POS0031 FUNCTIONAL GENOMICS INVESTIGATION OF THE ANKYLOSING SPONDYLITIS ASSOCIATED LOCUS RUNX3

Background

Ankylosing Spondylitis (AS), is a highly heritable disease with >100 genomic loci incriminated. Among these, RUNX3, a transcription factor (TF) involved in diverse immunological processes, is robustly (10−15) associated. [1] We have extensively investigated the single nucleotide polymorphism (SNP) rs4648889 located in a 2kb regulatory locus upstream of the RUNX3 promoter. We have demonstrated that the association between AS and this SNP can be explained by allele-specific effects on TF recruitment (including IRF4, IRF5 and the NuRD complex) that alter gene expression, specifically in CD8+ T-cells, and having a crucial role in CD8+ T-cells function. [2, 3]

Further, we have recently shown a clear chromatin looping event between the region encompassing SNP rs4648889 and the RUNX3 promoter confirming the functional role of this genetic variant. [4]

Objectives

The purpose of this work is: (1) to better characterise the chromatin looping landscape of the whole AS-associated RUNX3 genomic locus and (2) to determine the single-cell expression of the RUNX3-related genes identified previously [2, 3] in CD8+ T-cells lymphocytes.

Methods

(1) Chromosome conformation capture (3C) technique followed by qPCR was performed to define the chromatin looping events at the RUNX3 genomic locus in relevant cell lines, including Jurkat T-cells and U937 monocytes-like cells. (2) 10X Chromium single-cell (sc) sequencing was performed to define RUNX3 and RUNX3-related genes expression profile in CD8+ T cells obtained from AS cases.

Results

(1) In addition to the recent results published, [4] 3C-qPCR experiments revealed a high interaction frequency between the distal promoter of RUNX3 and an intronic region (called Int2), overlapping open chromatin and TF binding sites. This was highly reproducible in both cell lines analysed. (2) Four different clusters were identified in CD8+ T-cells obtained from AS peripheral blood via 10x sc-seq based on the expression of RUNX3. Five other genes (TBX21, EOMES, CHD4, IRF5 and IKZF3) previously identified [2] were considered: cluster 1 showed a strong co-expression for RUNX3, IKZF3, CHD4 and EOMES. Further analysis is required to better characterize this subpopulation.

Conclusion

The AS-associated RUNX3 genomic locus has a plausible functional role in AS, probably by regulating gene transcription and DNA looping. These observations are critically important in defining dysregulated pathways and potential therapeutic drug targets.

References

[1]IGAS et al. Nat Genet. 2013 Jul;45(7):730-8.

[2]Vecellio M. et al, Ann Rheum Dis. 2016 Aug;75(8):1534-40.

[3]Vecellio M. et al, Arthritis Rheumatol 2020. doi: 10.1002/art.41628.

[4]Cohen CJ. et al, Front Genet 2022 doi.org/10.3389/fgene.2021.741867.

Disclosure of Interests

Carla Cohen: None declared, Davide Simone: None declared, Carlo Selmi Speakers bureau: Speakers fee (AbbVie, Amgen, Alfa-Wassermann, Biogen, Celgene, Eli-Lilly, Gilead, Janssen, MSD, Novartis, Pfizer, Sanofi-Genzyme), Consultant of: Consulting (AbbVie, Amgen, Alfa-Wassermann, Biogen, Celgene, Eli-Lilly, Gilead, Janssen, MSD, Novartis, Pfizer, Sanofi-Genzyme), Grant/research support from: Research support (AbbVie, Amgen, Janssen, Pfizer), aul Bowness Grant/research support from: Regeneron, Celgene/BMS and GSK, Paul Bryan Wordsworth: None declared, Matteo Vecellio: None declared

OP0032 SINGLE CELL ANALYSIS OF SPONDYLOARTHRITIS REGULATORY T CELLS IDENTIFIES DISTINCT SYNOVIAL GENE EXPRESSION PATTERNS AND CLONAL FATES

Background:

Regulatory T cells (Tregs) play an important role in controlling inflammation and limiting autoimmunity, but their phenotypes at inflammatory sites in human disease are poorly understood. Whilst the phenotype and transcriptional profile of Tregs have been studied in some immune mediated conditions, they have been little studied (especially at the single cell level) in synovial fluid in the course of inflammatory arthritis. In Spondyloarthritis (SpA), in particular, where pathogenesis and inflammation is driven by dysregulated effector immunity, the role of the regulatory arm of immunity is largely unknown.

Objectives:

We aimed to draw an atlas of Tregs in the context of SpA joint inflammation using single cell RNA sequencing of blood and SF Tregs of patients with Ankylosing Spondylitis (AS) and Psoriatic Arthritis (PsA). Functionally distinct specialised Treg subtypes, and specific changes in transcriptional profile occurring in synovial fluid Tregs, providing an insight on Treg adaptation during inflammation. Furthermore, by coupling gene expression analysis with TCR sequencing, we aimed to describe clonally expanded and likely antigen-driven Tregs in the SF.

Methods:

Fluorescent activated cell sorting (FACS) was used to isolate 13,400 memory CD3+ CD45RA-ve CD25 + 127low Tregs from the blood and synovial fluid (SF) of 2 patients with HLA-B27+ AS presenting with active knee arthritis. Single-cell RNA sequencing (scRNA-seq) using 5’ V(D)J 10x Genomics technology allowed both transcriptional definition of Tregs, and exploration of their immune TCR repertoire. Findings were compared to >3,000 SF and blood Tregs from 3 patients with olygoarticular PsA 1. Multicolor flow cytometry and in vitro cell-based assays using patient-derived cells were used to confirm and expand, at protein and functional level, the findings that emerged from the gene expression analysis.

Results:

We report a large scRNAseq dataset (approx. 17,000 cells) comparing Tregs from SpA blood and joints. We identify multiple Treg clusters with distinct transcriptomic profiles, including, among others, a regulatory CD8+ subset expressing cytotoxic markers/genes, and a Th17-like RORC+ Treg subset characterized by IL-10 and LAG-3 expression. Synovial Tregs show upregulation of interferon signature and TNF receptor superfamily genes, and marked clonal expansion, consistent with tissue adaptation and antigen contact respectively. Individual synovial Treg clones map to different clusters indicating cell fate divergence. Finally, we demonstrate that LAG-3 directly inhibits IL-12/23 and TNF secretion by patient-derived monocytes, a mechanism with translational potential in SpA.

Conclusion:

Our detailed characterization of Tregs at an important inflammatory site illustrates the marked specialization of Treg subpopulations and identifies a broad transcriptional profile upregulated across all synovial regulatory cells. Our TCR analysis provides evidence of Treg clonal expansion, which may be driven by antigen, and confirms functional specialisation of individual clones. We also propose a new insight into a Treg functional mechanism through LAG-3 that suggests a novel therapeutic approach to immune-driven diseases.

References:

[1]Penkava et al., Nature Communications, 2020

Disclosure of Interests:

Davide Simone: None declared, Frank Penkava: None declared, Anna Ridley: None declared, Stephen Sansom: None declared, Hussein Al Mossawi Employee of: UCB, Paul Bowness Grant/research support from: Regeneron, Celgene/BMS and GSK

Is Behçet's disease a 'class 1-opathy'? The role of HLA-B*51 in the pathogenesis of Behçet's disease

The association between carriage of the human leucocyte antigen (HLA)-B*51 allele and development of Behçet's disease (BD) has been known since the early 1970s, but the exact mechanisms responsible for its role in pathogenesis remain much-debated. In an effort to explain the disease process, it has been suggested that BD constitutes one of a newly termed group of diseases, the 'MHC-I-opathies'. Other MHC-I-opathies include ankylosing spondylitis and HLA-B*27-associated spondyloarthropathies and HLA-C*0602-associated skin psoriasis. Recent work analysing the peptidome of HLA-B*51 suggests that altered peptide presentation by HLA-B*51 is vital to the disease process. In this review, we argue that immune receptor interactions with HLA-B*51 or the HLA-B*51-peptide complex could lead to development of inflammation in BD. The evidence for CD8⁺ T cell involvement is weak, and based on emerging studies it seems more likely that natural killer (NK) or other cell interactions, perhaps mediated by leucocyte immunoglobulin-like receptor (LILR) or killer immunoglobulin-like receptor (KIR) receptors, are culpable in pathogenesis. HLA misfolding leading directly to inflammation is another hypothesis for BD pathogenesis that deserves greater investigation. Ultimately, greater understanding of HLA-B*51's unique role in BD will probably lead to improved development of therapeutic strategies.

miR-10b-5p is a novel Th17 regulator present in Th17 cells from ankylosing spondylitis

OBJECTIVE

To determine the microRNA (miR) signature in ankylosing spondylitis (AS) T helper (Th)17 cells.

METHODS

Interleukin (IL)-17A-producing CD4+ T cells from patients with AS and healthy controls were FACS-sorted for miR sequencing and qPCR validation. miR-10b function was determined by miR mimic expression followed by cytokine measurement, transcriptome analysis, qPCR and luciferase assays.

RESULTS

AS Th17 cells exhibited a miR signature characterised by upregulation of miR-155-5p, miR-210-3p and miR-10b. miR-10b has not been described previously in Th17 cells and was selected for further characterisation. miR-10b is transiently induced in in vitro differentiated Th17 cells. Transcriptome, qPCR and luciferase assays suggest that MAP3K7 is targeted by miR-10b. Both miR-10b overexpression and MAP3K7 silencing inhibited production of IL-17A by both total CD4 and differentiating Th17 cells.

CONCLUSIONS

AS Th17 cells have a specific miR signature and upregulate miR-10b in vitro. Our data suggest that miR-10b is upregulated by proinflammatory cytokines and may act as a feedback loop to suppress IL-17A by targeting MAP3K7. miR-10b is a potential therapeutic candidate to suppress pathogenic Th17 cell function in patients with AS.

The interleukin (IL)-23/IL-17 axis in ankylosing spondylitis: new advances and potentials for treatment

Ankylosing spondylitis (AS), the most common form of spondyloarthropathy, is a chronic, progressive multi-system inflammatory disorder characteristically affecting the sacroiliac joints and axial skeleton. Although the exact mechanisms underlying the pathogenesis of AS remain to be elucidated, the presence of human leucocyte antigen (HLA)-B27 is known to markedly increase its risk of development. Current treatments include non-steroidal anti-inflammatory drugs (NSAIDs) and tumour necrosis factor (TNF) blockers. In recent years, the interleukin (IL)-23/IL-17 pathway has been shown to have significance in the pathogenesis of AS and treatment modalities targeting this pathway have been shown to be beneficial in various other inflammatory conditions. This review provides an overview of the IL-23/IL-17 pathway in the pathogenesis of AS and summarizes new potential treatments for AS and related inflammatory diseases.

Ankylosing spondylitis confers substantially increased risk of clinical spine fractures: a nationwide case-control study

Ankylosing spondylitis (AS) leads to osteopenia/osteoporosis and spine rigidity. We conducted a case-control study and found that AS-affected patients have a 5-fold and 50% increased risk of clinical spine and all clinical fractures, respectively. Excess risk of both is highest in the first years and warrants an early bone health assessment after diagnosis.

INTRODUCTION

Ankylosing spondylitis (AS) is related to spine rigidity and reduced bone mass, but data on its impact on fracture risk are scarce. We aimed to study the association between AS and clinical fractures using a case-control design.

METHODS

From the Danish Health Registries, we identified all subjects who sustained a fracture in the year 2000 (cases) and matched up to three controls by year of birth, gender and region. Clinically diagnosed AS was identified using International Classification of Diseases, 8th revision (ICD-8; 71249), and International Classification of Diseases, 10th revision (ICD-10; M45) codes. We also studied the impact of AS duration. Conditional logistic regression was used to estimate crude and adjusted odds ratios (ORs) for non-traumatic fractures (any site, clinical spine and non-vertebral) according to AS status and time since AS diagnosis. Multivariate models were adjusted for fracture history, socio-economic status, previous medical consultations, alcoholism and use of oral glucocorticoids.

RESULTS

We identified 139/124,655 (0.11%) AS fracture cases, compared to 271/373,962 (0.07%) AS controls. Unadjusted (age- and gender-matched) odds ratio (OR) were 1.54 [95% confidence interval (95%CI) 1.26-1.89] for any fracture, 5.42 [2.50-11.70] for spine and 1.39 [1.12-1.73] for non-vertebral fracture. The risk peaked in the first 2.5 years following AS diagnosis: OR 2.69 [1.84-3.92] for any fracture.

CONCLUSIONS

Patients with AS have a 5-fold higher risk of clinical spine fracture and a 35% increased risk of non-vertebral fracture. This excess risk peaks early, in the first 2.5 years of AS disease. Patients should be assessed for fracture risk early after AS diagnosis.

Ankylosing spondylitis monocytes show upregulation of proteins involved in inflammation and the ubiquitin proteasome pathway

OBJECTIVES

To determine if peripheral blood monocytes from patients with ankylosing spondylitis (AS) differed in protein expression compared to rheumatoid arthritis (RA) and healthy controls (HC).

METHODS

Monocyte protein expression was characterised by 2D gel electrophoresis and by label-free quantitative expression profiling, using nano-ultra performance liquid chromatography coupled to electrospray ionisation mass spectrometry (ESI-MS(E), where (E) refers to low/high collision energy switching). Data sets were analysed using the Waters expression profiling system and Ingenuity pathway analysis (IPA).

RESULTS

Two-dimensional gel electrophoresis showed upregulation of proteasomal constituents in AS monocytes, including the beta subunit of proteasome activator (PA)28. Monocyte expression profiling and IPA showed that significant changes in protein expression within the ubiquitin proteasome pathway (UPP) were restricted to AS monocytes. Statistically significant differences in protein expression involving the leucocyte extravasation, vascular endothelial growth factor, integrin and Toll-like receptor signalling pathways were seen in AS and RA monocytes compared to healthy controls. No evidence of upregulation of proteins involved in the endoplasmic reticulum stress response pathway was found in either AS or RA monocytes. Finally, the PA28 complex was shown to increase the generation of human leucocyte antigen (HLA)-B27 antigenic epitopes by the proteasome in vitro.

CONCLUSIONS

Our proteomic analyses support the hypothesis that monocytes play an important role in the pathogenesis of AS and RA, and further suggest a specific role in AS for the UPP. Quantitative proteomic expression profiling constitutes a powerful new tool for rheumatology research.

Consistent patterns of expression of HLA class I free heavy chains in healthy individuals and raised expression in spondyloarthropathy patients point to physiological and pathological roles

OBJECTIVES

Major histocompatibility complex class I (MHC-I) proteins exist at the cell surface in antigen presenting forms and as beta2m-independent free heavy chains (FHCs). FHCs have been implicated in spondyloarthritis, but little is known about their expression in healthy individuals. We studied FHC expression on various human cell types, comparing spondyloarthropathy patients with healthy and rheumatoid arthritis (RA) patient controls.

METHODS

MHC-I expression was analysed by flow cytometry. FHC levels were normalized for overall MHC-I to generate a relative expression level. Relative FHC levels were analysed for peripheral blood and trophoblast samples from healthy volunteers, RA and spondyloarthropathy patients. Macrophages and dendritic cells were cultured in vitro to analyse changes following activation. Peripheral blood leucocytes from patients with ankylosing spondylitis (AS) and RA were treated with inflammatory stimuli and subsequent alterations in their relative FHC levels were analysed.

RESULTS

We found consistent patterns of differential relative FHC expression across lymphocyte subpopulations and particularly high expression on extravillous trophoblast. FHCs were present at higher levels in a reactive arthritis (ReA) population than in healthy controls and RA patients; differences not merely due to the presence of Human Leucocyte Antigen (HLA) B27. Treatment of leucocytes from arthritic patients with bacterial lipopolysaccharide resulted in significant up-regulation of FHC compared with an HLA B27+ control population.

CONCLUSIONS

Our findings define normal levels and tissue expression of FHCs, and support the hypothesis that disregulation of heavy chain expression may play a pathogenic role in spondyloarthropathy.

A highly restricted T-cell receptor dominates the CD8+ T-cell response to parvovirus B19 infection in HLA-A*2402-positive individuals

Six of seven HLA-A*2402-positive individuals with acute parvovirus B19 infections made vigorous CD8-positive cytotoxic T-cell (CTL) responses to the viral epitope FYTPLADQF. All responders showed highly focused T-cell receptor (TCR) usage, using almost exclusively BV5.1. The BV5.1 TCR dominated the acute response, was maintained over time, and was also used by a remotely infected individual. Nine CTL clones and two oligoclonal lines obtained from three unrelated individuals used BV5.1, BJ2.1, and a conserved TCR CDR3 of nine amino acids. This commonly recognized epitope is likely important in long-term protective immunity and should be included in vaccine design.

Expansion and enhanced survival of natural killer cells expressing the killer immunoglobulin-like receptor KIR3DL2 in spondylarthritis

OBJECTIVE

The spondylarthritides (SpA) are strongly associated with possession of HLA-B27. We hypothesized that the expression of abnormal forms of HLA-B27 in SpA may have a pathogenic role through interaction with cells bearing natural killer (NK) receptors, in particular, killer immunoglobulin-like receptor (KIR) KIR3DL2, a receptor for HLA-B27 homodimer (B27(2)). We therefore undertook the present study to determine the number and function of NK and T cells bearing KIR3DL2 in SpA.

METHODS

Expression of KIR3DL2 on NK and T cells was quantified in peripheral blood (PB) from 35 patients with SpA and 5 patients with juvenile enthesitis-related arthritis (juvenile ERA); samples were compared with samples from healthy and rheumatoid arthritis (RA) controls. Paired synovial fluid (SF) was studied where available. Expression of other KIRs as well as activation, memory, and homing markers on KIR3DL2+ NK and T cells was quantified. NK cell survival was assessed using the apoptotic markers annexin V and 7-aminoactinomycin D, and cytotoxicity by (51)Cr release assay.

RESULTS

In SpA, an increased number of PB and SF NK and CD4+ T cells expressed the KIR3DL2 receptor compared with controls. In ERA, KIR3DL2 expression was increased in PB and SF CD4 T cells (and SF NK cells) compared with RA controls. KIR3DL2+ NK cells had an activated phenotype, and were protected from apoptosis by culture with a cell line expressing B27(2). SpA PB mononuclear NK cells from SpA patients showed greater cytotoxicity than those from controls.

CONCLUSION

KIR3DL2 expression on NK cells and CD4 lymphocytes is increased in SpA and ERA. These cells are activated and may have a pathogenic role.

HLA-B27 and disease pathogenesis: new structural and functional insights

The human leukocyte antigen class I allele HLA-B27 is a major histocompatibility complex (MHC) antigen that is strongly associated with the spondyloarthritic group of human rheumatic diseases, the most commmon of which is ankylosing spondylitis. Although the mechanism underlying this disease association remains unknown, numerous theories have been proposed. Much more is known of the natural role of HLA-B27 in binding and presenting antigenic peptides to T cells. The ‘arthritogenic peptide hypothesis’ suggests that the role of HLA-B27 in disease relates to its specificity for binding certain peptides. Recently, it has also been shown that HLA-B27 has an unusual cell biology and can adopt a novel homodimeric structure. In this review, a molecular model of the HLA-B27 homodimer is presented and the possible pathogenic significance of such a structure is discussed.

Conserved TCR beta chain usage in reactive arthritis; evidence for selection by a putative HLA-B27-associated autoantigen

Previous work suggested that expanded CD8+ T-cell clones in the synovial fluid (SF) of HLA-B27+ patients with reactive arthritis (ReA) preferentially use the T-cell receptor variable region (TCRBV) 1, similar CDR3 sequences, and joining region (BJ) 2S3. To determine the range of conservation and disease-specificity of CDR3-sequences, we analyzed the TCRBV1-J2S3 repertoire from 33 healthy HLA-B27+ individuals, patients with various types of spondyloarthropathies (SpA), and with rheumatoid arthritis (RA) by CDR3-spectratyping. After collection and database submission of all available TCRB-CDR3 from HLA-B27-restricted or SpA-derived T cells, we systematically screened the entire human sequence database for sequences similar to the B27/SpA-related CDR3. Spectratyping revealed expanded T cell clones using conserved TCRBV1J2S3 in the SF from 5/6 of the patients with acute ReA but not among the controls. In database searches, 50 HLA-B27 or SpA-related CDR3-sequences generated similar clusters of matched sequences, and matched reciprocally. Identical or closely related sequences were identified in 15 different individuals and a canonical ReA-associated TCRB was defined [BV1-CASSVG(V/I/L)(Y/F)STDTQYF-J2S3]. All but one patient-derived conserved sequences originated from acute stage ReA-patients, and were not present among approximately 3800 other human TCRB sequences in the database. Five of the conserved sequences originated from T cell clones that recognized uninfected cells in an HLA-B27-restricted fashion, implying a role of HLA-B27-restricted CD8+ T cells specific for a ubiquitous self- or cross-reactive microbial determinant in the early phase of ReA. Related sequences were independently identified in four different laboratories. The consensus TCRB motif could be a helpful diagnostic marker in HLA-B27-associated 'undifferentiated arthritis'.

HLA B27 in health and disease: a double-edged sword?

The strong association of the HLA class 1 allele HLA B27 with ankylosing spondylitis (AS) has been recognized for over 25 yr, however the pathogenic mechanism linking HLA B27 with AS and other spondyloarthropathies remains a mystery. We now know that the principal natural function of HLA B27 is an immunologic one, namely to bind antigenic peptides and then present them to T lymphocytes. I have shown that HLA B27 functions as an excellent antigen-presenting molecule in both spondyloarthropathy patients and healthy individuals. A working molecular model of how T cells recognize HLA B27 has been generated and tested. Evidence that T cells have a role in spondyloarthritis has also been found. First, expanded populations of T lymphocytes were found in both the blood and synovial fluid of patients with reactive arthritis (ReA). Secondly, a strong cytotoxic T-cell response to an HLA B27-restricted peptide epitope from Chlamydia trachomatis was found in a patient with ReA. This peptide, derived from a bacterium known to trigger ReA, is thus a candidate 'arthritogenic' peptide. We have also found evidence that HLA B27 has an unusual cell biology compared with other HLA molecules. HLA B27 demonstrates an unusual ability to form heavy chain homodimers in vitro. Dimerization is dependent upon disulphide bonding through an unpaired cysteine at position 67. Remarkably these dimers lack beta2 microglobulin, previously thought to be an essential component of all mature MHC class 1 molecules. HLA B27 homodimer formation has also been demonstrated in certain cell lines in vivo, and preliminary data suggest that significant numbers of T cells from patients with spondyloarthropathy express a ligand for HLA B27 homodimers. These findings have extended our understanding of the beneficial immunologic function of HLA B27, and have also led us to propose the testable new hypothesis that HLA B27 heavy chain dimerization may be involved in the pathogenesis of spondyloarthritis.

The quantity of naturally processed peptides stably bound by HLA-A*0201 is significantly reduced in the absence of tapasin

Tapasin plays a critical role in promoting peptide binding by major histocompatibility complex (MHC) class I molecules in the endoplasmic reticulum. In its absence, cell surface expression of most allotypes is significantly reduced. Two exceptions are HLA-A*0201 and HLA-B*2705. In this study, the repertoire of peptides bound endogenously by these allotypes in the absence of tapasin was examined and stability of the HLA class I/peptide complexes assessed. Similar quantities of peptides were recovered from B*2705 complexes expressed in the absence and presence of tapasin and the composition of the peptide pools were not radically different. However, the stability of B*2705 molecules expressed at the surface of tapasin-deficient cells was found to be reduced which suggests there are subtle changes to the peptide repertoire. The impact of the absence of tapasin was more dramatic for A*0201. Although equivalent levels of cell surface A*0201 are expressed in the presence and absence of tapasin, very little A*0201 glycoprotein was recovered from tapasin-deficient cells suggesting the complexes readily dissociate. Consistent with reduced stability, A*0201 complexes were found to be rapidly lost from the surface of tapasin-deficient cells. Analysis of the small quantity of endogenously bound peptides recovered from A*0201 expressed in the absence of tapasin revealed a complex mixture typical of A*0201 molecules expressed in normal cells. Therefore these molecules are unable to exploit the alternative supply of TAP-independent A*0201-binding peptides present in the endoplasmic reticulum. Loading of A*0201 with peptides from both TAP-dependent and TAP-independent sources is significantly compromised without tapasin.

Identification of HLA-B27-restricted peptides from the Chlamydia trachomatis proteome with possible relevance to HLA-B27-associated diseases

The association of HLA-B27 with ankylosing spondylitis and reactive arthritis is the strongest one known between an MHC class I Ag and a disease. We have searched the proteome of the bacterium Chlamydia trachomatis for HLA-B27 binding peptides that are stimulatory for CD8(+) cells both in a model of HLA-B27 transgenic mice and in patients. This was done by combining two biomathematical computer programs, the first of which predicts HLA-B27 peptide binding epitopes, and the second the probability of HLA-B27 peptide generation by the proteasome system. After preselection, immunodominant peptides were identified by Ag-specific flow cytometry. Using this approach we have identified for the first time nine peptides derived from different C. trachomatis proteins that are stimulatory for CD8(+) T cells. Eight of these nine murine-derived peptides were recognized by cytotoxic T cells. The same strategy was used to identify B27-restricted chlamydial peptides in three patients with reactive arthritis. Eleven peptides were found to be stimulatory for patient-derived CD8(+) T cells, of which eight overlapped those found in mice. Additionally, we applied the tetramer technology, showing that a B27/chlamydial peptide containing one of the chlamydial peptides stained CD8(+) T cells in patients with Chlamydia-induced arthritis. This comprehensive approach offers the possibility of clarifying the pathogenesis of B27-associated diseases.

MHC class I multimers

T lymphocytes play a key role in the immune response to both foreign and self peptide antigens, which they recognize in combination with MHC molecules. In the past it has been difficult to analyse objectively the specificity, frequency and intensity of T cell responses. The recent application of fluorescent-labelled MHC class I multimers, however, has provided a powerful experimental approach to the direct visualisation of antigen-specific T cells. As a result, our perspective of how T cells respond to both viruses and other antigens in vivo has been greatly enhanced.

The role of HLA-B27 in spondyloarthritis

The human major histocompatibility complex (MHC) class I allele HLA-B27 bears a striking association with the spondylolarthritic group of inflammatory arthritides, yet despite extensive studies its role in the disease process remains obscure. As an MHC class I protein, the primary function of HLA-B27 is to complex with beta(2)-microglobulin forming a structure that presents short antigenic peptides for recognition by cytotoxic T lymphocytes (CTL). It has been proposed that the role of HLA-B27 in spondyloarthropathy involves this process of antigen presentation, and of the numerous theories proposed to explain the association, the most popular have involved the binding and presentation of "arthritogenic" peptides. Transgenic rodent studies directly implicate HLA-B27 heavy chains in disease pathogenesis, but suggest that the mechanism may be distinct from their primary function. The recent demonstration that HLA-B27 heavy chains can form stable homodimers may thus be of relevance. This review summarizes the evidence supporting current theories of disease association and proposes an alternative model of disease based on recent findings.

Cutting edge: HLA-B27 can form a novel beta 2-microglobulin-free heavy chain homodimer structure

HLA-B27 has a striking association with inflammatory arthritis. We show that free HLA-B27 heavy chains can form a disulfide-bonded homodimer, dependent on residue Cys67 in their extracellular alpha 1 domain. Despite the absence of beta 2-microglobulin, HLA-B27 heavy chain homodimers (termed HC-B27) were stabilized by a known peptide epitope. HC-B27 complexes were recognized by the conformation-specific Ab W6/32, but not the ME1 Ab. Surface labeling and immunoprecipitation demonstrated the presence of similar W6/32-reactive free heavy chains at the surface of HLA-B27-transfected T2 cells. HC-B27 homodimer formation might explain the ability of HLA-B27 to induce spondyloarthropathy in beta 2-microglobulin-deficient mice.

Importance of a conserved TCR J alpha-encoded tyrosine for T cell recognition of an HLA B27/peptide complex

Human HLA B27-restricted cytotoxic T lymphocytes (CTL) specific for the influenza A epitope NP383-391 use similar TCR alpha and beta chains, with two closely related J alpha segments used by six of nine CTL clones from three unrelated donors (Bowness et al., Eur J. Immunol. 1993. 23: 1417-1421). The role of TCR complementarity-determining region (CDR)3alpha residues 93 and 100-102 was examined by site-directed mutagenesis, following expression of the TCR alpha and beta extracellular domains from one clone as a TCR zeta fusion heterodimer in rat basophil leukemia (RBL) cells. For the first time we have measured direct binding of tetrameric HLA B*2705/NP383-391 complexes to transfected TCR. Independently peptide-pulsed antigen-presenting cells (APC) were used to induce TCR-mediated degranulation of RBL transfectants. Our results show a key role for the conserved TCRalpha CDR3 J alpha-encoded residue Y102 in recognition of HLA B27/NP383-391. Thus the Y102D mutation abolished both tetramer binding and degranulation in the presence of peptide-pulsed APC. Even the Y102F mutation, differing only by a single hydroxyl group from the native TCR, abolished detectable degranulation. Further mutations F93A and S100R also abolished recognition. Interestingly, the N101A mutation recognized HLA B27/NP in functional assays despite having significantly reduced tetramer binding, a finding consistent with "kinetic editing" models of T cell activation. Modeling of the GRb TCR CDR3alpha loop suggests that residue Y102 contacts the HLA B*2705 alpha1 helix. It is thus possible that selection of germ-line TCRAJ-encoded residues at position 102 may be MHC driven.

Multiple T cell expansions are found in the blood and synovial fluid of patients with reactive arthritis

OBJECTIVE

To look for evidence of T lymphocyte expansions in the blood and synovial fluid (SF) of patients with reactive arthritis (ReA).

METHODS

Paired peripheral blood and synovial samples from 10 patients with ReA were studied by dual color flow cytometry using T cell receptor (TCR) V beta specific and CD4 or CD8 specific antibodies. Two synovial CD8 expansions were studied by 3 color flow cytometry. Peripheral blood samples from 13 healthy, age matched individuals were studied as controls.

RESULTS

Statistically significant expansions were observed in all patients, occurring in blood and SF CD4 and CD8 compartments, but were most common in the synovial CD8 compartment. Expansions studied in further detail displayed an activated "memory" phenotype. A synovial BV22S1/CD8 expansion was seen in 5/6 patients with sexually acquired ReA.

CONCLUSION

Multiple T lymphocyte expansions are found in both the blood and SF of patients with ReA. Expansions were most commonly found in the synovial CD8 compartment, where they appeared to express both activation and memory markers. This indicates that T lymphocytes (and in particular cytotoxic T cells) may play a pathogenic role in ReA. These findings are consistent with either an antigen or a superantigen driven response.

Selection of T cell receptor variable gene-encoded amino acids on the third binding site loop: a factor influencing variable chain selection in a T cell response

The 3' end of the T cell receptor V beta 7.1 gene contains the five nucleotides CAAGA between the broadly conserved consensus sequence of nucleotides TGC/T GCC AGC AGC (which encode cysteine, alanine, serine and serine at positions 92-95 of the beta chain) and the heptamer that signals rearrangement. These nucleotides are frequently preserved during gene rearrangement, resulting in the common presence of glutamine at position 96 and of aspartate or glutamate at position 97 of the V beta 7.1 chain CDR3 loop in peripheral blood lymphocytes. There is selection of V beta 7.1 and of the V beta 7.1 gene-encoded glutamate at position 97 of the beta chain CDR3 loop in the cytotoxic T lymphocyte response to the HLA B2705-restricted influenza A nucleoprotein epitope SRYWAIRTR. Our results indicate that selection of V beta 7.1 gene-encoded amino acid residues on CDR3 loops may be one factor driving selection of V beta 7.1 in this response.

Identification of T cell receptor recognition residues for a viral peptide presented by HLA B27

The fine specificity of T cell recognition of peptide analogues of the influenza nucleoprotein epitope, NP 383-391 SRYWAIRTR, was studied using HLA B27-restricted influenza-specific cytotoxic T cell (CTL) clones, of defined T cell receptor (TcR) usage, derived from unrelated individuals following natural infection. Even conservative amino acid substitutions of the peptide residues P4, P7 and P8 influenced CTL recognition. These side chains are probably directly contacted by the TcR. CTL clones which used the TcR V alpha 14 gene segment (but not those using TcR V alpha 12) were also sensitive to P1 substitutions, suggesting that the TcR alpha chain of these clones lies over the N terminus of bound peptide, and that the "footprint" of certain TcR can span all exposed residues of a peptide bound to a major histocompatibility complex class I molecule. These results, taken together with previous structural and functional data, suggest that, for nonamer peptides bound to HLA B27, P1, P4 and P8 are "flag" residues with TcR-accessible side chains.

Hereditary C1q deficiency and systemic lupus erythematosus

We describe a 27-year-old women with systemic lupus erythematosus, C1q deficiency and cytomegalovirus retinitis. She suffered from severe SLE, with cutaneous and CNS involvement, and died of CNS disease aged 28. Review of 29 other published cases of C1q deficiency shows that SLE in these patients is often severe (five with CNS disease, ten with glomerulonephritis). The results of autoantibody studies in this and another patient with C1q deficiency and SLE are presented--both patients had autoantibodies to the extractable nuclear antigens, Sm, RNP and Ro, and one patient had high titres of antibodies to dsDNA. One of the patients had previously been treated with fresh frozen plasma, and antibodies to C1q were present in his serum. Homozygous C1q deficiency is associated with a very high prevalence of severe SLE with the full panoply of autoantibodies characteristic of this disease.

A method for producing monoclonal antibodies to human T-cell-receptor beta-chain variable regions

Study of the T-cell repertoire in humans has been hampered by the lack of monoclonal antibodies (mAbs) to the T-cell receptor (TCR) variable region (V) gene products. We describe a method for producing mAbs to the human TCR beta-chain V (V beta) gene products in which mice were immunized with a rat basophil cell line (RBL-2H3) transfected with the extracellular domain of the TCR heterodimer fused to the lambda chain of CD3. These cells acted as excellent immunogens for raising anti-TCR mAb and also formed the basis of a rapid screening assay. We generated mAbs against V beta protein of the TCR, showed that these mAbs stained approximately 1% of peripheral blood T cells, and further showed that the mAbs could stimulate proliferation of these T cells. We then characterized the mAbs by amplifying TCR cDNA derived from mAb-stimulated cells and sequencing the beta chain. All clones sequenced used the V beta 7.1 chain, proving conclusively that the mAbs generated were specific for V beta 7.1 subfamily. This method generates mAbs to human TCR V beta proteins efficiently and might allow production of a complete panel of mAbs directed against human TCR V beta proteins.

Conservation of T cell receptor usage by HLA B27-restricted influenza-specific cytotoxic T lymphocytes suggests a general pattern for antigen-specific major histocompatibility complex class I-restricted responses

Eight HLA B27-restricted influenza A virus nucleoprotein 383-391-specific cytotoxic T lymphocyte (CTL) clones were obtained from three unrelated donors following natural infection. T cell receptor (TcR) usage was studied using the "anchored" polymerase chain reaction. TcR alpha-chain usage was restricted with three predominant V alpha (V alpha 12.1, 14.1, 22) and two predominant J alpha segments. beta-chain variable-region usage was also conserved, with V beta 7 being used by five clones despite contributing less than 2% of peripheral blood lymphocyte V beta sequences of one individual studied. The TcR beta-chain junctional region was highly conserved even between CTL clones from unrelated individuals, with a negatively charged amino acid, contributed to by N-region addition, encoded at position 97 in all but two clones. This study shows that peptide-specific HLA B27-restricted CTL following influenza virus infection use very similar TcR and, when considered with previous studies, suggests a pattern of TcR conservation for major histocompatibility complex class I-restricted responses. No difference in TcR usage was detected between one healthy donor and two with HLA B27-associated arthritis.

Clostridium perfringens enterotoxin is a superantigen reactive with human T cell receptors V beta 6.9 and V beta 22

Candidate superantigens were screened for their ability to induce lysis of human histocompatibility leukocyte antigen class II-positive targets by human CD8+ influenza-specific cytotoxic T cell (CTL) lines. Clostridium perfringens enterotoxin (CPET) induced major histocompatibility complex unrestricted killing by some but not all CTL lines. Using "anchored" polymerase chain reactions, CPET was shown to selectively stimulate peripheral blood lymphocytes bearing T cell receptor V beta 6.9 and V beta 22 in five healthy donors. V beta 24, V beta 21, V beta 18, V beta 5, and V beta 6.1-5 appeared to be weakly stimulated. Antigen processing was not required for CPET to induce proliferation. Like the staphylococcal enterotoxins, CPET is a major cause of food poisoning. These data suggest that superantigenic and enterotoxigenic properties may be closely linked.

T-cell receptors and rheumatic disease: approaches to repertoire analysis

T-lymphocytes are thought to play a major role in the pathogenesis of a number of autoimmune rheumatic diseases. Techniques have recently been developed to study the T-cell receptor (TCR) usage of individual T-cells, and are likely to give major insight into the pathogenesis of rheumatic diseases. We describe the development of the TCR repertoire and the techniques available to study it. There is evidence that germline TCR complex polymorphisms may contribute to genetic susceptibility to rheumatoid arthritis. A number of studies have looked at rheumatoid synovial T-lymphocytes, some of which have found restricted TCR usage.

Reduction in T gamma delta cell numbers and alteration in subset distribution in systemic lupus erythematosus

We have studied the distribution of T gamma delta cells in the peripheral blood of 35 patients with systemic lupus erythematosus (SLE) and 36 age-matched controls. The monoclonal antibodies A13, BB3 and Ti gamma A, which are specific for the V delta 1, V delta 2 and V delta 9 gene products respectively, were used to define T gamma delta cell subsets. A significantly lower frequency of T gamma delta cells was found in peripheral blood lymphocytes of SLE patients compared with normal subjects (3.2% versus 5.9%). There was a marked reduction in the V delta 2+ subset of T gamma delta cells, which resulted in a reversal of the ratio of V delta 2+/V delta 1+ cells from 4.34 to 0.56. No correlation was found with either clinical or laboratory measures of disease activity. These results suggest that the observed changed in T gamma delta subset distribution are related to the SLE itself, and not secondary to changes in disease activity.

Prevalence of hypothyroidism in patients with polymyalgia rheumatica and giant cell arteritis

The prevalence of thyroid disease and thyroid autoantibodies was evaluated in 367 patients with polymyalgia rheumatica (PMR) and/or giant cell arteritis (GCA). Thirty-seven patients had antibodies to thyroid microsomes or thyroglobulin; 18 had hypothyroidism requiring thyroxine replacement therapy. The prevalence of hypothyroidism (4.9%) was significantly greater than that found in 84 control subjects.