellular concentration of Ca2+, resulting in activation of Ca(2+)-dependent K+ conductance of mouse thymocytes.

Immune responses and resistance to viral-induced myocarditis in mice exposed to cadmium

The effects of 10 weeks of treatment with cadmium (Cd) on the immune function and resistance to coxsackievirus B3 (CB3)-induced myocarditis in female Balb/c mice were investigated. A 2mM dose of Cd in the drinking water did not influence mortality due to the CB3 infection. The inflammatory and necrotic lesions in the ventricular myocardium seven days after inoculation (2.94% of tissue section area) were not increased by Cd (2.82% of tissue section area). The response pattern of lymphocyte subsets in situ in myocardial inflammatory lesions was elucidated by an immune histochemical staining technique. With Cd treatment the number of cytotoxic T cells and B cells in these lesions decreased by 22% (n.s.) and 21% (p < 0.05), respectively. Spleen weight and the lymphoproliferative response to the B-lymphocyte mitogen increased by 19% (p < 0.05) and 23% (n.s.), respectively. The titers of neutralizing antibodies increased by 22% (n.s.) with Cd treatment. However, the activity of spleen T lymphocytes and spontaneous cell-mediated cytotoxicity (NK-cell) was unchanged. Thymus weight and WBC count in peripheral blood tended to decrease. Thus, Cd exposure seems to result in a decreased maturation and mobilization of T and B lymphocytes, but increased humoral immune host responses.

Changed distribution and immune effects of nickel augment viral-induced inflammatory heart lesions in mice

We have used the myocarditic coxsackievirus B3 (CB3) infection in Balb/c mice to investigate immunotoxic effects of a ten-week low-dose (0.002 M) administration of nickel chloride (NiCl2) prior to infection. This dose did not influence CB3-induced mortality. Whole-body autoradiography of [63Ni] during the disease showed the pancreas, lungs and myocardium to be new target organs in this disease. Seven days after the inoculation, impulse counting of these organs showed the infection-induced increase of [63Ni] to be 5-fold (P < 0.01) in the pancreas, 2.2-fold (P < 0.05) in the lungs and 1.3-fold (P < 0.05) in the heart. Nickel tended to increase spleen B- and T-cell activities, but thymocyte activity was unaffected. The activity of spleen natural killer (NK) cells decreased by 30% (P < 0.05), whereas blood-cell activity in fact increased by 51% (P < 0.05). The inflammatory and necrotic lesions in the ventricular myocardium seven days after the inoculation covered 3.31% of the tissue section area in infected control mice. This damage was increased by 43% (to 4.74% of the tissue section area) in nickel-treated mice. The response pattern of lymphocyte subsets in situ in myocardial inflammatory lesions was elucidated by an immune histochemical staining technique. The number of cytotoxic T-cells, helper T-cells and Mac 2+ cells (macrophages) in these lesions decreased by 46% (P < 0.05), 41% (P < 0.05) and 27% (not significant), respectively, with the nickel treatment. The number of helper T-cells was negatively correlated to the size of the inflammatory area (r = -0.529, P < 0.02). The results indicate that nickel may contribute to the progression of target organ pathology in infection-induced diseases of an autoimmune and/or inflammatory character, such as diabetes and myocarditis.

Cytometric profiles of bone marrow and spleen lymphoid cells after mercury exposure in mice

The potential immunotoxic effects of mercury chloride on murine bone marrow (bm) cell subpopulations, including analysis of maturation patterns for B-cells, were evaluated by flow cytometric analysis. CD-1 outbred mice were exposed for 28 days to relatively low doses of 25-100 ppm HgCl2 in drinking water and the mercury-related functional cellular changes were validated in a macrophage phagocytosis assay. Lymphocyte subsets from the bone marrow population were stained with PNA lectin and a panel of monoclonal antibodies against cell surface antigens. The incidence of subset-specific staining was also monitored in spleens and thymuses. A dose-effect correlation was noted for the mercury-related activation of macrophage phagocytosis. Subchronic exposure to mercuric chloride resulted in a transient (7-14 day) decrease of the lymphoid/total bm cell ratio and affected the incidence of splenic T-cell subsets, however, without a clear dose-response correlation. The B-cell population in spleen and maturation patterns of B-cells in bm appeared to be unaffected by the mercury exposure. Overall, cytometric analysis of lymphoid cell subsets in murine bone marrow revealed transient and subset-non-specific cell fluctuations after subchronic exposure to inorganic mercury.

Immunotoxic effects of mercuric compounds on human lymphocytes and monocytes. IV. Alterations in cellular glutathione content

The major goal of this investigation was to determine if the sensitivity of lymphocytes and monocytes to mercury (Hg++) was related to intracellular glutathione (GSH) levels and the thiol redox status [GSH/glutathione disulfide (GSSG)]. To isolate cells based upon their GSH content, T and B-cells were stained with monochlorobimane (MCB) and separated into high and low fluorescent groups by FACS analysis. Cells with high GSH fluorescence were found to be resistant to both the cytotoxic and immunotoxic effects of HgCl2 as evidenced by cell viability and their responsiveness to mitogen, respectively. In contrast, cells with low levels of GSH were extremely sensitive to mercury. To further examine the relationship between GSH level and mercury exposure, T-cells, B-cells and monocytes were treated with different doses of HgCl2 for 12 hrs. All cells exhibited a dose-dependent decrease in GSH content with a concomitant reduction in GSSG levels. However, the GSH/GSSG ratio in these cells remained constant, or increased following exposure to mercury. GSH levels were also reduced in monocytes following exposure to HgCl2; in this case, GSSG levels remained constant and a decline in the GSH/GSSG ratio was observed. For all cell types, mercury did not inhibit the activities of GSH reductase and GSH peroxidase, enzymes responsible for oxidation/reduction of GSH and GSSG, respectively. Results of the study clearly show that susceptibility to the immunotoxic effects of HgCl2 is, in part, dependent upon GSH levels and further that mercury inhibits GSH generation by lymphocytes and monocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of inorganic and organic mercury on intracellular calcium levels in rat T lymphocytes

The importance of cytosolic free calcium level ([Ca2+]i) in lymphocyte activation prompted us to investigate changes in [Ca2+]i in T cells caused by mercury compounds, which have been shown to have immunomodulatory and immunotoxic properties. Using fura-2 as fluorescent Ca2+ indicator, we found that both methyl-mercury (MeHg; 0.02-2 microM) and inorganic mercury (HgCl2; 0.01-1 microM) increased [Ca2+]i in lymphocytes from rat spleen in a concentration-dependent manner. The effect of MeHg was rapid and the increase of Ca2+ level was sustained in time, while HgCl2 caused a slow rise in [Ca2+]i. The effects of mercury compounds did not appear to be associated with alterations of membrane integrity, since there was no significant difference in the extent of MnCl2 quench between control and mercury-treated cells. However, HgCl2 (1 microM) and MeHg (2 microM) appeared to cause membrane damage at longer incubation times (15 min). When cells were incubated in Ca(2+)-free medium (in the presence of 1 mM EDTA) MeHg still increased [Ca2+]i, though to a lesser extent, while HgCl2 had no effect. Heparin, an inhibitor of inositol 1,4,5-trisphosphate-induced Ca2+ mobilization partially blocked this rise of [Ca2+]i, while carbonyl cyanide m-chlorophenylhydraxone (CCCP), an inhibitor of mitochondrial function, had a lesser effect. When added together, heparin and CCCP almost completely block the response to MeHg. These results suggest that MeHg and HgCl2 exert their effects of [Ca2+]i in different ways: MeHg-induced increases in [Ca2+]i are due to influx from outside the cells as well as to mobilization from intracellular stores, possibly the endoplasmic reticulum, and, to a minor extent, the mitochondria; on the other hand, HgCl2 causes only Ca2+ influx from the extracellular medium.

Immunotoxic effects of mercuric compounds on human lymphocytes and monocytes. III. Alterations in B-cell function and viability

The major goal of the study was to determine the effects of high and low levels of mercury on human B-cells. Following treatment of B-cells with HgCl2 (0-1000 ng) and MeHgCl2 (0-100 ng), their activation by mitogens was evaluated. Both forms of mercury caused a dose dependent reduction in B-cell proliferation in the presence or absence of monocytes. MeHgCl was approximately 10 times more potent than HgCl2. Mercury also inhibited the ability of these cells to synthesize IgM and IgG. Analysis of the expression of activation markers indicated that CD69, an early marker of cell activation, was not effected by mercury. In comparison, B-cell expression of the low affinity IgE receptor and the transferrin receptor were significantly reduced. Of particular interest, cells activated by mitogen for 48 hr became refractory to the immunotoxic effects of mercury. When exposed to high levels of HgCl2 (0.5-10 micrograms/ml) and MeHgCl (0.05-1 micrograms/ml), there was minimal reduction in B-cell viability at 1-4 hr, however, after exposure to mercury for 24 hr, cell death was apparent. MeHgCl was approximately 5-10 times more potent than HgCl2. Electron microscopic analysis revealed early nuclear alterations characterized by hyperchromaticity, nuclear fragmentation and condensation of nucleoplasm. Both forms of mercury caused a rapid and sustained elevation in the intracellular levels of Ca++. The results of this investigation clearly show that mercury-containing compounds are immunomodulatory; moreover, the decrease in B-cell function indicates that this metal is immunotoxic at very low exposure levels. Furthermore, the cytotoxic events are consistent with the notion that mercury initiates changes associated with programmed cell death.

Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on blood and spleen natural killer (NK) cell activity in the mouse

The immunotoxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) were studied in male A/J mice after a loading dose of 5 micrograms TCDD/kg body wt. followed by 3 weekly maintenance doses of 1.42 micrograms TCDD/kg b.w. administered intraperitoneally. Tissue samples and immune cells were prepared on two occasions, i.e. on days 28 and 120 after the first injection of TCDD. This dose of TCDD evoked classical histological signs of liver damage and lipid accumulation, as well as thymic atrophy. Red (RBC) blood cell counts were significantly lowered in the TCDD group on day 28, but were normal on day 120. White (WBC) blood cell counts were normal in the TCDD group. Natural killer (NK) cell activity increased 3.4-fold (P less than 0.01) and 2.2-fold (P less than 0.01) in the blood and spleen, respectively, after 28 days, and these effects persisted on day 120. The increased NK-cell activity occurred concomitantly with a decreased proliferative response of spleen lymphocytes to the T-cell mitogen concanavalin A after both 28 (65%) and 120 days (58%). The proliferative response of spleen cells to the B-cell mitogen lipopolysaccharide seemed, however, unaffected. We have thus shown for the first time that TCDD induces an increased activity of NK cells that occurs simultaneously in the blood and spleen. This effect may indicate a general compensatory activation of the body's defences brought about by disturbances in the function of other arms of the immune system.

Immunotoxic effects of mercuric compounds on human lymphocytes and monocytes. I. Suppression of T-cell activation

Considerable attention has been directed at defining the health deficits associated with exposure to mercurial compounds. While numerous studies have been conducted, the findings have been somewhat contradictory and have led to a confused understanding of the immunotoxicology of mercury. It is becoming clear, however, that the immunotoxic effects of heavy metals in general, and mercury in particular, are dependent upon the assays and source of cells. The major goal of our study was to assess whether low level mercury exposure modulates human T-cell function. Following treatment of T-cells with HgCl2 (0-1000 ng) and MeHgCl (0-100 ng), their activation by mitogens was evaluated. Both forms of mercury caused a dose dependent reduction in T cell proliferation, however, the effect was dependent upon the presence of monocytes. Moreover, in the absence of monocytes, HgCl2 enhance PMA induced T-cell proliferation. MeHgCl was approximately 5-10 times more potent than HgCl2. Mercury also inhibited the ability of these cells to synthesize and secrete IL-1. Analysis of the expression of activation markers on the cell surface indicated that one of the earliest markers of lymphocyte activation, CD69, was not effected by mercury. In comparison, T-cell expression of IL-2R and the transferrin receptor was impaired. Of particular interest, cells activated by mitogen for 24 hr became refractory to the immunotoxic effects of mercury. The results of this investigation clearly show that mercury-containing compounds are immunomodulatory; moreover, the decrease in T-cell function following exposure to mercury indicates that this metal is immunotoxic at very low exposure levels.

Methyl mercury exposure via placenta and milk impairs natural killer (NK) cell function in newborn rats

The effect of methyl mercury (MeHg) exposure (3.9 micrograms/g diet) on the development of immune function was studied in the newborn Sprague-Dawley rat after MeHg exposure via placenta and/or milk. No consistent alterations were observed between control and treated offspring (at the age of 15 days) on the following parameters: body weights, lymphoid organ weights or cell number, and the lymphoproliferative response to B-cell mitogen. The lymphoproliferative response to T-cell mitogen was increased in thymocytes (by 30-48%), but decreased in splenocytes (by 30-32%). This decreased activity was only observed in the groups exposed during lactation. White blood cell counts (WBC) were increased in all groups. Natural killer (NK) cell activity was reduced (by 42%, P less than 0.01) in the group that was exposed both via placenta and milk. These results indicate that placental and lactational transfer of MeHg does adversely affect the developing immune system of the rat.