Breaking the rules: the unconventional recognition of HLA-B27 by CD4+ T lymphocytes as an insight into the pathogenesis of the spondyloarthropathies

Despite extensive research, it remains unclear why a small proportion of HLA- B27(+) individuals develop spondyloarthropathies (SpA). Because the function of HLA-B27, as a major histocompatibility complex (MHC) class I molecule, is peptide presentation to CD8(+) T cells, research has concentrated on the role of HLA-B27 as a restriction element for CD8(+) cytotoxic T lymphocytes in pathogenesis. However, findings in the B27-transgenic animal models, together with the identification of unusual processing and presentation features of HLA-B27, have raised alternative hypotheses for the pathogenic role of HLA-B27. One such hypothesis is that HLA-B27 can be recognized by CD4(+) T lymphocytes. Here we report the identification of such unusual cells, which break the conventional rules of MHC restriction, and propose a model for the role of such CD4(+) T cells in SpA.

Sporadic enteric reactive arthritis and undifferentiated spondyloarthropathy: evidence for involvement of Salmonella typhimurium

OBJECTIVE

To define the candidate bacterial trigger and cytokine profile of synovial fluid mononuclear cells (SFMC) in patients with sporadic enteric reactive arthritis (ReA) and undifferentiated spondyloarthropathy (uSpA).

METHODS

The study group comprised 10 patients with ReA and 23 with uSpA who fulfilled European Spondylarthropathy Study Group criteria. Ten patients with rheumatoid arthritis (RA) served as disease controls. IgG, IgA, and IgM antibodies to Shigella flexneri, Salmonella typhimurium, and Yersinia enterocolitica were measured in sera and SF by ELISA. Peripheral blood mononuclear cell (PBMC) and SFMC proliferation assays were done in the presence or absence of crude bacterial lysates. Bacterial antigens and DNA in synovial cells were detected by indirect immunofluorescence and polymerase chain reaction, respectively. Interferon-g (IFN-g), interleukin 10 (IL-10), and IL-4 were measured in 18 h SFMC culture supernatants in presence of bacterial lysate.

RESULTS

Antibodies to S. typhimurium were significantly elevated in the sera of 8 of 25 patients compared to controls (0/22; p < 0.05). The ratio of SF:serum anti-salmonella IgA was significantly higher in patients compared to controls (p < 0.0002). The ratio of SF:serum IgA antibodies to S. typhimurium was higher than that for S. flexneri (p < 0.007) and Y. enterocolitica (p < 0.05). Out of 25 patients, 8, 2, and none had elevated antigen-specific SFMC proliferation response to S. typhimurium, S. flexneri, and Y. enterocolitica, respectively, whereas no control had elevated response. Salmonella antigens were detected in the synovial cells of 4 out of 14 patients. There was significantly higher IFN-g production from SFMC of patients who had increased proliferative response to Salmonella (LTT+) in the presence of Salmonella antigens compared to antigen control. The mean +/- SD of the ratio of IFN-g:IL-10 in the LTT+ patients was significantly lower compared to controls. Conclusion. S. typhimurium is probably one of the triggers for enteric ReA and uSpA in our cohort of patients, and the immune response is characterized by increased production of both IL-10 and IFN-g.

The role of infection in the pathogenesis of spondyloarthropathies with special reference to human leukocyte antigen-B27

Spondyloarthropathies consist of many inflammatory diseases that are closely associated with human leukocyte antigen (HLA)-B27. One of these diseases is reactive arthritis (ReA), which is a joint inflammation that occurs after infections that are caused by certain gram-negative bacteria. The importance of these infections as causative agents of ReA has been clearly established. It is not clear, however, whether these infections contribute to the development of other forms of spondyloarthropathies. The exact mechanism by which HLA-B27 influences disease susceptibility in spondyloarthropathies remains to be determined. The role of HLA-B27 as an antigen-presenting molecule is certainly important in the pathogenesis of these diseases; however, recent data indicate that this molecule may exhibit other functions unrelated to antigen presentation, which may be important in the pathogenesis of ReA. In this paper, the authors summarize the current knowledge of the role of infection in the spondyloarthropathies.

Gut inflammation and spondyloarthropathies

Spondyloarthropathies (SpA) are a group of related disorders with common clinical and genetic characteristics. The prototype disease in this group is ankylosing spondylitis; other entities include reactive arthritis, psoriatic arthritis, and arthritis in patients with inflammatory bowel disease. Over recent years, there has been a special interest in the relation between spondylitis/synovitis and gut inflammation in patients with SpA. Two thirds of patients with undifferentiated SpA show histologic signs of gut inflammation, and a fraction of these patients go on to develop clinically overt Crohn's disease. In this review, the authors will focus on 1) the growing evidence that has been provided that gut inflammation in SpA is immunologically related to Crohn's disease, based on the molecular characterization of the inflammation (lymphocyte homing markers and ligands, T cell cytokines, macrophage markers, and serology); and 2) on the therapeutic implications resulting from this concept. The recent introduction and positioning of anti-tumor necrosis factor-alpha therapy in patients with ankylosing spondylitis and other types of SpA is, in large part, based on this concept.

Increase in lymphoid follicles and leukocyte adhesion molecules emphasizes a role for the gut in spondyloarthropathy pathogenesis

The aim of this study was to investigate the expression of leukocyte adhesion molecules and the number of lymphoid follicles in gut mucosa of patients with spondyloarthropathy (SpA) in comparison with controls, in search for early immune alterations in the development of SpA-related gut inflammation. Histological evaluation and immunohistochemistry were performed on the ileum and colon of 14 SpA patients without macroscopic or microscopic gut inflammation and those of 21 controls. Lymphoid follicles were counted and immunohistochemical staining for leukocyte adhesion molecules, lymphocyte subtypes, macrophages, and plasma cells was scored semi-quantitatively. The number of lymphoid follicles was increased in both the ileum (p < 0.01) and the colon (p < 0.01) of SpA patients. SpA ileum showed an increase in leukocytes expressing CD11c (p < 0.01), whereas CD11a(+) (p < 0.02) and VCAM-1(+) cells (p < 0.05) were increased in SpA colon. Macrophages, characterized by the expression of CD68, were more numerous in colonic mucosa from SpA patients (p < 0.05). The amount of lymphoid follicles and lamina propria mononuclear cells expressing CD11a, CD11c, and VCAM-1 was increased in non-inflamed gut mucosa from SpA patients. These findings might point to increased antigen handling and presentation and augmented maturation of naïve T cells towards memory T cells in the SpA gut, which supports the concept that the gut is involved in the pathogenesis of SpA.

Advances in the understanding of entheseal inflammation

The importance of enthesitis in the pathogenesis of spondyloarthropathy (SpA) is now well recognized. Several entheses comprise more than simply the insertion site, and they are part of a complex biomechanical organ to resist shear and compression. It is also evident that tendons that wrap around bony pulleys form an integral part of joint capsules, and share, along with imaging abnormalities and histopathologic changes, common anatomic, histologic, and biomechanical features with classically defined entheses. Researchers have called these regions of tendons functional entheses. Furthermore, certain synovial joints have much in common with classic entheses--most notably those lined with fibrocartilage rather than hyaline cartilage. These observations provide a unifying anatomic basis for SpA. Enthesitis is associated with underlying osteitis, whether mechanically induced or inflammatory-related--with the extent of osteitis determined by the human leukocyte antigen-B27 gene. Until recently, there was no effective therapy for resistant enthesitis, but it is now evident that enthesitis responds well to biologic blockade with anti-tumor necrosis factor. Unraveling the pathogenic basis of enthesitis will have important implications for understanding and defining therapies in SpA.

Thoughts concerning the early diagnosis of ankylosing spondylitis and related diseases

The diagnosis of ankylosing spondylitis is mainly based on a radiograph of the sacroiliac joints. Thus, this is the standard imaging test. However, in the early phase of disease, conventional radiographs are often too insensitive to show sacroiliitis. In this clinical situation, HLA B27 testing and new imaging modalities such as magnetic resonance imaging may be helpful. Early forms of AS can be initially classified as undifferentiated spondyloarthritis. All subsets of spondyloarthritides may evolve later into AS. Since AS in association with psoriasis and chronic inflammatory bowel diseases is often HLA B27-negative, this test is of limited value under these circumstances. The usefulness of testing for HLA B27 and its subtypes differs among ethnic and racial groups. The value of this test for diagnosis depends on the individual pre-test probability in each setting.

Juvenile onset spondyloarthropathies: therapeutic aspects

Juvenile onset spondyloarthropathy (SpA) is a term that refers to a group of human leucocyte antigen (HLA)-B27 associated inflammatory disorders affecting children under the age of 16 years, producing a continuum of clinical symptoms through adulthood. This disease is characterised by enthesopathy and arthropathy affecting the joints of the lower extremities and seronegativity for IgM rheumatoid factor and antinuclear antibodies. Children usually present with undifferentiated SpA and progress to differentiated forms over time. Except for the prevalence of some clinical features at onset, the pathogenic and clinical aspects of juvenile onset SpAs resemble those of the adult disease. Thus application of the same or similar therapeutic measures for both juvenile and adult onset SpAs seems logical. Current treatments for juvenile onset SpA provide symptomatic improvement, but do not alter disease progression. The increased expression of tumour necrosis factor alpha (TNFalpha) in synovial tissue of patients with adult and juvenile onset SpA and its correlation with infiltration of inflammatory mediators into the synovia suggest a significant pathogenic role of this cytokine. Clinical trials of anti-TNFalpha antibody (infliximab) therapy in patients with adult onset SpA have demonstrated significant clinical improvement in inflammatory pain, function, disease activity, and quality of life in correlation with histological and immunohistochemical evidence of modulation of synovial inflammatory processes. These promising findings suggest that anti-TNFalpha therapy may confer similar benefits in patients with juvenile onset SpA.

Serum levels of IL-1 beta, TNF-alpha, IL-8, and acute phase proteins in seronegative spondyloarthropathies

OBJECTIVES

Some immunological abnormalities have been described in seronegative spondyloarthropathies (SpA). The aim of this study is to determine the serum levels of IL-1beta, TNF-alpha and IL-8, which are proinflammatory cytokines in active and inactive patients with SpA, to compare the results with those of controls and to investigate a relationship with clinical activity and acute phase proteins.

METHODS

Forty-two patients (34 males and eight females) and 22 healthy controls (17 M and 5 F) were included in the study. All patients fulfilled Amor criteria for the classification of SpA. Among patients 23 had active and 19 had inactive disease. IL-1beta, TNF-alpha and IL-8 were determined by enzyme-linked immunosorbent assay ( ELISA), acute phase proteins were measured by nephelometric assay.

RESULTS

There was no statistically significant difference between mean IL-1beta levels of patient groups and controls. Serum mean TNF-a levels in active and inactive patients were significantly increased as compared to that in the controls (P < 0.05, P < 0.05, respectively). Serum mean IL-8 levels in active patients was significantly increased as compared to that in the controls and in inactive patients (P < 0.01, P < 0.01, respectively). High serum IL-8 levels correlated well with C-reactive protein and haptoglobulin, but there was no correlation between IL-1beta or TNF-alpha levels and acute phase proteins such as C-reactive protein, alpha-1 acid glycoprotein, alpha-1 antitrypsin and haptoglobulin.

CONCLUSIONS

These results suggest that serum IL-8 may reflect clinical activity of the disease and may be helpful for monitoring patients with SpA.

Ulcerative colitis, seronegative spondyloarthropathies and allergic diseases: the search for a link

BACKGROUND

Allergic diseases and seronegative spondyloarthropathies are frequently observed in ulcerative colitis (UC). In this report we have investigated possible relationships between IgE-mediated allergic disease (AD), allergic contact dermatitis (ACD) and seronegative spondyloarthropathy (SpA) in UC patients at different grades and extensions of mucosa inflammation.

METHODS

Forty-five UC consecutive outpatients were graded according to clinical, endoscopic and histologic activity scores. SpA was diagnosed according to the European Spondyloarthropathy Study Group criteria. AD was detected by skin prick tests and confirmed by specific provocation tests, while ACD was diagnosed using the European standard series of patch tests. Thirty-seven patients' spouses or partners served as controls.

RESULTS

Fourteen patients and 1 control subject showed SpA (P = 0.001). Diagnosis of rhinitis, conjunctivitis or asthma was made in 19 patients and in 5 controls (P = 0.004), while ACD was found in 10 and in 4 (P = 0.17), respectively. In UC, AD coexisted with SpA in 2 cases (P = 0.01), AD with ACD in 1 case (P = 0.03) and ACD with SpA in 5 (P = 0.24).

CONCLUSIONS

Notwithstanding the high frequency of AD and SpA found in UC, the concurrence of AD with SpA or ACD is an unusual finding, while SpA and ACD may coexist. These data suggest that, in UC, atopy and seronegative arthritis, as well as atopy and delayed-type allergy, are strongly polarized conditions tending to mutual exclusion. In UC, the presence of AD without SpA or ACD, and of SpA or ACD without AD may indicate subgroups of patients in which T-helper-2 cell or T-helper-1 cell responses predominate.

[Intestines and joints: an entity?]

The intestinal inflammation and the inflammatory arthropathy in Crohn's disease and in spondyloarthropathy are tightly linked. Both forms of inflammation occur in clinical and subclinical forms in both diseases: 60% of patients with Crohn's disease have clinical and/or radiological signs of articular involvement--65% of patients belonging to the concept of spondyloarthropathy have endoscopic and/or histological signs of gut inflammation. The macrophages and the lymphocytes play a role either by the transport of bacterial antigens by macrophages from the gut to the synovium, either by the recirculation of activated lymphocytes attracted to the tissue by adhesion molecules. In both diseases, TNF alpha play a central role resulting in a rapid and spectacular improvement of the intestinal and articular inflammation by the administration of a monoclonal chimeric antibody directed against this cytokine (Infliximab). This clinical effect is associated or secondary to a restoration of the production of proinflammatory cytokines. According the importance of genetic factors in the etiopathogenesis of both diseases (mutation in the NOD2 gene for Crohn--HLA-B27 phenotype for spondyloarthropathy) future studies are necessary to find a common alteration explaining the link between gut and joint. This knowledge can help in the elucidation of the origin of both diseases.

High variability of HLA-B27 alleles in ankylosing spondylitis and related spondyloarthropathies in the population of northern Spain

The distribution of B27 alleles (B*2701-23) was characterized by PCR-SSP in ankylosing spondylitis and related spondyloarthropathies (SpA) in a sample of B27 positive patients from northern Spain. Six B27 alleles were identified: B*2705,02,03,07,08 and B*2713. B*2705 and 02 were the most common alleles in the SpA studied: ankylosing spondylitis (AS) (n = 89), reactive arthritis (ReA) (n = 11), psoriatic arthritis (PsA) (n = 29), and inflammatory bowel disease (IBD) (n = 21). B*2707 and B*2708 were found in PsA patients and B*2703 in one patient with IBD. B*2713 was identified in a healthy control family. B*2713 has not been reported to be represented in either ethnic group. Thus, this population shows higher levels of B27 diversity than other Caucasian groups.

Innate immunity in host-microbial interactions: beyond B27 in the spondyloarthropathies

The spondyloarthropathies are diseases influenced by genetic predisposition and, to a varying extent, infectious triggers. A causal role for bacterial infections is most clear for reactive arthritis. Recent insights into arthritogenic components of bacteria may set the stage for a better understanding of disease pathogenesis, the role of heat shock proteins in antigen processing and immune activation, and the adjuvant effect of CpG-DNA. Recent developments in the area of innate immunity broaden current concepts of genetically defined factors in host-pathogen interactions. In particular, the biology of toll-like receptors as important elements in the innate immune response to pathogens is being defined. These factors in innate immunity may have important implications for sequelae of infections, such as reactive arthritis.

Immune linkages between inflammatory bowel disease and spondyloarthropathies

Gut involvement is a prominent feature of spondyloarthropathy (SpA). Analysis of immune alterations of the gut in SpA have shown two distinct aspects. On the one hand, gut inflammation in SpA seems closely related with gut inflammation seen in Crohn disease. On the other hand, gut inflammation in SpA is associated with peripheral joint inflammation. Recent studies have provided new insights into this gut-synovium axis. First, there is little new evidence to support the concept of viable microbial pathogens recirculating to the joint. In contrast, it seems likely that both bacterial antigens and reactive T cell clones home to the joint, and that adhesion molecules such as the beta7 integrins and VAP1 play an important role in this process. Second, there is increasing evidence that the different disease localizations in SpA are characterized by alterations of the innate immune system, which contribute to a breakdown of the immune tolerance and the creation of an inflammation-prone environment. Mediators of the innate immune system, such as scavenger receptors, interleukin-10 (IL-10), and tumor necrosis factor alpha (TNF-alpha), may therefore be interesting targets for therapeutic intervention, as illustrated by the effect of TNF-alpha blockade in SpA.

HLA-B27 and pathogenesis of spondyloarthropathies

Although the influence of HLA-B27 on the development of spondyloarthropathies is undisputed, its role in pathogenesis remains unclear. New ideas have focused on abnormal characteristics of HLA-B27 resulting from aberrant folding, disulfide bond formation, or both, rather than a predilection for selecting arthritogenic peptides. This reflects, in part, unanswered questions about whether immunologic recognition of HLA-B27 is required for disease. Recent studies suggest that CD4+ T cells, immunomodulatory killer cell Ig receptors, and Ig-like transcript receptors may recognize aberrant forms of HLA-B27. Other reports suggest that HLA-B27 expression can alter cytokine production from monocytes and T cells-effects that appear unrelated to antigen presentation. Novel bioinformatics approaches have led to the identification of HLA-B27-restricted pathogen-derived peptides and may prove useful in determining whether HLA-B27 presents arthritogenic peptides. Elucidating the role of HLA-B27 in the pathogenesis of these conditions will require an integration of information from animal models, genome-wide screens for susceptibility alleles, and translational studies using human samples.

Macrophages expressing the scavenger receptor CD163: a link between immune alterations of the gut and synovial inflammation in spondyloarthropathy

The objective of this study was to investigate CD163+ macrophages in the synovial membrane of patients with spondyloarthropathy (SpA). Immunohistochemistry was performed on synovium of 17 SpA and 18 rheumatoid arthritis (RA) patients, on colonic biopsies of 16 SpA patients and ten healthy controls, and on paired synovial biopsies of eight SpA patients, before and after anti-TNFalpha therapy. Phenotype and cytokine production were analysed by flow cytometry. CD163+ macrophages were increased in the synovial lining and sublining in SpA versus RA, as well as in colonic lamina propria in SpA versus controls. The number of CD163+ macrophages in the synovial sublining correlated with C-reactive protein levels and erythrocyte sedimentation rate. Paralleling the increase of CD163, HLA-DR was increased in the synovial lining and sublining of SpA. In contrast, the co-stimulatory molecules CD80 and CD86 and the dendritic cell markers CD1a and CD83 were scarce in SpA synovium. Flow cytometry indicated that CD163+ macrophages expressed high levels of HLA-DR and could produce in vitro tumour necrosis factor alpha (TNFalpha) but not interleukin-10 (IL-10). Finally, anti-TNFalpha therapy in vivo induced a decrease of CD163+ macrophages in the synovial lining and sublining. In conclusion, macrophages expressing the scavenger receptor CD163 are increased in synovium and in colonic mucosa in SpA, highlighting the relationship between joint and gut in this disease. The correlation with inflammatory parameters, the expression of HLA-DR, the production of TNFalpha but not IL-10, and the reduction by anti-TNFalpha therapy support a role for CD163+ macrophages in the synovial inflammation in SpA.

Repeated infusions of infliximab, a chimeric anti-TNFalpha monoclonal antibody, in patients with active spondyloarthropathy: one year follow up

BACKGROUND

In a pilot study, the anti-tumour necrosis factor alpha monoclonal antibody, infliximab, induced a rapid and significant improvement in global, peripheral, and axial disease manifestations of patients with active spondyloarthropathy.

OBJECTIVE

To determine whether repeated infusions of infliximab would effectively and safely maintain the observed effect.

METHODS

Safety and efficacy of a maintenance regimen (5 mg/kg infliximab every 14 weeks) was evaluated using the measurements reported in the pilot study. Of the 21 patients, 19 completed the one year follow up for efficacy; two patients changed to another dosing regimen after week 12 owing to partial lack of efficacy. However, they are still being followed up for safety analysis.

RESULTS

After each re-treatment a sustained significant decrease of all disease manifestations was observed. Before re-treatment, symptoms recurred in 3/19 (16%) at week 20, in 13/19 (68%) at week 34, and in 15/19 (79%) at week 48. No withdrawals due to adverse events occurred. Twelve minor infectious episodes were observed. Twelve patients (57%) developed antinuclear antibodies; in four of them (19%) anti-dsDNA antibodies were detected. However, no lupus-like symptoms occurred.

CONCLUSION

In this open study of infliximab in patients with active spondyloarthropathy, the significant improvement of all disease manifestations was maintained over a one year follow up period without major adverse events. Although recurrence of symptoms was noted in a rising number of patients before each re-treatment, no loss of efficacy was observed after re-treatment.

Successful short term treatment of severe undifferentiated spondyloarthropathy with the anti-tumor necrosis factor-alpha monoclonal antibody infliximab

OBJECTIVE

Tumor necrosis factor-alpha (TNF-alpha) has been detected in sacroiliac joints of patients with spondyloarthropathies (SpA). Anti-TNF-a therapy has been efficacious in patients with active ankylosing spondylitis (AS) and psoriatic arthritis. Similar to these SpA subtypes, therapeutic options in undifferentiated SpA (uSpA) are also limited. We tested the efficacy of the monoclonal anti-TNF-alpha antibody infliximab in patients with active and severe uSpA in an open observation trial.

METHODS

Six patients with uSpA were treated with 3 infusions of infliximab in a dosage of 3 (n = 3) or 5 mg/kg (n = 3) at Weeks 0, 2, and 6. The total observational period was 12 weeks. The Bath AS Disease Activity Index (BASDAI), the Functional Index (BASFI), pain on a visual analog scale, the Bath AS Metrology Index (BASMI), and quality of life (SF-36) were assessed before, during, and after therapy.

RESULTS

Significant improvement at Day 1 after the first infusion lasting until Week 12 was reported by 5/6 patients. Improvement of > or = 50% in all activity, function, pain, and swollen joint scores was observed in the patients taking 5 mg/kg. The 3 mg/kg dose was less effective, resulting in > or = 15% improvement in outcome variables. Peripheral arthritis, enthesitis, and spinal symptoms improved equally. C-reactive protein dropped in 4 patients. Health related quality of life increased. No serious side effects or infections occurred.

CONCLUSION

These observations suggest that anti-TNF-alpha therapy has significant short term efficacy in patients with severe uSpA.

Insights into the Role of Infection in the Spondyloarthropathies

Certain infections play an important role in the pathogenesis of the human leukocyte antigen (HLA)-B27-associated reactive arthritis. Whether infections play a role in other forms of spondyloarthropathies is not as clear. The role of HLA-B27 as an antigen-presenting molecule is important in the pathogenesis of these diseases. Recent evidence has been obtained indicating that this molecule may have other functions unrelated to antigen-presentation in the interaction of reactive arthritis-triggering microbes and host. This paper reviews the recent studies on the role of infection in the spondyloarthropathies.

The recognition of HLA-B27 by human CD4(+) T lymphocytes

HLA-B27 transgenic animal models suggest a role for CD4(+) T lymphocytes in the pathogenesis of the spondyloarthropathies, and murine studies have raised the possibility that unusual forms of B27 may be involved in disease. We demonstrate that CD4(+) T cells capable of recognizing B27 can be isolated from humans by coculture with the MHC class II-negative cell line T2 transfected with B27. These CD4(+) T cells recognize a panel of B27-transfected cell lines that are defective in Ag-processing pathways, but not the nontransfected parental cell lines, in a CD4-dependent fashion. Inhibition of responses by the MHC class I-specific mAb w6/32 and the B27 binding mAb ME1 implicates the recognition of a form of B27 recognized by both of these Abs. We suggest that B27-reactive CD4(+) T cells may be pathogenic in spondyloarthropathies, particularly if factors such as infection influence expression of abnormal forms of B27.

Current use of biologicals for the treatment of spondyloarthropathies

Spondyloarthropathies (SpA) are a group of related disorders. The hallmark symptoms include spondylitis, pauci-articular synovitis and enthesiopathy. In an important number of cases, subclinical gut inflammation with pathological findings resembling Crohn's disease can be found. Some of these patients may eventually develop overt Crohn's disease. Conventional medical therapy in patients with SpA consists of non-steroidal anti-inflammatory drugs (NSAIDs). Sulphasalazin can be co-administered, especially in cases of chronic synovitis or enthesiopathy. Recently, experience with anti-TNF-alpha monoclonal antibodies (infliximab), a new class of biological compounds, has opened new avenues for treating patients with SpA. In particular, infliximab used in two open studies gave significant benefit on the locomotor manifestations in patients with Crohn's disease, in patients with ankylosing spondylitis, undifferentiated SpA and psoriatic arthritis. Etanercept, another TNF-alpha antagonist (soluble receptor), was shown to induce benefit in a placebo-controlled study in patients with psoriatic arthritis. The relationship between SpA and inflammatory bowel disease lead to the hypothesis that interfering with gut inflammation in patients with SpA would yield a potential target for modulating the synovitis in these patients. Thus, besides TNF-alpha blockade, other strategies with potential efficacy can be envisioned, such as IL-10, ICAM-1 antisense or anti-(4)beta(7) antibodies.

T-cell studies in the spondyloarthropathies

A growing body of evidence suggests that T lymphocytes play an important role in initiating and maintaining the inflammatory process characteristic of the human leukocyte antigen (HLA)-B27-associated spondyloarthropathies. T cells seem to be involved in the primary defense reaction against arthritis-triggering gram-negative bacteria at the site of extra-articular infection, in determining the systemic cytokine pattern, in the recirculation process between gut mucosa and the joint, and in mediating secondary autoimmune joint inflammation. The factors involved in disease chronicity (namely in ankylosing spondylitis and psoriatic arthritis) are still unknown. Autoreactive T cells may contribute to this process by recognition of cross-reactive self-epitopes (ie, molecular mimicry between bacterial and self-antigens). Autoreactive T cells may as well be inappropriately upregulated by bacterial superantigens, or by local inflammatory reactions leading to the uncovering of former cryptic self-epitopes. In this paper, we review recent studies on peripheral blood and synovial T cells in patients with reactive arthritis, enteropathic spondyloarthropathy, psoriatic arthritis, and ankylosing spondylitis.

Animal models of the spondyloarthropathies

Several lines of rats transgenic for human leukocyte antigen (HLA)-B27 spontaneously develop a multisystemic inflammatory disease resembling human spondyloarthropathies. This disease is mediated by cells of the immune system and is dependent on the presence of a normal bacterial flora. Both antigen-presenting cells expressing high levels of HLA-B27 and T cells appear to be of importance in the pathogenesis of this model. HLA-B27 transgenic/b2- microglobulin deficient mice also develop arthritis, under the influence of the bacterial flora. In both types of model, CD8+ T cells appear to be unnecessary, arguing against the "arthritogenic peptide" hypothesis.