Resistance to xenobiotic-induced autoimmunity maps to chromosome 1

Drug-Induced Membranous Nephropathy: Piecing Together Clues to Understand Disease Mechanisms

There is a resurgence of interest in drug-induced membranous nephropathy because of the widespread availability of recently discovered culprit medications, such as lipoic acid supplements, mercury in skin-lightening creams, and nonsteroidal anti-inflammatory drugs, and the relationship between these drugs and newly described target antigens. The clinical syndromes associated with drug-induced membranous nephropathy are similar in that proteinuria ranges from low grade to nephrotic range and generally remits within months of drug cessation. Histology is notable for subepithelial deposits that are IgG1 subclass predominant, sometimes with a unique segmental distribution. The two antigens associated with drug-induced membranous nephropathy are neural epidermal growth factor-like 1 and proprotein convertase subtilisin/kexin type 6. Notably, several of the culprit drugs contain one or more sulfhydryl groups that may have potential mechanistic relevance. In this review, we explore past research investigations into mechanisms of membranous nephropathy associated with gold salts, penicillamine, and mercury and use these historical studies as the basis for formulating new hypotheses on how drugs might promote immune dysregulation and, ultimately, membranous nephropathy.

Mercury-induced inflammation and autoimmunity

BACKGROUND

Human exposure to mercury leads to a variety of pathologies involving numerous organ systems including the immune system. A paucity of epidemiological studies and suitable diagnostic criteria, however, has hampered collection of sufficient data to support a causative role for mercury in autoimmune diseases. Nevertheless, there is evidence that mercury exposure in humans is linked to markers of inflammation and autoimmunity. This is supported by experimental animal model studies, which convincingly demonstrate the biological plausibility of mercury as a factor in the pathogenesis of autoimmune disease.

SCOPE OF THE REVIEW

In this review, we focus on ability of mercury to elicit inflammatory and autoimmune responses in both humans and experimental animal models.

MAJOR CONCLUSIONS

Although subtle differences exist, the inflammatory and autoimmune responses elicited by mercury exposure in humans and experimental animal models show many similarities. Proinflammatory cytokine expression, lymphoproliferation, autoantibody production, and nephropathy are common outcomes. Animal studies have revealed significant strain dependent differences in inflammation and autoimmunity suggesting genetic regulation. This has been confirmed by the requirement for individual genes as well as genome wide association studies. Importantly, many of the genes required for mercury-induced inflammation and autoimmunity are also required for idiopathic systemic autoimmunity. A notable difference is that mercury-induced autoimmunity does not require type I IFN. This observation suggests that mercury-induced autoimmunity may arise by both common and specific pathways, thereby raising the possibility of devising criteria for environmentally associated autoimmunity.

GENERAL SIGNIFICANCE

Mercury exposure likely contributes to the pathogenesis of autoimmunity.

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.

Induction of Systemic Autoimmunity by a Xenobiotic Requires Endosomal TLR Trafficking and Signaling from the Late Endosome and Endolysosome but Not Type I IFN

Type I IFN and nucleic acid-sensing TLRs are both strongly implicated in the pathogenesis of lupus, with most patients expressing IFN-induced genes in peripheral blood cells and with TLRs promoting type I IFNs and autoreactive B cells. About a third of systemic lupus erythematosus patients, however, lack the IFN signature, suggesting the possibility of type I IFN-independent mechanisms. In this study, we examined the role of type I IFN and TLR trafficking and signaling in xenobiotic systemic mercury-induced autoimmunity (HgIA). Strikingly, autoantibody production in HgIA was not dependent on the type I IFN receptor even in NZB mice that require type I IFN signaling for spontaneous disease, but was dependent on the endosomal TLR transporter UNC93B1 and the endosomal proton transporter, solute carrier family 15, member 4. HgIA also required the adaptor protein-3 complex, which transports TLRs from the early endosome to the late endolysosomal compartments. Examination of TLR signaling pathways implicated the canonical NF-κB pathway and the proinflammatory cytokine IL-6 in autoantibody production, but not IFN regulatory factor 7. These findings identify HgIA as a novel type I IFN-independent model of systemic autoimmunity and implicate TLR-mediated NF-κB proinflammatory signaling from the late endocytic pathway compartments in autoantibody generation.

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.

Mercury as an environmental stimulus in the development of autoimmunity - A systematic review

Autoimmune diseases result from an interplay of genetic predisposition and factors which stimulate the onset of disease. Mercury (Hg), a well-established toxicant, is an environmental factor reported to be linked with autoimmunity. Hg exists in several chemical forms and is encountered by humans in dental amalgams, certain vaccines, occupational exposure, atmospheric pollution and seafood. Several studies have investigated the effect of the various forms of Hg, including elemental (Hg⁰), inorganic (iHg) and organic mercury (oHg) and their association with autoimmunity. In vitro studies using peripheral blood mononuclear cells (PBMC) from healthy participants have shown that methylmercury (MeHg) causes cell death at lower concentrations than iHg albeit exposure to iHg results in a more enhanced pro-inflammatory profile in comparison to MeHg. In vivo research utilising murine models susceptible to the development of metal-induced autoimmunity report that exposure to iHg results in a lupus-like syndrome, whilst mice exposed to MeHg develop autoimmunity without the formation of immune complexes. Furthermore, lower concentrations of IgE are detected in MeHg-treated animals in comparison with those treated with iHg. It appears that, oHg has a negative impact on animal models with existing autoimmunity. The research conducted on humans in this area is diverse in study design and the results are conflicting. There is currently no evidence to implicate a role for Hg⁰ exposure from dental amalgams in the development or perpetuation of autoimmune disease, apart from some suggestion of individual sensitivity. Several studies have consistently shown a positive correlation between iHg exposure and serum autoantibody concentrations in gold miners, although the clinical impact of iHg remains unknown. Furthermore, a limited number of studies have reported individuals with autoimmune disease have higher concentrations of blood Hg compared to healthy controls. In summary, it appears that iHg perpetuates markers of autoimmunity to a greater extent than oHg, albeit the impact on clinical outcomes in humans is yet to be elucidated.

Cathepsin B regulates the appearance and severity of mercury-induced inflammation and autoimmunity

Susceptibility and resistance to systemic autoimmunity are genetically regulated. This is particularly true for murine mercury-induced autoimmunity (mHgIA) where DBA/2J mice are considered resistant to disease including polyclonal B cell activation, autoantibody responses, and immune complex deposits. To identify possible mechanisms for the resistance to mHgIA, we exposed mHgIA sensitive B10.S and resistant DBA/2J mice to HgCl2 and assessed inflammation and pro-inflammatory responses at the site of exposure and subsequent development of markers of systemic autoimmunity. DBA/2J mice showed little evidence of induration at the site of exposure, expression of proinflammatory cytokines, T cell activation, or autoantibody production, although they did exhibit increased levels of total serum IgG and IgG1. In contrast B10.S mice developed significant inflammation together with increased expression of inflammasome component NLRP3, proinflammatory cytokines IL-1β, TNF-α, and IFN-γ, hypergammaglobulinemia, splenomegaly, CD4(+) T-cell activation, and production of autoantibodies. Inflammation in B10.S mice was associated with a selective increase in activity of cysteine cathepsin B but not cathepsins L or S. Increased cathepsin B activity was not dependent on cytokines required for mHgIA but treatment with CA-074, a cathepsin B inhibitor, led to transient reduction of local induration, expression of inflammatory cytokines, and subsequent attenuation of the systemic adaptive immune response. These findings demonstrate that sensitivity to mHgIA is linked to an early cathepsin B regulated inflammatory response which can be pharmacologically exploited to abrogate the subsequent adaptive autoimmune response which leads to disease.

Expert panel workshop consensus statement on the role of the environment in the development of autoimmune disease

Autoimmune diseases include 80 or more complex disorders characterized by self-reactive, pathologic immune responses in which genetic susceptibility is largely insufficient to determine disease onset. In September 2010, the National Institute of Environmental Health Sciences (NIEHS) organized an expert panel workshop to evaluate the role of environmental factors in autoimmune diseases, and the state of the science regarding relevant mechanisms, animal models, and human studies. The objective of the workshop was to analyze the existing data to identify conclusions that could be drawn regarding environmental exposures and autoimmunity and to identify critical knowledge gaps and areas of uncertainty for future study. This consensus document summarizes key findings from published workshop monographs on areas in which “confident” and “likely” assessments were made, with recommendations for further research. Transcribed notes and slides were reviewed to synthesize an overview on exposure assessment and questions addressed by interdisciplinary panels. Critical advances in the field of autoimmune disease research have been made in the past decade. Collaborative translational and interdisciplinary research is needed to elucidate the role of environmental factors in autoimmune diseases. A focus on exposure assessment methodology is needed to improve the effectiveness of human studies, and more experimental studies are needed to focus on causal mechanisms underlying observed associations of environmental factors with autoimmune disease in humans.

A tandem repeat in decay accelerating factor 1 is associated with severity of murine mercury-induced autoimmunity

Decay accelerating factor (DAF), a complement-regulatory protein, protects cells from bystander complement-mediated lysis and negatively regulates T cells. Reduced expression of DAF occurs in several systemic autoimmune diseases including systemic lupus erythematosus, and DAF deficiency exacerbates disease in several autoimmune models, including murine mercury-induced autoimmunity (mHgIA). Daf1, located within Hmr1, a chromosome 1 locus associated in DBA/2 mice with resistance to mHgIA, could be a candidate. Here we show that reduced Daf1 transcription in lupus-prone mice was not associated with a reduction in the Daf1 transcription factor SP1. Studies of NZB mice congenic for the mHgIA-resistant DBA/2 Hmr1 locus suggested that Daf1 expression was controlled by the host genome and not the Hmr1 locus. A unique pentanucleotide repeat variant in the second intron of Daf1 in DBA/2 mice was identified and shown in F2 intercrosses to be associated with less severe disease; however, analysis of Hmr1 congenics indicated that this most likely reflected the presence of autoimmunity-predisposing genetic variants within the Hmr1 locus or that Daf1 expression is mediated by the tandem repeat in epistasis with other genetic variants present in autoimmune-prone mice. These studies argue that the effect of DAF on autoimmunity is complex and may require multiple genetic elements.

Depletion of complement does not impact initiation of xenobiotic-induced autoimmune disease

Deficiency in Daf1, a complement regulatory protein, has been shown to exacerbate development of various autoimmune diseases and recent studies have suggested that this may be explained by Daf1 acting to limit T-cell hyper-responsiveness. It has been suggested that the absence of Daf1 aggravates autoimmune disease in a complement-dependent manner, but others have shown that activation of T cells in the absence of Daf1 can be complement independent. However, the relationship between Daf1, complement components, lymphocyte activation, cytokine expression and antibody production remains to be determined in mice that are not Daf1 deficient. We have recently demonstrated, in murine mercury-induced autoimmunity (mHgIA), that an accumulation of CD44(high) Daf(low) CD4(+) T cells is associated with the development of autoimmunity. In this study we observed that complement depletion does not affect the accumulation of activated CD4(+) T cells, elevation of splenic interleukin-4 expression and autoantibody production in mHgIA. In addition, neither the accumulation of CD44(high) Daf(low) CD4(+) T cells nor the down-regulation of Daf1 expression on CD4(+) T cells was influenced by a lack of complement. In conclusion, these studies show that initiating events in xenobiotic-induced autoimmunity, including lymphocyte activation, cytokine expression and autoantibody production, are not dependent on complement.

The multi-systemic nature of diabetes mellitus: Genotype or phenotype?

BACKGROUND

This article discusses factors which materially influence the diagnosis, prevention and treatment of diabetes mellitus but which may be overlooked by the prevailing biomedical paradigm. That cognition can be mathematically linked to the function of the autonomic nervous system and physiological systems casts new light upon the mechanisms responsible for homeostasis and origins of disease. In particular, it highlights the limitations of the reductionist biomedical approach which considers mainly the biochemistry of single pathologies rather than considering the neural mechanisms which regulate the function of physiological systems, and inherent visceral organs; and which are subsequently manifest as biochemistries of varying degrees of complexity and severity. As a consequence, histopathological tests are fraught with inherent limitations and many categories of drugs are significantly ineffective.

AIMS

Such limitations may be explained if disease (in particular diabetes mellitus) has multiple origins, is multi-systemic in nature and, depending upon the characteristics of each pathology, is influenced by genotype and/or phenotype.

RESULTS

This article highlights the influence of factors which are not yet considered re. the aetiology of diabetes mellitus e.g. the influence of light and sensory input upon the stability of the autonomic nervous system; the influence of raised plasma viscosity upon rates of reaction; the influence of viruses and/or of modified live viruses given in vaccinations; systemic instability, in particular the adverse influence of drinks and lack of exercise upon the body's prevailing pH and its subsequent influence upon levels of magnesium and other essential trace elements.

CONCLUSIONS

This application of the top-down systems biology approach may provide a plausible and inclusive explanation for the nature and occurrence of diabetes mellitus.

Toxicology of autoimmune diseases

Susceptibility to most autoimmune diseases is dependent on polygenic inheritance, environmental factors, and poorly defined stochastic events. One of the significant challenges facing autoimmune disease research is in identifying the specific events that trigger loss of tolerance and autoimmunity. Although many intrinsic factors, including age, sex, and genetics, contribute to autoimmunity, extrinsic factors such as drugs, chemicals, microbes, or other environmental factors can also act as important initiators. This review explores how certain extrinsic factors, namely, drugs and chemicals, can promote the development of autoimmunity, focusing on a few better characterized agents that, in most instances, have been shown to produce autoimmune manifestations in human populations. Mechanisms of autoimmune disease induction are discussed in terms of research obtained using specific animal models. Although a number of different pathways have been delineated for drug/chemical-induced autoimmunity, some similarities do exist, and a working model is proposed.

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

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

Environmental contaminant trichloroethylene promotes autoimmune disease and inhibits T-cell apoptosis in MRL(+/+) mice

The ability of environmental contaminant trichloroethylene to alter immune function and promote autoimmunity was tested in female MRL(+/+) mice. MRL(+/+) mice exposed to occupationally relevant doses of trichloroethylene in their drinking water for 32 weeks developed autoantibodies and pathological evidence of autoimmune hepatitis. The ability of trichloroethylene (TCE) to promote autoimmunity was associated with the expansion of activated (CD44(hi) CD62L(lo)) CD4(+) T-lymphocytes that produced increased levels of the pro-inflammatory cytokine interferon (IFN)-gamma. Activated T-lymphocytes can accumulate if activation-induced apoptosis is suppressed. Consequently, the effect of TCE on apoptosis in CD4(+) T-lymphocytes was investigated. These experiments were conducted with TCE and one of the major oxidative metabolites of trichloroethylene, namely trichloroacetaldehyde hydrate (TCAH). CD4(+) T-lymphocytes isolated from MRL(+/+) mice exposed to TCE or TCAH in their drinking water for 4 weeks were resistant to activation-induced apoptosis in vitro. The TCE-or TCAH-induced decrease in activation-induced apoptosis was associated with decreased expression of FasL, one of the cell surface molecules that mediate apoptosis. These results suggest that exposure to the common water contaminant TCE or its metabolite TCAH inhibits activation-induced apoptosis in CD4+ T-lymphocytes, thereby promoting autoimmune disease by suppressing the process that would otherwise delete activated self-reactive T-lymphocytes.

Ability of trichloroethylene metabolite to promote immune pathology is strain-specific

Chronic low-level exposure to the environmental pollutant trichloroethylene has been shown to promote autoimmune disease in association with CD4(+) T-lymphocyte activation in lupus-prone MRL(+/+) mice. One of the primary metabolites of trichloroethylene, trichloroacetaldehyde hydrate (TCAH), was similarly shown to increase the percentage of IFNgamma-producing CD4(+) T-lymphocytes when added to the drinking water of MRL(+/+) mice. In addition, TCAH-treated MRL(+/+) mice developed skin inflammation and alopecia. In the present study TCAH was tested for its ability to accelerate the development of alopecia in C3H/HeJ mice which tend to develop the disorder spontaneously late in life. In contrast to MRL(+/+) mice, C3H/HeJ mice treated with TCAH did not develop alopecia at an increased rate. In addition, TCAH did not promote the expansion of activated IFNgamma-producing CD4(+) T-lymphocytes in C3H/HeJ mice. CD4(+) T-lymphocytes from TCAH-treated C3H/HeJ mice, unlike their MRL(+/+) counterparts, did not become resistant to activation-induced apoptosis following in vivo exposure to TCAH. Taken together, it appears that the ability of TCAH to promote immune-mediated pathology is strain-specific and may require an autoimmune-prone genetic background.

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.

Regulatory roles for NKT cell ligands in environmentally induced autoimmunity

The development of autoimmune diseases is frequently linked to exposure to environmental factors such as chemicals, drugs, or infections. In the experimental model of metal-induced autoimmunity, administration of subtoxic doses of mercury (a common environmental pollutant) to genetically susceptible mice induces an autoimmune syndrome with rapid anti-nucleolar Ab production and immune system activation. Regulatory components of the innate immune system such as NKT cells and TLRs can also modulate the autoimmune process. We examined the interplay among environmental chemicals and NKT cells in the regulation of autoimmunity. Additionally, we studied NKT and TLR ligands in a tolerance model in which preadministration of a low dose of mercury in the steady state renders animals tolerant to metal-induced autoimmunity. We also studied the effect of Sphingomonas capsulata, a bacterial strain that carries both NKT cell and TLR ligands, on metal-induced autoimmunity. Overall, NKT cell activation by synthetic ligands enhanced the manifestations of metal-induced autoimmunity. Exposure to S. capsulata exacerbated autoimmunity elicited by mercury. Although the synthetic NKT cell ligands that we used are reportedly similar in their ability to activate NKT cells, they displayed pronounced differences when coinjected with environmental agents or TLR ligands. Individual NKT ligands differed in their ability to prevent or break tolerance induced by low-dose mercury treatment. Likewise, different NKT ligands either dramatically potentiated or inhibited the ability of TLR9 agonistic oligonucleotides to disrupt tolerance to mercury. Our data suggest that these differences could be mediated by the modification of cytokine profiles and regulatory T cell numbers.

Reduced expression of decay-accelerating factor 1 on CD4+ T cells in murine systemic autoimmune disease

OBJECTIVE

Deficiency of decay-accelerating factor 1 (termed Daf1 in mice) has been shown to exacerbate autoimmunity, and recent studies have suggested that this may be explained by Daf1 acting as a regulator of T cell immunity. The aim of this study was to determine whether Daf1 expression on T cells is modulated during development of autoimmunity in mice.

METHODS

To test this hypothesis, we examined Daf1 levels in NZB, DBA/2, and B10.S mice before and after induction of murine mercury-induced autoimmunity (mHgIA). Daf1 was measured by real-time polymerase chain reaction and flow cytometry, and levels of Daf1 were correlated with markers of lymphocyte activation and cytokine production.

RESULTS

Autoimmune-prone NZB mice had low endogenous levels of Daf1 irrespective of the induction of mHgIA. Induction of autoimmunity reduced Daf1 expression in mHgIA-sensitive B10.S mice, particularly on activated/memory (CD44(high)) CD4+ T cells that accumulate as a result of exposure to mercury. Murine mercury-induced autoimmunity-resistant DBA/2 mice, which fail to accumulate CD44(high) T cells, showed no change in Daf1 expression. Modulation of Daf1 expression was found to require CD4+ T cell costimulation, since B10.S mice deficient in CD28 were unable to down-regulate Daf1 or accumulate activated/memory CD4+ T cells. In B10.S mice exposed to mercury, the production of interleukin-4 (IL-4), but not that of IL-2 or interferon-gamma, in the spleen was associated with CD44(high),Daf1(low),CD4+ T cells.

CONCLUSION

These findings demonstrate that reduction of Daf1 expression is closely associated with CD4+ T cell activation and the accumulation of CD44(high)(activated/memory),CD4+ T cells in both spontaneous and induced systemic autoimmune disease.

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.

Genetics of SLE in mice

Genetic studies in spontaneous, induced, and gene-manipulated mouse models of SLE have provided significant insights into the potential number and diversity of genes that can promote, resist, and modify lupus susceptibility. Novel genes and mechanisms of disease pathogenesis have also been identified. Importantly, mouse models have provided an initial view of the genomic landscape of lupus-affecting genes, and have documented the complexities of verifying and determining the role of specific candidate loci and genes. Mouse models of lupus should continue to serve as a vital approach to defining the genetics of SLE.

The role of Fc-receptors in murine mercury-induced systemic autoimmunity

Inorganic mercury (Hg) in genetically susceptible mouse strains induces a T cell-dependent, systemic autoimmune condition (HgIA) characterized by immunostimulation, anti-nuclear antibodies (ANA) and systemic immune-complex (IC) deposits. The exact phenotypic expression of HgIA in different strains depends on H-2 and non-H-2 genes. Fc receptors (FcRs) are important in the development of many autoimmune diseases. In this study, the effect of targeted mutations for activating and inhibiting FcRs in the BALB/c model of HgIA was examined. Hg-treated BALB/c mice without mutation (wild-type, wt) showed heavy IC deposits in the renal glomerular mesangium, as well as in renal and splenic vessel walls. The renal mesangial IC deposits were severely reduced in Hg-treated BALB/c mice without the gamma-chain (lack of the activating receptors FcgammaRI, FcgammaRIII and FcinRI), but unchanged in mice lacking the inhibitory FcgammaRIIB. The Hg-induced vessel wall IC deposits present in wt mice were abolished and reduced in the FcRgamma and FcgammaRIIB strains, respectively. Hg-treated BALB/c wt mice and mice without the gamma-chain showed an increase in serum IgE, while the increase in IgG1 was attenuated in the latter strain. In contrast, absence of the inhibiting FcgammaRIIB augmented the Hg-induced increase of both serum IgG1 and IgE. In conclusion, FcRs are important mainly for the induction of systmeic IC deposits in the HgIA model, but also affects serum IgG1 and IgE levels.

The effect of xenobiotic exposure on spontaneous autoimmunity in (SWR x SJL)F1 hybrid mice

F1 hybrids of SWR (H-2(q)) and SJL (H-2(s)) mice spontaneously develop a lupuslike condition in an age-dependent manner, and these two H-2 haplotypes also confer susceptibility to induction of systemic autoimmunity by heavy metals such as mercury, silver, and gold with anti-fibrillarin antibodies (AFA) as marker. The aim of this study was to determine how the mixing of two susceptible genomes might influence expression of idiopathic and induced autoimmunity over a period of 14 mo of exposure to mercury and silver. Spontaneous autoimmunity first appeared as antinuclear antibodies (ANA) in females at 10 wk of age and in males at 10 mo of age, and was followed by development of anti-chromatin antibodies. Antibodies to double-stranded DNA developed in 60% of males and 20% of females. Thirty percent of males and 10% of females developed a coarsely speckled ANA pattern associated with high titers of anti-Sm antibodies. Glomerular immune complex (IC) deposits and a proliferative glomerulonephritis were seen at 17 mo of age. The F1 hybrids treated with metals showed no exaggeration of spontaneous autoimmunity. However, the metals suppressed the spontaneous development of anti-Sm and antichromatin antibodies. The metal-induced AFA, linked to the H-2(s) and H-2(q) haplotype, reached a maximum after 3-4 mo of treatment and then declined; 33% of the silver-treated hybrids finally became AFA-negative, despite continuous treatment. The decline in ANoA during metal treatment is contrary to the situation in metal-treated SJL mice. This indicates that dominant SWR background genes suppressed induction of certain autoimmune traits in the (SWR x SJL)F1 hybrid mice.

Bacterial lipopolysaccharide both renders resistant mice susceptible to mercury-induced autoimmunity and exacerbates such autoimmunity in susceptible mice

The initiation and severity of systemic autoimmune diseases are influenced by a variety of genetic and environmental factors, in particular bacterial infections and products. Here, we have employed bacterial lipopolysaccharide (LPS), which non-specifically activates the immune system, to explore the involvement of innate immunity in mercury-induced autoimmunity in mice. Following treatment of mouse strains resistant [DBA/2 (H-2(d))] or susceptible [SJL(H-2(s))] to such autoimmunity with mercuric chloride and/or LPS or with physiological saline alone (control), their immune/autoimmune responses were monitored. Resistant DBA/2 mice were rendered susceptible to mercury-induced autoimmunity by co-administration of LPS, exhibiting pronounced increases in the synthesis of IgG1 and IgE, high titres of IgG1 deposits in the kidneys and elevated circulating levels of IgG1 antibodies of different specificities. Furthermore, the percentages of the T cells isolated from the spleens of DBA/2 mice exposed to both mercury and LPS that produced pro-inflammatory cytokines were markedly increased by in vitro stimulation with phorbol myristate acetate (PMA) and ionomycin, which was not the case for splenic T cells isolated from mice receiving mercuric chloride, LPS or saline alone. In addition, exposure of susceptible SJL mice to mercury in combination with LPS aggravated the characteristic features of mercury-induced autoimmunity, including increased synthesis of IgG1 and IgE, the production of IgG1 anti-nucleolar antibodies (ANolA) and the formation of renal deposits of IgG1. In summary, our findings indicate that activation of the innate immune system plays a key role in both the induction and severity of chemically induced autoimmunity.

Interleukin-10 in murine metal-induced systemic autoimmunity

Systemic autoimmune diseases have a complicated and largely unknown aetiology and pathogenesis, but they are at least partly obeying the rules of an ordinary immune response. Cytokines are therefore important in the pathogenesis as demonstrated by the recent success in treating rheumatoid arthritis with anti-cytokine agents. The suppressive functions in the immune system have lately received much interest. One of the cytokines in focus in this respect is interleukin (IL)-10. We recently observed that in heavy-metal induced systemic autoimmunity, genetically resistant mice show a strong increase in IL-10 mRNA expression, which was not seen in susceptible mice. We have therefore examined the possible regulating effect of IL-10 on the induction and manifestation of systemic autoimmunity in this model. We took two approaches: a targeted mutation of the IL-10 gene in a strain resistant to heavy metal-induced autoimmunity, and treatment with recombinant IL-10 in the genetically susceptible A.SW strain during the induction of autoimmunity by metals. The wild-type C57BL/6 J (B6-WT) strain did not react with lymphoproliferation, polyclonal B cell activation, anti-nucleoar autoantibodies (ANoA) or tissue immune-complex (IC) deposits in response to inorganic mercury (Hg) or silver (Ag). However, serum IgG1 and IgE showed a modest increase during Hg treatment, while Ag caused a weak increase in IgE and IgG2a. The B6.129P2-Il10(tm1Cgn)/J strain (IL-10-deficient mice) did not develop antinucleolar antibodies (ANoA) during Hg treatment, but showed a higher median titre of homogeneous ANA compared with Hg-treated B6-WT mice. Both control and Hg-treated (but not Ag-treated) IL-10-deficient mice showed an increase in splenic weight and serum IgG1 compared with B6-WT control and Hg-treated mice. An early, significant increase in serum IgE was seen in Hg-treated IL-10-deficient and WT mice compared with the controls; the increase was 42- and sixfold, respectively. During ongoing intense treatment with rIL-10 in combination with Hg the susceptible A.SW mice showed a reduced development of ANoA and antichromatin antibodies, as well as serum IgE, compared with mice receiving Hg but not rIL-10. In conclusion, IL-10 suppresses several aspects of HgIA, but is not crucial for resistance to heavy metal-induced autoimmunity. Peroral silver treatment suppresses the spontaneous immune activation seen in IL-10-deficient mice.

Mechanisms of heavy metal-induced autoimmunity

Chemical exposure can trigger or accelerate the development of autoimmune manifestations. Although heavy metals are elementary chemical structures, they can have profound and complex effects on the immune system. In genetically susceptible mice or rats, administration of subtoxic doses of mercury induces both the production of highly specific autoantibodies and a polyclonal activation of the immune system. We review in this article some of the mechanisms by which heavy metal exposure can lead to autoimmunity.

Exposure to mercuric chloride during the induction phase and after the onset of collagen-induced arthritis enhances immune/autoimmune responses and exacerbates the disease in DBA/1 mice

In susceptible mice, mercuric chloride induces a systemic autoimmune response that is characterized by elevated serum levels of immunoglobulin G1 (IgG1) and immunoglobulin E (IgE), production of anti-nucleolar antibodies (ANolAs) and the formation of renal IgG deposits. We have previously shown that mercury can also enhance immune/autoimmune responses in mouse strains genetically prone to develop spontaneous autoimmune disease. Here, we investigated whether mercury can enhance the severity of murine collagen-induced arthritis (CIA), an inducible (acquired) autoimmune disease that cannot be induced by mercury itself. While mercury administered prior to the induction phase of CIA exerted little, if any, influence, administration of mercury during the induction phase and following onset aggravated the symptoms of this disease and increased the serum levels of IgE and IgG2a antibodies directed against collagen type II (CII). Furthermore, while animals injected with mercury alone exhibited a significant decrease in the ratio of the levels of interferon-gamma (IFN-gamma) to interleukin-4 (IL-4) mRNA in their spleens, this ratio was increased in mice with CIA, with or without administration of mercury. Finally, the production of anti-nuclear antibodies, a hallmark of autoimmunity in response to mercury, was observed in all mice with CIA treated with this heavy metal. Our findings suggest that exposure to mercury during the development of CIA may influence immunological factors in such a way as to synergistically promote disease development.

Activation and attenuation of apoptosis of CD4+ T cells following in vivo exposure to two common environmental toxicants, trichloroacetaldehyde hydrate and trichloroacetic acid

Exposure to occupationally relevant concentrations of the environmental pollutant, trichloroethylene (TCE), in the drinking water of autoimmune-prone MRL+/+ mice has been shown to promote the generation of lupus and autoimmune hepatitis in association with the activation of Interferon-gamma (IFN-gamma)-producing CD4+ T cells. Since blocking TCE metabolism suppressed the TCE-induced alteration in immune function, the present study was initiated to determine whether the major metabolites of TCE, trichloroacetaldehyde hydrate (TCAH) and trichloroacetic acid (TCA) could also mediate these immunoregulatory affects in vivo. TCAH and TCA were administered to the drinking water of MRL+/+ mice for 4 weeks. CD4+ T cells from TCAH and TCA-treated MRL+/+ mice, unlike CD4+ T cells from control mice, demonstrated functional and phenotypic signs of activation, as evidenced by increased IFN-gamma production in association with the increased percentage of CD62L(lo) CD4+ T cells. Interestingly, it was also found that the CD4+ T cells from the TCAH and TCA-treated mice showed a decreased susceptibility to the activation-induced cell death (AICD) form of apoptosis following re-stimulation in vitro. By demonstrating that TCAH and TCA can activate CD4+ T cells and inhibit their apoptosis following in vivo exposure represents a mechanism by which environmental toxicants may induce or accelerate the development of autoimmune disease.

Inhibitory signal override increases susceptibility to mercury-induced autoimmunity

After exposure to subtoxic doses of heavy metals such as mercury, H-2(s) 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 explore the role of two inhibitory immunoreceptors, CTLA-4 and FcgammaRIIB, in the regulation of mercury-induced autoimmunity. In susceptible mice treated with mercuric chloride (HgCl(2)), administration of a blocking anti-CTLA-4 Ab resulted in a further increase in anti-nucleolar autoantibodies and in total serum IgG1 levels. Furthermore, in some DBA/2 mice, which are normally resistant to heavy metal-induced autoimmunity, anti-CTLA-4 treatment leads to the production of anti-nucleolar Abs, thereby overcoming the genetic restriction of the disease. In mice deficient for the FcgammaRIIB, HgCl(2) administration did not trigger autoantibody production, but resulted in an increase in IgE serum levels. Taken together, these results indicate that different inhibitory mechanisms regulate various manifestations of this autoimmune syndrome.

Environmental exposure to mercury and its toxicopathologic implications for public health

Mercury is a toxic and hazardous metal that occurs naturally in the earth's crust. Natural phenomena such as erosion and volcanic eruptions, and anthropogenic activities like metal smelting and industrial production and use may lead to substantial contamination of the environment with mercury. Through consumption of mercury in food, the populations of many areas, particularly in the developing world, have been confronted with catastrophic outbreaks of mercury-induced diseases and mortality. Countries such as Japan, Iraq, Ghana, the Seychelles, and the Faroe Islands have faced such epidemics, which have unraveled the insidious and debilitating nature of mercury poisoning. Its creeping neurotoxicity is highly devastating, particularly in the central and peripheral nervous systems of children. Central nervous system defects and erethism as well as arrythmias, cardiomyopathies, and kidney damage have been associated with mercury exposure. Necrotizing bronchitis and pneumonitis arising from inhalation of mercury vapor can result in respiratory failure. Mercury is also considered a potent immunostimulant and -suppressant, depending on exposure dose and individual susceptibility, producing a number of pathologic sequelae including lymphoproliferation, hypergammaglobulinemia, and total systemic hyper- and hyporeactivities. In this review we discuss the sources of mercury and the potential for human exposure; its biogeochemical cycling in the environment; its systemic, immunotoxic, genotoxic/carcinogenic, and teratogenic health effects; and the dietary influences on its toxicity; as well as the important considerations in risk assessment and management of mercury poisoning.