Genetic bias in immune responses to a cassette shared by different microorganisms in patients with rheumatoid arthritis

Characteristics of the (Auto)Reactive T Cells in Rheumatoid Arthritis According to the Immune Epitope Database

T cells are known to be involved in the pathogenesis of rheumatoid arthritis (RA). Accordingly, and to better understand T cells' contribution to RA, a comprehensive review based on an analysis of the Immune Epitope Database (IEDB) was conducted. An immune CD8+ T cell senescence response is reported in RA and inflammatory diseases, which is driven by active viral antigens from latent viruses and cryptic self-apoptotic peptides. RA-associated pro-inflammatory CD4+ T cells are selected by MHC class II and immunodominant peptides, which are derived from molecular chaperones, host extra-cellular and cellular peptides that could be post-translationally modified (PTM), and bacterial cross-reactive peptides. A large panel of techniques have been used to characterize (auto)reactive T cells and RA-associated peptides with regards to their interaction with the MHC and TCR, capacity to enter the docking site of the shared epitope (DRB1-SE), capacity to induce T cell proliferation, capacity to select T cell subsets (Th1/Th17, Treg), and clinical contribution. Among docking DRB1-SE peptides, those with PTM expand autoreactive and high-affinity CD4+ memory T cells in RA patients with an active disease. Considering original therapeutic options in RA, mutated, or altered peptide ligands (APL) have been developed and are tested in clinical trials.

Complement and its environmental determinants in the progression of human rheumatoid arthritis

Rheumatoid arthritis (RA) is a complex autoimmune disease with an etiology that is not yet well understood, disproportionally affects women and also varies in incidence and prevalence by population. The presence of anti-citrullinated protein antibodies (ACPA) is a highly specific biomarker for the diagnosis of clinically apparent RA. ACPA are also present in the serum for an average of 3-5 years prior to the onset of RA during an asymptomatic period characterized by mucosal inflammation and local ACPA production at these sites. We hypothesized that systemic complement activation products might be generated during the pre-clinical initiation of RA and/or provide a second hit that promotes subsequent arthritis development in the joints. In addition, we evaluated which demographic and genetic features and environmental exposures could influence the complement activation process. We analyzed plasma from healthy subjects, subjects at-risk for the development of RA based on serum ACPA positivity in absence of inflammatory arthritis (IA), and ACPA positive RA subjects by Multiplex Assay and ELISA for eighteen complement system components, factors and activation products belonging to the classical, lectin and alternative pathways. By using regression models, associations between complement proteins and various demographic, genetic, and environmental factors previously found to be associated with RA, including sex, smoking, shared epitope, and oral contraceptive use, were examined. We found no evidence of systemic complement activation in ACPA positive subjects without IA, but in contrast found evidence of systemic involvement of the both classical and alternative pathways during the stage of the disease where classified RA is present, (i.e. during joint inflammation and damage). With regard to the demographic, genetic, and environmental variables, females who reported current or past oral contraceptive use and subjects with current tobacco exposure demonstrated alterations of the alternative pathway of complement. Furthermore, RA subjects with established disease who have a body mass index categorized as obese demonstrated higher levels of C2 compared to RA subjects who are not considered obese. In sum, the complement system may be involved in the pathogenesis of RA, with only localized mucosal effects during the preclinical period in those at-risk for RA but in the joint as well as systemically in those who have developed clinically apparent arthritis.

Targeting of tolerogenic dendritic cells towards heat-shock proteins: a novel therapeutic strategy for autoimmune diseases?

Tolerogenic dendritic cells (tolDCs) are a promising therapeutic tool to restore immune tolerance in autoimmune diseases. The rationale of using tolDCs is that they can specifically target the pathogenic T-cell response while leaving other, protective, T-cell responses intact. Several ways of generating therapeutic tolDCs have been described, but whether these tolDCs should be loaded with autoantigen(s), and if so, with which autoantigen(s), remains unclear. Autoimmune diseases, such as rheumatoid arthritis, are not commonly defined by a single, universal, autoantigen. A possible solution is to use surrogate autoantigens for loading of tolDCs. We propose that heat-shock proteins may be a relevant surrogate antigen, as they are evolutionarily conserved between species, ubiquitously expressed in inflamed tissues and have been shown to induce regulatory T cells, ameliorating disease in various arthritis mouse models. In this review, we provide an overview on how immune tolerance may be restored by tolDCs, the problem of selecting relevant autoantigens for loading of tolDCs, and why heat-shock proteins could be used as surrogate autoantigens.

Genetics of rheumatoid arthritis: a new boost is needed in Latin American populations

Rheumatoid arthritis (RA) is an autoimmune inflammatory rheumatic disease which affects several organs and tissue, predominantly the synovial joints. Like many other autoimmune diseases, RA is a complex disease, where genetic variants, environmental factors and random events interact to trigger pathological pathways. Genetic implication in RA is evident, and recent advances have expanded our knowledge about the genetic factors that contribute to RA. An exponential increment in the number of genes associated with the disease has been described, mainly through gene wide screen studies (GWAS) involving international consortia with large patient cohorts. However, there are a few studies on Latin American populations. This article describes what is known about the RA genetics, the future that is emerging, and how this will develop a more personalized approach for the treatment of the disease. Latin American RA patients cannot be excluded from this final aim, and a higher collaboration with the international consortia may be needed for a better knowledge of the genetic profile of patients from this origin.

Type I IFNs as biomarkers in rheumatoid arthritis: towards disease profiling and personalized medicine

RA (rheumatoid arthritis) is a chronic rheumatic condition hallmarked by joint inflammation and destruction by self-reactive immune responses. Clinical management of RA patients is often hampered by its heterogeneous nature in both clinical presentation and outcome, thereby highlighting the need for new predictive biomarkers. In this sense, several studies have recently revealed a role for type I IFNs (interferons), mainly IFNα, in the pathogenesis of a subset of RA patients. Genetic variants associated with the type I IFN pathway have been linked with RA development, as well as with clinical features. Moreover, a role for IFNα as a trigger for RA development has also been described. Additionally, a type I IFN signature has been associated with the early diagnosis of RA and clinical outcome prediction in patients undergoing biological drug treatment, two challenging issues for decision-making in the clinical setting. Moreover, these cytokines have been related to endothelial damage and vascular repair failure in different autoimmune disorders. Therefore, together with chronic inflammation and disease features, they could probably account for the increased cardiovascular disease morbidity and mortality of these patients. The main aim of the present review is to provide recent evidence supporting a role for type I IFNs in the immunopathology of RA, as well as to analyse their possible role as biomarkers for disease management.

A small shared epitope-mimetic compound potently accelerates osteoclast-mediated bone damage in autoimmune arthritis

We have recently proposed that the shared epitope (SE) may contribute to rheumatoid arthritis pathogenesis by acting as a ligand that activates proarthritogenic signal transduction events. To examine this hypothesis, in this study we characterized a novel small SE-mimetic compound, c(HS4-4), containing the SE primary sequence motif QKRAA, which was synthesized using a backbone cyclization method. The SE-mimetic c(HS4-4) compound interacted strongly with the SE receptor calreticulin, potently activated NO and reactive oxygen species production, and markedly facilitated osteoclast differentiation and function in vitro. The pro-osteoclastogenic potency of c(HS4-4) was 100,000- to 1,000,000-fold higher than the potency of a recently described linear SE peptidic ligand. When administered in vivo at nanogram doses, c(HS4-4) enhanced Th17 expansion, and in mice with collagen-induced arthritis it facilitated disease onset, increased disease incidence and severity, enhanced osteoclast abundance in synovial tissues and osteoclastogenic propensities of bone marrow-derived cells, and augmented bone destruction. In conclusion, c(HS4-4), a highly potent small SE-mimetic compound enhances bone damage and disease severity in inflammatory arthritis. These findings support the hypothesis that the SE acts as a signal transduction ligand that activates a CRT-mediated proarthritogenic pathway.

Epstein-Barr virus in systemic lupus erythematosus, rheumatoid arthritis and multiple sclerosis—association and causation

Epidemiological data suggest that the Epstein-Barr virus (EBV) is associated with several autoimmune diseases, such as systemic lupus erythematosus, rheumatoid arthritis and multiple sclerosis. However, it is not clear whether EBV plays a role in the pathogenesis of these diseases, and if so, by which mechanisms the virus may contribute. In this review, we discuss possible viral and immunological mechanisms that might explain associations between EBV and autoimmune diseases and whether these associations represent causes or effects of inflammation and autoimmunity.

New insights into the functional role of the rheumatoid arthritis shared epitope

The shared epitope (SE) - an HLA-DRB1-encoded 5-amino acid sequence motif carried by the vast majority of rheumatoid arthritis (RA) patients - is a risk factor for severe disease. The mechanistic basis of RA-SE association is unknown. This group has previously demonstrated that the SE acts as a signal transduction ligand that activates nitric oxide and reactive oxygen species production. SE-activated signaling depends on cell surface calreticulin, a known innate immunity receptor previously implicated in immune regulation, autoimmunity and angiogenesis. Recent evidence that the SE enhances the polarization of Th17 cells, which is a key mechanism in autoimmunity, is discussed highlighting one of several potential functional effects of the SE in RA.

MHC molecules in health and disease: At the cusp of a paradigm shift

Half a century after the major histocompatibility complex (MHC) was discovered, its functional roles in health and disease remain poorly understood. Many hallmarks of the MHC, including its unusual evolution, structurefunction properties of its gene products and allele-specific associations with dozens of diseases and health traits cannot be convincingly explained by the tenets of existing paradigms. It is therefore becoming increasingly apparent that in order to better understand MHC-health/disease association-a phenomenon that impacts the health of millions-heterodox ideas are critically needed. Here we propose a testable, novel theory concerning the functional role of MHC molecules in health and disease. At the focus of this theory is an evolutionarily-conserved, tri-dimensional cusp-like prominence ('kink'), found in the midst of one of the two α helices that form the perimeter of the groove of all MHC molecules. Based on structural, functional and evolutionary considerations, as well as our recent experimental data, it is proposed here that the MHC cusp region is enriched in allele-specific signal transduction ligands that interact with non-MHC cell surface receptors and trigger signaling events. Aberrations in these pathways could lead to disease development, or affect the severity of such diseases.

A role for calreticulin in the pathogenesis of rheumatoid arthritis

Calreticulin (CRT) plays a role in the clearance of dying cells and has been implicated in autoimmunity. Recent evidence indicates that cell surface CRT (csCRT) acts as a signal transducing receptor for the rheumatoid arthritis (RA) shared epitope (SE). The SE binding site on CRT has been mapped to amino acid residues 217-223 in the P-domain. Upon interaction with dendritic cells (DCs), the SE activates potent immune regulatory events. In CD8α(+) DCs, which express higher abundance of csCRT, the SE inhibits the tolerogenic enzyme indoleamine 2,3 dioxygenase with resultant inhibition of regulatory T (Treg) cell differentiation. In CD8α(-) DCs, the SE ligand increases secretion of IL-6 and IL-23 and facilitates generation of Th17 cells, a T cell subset known to play a role in autoimmunity. On the basis of these recent findings, we discuss the possibility that the csCRT may play a pathogenic role in RA by transducing SE-activated Th17-polarizing signals.

Identification of the rheumatoid arthritis shared epitope binding site on calreticulin

BACKGROUND

The rheumatoid arthritis (RA) shared epitope (SE), a major risk factor for severe disease, is a five amino acid motif in the third allelic hypervariable region of the HLA-DRbeta chain. The molecular mechanisms by which the SE affects susceptibility to--and severity of--RA are unknown. We have recently demonstrated that the SE acts as a ligand that interacts with cell surface calreticulin (CRT) and activates innate immune signaling. In order to better understand the molecular basis of SE-RA association, here we have undertaken to map the SE binding site on CRT.

PRINCIPAL FINDINGS

Surface plasmon resonance (SPR) experiments with domain deletion mutants suggested that the SE binding site is located in the P-domain of CRT. The role of this domain as a SE-binding region was further confirmed by a sulfosuccinimidyl-2-[6-(biotinamido)-2-(p-azido-benzamido) hexanoamido] ethyl-1,3-dithiopropionate (sulfo-SBED) photoactive cross-linking method. In silico analysis of docking interactions between a conformationally intact SE ligand and the CRT P-domain predicted the region within amino acid residues 217-224 as a potential SE binding site. Site-directed mutagenesis demonstrated involvement of residues Glu(217) and Glu(223)--and to a lesser extent residue Asp(220)--in cell-free SPR-based binding and signal transduction assays.

SIGNIFICANCE

We have characterized here the molecular basis of a novel ligand-receptor interaction between the SE and CRT. The interaction represents a structurally and functionally well-defined example of cross talk between the adaptive and innate immune systems that could advance our understanding of the pathogenesis of autoimmunity.

Immune dysregulation by the rheumatoid arthritis shared epitope

Rheumatoid arthritis (RA) is closely associated with HLA-DRB1 alleles that code a five-amino acid sequence motif in positions 70-74 of the HLA-DRbeta-chain, called the shared epitope (SE). The mechanistic basis of SE-RA association is unknown. We recently found that the SE functions as an allele-specific signal-transducing ligand that activates an NO-mediated pathway in other cells. To better understand the role of the SE in the immune system, we examined its effect on T cell polarization in mice. In CD11c(+)CD8(+) dendritic cells (DCs), the SE inhibited the enzymatic activity of indoleamine 2,3 dioxygenase, a key enzyme in immune tolerance and T cell regulation, whereas in CD11c(+)CD8(-) DCs, the ligand activated robust production of IL-6. When SE-activated DCs were cocultured with CD4(+) T cells, the differentiation of Foxp3(+) T regulatory cells was suppressed, whereas Th17 cells were expanded. The polarizing effects could be seen with SE(+) synthetic peptides, but even more so when the SE was in its natural tridimensional conformation as part of HLA-DR tetrameric proteins. In vivo administration of the SE ligand resulted in a greater abundance of Th17 cells in the draining lymph nodes and increased IL-17 production by splenocytes. Thus, we conclude that the SE acts as a potent immune-stimulatory ligand that can polarize T cell differentiation toward Th17 cells, a T cell subset that was recently implicated in the pathogenesis of autoimmune diseases, including RA.

Epitope-specific immunotherapy of rheumatoid arthritis: clinical responsiveness occurs with immune deviation and relies on the expression of a cluster of molecules associated with T cell tolerance in a double-blind, placebo-controlled, pilot phase II trial

OBJECTIVE

Induction of immune tolerance to maintain clinical control with a minimal drug regimen is a current research focus in rheumatoid arthritis (RA). Accordingly, we are developing a tolerization approach to dnaJP1, a peptide part of a pathogenic mechanism that contributes to autoimmune inflammation in RA. We undertook this study to test 2 hypotheses: 1) that mucosal induction of immune tolerance to dnaJP1 would lead to a qualitative change from a proinflammatory phenotype to a more tolerogenic functional phenotype, and 2) that immune deviation of responses to an inflammatory epitope might translate into clinical improvement.

METHODS

One hundred sixty patients with active RA and with immunologic reactivity to dnaJP1 were enrolled in a pilot phase II trial. They received oral doses of 25 mg of dnaJP1 or placebo daily for 6 months.

RESULTS

The dnaJP1 peptide was safe and well-tolerated. In response to treatment with dnaJP1, there was a significant reduction in the percentage of T cells producing tumor necrosis factor alpha and a corresponding trend toward an increased percentage of T cells producing interleukin-10. Coexpression of a cluster of molecules (programmed death 1 and its ligands) associated with T cell regulation was also found to be a prerequisite for successful tolerization in clinical responders. Analysis of the primary efficacy end point (meeting the American College of Rheumatology 20% improvement criteria at least once on day 112, 140, or 168) showed a difference between treatment groups that became significant in post hoc analysis using generalized estimating equations. Differences in clinical responses were also found between treatment groups on day 140 and at followup. Post hoc analysis showed that the combination of dnaJP1 and hydroxychloroquine (HCQ) was superior to the combination of HCQ and placebo.

CONCLUSION

Tolerization to dnaJP1 leads to immune deviation and a trend toward clinical efficacy. Susceptibility to treatment relies on the coexpression of molecules that can down-regulate adaptive immunity.

Increased frequency of EBV-specific effector memory CD8+ T cells correlates with higher viral load in rheumatoid arthritis

EBV is a candidate trigger of rheumatoid arthritis (RA). We determined both EBV-specific T cell and B cell responses and cell-associated EBV DNA copies in patients with RA and demographically matched healthy virus carriers. Patients with RA showed increased and broadened IgG responses to lytic and latent EBV-encoded Ags and 7-fold higher levels of EBV copy numbers in circulating blood cells. Additionally, patients with RA exhibited substantial expansions of CD8(+) T cells specific for pooled EBV Ags expressed during both B cell transformation and productive viral replication and the frequency of CD8(+) T cells specific for these Ags correlated with cellular EBV copy numbers. In contrast, CD4(+) T cell responses to EBV and T cell responses to human CMV Ags were unchanged, altogether arguing against a defective control of latent EBV infection in RA. Our data show that the regulation of EBV infection is perturbed in RA and suggest that increased EBV-specific effector T cell and Ab responses are driven by an elevated EBV load in RA.

Pathophysiological links between rheumatoid arthritis and the Epstein–Barr virus: An update

Numerous associations have been documented between the Epstein-Barr virus (EBV) and rheumatoid arthritis (RA). Thus, anti-EBV antibody titers are higher in RA patients than in healthy controls. Lymphocytes from RA patients show impaired responses to EBV. Several EBV antigens share similarities with self antigens; more specifically, the glycine/alanine repeats in EBNA-1 resemble synovial proteins and the EBV gp110 glycoprotein contains a copy of the shared epitope. Cell-mediated responses to EBV replicative cycle proteins and to gp110 have been documented in joint fluid from RA patients. In situ hybridization and PCR techniques have identified EBV antigens and genetic material within the rheumatoid synovium, albeit with variable yields. The EBV burden in peripheral blood mononuclear cells is higher in RA patients than in controls. EBNA-1 can undergo citrullination, and the EBV can induce antibodies to citrullinated peptides. RA patients are at increased risk for lymphoma, including EBV-associated lymphoma. Despite these multiple and complex links between EBV and RA, proof of a causal association is lacking. EBV infection may contribute indirectly to the pathophysiology of RA by impairing immune control of EBV replication, causing increased exposure to EBV antigens and, thereby, chronic inflammation. The effect of biotherapies for RA on EBV-host relations needs to be investigated.

Nitric Oxide Signaling Triggered by the Rheumatoid Arthritis Shared Epitope: A New Paradigm for MHC Disease Association?

Many immune-mediated diseases are associated with particular MHC class I or class II alleles. In rheumatoid arthritis (RA-shared), the vast majority of patients possess HLA-DRB1 alleles encoding a shared epitope, which is a five-amino acid sequence motif in positions 70-74 of the HLA-DRbeta chain. The mechanistic basis for this association is unknown. Here we discuss recent evidence suggesting that the shared epitope may act as an allele-specific ligand that triggers increased nitric oxide (NO) production in opposite cells with resultant immune dysregulation. We propose that by doing that, the RA-shared shared epitope may form an unintended bridge between the innate and adaptive immune systems, thereby allowing aberrant signaling events that could trigger disease.

70-kDa heat shock proteins: specific interactions with HLA-DR molecules and their peptide fragments

Heat shock protein 70 (HSP70):peptide complexes are involved in MHC class I and class II-restricted antigen presentation enabling enhanced activation of antigen-specific T cells. Here, we investigated the potential of bacterial and mammalian HSP70 molecules to interact with peptide fragments from HLA-DR and the corresponding complete HLA-DR molecules. Peptide fragments were found to interact with DnaK, the HSP70 homologue from E. coli, but less with stress-inducible human Hsp70. Only a peptide sequence exclusively found in rheumatoid arthritis-protective HLA-DR molecules did not interact with DnaK. Subsequently, we investigated the interaction of complete HLA-DR molecules with HSP70 and detected a specific HSP70:HLA-DR interaction, with highest affinity for human stress-inducible Hsp70. In contrast to the peptide fragments, no allele-specific differences in Hsp70 affinity were detected with complete HLA-DR molecules. Interaction with HLA-DR molecules was increased at lowered pH values, whereas HSP70-chaperoned peptides were released at acidic pH, thus HSP70 could serve as scanner and carrier for antigenic peptides of self or foreign origin and transfer chaperoned peptides onto MHC class II molecules in acidic late endosomal compartments. Our findings indicate that direct interaction between mammalian HSP70 and HLA-DR molecules could be involved in the HSP70-mediated enhancement of MHC class II-restricted peptide presentation and CD4(+) T cell activation.

Infection and musculoskeletal conditions: Viral causes of arthritis

Several viruses cause postinfectious arthritis. The disease is a typical manifestation of arthritogenic alphaviruses, rubella virus and human parvovirus B19. In addition, arthritis is not uncommon after infection by HIV, cytomegalovirus, hepatitis B virus, hepatitis C virus, or Epstein-Barr virus (EBV). Also prolonged arthritis may result from viral infections, particularly with alphaviruses and human parvovirus B19. Viruses such as EBV and B19 may have significant roles in initiating chronic arthropathies, which in some cases may be indistinguishable from rheumatoid arthritis.

Modulation of T cell function by combination of epitope specific and low dose anticytokine therapy controls autoimmune arthritis

Innate and adaptive immunity contribute to the pathogenesis of autoimmune arthritis by generating and maintaining inflammation, which leads to tissue damage. Current biological therapies target innate immunity, eminently by interfering with single pro-inflammatory cytokine pathways. This approach has shown excellent efficacy in a good proportion of patients with Rheumatoid Arthritis (RA), but is limited by cost and side effects. Adaptive immunity, particularly T cells with a regulatory function, plays a fundamental role in controlling inflammation in physiologic conditions. A growing body of evidence suggests that modulation of T cell function is impaired in autoimmunity. Restoration of such function could be of significant therapeutic value. We have recently demonstrated that epitope-specific therapy can restore modulation of T cell function in RA patients. Here, we tested the hypothesis that a combination of anti-cytokine and epitope-specific immunotherapy may facilitate the control of autoimmune inflammation by generating active T cell regulation. This novel combination of mucosal tolerization to a pathogenic T cell epitope and single low dose anti-TNFα was as therapeutically effective as full dose anti-TNFα treatment. Analysis of the underlying immunological mechanisms showed induction of T cell immune deviation.

Translating the concept of suppressor/regulatory T cells to clinical applications

The in vivo expansion of suppressor/regulatory T cells (Tregs) is a desirable event in autoimmunity and transplantation. Here we summarize the general rules involved in antigen recognition by T cells and describe Tregs and their requirements, discussing different levels of immune intervention.

Activation of nitric oxide signaling by the rheumatoid arthritis shared epitope

OBJECTIVE

Susceptibility to rheumatoid arthritis (RA) is closely associated with HLA-DRB1 alleles encoding a shared epitope (SE) in positions 70-74 of the HLA-DRbeta chain. The mechanistic basis for this association is unknown. Given the proposed pathogenic role of nitric oxide (NO) in RA, this study was undertaken to examine whether the SE can trigger NO signaling events.

METHODS

The intracellular levels of NO were measured with the fluorescent NO probe 4,5-diaminofluorescein diacetate and by the 2,3-diaminonaphthalene method. NO synthase activity was determined by measuring the rate of conversion of radioactive arginine to citrulline. Levels of cGMP were measured with a commercial enzyme-linked immunosorbent assay, and the cytolytic activity of T cells was measured using a standard (51)Cr release assay.

RESULTS

Lymphoblastoid B cell lines carrying SE-positive HLA-DR alleles displayed a higher rate of spontaneous NO production compared with SE-negative cells. L cell transfectants expressing SE-positive DR molecules on their surface also generated higher levels of NO. Tetrameric HLA-DR molecules containing a DRbeta-chain encoded by the SE-positive DRB1*0401 allele stimulated fibroblast cells to produce higher levels of NO compared with cells stimulated with a control HLA-DR tetramer. Multimeric hepatitis B core proteins engineered to express region 65-79 encoded by the DRB1*0401 allele, but not the same region encoded by the control allele DRB1*0402, stimulated NO production in fibroblasts. Similarly, synthetic 15-mer peptides corresponding to the region 65-79 encoded by SE-positive alleles triggered increased NO levels when incubated with class II major histocompatibility complex-negative cells. The signaling pathway was found to involve NO synthase activation, followed by increased production of cGMP. SE-triggered increased NO levels inhibited cytolytic elimination of target cells.

CONCLUSION

The SE can trigger NO-mediated signaling events in opposite cells, and may thereby contribute to RA pathogenesis.

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.

Epstein-Barr virus etiology in rheumatoid synovitis

The etiology of rheumatoid arthritis (RA) has remained unknown, although it has been investigated and speculated that both genetic and environmental components contribute to the cause of this disease. Epstein-Barr virus (EBV) has been a strong candidate about for over 25 years as environmental infectious agent(s). There are many circumstantial evidence for association between EBV and RA, but definite evidence is wanting. In present article, we review an increase circumstantial proof which has been investigated so far and demonstrate direct evidence for the presence of EBV in inflamed synovial cells in patients with RA and discuss on the recent finding of signaling lymphocytic-activation molecule (SLAM)-associated protein (SAP), which opened a new approach to understand on impaired function of cytotoxic T cell for EBV in patients with RA.

The role of immune tolerance in preventing and treating arthritis

It has become increasingly clear that the innate and adaptive arms of the immune response cooperate in generating autoimmune damage in the pathogenesis of rheumatoid arthritis and juvenile idiopathic arthritis. Treatment targets the immunologic pathophysiology of the disease and is based on regaining immune tolerance. Recently introduced biological agents neutralize or simply block cytokines and their proinflammatory pathways, with favorable clinical outcome. However, major downsides are their lack of specificity and the need of continuous administration to be effective. Possibly, more can be gained from a specific approach. Indeed, recent findings suggest that targeting antigen-specific T cells can reinstate regulatory mechanisms and thus induce immune tolerization. This improved understanding has paved the way to novel immunotherapeutic approaches, some of which will be discussed here.

Epitope-specific immunotherapy induces immune deviation of proinflammatory T cells in rheumatoid arthritis

Modulation of epitope-specific immune responses would represent a major addition to available therapeutic options for many autoimmune diseases. The objective of this work was to induce immune deviation by mucosal peptide-specific immunotherapy in rheumatoid arthritis (RA) patients, and to dissect the related immunological mechanisms by using a technology for the detection of low-affinity class II-restricted peptide-specific T cells. A group of patients with early RA was treated for 6 months orally with dnaJP1, a peptide that induces proinflammatory T cell responses in naive RA patients. Immunological analysis at initial, intermediate and end treatment points showed an intriguing change from proinflammatory to regulatory T cell function. In fact, dnaJP1-induced T cell production of IL-4 and IL-10 increased significantly when initial and end treatment points were compared, whereas dnaJP1-induced T cell proliferation and production of IL-2, IFN-gamma, and tumor necrosis factor-alpha decreased significantly. The total number of dnaJP1-specific cells did not change over time, whereas expression of foxP3 by CD4+CD25(bright) cells increased, suggesting that the treatment affected regulatory T cell function. Thus, rather than clonal deletion, the observed change in immune reactivity to dnaJP1 was the outcome of treatment-induced emergence of T cells with a different functional phenotype. This study contributes to our knowledge of mechanisms and tools needed for antigen-specific immune modulation in humans, thus laying the foundation for exploitation of this approach for therapeutic purposes.

Induction of arthritis in SCID mice by T cells specific for the “shared epitope” sequence in the G3 domain of human cartilage proteoglycan

OBJECTIVE

To study the immunologic function and determine the fine epitope structure of a synthetic peptide p135H ((2373)TTYKRRLQKRSSRHP) of the G3 domain of human cartilage proteoglycan (aggrecan), which contains a highly homologous sequence motif of the shared epitope (QKRAA), the most common sequence motif in HLA-DR4 alleles, which predispose humans to the development of rheumatoid arthritis (RA).

METHODS

Synthetic p135 peptides with altered sequences were used for (hyper)immunization of arthritis-susceptible BALB/c mice and then challenged with a single dose of cartilage proteoglycan. Human p135 (p135H) and mouse p135 (p135M) synthetic peptides of the G3 domain of aggrecan were used to prime lymphocytes, which were then used for adoptive transfer of arthritis into "presensitized" SCID mice, determining cross-reactivity among p135 peptides and their analogous sequences, and generating T cell hybridomas. T cell hybridomas were also used for arthritis transfer into SCID mice and for characterizing the fine epitope structure of T cell receptor (TCR) and major histo-compatibility complex (MHC) binding sites of the immunogenic/arthritogenic p135H sequence.

RESULTS

While p135H peptide-(hyper)immunized mice became sensitized, they developed arthritis only after injection of a single dose of cartilage proteoglycan aggrecan. An altered peptide sequence (p135H-AA) carrying the shared epitope motif (QKRAA) was as effective as the natural peptide p135H sequence for inducing arthritis. Mouse p135M-specific lymphocytes induced arthritis with a lower incidence, but synthetic peptides to Escherichia coli heat-shock protein (DnaJ) or HLA-DR4 allele (both having the shared epitope sequence with different flanking regions) were also positive. Fine epitope sequence recognition of an arthritogenic T cell hybridoma derived from p135H-primed lymphocyte population was determined. Interestingly, in the most central position, a basic amino acid triplet of p135H peptide was found to be the MHC-binding motif, whereas the flanking amino acids bound to the TCR.

CONCLUSION

Peptide p135H, corresponding to the peptide sequence in the G3 domain of human cartilage proteoglycan aggrecan, is immunogenic/arthritogenic in BALB/c mice. Peptide p135H includes a highly homologous motif of the shared epitope, a sequence that is overrepresented in bacterial heat-shock proteins, envelope protein of human JC polyomavirus, and numerous HLA-DR4 alleles. Since the G3 domain of cartilage proteoglycan aggrecan with the p135 sequence is "lost" during the normal metabolic turnover of cartilage proteoglycan or in pathologic conditions, an antigenoriented T cell migration into joints of presensitized (susceptible) individuals may contribute to the organ-specificity of RA.

Association of HLA-DRB1*0401 allele with chronic pancreatitis

INTRODUCTION

Chronic pancreatitis (CP) is characterized by irreversible morphologic and functional alterations of the pancreas, clinically presenting with upper abdominal pain as well as exocrine and endocrine insufficiencies. According to a more recent hypothesis, the pathogenesis may involve genetic and immunologic factors.

AIM

To investigate the major histocompatibility complex (MHC) genes as a genetic background of chronic pancreatitis.

METHODOLOGY

Allelic polymorphisms were investigated in the genes of the MHC region (HLA B, DRB, DQB) with PCR-based methodologies (PCR-SSP) in 56 patients with CP (44 males and 12 females) and 183 normal controls (78 males and 105 females) of the same ethnic group. All patients and controls gave their informed consent.

RESULTS

Among HLA-DRB1 genes, DRB1*04 was significantly higher in CP patients than in controls (26.78% versus 8.1%; pc < 0.003; OR = 4.1; CI = 1.85-9.06). DRB1*04 allele specificities in the DRB1*04-positive patients demonstrated significantly higher frequencies of DRB1*0401 allele (14.3% versus 1.1%; p = 0.00017; OR = 15.08; CI = 3.1-73.36). Neither HLA-B nor HLA-DQB1 associations with the disease were found.

CONCLUSIONS

This study supports a role of HLA-DRB1*0401 as a susceptibility factor for patients with CP. HLA DRB1*0401 contains the 70QKRAA74 amino acid sequence, which is also expressed by several human pathogens, including Epstein-Barr virus. T cells may be triggered in the pancreatic tissue upon exposure to foreign peptides similar enough to cross-react and to break immunologic tolerance.

Self epitopes shared between human skeletal myosin and Streptococcus pyogenes M5 protein are targets of immune responses in active juvenile dermatomyositis

OBJECTIVE

To identify self T cell epitopes associated with proinflammatory immune responses and clinically active juvenile dermatomyositis (juvenile DM). The target of our search for relevant epitopes was represented by amino acid sequences shared between human skeletal myosin and Streptococcus pyogenes M5 protein. The long-term objective of the project is to identify suitable targets for immunotherapy of the disease.

METHODS

We used computerized algorithms to identify putative agretopes on both the human myosin and Streptococcus M5 proteins. Direct binding assays for homolog peptides were used to confirm such predictions. Antigenicity and functional cross-reactivity were evaluated by cytotoxicity assays and by measurement of cytokine levels. Specific T cells were isolated by T cell capture, and T cell receptor (TCR) V(beta) gene usage was identified by reverse transcriptase-polymerase chain reaction.

RESULTS

We identified peptides that are targets of disease-specific cytotoxic T cell responses. T cell reactivity against the self peptides correlates with clinical signs of early, active myositis. Such reactivity is accompanied by production of proinflammatory cytokines, which may contribute to the damage. T cell cross-recognition of bacterial and human homologs was shown functionally as well as by sorting peptide-specific T cells and identifying oligoclonal and largely overlapping TCR V(beta) gene usage.

CONCLUSION

These findings represent the first identification of a self epitope in juvenile DM, providing a potential candidate for antigen-specific immune therapy.

Proinflammatory responses to self HLA epitopes are triggered by molecular mimicry to Epstein-Barr virus proteins in oligoarticular juvenile idiopathic arthritis

OBJECTIVE

To evaluate whether abnormal T cell recognition may be generated by exposure to exogenous antigens presenting sequence homology with epitopes contained in self HLA alleles, and if such recognition may be part of the mechanisms that fuel inflammation in autoimmune diseases associated with certain HLA alleles.

METHODS

Cytotoxic responses of peripheral blood mononuclear cells to 9-mer peptides derived from HLA molecules (DRB1*1101, DRB1*0801, or DPB1*0201) associated with oligoarticular juvenile idiopathic arthritis (JIA) or homologous peptides derived from Epstein-Barr virus (EBV) proteins (Bolf1 or Balf2) were analyzed in patients with oligoarticular JIA and in healthy controls matched for HLA-DRB1*1101, DRB1*0801, or DPB1*0201. Production of proinflammatory cytokines in culture supernatants was determined by enzyme-linked immunosorbent assay.

RESULTS

T cell cytotoxic responses and production of proinflammatory cytokines in response to stimulation with self HLA-derived peptides were found only in patients with oligoarticular JIA, and not in controls. Patients with oligoarticular JIA, but none of the healthy controls, had EBV-self HLA cross-reactive T cells.

CONCLUSION

Our data suggest a disease- and allele-specific mechanism of autoimmunity in oligoarticular JIA. This mechanism may be part of the pathogenesis of the disease, and could be the basis of one of the likely multiple candidates for antigen-specific immunotherapy approaches in the future.

Induction of transient arthritis by the adoptive transfer of a collagen II specific Th1 clone to HLA-DR4 (B1*0401) transgenic mice

Collagen II arthritis (CIA) represents an animal model of human RA that can be induced in DBA/1J (H-2(q)) but not in C57BL/6 mice (H-2(b)). A vigorous CII specific CD4 Th1-cell response but not IgG2 anti-CII antibody or CIA could be induced in C57BL/6 mice made transgenic for the RA shared epitope DR4 (B1*0401). We developed CD4 Th1-cell clones specific for CII from these transgenic (tg) mice in order to determine if the adoptive transfer of these clones into syngeneic tg C57BL/6 recipients could induce CIA. Three bovine CII specific (bCII) CD4 Th1-cell clones and one T-cell line specific for an immunodominant region of bCII (p261-273) were generated. Among these only one clone that could up-regulate anti-CII, IgG2 antibody in the recipient mice was able to induce transient arthritis. However, this level of IgG2 anti-CII antibody was only one-third of that seen in CII immunized DBA/1J mice that develop persistent arthritis. These results confirm our previous observations that the induction of CIA requires a sustained IgG2 antibody response to CII, an effect difficult to achieve even in DR4 (B1*0401) tg mice reconstituted with CD4 Th1 cells. This suggests that a rate limiting step in the development of human RA among those individuals expressing the RA shared epitope may be the requirement to generate sustained levels of complement fixing antibody to arthritogenic antigens.

Effect of tandem rare codon substitution and vector-host combinations on the expression of the EBV gp110 C-terminal domain in Escherichia coli

Gp110 of Epstein-Barr virus (EBV) is a glycoprotein that functions exclusively during the assembly of EBV nucleocapsid and the release of infectious EBV. Its C-terminal tail domain (gp110 CTD) is essential for gp110's function and may provide signals that are responsible for the assembly and release of EBV. In the present study, to get large amounts of gp110 CTD for structural analysis, the effects of vector system, codon usage, and host strain on expression levels of gp110 CTD in Escherichia coli have been investigated. The coding region of gp110 CTD (11 kDa) was subcloned into the expression vectors pSE 280, pET-15b, pET-29a, pMAL-c2x, and pGEX-4T-1. Except the pMAL-c2x construct, all the others failed to express detectable amounts of recombinant gp110 CTD. Substituting a tandem rare AGA (Arg) codon with a synonymous CGC (Arg) codon facilitated expression of the recombinant protein, while a protease-deficient host E. coli strain helped in the accumulation of a soluble form of gp110 CTD fusion. The secondary structures of the obtained recombinant gp110 CTD purified from soluble extracts and inclusion bodies were compared using circular dichroism analysis. In aqueous solutions, both samples equally adopt a mixed alpha-helix and beta-sheet conformation as well as a partly unordered structure. Notably, in the membrane-mimicking environments the helical propensity of gp110 CTD increased up to the previously predicted level based on its sequence, suggesting that gp110 CTD may fold into a more stable conformation through interactions with the cell membrane.

The genetics of the target tissue in rheumatoid arthritis

The genetic mechanisms that are complementary in predisposing and then establishing disease are yet to be fully elucidated. During a lifetime, the genetic composition of the host is not only hereditary but undergoes rearrangements, integrations, and more subtle single-base pair alterations. These changes can be inconsequential or lead to aberrant and deleterious pathologic changes. In a complex multifactorial disease such as RA, the relative roles of the dynamic versus germline elements of the disease have yet to be fully determined. Further studies of large populations are likely to segregate out factors affecting specific ethnic, clinical, and genetic subgroups.

Why do we not have a cure for rheumatoid arthritis?

There are currently unprecedented opportunities to treat rheumatoid arthritis using well-designed, highly effective, targeted therapies. This will result in a substantial improvement in the outcome of this disorder for most affected individuals, if they can afford these therapies. Yet our lack of understanding of the basic mechanisms that initiate and sustain this disease remains a major obstacle in the search for a definitive cure. It is possible, if not likely, that our best approach will be to identify individuals at risk and devise reliable, safe methods of preventing the disease before it occurs. The means to do this are currently unknown but should serve as a major focus of research.

Artificial antigen-presenting cells as a tool to exploit the immune 'synapse'

Recent progress in molecular medicine has provided important tools to identify antigen-specific T cells. In most cases, the approach is based on oligomeric combinations of recombinant major histocompatibility complex-peptide complexes fixed to various rigid supports available for binding by the T-cell receptor. These tools have greatly increased our insight into mechanisms of immune responses mediated by CD8+ T cells. Examples of the diverse fields of application for this technology include immunization, viral infections and oral tolerance induction.

Twins: mirrors of the immune system

Twin studies are a powerful tool to assess genetic and nongenetic factors in multifactorial, immune-mediated diseases. Here, Marco Salvetti and colleagues review important results from such studies and highlight their potential value. Future developments that should help to realize the potential of twin studies are discussed.

Modulation of immune function by dietary lectins in rheumatoid arthritis

Despite the almost universal clinical observation that inflammation of the gut is frequently associated with inflammation of the joints and vice versa, the nature of this relationship remains elusive. In the present review, we provide evidence for how the interaction of dietary lectins with enterocytes and lymphocytes may facilitate the translocation of both dietary and gut-derived pathogenic antigens to peripheral tissues, which in turn causes persistent peripheral antigenic stimulation. In genetically susceptible individuals, this antigenic stimulation may ultimately result in the expression of overt rheumatoid arthritis (RA) via molecular mimicry, a process whereby foreign peptides, similar in structure to endogenous peptides, may cause antibodies or T-lymphocytes to cross-react with both foreign and endogenous peptides and thereby break immunological tolerance. By eliminating dietary elements, particularly lectins, which adversely influence both enterocyte and lymphocyte structure and function, it is proposed that the peripheral antigenic stimulus (both pathogenic and dietary) will be reduced and thereby result in a diminution of disease symptoms in certain patients with RA.

Interaction cloning and characterization of RoBPI, a novel protein binding to human Ro ribonucleoproteins

Human Ro ribonucleoproteins (RNPs) are autoantigenic particles of unknown function(s) that consist of a 60-kDa protein (Ro60) associated with one hY RNA (hY1-5). Using a modified yeast three-hybrid system, named RNP interaction trap assay (RITA), we cloned a novel Ro RNP-binding protein (RoBPI), based on its property to interact in vivo in yeast with an RNP complex made of recombinant Ro60 (rRo60) protein and hY5 (rhY5) RNA. RoBPI cDNA contains three conserved RNA recognition motifs (RRM) and is present as a family of isoforms differing slightly at their 5' end. The 2.0-kb RoBPI mRNA was detected in all human tissues tested. Highly homologous cDNA sequences were found in banks of expressed sequence tags (ESTs) from mice. Two-hybrid, three-hybrid, and RITA experiments respectively established that 60 kDa RoBPI did not interact in yeast with rRo60 alone, with rhY5 RNA alone, or with bait RNPs consisting of rRo60 and recombinant hY1, hY3, or hY4 RNAs. RoBPI coimmunoprecipitated with Ro RNPs from HeLa cell extracts and partially colocalized with Ro60 in nuclei of cultured cells. Because hY5 RNA and RohY5 RNPs are recent evolutionary additions seen only in primates, but RoBPI seems more conserved, their interaction may represent a gain of function for Ro RNPs. Alternatively, interaction of RohY5 RNPs with RoBPI may have no functional bearing, but may underlie some of the unique biochemical and immunological properties of these RNPs.

Ontogeny of synonymous T cell populations with specificity for a self MHC epitope mimicked by a bacterial homologoue: an antigen-specific T cell analysis in a non-transgenic system

By means of a novel technique for identification and isolation of MHC class II-restricted antigen-specific T cells, we describe here in non-transgenic BALB / c mice physiological positive selection of an oligoclonal population of T cells which recognizes both a self MHC-derived peptide (Ialpha52) and a bacterial homologoue (Hi15). The results support a model for self peptide-mediated generation of T cells which have specificity for microbial antigens through molecular mimicry. This mechanism may be a model for the ontogeny of a physiological T cell response to infectious agents. Loss of control of these circuits may be part of the inciting factors of autoimmunity.

Synovial Epstein-Barr virus infection increases the risk of rheumatoid arthritis in individuals with the shared HLA-DR4 epitope

OBJECTIVE

To investigate the presence of the Epstein-Barr virus (EBV) in rheumatoid arthritis (RA) synovium and its correlation with the HLA genotype in an attempt to elucidate the role of EBV in the pathogenesis of RA.

METHODS

EBV DNA/RNA was investigated by polymerase chain reaction (PCR) analysis of synovial tissue from 84 patients with RA and from 81 patients with non-RA arthritis (controls) and was correlated with the patients' HLA genotype.

RESULTS

EBV DNA and EBV-encoded RNA 1 transcripts were significantly more frequently present in synovial tissue from the RA patients (29 of 84) than in that from the non-RA patient controls (8 of 81). EBV DNA-positive individuals had a 5.47 times higher risk of presenting with RA than did EBV DNA-negative individuals. In HLA-DRB1*0401,0404,0405,0408-positive or shared epitope-positive patients, the risk was further increased (odds ratio for EBV and HLA-DR4 approximately 41, for EBV and the shared epitope approximately 15) compared with those who lacked both EBV DNA and RA-linked HLA genotypes.

CONCLUSION

EBV seems to function as an environmental risk factor for RA, particularly in patients with the RA-linked HLA-DRB1 alleles.

T-cell responses in rheumatoid arthritis: systemic abnormalities-local disease

One manifestation of rheumatoid arthritis (RA) is a destructive inflammation of the joint, but many other organs can be targeted by this disease, classifying it as a truly systemic disorder. Accordingly, pathogenic models have to account for the multiorgan character of RA. This article proposes that the primary abnormalities in RA lie in the assembly of the T-cell pool and in the maintenance of T-cell homeostasis. Evidence has accumulated that the repertoire of CD4 T cells in RA patients is distinct and includes a high frequency of disease-relevant T cells. Emergence of T cells with self-aggressive potential could indicate a failure of negative selection in the thymus. Also, the turnover of mature T cells in the periphery is altered in RA patients with a sharp contraction in diversity. Loss of diversity results from the replacement of rare T-cell specificities by multiplying T-cell clones. Large clonal T-cell populations in RA patients acquire a distinct phenotype (CD4+CD28null) and functional profile (overproduction of interferon-gamma, cytotoxicity), giving them the ability to function as proinflammatory cells. Optimal conditions for T-cell stimulation are encountered in the synovium, where ectopic lymphoid tissue with germinal centers is formed. Considering the systemic nature of RA, therapeutic strategies suppressing synovial inflammation while ignoring systemic abnormalities could lack the potential of a curative intervention.

Evidence that patients with rheumatoid arthritis have asymptomatic 'non-significant' Proteus mirabilis bacteriuria more frequently than healthy controls

OBJECTIVES

patients with rheumatoid arthritis (RA) are reported to have in their sera raised levels of antibody specific to Proteus mirabilis. The aim of the study was to verify this and to determine an explanation for it by investigating the frequency of P. mirabilis urinary tract infection in RA patients and matched controls.

METHODS

freshly voided urine was examined for the presence, number and identity of infecting bacteria. The levels of antibody in blood and in urine of the IgM, IgA and IgG classes to the common O serotypes of P. mirabilis and the antigens to which they reacted were determined by enzyme-linked immunosorbent assay (ELISA) and immunoblotting.

RESULTS

analysis of urine from 76 patients with RA and 48 age- and gender-matched healthy controls showed that only two (4%) of the control urines but 25 (33%) of those from the RA patients were infected. The commonest infecting organism in the RA patients' urine was Proteus mirabilis which occurred twice as frequently as Escherichia coli. Proteus mirabilis was found in 52% of the infected urines of the RA patients and was always detected as a pure growth and usually in insignificant (< 10(4)/ml) numbers. It is highly improbable that this finding was the outcome of differences in age, physical ability or medication between the RA and control patient groups. Comparison of antibody levels to P. mirabilis by ELISA showed RA patients had raised (P < 0.0001, P = 0.001, P = 0.0063) levels of IgA, IgG and IgM respectively in their sera and raised (P < 0.0001, P < 0.0001, P = 0.0001) levels of IgG, IgM and IgA respectively in their urine compared with the control group. It was not possible to detect an antibody reacting to a P. mirabilis antigen that was specific to the RA patients.

CONCLUSION

the results confirm that RA patients have raised levels of antibody to P. mirabilis not only in blood but also in urine and suggest that this arises because RA patients have an asymptomatic, non-significant P. mirabilis bacteriuria more frequently or more prolonged than control patients. This may be the trigger for their RA condition.

Genetics of rheumatoid arthritis: confronting complexity

The genetic basis for rheumatoid arthritis (RA) is likely to be extremely complex. Even the role of MHC genes remains to be fully defined, and may involve interactive genetic effects. The difficulty of precisely defining the clinical phenotype, as well as underlying genetic heterogeneity, complicates the problem. In addition, stochastic genetic or physiologic events may contribute to the low penetrance of susceptibility genes. This situation parallels developing paradigms for other autoimmune disorders, in which many different genes each appear to contribute a small amount to overall risk for disease, and where severity and specific phenotypic subtypes are subject to genetic effects. The completion of the human genome project, along with advances in informatics, will be required to reach a deeper understanding of RA. It is likely that this will involve an iterative and interactive process between several different scientific disciplines.

Mucosal modulation of immune responses to heat shock proteins in autoimmune arthritis

Induction of oral tolerance to antigens that are targets of self-reactive immune responses is an attractive approach to antigen-specific immune therapy of autoimmune diseases. Oral tolerization has indeed proven to be safe and effective in amelioration of autoimmune diseases in animal models. In humans, results have been somewhat controversial. The emphasis given to clinical outcome rather than to immunomodulation, and the difficulty in identifying appropriate candidate antigens contribute to the controversy. Heat shock proteins are promising targets for immune intervention. Immune reactivity to heat shock proteins has indeed been correlated with autoimmune arthritis in animal models, and abnormal immune responses to heat shock proteins have been described in human arthritis as well. Despite significant recent progress, little is known at a molecular level regarding the mechanisms which are responsible for a switch from autoimmunity to tolerance in humans. This is particularly true with respect to sequential analysis of several molecular and immunologic markers during both the course and treatment of disease. Novel approaches are currently under way to fill the gaps. We will briefly detail here the experience gained to date, and identify some of the avenues which future research will explore.