ARTHRITIS & RHEUMATISM Vol. 46, No. 3, March 2002, pp 606–613 DOI 10.1002/art.10041 © 2002, American College of Rheumatology CONFERENCE SUMMARY The Cutting Edge of Spondylarthropathy Research in the Millennium Kaisa Granfors,1 Elisabeth Märker-Hermann,2 Filip de Keyser,3 Muhammad A. Khan,4 Eric M. Veys,3 and David T. Y. Yu5 tissues linking tendon and ligament to bone. They are located at the metaphyses and diaphyses of long bones. Fibrocartilage entheses have an additional transitional zone of fibrocartilage at the bony interface (Figure 1) (2). They are located at sites with a great deal of joint movement, probably because fibrocartilage can dissipate mechanical stress. Fibrocartilage entheses have 4 consecutive zones (Figure 1), as follows: 1) a tendon beginning with sparse, longitudinally oriented fibroblasts which then merge into dense fibrous connective tissue; 2) a zone of uncalcified fibrocartilage where cells now assume the morphology of chondrocytes; 3) a fairly abrupt transition to calcified fibrocartilage; and 4) the bone. This tidemark is in continuity with the tidemark of the neighboring articular cartilage. The calcified fibrocartilage anchors the ligament/tendon into the bone using tiny vanguards of collagen fibers which penetrate into the bone trabeculae. It is an important concept, when considering the pathogenesis of SpA, that the above-described structure is not a static one. The enthesis has a high capacity for dynamic tissue turnover in continual response to changes in mechanical factors. This would explain why this is a target for inflammation. Because entheseal insertions are quite ubiquitous, there is a corresponding diversity of entheseal-associated pathologic and clinical manifestations in SpA. In addition to defining the gross anatomy, Benjamin and Ralphs (1,2) have also characterized the biochemistry of the entheses using immunohistochemistry, Western blotting, and polymerase chain reaction (PCR). Type II collagen and proteoglycan aggrecan messenger RNA (mRNA) synthesized by fibrocartilage cells are consistently found in the enthesis distal to the mid-tendon. The ability of the entheseal fibrocartilage to resist compression is the result of the presence of these type II collagen and aggrecan messages in the extracellular matrix. This distribution of proteoglycan Introduction In the last few years, with advances in technology and concept, research on the spondylarthropathies (SpA) has moved from random harvesting of piecemeal data to systematic evaluations of core puzzles. In the Second International Congress of Spondylarthropathies, held in Ghent, Belgium, on October 4–7, 2000, the most recent data were presented and these core puzzles were defined. The factors that are unique to SpA are 1) the site of inflammation is not only the synovium, but also the enthesis; 2) the essential predisposing gene is HLA– B27; 3) a number of other genes are required for development of ankylosing spondylitis (AS), a prototype of SpA; and 4) certain facultative intracellular Gramnegative bacteria can induce reactive arthritis (ReA), a form of SpA. Inflammation in SpA Enthesitis is the hallmark that distinguishes SpA from all other arthritides (1). Because of its relative inaccessibility, the enthesis has eluded scientists until now. Dr. M. Benjamin (Wales, UK) defines the enthesis as the area of insertion of tendon, ligament, joint capsule, or fascia to bone. There are 2 types: fibrous entheses and the more common fibrocartilage entheses. Fibrous entheses are simply dense fibrous connective 1 Kaisa Granfors, PhD: National Public Health Institute, Turku, Finland; 2Elisabeth Märker-Hermann, MD: Johannes Gutenberg University of Mainz, Mainz, Germany; 3Filip de Keyser, MD, Eric M. Veys, MD: Ghent University Hospital, Ghent, Belgium; 4Muhammad A. Khan, MD: Case Western Reserve University, Cleveland, Ohio; David T. Y. Yu, MD: UCLA School of Medicine, Los Angeles, California. Address correspondence and reprint requests to Kaisa Granfors, PhD, National Public Health Institute, Department in Turku, Kiinamyllynkatu 13, FIN-20520 Turku, Finland. E-mail: kaisa. firstname.lastname@example.org. Submitted for publication May 15, 2001; accepted in revised form August 14, 2001. 606 RESEARCH ON THE SPONDYLARTHROPATHIES 607 the synovial lining layer and an increase in ␣v␤5 integrins in the sublining layer. Because engagement of ␣v integrins regulates the proliferation, migration, and collagenase expression of a variety of cell types, this differential integrin expression may play an important role in the aggressive growth of the synovial pannus in RA. How does HLA–B27, the essential gene, mediate arthritis? Figure 1. The normal structure of fibrocartilage entheses, showing the 3 fibrocartilage types that reduce wear and tear at the attachment of the human Achilles tendon (T). In addition to enthesis fibrocartilage (EF), there is a sesamoid fibrocartilage (SF) on the deep surface of the Achilles tendon and a periosteal fibrocartilage (PF) on the calcaneus. These protect the bone and tendon, where they press against each other during dorsiflexion of the foot. The free movement of the tendon is promoted by the retrocalcaneal bursa (RB). (Toluidine blue stained sagittal section; original magnification ⫻ 4.) Reproduced, with permission, from ref. 2. aggrecan and type II collagen is of interest to investigators of SpA. Autoimmune reactivities to these molecules in mice can result in arthritis. Although peripheral arthritis is not uncommon in SpA, histologic studies of SpA synovial membranes were infrequent until the mid-1990s. A crucial question is, how does the histopathology of SpA synovitis differ from that of rheumatoid arthritis (RA)? This was examined quantitatively by Dr. D. Baeten (Ghent, Belgium) (3). The discriminatory features are the following. 1) The single interesting feature in SpA synovitis is the overexpression of CD163 by activated macrophages. Since CD163⫹ macrophages secrete proinflammatory cytokines, these data underline the prominent role of macrophages in the pathogenesis of SpA. 2) Lymphoid aggregates are less frequent in SpA compared with RA, while CD3⫹, CD4⫹, and CD20⫹ lymphocytes are also expressed at lower levels in SpA. 3) Vascularity is more prominent and more tortuous in SpA. In psoriatic arthritis (PsA), as described by Dr. D. Veale (Leeds, UK), tortuosity is caused by abnormal angiogenesis mediated by transforming growth factor ␤ (TGF␤) and vascular endothelial growth factor. Distribution of integrins on synovial fibroblasts is a distinguishing feature. RA is characterized by a decrease in ␣v␤3 integrins in Initial hypotheses on the role of HLA–B27 in disease pathogenesis followed the footsteps of crystallographers in assuming that HLA–B27 mediates arthritis through its physiologic function as an antigen-presenting molecule, consisting of a standard trimeric structure of the heavy chain, the ␤2-microglobulin, and a peptide. New data on this concept were presented in a roundtable discussion. It is now obvious that the presentation of an arthritogenic peptide to disease-inducing CD8⫹ T cells can be influenced by the molecular structure of the antigen-binding groove, and that this groove differs between certain disease-associated and nonassociated HLA–B27 subtypes. Dr. J. Lopez de Castro (Madrid, Spain) analyzed the peptide repertoires of 2 closely related pairs of HLA–B27 subtypes, B*2705 versus B*2709 and B*2704 versus B*2706, using high-performance liquid chromatography and mass spectrometry (4). B*2709 and B*2706 are less associated with AS compared with B*2705 and B*2704. There is only a 30% difference in the peptide repertoires of these subtype pairs. However, identification of peptides common to AS-associated HLA–B27 subtypes might not be the answer. Dr. Lopez de Castro also showed that although the same peptide can be immunogenic when presented by the ASassociated B*2705, B*2702, and B*2704, the cytotoxic T cell responses elicited in the context of each subtype are different; hence the “antigenic” properties of the peptide change upon binding to each subtype. In addition to basic biochemistry studies, actual testing with patient materials was carried out by Dr. E. Märker-Hermann (Mainz, Germany). She found that among several HLA–B27 binding peptides, the HLA–B27/ enterobacteriae cross-reactive peptide (LRRYLENGK), previously reported by Scofield et al (5), was the only peptide recognized more often by HLA–B27–restricted CD8⫹ T cells from AS patients compared with healthy controls (6). Identification of other disease-related immunodominant peptides is urgently needed. Dr. J. Sieper (Berlin, Germany) described a novel approach to search for biologically significant antigenic 608 peptides by screening all chlamydial proteins and peptides derived from those for binding to HLA–B27, and determined whether these peptides would be cut by proteasomes using special computer programs. T cells from patients with Chlamydia-induced ReA recognized 3 such peptides. The identification of these peptides would be important if there is an oligoclonal T cell response in SpA. Actually, this has been tested by Dr. E. May (Mainz, Germany/Dallas, TX). He analyzed the GenBank data of more than 100 T cell receptor (TCR) CDR3 sequences derived from ReA patients from different groups. Closely related sequences were found in all 7 patients examined. When T cells using this motif were expanded in vivo and characterized functionally, clones were found that are CD8⫹ and HLA–B27 autoreactive. This finding of a conserved TCR motif may indicate that 1 or a few arthritogenic peptides are recognized in the context of HLA–B27, and that autoreactive CD8 T cells may be involved in the disease process. Dr. P. Bowness (Oxford, UK) pointed out that in addition to the fact that HLA class I molecules, such as HLA–B27, have a key role in initiating an immune response by binding small antigenic peptides and presenting them to CD8⫹ T cells, HLA–B27 has a unique structural feature that may contribute to the pathogenesis of SpA. HLA–B27 has an unpaired cysteine residue (Cys67) in the extracellular ␣-1 domain, and free HLA– B27 heavy chains can form a stable disulfide-bonded heavy chain homodimer (termed HC-B27) on the cell surface dependent on this Cys67 residue (7–9). This may result in altered function that can be pathogenic. Incidentally, higher levels of cell surface HC-B27 have been detected in 2 SpA patients, compared with healthy individuals possessing HLA–B27. The special characteristic of ReA-triggering bacteria, which is the ability to live intracellularly, has stimulated several groups to conduct studies on the interaction between the causative bacteria and HLA– B27–positive and –negative host cells in vitro. In these studies, a possible role of HLA–B27 cannot be the classic one, i.e., antigen presentation, since usually only cells of one type are in culture with the bacteria. Considering the pathogenesis of the infections caused by ReA-triggering bacteria and ReA itself, 2 steps have been of special interest: invasion and intracellular survival of the bacteria. During the roundtable discussion (Drs. R. Inman, Toronto, Canada, K. Granfors, Turku, Finland, J. Kuipers, Hannover, Germany, and D. Elewaut, La Jolla, CA), no uniform conclusion about the effect of HLA–B27 on invasion or uptake of these GRANFORS ET AL bacteria into cells of different types was achieved. However, the level of invasion of ReA-triggering bacteria into HLA–B27–positive and –negative cells might not be the main issue in the pathogenesis of ReA. There is evidence that HLA–B27 plays a modulatory role in the early signal transduction events induced by Salmonella invasion (Dr. D. Yu, Los Angeles, CA) (10). In several studies (Dr. K. Granfors, Turku, Finland [11,12]; Dr. R. Inman, Toronto, Canada), HLA–B27 seems to confer the defect in intracellular elimination of ReA-triggering bacteria both in transfected cell lines and in monocytes from healthy persons. However, the molecular basis for these phenomena is unclear. The interesting recent observations in relation to these findings were presented by Dr. R. Colbert (Cincinnati, OH). He showed evidence that the HLA–B27 heavy chain tends to misfold during assembly. This may be relevant, since protein misfolding can influence intracellular signaling pathways (13–15) and thus could be responsible for the non–antigen presentation effects. HLA–B27 misfolding and accumulation might contribute an endoplasmic reticulum stress response, leading to nuclear factor B (NF-B) activation. Consequently, this could stimulate synthesis of proinflammatory cytokines such as tumor necrosis factor ␣ (TNF␣) in monocytes and macrophages. It is of particular interest that monocytes expressing HLA–B27 have enhanced NF-B activation and TNF␣ production compared with control monocytes upon Salmonella lipopolysaccharide (LPS) stimulation (Dr. M. Penttinen, Turku, Finland) (16). Misfolding offers a plausible explanation for the effects of HLA–B27 that are independent of its antigenpresentation properties. Which other genes contribute to AS? Recent studies of families and twins affected by AS suggest a polygenic model of genetic susceptibility. Considerable epidemiologic and transgenic animal model data indicate a direct role for HLA–B27, but additional non–HLA–B27 genes, both within the major histocompatibility complex (MHC) region on chromosome 6 and on other chromosomes, are also necessary for disease development. The results from the ongoing European and North American genome-wide searches for these susceptibility and severity genes in AS patients were discussed in a roundtable discussion with presentations by Drs. M. Brown (Oxford, UK), M. Breban and C. Miceli-Richard (Paris, France), J. Reveille (Houston, TX), and M. Khan (Cleveland, OH). The task of all these studies is to define regions on different chromo- RESEARCH ON THE SPONDYLARTHROPATHIES somes likely to contain AS-susceptibility genes and finally to identify the actual genes lying within these regions. In genome-wide screens, microsatellites are used which are defined as highly polymorphic dinucleotide repeats, mostly noncoding sequences, that can be used to establish linkage of a certain chromosome region with a disease. Microsatellites are usually amplified using PCR, and fragments are then separated on polyacrylamide gels and detected by autoradiography or by using fluorescence-labeled primers in automatic sequencers. Dr. M. Brown has observed markers of interest on chromosome 2q, in the vicinity of the interleukin-1 (IL-1) and IL-1RA gene family; these are chromosomes 10, 16, and 19 (17). His group has collected informative data from 230 families with AS; he hopes that the number will exceed 300 by the end of 2001. The results of French and North American studies support the presence of additional susceptibility/severity genes in the MHC region, but do not confirm British results regarding markers of interest on other chromosomes. French investigators have studied somewhat similar numbers of families with SpA, and the group in the United States has analyzed 96 families with AS in the first year of their study. Dr. C. Miceli-Richard found that the best linkage outside the MHC lies on chromosome 14. Remarkably, another region of interest was identified at the telomeric site of the X chromosome. Dr. M. Khan pointed out that the 3 studies have used different criteria for disease classification, and maximization of resource utility by international collaboration (pooled data) as well as genetic studies of isolated, genetically more homogeneous populations for linkage disequilibrium mapping will be very helpful. He presented HLA–B27 polymorphism data which showed the structural differences between the 21 different alleles (subtypes) of HLA–B27, and reported observing the second family known to date with HLA–B*2708 and AS (18). Dr. D. Yu (Los Angeles, CA) discussed the differentially expressed genes in the joints and peripheral blood of patients with AS and related SpA, as studied by DNA microarrays, which are glass microslides or nylon membranes containing complementary DNA (cDNA) samples in an ordered 2-dimensional matrix. His laboratory is using this method to study whether the genes expressed in SpA are different from those of other chronic inflammatory arthritides, such as RA and PsA, to identify potential mediators or signaling pathways of inflammation, and to test if they are altered by specific antiarthritic drug therapy. Gene-expression profiles of such patients were 609 generated by measuring the hybridization of isotopelabeled mRNA to the microarrays of 588–1176 cDNA. The microarrays showed that at least 30 genes of diverse characters are activated in the peripheral blood mononuclear cells (PBMC) of RA patients; these include genes for cytokines/chemokines, their receptors, and adhesion/signaling molecules. In contrast, in SpA, only ⬃6 of such genes are activated, and include TNF␣, IL-8, and intracellular adhesion molecule 1 genes. When comparing both PBMC and synovial fluid mononuclear cells (SFMC) in the same patients, both in RA and in SpA, the SFMC repertoires appear to be very limited, with TNF␣ and IL-1␤ being the dominant genes. But, in spite of the diversity in the PBMC in RA, cells that selectively migrate into the joints carry a smaller repertoire, and there is dominance of TNF␣ that extends to the synovial tissues. Regarding signaling molecules, cjun/ cfos are activated in almost all SFMC samples. On global activation (by anti-CD3) of synovial T lymphocyte clones, both the proinflammatory gene TGF␤ and the antiinflammatory gene IL-13 are expressed, indicating that each clone is potentially arthritis-mediating or suppressive, perhaps depending on the activating ligand. How do bacteria induce SpA? It is well established that ReA is a joint inflammation following infections caused by certain Gramnegative bacteria. The role of infection in the pathogenesis of other SpA is suggested as well, but these associations are not as clear. The ReA-triggering bacteria share certain characteristics which may be important in the pathogenesis of the disease, e.g., they are able to live intracellularly, they have LPS as an important component of the outer membrane, and they cause original infections on mucosa. During the Congress, interaction of the ReA-triggering bacteria and host cells was discussed in several sessions, and from different points of view. It is currently generally accepted that this interaction is abnormal in HLA–B27–positive persons developing ReA and the causative bacteria persist in their bodies for long times. How these bacteria are able to hide in the host is not clear. The bacteriologic view was given by Dr. J. Galan (New Haven, CT) in his introductory lecture. He described a remarkable biochemical cross-talk which happens when Salmonella modulates host cellular functions (19,20). This interaction leads to the activation of a type III protein secretion system that directs the export and translocation of a battery of bacterial effector proteins into the host cells. These effector proteins, such as SopE 610 and SipA, can stimulate and interfere with a variety of functions of the host cell. They stimulate marked actin cytoskeletal reorganization via a signaling process dependent on small GTP-binding proteins called CDC42 and Rac, leading to membrane ruffling and macropinocytosis that ultimately results in the internalization of the bacteria. Internalization into nonphagocytic cells is essential for the pathogenicity of Salmonella. The cellular responses induced by Salmonella are short lived, and when inside the cell, Salmonella turns off host cellular responses and the cells regain their normal morphology. This phenomenon is mediated by SptP, which, upon delivery into the host cell, down-modulates the bacteriainduced cellular responses by acting as a GTPaseactivating protein for CDC42 and Rac. By alternately activating and down-modulating the function of GTPases, Salmonella modulates actin cytoskeleton and host cellular functions. How these functions may be affected by HLA–B27 is not yet clear. In another introductory lecture, Dr. H. R. Schumacher (Philadelphia, PA) also discussed the host and environmental balance, focusing on Chlamydia. Dr. Schumacher and Dr. A. Hudson (Detroit, MI) have found that in ReA, Chlamydia often causes persistent infection of the synovium (21). The organisms in the synovium are metabolically active, although at a low state. Chlamydial genes encoding products required for DNA synthesis and partitioning (dnaA, polA, mutS, parB, minD) are expressed, but genes encoding products required for cytokinesis (ftsK, ftsW) are not. A similar expression of genes was also seen in in vitro models of chlamydial persistence. Interferon-␥ (IFN␥) was shown to be an important factor for persistent infection. Removal of this proinflammatory molecule from the culture medium led to release from persistence. Obviously, there are other important factors as well, and continuing research on these factors and how they may be related to the triggering, perpetuating, and healing of SpA would be important. Presence of causative microbes (Chlamydia) or components of causative microbes (enterobacteriae) in the joint is obviously important in triggering ReA. When an antichlamydial vaccine reduced the synovial levels of chlamydial DNA by 26–60% in mice, joint histopathology was also reduced (Dr. J. Whittum-Hudson, Detroit, MI) (22). Biologic therapy for SpA Anti-TNF␣. Trials of anti-TNF␣ therapy. TNF␣ is a key molecule mediating the inflammatory process in GRANFORS ET AL RA. TNF␣ blockade can be achieved therapeutically with several biologic agents, including anti-TNF␣ monoclonal antibodies such as infliximab (Remicade; Centocor, Malvern, PA) and soluble TNF␣ receptors (23). Several successful clinical trials with infliximab in patients with Crohn’s disease and RA have been reported. Data on its use in SpA have become available only over the last 2 years. The very recent experience with infliximab in SpA was presented at the meeting by the groups from Ghent (Belgium), Berlin (Germany), and Erlangen (Germany). The Ghent group treated 4 patients who had refractory Crohn’s disease associated with SpA with infliximab (24). The duration of articular symptoms ranged from 2 months to 25 years. One patient had AS with severe inflammatory axial symptoms, a second patient had AS with peripheral arthritis, and the 2 other patients had peripheral arthritis. In all 4 patients, infliximab induced not only remission of their gastrointestinal symptoms, but also remission of articular symptoms. The onset of this effect occurred shortly after the infliximab infusion. This preliminary experience with TNF␣ blockade in patients with SpA associated with inflammatory bowel disease led to a further open-label trial with infliximab in 21 patients with SpA (25). Patients received 3 infusions of 5 mg/kg of infliximab at weeks 0, 2, and 6. Eleven of the 21 included patients had AS, and all had active disease. Spinal pain improved significantly in 7 of the 11 patients, shortly after the first infusion. Almost all patients responded well after the induction therapy, with an infusion every 14 weeks (Figure 2). Nine patients included in the study had PsA. This subgroup responded to the treatment in a similar way as did the total SpA cohort. A similar favorable response was observed in the 2 patients with undifferentiated SpA. The Berlin group treated 11 patients with active AS, by administering 3 infusions of 5 mg/kg of infliximab on weeks 0, 2, and 6 (26). One patient was withdrawn because of urticarial xanthoma. Significant improvement was documented in 9 of the 10 patients and lasted for 6 weeks after the third infusion in 8 of the 10 patients. Magnetic resonance imaging (MRI) of the spine was performed in 5 patients. At study enrollment, 3 of the 5 patients had evidence of spinal inflammation as detected by MRI. The followup MRI performed 2–6 weeks after the third infusion revealed improvement in 2 patients. Dr. C. Antoni (Erlangen, Germany) reported on the use of infliximab to treat 10 patients with severe PsA. Seven of the 10 exhibited an American College of Rheumatology 70% (ACR70) improvement response. RESEARCH ON THE SPONDYLARTHROPATHIES 611 Figure 2. Efficacy of infliximab in 21 patients with spondylarthropathies. Patient global assessment on a 100-mm visual analog scale (VAS) (A) and swollen joint count (B) were assessed over time during 36 weeks’ followup. The box and whisker plots show the median value (horizontal line) and range (first to third quartiles in boxes, 98% of values between enclosed bars, outliers indicated by open circles) of the chosen parameter over time. Significant differences were calculated by Wilcoxon signed rank test. ⴱ ⫽ P ⱕ 0.01 and ⴱⴱ ⫽ P ⱕ 0.001 versus baseline. The Psoriasis Area and Severity Index (PASI) of the psoriatic lesions showed improvement of 71%. Examination of the skin biopsy samples showed a remarkable reduction in inflammation. Patients were re-treated every 8 weeks and showed a continuous response over 1 year. Published data on the clinical efficacy of other anti-TNF␣ preparations are very limited. Mease et al (27) reported the findings from their study with etanercept in patients with psoriasis and PsA. They treated 60 patients in a randomized, double-blind, placebocontrolled 12-week study. Eighty-seven percent of the etanercept-treated patients met the PsA response criteria, compared with 23% of the placebo-controlled patients. The ACR20 preliminary criteria for improvement were achieved by 73% of the etanercept-treated patients compared with 13% of the placebo-controlled patients. Of the 19 patients in each treatment group who could be assessed for psoriasis, 26% of the etanercept-treated patients achieved a 75% improvement in the PASI, compared with none of the placebo-treated patients. Biologic effects of anti-TNF␣ therapy. Data on the effect of infliximab therapy on T cell cytokines and on the immunopathology of the synovial membrane were reported at the meeting. Treatment with 3 infusions of infliximab in SpA patients (Ghent cohort) resulted in a rapid and sustained increase in Th1 cytokines (IFN␥ and IL-2) to levels comparable with those in healthy con- trols. A reduction in IL-10–positive T cells was observed in the first 4 weeks in those patients with high baseline values. No effect was seen on IL-4 production. In the Berlin cohort of AS patients, lymphocyte counts were decreased after infliximab therapy. The TNF␣ secretion capacity of peripheral blood T cells was found to be enhanced. Together, these data support the view that TNF␣ blockade essentially reverses the state of anergy of Th1 cells, while no significant effect is observed on Th2 cells. In the Ghent patient cohort, synovial biopsy samples were obtained from 8 patients with active knee synovitis at baseline (28). A followup biopsy in these patients was obtained at weeks 2 and 12. In all 8 patients, there was a clear clinical improvement after anti-TNF␣ therapy. Histologic analysis showed no significant changes in the overall degree of inflammatory infiltration, since the number of CD20⫹ lymphocytes and plasma cells increased. When examined in detail, the thickness of the synovial layer tended to decrease, with a significant reduction in CD55⫹ synoviocytes at week 12. Vascularity in the sublining layer was reduced, with decreased endothelial expression of vascular cell adhesion molecule 1. The numbers of neutrophils, CD68⫹ macrophages, and CD163⫹ macrophages were all decreased. IL-10. IL-10 is required to maintain immune homeostasis. It inhibits TNF␣ and IL-1 and may also 612 up-regulate endogenous cytokine inhibitors. Dysregulation is involved in the development of inflammatory bowel disease and arthritis. IL-10–deficient mice develop enteritis (29). IL-10 supplementation in these mice is an effective treatment. Of interest in this regard are certainly the data presented at the meeting by Dr. L. Steidler (Ghent, Belgium), who reported that intragastric administration of IL-10–secreting Lactococcus lactis caused a 50% reduction in colitis in mice treated with dextran sulfate sodium and prevented the onset of colitis in IL-10(⫺/⫺) mice (30). Subreum. Subreum (OM 8980) is a fractionated lyophilized extract from several forms of Escherichia coli containing immunoreactive peptide fragments, including heat-shock proteins (hsp70 and hsp60) (31). Subreum has been shown to be effective in RA and it was suggested that the efficacy could be a result of induction of oral tolerance. In a double-blind, placebo-controlled, single-center study, the results of which were presented at the meeting by Dr. H. Mielants (Ghent, Belgium), subreum was given to treat different forms of SpA for 48 weeks and compared against the effects of placebo. Fifty-nine patients (23 with AS, 18 with PsA, 3 with ReA, and 15 with undifferentiated SpA) were evaluated in intention-to-treat analyses. In the subgroup of patients with undifferentiated SpA, a statistically significant improvement was found for all clinical parameters in the subreum group versus placebo; 6 of the 8 patients came into clinical remission versus 1 of the 7 placebo patients after 24–36 weeks of treatment. Since 20% of these patients will develop AS during disease evolution, subreum administration could potentially influence this evolution. Summary and conclusions The recent International Congress on Spondylarthropathies yielded new insights that challenged some accepted paradigms. In addition to synovium, the enthesis seems to be a site of inflammation. In considering the pathogenesis of SpA, the role of the most important predisposing gene, HLA–B27, may be more complex than earlier thought. Current data suggest that in addition to antigen presentation, HLA–B27 may also act in another way. Misfolding of HLA–B27 and accumulation in the endoplasmic reticulum could explain the strong activation of HLA–B27–positive cells, e.g., during stimulation with LPS. It is obvious that other genes, in addition to HLA–B27, are involved in the pathogenesis of SpA. At least some of them will be determined in the near future with the aid of new, powerful techniques that GRANFORS ET AL are being used in ongoing European and North American genome-wide searches for susceptibility and severity genes in AS. The role of infection in the pathogenesis of a form of SpA, ReA, is inevitable. Currently, the rapid growth in knowledge about cross-talk between ReAtriggering bacteria and host cells will help us to understand how these bacteria modulate host cellular functions in order to be able to live and replicate intracellularly. The results of the initial studies with biologic treatments (especially with anti-TNF␣) give a lot of hope for successful treatment of SpA in the near future. In this most recent Congress, essential new information was presented that will prove to be important in the ongoing investigations in this field. ACKNOWLEDGMENTS The International Congress of Spondylarthropathies was organized under the auspices of the International League of Associations for Rheumatology, and additionally sponsored by several pharmaceutical companies (major sponsors: Boehringer Ingelheim, Centocor—Schering Plough, Merck Sharp & Dohme, OM Pharma, Pharmacia & Upjohn, and Pfizer; other sponsors: AHP Pharma, Wyeth Lederle, Aventis Pharma, AstraZeneca, Becton Dickinson, Searle, and UCB Pharma). REFERENCES 1. Benjamin M, Ralphs JR. The cell and developmental biology of tendons and ligaments. Int Rev Cytol 2000;196:85–130. 2. Benjamin M, Ralphs JR. Fibrocartilage in tendons and ligaments: an adaptation to compressive load. J Anat 1998;193:481–94. 3. Baeten D, Demetter P, Cuvelier C, Van Den Bosch F, Kruithof E, Van Damme N, et al. 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