Kinetics and pathogenicity of autoantibodies induced by mercuric chloride in the brown Norway rat

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

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

Type of fish consumed and thyroid autoimmunity in pregnancy and postpartum

Fish consumption or supplementation with omega-3 fatty acids was reported to cure and/or prevent autoimmune and nonautoimmune disorders. Serum positivity for thyroid autoantibodies is a predictive marker of postpartum thyroiditis and postpartum depression. We hypothesized that stable consumption of the omega-3-rich oily fish was associated with a more favorable profile of serum thyroid antibodies throughout pregnancy and early postpartum compared with stable consumption of swordfish, a predator that concentrates pollutants. We prospectively measured serum thyroglobulin antibodies and thyroperoxidase antibodies in pregnancy (first, second trimesters) and postpartum (day 4), in 236 thyroid disease-free, nonsmoker Caucasian women with stable dietary habits. We did not measure thyroid autoantibodies prior to pregnancy. Women were divided into groups A (n = 48; swordfish), B (n = 52; oily fish), C (n = 68; swordfish + other fish, not necessarily oily fish), and D (n = 68; fish other than swordfish and oily fish). Major endpoints were positivity rates and serum concentrations of the two autoantibodies. We resorted to previous studies for the estimated content of fatty acids and microelements in the consumed fish. Positivity rates and serum concentrations of both antibodies were the greatest in group A and the lowest in group B (P < 0.001 and P < 0.05 to < 0.001, respectively). Relationship between monthly fish consumption and serum concentrations of either antibody was direct in group A but inverse in group B. The estimated content of omega-3 fatty acids in fish consumed by group B was the greatest (P < 0.001 vs. any other group). These data reinforce recommendations that pregnant women should avoid consuming swordfish and indicate consumption of oily fish as a favorable alternative. Because thyroid autoantibodies are markers of autoimmune-related postpartum problems, our data suggest a dietary prophylaxis of such problems.

Temporal evolution of human autoantibody response to cytoplasmic rods and rings structure during anti-HCV therapy with ribavirin and interferon-α

Autoantibodies to inosine monophosphate dehydrogenase-2 (IMPDH2), an enzyme involved in de novo biosynthesis of guanine nucleotides, are observed in a subset of hepatitis C virus (HCV) patients receiving interferon alpha (IFN-α) plus ribavirin. Anti-IMPDH2 antibodies display a peculiar cytoplasmic "rod/ring" (RR) pattern in IIF-HEp-2. We examined the dynamics of anti-RR autoimmune response with respect to immunoglobulin isotypes, titer, avidity, and protein targets in 80 sequential samples from 15 HCV patients (plus 12 randomly selected anti-RR-positive, totalizing 92 samples) collected over an 18-month period, including samples collected before, during, and after IFN-α + ribavirin treatment. Immunoprecipitation showed reactivity with the 55 kDa IMPDH2 protein in 12/15 patients (80 %) and 11/15 (73 %) reacted with IMPDH2 in a sandwich ELISA. During treatment, anti-IMPDH2 autoantibodies hit their highest levels after 6-12 months of treatment and decreased post-treatment, while anti-HCV antibodies levels were stable over time. Anti-IMPDH2 IgM levels increased up until the sixth month of treatment and remained stable thereafter, while IgG levels increased steadily up to the twelfth month. Both IgG and IgM decreased during the post-treatment period. IgG avidity increased steadily up to the twelfth month of treatment. In conclusion, this study showed that the temporal kinetics of IFN-α + ribavirin-induced humoral autoimmune response to IMPDH2 exhibited a considerably delayed pace of increase in antibody levels and avidity as well as in isotype class switch in comparison with a conventional humoral response to infectious agents. These unique findings uncover intriguing differences between the autoimmune response and the immune response to exogenous agents in humans.

Mercury and thyroid autoantibodies in U.S. women, NHANES 2007-2008

Associations between positive thyroid autoantibodies and total blood mercury in women were evaluated using the National Health and Nutrition Examination Survey (NHANES), 2007-2008. Women are at increased risk for autoimmune disorders, mercury exposure has been associated with cellular autoimmunity and mercury accumulates in the thyroid gland. We used multiple logistic regression to evaluate the associations between total bloodmercury and thyroglobulin autoantibody antibody positivity and thyroid peroxidase autoantibody positivity in non-pregnant, non-lactating women aged 20 and older not currently using birth control pills or other hormone therapies, adjusted for demographic factors, menopausal status, nutrient intake and urine iodine (n=2047). Relative to women with the lowest mercury levels (≤0.40 μg/L), women with mercury >1.81 μg/L (upper quintile) showed 2.24 (95% CI=1.22, 4.12) greater odds for thyroglobulin autoantibody positivity (p(trend)=0.032); this relationship was not evident for thyroid peroxidase autoantibody positivity. Results suggest an association between mercury and thyroglobulin autoantibody positivity.

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.

Mercuric chloride-induced autoimmunity

This unit describes methods for inducing autoimmune disease in Brown Norway rats through HgCl(2) injections as well for assessing parameters that characterize the disease by serum IgE concentration assays, anti-laminin antibody measurement, and renal immunofluorescence studies to detect autoantibodies. Also covered are disease induction using autoreactive CD4(+) T(H)2 anti-self MHC class II molecules and preparation of T cell lines. IL-4 is produced very early after the first HgCl(2) injection (beginning at day 3, peaking at day 14, and continuing up to day 30). Thus, IL-4 mRNA expression may be detected in spleen and lymph nodes from HgCl(2)-injected BN rats. The fact that HgCl(2) induces in vitro mRNA IL-4 gene expression in normal BN T cells but not in LEW T cells is probably crucial to susceptibility to the development of autoimmunity in the sense that it may condition the development of autoreactive T cells into pathogenic T(H)2 cells; a test for this condition is therefore also included.

Therapeutic effect of all-trans-retinoic acid (at-RA) on an autoimmune nephritis experimental model: role of the VLA-4 integrin

Background

Mercuric chloride (HgCl₂) induces an autoimmune nephritis in the Brown Norway (BN) rats characterized by anti-glomerular basement membrane antibodies (anti-GBM Ab) deposition, proteinuria and a severe interstitial nephritis, all evident at day 13 of the disease. We assessed the effects of all-trans retinoic acid (at-RA) in this experimental model. At-RA is a vitamin A metabolite which has shown beneficial effects on several nephropathies, even though no clear targets for at-RA were provided.

Methods

We separated animals in four different experimental groups (HgCl₂, HgCl₂+at-RA, at-RA and vehicle). From each animal we collected, at days 0 and 13, numerous biological samples: urine, to measure proteinuria by colorimetry; blood to determine VLA-4 expression by flow citometry; renal tissue to study the expression of VCAM-1 by Western blot, the presence of cellular infiltrates by immunohistochemistry, the IgG deposition by immunofluorescence, and the cytokines expression by RT-PCR. Additionally, adhesion assays to VCAM-1 were performed using K562 α4 transfectant cells. ANOVA tests were used for statistical significance estimation.

Results

We found that at-RA significantly decreased the serum levels of anti-GBM and consequently its deposition along the glomerular membrane. At-RA markedly reduced proteinuria as well as the number of cellular infiltrates in the renal interstitium, the levels of TNF-α and IL-1β cytokines and VCAM-1 expression in renal tissue. Moreover, we reported here for the first time in an in vivo model that at-RA reduced, to basal levels, the expression of VLA-4 (α4β1) integrin induced by mercury on peripheral blood leukocytes (PBLs). In addition, using K562 α4 stable transfectant cells, we found that at-RA inhibited VLA-4 dependent cell adhesion to VCAM-1.

Conclusion

Here we demonstrate a therapeutic effect of at-RA on an autoimmune experimental nephritis model in rats. We report a significant reduction of the VLA-4 integrin expression on PBLs as well as the inhibition of the VLA4/VCAM1-dependent leukocyte adhesion by at-RA treatment. Thereby we point out the VLA-4 integrin as a target for at-RA in vivo.

Silver activates mast cells through reactive oxygen species production and a thiol-sensitive store-independent Ca2+ influx

In genetically susceptible human and/or experimental animals, heavy metals such as mercury, gold, and silver have been shown to highly induce adverse immunological reactions such as allergy and autoimmunity, in which mast cell degranulation is implicated as playing a role. We previously reported that silver activates mast cells and induces Ca2+ influx without stimulating intracellular signaling events required for activation of store-operated Ca2+ channels (SOCs). The purpose of the present study was to elucidate the possible involvement of reactive oxygen species (ROS) in the biological effects of silver. Analysis using oxidant-sensitive fluorescent probes such as dichlorodihydrofluorescein and scopoletin, as well as MCLA-amplified chemiluminescence, showed that silver induced intracellular production and/or extracellular release of ROS. Silver induced mast cell degranulation in a Ca2+ -dependent manner. Unlike IgE antigen, silver-induced Ca2+ influx was not affected by depletion of internal Ca2+ stores. Instead, the metal-induced Ca2+ influx was abolished and reversed by the cell-impermeant thiol-reducing agent dithiothreitol, indicating the regulation by oxidation of vicinal thiols on the cell surface. Consistent with this view, Ca2+ influx was blocked by the glutathione peroxidase mimetic ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one) and the superoxide dismutase mimetic manganese(III) tetrakis 4-(benzoic acid)porphyrin, but not by exogenously added catalase or superoxide dismutase. These findings indicate that silver evokes the release of ROS and oxidation of thiols critical for the activation of a Ca2+ channel other than SOC. Such a novel ROS-dependent pathway might play a role in mast cell degranulation in metal-induced allergic and autoimmune reactions.

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.

A role for alphabeta T cells in the resistant phase of the Brown Norway rat model of vasculitis

Administration of mercuric chloride (HgCl(2)) to Brown Norway rats causes Th2 dominated autoimmunity including a caecal vasculitis. Disease peaks 14 days after starting HgCl(2) after which animals immunoregulate spontaneously. In a third phase, if animals are rechallenged with HgCl(2) 6 weeks later they appear resistant, developing only attenuated disease. Previous studies suggested a role for CD8(+) cells as partial mediators of resistance but no groups had studied the role of alphabeta T cells, gammadelta T cells or natural killer (NK) cells in resistance. We used adoptive transfer and in vitro cell depletion to show that alphabeta T cells are also partially responsible for resistance. Donor animals were treated with HgCl(2) or saline and killed 21 days later. Cells from donor spleens were transferred into recipient animals which were challenged with HgCl(2) and killed 14 days later. Test recipients received spleen cells from HgCl(2)-treated donors after in vitro depletion of one subset of cells. Recipients receiving spleen cells from saline-treated donors remained susceptible to HgCl(2)-induced vasculitis; those receiving spleen cells from HgCl(2)-treated donors were resistant. Animals receiving alphabeta T-cell-depleted spleen cells from HgCl(2)-treated donors showed partial reversal of resistance. Our results suggest a role for alphabeta T cells in the resistant phase of the Brown Norway rat model of vasculitis.

Resistance to re-challenge in the Brown Norway rat model of vasculitis is not always complete and may reveal separate effector and regulatory populations

Administration of mercuric chloride to Brown Norway rats results in T helper type 2 (Th2)- dominated autoimmunity characterized by high immunoglobulin E (IgE) concentrations, the production of multiple IgG autoantibodies, including those to glomerular basement membrane (GBM), arthritis and caecal vasculitis. After 14 days animals immunoregulate and auto-immunity resolves even if mercuric chloride injections are continued. In a third phase, if animals are re-challenged with mercuric chloride 6 weeks later, they show only attenuated autoimmunity with lower anti-GBM antibody concentrations and arthritis scores. Resistance to the induction of anti-GBM antibodies can also be achieved following an initial challenge with low-dose (one-tenth standard dose) mercuric chloride. We have now studied this resistant phase in more detail. We have shown, first, that following an initial full-dose mercuric chloride challenge, resistance also affects susceptibility to caecal vasculitis. Second, following an initial full-dose mercuric chloride challenge, the IgE response upon re-challenge is initially accelerated but subsequently enters a resistant phase and third, following an initial challenge with low-dose mercuric chloride, resistance is also seen to the induction of caecal vasculitis but is not seen in IgE serology (where results suggest competing effector and regulatory cell populations). Studying such regulatory phases in animal models of autoimmunity may be of benefit in the future in designing new therapies for human vasculitis.

A central role for the mast cell in early phase vasculitis in the Brown Norway rat model of vasculitis: a histological study

Administration of mercuric chloride (HgCl(2)) to Brown Norway rats causes Th2-dominated autoimmunity with raised immunoglobulin E concentrations and gut vasculitis, both of which are T-cell dependent, peak at 14 days after starting HgCl(2) and then spontaneously resolve. If animals are re-challenged with HgCl(2) 6 weeks after initial exposure, they are resistant to autoimmunity, developing only attenuated disease. Recently, a separate phase of early caecal vasculitis was described beginning 24 h after initiating HgCl(2) and prior to caecal entry of T cells. Previous work suggested this early vasculitis was alpha beta T-cell independent and implied a role for mast cells. We further tested this hypothesis by performing a histological study during the first 93 h following HgCl(2) challenge defining the precise relationship between gut mast cell degranulation and appearing caecal vasculitis. We also studied whether early caecal vasculitis enters a resistant phase upon re-challenge with HgCl(2). We show a direct correlation between mast cell degranulation and early caecal vasculitis following initial HgCl(2) challenge. We demonstrate resistance to re-challenge in this phase of injury, with results at re-challenge also showing a correlation between mast cell degranulation and early caecal injury.

VLA-4 integrin concentrates at the peripheral supramolecular activation complex of the immune synapse and drives T helper 1 responses

The integrin alpha 4 beta 1 (VLA-4) not only mediates the adhesion and transendothelial migration of leukocytes, but also provides costimulatory signals that contribute to the activation of T lymphocytes. However, the behavior of alpha 4 beta 1 during the formation of the immune synapse is currently unknown. Here, we show that alpha 4 beta 1 is recruited to both human and murine antigen-dependent immune synapses, when the antigen-presenting cell is a B lymphocyte or a dendritic cell, colocalizing with LFA-1 at the peripheral supramolecular activation complex. However, when conjugates are formed in the presence of anti-alpha 4 antibodies, VLA-4 colocalizes with the CD3-zeta chain at the center of the synapse. In addition, antibody engagement of alpha 4 integrin promotes polarization toward a T helper 1 (Th1) response in human in vitro models of CD4(+) T cell differentiation and naïve T cell priming by dendritic cells. The in vivo administration of anti-alpha 4 integrin antibodies also induces an immune deviation to Th1 response that dampens a Th2-driven autoimmune nephritis in Brown Norway rats. These data reveal a regulatory role of alpha 4 integrins on T lymphocyte-antigen presenting cell cognate immune interactions.

Neonatal tolerance to a Th2-mediated autoimmune disease generates CD8+ Tc1 regulatory cells

Immunological tolerance can be achieved in animals by exposure of newborn to a foreign antigen. Depending on the dose and timing of the antigenic challenge, tolerance has been reported to result in clonal deletion, anergy or active suppression. In this latter case, regulatory T cells prevent autoimmunity by suppressing the reactivity of pathogenic self-reactive T cells. We have previously reported the generation of a neonatal, mercury-specific, and dominant tolerance to autoimmunity induced by mercury salts in rats. Chronic exposure to mercury salts can lead to SLE-like autoimmune responses, mediated by autoreactive CD4+ Th2 cells, that regulate and are followed by a resistant state mediated by protective CD8+ T cells. The aim of the study was to compare the resistance to the neonatal tolerance to mercury disease, and to further characterize the CD8+ T cells endowed with regulatory capacity in the neonatal tolerance model. We report here that resistance to mercury disease is long lasting and not mercury-specific, suggesting that different CD8+ T cells are involved in resistance and neonatal tolerance, and that regulatory CD8+ Tc1 cells generated in tolerance are required to control the CD8- cell population from developing Th2-mediated autoimmunity. Upon mercury recall, CD8+ CD45RC(high) T cells, that represent the Tc1 subset in the rat, expanded and were polarized towards IFNgamma production. Interestingly, identical results were obtained with the CD8+ CD25+T cell population. Substantial amounts of FasL gene expression were detected in CD8+ T lymphocytes upon recall with the tolerogen. AICD may be one of the regulatory mechanisms used by these regulatory CD8+ Tc1 cells that control neonatal tolerance to a Th2-mediated autoimmune disorder.

Spontaneous downregulation of antibody/autoantibody synthesis in susceptible mice upon chronic exposure to mercuric chloride is not owing to a general immunosuppression

Administration of mercuric chloride into susceptible rats and mice induces a systemic autoimmune disease, which is characterized by a T-cell-dependent polyclonal B-cell activation, an increase in serum levels of immunoglobulin (Ig)G1 and IgE, production of antibodies of different specificities and development of renal IgG deposits. A peculiar feature of mercury-induced autoimmunity is that the polyclonal B-cell activation spontaneously disappears in spite of continuous injection of mercury. The exact mechanism(s) for autoregulation of mercury-induced autoimmunity is not well understood. In the present study, we analysed the regulation of mercury-induced immune/autoimmune responses in mice and tested whether spontaneous downregulation of these responses is owing to a general immunosuppression. Mercury-susceptible [SJL (H-2s)] and -resistant [DBA/2 (H-2d)] mice were injected with mercury for 4, 10, 15 and 17 weeks. Immune/autoimmune responses were monitored in these mice. Thereafter, mercury-injected mice for 17 weeks were further immunized with horse red blood cells (HRBC) to study whether the subsequent humoral immune response to a foreign antigen is suppressed. We found that except for IgG1 anti-nucleolar antibody production and renal IgG1 deposition, other characteristics of mercury-induced autoimmunity were downregulated in SJL (H-2s) mice after chronic treatment with mercury. However, these mice did not show any reduction in the number of splenic antibody-secreting cells and/or in serum titres of specific IgM, IgG1 and IgG2a anti-HRBC antibodies in response to HRBC as compared with naïve mice. Similarly, in mercury-resistant DBA/2 (H-2d) mice, chronic treatment with mercury did not either suppress specific antibody responses against HRBC. Our findings show that the autoregulation of mercury-induced immune/autoimmune responses observed after chronic treatment with mercury is not owing to a general immunosuppression.

IL-4 gene expression up-regulated by mercury in rat mast cells: a role of oxidant stress in IL-4 transcription

In the Brown Norway (BN) rat, chemical compounds [mercuric chloride (HgCl2), D-penicillamine or gold salts] induce a T(h)2-dominated autoimmune syndrome with tissue injury in the form of a vasculitis and arthritis. An early phase of vasculitis in the model occurs within 24 h of an injection of HgCl2, is alphabeta T cell independent and involves the mast cell. In addition, HgCl2 induces IL-4 mRNA in mast cells from BN rats. Our recent work has demonstrated that the balance of oxidative/antioxidative influences plays an important role in the modulation of mast cell function (degranulation) in chemically induced autoimmunity. The aim of this study was to determine, in mast cells, whether oxidative status influences IL-4 transcription and translation, which is required for the development of a T(h)2 response. Exposure of the mast cell line RBL-2H3 to HgCl2 enhanced both IL-4 mRNA and its promoter activity. Oxidative stress by hydrogen peroxide mimicked the effects of HgCl2 in enhancing IL-4 promoter activity. The enhancement of IL-4 gene expression by HgCl2 was significantly reduced by antioxidants (both sulphydryl and non-sulphydryl containing). The same pattern of regulation was also observed on IL-4 protein expression in the mast cells. These data suggest a novel mechanism of IL-4 transcriptional up-regulation by oxidative stress. Our results provide evidence to support our hypothesis that alterations in intracellular reactive oxygen species production modulate both IL-4 gene expression and mast cell function.

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.

Are animal models of vasculitis suitable tools?

Several rodent models have been proposed for various forms of systemic vasculitis. The MRL-lpr mouse has been studied extensively as a model for systemic lupus erythematosus. Backcross experiments in combination with genetic linkage studies have firmly established that the phenotype of autoimmune disease is dependent on the combination of various background genes. It has also become apparent that environmental factors, particularly infections, modulate the disease phenotype. Specific interventions, such as the treatment of Brown Norway rats with agents resulting in polyclonal B cell stimulation or immunization with human myeloperoxidase and subsequent localized perfusion with neutrophil lysosomal extract and H2O2, have provided substantial insights into the cellular and molecular mechanisms leading to the development of vasculitis and glomerulonephritis. Even though the existing models may not exactly mirror any specific human disease, they offer reproducible, highly controlled conditions to answer specific questions about pathogenesis and novel therapeutic approaches.

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.

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.

IL-2 may be a limiting factor precluding lymphocytes from genetically resistant mice from responding to HgCl2

It is unclear how HgCl2 causes autoimmune disorders in genetically predisposed rodents. We investigated the cytokine profile induced by HgCl2 in vitro, and found a high frequency of IL-2-secreting cells in splenocytes from susceptible A.SW and BALB/c mice, whereas the frequency was low in cells from resistant DBA/2 mice. More IL-2-secreting cells were induced in splenocytes from the high responder A.SW mice than in cells from the intermediate responder BALB/c mice. Unexpectedly, a similar level of IL-4 production was induced in splenocytes from BALB/c and DBA/2 mice. IL-4 production was high in unstimulated cells from A.SW mice and was further increased by HgCl2. IFN-gamma-secreting cells were detectable in splenocytes from all three strains after activation by HgCl2. The highest frequency of IL-10-secreting cells was found in splenocytes from A.SW mice after activation, whereas the frequency was lower in cells from BALB/c mice, followed by cells from DBA/2 mice. We showed that neutralizing anti-IL-2 antibody profoundly inhibited the in vitro response to HgCl2. In contrast, antibodies against IL-4, IFN-gamma and IL-10 did not significantly affect the response of splenocytes from either A.SW or DBA/2 mice. The addition of IL-2 into cultures enhanced the proliferative response to HgCl2 in splenocytes from DBA/2 mice to a level comparable with that in cells from BALB/c mice. We found no evidence for the suggestion that HgCl2 induces a Th1/Th2 imbalance in resistant/susceptible strains. We conclude that IL-2 may be a limiting factor precluding lymphocytes from resistant mice from responding to HgCl2.

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.

Non-immunoglobulin serum proteins prevent the binding of IgG from normal rats and from rats with Th2-mediated autoimmune glomerulonephritis to various autoantigens including glomerular antigens

It is now well established in normal humans and mice that purification of IgG from serum unmasks their autoantibody activity. Mercuric chloride (HgCl2) induces in Brown-Norway (BN) rats a Th2-dependent polyclonal B cell activation, a huge increase in serum IgE and IgG1 concentrations, the production of numerous autoantibodies and an autoantibody-mediated glomerulonephritis. In the present study we have compared the IgG autoantibody activity in the serum and in the purified IgG fraction from normal and HgCl2-injected BN rats. IgG autoantibodies were found to be masked in normal serum by non-immunoglobulin (nonIg) serum proteins and, provided these IgG did not encounter normal serum proteins, they could bind to glomerular antigens as assessed by immunofluorescence in a unilateral perfused kidney model. As a consequence of HgCl2-induced polyclonal activation of B cells, IgG autoantibodies were no longer complexed to non-Ig serum proteins, they were easily detected in the serum and could therefore reach their glomerular target. However, these autoantibodies could still be blocked by normal non-Ig serum proteins not only in vitro but also in a unilateral perfused kidney model so that their binding to glomerular antigens could be prevented. These findings indicate that the ratio between autoantibody level and the amount of non-Ig serum proteins may be crucial in autoantibody-mediated autoimmune diseases.

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.

Oral, perioral and systemic pathosis in HgCl2-induced autoimmunity in the BN rat

Male BN rats were repeatedly skin-injected with HgCl2 solution and sacrificed after 6, 9, 14, 21, 28 or 24 days. Mononuclear cell infiltrates were observed in the oral mucosa and in lacrimal, salivary and thyroid glands from 6-9 days onwards, with a peak at 14-21 days. Immunohistochemistry identified these cells as predominantly T cells with some NK cells but very few B cells. Reversible parenchymal changes were observed but there was no obvious persistent tissue destruction. Serum titers of IgE, IgG1, anti-laminin and anti-DNP, but not IgG2a antibodies, were raised and peaked at 14-21 days. However, there was no correlation, within animals, between these titers and the extent of mononuclear cell infiltration. Mercury was histochemically detected within dendritic cells/macrophages in the connective tissue stroma of the glands and in the oral mucosa, but no correlation was found between the distribution of mercury and the degree of inflammation. We conclude that the accumulation of mononuclear cells in oral and perioral tissues of HgCl2-treated BN rats does not represent a local immune response to tissue-retained Hg. Instead, we propose that the extravasation represents an epiphenomenon that is not necessarily deleterious to the infiltrated organ.

Alterations in intracellular reactive oxygen species generation and redox potential modulate mast cell function

The administration of mercuric chloride (HgCl2), gold compounds, or D-penicillamine to Brown Norway (BN) rats causes a T helper (Th)2 cell-associated autoimmune syndrome characterized by the production of a number of autoantibodies, marked elevation of serum IgE concentration, and tissue injury in the form of a vasculitis and arthritis. We have recently shown that the same compounds in vitro sensitize BN rat peritoneal mast cells for IgE-triggered mediator release and interleukin-4 mRNA production. We wished to test the hypothesis that these agents influence mast cell function via an effect on intracellular reactive oxygen species (ROS) production/redox balance. Mast cells were obtained from BN rats by peritoneal washout. Incubation with HgCl2, gold compounds or D-penicillamine (the latter only in the presence of copper ions) led to the intracellular production of ROS as shown by the oxidative production of the fluorescent compound 2',7'-dichlorofluorescein. Mast cells were more sensitive than splenocytes to this effect. Direct oxidative stress (exposure to H2O2) produced a similar sensitization for mediator release to that caused by HgCl2. Inhibition of ROS formation by desferrioxamine or catalase diminished the enhancement of IgE-mediated serotonin release caused by HgCl2, as did replenishment of intracellular glutathione. 2-Mercaptoethanol exacerbated the toxicity of HgCl2, perhaps due to the formation of a lipophilic complex that enhanced HgCl2 uptake. Blocking of glutathione synthesis increased the toxicity of HgCl2, but also abolished any sensitizing effect on mediator release. These results support three main predictions of our hypothesis: (1) the compounds known to influence mast cell function all lead to the generation of ROS within the mast cell; (2) direct oxidative stress causes sensitization for mediator release by the mast cell; and (3) modulation of ROS production/redox balance within the mast cell modulates the effects of these compounds on mast cell function. The balance of oxidative/antioxidative influences may play an important role in the modulation of mast cell function, particularly in the context of chemically induced autoimmunity.

The strain difference in the effect of mercuric chloride on antigen-triggered serotonin release from rat mast cells is not mediated via interferon-gamma

Previous work has shown that in vitro exposure of Brown-Norway (BN) rat peritoneal mast cells to mercuric chloride (HgCl2) causes enhancement of subsequent mediator release induced by cross-linking of surface immunoglobulin E (IgE). This enhancing effect is seen significantly less often with peritoneal cells from Lewis rats. In addition HgCl2 has been shown to suppress interferon (IFN)-gamma production by BN but not Lewis splenocytes. Given that IFN-gamma is known to inhibit mediator release by mast cells, we hypothesized that the strain difference in the effect of HgCl2 on mediator release was mediated via a differential effect on IFN-gamma release from T cells in the mixed peritoneal cell population: IFN-gamma release would be suppressed in the case of the BN rat, releasing the mast cells from inhibition and resulting in the enhancing effect of HgCl2. The aim of the study was to test two predictions of this hypothesis. Exposure of BN rat mast cells to IFN-gamma inhibited subsequent antigen-induced mediator release but did not significantly reduce HgCl2-mediated enhancement of this release. Exposure of Lewis rat mast cells to blocking concentrations of anti-IFN-gamma did not reveal any HgCl2-mediated enhancement of mediator release. These observations provide strong evidence against the hypothesis that the differential effects of HgCl2 on BN and Lewis rat mast cells are mediated via IFN-gamma. In addition the results revealed that BN rat mast cells are significantly more sensitive than Lewis rat mast cells to the inhibitory effects of IFN-gamma on antigen-induced mediator release.

Classification, pathogenesis, and treatment of systemic vasculitis

Patients with systemic vasculitis (SV), especially Wegener's granulomatosis and microscopic polyangiitis, regularly present with renal involvement. Although considered a rare disease, either the incidence of SV is increasing or it is being increasingly recognized. Accurate classification systems are required to allow comparison of data from different groups investigating and treating these patients. Systemic vasculitis is known to be an autoimmune disease, but the mechanisms of pathogenesis have not been established, despite many studies on this topic in recent years. Most of this work has been done in vitro, although development of animal models is underway. Patient and renal survival have improved with aggressive immunosuppressive treatment, but morbidity is high and controversies remain in establishing the most effective regimens with minimum adverse effects. In this review we discuss the classification of SV, review the current knowledge of pathogenic mechanisms, and consider the relative merits of different treatment protocols.

Compounds that induce autoimmunity in the brown Norway rat sensitize mast cells for mediator release and interleukin-4 expression

Brown Norway (BN) rats given mercuric chloride (HgCl2), gold (Au) salts or D-penicillamine develop a T helper 2 (Th2) cell-mediated autoimmune syndrome. The recent observation of tissue injury within 24 h of HgCl2 treatment suggested the involvement of a non-T cell. We therefore examined the effect of these compounds on rat mast cells in vitro. Incubation of BN rat peritoneal mast cells with HgCl2 enhanced the release of serotonin in response to IgE cross-linking agents. Mast cells from Lewis rats, a strain not susceptible to the autoimmune syndrome in vivo, were affected to a lesser extent. The effect was observed with purified BN mast cells, suggesting a direct action. Similar effects were seen with D-penicillamine in the presence of copper ions, a combination that produces hydrogen peroxide, and Au. HgCl2 caused significant induction of interleukin (IL)-4 mRNA in mast cells from BN, but not Lewis rats. The data demonstrate a novel enhancing effect of a number of compounds on mast cell mediator release, and an inducing effect of HgCl2 on mast cell IL-4, expression. These findings are consistent with our hypotheses that mast cells may contribute to early tissue injury, and also, via production of IL-4, may initiate and/or augment, the Th2 response in the BN rat model of chemical-induced autoimmunity.

Animal models in ANCA-vasculitis

The animal models described to date suggest pathogenicity of ANCA. Unfortunately, none of the models unequivocally proves that ANCA are pathogenic. Further search for a suitable animal model to document or exclude causal significance of ANCA in vasculitis is needed.

Interleukin-4 gene expression in mercury-induced autoimmunity

Mercuric chloride (HgCl2) induces autoimmunity in Brown Norway (BN) rats, with necrotizing vasculitis in the gut. Circumstantial evidence implicates the Th2 subset of CD4+ T lymphocytes, which produces IL-4. We developed a quantitative polymerase chain reaction (PCR) technique to quantify IL-4 gene expression. A phagemid containing rat IL-4 cDNA was modified to act as the template for a synthetic RNA construct; a known amount of synthetic RNA was added to total RNA from spleen and caecum of BN rats at various times after HgCl2, followed by reverse transcriptase PCR. IL-4 gene expression increased markedly in spleen and caecum after HgCl2. Splenic levels peaked by 10 days at approximately five-times baseline, then returned towards normal as the autoimmune response was spontaneously regulated. Caecal IL-4 expression peaked at 48 h, at which time we observed a previously unreported early phase of tissue injury, with necrotizing vasculitis qualitatively similar to that reported previously in the later phases of the model. These data support a key role for IL-4 in this experimental model of autoimmunity. The quantitative PCR technique can be modified for analysis of other cytokines, allowing further investigation of the role of T cell subsets in this model.

Characteristics of polyreactive and monospecific IgG anti-laminin autoantibodies in the rat mercury model

Brown-Norway (BN) rats injected with HgCl2 produce anti-laminin antibodies responsible for an autoimmune glomerulonephritis. The properties of three IgG1 monoclonal antibodies (mAb) previously obtained in this model, and of immunoglobulins eluted from kidneys of diseased rats, were compared in the present study. Two mAb (Hg15 and Hg16) recognized laminin only, while the third one (Hg17) was polyreactive, as were some of the kidney-eluted immunoglobulins; they reacted with laminin and with several other antigens including 2,4,6-trinitrophenyl (TNP). The Hg17 mAb and kidney-eluted polyreactive antibodies were affinity purified using a TNP-bovine serum albumin (BSA) column; their affinity for TNP was high (2 x 10(-8)M, and 1 x 10(-8)M, respectively) but less than that of a TNP-specific (LO-DNP-2) mAb (2 x 10(-11) M). The Hg17 mAb and kidney-eluted antibodies reacted more effectively with TNP28-BSA than with TNP8.5-BSA, while the TNP-specific mAb reacted equally well with both conjugates. The Hg17 mAb was the most cationic (pI: 7) of the anti-laminin mAb and this was even more evident when F(ab')2 fragments were studied (pI: 8.2). The polyreactive kidney-eluted immunoglobulins that bound TNP were also more cationic (pI: 7.4-9.3) than the fraction that did not recognize TNP (pI: 5.8-8.6). The anti-laminin mAb bound in vivo to the glomerular basement membrane, but only the Hg17 mAb could be eluted with DNP alone. This study shows that polyreactive anti-laminin antibodies are produced during this autoimmune disease, and indicates that they may have pathogenic potential.

Use of methyl prednisolone and antioxidants in mercuric chloride-induced experimental vasculitis

The systemic vasculitides are characterized by necrotizing inflammation of blood vessels. Neutrophils are implicated in tissue damage by their presence at the site of injury. They can mediate injury by release of cellular contents including proteinases, cytokines and reactive oxygen species. Antioxidants such as vitamin E and N-acetyl cysteine (NAC) may therefore be predicted to ameliorate oxidative damage in vivo and could be a cheap and non-toxic form of therapy. We examined this hypothesis in an experimental model of vasculitis which has some similarities to human disease, and in which depletion of neutrophils ameliorates tissue injury. Mercuric chloride (HgCl2) treatment induces an autoimmune syndrome and necrotizing leucocytoclastic vasculitis in the Brown Norway (BN) rat; anti-myeloperoxidase (MPO) and anti-glomerular basement (GBM) antibodies are present, and vasculitis is reduced by antimicrobials. Methyl prednisolone given intravenously was effective in reducing tissue injury, demonstrating that the model was responsive to a treatment used in man. Vitamin E and NAC were given as daily injections intraperitoneally to BN rats either before, during or after HgCl2 administration. Serial blood samples were taken for anti-MPO and IgE antibodies, which were assayed by ELISA. Necropsies were performed on animals killed at peak disease. At doses of 50-200 mg/kg per day vitamin E had no beneficial effect on tissue injury, regardless of timing of treatment. NAC at 100 or 200 mg/kg also had no significant protective effect on vasculitis. Autoantibody and IgE levels were not affected by either methyl prednisolone or the antioxidants. The lack of benefit of vitamin E and NAC suggests that oxidative damage, whether generated by neutrophils or other cells, does not play a major role in the pathogenesis of vasculitis, and that antioxidant therapy is unlikely to be of benefit in systemic vasculitis in man.

In vivo treatment with a monoclonal antibody to T helper cells in experimental autoimmune glomerulonephritis in the BN rat

Experimental autoimmune glomerulonephritis (EAG) was induced in brown Norway (BN) rats by a single i.m. injection of homologous glomerular basement membrane (GBM) in Freund's complete adjuvant. This model of anti-GBM disease is characterized by the development, over several weeks, of circulating and deposited anti-GBM antibodies, accompanied by albuminuria. We examined the effects of treatment with MoAb W3/25 (anti-CD4) at different doses, starting at the time of immunization and continued for the duration of the study or for a limited period only. Continued treatment with W3/25, at a dose of 5 or 10 mg/kg intraperitoneally three times per week for 4 weeks, produced a marked reduction in circulating anti-GBM antibodies, absence of detectable deposited antibody and virtual absence of albuminuria. When W3/25 treatment, at 5 or 10 mg/kg, was stopped after 2 weeks, there was still a significant reduction in anti-GBM antibodies and albuminuria at 4 weeks. A similar effect on the disease was achieved when W3/25 was administered only three times during the first week at a dose of 30 mg/kg. Animals injected with W3/25 at a dose of 10 mg/kg through the course of disease showed < 10% W3/25+ cells by FACS analysis of splenic lymphocytes at week 4, while controls and animals treated for shorter periods showed > 30% W3/25+ cells. These results demonstrate that W3/25 can prevent the development of EAG, and that this effect is not dependent on persistent depletion of T cells. Further work is necessary to determine whether anti-T cell therapy is effective in established EAG, and may be worth investigating in human anti-GBM disease.

Regulatory role of OX22high T cells in mercury-induced autoimmunity in the brown Norway rat

The monoclonal antibody OX22 defines a functional split within CD4+ T cells in the rat, with OX22high cells mainly producing interleukin 2 (IL-2) and interferon gamma and responsible for delayed-type hypersensitivity responses, and OX22low cells mainly producing IL-4 and -5 and responsible for providing B cell help. There are reciprocal interactions between OX22high and OX22low cells, and it has been suggested that the OX22low subset has a role in the prevention of autoimmunity. We have used OX22 in vivo to define the role of these subsets in mercuric chloride-induced autoimmunity in the Brown Norway rat. In this model, there is polyclonal B cell activation and animals develop widespread tissue injury. Treatment of thymectomized animals with OX22 led to a profound reduction in the number of OX22high T cells in the peripheral blood. OX22-treated animals consistently developed more severe tissue injury than controls given an irrelevant antibody of the same isotype. Control animals pretreated with broad spectrum antimicrobial drugs showed milder tissue injury, but this protective effect of antimicrobials was lost in OX22-treated animals. Transfer of naive T cells to OX22-treated animals provided protection, but if T cells were depleted in vitro of OX22high cells before transfer, this effect was lost. These data provide evidence for a protective immunoregulatory role for OX22high T cells in mercuric chloride-induced autoimmunity.

Markers of early renal changes induced by industrial pollutants. I. Application to workers exposed to mercury vapour

Several markers of renal changes have been measured in a cohort of 50 workers exposed to elemental mercury (Hg) and in 50 control workers. After application of selection criteria 44 exposed and 49 control workers were retained for the final statistical analysis. Exposed workers excreted on average 22 micrograms Hg/g creatinine and their mean duration of exposure was 11 years. Three types of renal markers were studied--namely, functional markers (creatinine and beta 2-microglobulin in serum, urinary proteins of low or high molecular weight); cytotoxicity markers (tubular antigens and enzymes in urine), and biochemical markers (eicosanoids, thromboxane, fibronectin, kallikrein, sialic acid, glycosaminoglycans in urine, red blood cell membrane negative charges). Several bloodborne indicators of polyclonal activation were also measured to test the hypothesis that an immune mechanism might be involved in the renal toxicity of elemental Hg. The main renal changes associated with exposure to Hg were indicative of tubular cytotoxicity (increased leakage of tubular antigens and enzymes in urine) and biochemical alterations (decreased urinary excretion of some eicosanoids and glycosaminoglycans and lowering of urinary pH). The concentrations of anti-DNA antibodies and total immunoglobulin E in serum were also positively associated with the concentration of Hg in urine and in blood respectively. The renal effects were mainly found in workers excreting more than 50 micrograms Hg/g creatinine, which corroborates our previous estimate of the biological threshold of Hg in urine. As these effects, however, were unrelated to the duration of exposure and not accompanied by functional changes (for example, microproteinuria), they may not necessarily represent clinically significant alterations of renal function.

Single and combined effects of the vitamin D analogue KH1060 and cyclosporin A on mercuric-chloride-induced autoimmune disease in the BN rat

Mercuric chloride induces in BN rats a self-limiting systemic autoimmune disease characterized by proliferation of autoreactive CD4+ T lymphocytes, polyclonal activation of B lymphocytes, and the development of an anti-glomerular basement membrane (GBM) nephritis with concomitant nephrotic range proteinuria. We have used this model of autoimmune disease to test the immunosuppressive ability of a novel vitamin D3 analogue KH1060. This compound prevents autoimmune manifestations including proteinuria, serum IgE, and serum anti-laminin antibodies in a dose-dependent manner, as does cyclosporin A (CyA). When dosages of KH1060 capable of partial reduction of proteinuria without causing significant hypercalcaemia are combined with small dosages of CyA also capable of partial prevention of proteinuria, an additive effect is seen, leading to complete prevention of proteinuria and substantial reductions in serum IgE and anti-laminin levels. Possible mechanisms of action are discussed and it is suggested that KH1060 could prove useful as an immunosuppressive agent in the treatment of autoimmune diseases.

Immunoregulation of mercuric chloride-induced autoimmunity in Brown Norway rats: a role for CD8+ T cells revealed by in vivo depletion studies

Mercuric chloride (HgCl2) induces the production of autoantibodies to glomerular basement membrane (GBM) in the Brown Norway (BN) rat. The autoimmune response is self-limiting and thereafter the animals are resistant to rechallenge with HgCl2. Resistance can be transferred to naive animals by spleen cells from HgCl2-treated rats. A similar state of resistance can be induced with a low dose of HgCl2, insufficient in itself to induce autoimmunity. We have examined the role of CD8+ T cells in the immunoregulation of this experimental model by depleting this subset in vivo. We have also used inhibition studies in a solid-phase radioimmunoassay in an attempt to demonstrate any effect of anti-idiotypic antibodies in the spontaneous resolution of the anti-GBM antibody response. The initial induction and spontaneous resolution of anti-GBM antibodies were unaffected by depletion of CD8+ T cells. However, CD8-depleted animals were no longer resistant to rechallenge with HgCl2. Cell transfer studies showed that spleen cells from CD8-depleted animals conferred less resistance to HgCl2 than those from animals which had received control antibody. CD8 depletion also reduced the resistance induced by pretreatment with low-dose HgCl2. Studies in which peak sera were pre-incubated with post-recovery sera before testing in a solid-phase anti-GBM radioimmunoassay did not support an important role for anti-idiotypic antibodies. We conclude that CD8+ T cells play an important role in the resistance to rechallenge with HgCl2 in the BN rat, although they are not required for the induction or spontaneous resolution of the initial autoimmune response. Demonstration of the reversal of a suppressive phenomenon in vivo using an anti-CD8 monoclonal antibody is unusual.

Cyclosporin A in the prevention and treatment of experimental autoimmune glomerulonephritis in the brown Norway rat

Experimental autoimmune glomerulonephritis (EAG) was induced in brown Norway (BN) rats by a single i.m. injection of collagenase-solubilized homologous glomerular basement membrane (GBM) in Freund's complete adjuvant. This model of anti-GBM disease is characterized by the development, over several weeks, of circulating and deposited anti-GBM antibodies, accompanied by albuminuria. We examined the effects of treatment with oral cyclosporin A (CsA) at different doses, starting at the time of immunization and during the course of the disease. Pretreatment with CsA 5 mg kg daily produced a moderate reduction in circulating anti-GBM antibody levels, reduced deposition of antibody on the GBM and decreased albuminuria. Doses of 10 and 20 mg/kg CsA produced a marked reduction in circulating antibody, absence of detectable deposited antibody and virtual absence of albuminuria. Renal function remained normal in CsA-treated and control animals. When CsA treatment was introduced at 2 or 4 weeks after immunization, there were significant effects on the subsequent autoimmune response and albuminuria at 10 and 20 mg/kg daily. These studies demonstrate that CsA in conventional doses has a therapeutic effect in this model of anti-GBM disease, and suggest a role for T lymphocytes in the pathogenesis of EAG.

Autoantibodies to endothelial cells and neutrophil cytoplasmic antigens in systemic vasculitis

The interaction of circulating autoantibodies with the endothelium may be an important mechanism in the pathogenesis of systemic vasculitis. In a prospective study, we looked for circulating antiendothelial cell autoantibodies (AECA) and anti-neutrophil cytoplasm autoantibodies (ANCA) in 80 patients with suspected systemic vasculitis. AECA were measured using an isotype-specific cellular ELISA incorporating human umbilical vein endothelial cells. ANCA activity was determined by indirect immunofluorescence and radioimmunoassay. Sequential studies were performed on sera from four cases with dual positivity, where autoantibody binding was compared with von Willebrand factor (vWF) concentration and disease activity. IgG AECA were significantly higher in the 27 ANCA-positive sera as compared with normal controls (P = 0.027) with IgG (P = 0.009) and IgA (P = 0.046) AECA isotypes correlating with ANCA positivity; in contrast, no differences were found between AECA levels in the ANCA-negative sera and the normal controls. Cross-inhibition studies pointed to the co-existence of two autoantibody populations. An association between autoantibody binding, disease activity and vWF concentration was found for both ANCA and AECA. Some patients with systemic vasculitis have detectable AECA that recognize different epitopes to ANCA and like ANCA, their titre correlates with disease activity and thus they may have a pathogenetic role in these conditions.