Mercury-induced autoreactive anti-class II T cell line protects from experimental autoimmune encephalomyelitis by the bias of CD8+ antiergotypic cells in Lewis rats

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

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

Immunology of mercury

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

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.

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

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

Immunomodulation by metals

Occupational or environmental exposure to metals is believed to affect human health adversely. One mechanism whereby metals can alter health is through modulation of immune homeostasis. Imbalances in immune regulation by metals can lead to inadequate or excessive production of inflammatory cytokines. Alternatively, metals can lead to inappropriate activation of lymphoid subsets involved in acquired immunity to specific antigens. Some resultant pathologies may include chronic inflammatory processes and autoimmune diseases. Metals may change the response repertoire by direct and indirect means by influencing expression of new antigens, new peptides, and/or antigen presentation by modifying the antigen-presenting complex. The differences in metal-induced immune responses between humans and the mechanisms of metal immunomodulation are discussed.

Mercury enhances susceptibility to murine leishmaniasis

The genetic background of mice infected with Leishmania major determines the response to infection, resulting in a resistant or susceptible phenotype. Susceptible mice develop a T-helper type 2 (Th2)-type immune response following infection distinguished by the development of interleukin (IL)-4 secreting T cells in the lymph node and spleen. In SJL mice, which normally heal L. major lesions, subtoxic doses of mercury induce an autoimmune syndrome characterized by an expansion of Th2 cells. In this study, we examined the effect of mercury administration on the outcome of L. major infection in SJL mice. We show that subtoxic doses of mercuric chloride (HgCl2) exacerbate disease outcome in SJL mice resulting in increased footpad swelling and increased parasite burdens. Furthermore, the effects of HgCl2 treatment on resistance to L. major are time-dependent. The nonhealing phenotype was observed only if mice had been treated with HgCl2 prior to L. major infection for at least 1 week, a timepoint at which mice treated with HgCl2 alone had increased splenocyte IL-4 production. HgCl2 treatment also increased production of serum immunoglobulin (Ig)E and IgG1, two IL-4 dependent isotypes. These results show that HgCl2 treatment enhances the susceptibility to L. major in SJL mice, consistent with the induction of host Th2 parameters. These findings have implications for the role of mercury contamination in areas of endemic leishmaniasis.

Self major histocompatibility complex class-II-specific regulatory CD4 T cells prevent both Th1- and Th2-mediated autoimmune diseases in the rat

It is clear that functional heterogeneity of T cells may be explained by differential cytokine production. The aim of this paper was to review evidence for regulatory cells, generated after HgCl(2)-exposure. They differ from classical Th1 and Th2 cells, produce transforming growth factor-beta and interleukin-10 and exert their regulatory functions in a Th1/Th2-unrestricted fashion.

Induction of autoimmunity through bystander effects. Lessons from immunological disorders induced by heavy metals

Autoreactive T cells exist in healthy individuals and represent a potential reservoir of pathogenic effectors which, when stimulated by microbial adjuvants, could trigger an autoimmune disease. Experimental studies have indicated that xenobiotics, well defined from a chemical point of view, could promote the differentiation of autoreactive T cells towards a pathogenic pathway. It is therefore theoretically possible that compounds present in vaccines such as thiomersal or aluminium hydroxyde can trigger autoimmune reactions through bystander effects. Mercury and gold in rodents can induce immunological disorders with autoimmune reactions. In vitro, both activate signal transduction pathways that result in the expression of cytokines, particularly of IL-4 and IFNgamma. In a suitable microenvironment heavy metals could therefore favour the activation of autoreactive T cells. In that respect, genetic background is of major importance. Genome-wide searches in the rat have shown that overlapping chromosomal regions control the immunological disorders induced by gold salt treatment, the development of experimental autoimmune encephalomyelitis and the CD45RC(high)/CD45RC(low)CD4(+)T cells balance. The identification and functional characterization of genes controlling these phenotypes may shed light on key regulatory mechanisms of immune responses. This should help to improve efficacy and safety of vaccines.

Intralipid-based short-term total parenteral nutrition does not impair small intestinal mucosa-related cellular immune reactivity in the healthy rat

BACKGROUND

The lipid component of total parenteral nutrition (TPN) has reportedly been associated with trophic effects on the intestinal mucosa and suppressive effects on the immune system.

METHODS

We have challenged these hypotheses using a 7-day TPN rodent model comparing the effects of isocaloric, isonitrogenous lipid-based (TPN-lipid, 50% of calories as long-chain triacylglycerol) and carbohydrate-based TPN (TPN-CH, 100% of calories as carbohydrates) on mucosal morphology and immune function. Enterally fed animals were included to establish a baseline for immunologic read-outs. The study was performed in healthy, metabolically stable animals to avoid interference by septic or trauma-related stress factors.

RESULTS

Both TPN regimens resulted in a significantly smaller weight gain (TPN-lipid, 29.8 +/- 4.0 g; TPN-CH, 30.3 +/- 4.4 g) compared with enterally fed reference animals (49.2 +/- 3.2 g; p = .007), with no difference in nitrogen balance between the TPN groups. Mucosal sucrase activity was significantly lower in both TPN groups (TPN-lipid, 8.8 +/- 1.0 x 10(-7) katal per gram (kat/g) of protein; CH: 11.9 +/- 1.6 x 10(-7) kat/g of protein) compared with enteral feeding (17.4 +/- 0.9 x 10(-7) kat/g of protein; ANOVA: p = .0007). Morphometric analysis of the small intestine revealed no differences between the two TPN groups although a significantly depressed villus height in the TPN-lipid group could be observed in comparison to enterally fed reference rats (TPN-lipid, 0.47 +/- 0.02; TPN-CH, 0.50 +/- 0.01; enteral, 0.56 +/- 0.02 mm; ANOVA: p = .0298). Light and electron microscopy revealed a normal surface architecture in all three groups of rats. Cellular immune reactivity was evaluated using a novel specific immunization protocol: animals were immunized against OVA 4 weeks before TPN. OVA-induced lymphoproliferative responses and phenotypic data from draining popliteal and mesenteric lymph nodes were evaluated after the different regimens. Results did not differ among the three groups.

CONCLUSIONS

In healthy rodents, short-term lipid-based and carbohydrate-based TPN regimens lead to limited mucosal atrophy with preserved surface architecture compared with enteral feeding. However, peripheral and mesenteric cellular immune responsiveness after both TPN regimens remained comparable to enterally fed reference animals. Therefore, mesenteric and systemic cellular immune reactivity does not appear to be impaired by lipid-based or carbohydrate-based TPN.

Neonatal induction of tolerance to T(h)2-mediated autoimmunity in rats

Brown-Norway (BN) rats are highly susceptible to drug-induced immune dysregulations and when injected with mercuric chloride (HgCl(2)) or sodium aurothiopropanolsulfonate (ATPS), they develop a syndrome characterized by a polyclonal B cell activation depending upon CD4(+) T(h)2 cells that recognize self-MHC class II molecules. Since peripheral tolerance of T(h)2 cells might be crucial in the prevention of immunological manifestations such as allergy, establishing conditions for inducing tolerance to HgCl(2)- or ATPS-mediated immune manifestations appeared to be of large interest. We report here that BN rats neonatally injected with HgCl(2): (i) do not develop the mercury disease, (ii) remain resistant to HgCl(2)-induced autoimmunity at 8 weeks of age and later, provided they are regularly exposed to HgCl(2), (iii) are still susceptible to ATPS-induced immune manifestations, and (iv) exhibit spleen cells that adoptively transfer tolerance to HgCl(2)-induced autoimmunity in naive, slightly irradiated, syngeneic recipients. These findings demonstrate that dominant specific tolerance can be neonatally induced using a chemical otherwise responsible for T(h)2-mediated autoimmunity.

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.

Low-dose mercuric chloride induces resistance in brown norway rats to further mercuric chloride by up-regulation of interferon-gamma

Mercuric chloride induces autoimmunity in Brown Norway rats with polyclonal B-cell activation, hyper-IgE and multiple autoantibodies. Pre-treatment with low-dose HgCl2 (one-tenth of the standard dose) induces resistance to later full-dose HgCl2; we have studied the mechanism of this resistance. Brown Norway rats given low-dose HgCl2 showed only a modest increase in serum IgE level, three logs lower than rats given standard-dose HgCl2, and no up-regulation of splenic interleukin (IL)-4 mRNA. There was up-regulation of splenic interferon (IFN)-gamma gene expression and a progressive rise in serum IFN-gamma. Neither IL-12 nor IL-18 were induced, but there was up-regulation of IL-12 receptor beta2-chain (IL-12Rbeta2) expression. IL-10 and transforming growth factor (TGF)-beta expression did not change. Serum IgE and splenic IL-4 mRNA expression remained static when these rats were rechallenged, confirming resistance. Thereafter IFN-gamma expression gradually fell, after which IL-4 expression and serum IgE rose slightly. Our observations suggest that low-dose HgCl2 confers protection in Brown Norway rats to further HgCl2 by up-regulation of IFN-gamma, associated with enhanced IL-12Rbeta2 expression. The immunological response to HgCl2 in susceptible rat strains is more complex than previously appreciated and is dose dependent, with low doses inducing a T helper '(Th)1' type of response in contrast to the 'Th2' type response associated with standard doses.

Differential expression of T-cell adhesion molecules and LFA-1-dependent intercellular adhesion in HgCl2-induced autoimmunity and immune suppression

Exposure of Brown Norway (BN) rats to HgCl2 induces Th2-mediated systemic autoimmunity. In contrast, in Lewis rats, HgCl2 induces immune suppression, mediated by CD8+ T cells. HgCl2 was previously found to enhance expression of LFA-1, ICAM-1 and CD134 (OX40) on T cells in BN rats. In the present study, T cells from Lewis rats were studied at day 4 after injection of HgCl2. CD8+ T lymphoblasts were significantly increased, which were predominantly CD45RC(hi), and which showed enhanced LFA-1 expression. Furthermore, CD4+CD45RC(hi) T cells showed increased numbers of ICAM-1+ cells, whereas expression of CD134 and CD26 was relatively decreased in CD4+ T lymphoblasts. Ex vivo experiments demonstrated that HgCl2-exposure of BN rats, but not of Lewis rats, significantly enhances PMA [phorbol 12-myristate 13-acetate]-induced lymphocyte aggregation, mediated by LFA-1 and ICAM-1. In conclusion, HgCl2-injected Lewis rats show early signs of T-lymphocyte activation, predominantly on CD8+ cells. Strain-dependent effects of HgCl2 on cell adhesion molecules and expression of CD134 may play an important role in development of either autoimmunity or immune suppression.

Effects of HgCl2 on the expression of autoimmune responses and disease in diabetes-prone (DP) BB rats

Repeated exposure of Brown Norway (BN) rats to relatively low doses of HgCl2 induces autoantibodies to renal antigens (e.g., laminin) and a membranous glomerulonephropathy characterized by proteinuria. In contrast, Lewis (LEW) rats are "resistant" to the autoimmune effects of mercury and, when exposed to this metal, are protected against experimental autoimmune encephalomyelitis (EAE) and Heymann's nephritis. To date, there is no information on "suppressive" effects of mercury in naturally occurring (so-called "spontaneous") rat models of autoimmune disease. Therefore, we have administered HgCl2 to diabetes-prone (DP) BB rats, animals that spontaneously develop both insulin-dependent diabetes mellitus (IDDM) and thyroiditis. We found that DP rats treated with mercury or water for a period of 40-125 days developed autoantibodies to thyroglobulin, with a higher incidence in HgCl2-injected animals (92% vs. 56% in H2O-injected controls). A novel finding of our study was the detection of autoantibodies to laminin in the same rats, again with an increased incidence after HgCl2 treatment (83% vs. 44%). IgG2a was the most frequently detected isotype of antibodies to laminin, followed by IgG1, IgG2b and IgG2c. The IgG isotype profile suggests that treatment with HgCl2 may activate both Th1 and Th2 lymphocytes in BB rats. In spite of these stimulatory effects on autoantibody responses, we found that there was no difference in the incidence of IDDM and thyroiditis between HgCl2-treated and control animals. We conclude that the suppressive effects of mercury previously observed in EAE and Heymann's nephritis of LEW rats do not occur in "spontaneous" autoimmune IDDM and thyroiditis of BB rats. Therefore, immune suppression caused by HgCl2 cannot be considered a common phenomenon, but may be a genetically determined characteristic of LEW rats, possibly related to a specific or unique cytokine profile of this particular rat strain. In contrast, while mercury does not seem to recruit, induce or rescue regulatory T cell function in DP rats, it does stimulate autoantibody responses in these animals.

Differential regulation of expression of the MHC class II molecules RT1.B and RT1.D on rat B lymphocytes: effects of interleukin-4, interleukin-13 and interferon-gamma

Susceptibility to induction of both T helper 1- (Th1) and Th2-mediated autoimmunity is multifactorial and involves genetic linkage to the major histocompatibility complex (MHC) class II haplotype. Brown Norway (BN) rats exposed to mercuric chloride develop a Th2-dependent systemic autoimmunity, whereas Lewis rats, which are highly susceptible to Th1-mediated autoimmunity, develop immune suppression after mercuric chloride exposure. Exposure to mercuric chloride is known to enhance B-lymphocyte expression of the MHC class II molecule RT1.B, predominantly in BN rats. We demonstrate that, in contrast, expression of RT1.D was unmodified on these B cells, whereas both RT1.B and RT1.D were up-regulated on epithelial cells. Regulation of B-cell MHC class II isotype expression was further studied in vitro, using BN rat lymph node (LN) cells. Interleukin-4 (IL-4) strongly enhanced B-cell expression of RT1.B (2.8-fold), whereas RT1.D expression was only slightly, although significantly, modified (1.2-fold). B cells from Lewis rats showed a similar IL-4-induced enhancement of RT1.B expression (2.5-fold), whereas, in contrast, RT1.D expression was unmodified. Exposure of LN cells from BN rats to interferon-gamma induced a moderate increase of B-cell MHC class II expression, predominantly of RT1.B. Strong and rapid enhancement of B-cell RT1.D expression was observed after stimulation by phorbol 12-myristate 13-acetate and ionomycin. Rat IL-13 did not modify B-cell MHC class II expression; however, it induced typical morphological changes in peritoneal macrophages. These experiments demonstrate isotype-specific and strain-dependent regulation of MHC class II expression on rat B lymphocytes, which may be of pathophysiological relevance for the strain-dependent susceptibility for Th1- or Th2-mediated autoimmunity.

Thiol levels in CD134-defined subsets of rat T lymphocytes: possible implications for HgCl2-induced immune dysregulation

CD134 (OX40), a member of the tumour necrosis factor receptor family, is expressed on activated T cells and mediates T and B cell costimulation. Its expression is increased after exposure to the thiol-binding compound HgCl2 in BN rats, but not in Lewis rats, in association with induction of a T cell-dependent systemic autoimmune syndrome only in BN rats. Intracellular thiols are involved in regulation of activation and death in T lymphocytes. Therefore, we examined intracellular thiol levels in CD134-defined T cell subsets from BN and Lewis rats. Levels of total thiols and glutathione (GSH) were significantly higher in CD134+CD4+ cells than in CD134+CD4+ cells in both strains. In Lewis rats, total thiol levels in CD4+CD134+ cells, but not in CD4+CD134+ cells, were higher than in BN rats. In contrast, BN rats showed higher GSH levels in CD4+CD134+ cells, but not in CD4+CD134+ cells. In vitro exposure to HgCl2 decreased intracellular thiol levels, predominantly in CD4+CD134+ cells. Furthermore, HgCl2-induced enrichment of CD134+ viable cells was inversely correlated to HgCl2-induced cell death. Strain-dependent differences in thiol levels in CD134-defined subsets of CD4+ lymphocytes and subset-specific modification of thiol levels may contribute to differential lymphocyte activation by oxidizing chemicals.

Transforming growth factor beta (TGF-beta)-dependent inhibition of T helper cell 2 (Th2)-induced autoimmunity by self-major histocompatibility complex (MHC) class II-specific, regulatory CD4(+) T cell lines

Autoreactive anti-MHC class II T cells are found in Brown Norway (BN) and Lewis (LEW) rats that receive either HgCl2 or gold salts. These T cells have a T helper cell 2 (Th2) phenotype in the former strain and are responsible for Th2-mediated autoimmunity. In contrast, T cells that expand in LEW rats produce IL-2 and prevent experimental autoimmune encephalomyelitis, a cell-mediated autoimmune disease. The aim of this work was to investigate, using T cell lines derived from HgCl2-injected LEW rats (LEWHg), the effect of these autoreactive T cells on the development of Th2-mediated autoimmunity. The five LEWHg T cell lines obtained protect against Th2-mediated autoimmunity induced by HgCl2 in (LEW x BN)F1 hybrids. The lines produce, in addition to IL-2, IFN-gamma and TGF-beta, and the protective effect is TGF-beta dependent since protection is abrogated by anti-TGF-beta treatment. These results identify regulatory, TGF-beta-producing, autoreactive T cells that are distinct from classical Th1 or Th2 and inhibit both Th1- and Th2-mediated autoimmune diseases.

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.

CD4 T suppressor cells mediate interferon tau protection against experimental allergic encephalomyelitis

Interferon tau is a type I IFN that was originally identified as a pregnancy recognition hormone produced by trophoblast cells. It is as potent an antiviral agent as IFN alpha and IFN beta, but lacks the toxicity associated with high concentrations of these IFNs in tissue culture and in animal studies. We recently showed that IFN tau, like IFN beta, can prevent the development of experimental allergic encephalomyelitis (EAE). We report here that IFN tau prevents EAE in mice by induction of suppressor cells and suppressor factors. Suppressor cells can be induced by IFN tau in tissue culture, and in vivo by either intraperitoneal injection or by oral administration to mice. Incubation of suppressor cells with myelin basic protein (MBP)-sensitized T cells blocked or delayed the MBP-induced proliferation. Further intraperitoneal injection of suppressor cells into mice blocked induction of EAE by MBP. Suppressor cells possessed the CD4 T cell phenotype, and produced soluble suppressor factors that inhibited MBP activation of T cells from EAE mice. The suppressor factors were found to be IL-10 and TGF beta, which acted synergistically to inhibit the MBP activation of T cells from EAE mice. These findings are important for understanding the mechanism(s) by which type I IFNs protect against autoimmune disease.

Pretreatment of lymphocytes with mercury in vitro induces a response in T cells from genetically determined low-responders and a shift of the interleukin profile

Mercury can induce autoimmune disease in susceptible mouse strains. We found that in vitro mercuric chloride induced a high proliferative response in spleen lymphocytes from mercury-susceptible SJL mice, but a low response in resistant mice, such as C57BL/6 (H-2b), A/J (H-2a) and CBA (H-2k) mice. However, a high proliferative response was obtained with lymphocytes from all tested low-responder mice by pretreating them in vitro for 1-3 days with mercuric chloride and then wash away the excess mercury. Both CD4+ and CD8+ T cells were activated in the restored response, but CD4+ T cells was the major responding cell population, as in high-responder mice. We also measured the cytokine production at the protein level after mercury stimulation in vitro. We found that in mercury stimulation the different culture conditions resulted in different patterns of cytokine production. The continuous presence of mercury induced interleukin-2 (IL-2) and interferon-gamma, but not IL-4 production in spleen cells from both high- and low-responder mice. In contrast, by pretreating the cells with mercury and then washing, spleen cells from both high and low-responder mice produced IL-4. Our results suggest that spleen cells from both mercury-susceptible and -resistant mice have the potential to respond to mercury in vitro and produce both Th1- and Th2-type cytokines. But the mercury-induced cytokine profile can shift depending on the conditions for activation.

Th1/Th2 cytokine gene expression after mercuric chloride in susceptible and resistant rat strains

Mercuric chloride (HgCl2) has contrasting effects on different rat strains: susceptible strains, e.g. Brown Norway (BN) develop polyclonal B cell activation, multiple autoantibodies and widespread tissue injury. Lewis (LEW) rats are resistant: no autoimmune response occurs after HgCl2; instead, there is immunosuppression. We have previously shown, by fully quantitative polymerase chain reaction (PCR), up-regulation of interleukin-4 (IL-4) gene expression in HgCl2-treated BN rats, implicating Th2 cells in the autoimmune syndrome. Involvement of the reciprocal Th1 subset, producing interferon-gamma (IFN-gamma), in resistance of LEW rats to HgCl2 has been suggested. We now report extensive analysis of Th1 and Th2 cytokine gene expression in spleen and lymph nodes of susceptible (BN) and resistant (LEW) rats after HgCl2. IL-4 and IFN-gamma were analyzed by quantitative PCR, other cytokines were assessed using semiquantitative PCR: the relative merits of these two techniques are discussed. We show pronounced up-regulation of IL-4 and more modest up-regulation of IFN-gamma in BN rats, but no up-regulation of either in LEW rats. Baseline levels of IFN-gamma were higher in Lew rats. Semiquantitative PCR showed increased expression of IL-2, IL-6 and IL-10 in BN; in LEW rats only IL-10 was increased. There was no marked change in IL-5, IL-13 or transforming growth factor-beta (TGF-beta) in either strain. These data further support the key role of IL-4 in HgCl2-induced autoimmunity, and suggest that failure of up-regulation of IL-4, together with higher baseline IFN-gamma expression, accounts for resistance of LEW rats to HgCl2. However, neither IFN-gamma nor TGF-beta can be implicated in HgCl2-induced immunosuppression in the LEW rat in vivo: our data suggest a role for IL-10 in this phenomenon.

Metal ion induced autoimmunity

Metal-induced autoimmunity is a well established but poorly understood phenomenon. Recent work has begun to elucidate the molecular interactions of metal ions with immune cells and self-proteins. Metal-induced presentation of cryptic self-peptides emerges as a possible mechanism for activation of 'metal-specific' T cells, challenging the hypothesis of a random polyclonal activation of T and B cells by metals. A preferential T-helper cell type 2 response is involved in metal ion induced systemic autoimmune disease.

Mercuric chloride, a chemical responsible for T helper cell (Th)2-mediated autoimmunity in brown Norway rats, directly triggers T cells to produce interleukin-4

Mercurials may induce immune manifestations in susceptible individuals. Mercuric chloride (HgCl2) induced autoimmunity in the Brown Norway (BN) strain but an immuno-suppression in the Lewis strain with, however, autoreactive anti-class II T cells present in both strains. In the present study we looked at modifications of cytokine production by PCR and cytofluorometric analyses in normal BN and Lewis rat splenocytes, cultured with or without HgCl2. Unfractionated BN rat splenocytes and purified T cells exposed to HgCl2 expressed high levels of IL-4 mRNA. Increase in class II and CD23 molecule expression on B cells was partly inhibited by anti-IL-4 mAb showing that IL-4 was produced. By contrast, no overexpression of IL-4 mRNA could be seen in Lewis rats. Although an increase in class II molecule expression was observed suggesting that other T helper cell 2 cytokines were produced, there was also a concomitant decrease in CD23 molecule expression that was abrogated after addition of an anti-IFN-gamma mAb to the culture. IFN-gamma mRNA production was induced in unfractionated spleen cells and T cells from both strains after HgCl2 exposure. Altogether these findings demonstrate that HgCl2 has very early direct effects on cytokine production and that these effects differ depending on the strain. The early effect on IL-4 production observed on BN rat spleen cells and T cells may explain that the autoreactive anti-class II T cells that are found in HgCl2-injected BN rats have a Th2 phenotype.

Self-reactive anti-class II T helper type 2 cell lines derived from gold salt-injected rats trigger B cell polycolonal activation and transfer autoimmunity in CD8-depleted normal syngeneic recipients

Brown Norway (BN) rats given gold salts develop an autoimmune syndrome with an immune complex-type glomerulonephritis in the context of a polyclonal B cell activation that was suspected to be due to the emergence of anti-self major histocompatibility complex (MHC) class II T cells. In the present study, six anti-self MHC class II T cell lines have been derived from six gold salt-treated rats by repeated stimulations with normal syngeneic MHC class II-bearing cells. The T cell lines proliferated in the presence of self MHC class II-positive B cell-enriched or B cell-depleted cells and the proliferation was inhibited by preincubating stimulator cells with an anti-IA monoclonal antibody. The T cell lines produced interleukin (IL)-4 only or IL-4 and some interferon (IFN)-gamma and could, therefore, be considered as T helper type 2 (Th2) and Th0 cells, respectively. They triggered normal syngeneic B cells to produce in vitro IgE, anti-DNA, anti-laminin and anti-2,4-6-trinitrophenol antibodies through, at least in part, cognate interactions. More interestingly, these lines when transferred into normal BN rats induced an autoimmune syndrome similar to or even more severe than the one observed in the active gold model, provided the recipients were CD8 depleted. These manifestations included a dramatic increase in serum IgE concentration and the production of anti-DNA and anti-laminin antibodies. In addition, all recipients displayed an autoimmune glomerulonephritis due to anti-laminin antibodies, granular IgG deposits in the interstitium, in the vessel walls and along the tubular basement membranes and a severe tubulointerstitial nephritis with marked mononuclear cell infiltration. An anti-ovalbumin T cell line that produced IL-4 and low amounts of IFN-gamma was used as a control and did not induce autoimmunity. These results demonstrate for the first time the ability of autoreactive Th2 as well as Th0 cell lines to induce antibody-mediated autoimmunity. They also show that CD8+ cells play a crucial role in the control of such autoreactive cells. Finally, this work suggests that Th2 cells could initiate cell-mediated reactions either directly or indirectly.

Improvement of TH1 functions during the regulation phase of mercury disease in brown Norway rats

Brown Norway (BN) rats are poor responders to T-cell mitogens and alloantigens when compared to Lewis (LEW) rats. This is dependent partly upon a defect in IL-2 production. The TH2-mediated immune abnormalities observed in BN rats injected with mercuric chloride (HgCl2) are self-limited and it is probable that this regulation phase involves TH1-like cells. This paper reports on a study of the ability of lymph node cells (LNC) from normal BN and LEW rats and from HgCl2-injected BN rats to produce IL-2 and to proliferate when stimulated in vitro by Con A or alloantigens in mixed lymphocyte reaction (MLR), as well as to develop a cytotoxic T lymphocyte (CTL) response to alloantigens. This study will confirm that LNC from BN rats proliferate less than LNC from LEW rats, that the former produce less IL-2 than the latter, and that the proliferative response is restored partially after addition of IL-2. In addition, it is shown (1) that the CTL response is defective in normal BN rats when compared to that of normal LEW rats, and (2) that, after the second week of HgCl2 injections, the proliferative responses to Con A and alloantigens are improved as well as IL-2 production, and a complete restoration of CTL function is observed. These results show that normal BN rats are deficient in the induction of TH1-like cells and that, from the second week of HgCl2 injections, these TH1 functions improve.