Cellular immunity to the G1 domain of cartilage proteoglycan aggrecan is enhanced in patients with rheumatoid arthritis but only after removal of keratan sulfate

Functional Consequences of Keratan Sulfate Sulfation in Electrosensory Tissues and in Neuronal Regulation

Keratan sulfate (KS) is a functional electrosensory and neuro-instructive molecule. Recent studies have identified novel low sulfation KS in auditory and sensory tissues such as the tectorial membrane of the organ of Corti and the Ampullae of Lorenzini in elasmobranch fish. These are extremely sensitive proton gradient detection systems that send signals to neural interfaces to facilitate audition and electrolocation. High and low sulfation KS have differential functional roles in song learning in the immature male zebra song-finch with high charge density KS in song nuclei promoting brain development and cognitive learning. The conductive properties of KS are relevant to the excitable neural phenotype. High sulfation KS interacts with a large number of guidance and neuroregulatory proteins. The KS proteoglycan microtubule associated protein-1B (MAP1B) stabilizes actin and tubulin cytoskeletal development during neuritogenesis. A second 12 span transmembrane synaptic vesicle associated KS proteoglycan (SV2) provides a smart gel storage matrix for the storage of neurotransmitters. MAP1B and SV2 have prominent roles to play in neuroregulation. Aggrecan and phosphacan have roles in perineuronal net formation and in neuroregulation. A greater understanding of the biology of KS may be insightful as to how neural repair might be improved.

Keratan sulfate, a complex glycosaminoglycan with unique functional capability

From an evolutionary perspective keratan sulfate (KS) is the newest glycosaminoglycan (GAG) but the least understood. KS is a sophisticated molecule with a diverse structure, and unique functional roles continue to be uncovered for this GAG. The cornea is the richest tissue source of KS in the human body but the central and peripheral nervous systems also contain significant levels of KS and a diverse range of KS-proteoglycans with essential functional roles. KS also displays important cell regulatory properties in epithelial and mesenchymal tissues and in bone and in tumor development of diagnostic and prognostic utility. Corneal KS-I displays variable degrees of sulfation along the KS chain ranging from non-sulfated polylactosamine, mono-sulfated and disulfated disaccharide regions. Skeletal KS-II is almost completely sulfated consisting of disulfated disaccharides interrupted by occasional mono-sulfated N-acetyllactosamine residues. KS-III also contains highly sulfated KS disaccharides but differs from KS-I and KS-II through 2-O-mannose linkage to serine or threonine core protein residues on proteoglycans such as phosphacan and abakan in brain tissue. Historically, the major emphasis on the biology of KS has focused on its sulfated regions for good reason. The sulfation motifs on KS convey important molecular recognition information and direct cell behavior through a number of interactive proteins. Emerging evidence also suggest functional roles for the poly-N-acetyllactosamine regions of KS requiring further investigation. Thus further research is warranted to better understand the complexities of KS.

An epitope-specific DerG-PG70 LEAPS vaccine modulates T cell responses and suppresses arthritis progression in two related murine models of rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune joint disease maintained by aberrant immune responses involving CD4+ T helper (Th)1 and Th17 cells. In this study, we tested the therapeutic efficacy of Ligand Epitope Antigen Presentation System (LEAPS™) vaccines in two Th1 cell-driven mouse models of RA, cartilage proteoglycan (PG)-induced arthritis (PGIA) and PG G1-domain-induced arthritis (GIA). The immunodominant PG peptide PG70 was attached to a DerG or J immune cell binding peptide, and the DerG-PG70 and J-PG70 LEAPS vaccines were administered to the mice after the onset of PGIA or GIA symptoms. As indicated by significant decreases in visual and histopathological scores of arthritis, the DerG-PG70 vaccine inhibited disease progression in both PGIA and GIA, while the J-PG70 vaccine was ineffective. Splenic CD4+ cells from DerG-PG70-treated mice were diminished in Th1 and Th17 populations but enriched in Th2 and regulatory T (Treg) cells. In vitro spleen cell-secreted and serum cytokines from DerG-PG70-treated mice demonstrated a shift from a pro-inflammatory to an anti-inflammatory/regulatory profile. DerG-PG70 peptide tetramers preferentially bound to CD4+ T-cells of GIA spleen cells. We conclude that the DerG-PG70 vaccine (now designated CEL-4000) exerts its therapeutic effect by interacting with CD4+ cells, which results in an antigen-specific down-modulation of pathogenic T-cell responses in both the PGIA and GIA models of RA. Future studies will need to determine the potential of LEAPS vaccination to provide disease suppression in patients with RA.

Unconventional T-cell recognition of an arthritogenic epitope of proteoglycan aggrecan released from degrading cartilage

It has been proposed that peptide epitopes bind to MHC class II molecules to form distinct structural conformers of the same MHC II-peptide complex termed type A and type B, and that the two conformers of the same peptide-MHC II complex are recognized by distinct CD4 T cells, termed type A and type B T cells. Both types recognize short synthetic peptides but only type A recognize endosomally processed intact antigen. Type B T cells that recognize self peptides from exogenously degraded proteins have been shown to escape negative selection during thymic development and so have the potential to contribute to the pathogenesis of autoimmunity. We generated and characterized mouse CD4 T cells specific for an arthritogenic epitope of the candidate joint autoantigen proteoglycan aggrecan. Cloned T-cell hybridomas specific for a synthetic peptide containing the aggrecan epitope showed two distinct response patterns based on whether they could recognize processed intact aggrecan. Fine mapping demonstrated that both types of T-cell recognized the same core epitope. The results are consistent with the generation of aggrecan-specific type A and type B T cells. Type B T cells were activated by supernatants released from degrading cartilage, indicating the presence of antigenic extracellular peptides or fragments of aggrecan. Type B T cells could play a role in the pathogenesis of proteoglycan-induced arthritis in mice, a model for rheumatoid arthritis, by recognizing extracellular peptides or protein fragments of joint autoantigens released by inflamed cartilage.

DEC205+ Dendritic Cell-Targeted Tolerogenic Vaccination Promotes Immune Tolerance in Experimental Autoimmune Arthritis

Previous studies in mouse models of autoimmune diabetes and encephalomyelitis have indicated that the selective delivery of self-antigen to the endocytic receptor DEC205 on steady-state dendritic cells (DCs) may represent a suitable approach to induce Ag-specific immune tolerance. In this study, we aimed to examine whether DEC205(+) DC targeting of a single immunodominant peptide derived from human cartilage proteoglycan (PG) can promote immune tolerance in PG-induced arthritis (PGIA). Besides disease induction by immunization with whole PG protein with a high degree of antigenic complexity, PGIA substantially differs from previously studied autoimmune models not only in the target tissue of autoimmune destruction but also in the nature of pathogenic immune effector cells. Our results show that DEC205(+) DC targeting of the PG peptide 70-84 is sufficient to efficiently protect against PGIA development. Complementary mechanistic studies support a model in which DEC205(+) DC targeting leads to insufficient germinal center B cell support by PG-specific follicular helper T cells. Consequently, impaired germinal center formation results in lower Ab titers, severely compromising the development of PGIA. Overall, this study further corroborates the potential of prospective tolerogenic DEC205(+) DC vaccination to interfere with autoimmune diseases, such as rheumatoid arthritis.

Proteoglycan aggrecan conducting T cell activation and apoptosis in a murine model of rheumatoid arthritis

Rheumatoid arthritis (RA) is a systemic autoimmune disease and its targeting of the joints indicates the presence of a candidate autoantigen(s) in synovial joints. Patients with RA show immune responses in their peripheral blood to proteoglycan (PG) aggrecan. One of the most relevant animal models of RA appears to be proteoglycan-induced arthritis (PGIA), and CD4⁺ T cells seem to play a crucial role in the initiation of the disease. In this review, the role of various T cell epitopes of aggrecan in the induction of autoreactive T cell activation and arthritis is discussed. We pay special attention to two critically important arthritogenic epitopes, 5/4E8 and P135H, found in the G1 and G3 domains of PG aggrecan, respectively, in the induction of autoimmune arthritis. Finally, results obtained with the recently developed PG-specific TCR transgenic mice system showed that altered T cell apoptosis, the balance of activation, and apoptosis of autoreactive T cells are critical factors in the development of autoimmunity.

Induction of proliferation and pro-inflammatory cytokine production in rheumatoid arthritis peripheral blood mononuclear cells by a 65 KDa chondrocyte membrane-specific, constitutive target autoantigen (CH65)

OBJECTIVE

To analyze proliferation and pro-inflammatory cytokine production of peripheral blood mononuclear cells (PBMC) from rheumatoid arthritis (RA) patients following stimulation with a purified chondrocyte membrane-associated autoantigen (CH65).

METHODS

CH65 was highly purified from bovine chondrocyte membranes by solubilization and ion exchange chromatography. PBMC of RA patients (n = 37; 28 seropositive, nine seronegative) and non-arthritic donors (n = 20) were isolated by ficoll centrifugation and used in cell proliferation assays. The levels of interleukin (IL)-1, tumo necrosis factor (TNF) and IL-6 produced after stimulation with CH65 were determined by enzyme-linked immunosorbent assay (ELISA). Statistical analysis was performed using Mann-Whitney U-test and Spearman rank test and the software SPSS 13.0^TM (SPSS Inc.; Chicago, IL, USA).

RESULTS

Peripheral blood mononuclear cells exhibited a strong proliferative response to purified CH65 in approximately 50% of the RA patients (seropositive > seronegative), with a maximum reactivity at 0.15 or 0.30 μg/mL culture medium. In contrast, PBMC from normal donors did not show a proliferative response to CH65 at any dose. The proliferative response in RA patients peaked at days 7-9 and returned to control levels at day 13, indicating an antigen-driven process. CH65-stimulated RA PBMC produced moderate to high amounts of IL-1, TNF and IL-6. This was comparable to the response after exposure to isolated whole chondrocyte membranes or purified collagen type II.

CONCLUSION

These results demonstrate a significant cellular immune response to CH65 protein in RA patients. Given the high similarity between bovine and human CH65, the results suggest a pathogenetic involvement of this molecule as a cartilage-specific potential target autoantigen in RA.

Non-MHC risk alleles in rheumatoid arthritis and in the syntenic chromosome regions of corresponding animal models

Rheumatoid arthritis (RA) is a polygenic autoimmune disease primarily affecting the synovial joints. Numerous animal models show similarities to RA in humans; some of them not only mimic the clinical phenotypes but also demonstrate the involvement of homologous genomic regions in RA. This paper compares corresponding non-MHC genomic regions identified in rodent and human genome-wide association studies (GWAS). To date, over 30 non-MHC RA-associated loci have been identified in humans, and over 100 arthritis-associated loci have been identified in rodent models of RA. The genomic regions associated with the disease are designated by the name(s) of the gene having the most frequent and consistent RA-associated SNPs or a function suggesting their involvement in inflammatory or autoimmune processes. Animal studies on rats and mice preferentially have used single sequence length polymorphism (SSLP) markers to identify disease-associated qualitative and quantitative trait loci (QTLs) in the genome of F2 hybrids of arthritis-susceptible and arthritis-resistant rodent strains. Mouse GWAS appear to be far ahead of rat studies, and significantly more mouse QTLs correspond to human RA risk alleles.

Arthritogenic T cells drive the recovery of autoantibody-producing B cell homeostasis and the adoptive transfer of arthritis in SCID mice

T cells orchestrate joint inflammation in rheumatoid arthritis (RA), but B cells/B cell-derived factors are also involved in disease pathogenesis. The goal of this study was to understand the role of antigen-specific T and B cells in the pathological events of arthritis, which is impossible to study in humans due to the small number of antigen-specific cells. To determine the significance of antigen-specific lymphocytes and antibodies in the development of an autoimmune mouse model of RA, we generated TCR transgenic (TCR-Tg) mice specific for the dominant arthritogenic epitope of cartilage proteoglycan (PG) and performed a series of combined transfers of T cells, B cells and autoantibodies into BALB/c.Scid mice. The adoptive transfer of highly purified T cells from naive TCR-Tg, arthritic TCR-Tg or arthritic wild-type mice induced arthritis in SCID recipients, but the onset and severity of the disease were dependent on the sequential events of the T cell-supported reconstitution of PG-specific B cells and autoantibodies. The presence of activated PG-specific T cells was critical for disease induction, establishing a unique milieu for the selective homeostasis of autoantibody-producing B cells. In this permissive environment, anti-PG autoantibodies bound to cartilage and induced activation of the complement cascade, leading to irreversible cartilage destruction in affected joints. These findings may lead to a better understanding of the complex molecular and cellular mechanisms of RA.

Impaired activation-induced cell death promotes spontaneous arthritis in antigen (cartilage proteoglycan)-specific T cell receptor-transgenic mice

OBJECTIVE

To investigate whether genetic preponderance of a T cell receptor (TCR) recognizing an arthritogenic peptide of human cartilage proteoglycan (PG) is sufficient for development of arthritis.

METHODS

We performed a longitudinal study using BALB/c mice expressing a TCR that recognizes the arthritogenic ATEGRVRVNSAYQDK peptide of human cartilage PG. PG-specific TCR-transgenic (PG-TCR-Tg) mice were inspected weekly for peripheral arthritis until 12 months of age. Peripheral joints were examined histologically, and T cell responses, T cell activation markers, serum cytokines, and autoantibodies were measured. Apoptosis and signaling studies were performed in vitro on T cells from aged PG-TCR-Tg mice.

RESULTS

Spontaneous arthritis developed as early as 5-6 months of age, and the incidence increased to 40-50% by 12 months of age. Progressive inflammation began with cartilage and bone erosions in the interphalangeal joints, and later expanded to the proximal joints of the front and hind paws. Spontaneous arthritis was associated with a high proportion of activated CD4+ T cells, enhanced interferon-γ and interleukin-17 (IL-17) production, and elevated levels of serum autoantibodies. PG-TCR-Tg mice lacking IL-4 developed arthritis earlier and at a higher incidence than IL-4-sufficient mice. Antigen-specific activation-induced cell death was diminished in vitro in CD4+ T cells of PG-TCR-Tg mice with spontaneous arthritis, especially in those lacking IL-4.

CONCLUSION

The presence of CD4+ T cells expressing a TCR specific for an arthritogenic PG epitope is sufficient to trigger spontaneous autoimmune inflammation in the joints of BALB/c mice. IL-4 appears to be a negative regulator of this disease, through attenuation of activation-induced cell death.

Pan-DR-binding Hsp60 self epitopes induce an interleukin-10-mediated immune response in rheumatoid arthritis

OBJECTIVE

Human Hsp60 is expressed in the joints of patients with rheumatoid arthritis (RA) and can elicit a regulatory T cell response in the peripheral blood and synovial fluid. However, Hsp60 can also trigger strong proinflammatory pathways. Thus, to understand the nature of these Hsp60-directed responses in RA, it is necessary to study such responses at the molecular, epitope-specific level. This study was undertaken to characterize the disease specificity and function of pan-DR-binding Hsp60-derived epitopes as possible modulators of autoimmune inflammation in RA.

METHODS

Lymphocyte proliferation assays (using (3)H-thymidine incorporation and carboxyfluorescein diacetate succinimidyl ester [CFSE] staining) and measurement of cytokine production (using multiplex immunoassay and intracellular staining) were performed after in vitro activation of peripheral blood mononuclear cells from patients with RA, compared with healthy controls.

RESULTS

A disease (RA)-specific immune recognition, characterized by T cell proliferation as well as increased production of tumor necrosis factor alpha (TNFalpha), interleukin-1beta (IL-1beta), and IL-10, was found for 3 of the 8 selected peptides in patients with RA as compared with healthy controls (P < 0.05). Intracellular cytokine staining and CFSE labeling showed that CD4+ T cells were the subset primarily responsible for both the T cell proliferation and the cytokine production in RA. Interestingly, the human peptides had a remarkably different phenotype, with a 5-10-fold higher IL-10:TNFalpha ratio, compared with that of the microbial peptides.

CONCLUSION

These results suggest a disease-specific immune-modulatory role of epitope-specific T cells in the inflammatory processes of RA. Therefore, these pan-DR-binding epitopes could be used as a tool to study the autoreactive T cell response in RA and might be suitable candidates for use in immunotherapy.

Ankylosing spondylitis

Ankylosing spondylitis is a common inflammatory rheumatic disease that affects the axial skeleton, causing characteristic inflammatory back pain, which can lead to structural and functional impairments and a decrease in quality of life. New imaging techniques and therapies have substantially changed the management of this disease in the past decade. Whether inhibition of radiographic progression and structural damage can be reached with available drugs is as yet unclear. Furthermore, treatment with non-steroidal anti-inflammatory agents and physiotherapy remains an important approach to long-term management of patients with ankylosing spondylitis. The new treatment options with tumour necrosis factor blockers seems a breakthrough for patients refractory to conventional treatment.

Novel self-epitopes derived from aggrecan, fibrillin, and matrix metalloproteinase-3 drive distinct autoreactive T-cell responses in juvenile idiopathic arthritis and in health

Juvenile idiopathic arthritis (JIA) is a heterogeneous autoimmune disease characterized by chronic joint inflammation. Knowing which antigens drive the autoreactive T-cell response in JIA is crucial for the understanding of disease pathogenesis and additionally may provide targets for antigen-specific immune therapy. In this study, we tested 9 self-peptides derived from joint-related autoantigens for T-cell recognition (T-cell proliferative responses and cytokine production) in 36 JIA patients and 15 healthy controls. Positive T-cell proliferative responses (stimulation index ≥2) to one or more peptides were detected in peripheral blood mononuclear cells (PBMC) of 69% of JIA patients irrespective of major histocompatibility complex (MHC) genotype. The peptides derived from aggrecan, fibrillin, and matrix metalloproteinase (MMP)-3 yielded the highest frequency of T-cell proliferative responses in JIA patients. In both the oligoarticular and polyarticular subtypes of JIA, the aggrecan peptide induced T-cell proliferative responses that were inversely related with disease duration. The fibrillin peptide, to our knowledge, is the first identified autoantigen that is primarily recognized in polyarticular JIA patients. Finally, the epitope derived from MMP-3 elicited immune responses in both subtypes of JIA and in healthy controls. Cytokine production in short-term peptide-specific T-cell lines revealed production of interferon-γ (aggrecan/MMP-3) and interleukin (IL)-17 (aggrecan) and inhibition of IL-10 production (aggrecan). Here, we have identified a triplet of self-epitopes, each with distinct patterns of T-cell recognition in JIA patients. Additional experiments need to be performed to explore their qualities and role in disease pathogenesis in further detail.

The role of B cells and autoantibodies in rheumatoid arthritis

In this article, we will review B lymphocyte development and function, then discuss the role of B cells in RA, including immune complex formation; the K/BxN mouse model of RA; toll-like receptors; B cells as antigen presenting cells; germinal center-like structures in RA synovium; and influence on T cell activation, leukocyte infiltration, and angiogenesis. With regard to autoantibody production, we will focus on rheumatoid factor (RF) and anti-CCP antibodies, particularly mechanisms of their production; sensitivity and specificity in RA; and their roles as prognostic factors. Other autoantibodies will be discussed, as will treatment implications and future areas of investigation related to B cells and autoantibodies in RA.

Immunohistochemical analysis of hip arthritis in ankylosing spondylitis: Evaluation of the bone–cartilage interface and subchondral bone marrow

OBJECTIVE

Previous histopathologic and magnetic resonance imaging studies suggest that the subchondral bone marrow might be the primary site of inflammation in patients with ankylosing spondylitis (AS) and that this might be reflected by inflammation found in hip joints. The aim of this study was to conduct an immunohistologic assessment of the bone-cartilage interface and subchondral bone marrow in AS patients with hip arthritis.

METHODS

We collected femoral heads from patients with AS, osteoarthritis (OA), and rheumatoid arthritis (RA) who were undergoing hip replacement. The subchondral bone marrow and bone-cartilage interface were assessed immunohistochemically by evaluating infiltrating T cells, microvessel density, and osteoclasts. Areas of the femoral head surface with and without cartilage were assessed separately.

RESULTS

At sites with surface cartilage, we found subchondral infiltration of CD3+ T cell aggregates at significantly higher numbers in AS patients as compared with OA patients, but not RA patients. At sites of complete cartilage destruction, the frequency of CD3+ T cell aggregates was significantly reduced as compared with sites with cartilage on the surface in AS patients, but not in RA patients. Similar differences were found for CD4+ and CD8+ T cells. Only at sites with surface cartilage, but not those without, angiogenesis and osteoclastic foci in the subchondral bone marrow in AS patients were significantly increased as compared with RA patients and with OA patients.

CONCLUSION

These findings suggest that the subchondral bone marrow and bone-cartilage interface are primary sites of inflammation in AS and that cartilage might be necessary for the induction of inflammation.

Increased arthritis susceptibility in cartilage proteoglycan–specific T cell receptor–transgenic mice

OBJECTIVE

To better understand the role of antigen (arthritogenic epitope)-specific T cells in the development of autoimmune arthritis.

METHODS

A transgenic (Tg) mouse expressing the T cell receptor (TCR) Valpha1.1 and V(beta)4 chains specific for a dominant arthritogenic epitope (designated 5/4E8) of human cartilage proteoglycan (HuPG) aggrecan was generated. This TCR-Tg mouse strain was backcrossed into the PG-induced arthritis (PGIA)-susceptible BALB/c strain and tested for arthritis incidence and severity.

RESULTS

CD4+ TCR-Tg T cells carried functionally active TCR specific for a dominant arthritogenic epitope of HuPG (5/4E8). T cells of naive TCR-Tg mice were in an activated stage, since the in vitro response to HuPG or to peptide stimulation induced interferon-gamma and interleukin-4 production. TCR-Tg mice uniformly, without exception, developed severe and progressive polyarthritis, even without adjuvant. Inflamed joints showed extensive cartilage degradation and bone erosions, similar to that seen in the arthritic joints of wild-type BALB/c mice with PGIA. Spleen cells from both naive and HuPG-immunized arthritic TCR-Tg mice could adoptively transfer arthritis when injected into syngeneic BALB/c.SCID recipient mice.

CONCLUSION

TCR-Tg BALB/c mice display increased arthritis susceptibility and develop aggravated disease upon in vivo antigen stimulation. This model using TCR-Tg mice is a novel and valuable research tool for studying mechanisms of antigen (arthritogenic epitope)-driven regulation of arthritis and understanding how T cells recognize autoantigen in the joints. This type of mouse could also be used to develop new immunomodulatory strategies in T cell-mediated autoimmune diseases.

Molecular manipulation with the arthritogenic epitopes of the G1 domain of human cartilage proteoglycan aggrecan

Systemic immunization of BALB/c mice with human cartilage proteoglycan (PG) aggrecan induces progressive polyarthritis. The G1 domain of the PG aggrecan molecule contains most of the T cell epitopes, including three immunodominant ('arthritogenic') and at least six subdominant T cell epitopes. The three dominant T cell epitopes (P49, P70 and P155) were deleted individually or in combination by site directed mutagenesis, and the recombinant human G1 (rhG1) domain (wild type and mutated) proteins were used for immunization. Close to 100% of BALB/c mice immunized with the wild-type (nonmutated) rhG1 domain developed severe arthritis, which was 75% in the absence of P70 (5/4E8) epitope, and very low (< 10% incidence) when all three dominant T cell epitopes were deleted. The onset was delayed and the severity of arthritis reduced in animals when dominant T cell epitopes were missing from the immunizing rhG1 domain. The lack of T cell response to the deleted epitope(s) was specific, but the overall immune response against the wild-type rhG1 domain of human PG was not significantly affected. This study helped us to understand the dynamics and immune-regulatory mechanisms of arthritis, and supported the hypothesis that the development of autoimmune arthritis requires a concerted T cell response to multiple epitopes, rather than the immune response to a single arthritogenic structure.

Naive transgenic T cells expressing cartilage proteoglycan-specific TCR induce arthritis upon in vivo activation

Proteoglycan (PG)-induced arthritis (PGIA), a murine model for rheumatoid arthritis (RA), is driven by antigen (PG)-specific T and B cell activation. In order to analyze the pathogenic role of antigen-specific T cells in the development of autoimmune arthritis, we have generated a transgenic (Tg) mouse. The CD4(+) T cells of this TCR-5/4E8-Tg line express a functional T cell receptor (TCR) composed of the Valpha1.1 and Vbeta4 chains with specificity for the dominant arthritogenic T cell epitope of human cartilage PG. Adoptive transfer of naive TCR-5/4E8-Tg cells induced arthritis with severe clinical symptoms in syngeneic immunodeficient BALB/c.RAG2(-/-) mice. In vivo activation of TCR-5/4E8-Tg CD4(+)Vbeta4(+) cells with cartilage PG seemed to be critical for arthritis induction. Arthritis never developed after transfer of naive wild-type cells. The arthritis was characterized as a chronic progressive disease with intermittent spontaneous exacerbations and remissions. Inflamed joints showed extensive cartilage damage and bone erosions leading to massive ankylosis in peripheral joints. These PG epitope-specific TCR-5/4E8-Tg mice can be valuable research tools for studying antigen-driven T cell regulation in arthritis, and migration of T cells to the joints. In addition the model may be used for the development of immune modulating strategies in T cell-mediated autoimmune diseases.

T-cell recognition of differentially tolerated epitopes of cartilage proteoglycan aggrecan in arthritis

Proteoglycan (PG) aggrecan, a major macromolecular component of cartilage, is highly immunogenic; it induces arthritis in genetically susceptible BALB/c mice. The present study maps the T-cell epitope repertoire of cartilage PG by identifying a total of 27 distinct T-cell epitopes. An epitope hierarchy, accounting for the different effector functions of PG-specific T cells, and determinant spreading, has been found. T-cell responses to four epitopes were associated with arthritis induction. Some of the T-cell epitopes were full T-cell activators, whereas a number of subdominant and cryptic epitopes proved to be partial activators in vitro, inducing either cytokine secretion or T-cell proliferation, but not both. A few T-cell epitopes of the core protein of cartilage PG were clearly recognized by T cells in PG-immunized arthritic animals, but the corresponding peptides did not induce T-cell responses when injected into naive BALB/c mice; thus these T-cell epitopes were designated as "conditionally immunogenic."

A longitudinal study on an autoimmune murine model of ankylosing spondylitis

BACKGROUND

Proteoglycan aggrecan (PG)-induced arthritis (PGIA) is the only systemic autoimmune murine model which affects the axial skeleton, but no studies have been performed characterising the progression of spine involvement.

OBJECTIVES

To follow pathological events in experimental spondylitis, and underline its clinical, radiographic, and histological similarities to human ankylosing spondylitis (AS); and to determine whether the spondyloarthropathy is a shared phenomenon with PGIA, or an "independent" disease.

METHODS

Arthritis/spondylitis susceptible BALB/c and resistant DBA/2 mice, and their F1 and F2 hybrids were immunised with cartilage PG, and radiographic and histological studies were performed before onset and weekly during the progression of spondylitis.

RESULTS

About 70% of the PG immunised BALB/c mice develop spondyloarthropathy (proteoglycan-induced spondylitis (PGISp), and the progression of the disease is very similar to human AS. It begins with inflammation in the sacroiliac joints and with enthesitis, and then progresses upwards, affecting multiple intervertebral disks. In F2 hybrids of arthritis/spondylitis susceptible BALB/c and resistant DBA/2 mice the incidence of arthritis was 43.5%, whereas the incidence of spondylitis was >60%. Some arthritic F2 hybrid mice had no spondylitis, whereas others developed spondylitis in the absence of peripheral arthritis.

CONCLUSIONS

The PGISp model provides a valuable tool for studying autoimmune reactions in spondylitis, and identifying genetic loci associated with spondyloarthropathy.

Identification of Novel Human Aggrecan T Cell Epitopes in HLA-B27 Transgenic Mice Associated with Spondyloarthropathy

The pathology of ankylosing spondylitis, reactive arthritis, and other spondyloarthropathies (SpA) is closely associated with the human leukocyte class I Ag HLA-B27. A characteristic finding in SpA is inflammation of cartilage structures of the joint, in particular at the site of ligament/tendon and bone junction (enthesitis). In this study, we investigated the role of CD8+ T cells in response to the cartilage proteoglycan aggrecan as a potential candidate autoantigen in BALB/c-B27 transgenic mice. We identified four new HLA-B27-restricted nonamer peptides, one of them (no. 67) with a particularly strong T cell immunogenicity. Peptide no. 67 immunization was capable of stimulating HLA-B27-restricted, CD8+ T cells in BALB/c-B27 transgenic animals, but not in wild-type BALB/c mice. The peptide was specifically recognized on P815-B27 transfectants by HLA-B27-restricted CTLs, which were also detectable by HLA tetramer staining ex vivo as well as in situ. Most importantly, analysis of the joints from peptide no. 67-immunized mice induced typical histological signs of SpA. Our data indicate that HLA-B27-restricted epitopes derived from human aggrecan are involved in the induction of inflammation (tenosynovitis), underlining the importance of HLA-B27 in the pathogenesis of SpA.

Update on autoantibodies in rheumatoid arthritis

Detection of rheumatoid factor (RF) in the serum of patients with rheumatoid arthritis (RA) was one of the first indications of autoimmunity in RA. The role of RF in the diagnosis of RA has been well-documented, but it has suboptimal sensitivity and specificity. Although patients with RF-positive RA generally have more severe disease than those with RF-negative RA, RF is not a reliable predictor of disease severity in individual patients. Multiple other autoantibodies have been found in RA, with recent interest focused on those directed at cyclic citrullinated peptides. Panels of autoantibodies may ultimately prove useful in preclinical diagnosis and prediction of clinical course in patients with RA and other forms of arthritis, and provide insights into the pathogenesis of the disease.

Induction of arthritis in HLA-DR4-humanized and HLA-DQ8-humanized mice by human cartilage proteoglycan aggrecan but only in the presence of an appropriate (non-MHC) genetic background

OBJECTIVE

To determine whether the rheumatoid arthritis (RA)-predisposing class II molecules of the major histocompatibility complex (MHC) can present cartilage proteoglycan (PG) aggrecan, and if so, to determine the epitope repertoire of the human cartilage PG in HLA-transgenic mice and determine whether HLA-transgenic mice develop arthritis in response to immunization with human cartilage PG.

METHODS

Mice transgenic for HLA-DR2.Ab(0), DR3.Ab(0), DR4.Ab(0), and DQ8.Ab(0), lacking their own (mouse) class II antigens (Ab(0)), on the original (arthritis-resistant) and the arthritis-susceptible BALB/c backgrounds, were immunized with human cartilage PG. The T cell epitope repertoire presented by these class II MHC alleles was determined using a synthetic peptide library (143 peptides of the core protein of human cartilage PG), and arthritis development was monitored and compared in wild-type and HLA-transgenic/congenic BALB/c mice.

RESULTS

Mice of the 4 HLA-transgenic lines, either on the original mixed, arthritis-resistant background or DR4.Ab(0)- and DQ8.Ab(0)-transgenic/congenic mice on the arthritis-susceptible BALB/c genetic background, responded well to PG immunization (as assessed by T cell responses and antibody and cytokine production), and a number of T cell epitopes along the core protein of human cartilage PG were identified. DR4.Ab(0)- and DQ8.Ab(0)-transgenic mice immunized with human cartilage PG developed arthritis, but only when these class II MHC molecules were present on the arthritis-susceptible (BALB/c) genetic background.

CONCLUSION

A number of human cartilage PG epitopes can be presented by HLA alleles that predispose to the development of RA, but the epitopes of the cartilage PG presented by HLA-DR4 or HLA-DQ8 can induce arthritis only in the presence of an appropriate genetic (non-MHC) background.

Antigen-specific T cells in rheumatoid arthritis

There is considerable evidence of a key role for CD4+ T cells in the pathogenesis of rheumatoid arthritis. Several attractive candidate antigens, mostly joint-specific, have been studied, but information regarding T cell responses to these antigens in patients is limited and occasionally contradictory. Novel reagents (such as major histocompatibility complex and peptide tetramers) and sensitive techniques (such as intracellular cytokine staining) will aid in future studies to identify antigen-specific T cells. In addition, a new animal model of inflammatory arthritis has recently provided new perspective to the study of rheumatoid arthritis by drawing attention to systemic self-antigens as targets of autoimmunity and anti-self antibodies as markers of T cell activity and effectors of disease.

Suppression of T cell responses by chondromodulin I, a cartilage-derived angiogenesis inhibitory factor: Therapeutic potential in rheumatoid arthritis

OBJECTIVE

Chondromodulin I (ChM-I), a cartilage matrix protein, promotes the growth and proteoglycan synthesis of chondrocytes. However, it also inhibits angiogenesis. Since ChM-I is expressed not only in cartilage, but also in the thymus, we investigated the modulation of T cell function by ChM-I to assess its therapeutic potential in rheumatoid arthritis (RA).

METHODS

The localization of ChM-I expression in mouse thymus tissue was examined by in situ hybridization. The proliferative response of peripheral blood T cells and synovial cells obtained from patients with RA was evaluated by (3)H-thymidine incorporation assay. The effects of ChM-I were examined using recombinant human ChM-I (rHuChM-I). Modulation of the antigen-specific immune response was evaluated by the recall response of splenic T cells and the delayed-type hypersensitivity response induced in the ear of mice primed with ovalbumin (OVA). Antigen-induced arthritis (AIA) was induced in mice by injecting methylated bovine serum albumin into the ankle joints 2 weeks after the priming.

RESULTS

ChM-I was expressed in the cortex of the thymus. Recombinant human ChM-I suppressed the proliferative response of mouse splenic T cells and human peripheral blood T cells stimulated with anti-CD3/CD28 antibodies, in a dose-dependent manner. Production of interleukin-2 was decreased in rHuChM-I-treated mouse CD4 T cells. Ten micrograms of rHuChM-I injected intraperitoneally into OVA-primed mice suppressed the induction of the antigen-specific immune response. Finally, rHuChM-I suppressed the development of AIA, and also suppressed the proliferation of synovial cells prepared from the joints of patients with RA.

CONCLUSION

These results suggest that ChM-I suppresses T cell responses and synovial cell proliferation, implying that this cartilage matrix protein has a therapeutic potential in RA.

Deglycosylation of glycoproteins with trifluoromethanesulphonic acid: elucidation of molecular structure and function

The alteration of proteins by post-translational modifications, including phosphorylation, sulphation, processing by proteolysis, lipid attachment and glycosylation, gives rise to a broad range of molecules that can have an identical underlying protein core. An understanding of glycosylation of proteins is important in clarifying the nature of the numerous variants observed and in determining the biological roles of these modifications. Deglycosylation with TFMS (trifluoromethanesulphonic acid) [Edge, Faltynek, Hof, Reichert, and Weber, (1981) Anal. Biochem. 118, 131-137] has been used extensively to remove carbohydrate from glycoproteins, while leaving the protein backbone intact. Glycosylated proteins from animals, plants, fungi and bacteria have been deglycosylated with TFMS, and the most extensively studied types of carbohydrate chains in mammals, the N-linked, O-linked and glycosaminoglycan chains, are all removed by this procedure. The method is based on the finding that linkages between sugars are sensitive to cleavage by TFMS, whereas the peptide bond is stable and is not broken, even with prolonged deglycosylation. The relative susceptibility of individual sugars in glycosidic linkage varies with the substituents at C-2 and the occurrence of amido and acetyl groups, but even the most stable sugars are removed under conditions that are sufficiently mild to prevent scission of peptide bonds. The post-translational modifications of proteins have been shown to be required for diverse biological functions, and selective procedures to remove these modifications play an important role in the elucidation of protein structure and function.

Experimental immunity to the G1 domain of the proteoglycan versican induces spondylitis and sacroiliitis, of a kind seen in human spondylarthropathies

OBJECTIVE

Experimental immunity to the G1 domain of the cartilage proteoglycan (PG) aggrecan (AG1) leads to the development of spondylitis as well as polyarthritis in BALB/c mice. The PG versican contains a structurally similar G1 domain (VG1). This study was conducted to determine whether immunity to VG1 would elicit similar pathology in these mice.

METHODS

Recombinant natively folded VG1 and AG1 were prepared. BALB/c mice received either a series of 5 injections of human VG1 or AG1, or no protein. Polyarthritis was determined clinically, and spondylitis and sacroiliitis histologically. Immunohistochemistry of rat tissues was used to study the localization of versican. Enzyme-linked immunosorbent assays were employed to study humoral immunity to the recombinant proteins as well as to overlapping synthetic peptides covering all these human G1 domains and mouse homologs. Affinity-purified antibodies to human AG1 and VG1 were isolated from sera of hyperimmunized mice. T lymphocyte proliferation assays were performed using recombinant human proteins. T cell lines reactive with specific immunodominant T cell epitopes in human AG1 and VG1 were isolated. Synthetic peptides encoding sequences in these human proteins and in corresponding mouse proteins were used in these analyses. Guanidinium chloride extracts of mouse spines were also used in Western blots to study antibody cross-reactivity.

RESULTS

Immunity to recombinant VG1 did not result in clinical polyarthritis. There was, however, clear evidence that VG1, like AG1, could induce spondylitis in the lumbar spine and sacroiliitis. Accumulation of mononuclear cells was observed in spinal ligaments adjacent to the intervertebral disc, in the intervertebral disc, and in the sacroiliac joints, the same sites where versican is localized. In contrast to AG1-immunized mice, in which T cells reactive with human AG1 cross-reacted with mouse AG1, there was no evidence in VG1-immunized mice that T cell immunity to human VG1 was cross-reactive with a mouse synthetic peptide that contained the sequence corresponding to the single immunodominant T cell sequence recognized in human VG1. Antibodies to specific sequences in human VG1 did, however, cross-react with human AG1 and with corresponding peptide sequences in mouse versican and aggrecan and with mouse proteins containing VG1 and AG1, present in mouse spine extracts. Similarly, antibodies to human AG1 cross-reacted with human VG1 and with extracted mouse VG1 and AG1 and synthetic peptides containing mouse sequences that corresponded to the reactive human epitopes in AG1 and VG1.

CONCLUSION

These observations suggest that humoral immunity to human VG1 is involved in the induction of experimental spondylitis and sacroiliitis in BALB/c mice. This humoral immunity is cross-reactive with mouse versican and aggrecan but is not associated with polyarthritis, probably because of the lack of cross-reactive T cell immunity and the absence of detectable versican in articular cartilage limbs. Induction of polyarthritis by bovine or human aggrecan requires the involvement of immunity mediated by T lymphocytes that are cross-reactive to a mouse aggrecan epitope. Together these observations suggest that humoral immunity to versican as well as immunity to aggrecan may be of importance in the development of the spinal pathology characteristic of spondylarthropathies.

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.

Differential recognition of altered peptide ligands distinguishes two functionally discordant (arthritogenic and nonarthritogenic) autoreactive T cell hybridoma clones

Intravenous injection of a cartilage proteoglycan (aggrecan)-specific Th1 hybridoma clone 5/4E8 induced joint lesions similar to those seen in either primary or adoptively transferred arthritis in BALB/c mice. A sister clone, TA20, recognizing the same peptide epitope of human aggrecan and using the same Vbeta4 and Valpha1 segments, failed to induce joint inflammation. This study examines the fine epitope specificities of these two clones. Both 5/4E8 and TA20 hybridomas were generated using T cells from the same arthritic animal that has been immunized with human aggrecan, and both clones recognized peptides containing a consensus GRVRVNSAY sequence. However, flanking regions outside this nonapeptide sequence region had differential impact on peptide recognition by the two clones. Similarly, when single amino acid substitutions were introduced to the consensus sequence, significant differences were detected in the epitope recognition patterns of the T cell hybridomas. The 5/4E8 hybridoma showed greater flexibility in recognition, including a higher responsiveness to the corresponding self (mouse) aggrecan peptide, and produced more inflammatory cytokines (IFN-gamma and TNF-alpha), whereas hybridoma TA20 produced IL-5 in response to either human or mouse self peptide stimulation. These results demonstrate that, within the pool of immunodominant (foreign) peptide-activated lymphocytes, marked individual differences of degeneracy exist in T cell recognition, with possible implications to autopathogenic T cell functions.

Identification of HLA-B27-restricted peptides in reactive arthritis and other spondyloarthropathies: computer algorithms and fluorescent activated cell sorting analysis as tools for hunting of HLA-B27-restricted chlamydial and autologous crossreactive peptides involved in reactive arthritis and ankylosing spondylitis

The illustrated clinical and experimental results demonstrate the strong relationship between the MHC class I antigen HLA-B27 and synovial CD8+ T cells with specificity for bacterial and possible self-antigen in SpA. These new aspects obtained in recent experimental and clinical studies might also provide clues to the pathomechanisms of joint inflammation in SpA. In particular, the newly developed techniques will be of great relevance in the near future. New and more precise bioalgorithms reflecting new insights in the biology and biochemistry of proteins as recently presented [98, 99] can be helpful (e.g., a program with an improved prediction of the features of immunoproteasomes). Intracellular and secreted cytokine staining by FACScan allows examination of a great number of cells expressing certain antigens in response to certain stimuli. The analysis of T-cell responses with tetramer/peptide complexes can be useful to screen tissue sections for TCR, recognizing foreign or self-derived epitopes on those complexes loaded with selected (e.g., bacterial) peptides. Identification of arthritogenic peptides and a further understanding of the immunology of the pathomechanisms in SpA might open ways to design new peptide vaccines to prevent inflammation, autoimmunity, and other diseases by early intervention [100].

Animal models of inflammatory spinal and sacroiliac joint diseases

Many cartilage matrix proteins or domains such as collagen types II, IX, and XI, GP39, AG1, VG1, and LP are potential antigens that might induce polyarthritis in susceptible animals (Table 1). Ordinarily, spondylitis is not a feature of polyarthritis induced with collagen types II, IX, and XI, GP39, cartilage matrix protein (matrilin-1) and cartilage LP. It seems that only the proteoglycans aggrecan and versican are capable of inducing sacroiliitis and spondylitis. Both molecules are structural proteins in intervertebral discs. Moreover, the arthritogenic or spondylitogenic epitopes of both molecules have been localized to the homologous N-terminal G1 globular domains. This region of versican and aggrecan is highly conserved, with 52% identity of amino acids. The homology is seen exclusively in the G1 domain and is concentrated between residues 115 and 332 (AG1 numbering) near the natural cleavage DIPEN site of aggrecan [84, 85]. Extra-articular pathology is often seen in rheumatic diseases, especially in AS. Other tissues, such as the sclera of the eye [86] and the media of the arteries [86, 87], also contain type II collagen, AG1, VG1, and LP, and versican is present in the central and peripheral nervous systems. Thus, there is the potential for an immune response against cartilage G1 and LP to be directed against related structures in extra-articular tissues. The presence of versican in the tendon and trochlea of the human superior oblique muscle might account for the occurrence of transient attacks of acquired Brown syndrome in patients with juvenile and adult forms of chronic RA [88]. Thus, it will be interesting to determine whether or not extra-articular expression of these cartilage proteins is closely related to extra-articular pathogenic expression in rheumatic diseases. Uveitis develops in VG1-immunized BALB/c mice, which is not seen in AG1-, and LP-treated animals. There is evidence that aggrecan and LP are also localized at these sites in the eye, but only immunity to versican can induce uveitis. In sacroiliitis and enthesitis of AS patients, the inflammation is associated with chondrometaplasia. In versican-induced sacroiliitis, replacement of cartilage by bone is seen with relatively little inflammation, somewhat resembling the situation in AS (Fig. 2). Versican can also stimulate chondrocyte proliferation [43]. Three conserved domains of human cartilage matrix molecules, namely VG1, AG1, and LP, show considerable homology [77, 79, 80, 89], and each is capable of inducing a unique inflammatory arthritis in BALB/c mice, with VG1 inducing only spondylitis [65], LP inducing peripheral arthritis with no spondylitis [90], and AG1 inducing axial and peripheral arthritis [66, 91]. It remains a mystery why such similar molecules cause different pathology in different target tissues. The exact immunopathogenic mechanisms deserve further study.

Expression of recombination-activating genes and terminal deoxynucleotidyl transferase and secondary rearrangement of immunoglobulin kappa light chains in rheumatoid arthritis synovial tissue

OBJECTIVE

Lymphocytic infiltrates in rheumatoid arthritis (RA) synovium often resemble lymphoid follicles and contain clonally related Ig transcripts, suggesting in situ antigen-dependent B cell selection. Recent reports have shown expression of recombination-activating genes (RAGs) and concurrent secondary rearrangement of Ig genes in normal peripheral lymphoid organs (receptor revision). We sought to determine if RAG-mediated receptor revision of Ig kappa light chains occurs in B cells within the RA synovium. Because we previously reported enhanced N-region addition at V(L)-J(L) joins in clonally expanded light-chain transcripts from RA synovium, we also sought expression of terminal deoxynucleotidyl transferase (TdT), which is normally expressed only in B cell precursors or immature B cells.

METHODS

Reverse transcription-polymerase chain reaction (PCR) was used to detect RAG and TdT transcripts from unselected and B cell-enriched synovial and peripheral blood mononuclear cells obtained from 12 RA patients. Activity of RAG protein was sought using ligation-mediated PCR to detect recombination intermediates, and immunohistochemistry was performed to identify RAG+ cells within synovia.

RESULTS

We found evidence of RAG-mediated secondary Ig kappa light chain rearrangements in about one-third of RA synovia. TdT expression was found in several samples, but did not correlate with RAG expression.

CONCLUSION

RAG-mediated secondary Ig rearrangements of kappa light chains may contribute to the local production of antibodies to autoantigens (e.g., rheumatoid factor) or exogenous antigens, or it may represent a failed attempt at immune tolerance. TdT expression suggests the presence of immature B cells in RA synovia. These findings have important implications for the local generation of antibodies in RA and other chronic inflammatory diseases.

Specific presence of intracellular citrullinated proteins in rheumatoid arthritis synovium: relevance to antifilaggrin autoantibodies

OBJECTIVE

To investigate the presence of citrullinated proteins in the synovial membrane of patients with rheumatoid arthritis (RA) and controls, and to analyze a possible relationship with antifilaggrin autoantibody (AFA) reactivity.

METHODS

Synovial biopsy samples were obtained from 88 consecutive patients undergoing needle arthroscopy for knee synovitis associated with RA (n = 36), spondylarthropathy (n = 35), osteoarthritis (n = 9), or other diagnoses (n = 8). Tissue sections were stained with 2 different anticitrulline polyclonal antibodies and an antifilaggrin monoclonal antibody (mAb). The phenotype of citrulline-positive cells and the colocalization with affinity-purified AFA were investigated by double immunofluorescence on frozen sections.

RESULTS

Studies with the first antibody showed that citrulline is expressed intracellularly in the lining and sublining layers of RA synovial tissue. Staining with the second antibody, monospecific for proteins containing modified citrulline, and with anti-inducible nitric oxide synthetase confirmed the presence of citrullinated proteins rather than free citrulline in the synovium. Citrulline-positive cells were detected in 50% of the RA patients (18 of 36) but in none of the controls (0 of 52). The anticitrulline reactivity colocalized with affinity-purified AFA reactivity, although stainings with the antifilaggrin mAb indicated the absence of filaggrin in the synovium.

CONCLUSION

Intracellular citrullinated proteins, which are not recognized by an antifilaggrin mAb, are expressed in RA but not in control synovium. The high specificity of this finding and the colocalization with AFA reactivity boost the interest in citrullinated proteins as possible triggers of autoimmune responses in RA. Moreover, this is the first description of a specific histologic marker for RA synovium.

Pathogenesis of rheumatoid arthritis. Role of B lymphocytes

Despite many years of investigation, there remain many unanswered fundamental questions on the role of B cells in RA. Why is RF found in the sera of 80% of patients with RA and often in other chronic inflammatory diseases? What signals lead B lymphocytes to migrate into the subsynovial lining of joints? Does receptor revision in synovium play a role in the generation of autoantibodies in RA? What is the relative contribution of B-cell inhibition on the salutary effect of medications for RA? Can targeting autoreactive B cells, in conjunction with other therapies, provide therapeutic benefit in RA? We are hopeful that through continued basic, clinical, and translational research, these questions can be answered.

Implication of cartilage intermediate layer protein in cartilage destruction in subsets of patients with osteoarthritis and rheumatoid arthritis

OBJECTIVE

To investigate whether cartilage intermediate layer protein (CILP), a protein recently cloned from human articular cartilage, is recognized as an autoantigen in patients with osteoarthritis (OA) and rheumatoid arthritis (RA), and whether the immune response against CILP is involved in disease pathogenesis.

METHODS

Recombinant fusion proteins, which contain the first half (C1), second half (C2), or 3 fragments within the C2 region (designated C2F1, C2F2, and C2F3) of the non-porcine nucleotide pyrophosphohydrolase-homologous region of CILP, were prepared using Escherichia coli. Autoantibodies to these proteins in serum samples from patients with OA or RA and from age-matched healthy individuals were detected by enzyme-linked immunosorbent assay and Western blotting. In addition, mice were immunized with a mixture of the C1 and C2 fusion proteins to assess the arthrogenicity of CILP.

RESULTS

Production of antibodies to the C2 region was detected in 10.5% (11 of 105) of the tested OA patients and in 8.0% (7 of 88) of the tested RA patients, although antibodies to the C1 region were rarely detected in either patient group. All C2F1, C2F2, and C2F3 fragments were found to carry autoepitopes. The C2F2 fusion protein was recognized most frequently in the tested OA patients, whereas the C2F3 fusion protein was dominantly recognized in the tested RA patients. All 4 mice strains, DBA/1J, ICR, C57BL/6, and BALB/c, immunized with the CILP fusion proteins developed chronic arthritis; in particular, the ICR mice developed polyarthritis that was characterized by infiltration of mononuclear cells in the synovium and exfoliation of the surface of cartilage.

CONCLUSION

The immune response to CILP may play a role in the pathogenesis of inflammatory joint destruction. Our results support the role of an immune-mediated process in the joint destruction present in chronic arthropathies such as OA and RA. The results suggest that suppression of immune responses to various components of the cartilage, such as CILP, might be therapeutically beneficial in these chronic arthropathies.

Keratan sulfates from bovine tracheal cartilage structural studies of intact polymer chains using H and 13C NMR spectroscopy

Intact keratan sulfate chains derived from bovine tracheal cartilage have been examined using both one-dimensional methods and the two-dimensional experiments COSY-45 and TOCSY for homonuclear shift correlations and a modified COLOC (correlated spectroscopy for long-range couplings) approach for 13C-1H shift correlations. Partial 1H and 13C NMR signal assignments for residues within the intact polymer chain are reported; data derived from the repeat region signals and from chain cap residues are assigned by comparison with published data derived from oligosaccharides obtained through cleavage of keratan sulfate polymer chains using keratanase and keratanase II and are discussed in detail. The one-dimensional spectra for both 1H and 13C nuclei contain highly crowded signal clusters for which data analysis is not directly possible. COSY-45 analysis allow the correlation and assignment of many proton resonances located within the 3.4-4.8 p.p.m. chemical shift region while from the C/H correlation spectrum data are assignable for some signals within the complex set of carbon resonances which fall in the region between 68 and 86 p.p.m., This work using material from tracheal cartilage has permitted the first detailed combined 1H and 13C NMR examination of the primary keratan sulfate polymer structure; this sequence forms the basis for the more complex members of the keratan sulfate family present in other tissues such as articular cartilage and cornea where further residues such as (alpha1-3)-linked fucose and (alpha2-6)-linked N-acetylneuraminic acid are also present. This nondestructive method of analysis complements the currently available degradative methods for structure determination which may then subsequently be utilized.

Rheumatoid arthritis and its animal models: the role of TNF-alpha and the possible absence of specific immune reactions

Rheumatoid arthritis is an organ-specific inflammatory disease of humans. Recent studies have focused on associations with non-MHC genes, new autoantigens and the role of innate immune responses. The success of anti-TNF-alpha in the majority (but, interestingly, not all) of patients has implications for disease mechanisms but the dangers of long-term therapy are becoming clearer. A number of new models of arthritis have been defined and emphasize the importance of the genetic make-up of the host. Attention has also focused on why the joint is a particularly vulnerable site for inflammatory responses.

Transgenic mouse models of rheumatoid arthritis

A combined analysis of data available in the literature has demonstrated that the strongest association in rheumatoid arthritis (RA) is with DR genes rather than DQ or DP genes. Functional and structural data of RA-associated DR molecules suggest that selective binding of peptides is the molecular basis for this association. The establishment of functional transgenic mice expressing RA-associated HLA class II molecules has proven to be useful in the delineation of the role of these molecules in immune responses possibly related to RA and in the development of humanized models for this disease. Such humanized mice develop arthritis upon immunization with type II collagen (CII), which shows similarities with RA. Interestingly, the immunodominant T-cell determinant in CII is derived from positions 261-273, which overlap with a previously identified CII T-cell epitope restricted by the mouse Aq molecule, which is associated with collagen-induced arthritis. Studies in collagen transgenic mice have shown that recognition of this peptide may lead either to T-cell tolerance or to an arthritogenic response. It is therefore proposed that the T-cell recognition of the CII peptide bound by DR molecules is one of the molecular interactions of critical importance in the development of RA and accordingly also an important target for prevention and treatment of this disease.