Isolation and characteristics of autoreactive T cells specific to aggrecan G1 domain from rheumatoid arthritis patients

Antigen-specific T cells and autoimmunity

Autoimmune diseases (ADs) showcase the intricate balance between the immune system's protective functions and its potential for self-inflicted damage. These disorders arise from the immune system's erroneous targeting of the body's tissues, resulting in damage and disease. The ability of T cells to distinguish between self and non-self-antigens is pivotal to averting autoimmune reactions. Perturbations in this process contribute to AD development. Autoreactive T cells that elude thymic elimination are activated by mimics of self-antigens or are erroneously activated by self-antigens can trigger autoimmune responses. Various mechanisms, including molecular mimicry and bystander activation, contribute to AD initiation, with specific triggers and processes varying across the different ADs. In addition, the formation of neo-epitopes could also be implicated in the emergence of autoreactivity. The specificity of T cell responses centers on the antigen recognition sequences expressed by T cell receptors (TCRs), which recognize peptide fragments displayed by major histocompatibility complex (MHC) molecules. The assortment of TCR gene combinations yields a diverse array of T cell populations, each with distinct affinities for self and non-self antigens. However, new evidence challenges the traditional notion that clonal expansion solely steers the selection of higher-affinity T cells. Lower-affinity T cells also play a substantial role, prompting the "two-hit" hypothesis. High-affinity T cells incite initial responses, while their lower-affinity counterparts perpetuate autoimmunity. Precision treatments that target antigen-specific T cells hold promise for avoiding widespread immunosuppression. Nevertheless, detection of such antigen-specific T cells remains a challenge, and multiple technologies have been developed with different sensitivities while still harboring several drawbacks. In addition, elements such as human leukocyte antigen (HLA) haplotypes and validation through animal models are pivotal for advancing these strategies. In brief, this review delves into the intricate mechanisms contributing to ADs, accentuating the pivotal role(s) of antigen-specific T cells in steering immune responses and disease progression, as well as the novel strategies for the identification of antigen-specific cells and their possible future use in humans. Grasping the mechanisms behind ADs paves the way for targeted therapeutic interventions, potentially enhancing treatment choices while minimizing the risk of systemic immunosuppression.

Pan-Immune-Inflammation Index as a Biomarker for Rheumatoid Arthritis Progression and Diagnosis

Introduction Rheumatoid arthritis (RA) is a chronic autoimmune condition that causes systemic inflammation and affects multiple joints. It is characterized by joint warmth, swelling, pain, and the formation of invasive synovial tissue known as pannus, which contributes to cartilage and bone degradation. Pan-immune-inflammation value (PIV), a marker derived from complete blood count parameters, has shown promise in predicting prognosis in various cancer types and pediatric conditions associated with immune abnormalities. This study aims to explore the relationship between RA, characterized by chronic inflammation and immune system involvement, and PIV, potentially shedding light on novel insights into RA's clinical implications. Methods One hundred four participants, including 64 RA patients (both newly diagnosed and established cases) and 40 healthy controls, were included in the study. Exclusion criteria for RA patients included acute infection, cancer, diabetes, or chronic illness, while control participants were excluded for inflammatory disorders, active infection, diabetes, or malignancy. We assessed disease severity using Disease Activity Score 28 (DAS 28) and obtained complete blood count values, including neutrophil, lymphocyte, platelet, monocyte, and red cell distribution width. C-reactive peptide (CRP) and erythrocyte sedimentation rate were also added. Statistical analyses included correlation assessments, t-tests, Mann-Whitney U tests, and multivariate linear regression. A multiclass receiver operating characteristic analysis determined optimal PIV cut-off values for distinguishing control, remission, and active RA groups, with sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), accuracy, and odds ratios calculated. Results This study comprised a cohort of 104 participants, with a median age of 43.5±17.5. The Remission group was significantly younger than the Control group (p=0.006) but not compared to the Active RA group (p=0.393). CRP levels were significantly higher in the Active RA group (p<0.001). Neutrophil counts were highest in the Active RA group (p<0.001), as were monocyte counts. Lymphocyte counts were significantly lower in the Active RA group (p<0.001). There were no significant differences in sedimentation rate, hemoglobin, platelet count, and mean platelet volume. PIV was significantly elevated in the Active RA group (p<0.001) and higher in the Remission group than in the Control group (p=0.001). A PIV value of 353.48 exhibited 71.4% sensitivity, 86.2% specificity, 86.2% PPV, 71.4% NPV, and 78.13% test accuracy for distinguishing active rheumatoid arthritis (p<0.001). A PIV value exceeding 353.48 substantially increased the likelihood of a patient belonging to the active rheumatoid arthritis group, with a 14.62-fold higher probability. Furthermore, the study explored the relationship between clinical and laboratory variables and disease activity in RA patients, finding significant differences in PIV among DAS groups (p=0.025). Conclusions The PIV offers a notable advantage as its constituent parameters are routinely assessed in rheumatoid arthritis and involve cost-effective and straightforward tests. We demonstrated that PIV serves as a valuable marker for distinguishing between remission and active RA when compared to healthy individuals. Additionally, it proved to be an effective tool for assessing disease activity in patients with active rheumatoid arthritis.

Engineering approaches to investigate the roles of lymphatics vessels in rheumatoid arthritis

Rheumatoid arthritis (RA) is one of the most common chronic inflammatory joint disorders. While our understanding of the autoimmune processes that lead to synovial degradation has improved, a majority of patients are still resistant to current treatments and require new therapeutics. An understudied and promising area for therapy involves the roles of lymphatic vessels (LVs) in RA progression, which has been observed to have a significant effect on mediating chronic inflammation. RA disease progression has been shown to correlate with dramatic changes in LV structure and interstitial fluid drainage, manifesting in the retention of distinct immune cell phenotypes within the synovium. Advances in dynamic imaging technologies have demonstrated that LVs in RA undergo an initial expansion phase of increased LVs and abnormal contractions followed by a collapsed phase of reduced lymphatic function and immune cell clearance in vivo. However, current animal models of RA fail to decouple biological and biophysical factors that might be responsible for this lymphatic dysfunction in RA, and a few attempted in vitro models of the synovium in RA have not yet included the contributions from the LVs. Various methods of replicating LVs in vitro have been developed to study lymphatic biology, but these have yet not been integrated into the RA context. This review discusses the roles of LVs in RA and the current engineering approaches to improve our understanding of lymphatic pathophysiology in RA.

Emerging proteoglycans and proteoglycan-targeted therapies in rheumatoid arthritis

Rheumatoid arthritis (RA) is a common auto-immune disease-causing inflammation of the joints and damage of the cartilage and bone. The pathogenesis of RA is characterized in many patients by the presence of antibodies against citrullinated proteins. In the joints, proteoglycans are key structural elements of extracellular matrix in the articular cartilage and synovium and are secreted as lubricants in the synovial fluid. Alterations of proteoglycans contribute to mechanism of disease in RA. Proteoglycans such as aggrecan can be citrullinated and become potential targets of the rheumatoid auto-immune response. Proteoglycans are also up-regulated in RA joints and/or undergo alterations of their regulatory functions over cytokines and chemokines, which promotes inflammation and bone damage. Recent studies have aimed to not only clarify these mechanisms but also develop novel proteoglycan-modulating therapeutics. These include agents altering the function and signaling of proteoglycans as well as tolerizing agents based on citrullinated aggrecan. This mini-review summarizes the most recent findings regarding the dysregulation of proteoglycans that contributes to RA pathogenesis and the potential for proteoglycan-modulating agents to improve RA therapy.

Biomaterial Integration in the Joint: Pathological Considerations, Immunomodulation, and the Extracellular Matrix

Defects of articular joints are becoming an increasing societal burden due to a persistent increase in obesity and aging. For some patients suffering from cartilage erosion, joint replacement is the final option to regain proper motion and limit pain. Extensive research has been undertaken to identify novel strategies enabling earlier intervention to promote regeneration and cartilage healing. With the introduction of decellularized extracellular matrix (dECM), researchers have tapped into the potential for increased tissue regeneration by designing biomaterials with inherent biochemical and immunomodulatory signals. Compared to conventional and synthetic materials, dECM-based materials invoke a reduced foreign body response. It is therefore highly beneficial to understand the interplay of how these native tissue-based materials initiate a favorable remodeling process by the immune system. Yet, such an understanding also demands increasing considerations of the pathological environment and remodeling processes, especially for materials designed for early disease intervention. This knowledge would avoid rejection and help predict complications in conditions with inflammatory components such as arthritides. This review outlines general issues facing biomaterial integration and emphasizes the importance of tissue-derived macromolecular components in regulating essential homeostatic, immunological, and pathological processes to increase biomaterial integration for patients suffering from joint degenerative diseases. This article is protected by copyright. All rights reserved.

The Role of Gamma Delta T Cells in Autoimmune Rheumatic Diseases

Autoimmune rheumatic diseases (ARDs), affecting ~1-1.5% of all humans, are associated with considerable life long morbidity and early mortality. Early studies in the 1990s showed numerical changes of the recently discovered γδ T cells in the peripheral blood and in affected tissues of patients with a variety of ARDs, kindling interest in their role in the immuno-pathogenesis of these chronic inflammatory conditions. Indeed, later studies applied rapid developments in the understanding of γδ T cell biology, including antigens recognized by γδ T cells, their developmental programs, states of activation, and cytokine production profiles, to analyze their contribution to the pathological immune response in these disorders. Here we review the published studies addressing the role of γδ T in the major autoimmune rheumatic diseases, including rheumatoid arthritis, juvenile idiopathic arthritis, ankylosing spondylitis, systemic lupus erythematosus and scleroderma, and animal models thereof. Due to their unique properties spanning adaptive and innate immune functions, the ever deeper understanding of this unique T cell population is shedding new light on the pathogenesis of, while potentially enabling new therapeutic approaches to, these diseases.

Antigen Presentation, Autoantigens, and Immune Regulation in Multiple Sclerosis and Other Autoimmune Diseases

Antigen presentation is in the center of the immune system, both in host defense against pathogens, but also when the system is unbalanced and autoimmune diseases like multiple sclerosis (MS) develop. It is not just by chance that a major histocompatibility complex gene is the major genetic susceptibility locus in MS; a feature that MS shares with other autoimmune diseases. The exact etiology of the disease, however, has not been fully understood yet. T cells are regarded as the major players in the disease, but most probably a complex interplay of altered central and peripheral tolerance mechanisms, T-cell and B-cell functions, characteristics of putative autoantigens, and a possible interference of environmental factors like microorganisms are at work. In this review, new data on all these different aspects of antigen presentation and their role in MS will be discussed, probable autoantigens will be summarized, and comparisons to other autoimmune diseases will be drawn.

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.

Biologic-free remission of established rheumatoid arthritis after discontinuation of abatacept: a prospective, multicentre, observational study in Japan

Objective. The aim of this study was to determine whether biologic-free remission of RA is possible with discontinuation of abatacept.

Methods. Japanese RA patients in 28-joint DAS with CRP (DAS28-CRP) remission (<2.3) after >2 years of abatacept treatment in a phase II study and its long-term extension entered this 52 week, multicentre, non-blinded, prospective, observational study. At enrolment, the patients were offered the option to continue abatacept or not. The primary endpoint was the proportion of patients who remained biologic-free at 52 weeks after discontinuation. Clinical, functional and structural outcomes were compared between those who continued and those who discontinued abatacept.

Results. Of 51 patients enrolled, 34 discontinued and 17 continued abatacept treatment. After 52 weeks, 22 of the 34 patients (64.7%) remained biologic-free. Compared with the continuation group, the discontinuation group had a similar remission rate (41.2% vs 64.7%, P = 0.144) although they had a significantly higher mean DAS28-CRP score at week 52 (2.9 vs 2.0, P = 0.012). The two groups were also similar with regard to mean HAQ Disability Index (HAQ-DI) score (0.6 for both, P = 0.920), mean change in total Sharp score (ΔTSS; 0.80 vs 0.32, P = 0.374) and proportion of patients in radiographic remission (ΔTSS ≤ 0.5) at the endpoint (64.3% vs 70.6%, P = 0.752). Those attaining DAS28-CRP < 2.3 or < 2.7 without abatacept at the endpoint had significantly lower HAQ-DI score and/or CRP at enrolment. Non-serious adverse events occurred in three patients who continued or resumed abatacept.

Conclusion. Biologic-free remission of RA is possible in some patients after attaining clinical remission with abatacept. Lower baseline HAQ-DI or CRP may predict maintenance of remission or low disease activity after discontinuation of abatacept.

Trial registration: UMIN Clinical Trials Registry, http://www.umin.ac.jp/ctr/ (UMIN000004137).

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.

Cytokine-induced human IFN-gamma-secreting effector-memory Th cells in chronic autoimmune inflammation

T-helper (Th) cells activated by cytokines in the absence of T-cell receptor ligation are suspected to participate in inflammatory processes by production of interferon-gamma (IFN-gamma). Still, the relevance of such a mechanism has not been addressed in humans. Here we demonstrate that a subset of human effector-memory Th cells expressing functional interleukin-12R (IL-12R), IL-18Ralpha, and CCR5 ex vivo can be induced to secrete IFN-gamma by cytokines signaling via the IL-2R common gamma-chain in combination with IL-12 and IL-18. Cytokine-driven IFN-gamma production depends on JAK3- and p38 mitogen-activated kinase signals and is sensitive to suppression by CD25(++) regulatory T cells. Contrary to IFN-gamma(+) Th cells induced upon antigen-specific stimulation, their cytokine-activated counterparts characteristically lack expression of costimulator 4-1BB (CD137). Strikingly, the majority of Th cells infiltrating inflamed joints of rheumatoid arthritis patients is equipped with receptors prerequisite for cytokine-induced IFN-gamma secretion. Among these cells, we detected a substantial fraction that secretes IFN-gamma directly ex vivo but lacks 4-1BB expression, indicating that cytokine-induced IFN-gamma(+) Th cells operate in autoimmune inflammation. Our data provide a rationale for how human effector-memory Thcells can participate in perpetuating inflammatory processes in autoimmunity even in the absence of T-cell receptor ligation.

Morphologic and Volumetric Studies of the Meibomian Glands in Elderly Human Eyelids

PURPOSE

To study the microscopic structure of postmortem human Meibomian glands (MGs) in the elderly.

METHODS

Human MG samples from left lower eyelids were obtained at autopsy from 5 men and 4 women with a mean age of 63.1 +/- 7.67 years. The tissues were fixed and embedded in paraffin. Serial transverse sections 5 mum thick were stained with hematoxylin and eosin (H&E), van Gieson, and Masson blue stains. Computer-assisted 3-dimensional reconstructions of MGs were performed, and morphologic and volumetric data were analyzed.

RESULTS

The average length of human MGs in the nasal, central, and temporal areas was 1.551 +/- 0.43, 1.654 +/- 0.47, and 1.594 +/- 0.57 mm, respectively. The average surface area of the glands in the nasal, central, and temporal areas was 0.029 +/- 0.03, 0.033 +/- 0.01, and 0.056 +/- 0.03 mm, respectively. The average volume of glands in the nasal, central, and temporal areas was 0.054 +/- 00.4, 0.056 +/- 0.03, and 0.053 +/- 0.03 mm, respectively. A circular, floral arrangement of acini, surrounding the terminal duct just deep to the skin, is probably responsible for the circular arrangement seen clinically around each healthy orifice. We confirmed that most glands are embedded within a cylindrical, connective tissue matrix.

CONCLUSIONS

We report the dimensions of normal Meibomian acini in an older population. Some structural features observed may explain normal physiologic landmarks or contribute to glandular pathophysiology.

An immunohistochemical study of the triangular fibrocartilage complex of the wrist: regional variations in cartilage phenotype

The triangular fibrocartilage complex (TFCC) transmits load from the wrist to the ulna and stabilizes the distal radioulnar joint. Damage to it is a major cause of wrist pain. Although its basic structure is well established, little is known of its molecular composition. We have analysed the immunohistochemical labelling pattern of the extracellular matrix of the articular disc and the meniscal homologue of the TFCC in nine elderly individuals (age range 69-96 years), using a panel of monoclonal antibodies directed against collagens, glycosaminoglycans, proteoglycans and cartilage oligomeric matrix protein (COMP). Although many of the molecules (types I, III and VI collagen, chondroitin 4 sulphate, dermatan sulphate and keratan sulphate, the oversulphated epitope of chondroitin 6 sulphate, versican and COMP) were found in all parts of the TFCC, aggrecan, link protein and type II collagen were restricted to the articular disc and to entheses. They were thus not a feature of the meniscal homologue. The shift in tissue phenotype within the TFCC, from a fibrocartilaginous articular disc to a more fibrous meniscal homologue, correlates with biomechanical data suggesting that the radial region is stiff and subject to considerable stress concentration. The presence of aggrecan, link protein and type II collagen in the articular disc could explain why the TFCC is destroyed in rheumatoid arthritis, given that it has been suggested that autoimmunity to these antigens results in the destruction of articular cartilage. The differential distribution of aggrecan within the TFCC is likely to be reflected by regional differences in water content and mobility on the radial and ulnar side. This needs to be taken into account in the design of improved MRI protocols for visualizing this ulnocarpal complex of the wrist.

The structure of the coracoacromial ligament: fibrocartilage differentiation does not necessarily mean pathology

The coracoacromial ligament forms part of the coracoacromial arch and is implicated in impingement syndrome and acromial spur formation. Here, we describe its structure and the composition of its extracellular matrix. Ligaments were obtained from 15 cadavers, nine from older people (average age 74.7 years) and six from younger individuals (average age 24.2 years). Cryosections of methanol-fixed tissue were cut and sections were immunolabelled with monoclonal antibodies against collagens, glycosaminoglycans, proteoglycans, matrix proteins and neurofilament proteins. Both ligament entheses were highly fibrocartilaginous and immunolabelled strongly for type II collagen, aggrecan and link protein. The area of labelling was more extensive in older people. However, fibrocartilage also characterized the ligament midsubstance, particularly with increased age. Signs of fibrocartilage degeneration were more common in older people. Ligament fat (containing blood vessels and nerve fibers) was conspicuous in both age groups, especially between fiber bundles at the entheses. We conclude that fibrocartilage is a normal feature but becomes more pronounced with age. It is not necessarily pathological, for it simply indicates that the ligament is subject to compression and/or shear. Nevertheless, the prominence of fibrocartilage at the acromial enthesis may relate to the frequency with which enthesophytes develop.

Expression of extracellular matrix molecules typical of articular cartilage in the human scapholunate interosseous ligament

The scapholunate interosseous ligament (SLIL) connects the scaphoid and lunate bones and plays a crucial role in carpal kinematics. Its rupture leads to carpal instability and impairment of radiocarpal joint function. As the ligament is one of the first structures affected in rheumatoid arthritis, we conducted an immunohistochemical study of cadaveric tissue to determine whether it contains known autoantigens for rheumatoid arthritis. We immunolabelled the ligament from one hand in 12 cadavers with monoclonal antibodies directed against a wide range of extracellular matrix (ECM) molecules associated with both fibrous and cartilaginous tissues. The labelling profile has also enabled us to comment on how the molecular composition of the ligament relates to its mechanical function. All regions of the ligament labelled for types I, III and VI collagens, chondroitin 4 and 6 sulphates, keratan sulphate, dermatan sulphate, versican, tenascin and cartilage oligomeric matrix protein (COMP). However, both entheses labelled strongly for type II collagen, aggrecan and link protein and were distinctly fibrocartilaginous. In some regions, the ligament attached to bone via a region of hyaline cartilage that was continuous with articular cartilage. Labelling for cartilage molecules in the midsubstance was most evident dorsally. We conclude that the SLIL has an ECM which is typical of other highly fibrocartilaginous ligaments that experience both tensile load and shear. The presence of aggrecan, link protein, COMP and type II collagen could explain why the ligament may be a target for autoantigenic destruction in some forms of rheumatoid arthritis.

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."

An immunohistochemical study of the extracellular matrix of the tarsal plate in the upper eyelid in human beings

The superior tarsus is a plate of tissue that stiffens the upper eyelid, gives it support and determines its form. The purpose of the present study was to relate the composition of its extracellular matrix to its function and to report regional differences that may influence the activity of its Meibomian glands. Fourteen methanol-fixed specimens were cryosectioned for immunohistochemistry and labelled with a panel of monoclonal antibodies against a wide range of collagens, glycosaminoglycans and proteoglycans. Labelling was detected with avidin-biotin-peroxidase. A further six specimens were formalin-fixed for routine histology. The tarsal plate immunolabelled strongly for types I, III and VI collagen and for aggrecan, versican, tenascin, cartilage oligomeric matrix protein (COMP) together with a variety of glycosaminoglycans (notably chondroitin 6 sulphate). A region of strong labelling for aggrecan, dermatan sulphate and chondroitin 6 sulphate immediately surrounded the Meibomian glands. The site of labelling corresponded to a layer of acellular and amorphous matrix seen histologically that we have termed the 'territorial matrix'. The results suggested that the tarsal plate is a specialized connective tissue that is neither purely fibrous nor cartilaginous, yet has an aggrecan content that probably contributes to its stiffness. Its unique character highlights the challenge in choosing an ideal mechanical substitute. As patients with rheumatoid arthritis often have problems relating to tear film deficiency, the ability of aggrecan or COMP to act as autoantigens may be significant. An immune reaction directed against these molecules could alter tarsal gland function by interfering with the interaction between the glands and their territorial matrix.

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.

Role of soluble Fas ligand in autoimmune diseases

AIM: To investigate the role of soluble Fas ligand in autoimmune diseases.

METHODS: RT-PCR was performed to amplify sFasL cDNA from the total RNA extracted from activated human peripheral blood lymphocytes. DNA fragments were cloned into PCR vector. After sequenced, sFasL gene fragments were inserted into pQE-31 vector and expressed in E. Coli M15 respectively. Proteins were purified through affinity chromatography column with ligand of 6 × His tag and identified by SDS-PAGE and Western blot. Mice were immunized with sFasL protein and specific anti-serum was harvested 6 wk after immunization. Monoclonal anti-human FasL antibody was made from the immunized mice. Serum level of sFasL in different patients was detected using anti-FasL antibodies from the immunized mice.

RESULTS: The protein expressed was 24 ku by SDS-PAGE electrophrosis. The protein was specially bound to anti-human FasL antibody by Western blot analysis. The sFasL protein could induce Jurket cell apoptosis in vitro. The concentration of serum sFasL in patients with autoimmune diseases was higher than that in normal individuals. sFasL could reduce arthritis in collagen induced arthritis (CIA) mice model by subcutaneous injection.

CONCLUSION: sFasL may be involved in either induction of apoptosis or autoimmune diseases. Furthermore, sFasL may have potential application in treatment of autoimmune diseases.

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.

Direct Toll-like receptor 2 mediated co-stimulation of T cells in the mouse system as a basis for chronic inflammatory joint disease

The pathogenesis of chronic inflammatory joint diseases such as adult and juvenile rheumatoid arthritis and Lyme arthritis is still poorly understood. Central to the various hypotheses in this respect is the notable involvement of T and B cells. Here we develop the premise that the nominal antigen-independent, polyclonal activation of preactivated T cells via Toll-like receptor (TLR)-2 has a pivotal role in the initiation and perpetuation of pathogen-induced chronic inflammatory joint disease. We support this with the following evidence. Both naive and effector T cells express TLR-2. A prototypic lipoprotein, Lip-OspA, from the etiological agent of Lyme disease, namely Borrelia burgdorferi, but not its delipidated form or lipopolysaccharide, was able to provide direct antigen-nonspecific co-stimulatory signals to both antigen-sensitized naive T cells and cytotoxic T lymphocyte (CTL) lines via TLR-2. Lip-OspA induced the proliferation and interferon (IFN)-γ secretion of purified, anti-CD3-sensitized, naive T cells from C57BL/6 mice but not from TLR-2-deficient mice. Induction of proliferation and IFN-γ secretion of CTL lines by Lip-OspA was independent of T cell receptor (TCR) engagement but was considerably enhanced after suboptimal TCR activation and was inhibitable by monoclonal antibodies against TLR-2.

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.

Roles of B cells in rheumatoid arthritis

B lymphocytes play several critical roles in the pathogenesis of rheumatoid arthritis. They are the source of the rheumatoid factors and anticitrullinated protein antibodies, which contribute to immune complex formation and complement activation in the joints. B cells are also very efficient antigen-presenting cells, and can contribute to T cell activation through expression of costimulatory molecules. B cells both respond to and produce the chemokines and cytokines that promote leukocyte infiltration into the joints, formation of ectopic lymphoid structures, angiogenesis, and synovial hyperplasia. The success of B cell depletion therapy in rheumatoid arthritis may depend on disruption of all these diverse functions.

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.

Evolving concepts of rheumatoid arthritis

Rheumatoid arthritis is the most common inflammatory arthritis and is a major cause of disability. It existed in early Native American populations several thousand years ago but might not have appeared in Europe until the 17th century. Early theories on the pathogenesis of rheumatoid arthritis focused on autoantibodies and immune complexes. T-cell-mediated antigen-specific responses, T-cell-independent cytokine networks, and aggressive tumour-like behaviour of rheumatoid synovium have also been implicated. More recently, the contribution of autoantibodies has returned to the forefront. Based on the pathogenic mechanisms, specific therapeutic interventions can be designed to suppress synovial inflammation and joint destruction in rheumatoid arthritis.

HLA-DR1 (DRB1*0101) and DR4 (DRB1*0401) use the same anchor residues for binding an immunodominant peptide derived from human type II collagen

Rheumatoid arthritis is an autoimmune disease in which susceptibility is strongly associated with the expression of specific HLA-DR haplotypes, including DR1 (DRB1*0101) and DR4 (DRB1*0401). As transgenes, both of these class II molecules mediate susceptibility to an autoimmune arthritis induced by immunization with human type II collagen (hCII). The dominant T cell response of both the DR1 and DR4 transgenic mice to hCII is focused on the same determinant core, CII(263-270). Peptide binding studies revealed that the affinity of DR1 and DR4 for CII(263-270) was at least 10 times less than that of the model Ag HA(307-319), and that the affinity of DR4 for the CII peptide is 3-fold less than that of DR1. As predicted based on the crystal structures, the majority of the CII-peptide binding affinity for DR1 and DR4 is controlled by the Phe(263); however, unexpectedly the adjacent Lys(264) also contributed significantly to the binding affinity of the peptide. Only these two CII amino acids were found to provide binding anchors. Amino acid substitutions at the remaining positions had either no effect or significantly increased the affinity of the hCII peptide. Affinity-enhancing substitutions frequently involved replacement of a negative charge, or Gly or Pro, hallmark amino acids of CII structure. These data indicate that DR1 and DR4 bind this CII peptide in a nearly identical manner and that the primary structure of CII may dictate a different binding motif for DR1 and DR4 than has been described for other peptides that bind to these alleles.