Diversification of response to hsp65 during the course of autoimmune arthritis is regulatory rather than pathogenic

The Pathophysiological Role of Heat Shock Response in Autoimmunity: A Literature Review

Within the last two decades, there has been increasing evidence that heat-shock proteins can have a differential influence on the immune system. They can either provoke or ameliorate immune responses. This review focuses on outlining the stimulatory as well as the inhibitory effects of heat-shock proteins 27, 40, 70, 65, 60, and 90 in experimental and clinical autoimmune settings.

Modulation of Adjuvant Arthritis by Cellular and Humoral Immunity to Hsp65

Heat shock proteins (Hsps) are highly conserved, and their expression is upregulated in cells by heat and other stressful stimuli. These proteins play a vital role in preserving the structural and functional integrity of cells under stress. Despite the ubiquitous expression of Hsps in an individual, the immune system is not fully tolerant to them. In fact, Hsps are highly immunogenic in nature, and immune response to these proteins is observed in various inflammatory and autoimmune diseases. Studies on the immunopathogenesis of autoimmune arthritis in the rat adjuvant arthritis (AA) model of human rheumatoid arthritis (RA) as well as observations in patients with RA and juvenile idiopathic arthritis (JIA) have unraveled immunoregulatory attributes of self-Hsp65-directed immunity. Notable features of Hsp65 immunity in AA include protection rather than disease induction following immunization of Lewis rats with self (rat)-Hsp65; the diversification of T cell response to mycobacterial Hsp65 during the course of AA and its association with spontaneous induction of response to self-Hsp65; the cross-reactive T cells recognizing foreign and self homologs of Hsp65 and their role in disease suppression in rats; the suppressive effect of antibodies to Hsp65 in AA; and the use of Hsp65, its peptides, or altered peptide ligands in controlling autoimmune pathology. The results of studies in the AA model have relevance to RA and JIA. We believe that these insights into Hsp65 immunity would not only advance our understanding of the disease process in RA/JIA, but also lead to the development of novel therapeutic approaches for autoimmune arthritis.

Regulation of autoimmune arthritis by the pro-inflammatory cytokine interferon-gamma

The pathogenesis of T cell-mediated diseases like rheumatoid arthritis (RA) has typically been explained in the context of the Th1-Th2 paradigm: the initiation/propagation by pro-inflammatory cytokines, and downregulation by Th2 cytokines. However, in our study based on the adjuvant-induced arthritis (AA) model of RA, we observed that Lewis (LEW) (RT.1(l)) rats at the recovery phase of AA showed the highest level of IFN-gamma in recall response to mycobacterial heat-shock protein 65 (Bhsp65), whereas AA-resistant Wistar-Kyoto (WKY) (RT.1(l)) rats secreted high levels of IFN-gamma much earlier following disease induction. However, no significant secretion of IL-10 or TGF-beta was observed in either strain. Furthermore, pre-treatment of LEW rats with a peptide of self (rat) hsp65 (R465), which induced T cells secreting predominantly IFN-gamma, afforded protection against AA and decreased IL-17 expression by the arthritogenic epitope-restimulated T cells. These results provide a novel perspective on the pathogenesis of autoimmune arthritis.

Autoantibodies in rheumatoid arthritis: a review

Emerging insights into the importance of B cells in the pathogenesis of rheumatoid arthritis (RA) as highlighted by the efficacy of B cell depletion is one factor that has contributed to the upsurge of interest in the potential role of autoantibodies both as disease markers and with respect to a pathogenic role. Since the initial description of rheumatoid factor (RF), a large number of both disease-specific and non-specific autoantibodies have been described in patients with RA including antibodies to type II collagen (CII), immunoglobulin binding protein (BiP) and antibodies directed at citrullinated peptides (anti-CCP) and other citrullinated proteins such as vimentin (anti-Sa) . Despite some overlap the serological profile of RA does appear to be distinct from other diseases such as SLE . Although the precise mechanisms responsible for the formation of these antibodies have not been well defined their presence must reflect the interaction between T and B cells believed to be relevant to the pathogenesis of RA. The specificity of the association of such factors as anti-CCP and anti-BiP with RA may reflect unique pathogenic events leading to the processing and presentation of the "cryptic self" . Ease of measurement and stability make autoantibodies attractive diagnostic and prognostic markers particularly in early disease when it may be difficult to distinguish self-limiting synovitis from persistent disease . The purpose of this article is to provide an overview of the current state of knowledge of the spectrum of autoantibodies thus far characterised in individuals with rheumatoid arthritis, and discuss their diagnostic, prognostic and pathogenetic relevance.

A nephritogenic peptide induces intermolecular epitope spreading on collagen IV in experimental autoimmune glomerulonephritis

This group previously identified a peptide p13 of alpha3(IV)NC1 domain of type IV collagen that induces experimental autoimmune glomerulonephritis (EAG) in rats with generation of antibodies to sites on alpha3(IV)NC1 external to the peptide as a result of intramolecular epitope spreading. It was hypothesized that intermolecular epitope spreading to other collagen IV chains also was induced. Rats were immunized with nephritogenic peptide that was derived from the amino terminal part of rat alpha3(IV)NC1 domain, and serum and kidney eluate were examined for antibodies to both native and recombinant NC1 domains of collagen IV. Peptide induced EAG with proteinuria and decreased renal function and glomerular basement membrane IgG deposits. Sera from these rats were examined by ELISA, which revealed reactivity not only to immunizing peptide but also to human and rat alpha3(IV)NC1 and to human alpha4(IV)NC1 domains. Kidney eluate that was depleted of alpha3(IV)NC1 antibodies still reacted to alpha4(IV)NC1, and alpha3(IV)NC1 column-bound antibody reacted with alpha3(IV)NC1. There was minimal reactivity to other collagen chains. Eluate that was adsorbed to NC1 hexamer from rat glomerular basement membrane lost all reactivity to glomerular constituents, and the eluted antibodies reacted to alpha3(IV)NC1 and alpha4(IV)NC1 domains. These studies show that a T cell epitope of alpha3(IV)NC1 induces EAG, intramolecular epitope spreading along alpha3(IV)NC1, and intermolecular epitope spreading to alpha4(IV)NC1 domain with minimal or no reactivity to other collagen chains or glomerular constituents. This is the first demonstration in EAG of intermolecular epitope spreading and identification of the spread epitopes.

Cutting edge: IFN-gamma regulates the induction and expansion of IL-17-producing CD4 T cells during mycobacterial infection

T cell responses are important to the control of infection but are deleterious if not regulated. IFN-gamma-deficient mice infected with mycobacteria exhibit enhanced accumulation of activated effector T cells and neutrophils within granulomatous lesions. These cells do not control bacterial growth and compromise the integrity of the infected tissue. We show that IFN-gamma-deficient mice have increased numbers of IL-17-producing T cells following infection with Mycobacterium bovis bacille Calmette Guérin. Furthermore, exogenous IFN-gamma increases IL-12 and decreases IL-23 production by bacille Calmette Guérin-infected bone marrow-derived dendritic cells and reduces the frequency of IL-17-producing T cells induced by these bone marrow-derived dendritic cells. These data support the hypothesis that, during mycobacterial infection, both IFN-gamma- and IL-17-producing T cells are induced, but that IFN-gamma serves to limit the IL-17-producing T cell population. This counterregulation pathway may be an important factor in limiting mycobacterially associated immune-mediated pathology.

IL-23 compensates for the absence of IL-12p70 and is essential for the IL-17 response during tuberculosis but is dispensable for protection and antigen-specific IFN-gamma responses if IL-12p70 is available

IL-12p70 induced IFN-gamma is required to control Mycobacterium tuberculosis growth; however, in the absence of IL-12p70, an IL-12p40-dependent pathway mediates induction of IFN-gamma and initial bacteriostatic activity. IL-23 is an IL-12p40-dependent cytokine containing an IL-12p40 subunit covalently bound to a p19 subunit that is implicated in the induction of CD4 T cells associated with autoimmunity and inflammation. We show that in IL-23 p19-deficient mice, mycobacterial growth is controlled, and there is no diminution in either the number of IFN-gamma-producing Ag-specific CD4 T cells or local IFN-gamma mRNA expression. Conversely, there is an almost total loss of both IL-17-producing Ag-specific CD4 T cells and local production of IL-17 mRNA in these mice. The absence of IL-17 does not alter expression of the antimycobacterial genes, NO synthase 2 and LRG-47, and the absence of IL-23 or IL-17, both of which are implicated in mediating inflammation, fails to substantially affect the granulomatous response to M. tuberculosis infection of the lung. Despite this redundancy, IL-23 is required to provide a moderate level of protection in the absence of IL-12p70, and this protection correlates with a requirement for IL-23 in the IL-12p70-independent induction of Ag-specific, IFN-gamma-producing CD4 T cells. We also show that IL-23 is required for the induction of an IL-17-producing Ag-specific phenotype in naive CD4 T cells in vitro and that absence of IL-12p70 promotes an increase in the number of IL-17-producing Ag-specific CD4 T cells both in vitro and in vivo.

Stat4-null non-obese diabetic mice: protection from diabetes and experimental allergic encephalomyelitis, but with concomitant epitope spread

There is much interest in therapeutic manipulation of cytokine responses in autoimmunity, yet studies in mouse models have sometimes produced conflicting findings as to the role of particular mediators in disease. Examples include the contradictory findings regarding susceptibility to experimental allergic encephalomyelitis (EAE) or diabetes in knockout mice for various individual Th1 or Th2 cytokines or their receptors. An alternative approach to the analysis of Th1 and Th2 mechanisms in these diseases is to investigate strains carrying a null mutation for molecules involved in cytokine receptor signal transduction, signal transducer and activator of transcription (Stat4) and Stat6. Stat4 is pivotal in Th1 polarization, being activated when IL-12 binds the IL-12R and leading to the production of IFNgamma. We here report disease susceptibility in non-obese diabetic mice carrying a Stat4-null mutation. Knockout mice were almost completely protected from diabetes, only rarely showing pancreatic peri-islet infiltrates. Furthermore, there was near complete protection from the induction of EAE by either of the two encephalitogenic myelin epitopes. Despite this protection, Stat4-null mice showed clear epitope spread compared with controls during myelin oligodendrocyte glycoprotein-induced EAE as judged by T cell proliferation, although this was not associated with a strong Th1 response to the initial or spread epitope and, furthermore, there was no evidence of a switch to Th2 cytokines.

Identification of T-cell epitopes on U1A protein in MRL/lpr mice: double-negative T cells are the major responsive cells

Systemic lupus erythematosus (SLE) is characterized by the existence of a heterogeneous group of autoantibodies such as anti-DNA, chromatin, histone, and ribonucleoprotein antibodies (Abs). Although the B-cell antigenic determinants have been well characterized, very limited data about the T-cell epitopes of self-antigen (Ag) have been reported. In the present study, we analysed auto-T-cell epitopes using bone marrow-derived dendritic cells (BM-DCs) pulsed with murine U1A (mU1A) protein capable of activating autoreactive T cells from unprimed MRL/lpr mice in vitro. The data suggested that there are at least four T-cell epitopes on the U1A protein, U1A31-50, U1A61-80, U1A201-220 and U1A271-287, and U1A31-50 had the most significant T-cell proliferative response. In addition, the main responsive T cells are the CD4- CD8- double-negative subgroup of T cells. Furthermore, we also demonstrated that the activation of double-negative T cells is major histocompatibility complex class II restricted. The study here provides information on T-cell epitope analysis of the U1A antigen using BM-DCs as the effective antigen-presenting cells.

DNA vaccines coding for heat-shock proteins (HSPs): tools for the activation of HSP-specific regulatory T cells

Heat-shock proteins (HSPs) perform opposing functions in autoimmune arthritis. HSP-specific T cells drive the progression of adjuvant arthritis (AA), an experimental model of autoimmune arthritis. However, HSP-specific T cells can also have a regulatory phenotype, controlling arthritogenic T cells and inhibiting AA progression. This manuscript reviews the use of DNA vaccines coding for HSPs to analyse the role of these proteins in the regulation of arthritis. Recent studies suggest that HSPs participate in the control of pathological autoimmunity. Indeed, DNA vaccines coding for HSPs can be used to activate these HSP-specific built-in regulatory mechanisms. Thus, DNA vaccines coding for HSPs may serve not only as tools for the dissection of immunoregulatory mechanisms, but also as agents for the treatment of autoimmune disorders.

Rh autoantigen presentation to helper T cells in chronic lymphocytic leukemia by malignant B cells

Chronic lymphocytic leukemia (CLL) is frequently associated with autoimmune diseases directed against constituents of the blood, including hemolytic anemia (AIHA). We hypothesized that CLL cells predispose to hematologic autoimmunity by acting as aberrant antigen-presenting cells (APCs). Initially, it was confirmed that all studied patients with AIHA secondary to CLL harbored activated helper T (TH) cells specific for epitopes on the dominant red blood cell (RBC) autoantigens in primary AIHA, the Rh proteins. Rh-specific TH cells were also detected in a number of patients with CLL who, although they did not have AIHA, had low levels of anti-RBC antibody in their sera. Fractionation of putative APC populations from the peripheral blood of patients by negative selection showed that CD5+ CLL cells are the most effective cell type in processing and presenting purified Rh protein to autoreactive TH cells. This ability was confirmed using positively selected CD5+ CLL cells. Thus, our study provides the first evidence for malignant cells driving an autoimmune response by acting as aberrant APCs.

T-cell autoreactivity to Hsp in human transplantation may involve both proinflammatory and regulatory functions

Heat shock proteins (Hsp) are moving from the category of basically intracellular chaperone molecules to important proteins in both innate and acquired immune responses, with great potential for clinical application as immunomodulators. Both proinflammatory and regulatory Hsp-reactive T cells have been described in animal models of autoimmune diseases. To investigate the role of autoreactivity to Hsp60 and Hsp70 in human transplantation, we analyzed, sequentially, peripheral blood mononuclear cell proliferation and cytokine production before and at different time points after renal transplantation, as well as the modulation of proliferation to Hsp in the presence of exogenous cytokines. Proliferation to Hsp60 and Hsp70 in the pretransplantation (pre-Tx) period was significantly associated with rejection episodes in the first months post-Tx. In contrast, IL-4 production was significantly associated with absence of rejection. Addition of exogenous IL-4 distinctly modulated the proliferative response to Hsp60; inhibiting proliferation in 83% of patients in the early post-Tx period (0-6 months), in which rejection episodes occurred, and inducing proliferation in 62.5% of patients in the later period (>12-24 months), when no rejection was observed. Characterization of autoreactive anti-Hsp60 regulatory T cells may permit new approaches to control the proinflammatory response to the graft, as well as aggressive autoimmunity.

The regulatory C-terminal determinants within mycobacterial heat shock protein 65 are cryptic and cross-reactive with the dominant self homologs: implications for the pathogenesis of autoimmune arthritis

The 65-kDa mycobacterial heat shock protein (Bhsp65) has been invoked in the pathogenesis of both adjuvant arthritis (AA) in the Lewis rat (RT.1(l)) and human rheumatoid arthritis. Arthritic Lewis rats in the late phase of AA show diversification of the T cell response to Bhsp65 C-terminal determinants (BCTD), and pretreatment of naive Lewis rats with a mixture of peptides representing these neoepitopes affords protection against AA. However, the fine specificity and physiologic significance of the BCTD-directed T cell repertoire, and the role of homologous self (rat) hsp65 (Rhsp65), if any, in spreading of the T cell response to Bhsp65 have not yet been examined. We observed that T cells primed by peptides comprising BCTD can adoptively transfer protection against AA to the recipient Lewis rats. However, these T cells can be activated by preprocessed (peptide) form of BCTD, but not native Bhsp65, showing that BCTD are cryptic epitopes. The BCTD-reactive T cells can be activated by the naturally generated (dominant) C-terminal epitopes of both exogenous and endogenous Rhsp65 and vice versa. Furthermore, certain individual peptides constituting BCTD and their self homologs can also induce protection against AA. These results support a model for the diversification of T cell response to Bhsp65 during the course of AA involving up-regulation of the display of cryptic BCTD coupled with spontaneous induction of T cell response to the cross-reactive dominant C-terminal epitopes of Rhsp65. The identification of disease-regulating cryptic determinants in Ags implicated in arthritis provides a novel approach for immunotherapy of rheumatoid arthritis.

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.

Genomic absence of the gene encoding T cell receptor Vbeta7.2 is linked to the presence of autoantibodies in Sjögren's syndrome

OBJECTIVE

It is not yet known whether the absence of certain T cell receptor V(beta) (TCRBV) genes (e.g., due to genomic deletion) has functional significance. We examined this question in relation to a known 21.6-kb insertion/deletion-related polymorphism (IDRP) in the human BV locus.

METHODS

New polymerase chain reaction (PCR) genotyping methods were used. Monoclonal antibodies to TCRBV gene products were used to confirm the absence of the relevant proteins. Patients with Sjögren's syndrome (SS) or systemic lupus erythematosus (SLE) were compared with normal controls with regard to TCR genotypes and serologic profiles.

RESULTS

There are 3 known haplotypes (I, D1, D2) and 6 possible genotypes related to the 21.6-kb IDRP. Novel PCR-based methods were used to define these genotypes. In subjects with deleted/deleted (D/D) genotypes, T cells could not express V(beta)7.2 TCRs, as assayed with a new antibody specific for V(beta)7.2. This was the sole significant difference between subjects without the insertion and those with either 1 or 2 copies. Surprisingly, we found that the D/D genotype was associated with primary SS, but only when pathogenic autoantibodies were present.

CONCLUSION

These results suggest that T cells expressing TCRs with V(beta)7.2 are protective against a pathogenic immune response in SS. Thus, genomic polymorphism of TCR genes (along with the correct HLA alleles) determines whether T cells can direct a pathogenic autoimmune response.

The Wistar Kyoto (RT1(l)) rat is resistant to myelin basic protein-induced experimental autoimmune encephalomyelitis: comparison with the susceptible Lewis (RT1(l)) strain with regard to the MBP-directed CD4+ T cell repertoire and its regulation

Here, we demonstrate that the Wistar Kyoto (WKY/NHsd) rat, which bears the same RT1(l) haplotype as the experimental autoimmune encephalomyelitis (EAE)-susceptible Lewis rat strain, is highly resistant to myelin basic protein (MBP)-induced EAE. No differences between Lewis and WKY strains were found in T cell proliferative specificity or the use of Vbeta8.2 T cell receptors in response to MBP. A Th2 cytokine bias correlated with WKY's EAE resistance. MBP challenge of WKY-into-Lewis adoptive transfer recipients produced a novel biepisodic EAE. The WKY strain should be useful in studies of many tissue-specific autoimmune diseases to which the Lewis rat is susceptible.

Epitope spreading in immune-mediated diseases: implications for immunotherapy

Evidence continues to accumulate supporting the hypothesis that tissue damage during an immune response can lead to the priming of self-reactive T and/or B lymphocytes, regardless of the specificity of the initial insult. This review will focus primarily on epitope spreading at the T-cell level. Understanding the cellular and molecular basis of epitope spreading in various chronic immune-mediated human diseases and their animal models is crucial to understanding the pathogenesis of these diseases and to the ultimate goal of designing antigen-specific treatments.

Epitope spreading: protection from pathogens, but propagation of autoimmunity?

An epitope is an antigenic determinant, or a site on the surface of an antigenic molecule, to which a single antibody binds. Epitope spreading (ES) refers to the development of an immune response to epitopes distinct from, and noncross-reactive with, the disease-causing epitope. Diversification, or the ability of the immune system to attack multiple targets on a pathogen has obvious advantages. Here we review some of the evidence regarding its role in autoimmunity, in humans and in animal disease models. We consider the implications of ES on the development of highly specific therapies for autoimmune disease. We stress that pathogenic ES probably occurs in the context of inherent abnormalities in control mechanisms for the prevention of autoimmunity or other genetic predisposing factors.

Characterization of self-T-cell response and antigenic determinants of U1A protein with bone marrow-derived dendritic cells in NZB x NZW F1 mice

Systemic lupus erythematosus (SLE) is characterized by the existence of a heterogeneous group of autoantibodies directed against nuclear intact structures, such as nucleosomes and small nuclear ribonucleoproteins (snRNPs). Autoantibodies against snRNPs are of special interest because they are detectable in the majority of SLE patients. Although the B-cell antigenic determinants have been well characterized, very limited data have been reported in regard to the T-cell epitopes of snRNPs. Furthermore, several studies have demonstrated that determination of the auto-T-cell epitopes recognized by freshly isolated T cells is difficult from unprimed lupus mice when self-antigen-pulsed B cells or macrophages are used as antigen-presenting cells (APCs) in vitro. In the present study, we showed a novel approach for determining the auto-T-cell epitopes, using bone marrow-derived dendritic cells (BMDCs) pulsed with the murine U1A protein - an immunodominant antigen of the U1 snRNPs - which is capable of activating freshly isolated T cells from unprimed (NZB x NZW) F1 (BWF1) mice in vitro. The T-cell epitope area was found to be located at the C-terminus of U1A, overlapping the T-cell epitope of human U1A that has been reported in human SLE. Identification of the autoreactive T-cell epitope(s) in snRNPs will help to elucidate how reciprocal T-B determinant spreading of snRNPs emerges in lupus. The results presented here also indicate that it is feasible to use this approach to further explore strategies to design immunotherapy for patients with lupus.

Environmental modulation of autoimmune arthritis involves the spontaneous microbial induction of T cell responses to regulatory determinants within heat shock protein 65

Both genetic and environmental factors are believed to be involved in the induction of autoimmune diseases. Adjuvant arthritis (AA) is inducible in susceptible rat strains by injection of Mycobacterium tuberculosis, and arthritic rats raise T cell responses to the 65-kDa mycobacterial heat-shock protein (Bhsp65). We observed that Fischer 344 (F344) rats raised in a barrier facility (BF-F344) are susceptible to AA, whereas F344 rats maintained in a conventional facility (CV-F344) show significantly reduced incidence and severity of AA, despite responding well to the arthritogenic determinant within Bhsp65. The acquisition of protection from AA can be circumvented if rats are maintained on neomycin/acidified water. Strikingly, naive unimmunized CV-F344 rats but not BF-F344 rats raised T cell responses to Bhsp65 C-terminal determinants (BCTD) (we have previously shown that BCTD are involved in regulation of acute AA in the Lewis rat); however, T cells of naive CV-F344 and BF-F344 gave a comparable level of proliferative response to a mitogen, but no response at all to an irrelevant Ag. Furthermore, adoptive transfer into naive BF-F344 rats of splenic cells of naive CV-F344 rats (restimulated with BCTD in vitro) before induction of AA resulted in a considerably reduced severity of AA. These results suggest that spontaneous (inadvertent) priming of BCTD-reactive T cells, owing to determinant mimicry between Bhsp65 and its homologues in microbial agents in the conventional environment, is involved in modulating the severity of AA in CV-F344 rats. These results have important implications in broadening understanding of the host-microbe interaction in human autoimmune diseases.

Lipocalins as allergens

The term allergy refers to clinical conditions caused by an inappropriate immune response to innocuous proteins in genetically predisposed persons. Allergens of animal origin are responsible for a significant proportion of allergies. In recent years, it has become evident that practically all respiratory animal allergens characterized at the molecular level belong to the lipocalin family of proteins. The current list comprises the major allergens of horse, cow, dog, mouse, rat and cockroach as well as beta-lactoglobulin of cow's milk. While the molecular structure of all these allergens is known, far less information is available regarding their immunological characteristics. Knowing the way the immune system recognizes these allergens and reacts to them might, however, be the key for discovering the common denominator of the allergenicity of lipocalins. The human body contains numerous endogenous lipocalins, and the immune system has to adapt to their presence. We have proposed that under these conditions the immune response against the lipocalin allergens which are structurally related to endogenous lipocalins might be the pathway to allergy in genetically predisposed persons. The same might well apply also to other allergens with homologous endogenous counterparts.

[Heat shock proteins or "stress proteins"]

INTRODUCTION

Heat shock proteins (HSP) are molecular chaperones which facilitate the biosynthesis and maturation of proteins within cells (protein folding). They promote assembly and disassembly of polypeptides and play a major role in cellular function, not only during the stress response but also at basal state.

CURRENT KNOWLEDGE AND KEY POINTS

As HSP are immunogenic molecules and can be expressed on cellular membranes, their role in auto-immune and inflammatory diseases, particularly in systemic lupus erythematosus, Behçet's disease and rheumatoid arthritis, has been studied. Cellular immune response of T cells and humoral response with antibodies production against HSP occurring in the course of those diseases have been observed.

FUTURE PROSPECTS AND PROJECTS

Anti-HSP immune response might provide better understanding of the pathogenic mechanisms involved in those diseases. At present it is not known whether HSP can trigger them. Indeed, anti-HSP immunity could be induced by the immunological process or be part of a normal immunoregulatory response.

Animal models of rheumatoid arthritis and related inflammation

The major, extensively studied, experimentally-induced rat and mouse models of arthritis with features resembling rheumatoid arthritis are reviewed here. Etiopathogenetic studies that were recently published are emphasized. In summary, multiple triggering stimuli can induce disease in genetically-prone strains of inbred rats and mice. Multiple genetic loci, including both MHC and non-MHC, regulate disease expression in these animals. By comparison with other models of autoimmune disease, clustering of regulatory loci within and among species is increasingly becoming evident. At the cellular level, both innate and acquired immune systems are involved in the disease manifestations. At the molecular level, unbalanced chronic production of tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-1, IL-6 and IL-12, as opposed to IL-4 and IL-10, is correlated with arthritis disease susceptibility and severity.

Heat shock proteins and skin diseases

Heat shock proteins are chaperones to construct protein molecules and are widely distributed in prokaryotic and eukaryotic cells. They are also induced by environmental stress to protect cells. Human heat shock proteins cross-react with bacterial heat shock proteins to modulate immune responses to induce autoimmunity. They are involved in the differentiation and growth of neoplastic cells as well as normal cells. They are also involved in various inflammatory skin diseases and in fibrotic process. Heat shock proteins play important roles in the pathogenesis of many skin diseases.