Mercuric chloride induces autoantibodies against U3 small nuclear ribonucleoprotein in susceptible 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.

Autoreactive B cell responses targeting nuclear antigens in systemic sclerosis: Implications for disease pathogenesis

A hallmark of disease pathogenesis of systemic sclerosis (SSc) is the presence of autoreactive B cell responses targeting nuclear proteins. Almost all SSc-patients harbour circulating antinuclear autoantibodies of which anti-topoisomerase 1, anti-centromere protein, anti-RNA polymerase III and anti-fibrillarin autoantibodies (ATA, ACA, ARA and AFA, respectively) are the most common and specific for SSc. In clinical practice, autoantibodies serve as diagnostic biomarkers and can aid in the identification of clinical phenotypes of the disease. However, factors driving disease progression in SSc are still poorly understood, and it is difficult to predict disease trajectories in individual patients. Moreover, treatment decisions remain rather empirical, with variable response rates in clinical trials due to patient heterogeneity. Current evidence has indicated that certain patients may benefit from B cell targeting therapies. Hence, it is important to understand the contribution of the antinuclear autoantibodies and their underlying B cell response to the disease pathogenesis of SSc.

The Role of Exposomes in the Pathophysiology of Autoimmune Diseases I: Toxic Chemicals and Food

Autoimmune diseases affect 5–9% of the world’s population. It is now known that genetics play a relatively small part in the pathophysiology of autoimmune disorders in general, and that environmental factors have a greater role. In this review, we examine the role of the exposome, an individual’s lifetime exposure to external and internal factors, in the pathophysiology of autoimmune diseases. The most common of these environmental factors are toxic chemicals, food/diet, and infections. Toxic chemicals are in our food, drink, common products, the air, and even the land we walk on. Toxic chemicals can directly damage self-tissue and cause the release of autoantigens, or can bind to human tissue antigens and form neoantigens, which can provoke autoimmune response leading to autoimmunity. Other types of autoimmune responses can also be induced by toxic chemicals through various effects at the cellular and biochemical levels. The food we eat every day commonly has colorants, preservatives, or packaging-related chemical contamination. The food itself may be antigenic for susceptible individuals. The most common mechanism for food-related autoimmunity is molecular mimicry, in which the food’s molecular structure bears a similarity with the structure of one or more self-tissues. The solution is to detect the trigger, remove it from the environment or diet, then repair the damage to the individual’s body and health.

Thymodepressin-Unforeseen Immunosuppressor

The paper summarizes the available information concerning the biological properties and biomedical applications of Thymodepressin. This synthetic peptide drug displays pronounced immunoinhibitory activity across a wide range of conditions in vitro and in vivo. The history of its unforeseen discovery is briefly reviewed, and the current as well as potential expansion areas of medicinal practice are outlined. Additional experimental evidence is obtained, demonstrating several potential advantages of Thymodepressin over another actively used immunosuppressor drug, cyclosporin A.

Autoantibodies in outbred Swiss Webster mice following exposure to gold and mercury

Exposure to heavy metals may have toxic effects on several human organs causing morbidity and mortality. Metals may trigger or exacerbate autoimmunity in humans. Inbred mouse strains with certain H-2 haplotypes are susceptible to xenobiotic-induced autoimmunity; and their immune response to metals such as mercury, gold, and silver have been explored. Serum antinuclear antibodies (ANA), polyclonal B-cell activation, hypergammaglobulinemia and tissue immune complex deposition are the main features of metal-induced autoimmunity in inbred mice. However, inbred mouse strains do not represent the genetic heterogeneity in humans. In this study, outbred Swiss Webster (SW) mice exposed to gold or mercury salts showed immune and autoimmune responses. Intramuscular injection of 22.5 mg/kg.bw aurothiomalate (AuTM) induced IgG ANA in SW mice starting after 5 weeks that persisted until week 15 although with a lower intensity. This was accompanied by elevated serum levels of total IgG antibodies against chromatin and total histones. Exposure to gold led to development of serum IgG autoantibodies corresponding to H1 and H2A histones, and dsDNA. Both gold and mercury induced polyclonal B-cell activation. Eight mg/L mercuric chloride (HgCl₂) in drinking water, caused IgG antinucleolar antibodies (ANoA) after 5 weeks in SW mice accompanied by immune complex deposition in kidneys and spleen. Serum IgG antibodies corresponding to anti-fibrillarin, and anti-PM/Scl-100 antibodies, were observed in mercury-exposed SW mice. Gold and mercury trigger systemic autoimmune response in genetically heterogeneous outbred SW mice and suggest them as an appropriate model to study xenobiotic-induced autoimmunity.

Mercury Is Taken Up Selectively by Cells Involved in Joint, Bone, and Connective Tissue Disorders

Background: The causes of most arthropathies, osteoarthritis, and connective tissue disorders remain unknown, but exposure to toxic metals could play a part in their pathogenesis. Human exposure to mercury is common, so to determine whether mercury could be affecting joints, bones, and connective tissues we used a histochemical method to determine the cellular uptake of mercury in mice. Whole neonatal mice were examined since this allowed histological assessment of mercury in joint, bone, and connective tissue cells. Materials and Methods: Pregnant mice were exposed to a non-toxic dose of 0.5 mg/m3 of mercury vapor for 4 h a day on gestational days 14-18. Neonates were sacrificed at postnatal day 1, fixed in formalin, and transverse blocks of the body were processed for paraffin embedding. Seven micrometer sections were stained for inorganic mercury using silver nitrate autometallography, either alone or combined with CD44 immunostaining to detect progenitor cells. Control neonates were not exposed to mercury during gestation. Results: Uptake of mercury was marked in synovial cells, articular chondrocytes, and periosteal and tracheal cartilage cells. Mercury was seen in fibroblasts in the dermis, aorta, esophagus and striated muscle, some of which were CD44-positive progenitor cells, and in the endothelial cells of small blood vessels. Mercury was also present in renal tubules and liver periportal cells. Conclusions: Mercury is taken up selectively by cells that are predominantly affected in rheumatoid arthritis and osteoarthritis. In addition, fibroblasts in several organs often involved in multisystem connective tissue disorders take up mercury. Mercury provokes the autoimmune, inflammatory, genetic, and epigenetic changes that have been described in a range of arthropathies and bone and connective tissue disorders. These findings support the hypothesis that mercury exposure could trigger some of these disorders, particularly in people with a genetic susceptibility to autoimmunity.

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.

Mercury Exposure and Antinuclear Antibodies among Females of Reproductive Age in the United States: NHANES

BACKGROUND

Immune dysregulation associated with mercury has been suggested, although data in the general population are lacking. Chronic exposure to low levels of methylmercury (organic) and inorganic mercury is common, such as through fish consumption and dental amalgams.

OBJECTIVE

We examined associations between mercury biomarkers and antinuclear antibody (ANA) positivity and titer strength.

METHODS

Among females 16-49 years of age (n = 1,352) from the National Health and Nutrition Examination Survey (NHANES) 1999-2004, we examined cross-sectional associations between mercury and ANAs (indirect immunofluorescence; cutoff ≥ 1:80). Three biomarkers of mercury exposure were used: hair (available 1999-2000) and total blood (1999-2004) predominantly represented methylmercury, and urine (1999-2002) represented inorganic mercury. Survey statistics were used. Multivariable modeling adjusted for several covariates, including age and omega-3 fatty acids.

RESULTS

Sixteen percent of females were ANA positive; 96% of ANA positives had a nuclear speckled staining pattern. Geometric mean (geometric SD) mercury concentrations were 0.22 (0.03) ppm in hair, 0.92 (0.05) μg/L blood, and 0.62 (0.04) μg/L urine. Hair and blood, but not urinary, mercury were associated with ANA positivity (sample sizes 452, 1,352, and 804, respectively), after adjusting for confounders: for hair, odds ratio (OR) = 4.10 (95% CI: 1.66, 10.13); for blood, OR = 2.32 (95% CI: 1.07, 5.03) comparing highest versus lowest quantiles. Magnitudes of association were strongest for high-titer (≥ 1:1,280) ANA: hair, OR = 11.41 (95% CI: 1.60, 81.23); blood, OR = 5.93 (95% CI: 1.57, 22.47).

CONCLUSIONS

Methylmercury, at low levels generally considered safe, was associated with subclinical autoimmunity among reproductive-age females. Autoantibodies may predate clinical disease by years; thus, methylmercury exposure may be relevant to future autoimmune disease risk.

Low doses of mercuric chloride cause the main features of anti-nucleolar autoimmunity in female outbred CFW mice

The growth of the influence of anthropogenic factors aimed on the improvement of human life has its side effect, for example, living organisms receive increasing exposure to toxic mercuric compounds. Experimental data show that mercury (Hg) salts are able to induce systemic autoimmunity in rodents. This Hg-induced autoimmune process (HgIA) is characterized by T cell-dependent polyclonal activation of B lymphocytes, increased level of serum immunoglobulin G1 (IgG1) and immunoglobulin E (IgE), production of antinucleolar autoantibodies (ANoA), and immune complex deposition in multiple organs. HgIA in mice is used as a model of human systemic autoimmune disorders. However, the dose of mercuric chloride (HgCl2) usually used in laboratory mice to induce HgIA is above the allowable limit for everyday levels of Hg exposure in humans. So, we decided to determine the lowest dose of HgCl2 that is able to trigger autoimmunity in outbred Carworth Farms Swiss Webster (CFW) mice not genetically prone to HgIA development. The lowest dose (50 µg/kg body weight (b.w.)/week) was chosen to match the World Health Organization provisional weekly tolerable intake of total Hg for humans. We also tested HgCl2 at 500 and 1500 µg/kg b.w./week (6.5- and 2-fold less than usually used for induction of HgIA in mice). We found that even the lowest dose of Hg resulted in a statistically significant increase in serum level of IgG1 after 8 weeks of treatment. HgCl2 in doses 500 and 1500 µg/kg b.w./week resulted in a significant increase in serum level of IgG1 after 4 weeks of treatment, followed by ANoA production. Sera of HgCl2-treated mice stained the regions in which the major autoantigen in HgIA, fibrillarin, was revealed. These results suggest that low doses of Hg are able to induce the main features of HgIA in genetically heterozygous mice, and that humans chronically exposed to low doses of Hg may be at risk of autoimmunity induction regardless of their genetic background.

Antibodies as predictors of autoimmune diseases and cancer

BACKGROUND

Autoantibodies targeted against a variety of self-antigens are detected in autoimmune diseases and cancer. Emerging evidence has suggested the involvement of environmental factors such as infections and xenobiotics, and some dietary proteins and their antibodies in the pathogenesis of many autoimmune diseases. These antibodies appear in the blood years before presentation of symptoms in various disorders. Therefore, these antibodies may be used as biomarkers for early detection of various diseases.

OBJECTIVE

To provide an overview of antibody arrays that are measured against different human tissue antigens, crossreactive epitopes of infectious agents, dietary proteins, and haptenic chemicals in autoimmune diseases and cancer.

METHOD

Microarray analysis of antigen-antibody reaction.

CONCLUSION

The application of these antibody arrays to human autoimmune disease is expanding and is allowing for the identification of patterns or antibody signatures, thus establishing the premises for increased sensitivity and specificity of prediction, as well as positive predictive values. The presence of these antibodies would not necessarily mean that a patient would definitely become sick but may give a percentage of risk for different conditions that may develop over future months or years. Using this high-throughput microarray method, it is possible to screen rapidly for dozens of autoantibodies at low cost. This is an important factor in the implementation of autoantibody testing as a routine part of medical examinations.

T cells, murine chronic graft-versus-host disease and autoimmunity

The chronic graft-versus-host disease (cGVHD) in mice is characterized by the production of autoantibodies and immunopathology characteristic of systemic lupus erythematosus (lupus). The basic pathogenesis involves the cognate recognition of foreign MHC class II of host B cells by alloreactive CD4 T cells from the donor. CD4 T cells of the host are also necessary for the full maturation of host B cells before the transfer of donor T cells. CD8 T cells play critical roles as well. Donor CD8 T cells that are highly cytotoxic can ablate or prevent the lupus syndrome, in part by killing recipient B cells. Host CD8 T cells can reciprocally downregulate donor CD8 T cells, and thus prevent them from suppressing the autoimmune process. Thus, when the donor inoculum contains both CD4 T cells and CD8 T cells, the resultant syndrome depends on the balance of activities of these various cell populations. For example, in one cGVHD model (DBA/2(C57BL/6xDBA/2)F1, the disease is more severe in females, as it is in several of the spontaneous mouse models of lupus, as well as in human disease. The mechanism of this female skewing of disease appears to depend on the relative inability of CD8 cells of the female host to downregulate the donor CD4 T cells that drive the autoantibody response. In general, then, the abnormal CD4 T cell help and the modulating roles of CD8 T cells seen in cGVHD parallel the participation of T cells in genetic lupus in mice and human lupus, although these spontaneous syndromes are presumably not driven by overt alloreactivity.

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.

Antibodies as Predictors of Complex Autoimmune Diseases

Emerging evidence has suggested environmental factors such as infections and xenobiotics and some dietary proteins and peptides in the pathogenesis of many autoimmune diseases. Considering the fact that autoantibodies can often be detected prior to the onset of a disease, in this study an enzyme immunoassay was used for measurement of antibodies against different highly purified antigens or synthetic peptides originating not only from human tissue, but also from cross-reactive epitopes of infectious agents, dietary proteins and xenobiotics. The measurement of antibodies against a panel of antigens allows for identification of patterns or antibody signatures, rather than just one or two markers of autoimmunity, thus establishing the premise for increased sensitivity and specificity of prediction, as well as positive predictive values. This panel of different autoantibodies was applied to 420 patients with different autoimmune diseases, including pernicious anemia, celiac disease, thyroiditis, lupus, rheumatoid arthritis, osteoarthritis, Addison's disease, type 1 diabetes, cardiovascular disease and autoimmunity, which are presented in this article. In all cases, the levels of these antibodies were significantly elevated in patients versus controls. Antibody patterns related to neuroautoimmune disorders, cancer, and patients with somatic hypermutation will be shown in a subsequent article. We believe that this novel 96 antigen-specific autoantibody or predictive antibody screen should be studied for its incorporation into routine medical examinations. Clinicians should be aware that the detection of antibodies should not automatically mean that a patient will definitely become ill, but would rather give a percentage of risk for autoimmune disease over subsequent months or years.

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.

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.

Amelioration of Mercury-Induced Autoimmunity by 4-1BB

In certain strains of mice, subtoxic doses of HgCl2 (mercuric chloride; mercury) induce a complex autoimmune condition characterized by the production of antinucleolar IgG Abs, lymphoproliferation, increased serum levels of IgG1/IgE Abs, and deposition of renal immune complexes. 4-1BB is an important T cell costimulatory molecule that has been implicated in T cell proliferation and cytokine production, especially production of IFN-gamma. To elucidate T cell control mediated by the 4-1BB signaling pathway in this syndrome, we assessed the effect of administering agonistic anti-4-1BB mAb on mercury-induced autoimmunity. Groups of A.SW mice (H-2s) received mercury/control Ig or mercury/anti-4-1BB or PBS alone. Anti-4-1BB mAb treatment resulted in a dramatic reduction of mercury-induced antinucleolar Ab titers, serum IgG1/IgE induction, and renal Ig deposition. These effects may be related to the present finding that anti-4-1BB mAb decreases B cell numbers and function. The anti-4-1BB mAb-treated mercury group also showed a marked reduction in Th2-type cytokines but an increase in Th1-type cytokines and chemokines. Increased IFN-gamma production due to anti-4-1BB mAb treatment appears to be responsible for the observed B cell defects because neutralization of IFN-gamma in vivo substantially restored B cell numbers and partly restored IgG1/IgE. Collectively, our results indicate that 4-1BB mAb can down-regulate mercury-induced autoimmunity by affecting B cell function in an IFN-gamma-dependent manner and thus, preventing the development of autoantibody production and tissue Ig deposition.

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.

Xenobiotic-Induced Recruitment of Autoantigens to Nuclear Proteasomes Suggests a Role for Altered Antigen Processing in Scleroderma

The cell nucleus is a prominent target of autoantibodies in systemic autoimmune disorders. Approximately 2% of the population in Europe and North America suffers from systemic rheumatic diseases, such as rheumatoid arthritis, systemic lupus erythematosus (SLE), and scleroderma. The molecular mechanisms of systemic autoimmunity are largely unknown despite its high prevalence. Contributing factors that have been considered include (1) genetic predisposition, (2) influence of hormones, and (3) environmental factors. The latter are mainly correlated with the generation of scleroderma, as xenobiotic-induced subsets of this disease have been observed in individuals exposed to silica (SiO(2)) dusts, organic solvents, heavy metals, and certain drugs. In addition to the epidemiological relevance, animal models of xenobiotic-induced autoimmunity serve as elegant tools for controlled induction of antigen-driven autoimmune responses. Because antigen processing and presentation constitute the basis for every antigen-driven autoimmune response, effects of xenobiotics on degradation of nuclear autoantigens have been characterized to elucidate molecular mechanisms of autoimmunity that target the cell nucleus. By means of a cell-based disease model, it has been shown that xenobiotics such as mercuric chloride, platinum salts, and silica (nano)particles specifically alter structure, function, and proteolysis in the cell nucleus. Signature proteins of the cell nucleus redistribute to aberrant, nucleoplasmic clusters, where they colocalize with proteasomes and are subjected to proteasomal proteolysis. Recruitment of nuclear autoantigens to proteasomal degradation is correlated with autoimmune responses that specifically target these antigens in both animal models of xenobiotic-induced autoimmunity and patients with idiopathic scleroderma.

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.

Mercuric chloride induces a strong immune activation, but does not accelerate the development of dermal fibrosis in tight skin 1 mice

In susceptible mice, mercuric chloride induces a systemic autoimmune disease characterized by increased serum levels of immunoglobulin (Ig) G1 and IgE, production of anti-nucleolar autoantibodies (ANolA) and formation of renal IgG deposits. We have previously hypothesized that mercury confers more adverse immunological effects on those mouse strains, which are genetically prone to develop spontaneous autoimmune diseases than on normal strains. In this study, we tested our hypothesis in tight skin 1 (Tsk1/+) mice, a murine model for human scleroderma. As a support for our hypothesis, we observed that in Tsk1/+ mice, B cells were spontaneously hyperactive and that treatment with mercury induced a strong immune/autoimmune response in these mice, but not in their non-Tsk (+/+) littermates. This response was characterized by the formation of high numbers of splenic IgG1, IgG2b and IgG3 antibody-secreting cells, increased serum levels of IgE, production of IgG1 antibodies against single-stranded DNA (ssDNA), trinitrophenol (TNP) as well as thyroglobulin and the development of renal IgG1 deposits. Neither Tsk1/+ mice nor F1 hybrid crosses between this strain, and mercury susceptible B10.S (H-2(s)) were able to produce IgG1-ANolA in response to mercury. Moreover, mercury-induced immune activation in Tsk1/+ was not able to potentiate the progression of skin fibrosis in this strain. Thus, exposure to mercury accelerates the immune dysregulation, but not the development of skin fibrosis in Tsk1/+ mice.

Advances in B-cell epitope analysis of autoantigens in connective tissue diseases

The characterization of autoantibody specificities in rheumatic diseases is important in both diagnostic and basic research areas. Identification of the epitopes recognized by autoantibodies and their clinical and biological significance is not a trivial task. Epitopes may range in complexity from simple linear sequences of amino acids to complex quaternary structures. In addition to this structural complexity the frequency with which an autoantigen and its epitopes are recognized in a patient population may be useful in diagnosis, defining disease subgroups, and may offer information on disease prognosis. In this review recent advances in the epitope mapping of autoantigens in connective tissue diseases are discussed, with particular emphasis placed on the methodologies used to identify epitopes and the classification of the structural features of epitopes. To illustrate the identification of epitope structure, clinically relevant autoantigens, including CENP-A, PM/Scl-100, fibrillarin, filaggrin, Ro-52, and dsDNA, are discussed as examples of each type of epitope.

Xenobiotic metal-induced autoimmunity: mercury and silver differentially induce antinucleolar autoantibody production in susceptible H-2s, H-2q and H-2f mice

Xenobiotic-metals such as mercury (Hg) and silver (Ag) induce an H-2 linked antinucleolar autoantibody (ANolA) production in susceptible mice. The mechanism for induction of ANolA synthesis is not well understood. However, it has been suggested that both metals interact with nucleolar proteins and reveal cryptic self-peptides to nontolerant autoreactive T cells, which in turn stimulate specific autoreactive B cells. In this study, we considered this suggestion and asked if mercury and silver display, if not identical, similar cryptic self-peptides, they would induce comparable ANolA responses in H-2 susceptible mice. We analysed the development of ANolA production in mercury- and/or silver-treated mice of H-2s, H-2q and H-2f genotypes. We found that while mercury stimulated ANolA synthesis in all strains tested, silver induced ANolA responses of lower magnitudes in only H-2s and H-2q mice, but not in H-2f mice. Resistance to silver in H-2f mice was independent of the dosage/time-period of silver-treatment and non-H-2 genes. Further studies showed that F1 hybrid crosses between silver-susceptible A.SW (H-2s) and -resistant A.CA (H-2f) mice were resistant to silver, but not mercury with regard to ANolA production. Additionally, the magnitudes of mercury-induced ANolA responses in the F1 hybrids were lower than those of their parental strains. The above differential ANolA responses to mercury and silver can be explained by various factors, including the different display of nucleolar cryptic peptides by these xenobiotics, determinant capture and coexistence of different MHC molecules. Our findings also suggest that the ability of a xenobiotic metal merely to create cryptic self-peptides may not be sufficient for the induction of an ANolA response.

Subcellular recruitment of fibrillarin to nucleoplasmic proteasomes: implications for processing of a nucleolar autoantigen

A prerequisite for proteins to interact in a cell is that they are present in the same intracellular compartment. Although it is generally accepted that proteasomes occur in both, the cytoplasm and the nucleus, research has been focusing on cytoplasmic protein breakdown and antigen processing, respectively. Thus, little is known on the functional organization of the proteasome in the nucleus. Here we report that within the nucleus 20S and 26S proteasomes occur throughout the nucleoplasm and partially colocalize with splicing factor-containing speckles. Because proteasomes are absent from the nucleolus, a recruitment system was used to analyze the molecular fate of nucleolar protein fibrillarin: Subtoxic concentrations of mercuric chloride (HgCl(2)) induce subcellular redistribution of fibrillarin and substantial colocalization (33%) with nucleoplasmic proteasomes in different cell lines and in primary cells isolated from mercury-treated mice. Accumulation of fibrillarin and fibrillarin-ubiquitin conjugates in lactacystin-treated cells suggests that proteasome-dependent processing of this autoantigen occurs upon mercury induction. The latter observation might constitute the cell biological basis of autoimmune responses that specifically target fibrillarin in mercury-mouse models and scleroderma.

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.

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.

Expression of fibrillarin in bovine oocytes and preimplantation embryos developing in vitro

Studies in somatic cells have demonstrated the participation of some defined nucleolar specific proteins in pre-rRNA synthesis and processing. Fibrillarin, a 34 kd protein localized to the dense fibrillar component of the nucleolus, is involved in the earliest cleavage step of pre-rRNA processing. Expression of fibrillarin has not been characterized during the course of bovine preimplantation development. Specific aims of this study were to characterize the expression of fibrillarin in bovine oocytes and preimplantation embryos developing in vitro. Oocytes and embryos were labeled with an anti-fibrillarin primary antibody and an FITC-conjugated goat antihuman secondary antibody and dual stained with Hoechst 33342 DNA dye. In germinal vesicle (GV) stage oocytes, obtained from 2 to 6 mm follicles, fibrillarin appeared as several large distinct fluorescent spheres within the nucleoplasm, but was not strictly localized to the nucleolus. Fibrillarin was not detected in metaphase oocytes. Expression of fibrillarin was first detected in embryos at the pronucleate stage, appearing as small spots or distinct fluorescent spheres randomly distributed within the nucleoplasm; this pattern persisted in 2- and 4-cell stage embryos. Beginning at the 8-cell stage, fibrillarin signals appeared as distinct fluorescent rings encapsulating each nucleolus. From the 16-cell through the blastocyst stage, a branching immunofluorescent pattern was observed in association with fully reticulated nucleoli. Expression of fibrillarin was absent in 8-cell, but not pronucleate stage embryos cultured with alpha-amanitin, indicating that fibrillarin is initially recruited from maternal stores in pronucleate stage embryos, but then subsequently transcribed beginning at the 8-cell stage, coincident with the onset of nucleolar, transcription. Results from this study provide further insight into the organization and development of the embryonic nucleolus during bovine preimplantation development, and may have important implications for assisted reproductive technologies, including nucleus transfer.

Specific inhibition of rRNA transcription and dynamic relocation of fibrillarin induced by mercury

Current evidence suggests that the nucleolus is composed of different substructures that are dynamic and form in response to the requirement for new ribosome synthesis. Thus, agents that disrupt nucleolar organization may deregulate basic cellular events and eventually contribute to human disease. Here we report that environmentally relevant concentrations (5 microM) of inorganic mercury induce a redistribution of nucleolar protein fibrillarin from the nucleolus to the nucleoplasm in epithelial cell lines. Since treatment with transcription inhibitors led to a similar relocation of fibrillarin, the effects of mercury on transcription were studied by run-on transcription assays: mercuric ions specifically blocked synthesis of ribosomal RNA, whereas activity of RNA polymerase II remained unchanged and occurred throughout the nucleoplasm. Moreover, we show by double-labeling that inhibition of nucleolar transcription and redistribution of fibrillarin occur simultaneously, underlining that fibrillarin relocation is a consequence of the blockade of ribosomal RNA synthesis by mercury. We also detected redistribution of fibrillarin in vivo, e.g., in splenic cells of mice chronically exposed to HgCl(2). Thus, implications of this alteration of nuclear structure and function for mercury-induced autoimmunity are discussed.

Cytokine regulation of a rodent model of mercuric chloride-induced autoimmunity

Experimental models of chemically induced autoimmunity have contributed to our understanding of the development of autoimmune diseases in humans. Heavy metals such as mercury induce a dramatic activation of the immune system and autoantibody production in genetically susceptible rats and mice. This autoimmune syndrome is dependent on T cells, which are important for B-cell activation and cytokine secretion. Several studies have focused on the roles of T-helper (Th)1 and Th2 cells and their respective cytokines in the pathogenesis of mercury-induced disease. This article reviews recent studies that have examined the patterns of cytokine gene expression and where investigators have manipulated the Th1 and Th2 responses that occur during mercury-induced autoimmunity. Finally, we will discuss some biochemical/molecular mechanisms by which heavy metals may induce cytokine gene expression.

Immunopathogenesis of environmentally induced lupus in mice

Systemic lupus erythematosus (SLE) is a systemic autoimmune syndrome defined by clinical and serologic features, including arthritis, glomerulonephritis, and certain autoantibodies such as anti-nuclear ribonucleoprotein (nRNP)/Smith antigen (Sm), DNA, and ribosomal P. Although lupus is considered primarily a genetic disorder, we recently demonstrated the induction of a syndrome strikingly similar to spontaneous lupus in many nonautoimmune strains of mice exposed to the isoprenoid alkane pristane (2,6,10,14-tetramethylpentadecane), a component of mineral oil. Intraperitoneal injection of pristane leads to the formation of lipogranulomas consisting of phagocytic cells that have engulfed the oil and collections of lymphocytes. Subsequently, pristane-treated BALB/c and SJL mice develop autoantibodies characteristic of SLE, including anti-nRNP/Sm, antiribosomal P, anti-Su, antichromatin, anti-single-stranded DNA, and anti-double-stranded DNA. This is accompanied by a severe glomerulonephritis with immune complex deposition, mesangial or mesangiocapillary proliferation, and proteinuria. All inbred mice examined appear to be susceptible to this novel form of chemically induced lupus. Pristane-induced lupus is the only inducible model of autoimmunity associated with the clinical syndrome as well as with the characteristic serologic abnormalities of SLE. Defining the immunopathogenesis of pristane-induced lupus in mice may provide insight into the causes of spontaneous (idiopathic) lupus and also may lead to information concerning possible risks associated with the ingestion or inhalation of mineral oil and exposure to hydrocarbons in the environment.

Metals and kidney autoimmunity

The causes of autoimmune responses leading to human kidney pathology remain unknown. However, environmental agents such as microorganisms and/or xenobiotics are good candidates for that role. Metals, either present in the environment or administered for therapeutic reasons, are prototypical xenobiotics that cause decreases or enhancements of immune responses. In particular, exposure to gold and mercury may result in autoimmune responses to various self-antigens as well as autoimmune disease of the kidney and other tissues. Gold compounds, currently used in the treatment of patients with progressive polyarticular rheumatoid arthritis, can cause a nephrotic syndrome. Similarly, an immune-mediated membranous nephropathy frequently occurred when drugs containing mercury were commonly used. Recent epidemiologic studies have shown that occupational exposure to mercury does not usually result in autoimmunity. However, mercury induces antinuclear antibodies, sclerodermalike disease, lichen planus, or membranous nephropathy in some individuals. Laboratory investigations have confirmed that the administration of gold or mercury to experimental animals leads to autoimmune disease quite similar to that observed in human subjects exposed to these metals. In addition, studies of inbred mice and rats have revealed that a few strains are susceptible to the autoimmune effects of gold and mercury, whereas the majority of inbred strains are resistant. These findings have emphasized the importance of genetic (immunogenetic and pharmacogenetic) factors in the induction of metal-associated autoimmunity. (italic)In vitro(/italic) and (italic)in vivo(/italic) research of autoimmune disease caused by mercury and gold has already yielded valuable information and answered a number of important questions. At the same time it has raised new issues about possible immunostimulatory or immunosuppressive mechanisms of xenobiotic activity. Thus it is evident that investigations of metal-induced renal autoimmunity have the potential to produce new knowledge with relevance to autoimmune disease caused by xenobiotics in general as well as to idiopathic autoimmunity.

Environmentally induced autoimmune diseases: potential mechanisms

Environmental and other xenobiotic agents can cause autoimmunity. Examples include drug-induced lupus, toxic oil syndrome, and contaminated l-tryptophan ingestion. Numerous mechanisms, based on (italic)in vitro(/italic) evidence and animal models, have been proposed to explain how xenobiotics induce or accelerate autoimmunity. The majority of these can be divided into three general categories. The first is those inhibiting the processes involved in establishing tolerance by deletion. Inhibiting deletion can result in the release of newly generated autoreactive cells into the periphery. The second mechanism is the modification of gene expression in the cells participating in the immune response, permitting lymphocytes to respond to signals normally insufficient to initiate a response or allowing the antigen-presenting cells to abnormally stimulate a response. Abnormal gene expression can thus disrupt tolerance maintained by suppression or anergy, permitting activation of autoreactive cells. The third is the modification of self-molecules such that they are recognized by the immune system as foreign. Examples illustrating these concepts are presented, and related mechanisms that have the potential to similarly affect the immune system are noted. Some mechanisms appear to be common to a variety of agents, and different mechanisms appear to produce similar diseases. However, evidence that any of these mechanisms are actually responsible for xenobiotic-induced human autoimmune disease is still largely lacking, and the potential for numerous and as yet unidentified mechanisms also exists.

Murine mercury-induced autoimmunity: a model of chemically related autoimmunity in humans

Human exposure to certain compounds or therapeutic drugs can result in the development of an autoimmune syndrome. Mercury (Hg) induced autoimmunity is one of the few animal models in which administration of a chemical induces a specific loss of tolerance to self-antigens. After receiving subtoxic doses of Hg or other heavy metals, susceptible mouse strains rapidly develop highly specific antibodies to nucleolar antigens. In addition, these animals display a general activation of the immune system, especially pronounced for the Th2 subset and a transient glomerulonephritis with immunoglobulin deposits. Like many human autoimmune diseases, this syndrome is associated with the expression of susceptible major histocompatibility complex (MHC) class II genes. In this article, we review the essential features of this model, and we discuss the putative mechanisms by which Hg creates such a severe immune dysfunction.

Protection Against CD95-Mediated Apoptosis by Inorganic Mercury in Jurkat T Cells

Dysregulation of CD95/Fas-mediated apoptosis has been implicated as a contributing factor in autoimmune disorders. Animal studies clearly have established a connection between mercury exposure and autoimmune disease in rodents, while case reports have suggested a link between accidental mercury contamination and autoimmune disease in humans. The mechanism(s) for these associations are poorly understood. Using the Jurkat cell model, we have found that low levels (≤10 μM) of inorganic mercury (i.e., HgCl2) attenuated anti-CD95-mediated growth arrest and markedly enhanced cell survival. Several biochemical assays for apoptosis, including DNA degradation, poly(ADP-ribose) polymerase degradation, and phosphatidylserine externalization, directly verified that HgCl2 attenuated anti-CD95-mediated apoptosis. In an attempt to further characterize the effect of mercury on CD95-mediated apoptosis, several signaling components of the CD95 death pathway were analyzed to determine whether HgCl2 could modulate them. HgCl2 did not modulate CD95 expression; however, it did block CD95-induced caspase-3 activation. HgCl2 was not able to attenuate TNF-α-mediated apoptosis in U-937 cells, or ceramide-C6-mediated apoptosis in Jurkat cells, suggesting that mercury acts upstream of, or does not involve, these signals. Thus, inorganic mercury specifically attenuates CD95-mediated apoptosis likely by targeting a signaling component that is upstream of caspase-3 activation and downstream of CD95.

Mercury-induced anti-nucleolar autoantibodies can transgress the membrane of living cells in vivo and in vitro

Treatment with HgCl2 induces a systemic autoimmune disease in certain mice and rats. The major characteristic of this disease in mice with H-2s genotype is the production of anti-nucleolar autoantibodies (ANoIA). The exact mechanism(s) for the production and the functional role of mercury-induced ANoIA are not known. We have studied the ability of mercury-induced ANoIA to enter the living cells in vivo and in vitro. We found that in highly susceptible mice, treatment with mercury induced ANoIA capable of localizing in the nucleoli of kidney and liver cells in vivo. No detectable nucleoli localization of ANoIA were found in the cells of the heart, stomach, intestine and spleen. Consistent with the in vivo studies, mercury-induced ANoIA were also able to enter and translocate in the nucleoli of certain cells in vitro. The highest degree of antibody penetration was found in A-498 cells (a human kidney cell line) followed by 3T3 cells (a mouse fibroblast cell line), whereas the cells of lymphoid origin exhibited a very low degree of antibody penetration. Penetrated ANoIA could be recovered from the nucleoli of live 3T3 cells previously treated with ANoIA. The in vitro nucleolar translocation by ANoIA did not affect the DNA synthesis, but was found to be an active process dependent on time and temperature. Furthermore, pre-treatment of living cells with trypsin markedly inhibited both cell entry and nucleolar accumulation of ANoIA. Thus, mercury-induced ANoIA have a unique ability to transgress the membrane of certain living cells in vivo and in vitro, and to localize in the nucleoli.

Mechanism of mercury-induced autoimmunity: both T helper 1- and T helper 2-type responses are involved

Mercury can induce a systemic autoimmune disease in susceptible mouse strains. H-2s mice are particularly susceptible to mercury-induced autoimmunity and other mouse strains are more or less resistant. T helper 1/T helper 2 (Th1/Th2) dichotomy has been proposed for resistance or susceptibility, respectively. In the current study we show that mercury treatment induced a full autoimmune response in both C57BL/6 (H-2b) wild-type and interleukin-4 (IL-4)-deficient mice. Antibody production of all isotypes were induced, except that in IL-4-deficient mice there was no immunoglobulin E (IgE) and very low levels of immunoglobulin G1 (IgG1) antibody synthesis. Autoantibodies of different specificities were produced. The granular pattern of all IgG subclasses deposits were detected in the kidneys. In contrast to mercury-treated H-2s seconds mice, we did not detect any anti-nucleolar autoantibodies in the sera of mercury-treated wild-type or IL-4-deficient mice. To further explore the role of Th1/Th2 cytokines in the mercury model, we performed anti-interferon-gamma antibody treatment in IL-4-deficient mice together with mercury treatment and found that the production of IgG2a and IgG3, but not IgG2b, antibodies was downregulated. This indicated that besides Th2-type cytokines, Th1-type and other cytokines were involved as well in mercury-induced autoimmune response. Thus, C57BL/6 mice with H-2b genotype are highly susceptible to mercury-induced autoimmunity, and the genetic susceptibility to mercury involves more than a predisposition of a Th1-or Th2-type response.

Onset of nucleolar and extranucleolar transcription and expression of fibrillarin in macaque embryos developing in vitro

Specific aims were to characterize the onset of nucleolar and extranucleolar transcription and expression of the nucleolar protein fibrillarin during preimplantation development in vitro in macaque embryos using autoradiographic and immunocytochemical techniques. Autoradiography was performed on whole embryos cultured with [3H]uridine for assessment of nucleolar (rRNA) and extranucleolar (mRNA) transcription. Expression of fibrillarin was immunocytochemically assessed in whole embryos using a primary antibody against fibrillarin and a fluorescein isothiocyanate-conjugated secondary antibody. Extranucleolar incorporation of [3H]uridine was first detected in 2-cell embryos cultured 6-10 h with [3H]uridine. Culture with alpha-amanitin prevented incorporation of label in 2-cell embryos, and treatment with ribonuclease reduced the signal to background levels, indicating that [3H]uridine was incorporated into mRNA and not rRNA or DNA. Nucleolar incorporation of [3H]uridine was not evident in pronucleate-stage or 2- to 5-cell embryos, but it was detected in one 6-cell embryo and in all 8-cell to blastocyst-stage embryos. Fibrillarin was first expressed in some 6- to 7-cell embryos, but it was consistently expressed in all 8-cell embryos. Fibrillarin was localized to the perimeter of the nucleolar precursor bodies, forming a ring that completely encapsulated these structures. Fibrillarin was not expressed in 8- to 16-cell embryos cultured with alpha-amanitin, indicating that it is transcribed, rather than recruited, at the 8-cell stage. In conclusion, in in vitro-fertilized macaque embryos developing in vitro, extranucleolar synthesis of mRNA is initiated at the 2-cell stage while the onset of nucleolar transcription occurs at the 6- to 8-cell stage, coincident with expression of fibrillarin.

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.

Resistance to HgCl2-Induced Autoimmunity in Haplotype-Heterozygous Mice Is an Intrinsic Property of B Cells

Exposure to low doses of mercury chloride induces autoantibodies to the nucleolar protein fibrillarin in H-2s, but not in H-2b, mice. Surprisingly, F1 crosses between resistant and sensitive haplotypes are resistant. Previously, we have shown that the resistance in these F1 mice was due to coexpression of the resistant class II allele. Using adoptive transfer techniques we have examined several mechanisms by which the resistant haplotype could be down-regulating the antifibrillarin response in F1 (s/b) mice. Similar to other autoimmune models, mercury-induced autoimmunity requires cognate MHC-restricted T cell help. The absence of autoantibody production in F1 mice was not due to a difference in thymic education or to the absence of antifibrillarin-specific T cell help. These results suggest that the resistance is due to an intrinsic property of the haplotype-heterozygous B cells.

Class II haplotype differentially regulates immune response in HgCl2-treated mice

One of the most striking features of exposure to low doses of mercury in mice is the high-titer haplotype-linked anti-nucleolar (ANoA) autoantibody response. Mice of H-2(s) haplotype have been high responders, while H-2(b) mice have been low. This pattern has been attributed to the class II molecule itself, but the poor response of F1 crosses between high and low responders raised the possibility that the anti-fibrillarin specificity was actually due to a closely linked dominant negative gene. To test the role of class II explicitly, F1 crosses between congenic B6.SJL (H-2(s)) and C57BL/6 (H-2(b)) mice with a targeted deletion of I-AbAbeta were generated, creating mice heterozygous for all MHC loci, but expressing only I-As. In comparison with B6.SJL, no diminution of ANoA titers was found, proving that I-As itself was responsible for susceptibility and I-Ab for downregulation. Unlike I-A, expression of the I-E class II molecule could not downregulate the response in an otherwise susceptible mouse. These results suggest a complicated role for class II in the regulation of a novel, environmentally induced autoimmune response.

Effects of the murine genotype on T cell activation and cytokine production in murine mercury-induced autoimmunity

Mercury induces a systemic autoimmune condition characterized by auto-antibodies to the nucleolar protein fibrillarin (AFA) and systemic immune-complex (IC) deposits in genetically susceptible mouse strains. This study examines T cell activation and cytokine production following mercury exposure in genetically susceptible and resistant strains. Mercury injected s.c., according to the protocol for induction of autoimmunity, caused an early T cell activation, measured as an increase of IL-2-producing cells, and increased expression of the IL-2-receptor proteins CD25 and CD122 and of the proliferation marker CD71 on days 2-4 in the susceptible A.SW and A. TH strains. This was followed by a long-lasting increase in the number of T cells, dominated by CD4(+) cells. Mice of the susceptible A.SW strain showed a modest increase of TNF-alpha-, IFN-gamma-, and IL-4-producing cells after 4-6 days, and a very distinct increase of IL-4-producing cells on days 8-10. The susceptible SJL strain (H-2(s)), severely deficient in Th2-promoting CD4(+), NK1.1(+) T cells, showed no increase of IL-4(+) cells on days 8-10. Instead, the number of IFN-gamma-producing cells was increased. Susceptible mice developed an increase of Ig-producing cells, AFA, and systemic IC-deposits. Genetically mercury-resistant A.TL mice showed a minimal increase of T cells, but no increase in cytokine-producing cells. We conclude that autoimmunogenic doses of HgCl2 induce an activation and proliferation of T cells in genetically susceptible mouse strains, as well as a broad increase of cytokine-producing cells, followed by a late predominance of the Th2-associated IL-4. One strain, severely deficient in Th2-promoting CD4(+), NK1.1(+) T cells, lacked the increase in IL-4(+) cells, indicating that a predominantly Th2-response is not necessary for induction of autoimmunity by mercury. However, a Th2-dominated response led to a faster and stronger B cell activation.

Murine strain differences in response to mercuric chloride: antinucleolar antibodies production does not correlate with renal immune complex deposition

Mercuric chloride (HgCl2) induces the production of antinucleolar antibodies (ANucA) in susceptible strains of mice. Responder strains bearing the H-2(5) haplotype as well as several ANucA resistant strains have been shown to develop renal immune complex deposits after HgCl2 treatment. Sera obtained throughout 12 to 16 weeks of HgCl2 treatment from mice of four ANucA responder strains (A.SW/SnJ, A.CA/SnJ, DBA/1J, and P/J) and one ANucA-resistant strain (C57BL/10SnJ) were examined for ANucA production. Terminal sera were also tested for the presence of anti-glomerular basement membrane antibodies, and the kidneys were examined for the deposition of IgG and C3. Only one strain, A.SW, developed significant deposits of IgG in the renal glomeruli, although all four responder strains exhibited similar ANucA induction/production profiles. The differences seen by direct immunofluorescence assay (IFA) in renal immune complex deposition between the A.SW and histocompatibility congenic A.CA mice were corroborated by individually eluting and then quantitating the deposited IgG from renal tissues of Hg-treated A.SW and A.CA mice as well as control A.SW mice. The average amount of IgG eluted from A.SW renal tissue was significantly greater than that eluted from either A.CA or control A.SW renal tissues. All eluates from Hg-treated animals gave only a nucleolar fluorescence pattern when assayed by indirect IFA against a panel of rat organ tissues. In summary, no correlation was found between ANucA production and renal IgG deposition in response to treatment with HgCl2.

Effect of non-toxic mercury, zinc or cadmium pretreatment on the capacity of human monocytes to undergo lipopolysaccharide-induced activation

1. Metal salts can inhibit cell activity through direct toxicity to critical cellular molecules and structures. On the other hand, they can also change cell behaviour by inducing specific genes (including genes encoding members of the metallothionein [MT] gene family). Therefore, transition metals may affect cell functions either by acting as a toxin, or by transmitting or influencing signals controlling gene expression. 2. To explore the latter possibility, we measured the ability of low, non-toxic metal pretreatment to alter immune cell behaviour. We previously found that pretreatment of human monocytes with zinc induces metallothionein gene expression and alters their capacity to undergo a bacterial lipopolysaccharide-induced respiratory burst. We showed here that cadmium and mercury salts, at concentrations that exert no discernible toxicity, inhibit activation of human monocytic leukemia (THP-1) cells. CdCl2 1 microM, ZnCl2 20-40 microM or HgCl2 2 microM pretreatment for 20 h induced MT-2 mRNA and total MT protein accumulation and had no effect on proliferation potential or metabolic activity, but significantly inhibited the ability of subsequent lipopolysaccharide treatment to induce the oxidative burst, increased adhesion to plastic, and MT-2 and interleukin-1 beta (IL-1 beta) mRNA accumulation. 3. The phenomenon of metal-induced suppression of monocyte activation, at metal concentrations that have no effect on cell viability, has important implications for assessment of acceptable levels of human exposure to cadmium, zinc and mercury.

Antinuclear antibody in systemic sclerosis (scleroderma)

The presence of autoantibodies to intracellular molecules is the hallmark immunologic finding of SSc. Recent sophisticated methods have contributed to characterization of unidentified antigens of ANA in sera from patients with SSc. Antibodies to RNA polymerases are the third major SSc-specific ANA, in addition to anti-topo I and anticentromere antibodies, and it is now possible to identify over 85% of SSc patients. These antibodies have proved helpful in diagnosis of this disease. An immunogenetic predisposition to synthesis of the ANAs has been unveiled. Both antigen-driven and molecular mimicry hypotheses have been proposed for ANA production in SSc. Although the role of ANAs in the pathogenesis of SSc is not yet known, it is logical to assume that the origin of ANAs is linked to the causes of this disease because each antibody is associated with its own unique constellation of clinical features.

The autoimmunogenic chemicals HgCl2 and diphenylhydantoin stimulate IgG production to TNP-Ficoll and TNP-OVA, supporting and extending the graft-versus-host hypothesis for chemical induction of autoimmunity

Bypass of T-cell tolerance via non-cognate graft-versus-host (GVH)-like help from T-helper (Th) cells activated by chemically altered or induced epitopes, has been postulated as a mechanism underlying chemical induction of autoimmunity. To functionally test this hypothesis, we assessed whether the autoimmunogenic chemicals HgCl2 and diphenylhydantoin (DPH), like GVH reactions, stimulate specific immunoglobulin G (IgG) responses to trinitrophenyl (TNP)-Ficoll but not to TNP-ovalbumin. IgG responses were quantified in the popliteal lymph node by enzyme-linked immunosorbent spot-forming cell assay (ELISPOT) assays 7 days after s.c. injection of antigens, parental cells, chemicals or combinations thereof into the footpad of semi-allogeneic F1 mice. Antigens, chemicals, or cells alone induced few TNP-specific IgG antibody-forming cell (AFC) compared with untreated mice. Co-injection of parental cells or chemicals with TNP-Ficoll stimulated the TNP-specific response per lymph node approximately 50- and approximately 40-fold, respectively. In contrast, the IgG response to TNP-ovalbumin could not be stimulated by GVH reactions, whereas HgCl2 and DPH dose-dependently increased this response up to approximately 25- and approximately 250-fold, respectively. However, responses to TNP-ovalbumin pre-incubated with HgCl2 or DPH could be stimulated approximately 6-8 fold by GVH reactions. Observed similar adjuvanticity of chemicals and parental cells for TNP-Ficoll support a GVH-like action of autoimmunogenic chemicals. In addition, the chemicals modify TNP-ovalbumin such that B cells recognizing this antigen become susceptible to non-cognate stimulation by GVH reactions.

Mercury induces polyclonal B cell activation, autoantibody production and renal immune complex deposits in young (NZB x NZW)F1 hybrids

It is well established that in susceptible mouse strains, chronic treatment with subtoxic doses of mercuric chloride (HgCl2) induces a systemic autoimmune disease, which is characterized by increased serum levels of IgG1 and IgE antibodies, by the production of anti-nucleolar antibodies and by the development of immune complex-mediated glomerulonephritis. Susceptibility to mercury is partly under the control of major histocompatibility complex genes. To study the susceptibility to mercury further, we investigated the in vivo effects of mercury in young autoimmune disease prone (NZB x NZW)F1 (H-2d/z) mice prior to establishment of spontaneous autoimmune disease. Mercury-susceptible SJL (H-2s) mice and mercury low-responder BALB/c (H-2d) mice were used as positive and negative controls, respectively. In (NZB x NZW)F1 mice, treatment with mercury stimulated an intense antibody formation characterized by increased numbers of splenic IgG1 and IgG3 antibody-producing cells as well as by elevated serum IgE levels. Injection with mercury also induced an increased production of IgG1, IgG2b and IgE antibodies in SJL, but not in BALB/c mice. The mercury-induced IgG1 response in (NZB x NZW)F1 and SJL mice was found to be polyclonal and autoantibodies against double-stranded (ds)DNA, IgG, collagen, cardiolipin, phosphatidylethanolamine as well as antibodies against the hapten trinitrophenol were produced. In addition, SJL, but not (NZB x NZW)F1 or BALB/c mice, produced IgG1 anti-nucleolar antibodies after treatment with mercury. Further studies demonstrated that (NZB x NZW)F1 and SJL mice developed high titers of renal mesangial immune complex deposits containing IgG1 antibodies 3 weeks after injection with mercury. Thus, a mouse strain genetically prone to develop spontaneous autoimmune diseases is highly susceptible to mercury-induced immunopathological alterations.

Distinctive immune response patterns of human and murine autoimmune sera to U1 small nuclear ribonucleoprotein C protein

The Ul small nuclear ribonucleoprotein (snRNP), a complex of nine proteins with Ul RNA, is a frequent target of autoantibodies in human and murine systemic lupus erythematosus (SLE). Anti-Sm antibodies recognizing the B'/B, D, E, F, and G proteins of Ul snRNPs are highly specific for SLE, and are nearly always accompanied by anti-nRNP antibodies recognizing the Ul snRNP-specific 70K, A, and/or C proteins. Previous studies suggest that human anti-nRNP antibodies recognize primarily the U1-70K and Ul-A proteins, whereas recognition of Ul-C is less frequent. We report here that autoantibodies to U1-C are more common in human autoimmune sera than believed previously. Using a novel immunoprecipitation technique to detect autoantibodies to native Ul-C, 75/78 human sera with anti-nRNP/ Sm antibodies were anti-Ul-C (+). In striking contrast, only 1/65 anti-nRNP/Sm (+) MRL mouse sera of various Igh allotypes was positive. Two of ten anti-nRNP/Sm (+) sera from BALB/c mice with a lupus-like syndrome induced by pristane recognized Ul-C. Thus, lupus in MRL mice was characterized by a markedly lower frequency of anti-U1-C antibodies than seen in human SLE or pristane-induced lupus. The results may indicate different pathways of intermolecular-intrastructural diversification of autoantibody responses to the components of Ul snRNPs in human and murine lupus, possibly mediated by alterations in antigen processing induced by the autoantibodies themselves.

Anti-nuclear antibody production and immune-complex glomerulonephritis in BALB/c mice treated with pristane

The pathogenesis of systemic lupus erythematosus is thought to be primarily under genetic control, with environmental factors playing a secondary role. However, it has been shown recently that intraperitoneal injection of pristane (2,6,10,14-tetramethylpentadecane) induces autoantibodies typical of lupus in BALB/c mice, a strain not usually considered to be genetically susceptible to the disease. In this study, the induction of autoimmune disease by pristane was investigated. BALB/c mice receiving pristane were tested for autoantibody production and histopathological evidence of glomerulonephritis. Six of 11 mice developed IgM anti-single-stranded DNA antibodies shortly after receiving pristane and 4 developed IgM anti-histone antibodies, but anti-double-stranded DNA antibodies were absent. IgG anti-DNA and anti-histone antibodies were absent. In contrast, the lupus-associated anti-nuclear ribonucleoprotein/Sm and anti-Su autoantibodies produced by these mice were predominantly IgG. In addition to autoantibodies, most of the mice developed significant proteinuria. Light microscopy of the kidney showed segmental or diffuse proliferative glomerulonephritis. Electron microscopy showed subepithelial and mesangial immune-complex deposits and epithelial foot process effacement. Immunofluorescence revealed striking glomerular deposition of IgM, IgG, and C3 with a mesangial or mesangiocapillary distribution. Thus, pristane induces immune-complex glomerulonephritis in association with autoantibodies typical of lupus in BALB/c mice. These data support the idea that lupus is produced by an interplay of genetic and environmental factors and that unlike the MRL or (NZB x W)F1 mouse models, in which genetic susceptibility factors are of primary importance, environmental factors are of considerable importance in the autoimmune disease of pristane-treated BALB/c mice.

Antifibrillarin autoantibodies present in systemic sclerosis and other connective tissue diseases interact with similar epitopes

Autoantibodies specific against fibrillarin, a 34-kD nucleolar protein associated with U3-snRNP, are present in patients with systemic sclerosis (SSc). To understand the mechanisms involved in the induction of these autoantibodies, we prepared a series of human fibrillarin recombinant proteins covering the entire molecule and analyzed their interaction with the autoantibodies present in various connective tissue diseases. Our results showed that antifibrillarin autoantibodies are present not only in SSc, as previously reported, but also in a variety of other connective tissue diseases. Patients with SSc (58%), mixed connective tissue diseases (60%), CREST syndrome (calcinosis, Raynaud phenomenon, esophageal dismotility, sclerodactyly, and telangiectasia syndrome) (58%), systemic lupus erythematosus (39%), rheumatoid arthritis (60%), and Sjogern's syndrome (84%) showed presence of antifibrillarin autoantibodies. Results obtained from competitive inhibition radioimmunoassay and Western blot analyses with purified recombinant fusion proteins revealed that these autoantibodies react primarily with epitope(s) present in the NH2- (AA 1-80) and COOH-terminal (AA 276-321) domains of fibrillarin. Autoantibodies reacting with internal regions of fibrillarin are less frequent. Analysis of the hydrophilicity profiles of reactive peptides showed presence of three potential antigenic sites in the NH2- and two in the COOH-terminal regions. While a hexapeptide sequence NH2 terminus of fibrillarin is shared with an Epstein-Barr virus-encoded nuclear antigen, the COOH-terminal region shares sequence homology with P40, the capsid protein encoded by herpes virus type 1. Interestingly, these two regions of fibrillarin also contain the most immunodominant sequences, as predicted by surface probability and the Jameson and Wolf antigenic index. These observations suggest that molecular mimicry might play an important role in the induction of antifibrillarin autoantibodies.

Factors involved in nuclear reprogramming during early development in the rabbit

Mechanisms of nuclear reprogramming and assessment of potential malfunctions that could be deleterious for development were evaluated in rabbit zygotes, parthenotes, and nuclear transfer embryos by analysis of DNA replication, nucleolar fibrillarin label, and localization of nuclear material reactive to the MPM-2 antibody. Nuclear transfer embryos were derived from G1/early S-phase donor nuclei and MII oocytes. In nuclear transfer embryos, DNA rereplication was likely to have occurred because label was incorporated, possibly in the centromeric regions of the chromosomes, prior to premature chromosome condensation and again following pronuclear formation. In parthenotes, DNA replication began very late in the cell cycle, which may be due to deficiencies in the artificial activation stimulus. The presence of fibrillarin label in the nucleolus was used as an indication of nucleolar transcriptional activity. Fibrillarin label was absent in embryos of all types up to the 16-32-cell stage. Although fibrillarin reappeared in nuclear transfer and parthenote embryos at the appropriate stage, not all blastomeres showed label indicating impaired development in these embryos. Labelling of phosphorylated epitopes by MPM-2 antibody showed a change in pattern of labelling during early development. Early cleavage stage embryos did not exhibit labelling over the spindle poles as did blastomeres from 32-cell embryos and tissue culture cells. All cell types exhibited labelling during interphase as dots located primarily over the nucleus in blastomeres from 32-cell embryos and in tissue culture cells, together with cytoplasmic label in embryos at early cleavage stages. Nuclear transplant embryos had a normal pattern of MPM-2 label. In contrast, the appearance of MPM-2 label in parthenotes depended on the type of calcium stimulation. These results demonstrate defects in DNA synthesis, nucleolar activity, and specific phosphorylation events, likely resulting from an improper activation stimulus and chromosome condensation in the transplanted nucleus.