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

Recent Developments in HLA B27 Anterior Uveitis

There has been steady progress in understanding the pathogenesis, clinical features, and effective treatment of acute anterior uveitis (AU) over the past 5 years. Large gene wide association studies have confirmed that AU is a polygenic disease, with overlaps with the seronegative arthropathies and inflammatory bowel diseases, associations that have been repeatedly confirmed in clinical studies. The role of the microbiome in AU has received increased research attention, with recent evidence indicating that human leukocyte antigen B27 (HLA B27) may influence the composition of the gut microbiome in experimental animals. Extensive clinical investigations have confirmed the typical features of acute AU (AAU) and its response to topical, regional and systemic immunosuppressive treatment. Increased understanding of the role of cytokines has resulted in studies confirming the value of anti-cytokine therapy [anti-tumor necrosis factor (anti-TNF) and interleukin 6 (IL-6) therapy] in severe and recurrent cases of AAU, particularly in subjects with an associated spondyloarthopathy (SpA) and in juvenile idiopathic arthritis (JIA)-associated AAU.

Ankylosing spondylitis: etiology, pathogenesis, and treatments

Ankylosing spondylitis (AS), a common type of spondyloarthropathy, is a chronic inflammatory autoimmune disease that mainly affects spine joints, causing severe, chronic pain; additionally, in more advanced cases, it can cause spine fusion. Significant progress in its pathophysiology and treatment has been achieved in the last decade. Immune cells and innate cytokines have been suggested to be crucial in the pathogenesis of AS, especially human leukocyte antigen (HLA)‑B27 and the interleukin‑23/17 axis. However, the pathogenesis of AS remains unclear. The current study reviewed the etiology and pathogenesis of AS, including genome-wide association studies and cytokine pathways. This study also summarized the current pharmaceutical and surgical treatment with a discussion of future potential therapies.

Clinical Trial and In Vitro Study for the Role of Cartilage and Synovia in Acute Articular Infection

OBJECTIVE

Osteoarthritis is a long-term complication of acute articular infections. However, the roles of cartilage and synovia in this process are not yet fully understood.

METHODS

Patients with acute joint infections were enrolled in a prospective clinical trial and the cytokine composition of effusions compared in patients with arthroplasty (n = 8) or with intact joints (n = 67). Cytokines and cell function were also analyzed using a human in vitro model of joint infection.

RESULTS

Synovial IL-1β levels were significantly higher in patients with arthroplasty (p = 0.004). Higher IL-1β concentrations were also found in the in vitro model without chondrocytes (p < 0.05). The anti-inflammatory cytokines IL-4 and IL-10 were consistently expressed in vivo and in vitro, showing no association with the presence of cartilage or chondrocytes. In contrast, FasL levels increased steadily in vitro, reaching higher levels without chondrocytes (p < 0.05). Likewise, the viability of synovial fibroblasts (SFB) during infection was higher in the presence of chondrocytes. The cartilage-metabolism markers aggrecan and bFGF were at higher concentrations in intact joints, but also synthesized by SFB.

CONCLUSIONS

Our data suggest an anti-inflammatory effect of cartilage associated with the SFBs' increased resistance to infections, which displayed the ability to effectively synthesize cartilage metabolites.The trial is registered with DRKS 00003536, MISSinG.

The programmed cell death 1 gene polymorphisms (PD 1.3 G/A, PD 1.5 C/T and PD 1.9 C/T) and susceptibility to ankylosing spondylitis: a meta-analysis

OBJECTIVE

The objective is to integrate all the eligible studies and investigate whether the programmed cell death 1 (PDCD-1) gene polymorphisms (PD 1.3 G/A, PD 1.5 C/T, and PD 1.9 C/T polymorphism) are correlated with ankylosing spondylitis risk (AS). Ankylosing spondylitis is a chronic inflammatory disease, and several genetic and environmental factors play an important role in the development and progression of AS. Significant associations between PDCD-1 gene polymorphisms (PD 1.3 G/A, PD 1.5 C/T or PD 1.9 C/T) and AS risk have been reported; however, some of these results are controversial.

METHODS

A systematic online search was performed using PubMed, EMBASE, Web of Science, and the Cochrane Library to identify case-control studies investigating the relationship between PD 1.3 G/A, PD 1.5 C/T, and PD 1.9 C/T polymorphisms and the susceptibility of AS. The pooled odds ratio (OR) with 95 % confidence interval (CI; 95 %) was calculated to assess the associations, and subgroup meta-analyses were performed according to the ethnicity of the study populations.

RESULTS

Five studies involving 909 cases and 982 controls met the inclusion criteria after assessment by two reviewers. Overall, there were no significant associations between PD 1.3 G/A and PD 1.5 C/T polymorphisms and AS risk. With regard to PD 1.9 C/T polymorphism, a significant association was found under the allele contrast model (T vs. C: OR 1.74, 95 % CI 1.48-2.06, P < 0.001), heterozygote model (CT vs. CC: OR 2.43, 95 % CI 1.65-3.59, P < 0.001), homozygote model (TT vs. CC: OR 1.87, 95 % CI 1.30-2.71, P = 0.001), and dominant model (CT/TT vs. CC: OR 2.29, 95 % CI 1.65-3.18, P < 0.001). In the subgroup analysis of ethnicity, no significant associations were found between PD 1.3 G/A, PD 1.5 C/T polymorphisms, and AS risk in either Asian or Caucasian populations. However, our study suggested that PD 1.9 C/T polymorphism was significantly associated with AS in Asian populations (T vs. C: OR 1.72, 95 % CI 1.46-2.04, P < 0.001; CT vs. CC: OR 2.44, 95 % CI 1.56-3.82, P < 0.001; TT vs. CC: OR 1.88, 95 % CI 1.30-2.73, P = 0.001; and CT/TT vs. CC: OR 2.29, 95 % CI 1.58-3.32, P < 0.001) but not in Caucasian populations.

CONCLUSION

The PD 1.9 C/T polymorphism may be involved in susceptibility to AS, particular in Asian populations; however, no significant associations were found between PD 1.3 G/A, PD 1.5 C/T polymorphisms, and AS risk in either Asians or Caucasians.

Endoplasmic reticulum aminopeptidase-1 alleles associated with increased risk of ankylosing spondylitis reduce HLA-B27 mediated presentation of multiple antigens

Ankylosing spondylitis (AS) is a chronic systemic arthritic disease that leads to significant disability and loss of quality of life in the ∼0.5% of the worldwide human population it affects. There is currently no cure for AS and mechanisms underlying its pathogenesis remain unclear. AS is highly genetic, with over 70% of the genetic risk being associated with the presence of HLA-B27 and endoplasmic reticulum aminopeptidase-1 (ERAP1) alleles. Furthermore, gene-gene interactions between HLA-B27 and ERAP1 AS risk alleles have recently been confirmed. Here, we demonstrate that various ERAP1 alleles can differentially mediate surface expression of antigens presented by HLA-B27 on human cells. Specifically, for all peptides tested, we found that an ERAP1 variant containing high AS risk SNPs reduced the amount of the peptide presented by HLA-B27, relative to low AS risk ERAP1 variants. These results were further validated using peptide catalysis assays in vitro, suggesting that high AS risk alleles have an enhanced catalytic activity that more rapidly destroys many HLA-B27-destined peptides, a result that correlated with decreased HLA-B27 presentation of the same peptides. These findings suggest that one mechanism underlying AS pathogenesis may involve an altered ability for AS patients harboring both HLA-B27 and high AS risk ERAP1 alleles to correctly display a variety of peptides to the adaptive arm of the immune system, potentially exposing such individuals to higher AS risk due to abnormal display of pathogen or self-derived peptides by the adaptive immune system.

β-glucan triggers spondylarthritis and Crohn's disease-like ileitis in SKG mice

OBJECTIVE

The spondylarthritides (SpA), including ankylosing spondylitis (AS), psoriatic arthritis (PsA), reactive arthritis, and arthritis associated with inflammatory bowel disease, cause chronic inflammation of the large peripheral and axial joints, eyes, skin, ileum, and colon. Genetic studies reveal common candidate genes for AS, PsA, and Crohn's disease, including IL23R, IL12B, STAT3, and CARD9, all of which are associated with interleukin-23 (IL-23) signaling downstream of the dectin 1 β-glucan receptor. In autoimmune-prone SKG mice with mutated ZAP-70, which attenuates T cell receptor signaling and increases the autoreactivity of T cells in the peripheral repertoire, IL-17-dependent inflammatory arthritis developed after dectin 1-mediated fungal infection. This study was undertaken to determine whether SKG mice injected with 1,3-β-glucan (curdlan) develop evidence of SpA, and the relationship of innate and adaptive autoimmunity to this process.

METHODS

SKG mice and control BALB/c mice were injected once with curdlan or mannan. Arthritis was scored weekly, and organs were assessed for pathologic features. Anti-IL-23 monoclonal antibodies were injected into curdlan-treated SKG mice. CD4+ T cells were transferred from curdlan-treated mice to SCID mice, and sera were analyzed for autoantibodies.

RESULTS

After systemic injection of curdlan, SKG mice developed enthesitis, wrist, ankle, and sacroiliac joint arthritis, dactylitis, plantar fasciitis, vertebral inflammation, ileitis resembling Crohn's disease, and unilateral uveitis. Mannan triggered spondylitis and arthritis. Arthritis and spondylitis were T cell- and IL-23-dependent and were transferable to SCID recipients with CD4+ T cells. SpA was associated with collagen- and proteoglycan-specific autoantibodies.

CONCLUSION

Our findings indicate that the SKG ZAP-70W163C mutation predisposes BALB/c mice to SpA, resulting from innate and adaptive autoimmunity, after systemic β-glucan or mannan exposure.

The genetic background of ankylosing spondylitis

It has long been known that the major histocompatibility complex (MHC) is essentially involved in genetic susceptibility to ankylosing spondylitis (AS). The HLA-B27 antigen has been accounted for 20 to 50% of the total genetic risk for this disease. However, susceptibility to AS cannot be fully explained by associations with the MHC. Recent studies including linkage analyses as well as candidate gene and, most recently, genome-wide association studies indicate significant associations of the interleukin-1 gene cluster, interleukin-23 receptor and ARTS1 genes as well as other possible loci with AS. In the murine model of proteoglycan-induced spondylitis, two susceptibility loci termed Pgis1 and Pgis2 were identified. Thus, AS is not a single-gene disease and the involvement of multiple non-MHC genes may account for the individual as well as geographical differences seen in AS.

Programmed cell death 1 gene polymorphisms is associated with ankylosing spondylitis in Chinese Han population

Programmed cell death 1 (PD-1) has been reported to have a genetic association in several autoimmune diseases. The aim of this study was to investigate the association of PD-1 polymorphisms and haplotypes with ankylosing spondylitis (AS) in Chinese Han population. In a case-control association study, three single-nucleotide polymorphisms (SNP), PD-1.3 G/A, PD-1.5 C/T and PD-1.9 T/C, were genotyped in 216 AS patients and 264 healthy controls using polymerase chain reaction-restriction fragment length polymorphism assay. All genotype distributions in the patients and in the controls were in Hardy-Weinberg equilibrium. The associations of genotypes and alleles with AS were analyzed. The genotype distributions of PD-1.9 were significantly different between the patients with AS and the controls (P = 0.025). The frequencies of TC genotype and T allele of PD-1.9 were higher in the patients than those in the controls (P = 0.026 and 0.004). No association for PD-1.5 in AS was found, and PD-1.3 was non-polymorphic in Chinese Han population. Moreover, the frequency of the CT haplotype (PD-1.5 C/T, PD-1.9 T/C) was significantly higher in AS patients than the controls (21.6 vs. 13.9%, P = 0.002). The CC haplotype was more common in the controls than in the patients (57.1 vs. 44.6%, P = 0.000). The results support a genetic association between the PD-1 polymorphism and susceptibility to AS in Chinese Han population.

Reactive arthritis: clinical aspects and medical management

Reactive arthritis (ReA) is an inflammatory arthritis that arises after certain gastrointestinal or genitourinary infections, representing a classic interplay between host and environment. It belongs to the group of arthritidies known as the spondyloarthropathies. The classic syndrome is a triad of symptoms, including the urethra, conjunctiva, and synovium; however, the majority of patients do not present with this triad. Diagnostic criteria for ReA exist, but data suggest new criteria are needed. Epidemiologic and prospective studies have been difficult to perform because of over-reliance on the complete classic triad of symptoms and the different terms and eponyms used. Studies assessing various treatment strategies are ongoing.

Animal models of spondyloarthritis

Animal models are available for the study of several different aspects of spondyloarthritis. The models include naturally occurring spontaneous disorders in primates and rodents, spontaneous disorders in transgenic or gene-deleted rodents and induced disorders in rodents. Areas of investigation to which these models contribute include the role HLA-B27, processes of spinal and peripheral joint inflammation and calcification, immune responses to candidate antigens and the role of TNF.

Bone and cartilage turnover markers, bone mineral density, and radiographic damage in men with ankylosing spondylitis

PURPOSE

To determine the levels of bone and cartilage turnover markers in men with ankylosing spondylitis (AS) and to investigate their associations with disease activity, bone mineral density, and radiographic damage of the spine.

PATIENTS AND METHODS

This cross-sectional study enrolled 35 men with newly diagnosed AS. The bone mineral densities (BMD) of their lumbar spines and proximal femurs, Bath AS Disease Activity Index (BASDAI), and Bath AS Radiographic Index (BASRI) were evaluated. Urinary C-terminal telopeptide fragments of type I collagen (CTX-I) and type II collagen (CTX-II) levels were determined by enzyme-linked immunosorbent assay, and serum levels of bone-specific alkaline phosphatase (BALP) and osteocalcin were determined by an enzyme immunoassay. Levels of biochemical markers were compared with those of 70 age-matched healthy men.

RESULTS

Patients with AS had significantly higher mean urinary CTX-I and CTX-II levels than control subjects (p<0.05). Elevated urinary CTX-I levels correlated well with BASDAI, femoral BMD, and femoral T score (p<0.05), and elevated urinary CTX-II levels correlated well with spinal BASRI (p<0.05) in patients with AS. Mean serum BALP and osteocalcin levels did not differ between patients and controls and did not show any significant correlations with BMD, BASDAI, or BASRI in men with AS.

CONCLUSIONS

Elevated CTX-I reflects disease activity and loss of femoral BMD while elevated CTX-II levels correlate well with radiographic damage of the spine, suggesting the usefulness of these markers for monitoring disease activity, loss of BMD, and radiographic damage in men with AS.

The pathogenesis of ankylosing spondylitis

✓ Ankylosing spondylitis (AS) is a chronic inflammatory disease that can cause significant functional complications by affecting the sacroiliac joints and axial skeleton. Despite a longstanding knowledge about the familial associations of this disease, particularly among patients positive for human leukocyte antigen (HLA)–B27, the fundamental pathogenetic mechanism by which this disease arises in genetically susceptible individuals remains ill defined. Furthermore, the molecular predilection for characteristic articular site involvement remains under ongoing investigation. Current theories about the HLA-B27 association range from the presentation of novel arthritogenic peptides, to abnormal autoimmune stimulation, to anomalous microbial tolerance. The immune effectors of this damage include CD4+, CD8+, and natural killer cells, with marked heterogeneity at different sites. Biomechanical stresses may trigger this disease by exposing the body to previously immune-sequestered autoantigens or by providing a route for bacterial seeding. Environmental triggers such as infection have not been definitively established but may represent a primary pathogenic step in a molecular-mimicry process. In this article, the authors review the current literature on the origin and pathophysiology of AS, focusing on genetic and molecular associations, consequent pathomechanisms, and associated triggers. An improved understanding of the sequence of molecular events that predispose and initiate the onset of this disease will allow for more specific and targeted therapy and better avoidance of the significant side effects of systemic immunomodulation.

Interaction of HLA-B27 homodimers with KIR3DL1 and KIR3DL2, unlike HLA-B27 heterotrimers, is independent of the sequence of bound peptide

HLA-B27 can form beta-2 microglobulin (beta2m)-associated heterotrimers (HLA-B27) and beta2m-free homodimers (B27(2)). Here, we study the role of complexed peptide in the interaction of these forms of B27 with the killer cell immunoglobulin (Ig)-like receptors KIR3DL1 and KIR3DL2 and with Ig-like transcripts LILRB1 and LILRB2. HLA-B27 tetramers complexed with three of five different naturally processed self peptides and three of seven pathogen-derived epitopes bound to KIR3DL1-expressing transfectants and NK cells. Heterotrimeric complexes containing peptides with charged amino acids at position 8 did not bind to KIR3DL1; however, studies with analogue peptides demonstrated that these are not the only peptide residues involved in binding. KIR3DL1 ligation by HLA-B27 inhibited NK cell IFN-gamma production in a peptide-dependent fashion. B27 but not HLA-A2, B7 or B57 heavy chains formed homodimers in the presence of peptide epitopes. B27(2) bound to KIR3DL1, KIR3DL2 and LILRB2 but not LILRB1. KIR3DL2 ligation by B27(2) inhibited NK and T cell IFN-gamma production. By contrast with HLA heterotrimers, B27(2) binding to KIR did not depend on the sequence of the bound peptide. Differences in KIR binding to classical HLA and B27(2) could be involved in the pathogenesis of spondyloarthritis.

Identification of disease-associated proteins by proteomic approach in ankylosing spondylitis

Ankylosing spondylitis (AS) is a chronic systemic inflammatory disorder of the axial skeleton and shows significant inherited susceptibility. Auto-immune responses have been traditionally considered as a putative pathogenetic event in AS. However, no consistent self-antigen has been identified to responsible for the disorders in AS to this day. In this study, serum protein profiles of AS patients and healthy controls from a large Chinese AS family were investigated by two dimensional electrophoresis analysis. A group of four highly expressed protein spots was observed in all AS patients' profiles and subsequently identified as isoforms of haptoglobin precursor (pre-Hp) by ESI-Q-TOF MS/MS. Increased expression of haptoglobin precursor were also observed in sera of sporadic AS patients. Moreover, bioinformatics analysis revealed epitopes derived from haptoglobin precursor with high affinity binding to HLA-B( *)2705, a primary subtype associated with AS. These results indicate that pre-Hp may be involved in the pathogenesis of AS.

Reactive arthritis: defined etiologies, emerging pathophysiology, and unresolved treatment

ReA is unique in that it is one of the few disease states of which there is a known trigger. This insight into disease initiation has led to great advances in the pathophysiology. Despite this detailed knowledge, the proper treatment remains elusive. In the years to come it is possible that the specific treatment will be dictated by the triggering microbe.

The pathogenetic role of HLA-B27 and its subtypes

The strong association between HLA-B27 and ankylosing spondylitis has been known for more than 33 years, but the enigma of the pathogenetic role of the gene and its product has not yet been solved. Ongoing studies have produced evidence supporting different theories to explain this association, and structural and functional studies of HLA-B27 allele products at molecular level have provided information of broad and multidisciplinary value and disclosed new avenues leading to autoimmunity and immune disregulation.

HLA class I transgenic mice: development, utilisation and improvement

Classical major histocompatibility complex (MHC) class I antigens are trimeric molecules found on the surface of nucleated cells in all jawed vertebrates. MHC I are recognised by two families of receptors: clonotypic T cell receptors expressed on the surface of CD8+ cytotoxic T lymphocytes (CTLs), and monomorphic receptors expressed by both natural killer cells and CTLs. The production of MHC I molecules within the cells is a sequential process performed with the help of interacting proteins: proteases, chaperones, transporters and so on. Although largely homologous in their structure, organisation and function, the human and mouse MHC I antigen processing and presentation machineries show fine differences. Transgenesis and 'knockout' or 'knock-in' technologies permit the addition of relevant human genes or the replacement of mouse genes by their human orthologues in order to produce immunologically humanised mice. Such experimental animals are especially relevant for the comparative evaluation of immunotherapies and for the characterisation of MHC I peptide epitopes. This review presents the similarities and differences between mouse and human MHC I antigen processing machinery, and describes the development and utilisation of improving mouse models of human cytotoxic T cell immunity.

Spondyloarthropathy: disease at the crossroads of immunity

Up until recently, the prevailing paradigm relating to spondyloarthropathy (SpA) pathogenesis was that they were human leukocyte antigen (HLA)-associated, T-cell-driven autoimmune diseases. This view is now being questioned. Careful studies of well-characterised cohorts of patients with SpA, including detailed analysis of involved tissue, together with clinical trials of targeted treatments, in particular anti-tumour necrosis factor (TNF) therapies, have contributed enormously to both interest in and understanding of disease pathogenesis. In this chapter, our current knowledge and understanding of the relative contributions of the components of the innate and adaptive arms of the immune response to SpA pathogenesis is reviewed. It is clear that both arms of the immune response are involved and inter-dependent in SpA. With continued emphasis on discovery research, including detailed analysis of novel therapeutic interventions, significant additional breakthroughs in SpA are likely to be forthcoming.

Pathogenesis of spondyloarthritis: Insights from synovial membrane studies

Here, we review histopathologic studies of the cellular and molecular pathways of spondyloarthritis (SpA) synovial inflammation. In contrast with lymphocytes, specific macrophage subsets and polymorphonuclear cells selectively increase in SpA synovitis, correlate with global disease activity, decrease rapidly upon effective treatment with tumor necrosis factor (TNF)-alpha blockers, and serve as valuable biomarkers for treatment response in SpA. Functionally, increased Toll-like receptor triggering may be responsible for the proinflammatory response of these cells. Therefore, we propose that an exaggerated response of the innate immune system in genetically susceptible patients rather than a classic, lymphocyte-mediated autoimmune process is involved in the pathogenesis of SpA.

Experimental spondyloarthropathies: Animal models of ankylosing spondylitis

Spondyloarthropathies (SpAs), including ankylosing spondylitis, are chronic inflammatory diseases of the axial skeleton. Genomic scans of SpA families revealed the overwhelming complexity of the disease, which appears to be under the control of over 20 chromosome loci, including the major SpA gene HLA-B27 within class I of the major histocompatibility complex (MHC). Animal models confirmed the primary role of MHC in SpA susceptibility and supported the hypothesis that certain enterobacterial infections can trigger SpA. Immunization of mice with proteoglycan aggrecan also can provoke SpA, thus providing the opportunity to study genetic and clinical details of the disease initiation.

The genetics of spondyloarthropathies

The spondyloarthropathies constitute a group of inflammatory joint diseases linked by shared characteristics that include a strong common genetic background. Genetic factors include major histocompatibility complex (MHC) genes, among which HLA-B27 contributes 30% of the overall genetic susceptibility to spondyloarthropathies, and non-MHC genes, none of which have been identified to date. Genome screens have identified regions that may contain susceptibility genes for spondyloarthropathies. In particular, a locus on the long arm of chromosome 9 (9q31-34) was identified by two groups working independently from each other. Studies using the candidate gene approach ruled out a role for most of the tested genes, including CARD15/NOD2. However, several independent groups have reported significant associations between ankylosing spondylitis and the IL-1 gene cluster on the long arm of chromosome 2.

[Enthesis as a target element in spondylarthritides]

Enthesis is a structure frequently involved in spondyloarthritides. According to a recent hypothesis, it may play a key role in the pathogenesis of these entities. The present review discusses the most important aspects of current knowledge of enthesis, such as its anatomy and the extracellular matrix components present within it. Clinical evaluation and the new imaging techniques (magnetic resonance imaging and ultrasound) that complement its evaluation will be briefly described. Immunohistological studies as well as animal models developed with enthesis molecules underline the importance of enthesis in the pathogenesis of spondyloarthritides. Finally, the latest research assessing the T cell response to enthesis components in patients with ankylosing spondylitis will be reviewed.

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.

Pathogenesis of ankylosing spondylitis and reactive arthritis

PURPOSE OF REVIEW

The hallmark of ankylosing spondylitis is acute and chronic spinal inflammation initiating in the sacroiliac joints, often coupled with enthesitis, presenting as chronic inflammation at the sites of ligamentous and tendinous insertions into bone. Peripheral joint synovitis can be a prominent feature as well. Reactive arthritis is a sterile synovitis arising after an extra-articular infection of enteric or urogenital tracts. HLA-B27 has been known for about the past 30 years to be associated with ankylosing spondylitis and reactive arthritis, but the pathogenesis of ankylosing spondylitis and reactive arthritis is still not well defined. Although the clinical manifestations of ankylosing spondylitis and reactive arthritis may differ, this update discusses the two diseases together and focuses on recent evidence in both.

RECENT FINDINGS

With respect to HLA-B27 several recent studies address arthritogenic peptides, molecular mimicry, and aberrant forms of B27. Several candidate genes in addition to B27 have been implicated in recent genetic studies. With respect to bacterial infection, recent findings in bacterial antigenicity, host response through interactions of antigen-presenting cells, T cells, and cytokines are providing new understanding of host-pathogen interactions and the pathogenesis of arthritis. Endogenous host factors such as proteoglycans may play a role as autoantigens and contribute to chronic inflammation on that basis.

SUMMARY

Recent advances provide additional new insights into distinct pathogenetic mechanisms in AS and ReA that arise from a complex interplay between genetic factors including HLA-B27 and environmental factors.

Genetic control of experimental spondylarthropathy

OBJECTIVE

To characterize experimentally induced spondylarthropathy (SpA) in arthritis-susceptible inbred mice and in their F(1) and F(2) hybrid generations of susceptible and resistant mouse strains.

METHODS

SpA was induced in susceptible BALB/c and C3H/HeJCr (C3H) strains of mice, and in their F(1) and F(2) generations derived from intercrosses with arthritis- and/or spondylitis-resistant DBA/2 and DBA/1 parent strains, by systemic immunization with cartilage proteoglycan (PG) aggrecan. The incidence and severity of PG-induced spondylitis (PGIS) were scored histologically, and these scores for spine involvement were correlated with serum antibody and cytokine levels and with in vitro T cell responses to cartilage PG.

RESULTS

PGIS was induced by systemic immunization with cartilage PG in adjuvant, and approximately 60-70% of susceptible mouse strains and their F(2) hybrids developed spondylitis either with or without arthritis. Adjuvants, particularly those activating the innate immune system and enforcing the Th1 dominance, had significant effects on the outcome and progression of SpA. The DBA/1 strain appeared to carry genes protecting this strain and its F(1) and F(2) hybrids from spondylitis, whereas the DBA/2 strain, although resistant to PGIS, harbored genes permitting PGIS in its hybrid generations. Arthritis- and/or spondylitis-susceptible BALB/c and C3H parent strains and their F(2) hybrids exhibited the highest incidence and severity of spondylitis.

CONCLUSION

PGIS, a murine model of autoimmune spondylitis, shows similarities to ankylosing spondylitis. Segregation of susceptibility to PG-induced arthritis (PGIA) from that to PGIS in different genetic crosses suggests that PGIA and PGIS are separate diseases. Therefore, this model allows for the elucidation of genetic components involved in the etiology of SpA, independent of those controlling the susceptibility to PGIA.