Autoregulation of autoantibody synthesis in mercuric chloride nephritis in the Brown Norway rat. I. A role for T suppressor cells

Abrogation of mercuric chloride-induced nephritis in the Brown Norway rat by treatment with antibodies against TNFalpha

HgCl₂ induces an autoimmune disease in the Brown Norway rat characterized by synthesis of autoantibodies (mainly, anti-GBM Abs), severe proteinuria and interstitial nephritis. Also, HgCl₂- injected rats develop glomerular cell infiltrates consisting of ED1⁺ cells (monocyte/macrophage), starting on day 4 and reaching a maximum on day 8. Treatment with anti-TNF-α antiserum had preventative effects as it reduced the urinary protein levels to close to the normal range and also blocked the influx of inflammatory cells in the renal glomeruli and interstitium, but circulating anti-GBM and lineal glomerular IgG deposits were unmodified. In addition, whole isolated glomeruli from HgCl₂-induced nephritis secreted TNF-α commencing on day 8, being maximally detected on day 11 and preceding, between 2 to 3 days, the development of proteinuria. The administration of anti-TNF-α antiserum or anti-α4 integrin mAb completely abrogated the synthesis of TNF-α in glomeruli isolated from the respective treated groups of animals, in addition to the proteinuria. Taken together our results confirm that TNF-α plays an important role in the induction and development of HgCl₂-induced nephritis and highlights the pathogenic importance of the local release of TNF in those renal diseases in which prominent glomerular macrophage accumulation is a constant feature.

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.

Regulation of Autoantibody Responses to Glomerular Basement Membrane in Man and Experimental Animals

Autoantibodies reacting with the glomerular basement membrane (GBM) are a rare cause of severe nephritis in man. Their development is HLA-DR-associated and their pathogenicity has been demonstrated by transfer experiments. Their production is spontaneously self-limiting over a period of years but irreversible renal failure usually occurs within weeks or months in the untreated patient. A regimen of intensive plasma exchange together with cytotoxic drugs and steroids induces a rapid and permanent arrest of antibody synthesis; this is associated with recovery of renal function, provided that target organ injury is not irreversible when treatment is initiated. To understand the homeostatic mechanisms engaged by the therapeutic regimen we have studied an experimental model of autoimmune nephritis in the Brown Norway rat, where autoantibody-mediated injury to the GBM is induced by mercuric chloride. Suppressor cells and humoral factors (putatively anti-idiotypic antibodies) were found to regulate autoantibody production, and cyclophosphamide can prevent its reinduction. To identify the autoantigenic component in human GBM we have produced a mouse monoclonal antibody which recognizes the same components as are recognized by autoantibodies from all 35 patients tested. This monoclonal antibody can be used to study the autoregulatory components from human blood which we have found to be important in the animal model.

Manipulation of idiotype networks in autoimmunity

The spontaneous occurrence of anti-idiotypes associated with the amelioration of disease activity in some autoimmune disorders encourages the view that one may be able to develop a therapeutic strategy based upon manipulation of idiotype networks. Attempts to abrogate autoimmunity by using heterologous anti-idiotype reagents have been rather disappointing and there may well be an expansion of idiotype-negative antibody clones. We argue that idiotypic reagents based on T cells or antibodies derived from the species being treated are more likely to lead to success because they interact more profoundly with the individual's own networks than do heterologous antibodies.

Specific immunoabsorption

Rapidly progressive glomerulonephritis occurs in patients developing autoantibodies to the glomerular basement membrane (GBM) and in multisystem vasculitic syndromes such as Wegener's granulomatosis (WG) and microscopic polyarteritis (MPA). In anti-GBM disease the pathogenicity of the autoantibodies has been established by transfer experiments; new solid-phase radioimmunoassays (RIAs) for circulating autoantibodies allow early diagnosis and effective monitoring of treatment. Sequential measurements of antibody levels showed that their generation is self-limiting (even without treatment) and that their production can be arrested more quickly with immunosuppressive therapy (cyclophosphamide and high dose steroids) together with intensive plasma exchange. In systemic vasculitis, no pathogenic agent has been identified and the diseases are rarely self-remitting. In WG, antibodies to cytoplasmic components of normal human neutrophils (and monocytes) were reported to be detectable by indirect immunofluorescence, with titres correlating with disease activity. We confirmed this and showed that antigen can be extracted from normal human neutrophils and used as ligand in a solid-phase RIA. Sera from patients with other forms of systemic vasculitis, such as MPA, as well as WG, are positive in this assay. The antigens have been further characterized by HPLC fractionation on a Toyosoda TSK gel filtration column. In WG, antibodies were directed towards cytoplasmic fractions of 100, 6 and 2 kDa; in MPA, antibody reacted only with the 100 kDa fraction. These findings suggest a humoral pathogenesis in these disorders and indicate that this approach may be helpful in the classification, diagnosis and monitoring of therapy in the systemic vasculitides. Further characterization of the autoantigen and its potential use in specific immunoabsorption are discussed.

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.

Blockade of OX40-ligand after initial triggering of the T helper 2 response inhibits mercuric chloride-induced autoimmunity

Mercuric chloride (HgCl2)-induced autoimmunity in Brown Norway rats is a spontaneously resolving autoimmune response driven by the activation of T helper type 2 lymphocytes (Th2 cells). Treatment with antibody to OX40-ligand (OX40-L) from the time of the first HgCl2 injection for 12 days had little effect. Delayed treatment commenced 8 days after the first HgCl2 injection significantly suppressed immunoglobulin E production, splenomegaly, weight loss and mortality. This makes OX40/OX40-L signalling an attractive therapeutic target for Th2-driven autoimmune diseases. Intravenous administration of the murine antibody to OX-40-L elicited a vigorous anti-mouse immunoglobulin antibody response that was significantly enhanced compared to the response to control immunoglobulin. It is likely that this response significantly reduced the plasma half-life of the anti-OX40-L antibody and this observation has clear implications for the interpretation of data from experiments where anti-OX40-L is used in vivo.

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

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

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.

The Th2-response in mercuric chloride-induced autoimmunity requires continuing costimulation via CD28

Mercuric chloride (HgCl2)-induced autoimmunity in Brown Norway (BN) rats is a highly polarized polyclonal Th2-driven autoimmune response with increased IgE production, lymphoproliferation, vasculitis and proteinuria. The increase in serum IgE concentration is clearly measurable by day 4 after the first HgCl2 injection and peaks between days 15 and 20. Treatment with CD80 and CD86 antibodies prior to administration of HgCl2 completely suppresses the autoimmune process. To determine whether interruption of CD28 signalling after initial stimulation of the Th2-response would be suppressive, antibody treatment was delayed. BN rats were given 5 doses of HgCl2 subcutaneously on alternate days. CD80 and CD86 antibodies, or an isotype control, were given daily for 3 days and then on alternate days until day 12 commencing either on the day of the first HgCl2 injection (day 0) or on days 4 or 8. Treatment from day 0 reduced serum IgE concentrations to below baseline (median 9.34 microg/ml on day 0 versus 4.6 microg/ml, on day 5, P = 0.03) suggesting that ongoing costimulation via CD28 is required to maintain basal serum IgE production. Delaying treatment until day 4 or day 8 after the first HgCl2 injection resulted in significant inhibition of IgE secretion, lymphoproliferation, and vasculitis, although less markedly than when treatment was commenced on day 0. These data indicate that CD28-mediated costimulation is not only required for the initiation of the Th2-response but is required for maintenance of a maximal response, making this an attractive therapeutic target for antibody-mediated autoimmune diseases.

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.

Effects of mycophenolate mofetil in mercury-induced autoimmune nephritis

Mycophenolate mofetil (MMF) is a new immunosuppressive drug whose active metabolite, mycophenolic acid (MPA), blocks the action of inosine monophosphate dehydrogenase, resulting in the inhibition of the novo purine synthesis. Thus, MPA has an antiproliferative effect on T and B lymphocytes and also inhibits the glycosylation of cell surface adhesion proteins involved in cell-cell contact and in the recruitment of circulating leukocytes to sites of tissue damage and inflammation. In this study, the effect of MMF in the mercury model of nephritis was examined. Repeated exposure to HgCl(2) induces an autoreactive Th2 cell subset-inducing polyclonal B cell activation in the Brown Norway (BN) rat. This leads to the development of an autoimmune syndrome characterized by synthesis of autoantibodies (mainly anti-glomerular basement membrane [GBM] Abs) with glomerular linear deposits of IgG, proteinuria, and tubulointerstitial nephritis. Results show that MMF has a preventive effect on mercury-induced disease as it blocks anti-GBM Ab synthesis, thus avoiding glomerular IgG deposits and proteinuria and the development of interstitial nephritis. However, the therapeutic effect of MMF seems to be restricted to its antiinflammatory properties blocking the extravasation of circulating leukocytes to renal interstitium by interfering with the very late activation antigen 4/vascular cell adhesion molecule-1 (VCAM-1) cell adhesion pathway. Also, MMF administration to mercury-injected rats reduces the secretion of the proinflammatory cytokine tumor necrosis factor-alpha. These findings confirm that MMF has a strong effect on the primary immune response in this model. Nevertheless, when the disease is in progress, MMF acts exclusively on the inflammatory response. MMF could be useful in the treatment of diseases associated with renal inflammation.

CD80(B7.1) and CD86(B7.2) do not have distinct roles in setting the Th1/Th2 balance in autoimmunity in rats

Some data suggest that the interaction between CD28 and CD80 (B7.1) stimulates Th1-responses and that CD28 and CD86 (B7.2) stimulates Th2-responses, however this is controversial. We addressed this issue by using mercuric chloride (HgCl2)-induced autoimmunity in Brown Norway (BN) rats as a highly polarized Th2 model and experimental autoimmune encephalomyelitis (EAE) in Lewis rats as a highly polarized Th1 model. Monoclonal antibodies (MoAbs) to CD80 and CD86, given singly, had little effect in either model, however when given together they almost completely suppressed the HgCl2-induced autoimmunity: the peak immunoglobulin (Ig)E concentration was 3.25 microg/ml in treated animals versus 2770 microg/ml in controls (P < 0.0001); caecal vasculitis was suppressed with a median vasculitis score of 0 in treated animals versus 6 in controls (P < 0.0001); and new germinal centre formation was significantly suppressed. A combination of the antibodies also markedly reduced the severity of clinical EAE; from a median aggregate clinical score of 9 to 3 (P = 0.02) and delayed the onset from a median of 12.5 days to 16 days after immunization (P = 0.006). We have demonstrated profound suppression of both Th1 and Th2-driven autoimmunity in rats by a combination of anti-CD80 and CD86, but have been unable to demonstrate any clear differential effects.

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.

Functional relevance of activated beta1 integrins in mercury-induced nephritis

Cell adhesion through different adhesion molecules is a crucial event in the inflammatory response. Integrins can only bind and mediate cellular adhesion after their activation by different specific stimuli. The state of beta1 integrin activation can be assessed by a group of monoclonal antibodies (HUTS) that selectively recognize beta1 integrins in their active form. A similar activated epitope in the rat was defined using the anti-human monoclonal antibody HUTS-21, which recognizes an activation-dependent epitope on the beta1 chain. It was found that the divalent cations Mn(2+) and Hg(2+) were able to induce in vitro the activation of beta1 integrins on rat lymphocytes. The Hg(2+) cation induces an autoimmune disease in the Brown Norway rat characterized by synthesis and glomerular deposits of anti-glomerular basement membrane antibodies, proteinuria, and interstitial nephritis. Using the mercury model of nephritis, it was found that the expression of HUTS-21 epitope is induced in vivo in rat lymphocytes, and its appearance is correlated with the other parameters at the onset of the disease. In addition, the administration of HUTS-21 monoclonal antibody to HgCl(2)-treated rats offered evidence of its protective effects (1) against infiltration of renal interstitium by leukocytes, and (2) in the reduction of anti-glomerular basement membrane synthesis and glomerular deposition. Nevertheless, urinary protein values remained unaffected. These results demonstrate a key role of beta1-activated integrins in both leukocyte cell-cell interactions and leukocyte infiltration pathway mechanism, and also indicate that leukocyte migration may have less importance in the development of this disease than previously thought.

Role of beta1 and beta2 subunits of the interleukin-12 receptor in determining T helper 1/T helper 2 responses in vivo in the rat

Interleukin-12 (IL-12) responsiveness, and hence capacity to mount a T helper type 1(Th1) immune response, may be regulated via differential expression of the IL-12 receptor beta2 subunit at least in vitro in human and murine cells. To test whether a similar phenomenon operates in vivo in the rat we cloned and sequenced partial cDNAs for rat IL-12Rbeta1 and IL-12Rbeta2 subunits and analysed expression of these genes in vivo in two rat strains with different Th1/Th2 bias. After treatment with mercuric chloride (HgCl2), Brown-Norway rats develop Th2-biased autoimmunity whereas Lewis rats do not develop autoimmunity, instead becoming resistant to Th1-biased diseases to which they are normally susceptible. We report close sequence homology between the segments of the rat IL-12R genes sequenced and corresponding mouse genes (95.6% and 92% for IL-12Rbeta1 and IL-12Rbeta2, respectively). Both Brown-Norway and Lewis rats express both beta1 and beta2 subunits of IL-12 receptor in vivo in spleen; Brown-Norway rats express the beta2 subunit at a lower level than Lewis rats. After HgCl2 treatment, IL-12Rbeta1 expression was not altered but there was down-regulation of IL-12Rbeta2 expression in both strains. We conclude that relative under-expression of IL-12Rbeta2 by Brown-Norway rats contributes to their Th2 bias, and that down-regulation of IL-12Rbeta2 after HgCl2 administration in Lewis rats underlies subsequent resistance to induction of Th1-biased diseases.

The role of endogenous steroid hormones in the generation of T helper 2-mediated autoimmunity in mercuric chloride-treated Brown-Norway rats

Injection of Brown-Norway rats with mercuric chloride (HgCl2) activates a T helper type 2 (Th2) autoimmune response, with production of a number of autoantibodies and vasculitis primarily affecting the gut. Glucocorticoids have been shown to suppress Th1 and to promote the development of Th2-type responses. Conversely dehydroepiandrosterone (DHEA) promotes Th1 responses with suppression of Th2 responses. This study set out to define the role of these hormones in this animal model. Rats were adrenalectomized (Adx) with no steroid replacement (n = 11), Adx with basal steroid replacement given by a 25 mg corticosterone pellet inserted subcutaneously (n = 13), or sham-Adx (n = 14) prior to administration of HgCl2. In both groups of Adx animals there was a delay in the production of immunoglobulin E (IgE) and serum concentrations on day 9 were marginally lower (P = 0.035, repeated measures ANOVA). All of the animals Adx with no steroid replacement and two Adx animals with steroid replacement died between 10 and 14 days after HgCl2 challenge. There was no difference in the severity of caecal vasculitis between the groups. A significant increase in adrenal size was noted following administration of HgCl2. Administration of subcutaneous DHEA implants (100 mg and 200 mg) had no significant effect on IgE concentrations or severity of vasculitis. These observations do not support the hypothesis that corticosterone and DHEA play a central role in setting the Th1/Th2 balance in this experimental Th2-mediated autoimmune disease; in contrast with the Th1-mediated autoimmune disease experimental allergic encephalomyelitis where corticosterone plays a key role in immunoregulation.

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.

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

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

Autoimmunity and selected environmental factors of disease induction

Autoimmune diseases may be induced by physical and/or chemical environmental factors. A review of the available literature on mercuric chloride, iodine, silicone, anilides, L-tryptophan, vinyl chloride, and canavanine suggests three general mechanisms by which they may induce disease. First, oxidative damage probably is a frequent process involved in disease induction and pathogenesis. Second, certain compounds also may generate antigen-specific immune responses that could then cross-react with self-tissues. Other xenobiotics might bind to self-tissues and increase self-tissue immunogenicity. Third, physical and chemical agents may also modulate the immune system. Finally, in response to controversies surrounding the influence of human activities on global climate changes, the immunosuppressive effects of ozone and ultraviolet radiation are discussed.

Anti-interleukin-2 receptor monoclonal antibody therapy supports a role for Th1-like cells in HgCl2-induced autoimmunity in rats

Brown-Norway (BN) rats injected with HgCl2 develop an autoimmune disease characterized by a T-dependent polyclonal B-cell activation. Increase in major histocompatibility complex class II molecule expression on B cells concomitant with enhancement of serum IgE concentration supports the involvement of the T helper 2 (Th2)-like subset in the induction of the disease. The mercury disease is autoregulated and does not develop in Lewis (LEW) rats. Considering the reciprocal regulation, well defined in mice, between the Th1 and Th2 subsets, we addressed the role of the Th1-like subset in this disease. Brown-Norway and LEW rats injected with HgCl2 were treated with NDS61, a mouse anti-rat-IL-2R MoAb that blocks mainly Th1 cells. Data reported herein show that: (1) HgCl2 treatment does not modify either the percentage of IL-2R+ cells or IL-2R expression in both BN and LEW rats; (2) treatment of BN rats with NDS61 MoAb does not modify the induction phase of the mercury disease but delays in part the regulation phase; (3) such a treatment leads to some immune abnormalities in LEW rats; (4) HgCl2 markedly potentiates the anti-mouse Ig antibody response in BN rats which probably limits the effect of this treatment. This study supports a role for the Th1-like subset in HgCl2-induced autoimmunity in the rat.

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.

TH2 cells in systemic autoimmunity: insights from allogeneic diseases and chemically-induced autoimmunity

Systemic autoimmune diseases can be induced experimentally in rodents by graft-versus-host or host-versus-graft reactions and by chemicals such as HgCl2, gold salts and D-penicillamine. These models share several features, such as productions of anti-nuclear antibodies, immune glomerulonephritis, MHC class II hyperexpression on B cells, hyper-IgE, increased IL-4 activity and impairment of IL-2 production. This profile of cytokines suggests a central role for TH2-type cells in their pathogenesis. Here, Michel Goldman and colleagues review the data supporting this hypothesis and discuss the possible molecular bases for T-cell activation in chemically-induced systemic autoimmunity.

Reduction of the RT6.2+ subset of T lymphocytes in brown Norway rats with mercury-induced renal autoimmunity

Chemically induced autoimmunity is a recently recognized environmental hazard that may affect individuals genetically predisposed to autoimmune disease and chronically exposed to certain chemicals. For example, moderate concentrations of mercury may lead to renal autoimmune disease in a small but significant percentage of the exposed population. Mercury also induces autoimmune glomerulonephritis in susceptible Brown Norway (BN) and MAXX inbred strain rats. Autoimmune responses, directed to epitopes of the renal glomerular basement membrane (GBM), are rapid in onset and have a self-limiting course in mercury-treated rats. Both regulatory T cells and idiotype-anti-idiotype network have been implicated in the resolution of this autoimmune process. In our investigations of immune regulation of mercury-induced autoimmune glomerulonephritis, we have used flow cytometry to quantitate lymphocyte subpopulations in the spleen and lymph nodes of mercury-treated and control BN rats. Of particular interest was the RT6+ T cell subset, that appears to have important immunoregulatory properties in a rat model of autoimmune insulin-dependent diabetes mellitus. Spleen and lymph nodes from control BN rats contained 22 and 52%, respectively, RT6+ cells. Spleens from mercury-treated animals contained 21% RT6+ cells on Day 10 of treatment, 13% on Day 17, 16% on Day 24 and 20% on Day 30. Lymph nodes from the same rats had 36% RT6+ cells on Day 10, 23% on Day 17, 29% on Day 24, and 28% on Day 30. The decrease in RT6+ cells correlated inversely with autoimmune responses to GBM, which peaked on Days 17-24 and declined by Day 30. Moreover, autoimmune responses were also associated with elevated RT6-:RT6+ T cell ratios. Similar results were obtained in two additional groups of BN rats, comprising both younger and older animals, sacrificed at Day 18 of mercury treatment. Analysis of other lymphocyte subpopulations demonstrated a decrease of CD4+ and CD5+ cells, whereas B cells as well as CD8+, IL-2 receptor+, and MHC class II+ subsets showed no consistent correlation with the onset or resolution of the autoimmune process. These findings suggest that mercury-induced changes in RT6+ T lymphocytes may be related to the development of renal autoimmune disease in genetically predisposed BN rats.

Graft-versus-host reactions in the rat mimic toxin-induced autoimmunity

Gold salts, D-penicillamine or mercurials induce autoimmunity in Brown Norway (BN) rats and provoke an immunosuppression in Lewis (LEW) rats. It has been suggested that immunologically mediated manifestations induced by drugs could result from graft-versus-host (GVH) like reactions. We show that BN spleen cells transferred into (LEW x BN)F1 hybrids induce a chronic GVH reaction (GVHR). This reaction led to an autoimmune disease quite similar to that induced by drugs in BN rats. In both situations, a common part of the B cell repertoire is triggered. In contrast, LEW spleen cells transferred into (LEW x BN)F1 hybrids provoke a lethal GVHR. This is to be compared with the CD8-mediated immunosuppression observed in LEW rats injected with HgCl2. These findings are in agreement with the prediction that immune dysregulation induced by drugs leads to GVH-like reactions either stimulatory or suppressive depending upon the strain tested.

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

Repeated low-dose injections of mercuric chloride (HgCl2) in the brown Norway (BN) rat result in polyclonal activation which includes the induction of anti-glomerular basement membrane (GBM) autoantibodies. We examined the kinetics of various autoantibodies produced in vivo, general features of polyclonal activation such as total IgG levels and immune complex formation, and the relationship between organ specific autoimmunity and tissue injury in the kidney and thyroid. The production of immune complexes and autoantibodies to GBM and thyroglobulin was short lived, and the increase in levels of total IgG and antibodies to ssDNA and dsDNA was prolonged; the antibody response to collagen types I and II was intermediate in duration. Autoantibodies induced by HgCl2 caused only mild and variable tissue injury in the kidneys and did not induce abnormalities in the thyroid. These studies demonstrate that immunostimulation by mercury may result in the formation of a range of autoantibodies, with variable kinetics and pathogenicity.

A spontaneous hybridoma producing autoanti-idiotypic antibodies that recognize a V kappa-associated idiotope in mercury-induced autoimmunity

Anti-idiotypic (Id) antibodies have been suggested to play a role in the self regulation process observed in Brown-Norway rats developing mercury-induced autoimmunity. However, the presence of such antibodies has not yet been directly demonstrated. For that purpose, spleen cells from a mercury-injected rat were fused and the resulting hybridomas tested for their anti-Id activity against monoclonal anti-glomerular basement membrane (GBM) antibodies produced in this model. A monoclonal antibody (mAb) was obtained that specifically reacted in an enzyme-linked immunosorbent assay with an anti-GBM mAb and to a much lesser extent with another one produced in the same fusion. In Western blot experiments this autoanti-Id mAb reacted under reducing conditions with the kappa L chains but not with the H chains of the two anti-GBM mAb. It did not react with the kappa L chains of eight other rat mAb. This mAb is therefore an autoanti-Id mAb that recognizes a V kappa-associated Id expressed on two anti-GBM mAb. These results demonstrate that anti-GBM antibodies and their corresponding autoanti-Id antibodies are simultaneously produced during this disease. Whether or not these autoanti-Id antibodies have a regulatory and/or a pathogenic role in this disease remains to be established.

Autoimmunity and the pathogenesis of glomerulonephritis

Self-tolerance is maintained by: thymic influences on developing T cells; peripheral mechanisms that can tolerise post-thymic T cells; and to a variable extent the tolerisation of potentially autoreactive B cells. The presence of autoreactive T cells in normal individuals suggests that mechanisms to control the activity of such cells may be important. Failure of any of these processes may lead to autoimmunity. The relationship between glomerulonephritis and the mechanisms leading to breakdown of self-tolerance remains elusive. An important observation is that autoimmune diseases are strongly associated with particular products of the major histocompatibility complex (MHC). This association may reflect the intimate involvement of the MHC in thymic T cell education. Another explanation is that T cells only recognise antigens presented in the context of MHC molecules. Although there has been progress in identifying the targets recognised by autoantibodies in vasculitis and anti-GBM disease, nothing is known about the T cells involved. Despite our ignorance, therapy aimed specifically at the T cell can be effective. This approach is being supplemented by attempts to engage immunoregulatory mechanisms, such as idiotype-antiidiotype interactions. The hope is that such treatments, or combinations thereof, will allow a more focused suppression of the autoimmune response, in contrast to the non-specific (and therefore potentially dangerous) methods of immunosuppression available at present.

Role of CD8+ T cells in mercury-induced autoimmunity or immunosuppression in the rat

In Brown-Norway (BN) rats mercuric chloride induces an autoimmune disease characterized by an increase in serum IgE concentration, and by the production of anti-glomerular basement membrane antibodies responsible for a glomerulonephritis with a heavy proteinuria. (i) This disease results from a B-cell polyclonal activation probably due to frequent anti-class II T cells. (ii) The self limitation observed in this model is associated with both a decrease in the frequency of anti-class II T cells and the emergence of CD8+ T cells able to suppress these autoreactive T cells. (iii) In Lewis (LEW) rats which do not develop autoimmunity, HgCl2 provokes the appearance of non-antigen-specific CD8+ T cells responsible for a depression of T-cell functions. The aim of this work was to test the effect of treatment with an anti-CD8 monoclonal antibody (MoAb) in both BN and LEW rats. Anti-CD8 MoAb-treated rats were effectively depleted in CD8+ T cells. However, neither the induction nor regulation phases of mercury-induced autoimmunity were modified in BN rats. Mercury-induced immunosuppression in LEW rats was abrogated; however, depletion in CD8+ T cells did not allow the disease to occur in that strain. Finally, CD8 depletion induced in normal BN rats the appearance of rare anti-class II T cells showing that these cells are normally present in that strain but negatively controlled by suppressor T cells.

Contribution of immunological reactions to nephrotoxicity

Several toxic agents, such as mercurials and agents with a sulphydryl group (e.g., gold salts, D-penicillamine and captopril), are associated with the occurrence of membranous glomerulopathy. DR3 antigen-positive subjects and poor sulphoxidators are at higher risk than other patients when treated with gold salts or D-penicillamine. Other drugs, mainly nonsteroidal anti-inflammatory agents and lithium salts, are responsible for the nephrotic syndrome with minimal glomerular changes, a T-cell-mediated disease. Several models of drug-induced membranous glomerulonephritis have been developed. These have been used to confirm the role of most of the above-mentioned agents and have made it possible to shed some light on the possible mechanisms involved. Mercurials induce a polyclonal activation of B cells in rats which is related to the appearance of autoreactive T cells. Finally, numerous agents may induce immunologically mediated acute interstitial nephritis. Although cell-mediated immunity appears to be involved in most cases, experimental models are lacking to substantiate this hypothesis.

Immunological aspects of toxicology: premises not promises

The immune system is gaining increasing attention as a target of toxicant action. Many compounds, including metals, drugs, and pesticides, are able to alter immune functions. Additionally, the ability of toxicants to experimentally alter resistance to a variety of bacterial, viral, and tumor challenges is suggestive for the possible involvement of toxicants in morbidity and mortality. However, the implications of immunotoxicology as a subject of study may not be fully realized in some laboratories due to unfamiliarities into the workings of immunity by toxicologists. In an attempt to bridge this toxicology-immunology gap, this paper presents the major concepts of the immune system by reviewing specific examples of immune responses and their environmental interactions. Data from selected toxins are then used to illustrate how these responses may be altered.

Mercury-induced renal autoimmunity in the MAXX rat

Inbred Brown Norway (BN) rats treated with mercuric chloride develop autoantibodies to renal basement membranes and an immunologically mediated membranous glomerulonephritis. To date, this experimental rat model of chemically induced autoimmunity has been obtained only in the BN strain, whereas rats from 17 other strains were found to be resistant. This is a disadvantage for mechanistic studies, especially since BN rats have poor fertility. In the present paper we report that the same model can be obtained in another inbred strain of rats, the MAXX, which after exposure to mercury develop a glomerulonephritis characterized by the production of autoantibodies to renal basement membranes. The kinetics of the autoimmune response observed in MAXX rats, as well as the immunohistopathology, histopathology, and proteinuria, are similar to those previously described in BN rats. In addition, the MAXX strain is endowed with excellent fertility. Therefore, both rat strains can be used for comparative studies of the mechanisms of mercury-induced autoimmunity.

Autoreactive T cells in mercury-induced autoimmunity. Demonstration by limiting dilution analysis

Mercuric chloride is responsible in Brown-Norway rats for an autoimmune disease that is autoregulated. Previous studies have shown that this agent induces T cell-dependent polyclonal B cell activation in these rats. Evidence has also been obtained for the existence of autoreactive T cells which play a role in the evolution of this process. In the present study, limiting dilution analysis was used to demonstrate that (a) frequent autoreactive T helper cells which proliferate in the presence of T cells from HgCl2-injected rats are present from day 4; (b) frequent auto-anti-Ia T helper cells which recognize normal B cells as well as B cells from HgCl2-injected rats appear from day 6; and (c) less frequent T suppressor cells which could play a role in autoregulation emerge from day 14.

Long-term depletion of CD8+ T cells in vivo in the rat: no observed role for CD8+ (cytotoxic/suppressor) cells in the immunoregulation of experimental allergic encephalomyelitis

A method is described for the long-term depletion of CD8+ T cells in the rat. Employing Lewis rats depleted of this cell type it is shown that such animals acquire, and subsequently recover from both passively and actively induced experimental allergic encephalomyelitis (EAE) in a comparable fashion to normal animals. Furthermore, after spontaneous recovery from the initial bout of disease, CD8+ T cell-depleted rats do not show any signs of relapse and, like normal rats following recovery from active EAE, are still resistant to further attempts at disease induction. Overall, these data do not support a role for the classic cytotoxic/suppressor (CD8+) T cell in the immunoregulation of EAE in the Lewis rat.

Studies on the formation of glomerular immune deposits in brown Norway rats injected with mercuric chloride

Brown Norway rats injected with mercuric chloride (HgCl2) develop autoantibodies which immunolocalize along the glomerular basement membrane at first in a linear pattern and then in a granular pattern. The aim of this study was to characterize the specificity of these antibodies and to investigate the mechanisms responsible for the formation of granular immune deposits in the subepithelial zone of the glomerular basement membrane. The rats were found to develop circulating anti-laminin, anti-type IV collagen, anti-heparan sulfate proteoglycan, and anti-entactin antibodies. Antibodies against laminin and type IV collagen were found in relatively high titers in the sera and were specifically concentrated in the nephritic kidneys. Antibodies eluted from the nephritic kidneys with either linear or granular deposits reacted with basement membrane antigens synthesized and secreted by cultured rat glomerular visceral epithelial cells. Thus, in this model, the interaction of anti-laminin and type IV collagen antibodies with antigens secreted by glomerular visceral epithelial cells might, together with other mechanisms, contribute to the formation of granular immune deposits in the subepithelial part of the glomerular basement membrane.