The genotype determines the B cell response in mercury-treated mice

Secondary exposure to heavy metal in genetically susceptible mice leads to acceleration of autoimmune response

Exposure to mercury (Hg) and silver (Ag) has been shown to induce autoimmune diseases in genetically susceptible rodents. Here, A.SW mice were initially exposed to HgCl2, AgNO3 or tap water (control) for 3 weeks. After 13 weeks of stoppage, all mice had secondary exposure to 203HgCl2. After secondary exposure, higher and earlier ANoA titers were observed in mice initially exposed to Hg or Ag compared to control. Further, mice initially exposed to Ag showed higher total IgG1 and IgG2a, Whole Body Retention and lymph nodes and spleen accumulation of Hg compared to mice initially exposed to Hg and controls. These findings showed an earlier and stronger immunological response in A.SW mice compared with control, following re-exposure to heavy metals indicating an immunological memory. Additionally, secondary exposure to a different heavy metal may aggravate the effects of exposure of at least one of the metals indicating cross-reactivity.

Mercury-induced autoimmunity: Report of two adolescent siblings with Morvan syndrome "plus" and review of the literature

Heavy metal toxicity is a global health concern. Mercury intoxication has been implicated in the etiology and pathogenesis of autoimmune disease, including Morvan syndrome. We describe two siblings with overlapping features of distinct autoimmune syndromes following accidental exposure to elemental mercury. Morvan syndrome was the predominant clinical phenotype. In addition to the characteristic anti-leucine-rich glioma-inactivated protein 1 (LGI1) and anti-contactin-associated protein-like 2 (Caspr2) autoantibodies, glutamic acid decarboxylase 65-kilodalton isoform (GAD65), and N-type and P/Q-type voltage-gated calcium channel (VGCC) antibodies were detected. Treatment with chelation therapy, glucocorticoids, and intravenous immunoglobulin was unsuccessful, but complete resolution of symptoms was achieved following treatment with rituximab. Herein, we perform an extensive review of the literature with a focus on the emerging concepts of mercury-induced autoimmunity and the role of mercury in the etiopathogenesis of autoimmune diseases of the nervous system.

Bank1 and NF-kappaB as key regulators in anti-nucleolar antibody development

Systemic autoimmune rheumatic disorders (SARD) represent important causes of morbidity and mortality in humans. The mechanisms triggering autoimmune responses are complex and involve a network of genetic factors. Mercury-induced autoimmunity (HgIA) in mice is an established model to study the mechanisms of the development of antinuclear antibodies (ANA), which is a hallmark in the diagnosis of SARD. A.SW mice with HgIA show a significantly higher titer of antinucleolar antibodies (ANoA) than the B10.S mice, although both share the same MHC class II (H-2). We applied a genome-wide association study (GWAS) to their Hg-exposed F2 offspring to investigate the non-MHC genes involved in the development of ANoA. Quantitative trait locus (QTL) analysis showed a peak logarithm of odds ratio (LOD) score of 3.05 on chromosome 3. Microsatellites were used for haplotyping, and fine mapping was conducted with next generation sequencing. The candidate genes Bank1 (B-cell scaffold protein with ankyrin repeats 1) and Nfkb1 (nuclear factor kappa B subunit 1) were identified by additional QTL analysis. Expression of the Bank1 and Nfkb1 genes and their downstream target genes involved in the intracellular pathway (Tlr9, Il6, Tnf) was investigated in mercury-exposed A.SW and B10.S mice by real-time PCR. Bank1 showed significantly lower gene expression in the A.SW strain after Hg-exposure, whereas the B10.S strain showed no significant difference. Nfkb1, Tlr9, Il6 and Tnf had significantly higher gene expression in the A.SW strain after Hg-exposure, while the B10.S strain showed no difference. This study supports the roles of Bank1 (produced mainly in B-cells) and Nfkb1 (produced in most immune cells) as key regulators of ANoA development in HgIA.

How can a chemical element elicit complex immunopathology? Lessons from mercury-induced autoimmunity

Although most autoimmune diseases develop without a manifest cause, epidemiological studies indicate that external factors play an important role in triggering or aggravating autoimmune processes in genetically predisposed individuals. Nevertheless, most autoimmune disease-promoting environmental agents are unknown because their relationships to immune function are not understood. Thus, the study of animal models of chemically-induced autoimmunity should shed light on the pathways involved and allow us to identify these agents. The rodent model of heavy metal-induced autoimmunity is one of the most intriguing experimental systems available to address such questions. Although the ultimate pathophysiology of this model remains mysterious, recent studies have started to elucidate the mechanisms by which heavy metal exposure leads to immune activation and loss of self-tolerance.

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.

Gold- and silver-induced murine autoimmunity--requirement for cytokines and CD28 in murine heavy metal-induced autoimmunity

Treatment with gold in the form of aurothiomaleate, silver or mercury (Hg) in genetically susceptible mouse strains (H-2(s)) induces a systemic autoimmune condition characterized by anti-nuclear antibodies targeting the 34-kDa nucleolar protein fibrillarin, as well as lymphoproliferation and systemic immune-complex (IC) deposits. In this study we have examined the effect of single-gene deletions for interferon (IFN)-gamma, interleukin (IL)-4, IL-6 or CD28 in B10.S (H-2(s)) mice on heavy metal-induced autoimmunity. Targeting of the genes for IFN-gamma, IL-6 or CD28 abrogated the development of both anti-fibrillarin antibodies (AFA) and IC deposits using a modest dose of Hg (130 microg Hg/kg body weight/day). Deletion of IL-4 severely reduced the IgG1 AFA induced by all three metals, left the total IgG AFA response intact, but abrogated the Hg-induced systemic IC deposits. In conclusion, intact IFN-gamma and CD28 genes are necessary for induction of AFA with all three metals and systemic IC deposits using Hg, while lack of IL-4 distinctly skews the metal-induced AFA response towards T helper type 1. In a previous study using a higher dose of Hg (415 microg Hg/kg body weight/day), IC deposits were preserved in IL-4(-/-) and IL-6(-/-) mice, and also AFA in the latter mice. Therefore, the attenuated autoimmunity following loss of IL-4 and IL-6 is dose-dependent, as higher doses of Hg are able to override the attenuation observed using lower doses.

The roles of selenium and mercury in the pathogenesis of viral cardiomyopathy

Research on the pathogenesis of nonischemic dilated cardiomyopathy (DCM) has largely been focused on the role of viral pathogens and altered immunity. Trace elements have only rarely been considered; however, clinical observations that trace elements influence cardiovascular disease have been made in populations with extreme dietary deficiency or occupational exposure. Recently, animal models of DCM have been used to explore interactions among trace elements, viral pathogens, and the immune system. Discovery of interactions of trace elements with causes for DCM has heightened awareness of potential contributions of environmental variables to DCM pathogenesis. This article reviews the present knowledge regarding trace elements, in particular selenium and mercury, in the pathogenesis of viral and immune-mediated DCM. Based on recent studies, the authors propose a novel paradigm for the pathogenesis of viral DCM that incorporates trace element imbalance and its interactions with the cellular physiology of viral-induced cardiomyocyte dysfunction.

Gold causes genetically determined autoimmune and immunostimulatory responses in mice

Natrium aurothiomaleate (GSTM) is a useful disease-modifying anti-rheumatic drug, but causes a variety of immune-mediated adverse effects in many patients. A murine model was used to study further the interaction of GSTM with the immune system, including induction of systemic autoimmunity. Mice were given weekly intramuscular injections of GSTM and controls equimolar amounts of sodium thiomaleate. The effects of gold on lymphocyte subpopulations were determined by flow cytometry. Humoral autoimmunity was measured by indirect immunofluorescence and immunoblotting, and deposition of immunoglobulin and C3 used to assess immunopathology. Gold, in the form of GSTM, stimulated the murine immune system causing strain-dependent lymphoproliferation and autoimmunity, including a major histocompatibility complex (MHC)-restricted autoantibody response against the nucleolar protein fibrillarin. GSTM did not cause glomerular or vessel wall IgG deposits. However, it did elicit a strong B cell-stimulating effect, including both T helper 1 (Th1)- and Th2-dependent isotypes. All these effects on the immune system were dependent on the MHC genotype, emphasizing the clinical observations of a strong genetic linkage for the major adverse immune reactions seen with GSTM treatment.

Mercury exposure as a model for deviation of cytokine responses in experimental Lyme arthritis: HgCl2 treatment decreases T helper cell type 1-like responses and arthritis severity but delays eradication of Borrelia burgdorferi in C3H/HeN mice

Lyme borreliosis is a complex infection, where some individuals develop so-called 'chronic borreliosis'. The pathogenetic mechanisms are unknown, but the type of immune response is probably important for healing. A strong T helper cell type 1 (Th1)-like response has been suggested as crucial for eradication of Borrelia and for avoiding development of chronic disease. Many studies aimed at altering the Th1/Th2 balance in Lyme arthritis employed mice deficient in cytokine genes, but the outcome has not been clear-cut, due possibly to the high redundancy of cytokines. This study aimed at studying the importance of the Th1/Th2 balance in murine Borrelia arthritis by using the Th2-deviating effect of subtoxic doses of inorganic mercury. Ninety-eight C3H/HeN mice were divided into four groups: Borrelia-infected (Bb), Borrelia-infected exposed to HgCl(2) (BbHg), controls exposed to HgCl(2) alone and normal controls. Mice were killed on days 3, 16, 44 and 65 post-Borrelia inoculation. Arthritis severity was evaluated by histology, spirochaetal load determined by Borrelia culture, IgG2a- and IgE-levels analysed by enzyme-linked immunosorbemt assay (ELISA) and cytokine-secreting cells detected by enzyme-linked immunospot (ELISPOT). BbHg mice showed less severe histological arthritis, but delayed eradication of spirochaetes compared to Bb mice, associated with increased levels of IgE (Th2-induced) and decreased levels of IgG2a (Th1-induced), consistent with a Th2-deviation. Both the numbers of Th1 and Th2 cytokine-secreting cells were reduced in BbHg mice, possibly explained by the fact that numbers of cytokine-secreting cells do not correlate with cytokine concentration. In conclusion, this study supports the hypothesis that a Th1-like response is required for optimal eradication of Borrelia.

Immunomodulation by mercuric chloride in vitro: application of different cell activation pathways

Evidence is emerging that exposure to mercury (Hg) may elicit many pathological manifestations, including immunomodulation. We tested whether changing cellular activation pathways may affect the immunomodulation by Hg. Human cell cultures were set up where isolated peripheral blood mononuclear cells, activated by monoclonal antibodies (MoAb: anti-CD3/-CD28/-CD40) or heat-killed Salmonella enterica serovar Enteritidis (hk-SE), exposed to mercuric chloride (HgCl2) for 24 h. Cell vitality was assessed by MTT assay, and modulation of cytokine profiles were monitored by enzyme-linked immunosorbent assay (ELISA), intracellular cytokine staining and reverse transcription-polymerase chain reaction (RT-PCR). Results show that Hg doses above 15 ng/ml significantly reduced cell vitality (P < 0.05). Lower doses elicited distinct effects on T helper 1 (Th1) and Th2 cytokine expression depending on cellular activation pathways. In MoAb-stimulated cells, interferon (IFN)-gamma, tumour necrosis factor (TNF)-alpha and interleukin (IL)-6 production was reduced. Doses up to 0.150 and 0.5 microg/ml increased IL-10 and IL-4 production, respectively, resulting in significantly reduced Th1/Th2 ratios. Stimulation by hk-SE, however, elevated Th1/Th2 ratios due to induction of IFN-gamma versus IL-10 production. Taken together, we conclude that low-level exposure to Hg, in the absence of inflammation, polarizes the immune response toward Th2, but not in the case of Th1-polarized responses elicited by Salmonella antigens that can be promoted instead. This demonstrates differential in vitro effects of Hg on the Th1/Th2 balance produced by different stimuli, which may have important experimental and scientific implications.

Dose and Hg species determine the T-helper cell activation in murine autoimmunity

Inorganic mercury (mercuric chloride--HgCl(2)) induces in mice an autoimmune syndrome (HgIA) with T cell-dependent polyclonal B cell activation and hypergammaglobulinemia, dose- and H-2-dependent production of autoantibodies targeting the 34 kDa nucleolar protein fibrillarin (AFA), and systemic immune-complex deposits. The organic mercury species methylmercury (MeHg) and ethylmercury (EtHg--in the form of thimerosal) induce AFA, while the other manifestations of HgIA seen after treatment with HgCl(2) are present to varying extent. Since these organic Hg species are converted to the autoimmunogen Hg(2+) in the body, their primary autoimmunogen potential is uncertain and the subject of this study. A moderate dose of HgCl(2) (8 mg/L drinking water--internal dose 148 micro gHg/kg body weight [bw]/day) caused the fastest AFA response, while the induction was delayed after higher (25 mg/L) and lower (1.5 and 3 mg/L) doses. The lowest dose of HgCl(2) inducing AFA was 1.5 mg/L drinking water which corresponded to a renal Hg(2+) concentration of 0.53 micro g/g. Using a dose of 8 mg HgCl(2)/L this threshold concentration was reached within 24 h, and a consistent AFA response developed after 8-10 days. The time lag for the immunological part of the reaction leading to a consistent AFA response was therefore 7-9 days. A dose of thimerosal close to the threshold dose for induction of AFA (2 mg/L drinking water--internal dose 118 micro gHg/kg bw per day), caused a renal Hg(2+) concentration of 1.8 micro g/g. The autoimmunogen effect of EtHg might therefore be entirely due to Hg(2+) formed from EtHg in the body. The effect of organic and inorganic Hg species on T-helper type 1 and type 2 cells during induction of AFA was assessed as the presence and titre of AFA of the IgG1 and IgG2a isotype, respectively. EtHg induced a persistent Th1-skewed response irrespectively of the dose and time used. A low daily dose of HgCl(2) (1.5-3 mg/L) caused a Th1-skewed AFA response, while a moderate dose (8 mg/L) after 2 weeks resulted in a balanced or even Th2-skewed response. Higher daily doses of HgCl(2) (25 mg/L) caused a balanced Th2-Th1 response already from onset. In conclusion, while metabolically formed Hg(2+) might be the main AFA-inducing factor also after treatment with EtHg, the quality of the Hg-induced AFA response is modified by the species of Hg as well as the dose.

A role for B cell-activating factor of the TNF family in chemically induced autoimmunity

After exposure to subtoxic doses of heavy metals such as mercury, H-2s mice develop an autoimmune syndrome consisting of the rapid production of IgG autoantibodies that are highly specific for nucleolar autoantigens and a polyclonal increase in serum IgG1 and IgE. In this study, we observe that HgCl2 administration in susceptible mice results in the elevated production of B cell-activating factor of the TNF family ((BAFF) also known as BLyS, TALL-1, zTNF-4, THANK, and TNSF13B), a B cell growth factor belonging to the TNF family. A transmembrane activator and calcium-modulating and cyclophilin ligand interactor (TACI)-Ig fusion protein (which neutralizes both BAFF and a proliferation-inducing ligand (APRIL), another TNF family member) inhibited Hg-induced autoantibody or serum IgE production. These results are discussed in the context of the inhibitory effect of TACI-Ig on B cell maturation at the transitional stage.

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.

Neurotoxic effects of postnatal thimerosal are mouse strain dependent

The developing brain is uniquely susceptible to the neurotoxic hazard posed by mercurials. Host differences in maturation, metabolism, nutrition, sex, and autoimmunity influence outcomes. How population-based variability affects the safety of the ethylmercury-containing vaccine preservative, thimerosal, is unknown. Reported increases in the prevalence of autism, a highly heritable neuropsychiatric condition, are intensifying public focus on environmental exposures such as thimerosal. Immune profiles and family history in autism are frequently consistent with autoimmunity. We hypothesized that autoimmune propensity influences outcomes in mice following thimerosal challenges that mimic routine childhood immunizations. Autoimmune disease-sensitive SJL/J mice showed growth delay; reduced locomotion; exaggerated response to novelty; and densely packed, hyperchromic hippocampal neurons with altered glutamate receptors and transporters. Strains resistant to autoimmunity, C57BL/6J and BALB/cJ, were not susceptible. These findings implicate genetic influences and provide a model for investigating thimerosal-related neurotoxicity.

Short- and long-term effects of T-cell modulating agents in experimental autoimmunity

Due to the easy and reliable induction of a disease condition with many of the features present in human autoimmunity, mercury-induced autoimmunity (mHgAI) in rodents is a favourable autoimmune model. Genetically susceptible (H-2(s)) mice develop in response to mercury (Hg) a systemic autoimmune condition with antinucleolar antibodies (ANoA) targeting the protein fibrillarin, transient polyclonal B-cell activation, hyperimmunoglobulinemia, and systemic immune-complex (IC) deposits. In order to study the short- and long-term effects of treatment with immunomodulating agents on the disease parameters in HgAI, groups of B10.S (H-2(s)) mice were given 6 mg HgCl(2)/l drinking water for 22 weeks. Three weeks initial treatment with cyclosporin A (CyA), a high dose of tacrolimus (HD tacrolimus), or anti-CD4 monoclonal antibody (a-CD4) inhibited induction of ANoA and IC deposit by Hg. This effect persisted for the subsequent 19 weeks when the mice were only treated with Hg. Initial treatment with anti-IL-4 monoclonal antibody (a-IL-4) for 3 weeks inhibited induction of IgE and IC deposits by Hg, but not ANoA. However, subsequent treatment with Hg without a-IL-4 for 19 weeks induced IC deposits. The T-cell modulating agents aggravated some of the HgAI disease parameters: a-CD4 stimulated the polyclonal B-cell activation, a-IL-4 increased the IgG antichromatin antibody response, and a low dose of tacrolimus (LD tacrolimus) enhanced the ANoA, the polyclonal B-cell activation, and the IC deposits. We conclude that a short initial treatment with a-CD4 or CyA efficiently protects against induction of systemic autoimmunity for an extended period of time. However, some of the T-cell modulating agents, especially a low dose of tacrolimus, aggravate autoimmune manifestations not only during ongoing treatment, but also after treatment with these agents has ceased.

Dose–response study of thimerosal-induced murine systemic autoimmunity

The organic compound ethylmercurithiosalicylate (thimerosal), which is primarily present in the tissues as ethylmercury, has caused illness and several deaths due to erroneous handling when used as a disinfectant or as a preservative in medical preparations. Lately, possible health effects of thimerosal in childhood vaccines have been much discussed. Thimerosal is a well-known sensitizing agent, although usually of no clinical relevance. In rare cases, thimerosal has caused systemic immune reactions including acrodynia. We have studied if thimerosal might induce the systemic autoimmune condition observed in genetically susceptible mice after exposure to inorganic mercury. A.SW mice were exposed to 1.25-40 mg thimerosal/l drinking water for 70 days. Antinucleolar antibodies, targeting the 34-kDa protein fibrillarin, developed in a dose-related pattern and first appeared after 10 days in the two highest dose groups. The lowest observed adverse effect level (LOAEL) for antifibrillarin antibodies was 2.5 mg thimerosal/l, corresponding to an absorbed dose of 147 microg Hg/kg bw and a concentration of 21 and 1.9 microg Hg/g in the kidney and lymph nodes, respectively. The same LOAEL was found for tissue immune-complex deposits. The total serum concentration of IgE, IgG1, and IgG2a showed a significant dose-related increase in thimerosal-treated mice, with a LOAEL of 5 mg thimerosal/l for IgG1 and IgE, and 20 mg thimerosal/l for IgG2a. The polyclonal B-cell activation showed a significant dose-response relationship with a LOAEL of 10 mg thimerosal/l. Therefore, thimerosal induces in genetically susceptible mice a systemic autoimmune syndrome very similar to that seen after treatment with inorganic mercury, although a higher absorbed dose of Hg is needed using thimerosal. The autoimmune syndrome induced by thimerosal is different from the weaker and more restricted autoimmune reaction observed after treatment with an equipotent dose of methylmercury.

Effects of deviating the Th2-response in murine mercury-induced autoimmunity towards a Th1-response

T-helper cells type 1 (Th1) and type 2 (Th2) play an important role in the pathogenesis of autoimmune diseases. In many Th1-dependent autoimmune models, treatment with recombinant interleukin-12 (rIL-12) accelerates the autoimmune response. Mercury-induced autoimmunity (HgIA) in mice is an H-2 regulated condition with antinucleolar antibodies targeting fibrillarin (ANoA), systemic immune-complex (IC) deposits and transient polyclonal B-cell activation (PBA). HgIA has many characteristics of a Th2 type of reaction, including a strong increase of IgE, but disease induction is critically dependent on the Th1 cytokine IFN-gamma. The aim of this study was to investigate if a strong deviation of the immune response in HgIA towards Th1 would aggravate HgIA. Injections of both rIL-12 and anti-IL-4 monoclonal antibody (alpha-IL-4) reduced the HgCl2-(Hg-)induced concentration of the Th2-dependent serum IgE and IgG1, but increased the Th1-dependent serum IgG2a. The IgG-ANoA developed earlier and attained a higher titre after combined treatment, and the ANoA titre of the IgG1 isotype decreased while the ANoA titre of the Th1-associated IgG2a, IgG2b and IgG3-ANoA isotypes increased. Treatment with rIL-12 alone increased the Hg-induced IgG2a and IgG3 ANoA titres, the PBA, and the IC deposits in renal and splenic vessel walls, while treatment with alpha-IL-4 + Hg inhibited renal but not splenic vessel wall IC deposits. We conclude that manipulating the cytokine status, by altering the Th1/Th2 balance, will influence autoimmune disease manifestations. This might be an important way of modulating human autoimmune diseases.

Investigating the onset of autoimmunity in A.SW mice following treatment with 'toxic oils'

In 1981, over 20,000 people were struck with toxic oil syndrome (TOS). H-2s strains of mice have been shown to develop symptoms of TOS after exposure to toxic oil. We examined the effects of toxic oil on A.SW mice, which are susceptible to chemically-induced autoimmunity, but do not spontaneously develop autoimmune disease. Mice were treated with three types of toxic oil: CO756 (case oil from Spain), RSD99 (rapeseed oil with no 3-(N-phenylamino)-1-2-propanediol (PAP) derivatives) and RSA99 (rapeseed oil supplemented with PAP derivatives). Mercuric chloride treated mice were used as a positive control. After toxic oil treatment, there were no consistent differences in body weight or organ weight (liver, kidney, thymus and spleen) as a percent of body weight at any of these timepoints: 2.5, 5 or 10 weeks. We also found that treatment with toxic oil did not induce autoantibody formation or lead to increased serum levels of IgG1, IgG2a or IgE at these timepoints. Conversely, at all timepoints, there were significant increases in organ weight as a percent of body weight in the mercury treated mice. Additionally, mercuric chloride treated mice had elevated serum levels of IgG1, IgG2a and IgE and developed anti-nuclear and anti-collagen antibodies.

Immunoglobulin and autoantibody responses in MRL/lpr mice treated with 'toxic oils'

The toxic oil syndrome (TOS) occurred in Spain in 1981 as a result of ingestion of oil mixtures containing aniline-denatured rapeseed oil. The disease afflicted almost 20000 people, resulted in more than 400 deaths, and mimicked an autoimmune disease in all patients. Phenilamine-propanediol (PAP) has been implicated as a possible etiologic agent of TOS but absence of an acceptable animal model to evaluate the autoimmune potential of the 'case oil' has hindered identification of the actual etiologic agent(s). The purpose of this study was twofold; (1) to develop an animal model of human disease to investigate the immunological etiology and pathogenesis of TOS and (2) to determine if the 'case oil' responsible for TOS and/or two synthesized oils either induced or exacerbated the systemic autoimmune disease that occurs spontaneously in the MRL/lpr mouse. The oils tested were a denatured rapeseed oil collected from a family (case oil) who were affected by the TOS (CO756), a rapeseed oil denatured with 2% aniline and enriched with a mixture of diesters of PAP (RSD), and a rapeseed oil denatured with 2% aniline but contained no diesters of PAP (RSA). Female MRL/lpr mice, 7 weeks of age, received orally either an undiluted (neat) or a 1:10 diluted dose of each test oil, canola oil (oil control), water (nai;ve control), or 50-ppm mercury (positive control). Half of each group was sacrificed after 5 weeks of exposure and the remaining mice after 10 weeks of exposure. Serum IgG1, IgG2a, IgE isotypes and antinuclear (ANA), collagen type II, histone, single-stranded DNA (ssDNA), double-stranded DNA (dsDNA) and Sm autoantibody concentrations were determined after 5 and 10 weeks of exposure. The oils did not significantly affect the concentrations of the serum immunoglobulins, although a shift in the IgG1:IgG2a ratio towards IgG1 was noted from 12 to 17 weeks of age (5-10 weeks of treatment). The oils did however stimulate the systemic autoimmune response. The RSD neat treatment resulted in a nonsignificant but noted increase in autoantibodies to collagen (10 weeks), histone (10 weeks) and dsDNA (5 and 10 weeks). CO756 neat increased the serum levels of ANA (5 weeks), collagen (5 weeks) and dsDNA (5 and 10 weeks). The RSA 1:10 dilution increased ssDNA and dsDNA autoantibodies at 5 weeks. The results suggest that PAP is an active principle of these noted responses. These data, coupled with the toxicology and pathology data from this study (Toxicol. Path. 29 (2001) 630), revealed that the three oils incited induction of the lymphoproliferative syndrome and that the two oils containing PAP induced and enhanced the systemic autoimmune response that develops spontaneously at an early age in the MRL/lpr mouse. There was also a positive correlation noted between serum autoantibody concentrations and progression of the idiopathic autoimmune syndrome in the MRL/lpr mouse.

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.

Application of the popliteal lymph node assay in immunotoxicity testing: complementation of the direct popliteal lymph node assay with flow cytometric analyses

The popliteal lymph node assay (PLNA) has been proposed to measure the immunosensitizing potential of chemicals. The direct PLNA detects an immunomodulating effect but does not give insight into the mode of action of the chemical under test. Modifications of this test have been proposed, but they are difficult to perform in routine toxicity testing and require many animals. In the present investigation the direct PLNA was extended with the flow cytometric determinations of: (a) lymphoblasts; (b) the phenotyping of lymphoid subpopulations; (c) the determination of expression of proliferation/activation markers CD25, CD69 and CD62L/CD44 and (d) the analysis of intracellular cytokines interferon gamma, interleukin 2 and interleukin 4. Streptozotocin, hydrazine, HgCl2 and trinitrobenzene sulfonic acid were used as model chemicals. The different mode of action of these substances was well documented by the techniques applied. As the proposed flow cytometric methods can easily be performed and do not require additional test animals this complementation of the direct PLNA seems a promising approach in immunotoxicity testing.

Murine metal-induced systemic autoimmunity: baseline and stimulated cytokine mRNA expression in genetically susceptible and resistant strains

Cytokines play an important and complex role in the pathogenesis of systemic autoimmune diseases. In susceptible H-2s mice, inorganic mercury (Hg) induces lymphoproliferation, antinucleolar antibodies against the 34-kDa-protein fibrillarin, and systemic immune-complex (IC) deposits. Here, we report extensive analysis of cytokine mRNA levels in susceptible A.SW (H-2s) and resistant A.TL (H-2tl) mice under unstimulated conditions and during oral treatment with Hg and/or silver nitrate (Ag). Cytokine mRNA expression in lymphoid tissues was assessed using the ribonuclease protection assay and phosphorimaging. Baseline expression of IL-2 and IFN-gamma mRNA was higher in A.SW than in A.TL mice. In A.SW mice, Hg treatment caused early up-regulation of IL-2 and IFN-gamma levels, followed by substantial expression of IL-4 mRNA, which was significant compared to control A.SW and Hg-treated A.TL mice. Hg-exposed A.TL mice exhibited unchanged IFN-gamma, reduced IL-2 and greatly increased IL-10 mRNA expression. Ag-treated A.SW mice, which develop antifibrillarin antibodies (AFA) but exhibit minimal immune activation and no IC deposits, showed an early increase in IL-2 and IFN-gamma mRNA, but only a small and delayed rise in IL-4 mRNA. In conclusion, H-2-linked resistance to Hg-induced AFA is characterized by low constitutive expression of IL-2 and IFN-gamma mRNA, which is not increased by Hg, and a marked increase in IL-10 expression. Conversely, the key features of H-2-linked susceptibility to Hg- and Ag-induced AFA are up-regulation of IL-2, IFN-gamma and IL-4 mRNA expression, and down-regulation of IL-10 expression.

Resistance to xenobiotic-induced autoimmunity maps to chromosome 1

Although evidence indicates that environmental factors play a major role in precipitating systemic autoimmunity in genetically susceptible individuals, little is known about the mechanisms involved. Certain heavy metals, such as mercury, are potent environmental immunostimulants that produce a number of immunopathologic sequelae, including lymphoproliferation, hypergammaglobulinemia, and overt systemic autoimmunity. Predisposition to such metal-induced immunopathology has been shown to be influenced by both MHC and non-MHC genes, as well as susceptibility to spontaneous lupus, in mice and other experimental animals. Among the various mouse strains examined to date, the DBA/2 appears to uniquely lack susceptibility to mercury-induced autoimmunity (HgIA), despite expressing a susceptible H-2 haplotype (H-2d). To define the genetic basis for this trait, two genome-wide scans were conducted using F2 intercrosses of the DBA/2 strain with either the SJL or NZB strains, both of which are highly susceptible to HgIA. A single major quantitative trait locus on chromosome 1, designated Hmr1, was shown to be common to both crosses and encompassed a region containing several lupus susceptibility loci. Hmr1 was linked to glomerular immune complex deposits and not autoantibody production, suggesting that DBA/2 resistance to HgIA may primarily involve the later stages of disease pathogenesis. Identification and characterization of susceptibility/resistance genes and mechanisms relevant to the immunopathogenesis of mercury-induced autoimmunity should provide important insights into the pathogenesis of autoimmunity and may reveal novel targets for intervention.

The effect of dose, gender, and non-H-2 genes in murine mercury-induced autoimmunity

We have studied the effect of dose, treatment time, gender and non-H-2 genes on immune parameters and toxicokinetics in murine mercury-induced autoimmunity (HgAI). The partly-proven mechanism for HgAI is the modification of the autoantigen fibrillarin by mercury, followed by a T cell-dependent immune response driven by the modified fibrillarin. In the H-2 congenic (H-2(S)) mouse strains A.SW and B10.S given (203)HgCl(2) in a dose of 0.25-8 mg Hg/l drinking water for up to 10 weeks, the internal dose measured as the whole-body retention of mercury reached steady state within 5 weeks. Fifty percent of the steady state level was reached already after 2 days. Conditions therefore exist for a rapid modification of fibrillarin, followed by a T cell-dependent immune response, which is consistent with the presence of anti-fibrillarin antibodies (AFA) in serum after 2 weeks. AFA developed in a dose-dependent pattern. Serum IgE showed a dose-dependent increase with a maximum after 1-2.5 weeks followed by a distinct decline towards the baseline level. Substantial polyclonal B-cell activation (PBA) developed in the highest dose groups only. Since AFA developed using lower doses too, PBA can be excluded as a general mechanism for induction of AFA. Tissue immune-complex (IC) deposits were present in the highest dose groups only, indicating a possible causality between PBA and IC deposits. The substantially lower whole body and organ mercury level needed to induce AFA in the A.SW strain as compared with the H-2 congenic B10.S strain, demonstrates that genetic factors outside the H-2 region, and not related to toxicokinetics, modifies the autoimmune response. In contrast, the difference in mercury thresholds for induction of IgE was only slight between A.SW and B10.S mice, indicating basically different mechanisms for induction of AFA and serum IgE.

Genetic control of resistance to mercury-induced immune/autoimmune activation

Previous studies have shown that genetic factors control the susceptibility to mercury-induced immunoglobulin (Ig)G1 antibody formation, IgE synthesis, renal IgG deposits and antinucleolar autoantibodies (ANolA) production in the susceptible mice. In this study, we examined the genetic control of resistance to these characteristics after HgCl2 injection in F1 hybrid crosses between the highly mercury resistant DBA/2 and mercury susceptible NZB (H-2d), SJL (H-2 s), A.CA (H-2f) and DBA/1 (H-2q) mice and also in backcross hybrids between (DBA/2 x SJL)F1 and SJL mice. We observed that mercury-induced immune/autoimmune manifestations were profoundly downregulated in most (if not all) of the F1 hybrids, indicating that the resistance to mercury was a dominant trait. Analysis of mercury-induced immune/autoimmune responses in the (DBA/2 x SJL) x SJL backcross hybrids suggested that only one gene or a cluster of genes determined the resistance to the ANolA production, whereas the resistance to other characteristics was controlled by two and/or three gene loci. By H-2 genotyping the backcross mice, it was found that H-2d haplotype per se could confer resistance to ANolA production. However, we did not find any significant association between the H-2d haplotype and the resistance to increase of IgG1 and IgE synthesis and the development of renal IgG1 deposits. Thus, while in DBA/2 mice, gene(s) in the H-2 loci strictly contribute to the inheritance of resistance to ANolA production; non-H-2 genes mainly govern the inheritance of unresponsiveness regarding other characteristics.

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.

Contribution of H-2 and non-H-2 genes in the control of mercury-induced autoimmunity

Mercury-induced autoimmunity is characterized by a T cell-dependent B cell activation (mainly of IgG1 and IgE isotypes), production of anti-nucleolar autoantibodies (ANolA) and the formation of renal IgG deposits. The autoimmunity is to a large extent controlled by genetic factors. We studied 15 different inbred mouse strains of seven H-2 (mouse MHC) genotypes to determine the importance of H-2 and non-H-2 background genes in mercury-induced autoimmunity. The tested strains exhibited a diverse autoimmune response to mercury. In each H-2 genotype, there was at least one strain which responded to mercury by the production of high levels of IgG1 and IgE Ig as well as by the development of high titers of renal IgG1 deposits. Only mouse strains with H-2(s) and H-2(q) genotypes, irrespective of their background genes, produced ANolA after mercury treatment. Only SJL (H-2(s)) and A.SW (H-2(s)) mice were highly susceptible to all characteristics of mercury-induced autoimmunity. NZB (H-2(d)) mice were also highly susceptible, but they did not develop ANolA. Only the DBA/2 (H-2(d)) strain was found to be resistant to all tested mercury-induced autoimmune manifestations, suggesting that non-responsiveness to mercury in DBA/2 mice was largely influenced by non H-2 genes. These findings imply that H-2 genes mainly determine the susceptibility to mercury-induced ANolA production, whereas non-H-2 genes control the susceptibility to and the severity of the B cell activation and renal IgG deposition.

Characterization of mercuric mercury (Hg2+)-induced lymphoblasts from patients with mercury allergy and from healthy subjects

Hg2+ induces lymphocyte proliferation when added to cell cultures from both healthy and mercury-allergic subjects. Consequently, when measuring DNA synthesis a possible Hg2+-specific response, resulting from proliferating memory cells, cannot be discriminated from a non-allergic response. The mechanism behind this non-allergic response is unknown but a superantigenic effect of Hg2+ has been suggested. In this study, five mercury-allergic patients, with oral lichen planus (OLP) lesions adjacent to dental amalgam and a positive patch test to Hg0, and five healthy subjects without amalgam were examined. The immunophenotype and the T cell receptor Vbeta (TCR Vbeta) repertoire of Hg2+-induced lymphoblasts as well as the expression of the lymphocyte activation markers CD23 and CD134 were analysed for possible differences between healthy and allergic subjects. The mechanism of Hg2+-induced proliferation was examined by comparing the TCR Vbeta expression of Hg- and staphylococcal enterotoxin B (SEB)-activated lymphoblasts, the latter used as a positive superantigen control. It was not possible to discriminate between mercury-allergic and healthy subjects using the immunophenotype or the TCR Vbeta profile of the Hg2+-induced lymphoblasts or the expression of CD23 and CD134. However, Hg2+-induced CD4+ lymphoblasts showed a skewing towards Vbeta2. This relative increase in Vbeta2 was only detected in the CD4+ but not in the CD8+ lymphoblast population. In conclusion, Hg2+ induced a proliferation-dependent skewing towards CD4+ but not CD8+ lymphocytes expressing Vbeta2. In this respect Hg2+ differs from the classical bacterial superantigen SEB, which also stimulates unique TCR Vbeta families among CD8+ cells.

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.

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.