Highly autoproliferative T cells specific for 60-kDa heat shock protein produce IL-4/IL-10 and IFN-gamma and are protective in adjuvant arthritis

Boosting immunotherapy efficacy: Empowering the Potency of Dendritic cells loaded with breast cancer lysates through CTLA-4 suppression

Anticancer immunotherapies with a dendritic Cell (DC) basis are becoming more popular. However, it has been suggested that the tumor's immunosuppressive mechanisms, such as inhibitory immunological checkpoint molecules, reduce the effectiveness of anticancer immunogenicity mediated by DC. Thus, overcoming immune checkpoints and inducing effective antigen-specific T-cell responses uniquely produced with malignant cells represent the key challenges. Among the inhibitory immune checkpoints, DCs' ability to mature and present antigens is decreased by CTLA-4 expression. Consequently, we hypothesized that by expressing CTLA-4 cells on DCs, the T cells' activation against tumor antigens would be suppressed when confronted with these antigens presented by DCs. In this research, by loading cell lysate of breast cancer (BC) on DCs and the other hand by inhibiting the induction of CTLA-4 using small interfering RNA (siRNA), we assessed the functional activities and phenotypes of DCs, and also the responses associated with T-cells following co-culture DC/T cell. Our research has shown that the suppression of CTLA-4 enhanced the stimulating capabilities of DCs. Additionally, CTLA-4-suppressed BC cell lysate-loaded DCs produced more IL-4 and IFN-ϒ and increased T cell induction in contrast to DCs without CTLA-4 suppression. Together, our data point to CTLA-4-suppressed DCs loaded with BC cell lysate as a potentially effective treatment method. However, further research is required before employing this method in therapeutic contexts.

Heat Shock Response and Heat Shock Proteins: Current Understanding and Future Opportunities in Human Diseases

The heat shock response is an evolutionarily conserved mechanism that protects cells or organisms from the harmful effects of various stressors such as heat, chemicals toxins, UV radiation, and oxidizing agents. The heat shock response triggers the expression of a specific set of genes and proteins known as heat shock genes/proteins or molecular chaperones, including HSP100, HSP90, HSP70, HSP60, and small HSPs. Heat shock proteins (HSPs) play a crucial role in thermotolerance and aiding in protecting cells from harmful insults of stressors. HSPs are involved in essential cellular functions such as protein folding, eliminating misfolded proteins, apoptosis, and modulating cell signaling. The stress response to various environmental insults has been extensively studied in organisms from prokaryotes to higher organisms. The responses of organisms to various environmental stressors rely on the intensity and threshold of the stress stimuli, which vary among organisms and cellular contexts. Studies on heat shock proteins have primarily focused on HSP70, HSP90, HSP60, small HSPs, and ubiquitin, along with their applications in human biology. The current review highlighted a comprehensive mechanism of heat shock response and explores the function of heat shock proteins in stress management, as well as their potential as therapeutic agents and diagnostic markers for various diseases.

A peptide derived from HSP60 reduces proinflammatory cytokines and soluble mediators: a therapeutic approach to inflammation

Cytokines are secretion proteins that mediate and regulate immunity and inflammation. They are crucial in the progress of acute inflammatory diseases and autoimmunity. In fact, the inhibition of proinflammatory cytokines has been widely tested in the treatment of rheumatoid arthritis (RA). Some of these inhibitors have been used in the treatment of COVID-19 patients to improve survival rates. However, controlling the extent of inflammation with cytokine inhibitors is still a challenge because these molecules are redundant and pleiotropic. Here we review a novel therapeutic approach based on the use of the HSP60-derived Altered Peptide Ligand (APL) designed for RA and repositioned for the treatment of COVID-19 patients with hyperinflammation. HSP60 is a molecular chaperone found in all cells. It is involved in a wide diversity of cellular events including protein folding and trafficking. HSP60 concentration increases during cellular stress, for example inflammation. This protein has a dual role in immunity. Some HSP60-derived soluble epitopes induce inflammation, while others are immunoregulatory. Our HSP60-derived APL decreases the concentration of cytokines and induces the increase of FOXP3+ regulatory T cells (Treg) in various experimental systems. Furthermore, it decreases several cytokines and soluble mediators that are raised in RA, as well as decreases the excessive inflammatory response induced by SARS-CoV-2. This approach can be extended to other inflammatory diseases.

CTLA-4 silencing in dendritic cells loaded with colorectal cancer cell lysate improves autologous T cell responses in vitro

Dendritic cell (DC)-based immunotherapy has increased interest among anti-cancer immunotherapies. Nevertheless, the immunosuppressive mechanisms in the tumor milieu, e.g., inhibitory immune checkpoint molecules, have been implicated in diminishing the efficacy of DC-mediated anti-tumoral immune responses. Therefore, the main challenge is to overcome inhibitory immune checkpoint molecules and provoke efficient T-cell responses to antigens specifically expressed by cancerous cells. Among the inhibitory immune checkpoints, cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) expression on DCs diminishes their maturation and antigen presentation capability. Accordingly, we hypothesized that the expression of CTLA-4 on DCs inhibits the T cell-mediated anti-tumoral responses generated following the presentation of tumor antigens by DCs to T lymphocytes. In this study, we loaded colorectal cancer (CRC) cell lysate on DCs and inhibited the expression of CTLA-4 by small interfering RNA (siRNA) in them to investigate the DCs’ functional and phenotypical features, and T-cell mediated responses following DC/T cell co-culture. Our results demonstrated that blockade of CTLA-4 could promote stimulatory properties of DCs. In addition, CTLA-4 silenced CRC cell lysate-loaded DCs compared to the DCs without CTLA-4 silencing resulted in augmented T cell proliferation and cytokine production, i.e., IFN-γ and IL-4. Taken together, our findings suggest CTLA-4 silenced CRC cell lysate-loaded DCs as a promising therapeutic approach however further studies are needed before this strategy can be used in clinical practice.

Heat shock proteins and kidney disease: perspectives of HSP therapy

Heat shock proteins (HSPs) mediate a diverse range of cellular functions, prominently including folding and regulatory processes of cellular repair. A major property of these remarkable proteins, dependent on intracellular or extracellular location, is their capacity for immunoregulation that optimizes immune activity while avoiding hyperactivated inflammation. In this review, recent investigations are described, which examine roles of HSPs in protection of kidney tissue from various traumatic influences and demonstrate their potential for clinical management of nephritic disease. The HSP70 class is particularly attractive in this respect due to its multiple protective effects. The review also summarizes current understanding of HSP bioactivity in the pathophysiology of various kidney diseases, including acute kidney injury, diabetic nephropathy, chronic glomerulonephritis, and lupus nephritis-along with other promising strategies for their remediation, such as DNA vaccination.

APL-1, an altered peptide ligand derived from heat-shock protein, alone or combined with methotrexate attenuates murine collagen-induced arthritis

Induction of tolerance to autoantigens in vivo is a complex process that involves several mechanisms such as the induction of regulatory T cells and changes in the cytokine and chemokine profiles. This approach represents an attractive alternative for treatment of autoimmune diseases. APL-1 is an altered peptide ligand derived from a novel CD4 + T cell epitope of human heat-shock protein of 60 kDa (HSP60), an autoantigen involved in the pathogenesis of rheumatoid arthritis (RA). We have shown previously that this peptide efficiently inhibited the course of adjuvant-induced arthritis in Lewis rats and induced regulatory T cell (Treg) in ex vivo assay with PBMC isolated from RA patients. This study was undertaken to evaluate the therapeutic effect of APL-1 and its combination with methotrexate (MTX) in collagen-induced arthritis (CIA). CIA was induced in male DBA/1 mice at 8 weeks of age by immunization with chicken collagen. APL, MTX or both were administrated beginning from arthritis onset. Therapeutic effect was evaluated by arthritis and joint pathologic scores. In addition, TNFα and IL-10 in sera were measured by ELISA. Treg induction was assessed by FACS analysis. APL-1 inhibits efficiently the course of arthritis in CIA, similar to MTX. In addition, therapy with APL-1 plus MTX reduced CIA in mice, associated with an increase in Treg. These facts reinforce the therapeutic possibilities of APL-1 as a candidate drug for treatment of RA.

Mycobacterium leprae Hsp65 administration reduces the lifespan of aged high antibody producer mice

BACKGROUND

Aging process may result in immune modifications that lead to disruption of innate and acquired immunity mechanisms that may induce chronic-degenerative events. The heat shock proteins (Hsp), phylogeneticaly conserved among organisms, present as main function the ability of folding and refolding proteins, but they also are associated with chronic-degenerative disorders. Here were evaluated the role of M. leprae native Hsp65 (WT) and its point-mutated (K409A) on survival and anti-DNA and anti-Hsp65 antibody production of aged genetically selected mice for high (HIII) and low (LIII) antibody production; data from 120- and 270-days old mice (named "adult" or "aged", respectively) were compared.

RESULTS

WT Hsp65 administration induces reduction in the mean survival time of adult and aged female HIII mice, this effect being stronger in aged individuals. Surprisingly, the native protein administration increased the survival of aged female LIII when compared to K409A and control groups. No survival differences were observed in aged male mice after Hsp65 proteins inoculation. We observed increase in IgG1 anti-Hsp65 in WT and K409A aged HIII female mice groups and no marked changes in the anti-DNA (adult and aged HIII) and anti-Hsp65 IgG1 or IgG2a isotypes production in adult HIII female and aged male mice. LIII male mice presented increased anti-DNA and anti-Hsp65 IgG2a isotype production after WT or K409A injection, and LIII female groups showed no alterations.

CONCLUSIONS

The results revealed that the WT Hsp65 interferes with survival of aged HIII female mice without involvement of a remarkable IgG1 and IgG2a anti-DNA and anti-Hsp65 antibodies production. The deleterious effects of Hsp65 on survival time in aged HIII female mice could be linked to a gender-effect and are in agreement with those previously reported in lupus-prone mice.

Heat shock proteins can be targets of regulatory T cells for therapeutic intervention in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterised by excessive immune responses resulting in inflammation of the joints. Although current therapies can be successful in dampening inflammation, a long-lived state of tolerance is seldom achieved. Therefore, novel therapies are needed that restore and maintain tolerance in patients with RA. Targeting regulatory T cells (Tregs) is a successful strategy to achieve tolerance, as was shown in studies performed in animal models and in human clinical trials. The antigen-specificity of Tregs is crucial for their effectiveness and allows for very specific targeting of these cells. However, which antigen is suitable for autoimmune diseases such as RA, for which the autoantigens are largely unknown? Heat shock proteins (HSPs) are ubiquitously expressed and can be up-regulated during inflammation. Additionally, HSPs, or HSP-derived peptides are immunogenic and can be recognised by a variety of immune cells, including Tregs. Therefore, this review highlights the potential of HSP-specific Tregs to control inflammatory immune responses. Targeting HSP-specific Tregs in RA can be achieved via the administration of HSPs (derived peptides), thereby controlling inflammatory responses. This makes HSPs attractive candidates for therapeutic intervention in chronic autoimmune diseases, with the ultimate goal of inducing long-lasting tolerance.

Therapeutic effect of an altered peptide ligand derived from heat-shock protein 60 by suppressing of inflammatory cytokines secretion in two animal models of rheumatoid arthritis

Rheumatoid arthritis is a systemic autoimmune disease mediated by T cells. Productive engagement of T cell receptors by major histocompatibility complex-peptide leads to proliferation, differentiation and the definition of effector functions. Altered peptide ligands (APL) generated by amino acid substitutions in the antigenic peptide have diverse effects on T cell response. We predicted a novel T cell epitope from human heat-shock protein 60, an autoantigen involved in the pathogenesis of rheumatoid arthritis. Three APLs were designed from this epitope and it was demonstrated that these peptides induce the activation of T cells through their ability to modify cell cycle phase's distribution of CD4+T cells from RA patients. Also, IL-17, TNF-α and IL-10 levels were determined in PBMC from these patients. Unlike the wild-type peptide and the other two APLs, APL2 increased the IL-10 level and suppressed IL-17 secretion in these assays. Therapeutic effect of this APL in adjuvant arthritis (AA) and collagen-induced arthritis (CIA) models was also evaluated. Clinical score, histopathology, inflammatory and regulatory cytokine concentration were monitored in the animals. APL2 efficiently inhibited the progression of AA and CIA with a significant reduction of the clinical and histopathologic score. Therapeutic effect of APL2 on CIA was similar to that obtained with MTX; the standard treatment for RA. This effect was associated with a decrease of TNF-α and IL-17 levels. These results suggest that the therapeutic effect of APL2 is mediated in part by down-regulation of inflammatory cytokines and support the potential use of APL2 as a therapeutic drug in RA patients.

A case of mistaken identity: HSPs are no DAMPs but DAMPERs

Until recently, the immune system was seen solely as a defense system with its primary task being the elimination of unwanted microbial invaders. Currently, however, the functional significance of the immune system has obtained a much wider perspective, to include among others the maintenance and restoration of homeostasis following tissue damage. In this latter aspect, there is a growing interest in the identification of molecules involved, such as the so-called danger or damage-associated molecular patterns (DAMPs), also called alarmins. Since heat shock proteins are archetypical molecules produced under stressful conditions, such as tissue damage or inflammation, they are frequently mentioned as prime examples of DAMPs (Bianchi, J Leukoc Biol 81:1-5, 2007; Kono and Rock, Nat Rev Immunol 8:279-289, 2008; Martin-Murphy et al., Toxicol Lett 192:387-394, 2010). See for instance also a recent review (Chen and Nunez, Science 298:1395-1401, 2010). Contrary to this description, we recently presented some of the arguments against a role of heat shock protein as DAMPs (Broere et al., Nat Rev Immunol 11:565-c1, 2011). With this perspective and reflection article, we hope to elaborate on this debate and provide additional thoughts to further ignite this discussion on this critical and evolving issue.

A Mycobacterium leprae Hsp65 mutant as a candidate for mitigating lupus aggravation in mice

Hsp60 is an abundant and highly conserved family of intracellular molecules. Increased levels of this family of proteins have been observed in the extracellular compartment in chronic inflammation. Administration of M. leprae Hsp65 [WT] in [NZBxNZW]F₁ mice accelerates the Systemic Lupus Erythematosus [SLE] progression whereas the point mutated K⁴⁰⁹A Hsp65 protein delays the disease. Here, the biological effects of M. leprae Hsp65 Leader pep and K⁴⁰⁹A pep synthetic peptides, which cover residues 352–371, are presented. Peptides had immunomodulatory effects similar to that observed with their respective proteins on survival and the combined administration of K⁴⁰⁹A+Leader pep or K⁴⁰⁹A pep+WT showed that the mutant forms were able to inhibit the deleterious effect of WT on mortality, indicating the neutralizing potential of the mutant molecules in SLE progression. Molecular modeling showed that replacing Lysine by Alanine affects the electrostatic potential of the 352–371 region. The number of interactions observed for WT is much higher than for Hsp65 K⁴⁰⁹A and mouse Hsp60. The immunomodulatory effects of the point-mutated protein and peptide occurred regardless of the catalytic activity. These findings may be related to the lack of effect on survival when F₁ mice were inoculated with Hsp60 or K⁴⁰⁹A pep. Our findings indicate the use of point-mutated Hsp65 molecules, such as the K⁴⁰⁹A protein and its corresponding peptide, that may minimize or delay the onset of SLE, representing a new approach to the treatment of autoimmune diseases.

An altered peptide ligand corresponding to a novel epitope from heat-shock protein 60 induces regulatory T cells and suppresses pathogenic response in an animal model of adjuvant-induced arthritis

Induction of immune tolerance as therapeutic approach for autoimmune diseases constitutes a current research focal point. In this sense, we aimed to evaluate an altered peptide ligand (APL) for induction of peripheral tolerance in patients with rheumatoid arthritis (RA). A novel T-cell epitope from human heat-shock protein 60 (Hsp60), an autoantigen involved in the pathogenesis of RA, was identified by bioinformatics tools and an APL was design starting from this epitope. We investigated the ability of this APL for inducing regulatory T cells (Treg cells) in mice and evaluated the therapeutic effect of this peptide in an adjuvant-induced arthritis (AA) rat model. Clinical score, TNFα levels and histopathology were monitored, as well as the capacity of this APL for inducing Treg cells. Finally, the potentialities of the APL for inducing Treg cells were evaluated in ex vivo assays using mononuclear cells isolated from peripheral blood (PBMC). The APL induced an increase of the proportions of Treg cells in the draining lymph nodes of the injected site in mice. The APL efficiently inhibited the course of AA, with significant reduction of the clinical and histopathology score. This effect was associated with an increase of the proportions of Treg cells and a decrease of TNFα levels in spleen. Finally, stimulation of PBMCs from RA patients by the APL increases the proportions of the CD4(+)CD25(high)FoxP3(+) Treg cells. These results indicate a therapeutic potentiality of APL and support further investigation of this candidate drug for treatment of RA.

Extracellular proteomes of M-CSF (CSF-1) and GM-CSF-dependent macrophages

Macrophage colony-stimulating factor (M-CSF) (also known as CSF-1) and granulocyte-macrophage colony-stimulating factor (GM-CSF) have distinct effects on macrophage lineage populations, which are likely to be contributing to their functional heterogeneity. A comparative proteomic analysis of proteins released into culture media from such populations after M-CSF and GM-CSF exposure was carried out. Adherent macrophage populations, termed bone marrow-derived macrophage (BMM) and GM-BMM, were generated after treatment of murine bone marrow precursors with M-CSF and GM-CSF, respectively. Proteins in 16-h serum-free conditioned media (CM) were identified by two-dimensional gel electrophoresis and mass spectrometry. Respective protein profiles from BMM and GM-BMM CM were distinct and there was the suggestion of a switch from primarily signal peptide-driven secretion to non-classical secretion pathways from BMM to GM-BMM. Extracellular expression of cathepsins (lysosomal proteases) and their inhibitors seems to be a characteristic difference between these macrophage cell types with higher levels usually observed in BMM-CM. Furthermore, we have identified a number of proteins in BMM-CM and GM-BMM-CM that could be involved in various tissue regeneration and inflammatory (immune) processes, respectively. The uncharacterized protein C19orf10, a protein found at high levels in the synovial fluid of arthritis patients, was also differentially regulated; its extracellular levels were upregulated in the presence of GM-CSF.

A novel heat-shock protein coinducer boosts stress protein Hsp70 to activate T cell regulation of inflammation in autoimmune arthritis

OBJECTIVE

Stress proteins, such as members of the heat-shock protein (HSP) family, are up-regulated by cells in inflamed tissue and can be viewed functionally as "biomarkers" for the immune system to monitor inflammation. Exogenous administration of stress proteins has induced immunoregulation in various models of inflammation and has also been shown to be effective in clinical trials in humans. This study was undertaken to test the hypothesis that boosting of endogenous HSP expression can restore effective immunoregulation through T cells specific for stress proteins.

METHODS

Stress protein expression was manipulated in vivo and in vitro with a food component (carvacrol), and immune recognition of stress proteins was studied.

RESULTS

Carvacrol, a major compound in the oil of many Origanum species, had a notable capacity to coinduce cellular Hsp70 expression in vitro and, upon intragastric administration, in Peyer's patches of mice in vivo. As a consequence, carvacrol specifically promoted T cell recognition of endogenous Hsp70, as demonstrated in vitro by the activation of an Hsp70-specific T cell hybridoma and in vivo by amplified T cell responses to Hsp70. Carvacrol administration also increased the number of CD4+CD25+FoxP3+ T cells, systemically in the spleen and locally in the joint, and almost completely suppressed proteoglycan-induced experimental arthritis. Furthermore, protection against arthritis could be transferred with T cells isolated from carvacrol-fed mice.

CONCLUSION

These findings illustrate that a food component can boost protective T cell responses to a self stress protein and down-regulate inflammatory disease, i.e., that the immune system can respond to diet.

Hsp70 expression and induction as a readout for detection of immune modulatory components in food

Stress proteins such as heat shock proteins (Hsps) are up-regulated in cells in response to various forms of stress, like thermal and oxidative stress and inflammation. Hsps prevent cellular damage and increase immunoregulation by the activation of anti-inflammatory T-cells. Decreased capacity for stress-induced Hsp expression is associated with immune disorders. Thus, therapeutic boosting Hsp expression might restore or enhance cellular stress resistance and immunoregulation. Especially food- or herb-derived phytonutrients may be attractive compounds to restore optimal Hsp expression in response to stress. In the present study, we explored three readout systems to monitor Hsp70 expression in a manner relevant for the immune system and evaluated novel Hsp co-inducers. First, intracellular staining and analysis by flow cytometry was used to detect stress and/or dietary compound induced Hsp70 expression in multiple rodent cell types efficiently. This system was used to screen a panel of food-derived extracts with potent anti-oxidant capacity. This strategy yielded the identity of several new enhancers of stress-induced Hsp70 expression, among them carvacrol, found in thyme and oregano. Second, CD4(+) T-cell hybridomas were generated that specifically recognized an immunodominant Hsp70 peptide. These hybridomas were used to show that carvacrol enhanced Hsp70 levels increased T-cell activation. Third, we generated a DNAJB1-luc-O23 reporter cell line to show that carvacrol increased the transcriptional activation of a heat shock promoter in the presence of arsenite. These assay systems are generally applicable to identify compounds that affect the Hsp level in cells of the immune system.

Regulation of autoimmune inflammation by pro-inflammatory cytokines

The pro-inflammatory cytokines play a critical role in the initiation and propagation of autoimmune arthritis and many other disorders resulting from a dysregulated self-directed immune response. These cytokines influence the interplay among the cellular, immunological and biochemical mediators of inflammation at multiple levels. Regulation of the pro-inflammatory activity of these cytokines is generally perceived to be mediated by the anti-inflammatory and immunosuppressive cytokines such as IL-4, IL-10, or TGF-beta. However, increasing evidence is accumulating in support of the regulatory attributes of the pro-inflammatory cytokines themselves, in studies conducted in animal models of diabetes, multiple sclerosis, uveitis, and lupus. The results of our recent studies have shown that the pro-inflammatory cytokines, TNF-alpha and IFN-gamma, can suppress arthritic inflammation in rats, and also contribute to resistance against arthritis. These results are of paramount significance not only in fully understanding the pathogenesis of autoimmune arthritis, but also in anticipating the full ramifications of the in vivo neutralization of the pro-inflammatory cytokines, including that for therapeutic purposes.

Treatment with encapsulated Hsp60 peptide (p277) prolongs skin graft survival in a murine model of minor antigen disparity

The increased expression of heat shock protein (Hsp)60 in different kinds of graft tissues has been associated with a proinflammatory role and rejection. However, there are very few reports in which treatment with Hsp60 delays skin allograft rejection. The aim of this work was to evaluate the capacity of encapsulated human Hsp60-derived peptide p277 to delay graft rejection in two murine models of skin transplantation with minor antigen disparities. Briefly, BALB/c mice and C57BL/6 were intranasally pre-treated with five doses of Hsp60 p277 peptide encapsulated in polylactide-co-glycolide acid microspheres (PLGM), and received skin grafts from DBA2 mice and 129/B6 (F1) mice respectively. The treatment with the peptide increased skin graft survival more than 20 days in both the mouse strains, mainly in C57BL/6 recipients (P < 0.05). Also, p277-treated BALB/c and C57BL/6 mice showed IL-10 and IFN-gamma production, induced by p277 peptide. For the first time, a mucosal schedule using the Hsp60 C-terminal peptide p277 encapsulated in PLGM showed some survival prolongation of skin grafts bearing minor antigen disparities. Our results suggest a potential role for Hsp60-based therapy and the mucosal route as a useful tool to control the inflammatory response to allografts.

Diversity of physiological cell reactivity to heat shock protein 60 in different mouse strains

Heat shock proteins (Hsp) are families of highly conserved molecules and immunodominant antigens in some infections and in autoimmune diseases. Some reports suggest that different regions of the Hsp60 molecule induce distinct immune responses. However, there are no reports comparing physiological T-cell reactivity to Hsp60 in mice. In this study, we have analyzed T-cell proliferation and cytokine production induced by Hsp60, under physiological conditions, in three mouse strains bearing distinct major histocompatibility complex (MHC) backgrounds. Proliferative response predominantly was found in C57BL/6 mice, mostly induced by N-terminal and intermediate Hsp60 peptides (P < 0.0001). Interferon-gamma (IFNgamma) production was broadly induced by different regions of Hsp60 in all three mouse strains, although response was focused in different peptide groups in each strain. We did not observe an exclusive Th1 or Th2 cytokine profile induced by any particular region of Hsp60. However, we identified a strain hierarchy in IL-10 production induced by Hsp60 peptides from different regions, mostly detected in C3H/HePas, and in BALB/c, but not in C57BL/6 mice. In contrast, IL-4 production only was induced by the intermediate and C-terminal region peptides in both C3H/HePas and BALB/c mice. Our data give original information on physiological cellular reactivity to Hsp60. We also have identified peptides with the capacity to induce the production of anti-inflammatory cytokines, bringing perspectives for their use in immunotherapy of chronic inflammatory diseases and allograft rejection.

Chaperones As Part of Immune Networks

Network theory is increasingly accepted as a basic regulatory mechanism in diverse immunological functions. Heat shock proteins (Hsps) are involved in multiple networks in the immune system. Hsps themselves (foreign or endogenous) activate innate immunity and play important roles to deliver self or nonself materials to antigen presenting cells. However, Hsps are immunodominant antigens during infectious diseases making self Hsps endangered targets of autoimmunity by cross-reactive clones. Therefore, it is not surprising that the mechanism of protection of self Hsps is not clonal deletion in natural self tolerance; rather, self Hsps are protected by active regulating natural autoimmunity. The active regulatory/protective immunity is accomplished by natural autoantibodies and regulatory T cells, both recognizing Hsps. The multiple involvements of Hsps in immune networks make them ideal targets of therapy in autoimmune diseases. Indeed, immunotherapy with Hsps was recently reported to be effective treatment modality against cancer, arthritis or diabetes mellitus.

Stress, Heat Shock Proteins, and Autoimmunity: How Immune Responses to Heat Shock Proteins Are to Be Used for the Control of Chronic Inflammatory Diseases

Especially since the (re-)discovery of T cell subpopulations with specialized regulatory activities, mechanisms of anti-inflammatory T cell regulation are studied very actively and are expected to lead to the development of novel immunotherapeutic approaches, especially in chronic inflammatory diseases. Heat shock proteins (Hsp) are possible targets for regulatory T cells due to their enhanced expression in inflamed (stressed) tissues and the evidence that Hsp induce anti-inflammatory immunoregulatory T cell responses. Initial evidence for an immunoregulatory role of Hsp in chronic inflammation was obtained through analysis of T cell responses in the rat model of adjuvant arthritis and the findings that Hsp immunizations protected against the induction of various forms of autoimmune arthritis in rat and mouse models. Since then, immune reactivity to Hsp was found to result from inflammation in various disease models and human inflammatory conditions, such as rheumatoid arthritis (RA), type 1 diabetes, and atherosclerosis. Now, also in the light of a growing interest in T cell regulation, it is of interest to further explore the mechanisms through which Hsp can be utilized to trigger immunoregulatory pathways, capable of suppressing such a wide and diversified spectrum of inflammatory diseases.

A conjugate vaccine composed of a heat shock protein 60 T-cell epitope peptide (p458) and Neisseria meningitidis type B capsular polysaccharide

Neisseria meningitidis type B is a major world-health problem. The Meningococcus type B capsular polysaccharide (MnB) is very poorly immunogenic and no vaccine to the antigen exists. Here, we conjugated the MnB to a T-cell carrier peptide (p458) derived from the self-60kDa heat shock protein molecule. The conjugate vaccine was effective in inducing long-lasting IgG antibodies to the MnB antigen in mice. The vaccine was also immunogenic when injected in PBS. Thus, the p458 carrier peptide can induce T-cell help for the switch to IgG Ab to the MnB antigen.

Heat shock proteins in autoimmune diseases

Heat shock proteins (hsp's) are among the most conserved proteins in evolution. They have been identified as important pathogen-related antigens as well as autoantigens suitable for construction of novel vaccines. The high evolutionary homology of hsp's has raised the question about the safety of such vaccines. Experimental and clinical observations have confirmed that hsp proteins are involved in the regulation of some autoimmune disease such as autoimmune arthritis, type 1 diabetes mellitus, atherosclerosis, multiple sclerosis, and other autoimmune reactions. It has been shown in experimental animals that some hsp proteins (especially hsp60, hsp70, and hsp10) can either induce or prevent autoimmune reactions depending on the circumstances. This article discusses the involvement of hsp proteins in the etiology of autoimmune diseases and it presents promising experimental data on the effects of immunization with hsp proteins in the prevention and therapy of autoimmune diseases.

Stress proteins as inducers and targets of regulatory T cells in arthritis

Immunization with microbial or mammalian stress proteins or heat-shock proteins in models of experimental autoimmunity has been observed to lead to increased disease resistance. Furthermore, such immunization has been proposed to result in the induction and expansion of T cells that suppress disease upon transfer. Comparisons of microbial heat-shock proteins with other conserved immunogenic proteins of bacterial origin have indicated a unique capacity for heat-shock proteins to induce a regulatory phenotype in T cells, such as reflected by the production of IL10. Also, studies in children with chronic arthritis have indicated that T-cell responses to heat-shock proteins are associated with a benign course of the disease and with remission. Furthermore, in patients, heat-shock-protein-(HSP-) activated T cells were shown to display regulatory phenotypes consistent with CD4+ CD25+ T regulatory cells.

Heat-shock proteins induce T-cell regulation of chronic inflammation

Immune responses to certain heat-shock proteins (HSPs) develop in almost all inflammatory diseases; however, the significance of such responses is only now becoming clear. In experimental disease models, HSPs can prevent or arrest inflammatory damage, and in initial clinical trials in patients with chronic inflammatory disease, HSP-derived peptides have been shown to promote the production of anti-inflammatory cytokines, indicating that HSPs have immunoregulatory potential. In this Review, we discuss the unique characteristics of HSPs that endow them with these immunoregulatory qualities.

A paradoxical role of APCs in the induction of intravenous tolerance in experimental autoimmune encephalomyelitis

The central role of T cells in the induction of tolerance to autoantigens has been well documented. However, the role of antigen-presenting cells (APCs) in this process is not yet fully understood. To better understand the contribution of APCs in tolerance, we studied the interaction of purified APCs and CD4(+) T cells in a model of intravenous (i.v.) tolerance to experimental autoimmune encephalomyelitis (EAE). As expected, we found that T cells were tolerized to the autoantigen after i.v. injection. However, purified APCs obtained from MOG-i.v.-treated mice were paradoxically immuno-stimulatory, as they induced a non-specific Th1-type response both in vitro and in vivo. We conclude that blocking such APC activation would enhance the effectiveness of tolerance induction.

Inhibition of adjuvant-induced arthritis by DNA vaccination with the 70-kd or the 90-kd human heat-shock protein: immune cross-regulation with the 60-kd heat-shock protein

OBJECTIVE

Adjuvant arthritis can be induced in Lewis rats by immunization with Mycobacterium tuberculosis (Mt). The mycobacterial 65-kd heat-shock protein (Hsp65) is targeted by arthritogenic T cells. However, Hsp65 and the mycobacterial 71-kd heat-shock protein are also recognized by T cells that can down-regulate adjuvant-induced arthritis (AIA). We have recently demonstrated that vaccination with human Hsp60 DNA inhibits AIA. The present study was undertaken to analyze the role of the T cell responses to self HSP molecules other than Hsp60 in the control of AIA.

METHODS

Lewis rats were immunized with DNA vaccines coding for human Hsp70 or Hsp90 (Hsp70 plasmid [pHsp70] or pHsp90), and AIA was induced. The T cell response to Mt, Hsp60, Hsp70, and Hsp90 (proliferation and cytokine release) was studied, and the T cell response to Hsp60 was mapped with overlapping peptides.

RESULTS

The Hsp70 or Hsp90 DNA vaccines shifted the arthritogenic T cell response from a Th1 to a Th2/3 phenotype and inhibited AIA. We detected immune crosstalk between Hsp70/90 and Hsp60: both the Hsp70 and Hsp90 DNA vaccines induced Hsp60-specific T cell responses. Similarly, DNA vaccination with Hsp60 induced Hsp70-specific T cell immunity. Epitope mapping studies revealed that Hsp60-specific T cells induced by pHsp70 vaccination reacted with known regulatory Hsp60 epitopes.

CONCLUSION

T cell immunity to Hsp70 and to Hsp90, like Hsp60-specific immunity, can modulate the arthritogenic response in AIA. In addition, our results suggest that the regulatory mechanisms induced by Hsp60, Hsp70, and Hsp90 are reinforced by an immune network that connects their reactivities.

Immunological aspects of heat-shock proteins-the optimum stress of life

This review summarizes the complex role of heat-shock proteins (Hsp) in immune reactions, especially the cellular effects of heat-shock proteins during the recognition processes by innate immunity. The role of heat-shock proteins in the pathogenesis of two multifactorial diseases, i.e. inflammatory bowel disease (IBD) and atherosclerosis is highlighted. A new hypothesis on "immunodeficiency burden" is presented. According to this hypothesis, susceptibility to any multifactorial disease in any given subject and in the presence of specific environmental factors is the aggregate effect of polymorphisms resulting in the failure of protective immunity with consequent disease.

The T cells specific for the carboxyl-terminal determinants of self (rat) heat-shock protein 65 escape tolerance induction and are involved in regulation of autoimmune arthritis

Immunization of Lewis rats with heat-killed Mycobacterium tuberculosis H37Ra leads to development of polyarthritis (adjuvant-induced arthritis; AA) that shares several features with human rheumatoid arthritis (RA). Immune response to the 65-kDa mycobacterial heat-shock protein (Bhsp65) is believed to be involved in induction of AA as well as in experimental modulation of this disease. However, the understanding of several critical aspects of the pathogenesis of AA in the Lewis rat has severely been hampered by the lack of information both regarding the level as well as epitope specificity of tolerance to the mammalian self (rat) homologue of Bhsp65, 65-kDa rat heat-shock protein (Rhsp65), and about the functional attributes of the T cell repertoire specific for this self protein. In this study, we established that tolerance to Rhsp65 in the Lewis rat is incomplete, and that the residual T cells primed upon challenge with this self hsp65 are disease regulating in nature. We also have defined the T cell epitopes in the C-terminal region within Rhsp65 that contribute predominantly to the immune reactivity as well as the AA-protective effect of this self protein. Furthermore, the T cells primed by peptides comprising these C-terminal determinants can be efficiently restimulated by the naturally generated epitopes from endogenous Rhsp65, suggesting that self hsp65 might also be involved in natural remission from acute AA. These novel first experimental insights into the self hsp65-directed regulatory T cell repertoire in AA would help develop better immunotherapeutic approaches for autoimmune arthritis.

DNA vaccines expressing antigens with a stress protein-capturing domain display enhanced immunogenicity

An expression system for DNA vaccines is described, in which a fusion protein with an N-terminal, viral J-domain that captures heat-shock proteins (Hsps) is translated in-frame with C-terminal antigen-encoding sequences (of various lengths and origins). The system supports enhanced expression of chimeric antigens (of >800 residues in length) with an extended half life (>8 h). When used as a DNA vaccine, it delivers antigen together with the intrinsic adjuvant activity provided by bound Hsps. We describe the design of vectors for DNA vaccination that support the expression of different immunogenic domains of different origins as large, Hsp-capturing chimeric fusion antigens. The immunogenicity of the antigens produced by this expression system (when it is built into DNA vaccines) has been characterized in detail, with particular emphasis on priming CD8+ T-cell responses. We also discuss areas of vaccine research to which the new technology may provide useful contributions.

Induction of FOXP3-expressing regulatory CD4pos T cells by human mature autologous dendritic cells

Current literature suggests that T cells recognizing antigen on mature dendritic cells (DC) differentiate into effector T cells whereas tolerance is induced when antigen is presented by immature DC. We investigated the consequences of the interactions between immature or lipopolysaccharide-matured DC and CD4(pos) T lymphocytes in absence of foreign antigen. While immature DC did not induce significant CD4(pos) T cell activation, we observed that a significant fraction of CD4(pos) T cells cultured with mature autologous DC displayed phenotypic features of activation and produced IL-2, IFN-gamma, IL-10 and TGF-beta. Furthermore, CD4(pos) T lymphocytes primed by mature, but not immature, autologous DC acquired regulatory properties. Indeed, when added to an allogeneic mixed leukocyte reaction, they suppressed the response of alloreactive T lymphocytes to the priming DC while responses to third-party stimulators were spared. The generation of CD4(pos) T cells with regulatory function by autologous stimulation did not require the presence of natural CD4(pos)CD25(pos) regulatory T cells. In addition, the acquisition of regulatory function by CD4(pos)CD25(neg) T cells stimulated by autologous mature DC was accompanied by the induction of FOXP3 expression. Our data suggest that during inflammatory conditions, presentation of self antigens by mature DC to autologous T lymphocytes could contribute to the generation of regulatory mechanisms.

DNA fragments of the human 60-kDa heat shock protein (HSP60) vaccinate against adjuvant arthritis: identification of a regulatory HSP60 peptide

Adjuvant arthritis (AA) is induced by immunizing Lewis rats with Mycobacterium tuberculosis suspended in adjuvant. The mycobacterial 65-kDa heat shock protein (HSP65) contains at least one epitope associated with the pathogenesis of AA: T cell clones that recognize an epitope formed by aa 180-188 of HSP65 react with self-cartilage and can adoptively transfer AA. Nevertheless, vaccination with HSP65 or some of its T cell epitopes can prevent AA by a mechanism that seems to involve cross-reactivity with the self-60-kDa HSP60. We recently demonstrated that DNA vaccination with the human hsp60 gene can inhibit AA. In the present work, we searched for regulatory epitopes using DNA vaccination with HSP60 gene fragments. We now report that specific HSP60 DNA fragments can serve as effective vaccines. Using overlapping HSP60 peptides, we identified a regulatory peptide (Hu3) that was specifically recognized by the T cells of DNA-vaccinated rats. Vaccination with Hu3, or transfer of splenocytes from Hu3-vaccinated rats, inhibited the development of AA. Vaccination with the mycobacterial homologue of Hu3 had no effect. Effective DNA or peptide vaccination was associated with enhanced T cell proliferation to a variety of disease-associated Ags, along with a Th2/3-like shift (down-regulation of IFN-gamma secretion and enhanced secretion of IL-10 and/or tumor growth factor beta1) in response to peptide Mt176-190 (the 180-188 epitope of HSP65). The regulatory response to HSP60 or its Hu3 epitope included both Th1 (IFN-gamma) and Th2/3 (IL-10/tumor growth factor beta1) secretors. These results show that regulatory mechanisms can be activated by immunization with relevant self-HSP60 epitopes.

Facets of heat shock protein 70 show immunotherapeutic potential

Amongst the families of intracellular molecules that chaperone and assist with the trafficking of other proteins, notably during conditions of cellular stress, heat shock protein (hsp) 70 is one of the most studied. Although its name suggests that expression is exclusively induced during cellular hyperthermia, members of the hsp70 family of proteins can be constitutively expressed and/or induced by a range of other cellular insults. The ubiquitous presence of hsp70 in eukaryotic and prokaryotic cells, combined with its high degree of sequence homology and intrinsic immunogenicity, have prompted the suggestion that inappropriate immune reactivity to hsp70 might lead to pro-inflammatory responses and the development of autoimmune disease. Indeed, hsp70 has been shown to be a potent activator of innate immunity and aberrant expression of hsp70 in certain organs promotes immunopathology. However, studies also suggest that hsp70 might have immunotherapeutic potential, as hsp70 purified from malignant and virally infected cells can transfer and deliver antigenic peptides to antigen-presenting cells to elicit peptide-specific immunity and, in contrast to its reported pro-inflammatory effects, the administration of recombinant hsp70 can attenuate experimental autoimmune disease. This review focuses on the immunoregulatory capacity of hsp70 and its potential therapeutic value.

Heat shock proteins as regulators of the immune response

Until recently, heat shock proteins (also known as heat stress proteins) have mostly been regarded as intracellular molecules that mediate a range of essential housekeeping and cytoprotective functions. However, interest in their role as intercellular signalling molecules has been fuelled by the observations that these molecules can be released and are present in the extracellular environment under physiological conditions. They can elicit cytokine production by, and adhesion molecule expression of, a range of cell types, and they can deliver maturation signals and peptides to antigen presenting cells through receptor-mediated interactions. These functions suggest that heat shock proteins could be immunoregulatory agents with potent and widely-applicable therapeutic uses. Furthermore, the induction of self heat shock protein immune reactivity can attenuate autoimmunity and delay transplant rejection, and heat shock proteins derived from tumours and pathogens can elicit specific, protective immunity. This review will focus on this rapidly evolving area of heat shock protein biology.

Enhanced priming of multispecific, murine CD8+ T cell responses by DNA vaccines expressing stress protein-binding polytope peptides

A polytope DNA vaccine (pCI/pt10) was used that encodes within a 106-residue sequence 10-well characterized epitopes binding MHC class I molecules encoded by the K, D, or L locus (of H-2(d), H-2(b), and H-2(k) haplotype mice). The pCI/pt10 DNA vaccine efficiently primed all four K(b)/D(b)-restricted CD8(+) T cell responses in H-2(b) mice, but was deficient in stimulating most CD8(+) T cell responses in H-2(d) mice. Comparing CD8(+) T cell responses elicited with the pCI/pt10 DNA vaccine in L(d+) BALB/c and L(d-) BALB/c(dm2) (dm2) mice revealed that L(d)-restricted CD8(+) T cell responses down-regulated copriming of CD8(+) T cell responses to other epitopes regardless of their restriction or epitope specificity. Although the pt10 vaccine could thus efficiently co prime multispecific CD8(+) T cell responses, this priming was impaired by copriming L(d)-restricted CD8(+) T cell responses. When the pt10 sequence was fused to a 77-residue DnaJ-homologous, heat shock protein 73-binding domain (to generate a 183-residue cT(77)-pt10 fusion protein), expression and immunogenicity (for CD8(+) T cells) of the chimeric Ag were greatly enhanced. Furthermore, priming of multispecific CD8(+) T cell responses was readily elicited even under conditions in which the suppressive, L(d)-dependent immunodominance operated. The expression of polytope vaccines as chimeric peptides that endogenously capture stress proteins during in situ production thus facilitates copriming of CD8(+) T cell populations with a diverse repertoire.

The spontaneous remission of juvenile idiopathic arthritis is characterized by CD30+ T cells directed to human heat-shock protein 60 capable of producing the regulatory cytokine interleukin-10

OBJECTIVE

To test the hypothesis that T cell reactivity to self heat-shock protein 60 (Hsp60) in patients with remitting juvenile idiopathic arthritis (JIA) is part of an antiinflammatory, regulatory mechanism.

METHODS

Using peripheral blood-derived mononuclear cells (PBMCs) and synovial fluid-derived mononuclear cells (SFMCs) obtained from patients with JIA, we analyzed the expression of CD30 and the induction of regulatory cytokines in response to human and mycobacterial Hsp60.

RESULTS

In oligoarticular JIA patients, in vitro activation of PBMCs and SFMCs with Hsp60 induced a high expression of CD30 on CD4+, activated (HLA-DR-positive), memory (CD45RO+) T cells. The expression of CD30 induced by human Hsp60 was much higher than that induced by mycobacterial Hsp60. In oligoarticular JIA patients with active disease, the expression of CD30 in response to human Hsp60 was paralleled by a high interleukin-10 (IL-10):interferon-gamma (IFNgamma) ratio. In addition, restimulated human Hsp60-specific T cell lines from oligoarticular JIA patients showed a high production of IL-10 and a low production of IFNgamma. In contrast, PBMCs and SFMCs from polyarticular JIA patients responded to human Hsp60 with virtually no expression of CD30 and a low IL-10:IFNgamma ratio.

CONCLUSION

The results show that T cells responding to human Hsp60 in oligoarticular JIA patients express CD30, and during active phases of the disease, these T cells have a cytokine profile with a high IL-10:IFNgamma ratio. These findings suggest that in oligoarticular JIA patients, human Hsp60-specific CD4+ cells have a regulatory function and contribute to disease remission.

Different heat shock protein 60 species share pro-inflammatory activity but not binding sites on macrophages

In a study of seven different hsp60 species, we found that all mammalian and microbial proteins shared the property of eliciting an inflammatory response in mouse macrophages. In all cases, TNFalpha production was induced by 0.1 microM concentrations of hsp60. However, the different hsp60 preparations did not compete for the same binding site. The binding of fluorescence-labeled human hsp60 was inhibited by excess unlabeled human, rat or mouse hsp60, but not hamster, Escherichia coli, Chlamydia pneumoniae or Mycobacterium bovis hsp60. We conclude that phylogenetically separate hsp60 species interact with innate immune cells via different recognition pathways.

Alternative processing of endogenous or exogenous antigens extends the immunogenic, H-2 class I-restricted peptide repertoire

We investigated the murine, MHC class I-restricted cytotoxic T lymphocyte (CTL) response to a viral antigen delivered by different vaccination strategies to either the endogenous, or an alternative exogenous processing pathway. The immunization techniques used primed distinct (though overlapping) repertoires of CTL epitopes. In vitro studies revealed evidence for the generation of immunogenic, L(d)- and K(b)-binding peptides from endocytosed, exogenous antigen by alternative (endolysosomal) processing. Endogenous antigens expressed by DNA vaccines as a stress protein-associated fusion proteins gains access from the cytosol to endolysosomal processing. Hence, exogenous as well as endogenous protein antigens can gain access to alternative processing pathways and can give rise to an extended repertoire of antigenic epitopes. These studies indicate novel ways for the rational design of vaccine candidates that can prime CTL responses.

Inhibition of adjuvant arthritis by a DNA vaccine encoding human heat shock protein 60

Adjuvant arthritis (AA) is an autoimmune disease inducible in rats involving T cell reactivity to the mycobacterial 65-kDa heat shock protein (HSP65). HSP65-specific T cells cross-reactive with the mammalian 60-kDa heat shock protein (HSP60) are thought to participate in the modulation of AA. In this work we studied the effects on AA of DNA vaccination using constructs coding for HSP65 (pHSP65) or human HSP60 (pHSP60). We found that both constructs could inhibit AA, but that pHSP60 was more effective than pHSP65. The immune effects associated with specific DNA-induced suppression of AA were complex and included enhanced T cell proliferation to a variety of disease-associated Ags. Effective vaccination with HSP60 or HSP65 DNA led paradoxically to up-regulation of IFN-gamma secretion to HSP60 and, concomitantly, to down-regulation of IFN-gamma secretion to the P180-188 epitope of HSP65. There were also variable changes in the profiles of IL-10 secretion to different Ags. However, vaccination with pHSP60 or pHSP65 enhanced the production of TGFbeta1 to both HSP60 and HSP65 epitopes. Our results support a regulatory role for HSP60 autoreactivity in AA and demonstrate that this control mechanism can be activated by DNA vaccination with both HSP60 or HSP65.

Priming polyvalent immunity by DNA vaccines expressing chimeric antigens with a stress protein-capturing, viral J-domain

The N-terminal domain of large tumor antigens (T-Ag) of polyomaviruses forms a DnaJ-like structure with a conserved J domain that associates with constitutively expressed stress protein heat shock protein (hsp)73. Mutant (but not wild-type) SV40 T-Ag show stable, ATP-dependent binding to the stress protein hsp73 when expressed in cells from different vertebrate tissues. Intracellular T/hsp73 complexes accumulate to high steady-state levels. From this observation, we designed a vector system that supports stable expression of a large variety of hsp73-capturing, chimeric antigens containing an N-terminal, T-Ag-derived domain, and different C-terminal antigenic domains from unrelated antigens. Most antigenic domains tested could be stably expressed only in eukaryotic cells as fusion protein/hsp73 complexes. The N-terminal 77 residues representing the J domain of T-Ag were required for stable hsp73 binding and efficient expression of chimeric antigens. Hsp73-bound chimeric antigens expressed by DNA vaccines showed strikingly enhanced immunogenicity evident in humoral (antibody) and cellular cytolytic T lymphocytes (CTL) responses. The described system supports efficient expression of chimeric, polyvalent antigens and their codelivery with hsp73 as a "natural adjuvant" for enhanced immunogenicity for T and B cells.

The role of IL-12 in the induction of intravenous tolerance in experimental autoimmune encephalomyelitis

Intravenous administration of autoantigen is an effective method to induce Ag-specific tolerance against experimental autoimmune encephalomyelitis (EAE). IL-12 is a potent Th1 stimulator and an essential cytokine in the induction of EAE. The role of IL-12 in the induction of i.v. tolerance is not clear. In this study, we induced tolerance by i.v. administering myelin basic protein (MBP) peptide Ac1-11 (MBP1-11) in EAE. We observed significant suppression of IL-12 production by the lymph node cells of MBP1-11-injected mice. To see whether the low level of IL-12 is the cause or effect of tolerance, we administered IL-12 to the EAE mice at the time of i.v. MBP1-11 injection. Exogenous IL-12 abrogated the suppression of clinical and pathological EAE by i.v. tolerance. IL-12 blocked the suppressive effect of i.v. tolerance on the proliferative response to MBP1-11 and MBP1-11-induced production of IL-12 and IFN-gamma. Furthermore, IL-12 completely blocked the i.v. tolerance-induced type 1 T regulatory cell response. These data suggest that i.v. administration of autoantigen results in the suppression of endogenous IL-12 and the consequent switching of the immune response from an immunogenic to a tolerogenic form.