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Foxp3 is proposed to play a critical role in the development and function of regulatory T cells. Functional and transgenic studies in mice propose Foxp3 as a “regulatory T cell lineage specification factor” but conflicting data exist in humans. Expression of multiple Foxp3 splice variants in humans represents an additional layer of complexity for this transcription factor and acts as a possible mechanism of regulating protein diversity. We report the identification of a novel splice variant of Foxp3 , called Foxp3Δ7 , in ex vivo CD4+CD25+ T cells and CD8+ regulatory T cell clones. Foxp3Δ7 lacks the 81 bp region that encodes exon 7 of Foxp3 , which is a part of the leucine zipper domain of the protein. The three splice variants of Foxp3 namely Foxp3FL , Foxp3Δ2 and Foxp3Δ7 are co-expressed in ex vivo human CD4+CD25+ T cells and CD8+ Treg clones. Stimulation of freshly isolated CD4+CD25+ T cells with anti-CD3 and anti-CD28 antibodies leads to a 140-fold upregulation of Foxp3Δ7 within 24 h of stimulation, which is ∼10-fold greater than that observed in stimulated CD4+CD25− T cells. In addition, resting CD8+ Treg cells have decreased expression of Foxp3FL and Foxp3Δ2 ; however they have a 10-fold higher expression of Foxp3Δ7 , in comparison to ex vivo CD4+CD25+ T cells. In order to assess the functional effects of these Foxp3 isoforms, we carried out lentivirus expression studies. All three isoforms were capable of inducing increased levels of CD25 expression in primary human CD4+ T cells, along with a tendency to decreased levels of CD127. Further investigation into pathways that alter the relative proportions of Foxp3 isoforms, and hence their interaction with other transcriptional co-regulators, will help to define the role of Foxp3 isoforms in immune regulation.

Major histocompatibility complex class I (MHCI) glycoproteins present cytosolic peptides to CD8+ T cells and regulate NK cell activity. Their heavy chains (HC) are expressed from up to three MHC gene loci (human leukocyte antigen [HLA]-A, -B, and -C in humans), whose extensive polymorphism maps predominantly to the antigen-binding groove, diversifying the bound peptide repertoire. Codominant expression of MHCI alleles is thus functionally critical, but how it is regulated is not fully understood. Here, we have examined the effect of polymorphism on the turnover rates of MHCI molecules in cell lines with functional MHCI peptide loading pathways and in monocyte-derived dendritic cells (MoDCs). Proteins were labeled biosynthetically with heavy water (2H2O), folded MHCI molecules immunoprecipitated, and tryptic digests analysed by mass spectrometry. MHCI-derived peptides were assigned to specific alleles and isotypes, and turnover rates quantified by 2H incorporation, after correcting for cell growth. MHCI turnover half-lives ranged from undetectable to a few hours, depending on cell type, activation state, donor, and MHCI isotype. However, in all settings, the turnover half-lives of alleles of the same isotype were similar. Thus, MHCI protein turnover rates appear to be allele-independent in normal human cells. We propose that this is an important feature enabling the normal function and codominant expression of MHCI alleles.

It is clear that regulatory T cells (Treg) have an important role in preventing autoimmunity and modulating responses to pathogens. Full characterization of Treg cell function in human patients would be greatly facilitated by practical methods for expanding Treg in vitro. Methods for expansion have been reported but whether expression of surface and intracellular markers associated with freshly isolated Treg following expansion correlates with the maintenance of function is unclear. Our aim was to investigate the various methods of expansion and to correlate regulatory activity with expression of these markers. We show that, of the markers associated with freshly isolated Treg, only CD27 expression correlated with regulatory activity and could be used to isolate cells with regulatory activity from lines expanded from CD4+ CD25+ cells. Also, cells expressing high levels of the transcription factor forkhead box P3 (Foxp3) were confined to the CD27+ population within these lines. Expression of CD27 by cells in lines expanded from CD4+ CD25- cells varied depending on the stimulus used for expansion, but these lines did not have significant regulatory activity even when the CD27+ cells were tested. Analysis of synovial CD4+ CD25+ cells from reactive arthritis patients revealed that they were predominantly CD27 positive. This also applied to CD25(high) and CD25(intermediate) CD4+ cells, despite their reported different abilities to regulate. We conclude that, whilst CD27 is useful for identifying Treg in the cell lines obtained after expansion of CD4+ CD25+ cells, its expression may not reliably identify the Treg cell population in other T-cell populations such as those found in joints.

Despite substantial advances in our understanding of CD4+ CD25+ regulatory T cells, a possible equivalent regulatory subset within the CD8+ T cell population has received less attention. We now describe novel human CD8+/TCR alphabeta+ T cells that have a regulatory phenotype and function. We expanded and cloned these cells using autologous LPS-activated dendritic cells. The clones were not cytolytic, but responded in an autoreactive HLA class I-restricted fashion, by proliferation and production of IL-4, IL-5, IL-13 and TGFbeta1, but not IFN-gamma. They constitutively expressed CD69 and CD25 as well as molecules associated with CD4+ CD25+ regulatory T cells, including cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) and Foxp3. They suppressed IFN-gamma production and proliferation by CD4+ T cells in vitro in a cell contact-dependent manner, which could be blocked using a CTLA-4-specific mAb. They were more readily isolated from patients with ankylosing spondylitis and may therefore be up-regulated in response to inflammation. We suggest that they are the CD8+ counterparts of CD4+ CD25+ regulatory T cells. They resemble recently described CD8+ regulatory cells in the rat that were able to abrogate graft-versus-host disease. Likewise, human HLA-restricted CD8+ regulatory T cells that can be cloned and expanded in vitro may have therapeutic applications.

Although it is well established that CD4+ T cells generally recognize major histocompatibility complex (MHC) class II molecules, MHC class I-reactive CD4+ T cells have occasionally been reported. Here we describe the isolation and characterization of six MHC class I-reactive CD4+ T-cell lines, obtained by co-culture of CD4+ peripheral blood T cells with the MHC class II-negative, transporter associated with antigen processing (TAP)-negative cell line, T2, transfected with human leucocyte antigen (HLA)-B27. Responses were inhibited by the MHC class I-specific monoclonal antibody (mAb), W6/32, demonstrating the direct recognition of MHC class I molecules. In four cases, the restriction element was positively identified as HLA-A2, as responses by these clones were completely inhibited by MA2.1, an HLA-A2-specific mAb. Interestingly, three of the CD4+ T-cell lines only responded to cells expressing HLA-B27, irrespective of their restricting allele, implicating HLA-B27 as a possible source of peptides presented by the stimulatory MHC class I alleles. In addition, these CD4+ MHC class I alloreactive T-cell lines could recognize TAP-deficient cells and therefore may have particular clinical relevance to situations where the expression of TAP molecules is decreased, such as viral infection and transformation of cells.

Cross-reactive T cell recognition of self-heat shock proteins (hsp) has been ascribed a regulatory role in inflammatory arthritis in both animal models and human disease. The previous work implies that a repertoire for epitopes in self-hsp60 should exist in normal subjects. Accordingly, we sought to generate self-hsp60-reactive T cell clones from a healthy individual using a highly purified preparation of recombinant human (Hu) hsp60. Epitope mapping using synthetic peptides and truncated constructs indicated that the T cell clones obtained actually recognized hsp60 derived from Escherichia coli. Using a series of alanine-substituted peptides and additional appropriate synthetic peptides, it was demonstrated that the clones maintain self-tolerance because of their sensitivity to an asparagine to aspartic acid sequence difference between E. coli and HuHsp60 in the epitope-containing peptide. In addition, despite substantial conservation of sequence, the homologous peptide from HuHsp60 did not compete with the E. coli-derived peptide for recognition or antagonize responses by acting as an altered peptide ligand. The results suggest that, even when the immune system targets a highly conserved epitope in bacterial hsp60, self-tolerance is maintained. Furthermore, the finding that T cell clones specific for minor contaminant proteins in HuHsp60 preparations can readily be isolated raises the possibility that the HuHsp60 facilitates presentation of antigenic proteins to the immune system.

Previously we have shown that the T-cell response against the HLA-DR3 (17)-restricted heat shock protein (Mr 65 000)-derived peptide amino acids (aa) 3-13 (hsp65 aa 3-13) is recognized by the exclusive usage of the TRBV5 gene as well as a conserved CDR3 region in a tuberculoid leprosy patient. In the present study we analyzed the TcR of T-cell clones specific for hsp65 aa 3-13 derived from three healthy individuals with a response level similar to that of the leprosy patient. We show that unlike the tuberculoid leprosy patient, healthy high responders have a diverse T-cell response to hsp65 aa 3-13. However, a striking observation was made: even though high responders have a diverse specific TcR repertoire, TRBV5-expressing clones from two healthy individuals could be isolated that were nearly identical to a dominant clone in the tuberculoid leprosy patient. In conclusion, the data show that restriction of TcR specific for an antigen correlates with the presence of that antigen in disease. However, the preferred TcR can also be detected in healthy high responders. A natural infection in vivo, as with the tuberculoid leprosy patient, may be responsible for the observed trimming and preferential outgrowth of a certain TcR.

We have studied the human gamma delta T-cell response to Yersinia enterocolitica, a facultative intracellular bacterium which causes gastroenteritis and, particularly in human leucocyte antigen (HLA)-B27+ individuals, reactive arthritis (ReA). A marked proliferation of that cytotoxic gamma delta T cells is seen when Yersinia-infected lymphoblastoid cell lines or fixed intact Yersinia are added to cultures of mononuclear cells derived from the synovial fluid of ReA patients or from the peripheral blood of healthy donors. In contrast, heat-inactivated Yersinia fail to stimulate the gamma delta T-cell response. The gamma delta T-cell lines generated killed both autologous and allogeneic infected cell lines. Interestingly, a T-cell line generated from synovial fluid mononuclear cells (SFMC) killed infected autologous cell lines and a cell line matched for HLA-B27 less well than infected allogeneic target cells. gamma delta T-cell clones isolated from this line were found to express V gamma 9V delta 2 T-cell receptor (TCR) and also killed infected mismatched cells more efficiently than autologous targets. Moreover, from experiments using major histocompatability complex (MHC)-deficient cell lines, it was apparent that target cell recognition was MHC independent. Our results suggest that gamma delta T cells can be involved in immunity to Yersinia enterocolitica and should be taken into account when considering immunopathological mechanisms leading to reactive arthritis.

A panel of T-cell clones was generated that was specific for amino acid residues 4—13 of the mycobacterial 65-kd stress protein. All the clones were found to express a member of the Vβ5 family, as defined by PCR. However, the clones could be differentiated on the basis of different staining characteristics with the mAb 42/1C1. This antibody is known to recognize both Vβ5.2 and Vβ5.3, as was the PCR primer pair used in the analysis. Sequencing of the TCRs revealed that those clones which were not stained by 42/1C1 expressed a previously unidentified member of the Vβ5 family. By comparing the sequences of the Vβ5 family members that are recognized by 42/1C1 with those that are not, we were able to identify a probable epitope for the antibody. It is also clear from our data that the TCRs of T cells recognizing identical MHC-peptide combinations, although very similar, may be differentiated by mAbs, thereby posing potential problems in any proposed disease therapy involving treatment with monoclonals.

One of the most satisfying aspects of the genome-wide association studies conducted in patients withankylosing spondylitis (AS) has been the large numberof genes that have been shown to affect susceptibility todisease (1). The first gene of this kind to be identifiedwas the interleukin-23 receptor (IL-23R). A potentialrole of IL-23 signaling in the pathogenesis of AS wasfurther supported by additional genes associated withAS, including the following: 1) IL-12B, which encodesthe 40-kd (p40) chain, a component of both IL-12 andIL-23; in the latter, it is paired with a 19-kd protein(p19); 2) caspase recruitment domain 9 (CARD-9),which encodes a major signaling intermediate in thepathway whereby fungal products induce IL-23 produc-tion from dendritic cells (DCs); and 3) STAT-3, whichencodes the major signaling molecule activated by theIL-23R. Additionally, there are suggested associations(which need further confirmation) with JAK-2, whichencodes another important signaling molecule down-stream of IL-23R, and prostaglandin E receptor 2 sub-type EP

The endoplasmic reticulum (ER) stress response detects malfunctions in cellular physiology, and microbial pattern recognition receptors recognize external threats posed by infectious agents. This study has investigated whether proinflammatory cytokine expression by monocyte-derived dendritic cells is affected by the induction of ER stress. Activation of ER stress, in combination with Toll-like receptor (TLR) agonists, markedly enhanced expression of mRNA of the unique p19 subunit of IL-23, and also significantly augmented secretion of IL-23 protein. These effects were not seen for IL-12 secretion. The IL-23 gene was found to be a target of the ER stress-induced transcription factor C/EBP homologous protein (CHOP), which exhibited enhanced binding in the context of both ER stress and TLR stimulation. Knockdown of CHOP in U937 cells significantly reduced the synergistic effects of TLR and ER stress on IL-23p19 expression, but did not affect expression of other LPS-responsive genes. The integration of ER stress signals and the requirement for CHOP in the induction of IL-23 responses was also investigated in a physiological setting: infection of myeloid cells with Chlamydia trachomatis resulted in the expression of CHOP mRNA and induced the binding of CHOP to the IL-23 promoter. Furthermore, knockdown of CHOP significantly reduced the expression of IL-23 in response to this intracellular bacterium. Therefore, the effects of pathogens and other environmental factors on ER stress can profoundly affect the nature of innate and adaptive immune responses.

We have previously described critical and nonredundant roles for the phosphoinositide 3-kinase p110δ during the activation and differentiation of naive T cells, and p110δ inhibitors are currently being developed for clinical use. However, to effectively treat established inflammatory or autoimmune diseases, it is important to be able to inhibit previously activated or memory T cells. In this study, using the isoform-selective inhibitor IC87114, we show that sustained p110δ activity is required for interferon-γ production. Moreover, acute inhibition of p110δ inhibits cytokine production and reduces hypersensitivity responses in mice. Whether p110δ played a similar role in human T cells was unknown. Here we show that IC87114 potently blocked T-cell receptor–induced phosphoinositide 3-kinase signaling by both naive and effector/memory human T cells. Importantly, IC87114 reduced cytokine production by memory T cells from healthy and allergic donors and from inflammatory arthritis patients. These studies establish that previously activated memory T cells are at least as sensitive to p110δ inhibition as naive T cells and show that mouse models accurately predict p110δ function in human T cells. There is therefore a strong rationale for p110δ inhibitors to be considered for therapeutic use in T-cell–mediated autoimmune and inflammatory diseases.

The discovery of the association between spondyloarthritis (SpA) and HLA-B27 inevitably turned the spotlight on T-lymphocytes as the cells which recognize peptide antigens within the binding groove of the HLA-B27 molecule and then carry out effector functions. These include cytolysis, cytokine and chemokine production and activation of other effector cells, such as those which could destroy joints or drive new bone formation. In this view the T-cell assumed the role of “director” of the immune response and therefore, in inflammatory diseases such as SpA, of immuno-pathology. The important research questions under this paradigm were the identity of the peptides recognized by T-cells in disease, including whether they were derived from self proteins or from micro-organisms, the influence of HLA-B27 in selecting antigenic peptides for recognition by T-cells, the T-cell receptors used in recognition and the effector programmes which the T-cells initiated. Whilst these questions continue to be explored—many have not yet been answered—attention has shifted to a new “master regulator” of the immune response, namely the dendritic cell and the possibility that the genetic influences which contribute to susceptibility to SpA do so at the level of the dendritic cell (DC).

CD4+ T cell clones specific for the mycobacterial hsp 65 were obtained from synovial fluid of a DR4 homozygous rheumatoid arthritis (RA) patient. A stimulatory epitope was defined using both deletion mutants of the mycobacterial hsp 65 and synthetic peptides and proved to be in a highly conserved region of the molecule. Despite this, however, there was no recognition by these clones of either the recombinant human homologue of mycobacterial hsp 65, P60, nor of a synthetic peptide containing an amino acid sequence from P60 corresponding to the epitope defined in the mycobacterial hsp 65. When the pattern of HLA restriction shown by the hsp-65-specific T cell clones was investigated, all clones tested proved to be restricted by HLA-DP rather than the more usual HLA-DR. Inhibition experiments suggested that this restriction also applied to the polyclonal synovial T cell response to hsp 65, but not to other antigens. Exclusive restriction of T cell recognition of an antigen by HLA-DP has not been reported previously, and strongly suggests that in this case the T cell repertoire for recognizing hsp 65 in the context of DR4 is deficient. Such an association between DR4 and the inability to respond to an immunodominant bacterial antigen may have implications for the pathogenesis of RA.

We previously reported autoreactive CD8 + regulatory T cells (Tregs) that were expanded and cloned from human peripheral blood by coculture with autologous dendritic cells (DC). Here we demonstrate that these CD8 + Tregs require human leukocyte antigen (HLA)-class I restricted activation and then mediate cell-contact-dependent suppression of CD4 + T cells. CD8 + Tregs interacted with DC to suppress T-cell responses but DC were not irreversibly altered by this interaction because they could subsequently stimulate CD4 + T cells normally. The ability of DC to form conjugates with CD4 + T cells was reduced in the presence of CD8 + Tregs. Suppression was blocked by Abs to CD80 and CTLA-4, implicating CTLA-4:CD80 interactions in the function of CD8 + Tregs. CD8 + Tregs rapidly express very high levels of surface CTLA-4 following activation compared with conventional T cells. Related to this, the expression of TRAT1 mRNA (T-cell receptor interacting molecule, or TRIM) was highly upregulated in microarray analysis of CD8 + Tregs compared with conventional cytotoxic or nonregulatory CD8 + T cells. TRIM acts to chaperone CTLA-4 transport to the cell surface; this function would be required to account for the phenotypic and functional properties of CD8 + Tregs.

Because antigen-specific cells are the central coordinators of the immune response to infectious organisms, and the principal effector cells in autoimmune disease, there are many circumstances in which investigators may wish to examine the T-cell responses to particular antigens. This chapter outlines techniques for assessing the responses of polyclonal populations of T-lymphocytes by measuring a variety of outputs each of which gives different kinds of information about the response. The outputs discussed are proliferation and cytokine production, with methods for measuring cytokine secretion by the whole population together with techniques for making an estimate of the numbers of cells producing a cytokine in response to antigen, and examining the phenotype of the responsive cells. In many cases detailed information about responses to particular antigens requires the isolation and characterization of antigen-responsive T-cell clones, and this is also described together with methods of identifying unknown antigens by screening recombinant expression libraries. Lastly, because the techniques differ in many respects, methods for isolating antigen-specific CD8+ T-cells, particularly those which recognize bacteria, are also included.

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.

The MHC class I molecule, HLA-B27 can be expressed as a number of non-conventional forms, in addition to conventional HLA-B27 heterodimers presenting peptide. This has lead to new avenues of research to explain the association of this molecule with SpA. Surprisingly, HLA-B27 transgenic animal models implicated CD4+ T cells, which conventionally interact with MHC class II molecules, not MHC class I molecules, in the pathogenesis of SpA. One hypothesis to explain these finding is that non-conventional forms of HLA-B27, specifically HLA-B27 homodimers, might mimic MHC class II molecules and be recognised by CD4+ T cells. We investigated whether CD4+ T cells from AS patients can interact with HLA-B27, discovering that indeed CD4+ T cells can interact with various forms of HLA-B27. Here we discuss how such interactions between HLA-B27 and CD4+ T cells could occur in vivo and potential contributions of such interactions to the pathogenesis of SpA.

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

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

Infection with mycobacterial species, includingMycobacterium tuberculosis, has long been implicated in the etiopathology of rheumatoid arthritis (RA) on the basis of clinical and pathological similarities between tuberculosis and RA. Despite evidence of immune responses to mycobacterial antigens in RA patient synovial fluid, cross-reactivity between these and host joint antigens, and the presence ofM. tuberculosisprotein antigen in RA synovial fluid, a definite causal association with RA has not been shown. Previous studies from our laboratory using reverse transcriptase PCR (RT-PCR) of bacterial rRNAs have shown RA synovium to be colonized by a diverse range of bacteria, most of commensal origin. However,M. tuberculosisgroup organism (MTG) RNA sequences were found in one RA patient tissue. Since this was considered of sufficient interest to warrant further investigation, we devised aM. tuberculosis-specific nested RT-PCR test which could be used for detection of MTG in a mixed pool of bacterial crDNAs. This test was used to investigate the distribution of MTG in RA synovial tissue and also non-RA arthritis and healthy control tissues and was also used to examine the tissue distribution of MTG in an acute and chronic model ofM. tuberculosisinfection in the BALB/c mouse. MTG sequences were found in a high proportion of RA patient synovial tissues but also in non-RA arthritis control tissues at lower frequency. This likely reflects trafficking of persistentM. bovisBCG to inflamed joint tissue, irrespective of cause. MTG were not found in healthy synovial tissue or the tissue of patients with undifferentiated arthritis. In both the acute and chronic models of infection in BALB/c mice,M. tuberculosiswas also found to have trafficked to joint tissues, however, no signs of inflammation, arthritis, or pathology associated withM. tuberculosisinfection was seen. These combined results would argue against a specific causal role of MTG in RA-like arthritis; however, their role as adjuvant in immune dysfunction in an innately susceptible host cannot be excluded.

The aim of this study was to use TCR sequencing as a tool to address the frequency of antigen specific T cells in different T cell compartments from a rheumatoid arthritis patient. We have previously established a clear link between T cell recognition of a specific Mhsp60 epitope and the amino acid sequence in the CDR3 region of the TCRB chain. This information was used to determine the frequency of these characteristic sequences in unmanipulated synovial fluid (SF), peripheral blood (PB) and hyperplastic lymph node of the same patient by amplification and sequencing. TCRBV sequences identical to those seen in antigen-specific clones, and closely related sequences, were readily identified in SF, where they represented approximately 1% of all T cells, but were absent from PB or lymph node. The prevalence of putative Mhsp60 specific T cells within the SFMC is much greater than previously suggested by limiting dilution assays. Thus, amplification and sequencing may prove a superior technique for tracking the frequency of antigen-specific T cells in different tissues and in a longitudinal fashion.

Mycobacterium bovis-BCG infected macrophages were exposed in vitro to PPD-stimulated T lymphocytes from tuberculin responsive donors or to a panel of mycobacterial-antigen specific CD4+ T cell clones. Both polyclonal and clonal T cells caused considerable antigen-specific lysis of autologous or MHC class II matched macrophages. However, lysis of infected macrophages did not significantly affect the number of viable mycobacteria which were released into the culture media from lysed macrophages. In tuberculosis, CD4+ cytolytic T cells may be primarily involved in tissue destruction and lack a significant role in acquired cellular immunity.

In reactive and postinfectious arthritis the joints are generally sterile but the presence of bacterial antigens and nucleic acids has been reported. To investigate whether organisms traffic to affected joints in these conditions, we performed reverse transcription PCR using universal primers to amplify any bacterial 16S rRNA sequences present in synovial fluid. Bacterial sequences were detected in most cases, even after treatment of the synovial fluid with DNase, implying the presence of bacterial RNA and therefore of transcriptionally active bacteria. Analysis of a large number of sequences revealed that, as reported in rheumatoid arthritis, most were derived from gut and skin commensals. Organisms known to have triggered arthritis in each case were not found by sequencing the products obtained using universal primers, but could in some cases be shown to be present by amplifying with species specific primers. This was the case for Yersinia pseudotuberculosis and Chlamydia trachomatis. However, in arthritis thought to be related to Campylobacter infection the sequences obtained were not from Campylobacter jejuni or C. coli, but from other Campylobacter spp. that are not known to be associated with reactive arthritis and are probably present as commensals in the gut. We conclude that although rRNA from reactive arthritis associated organisms can be detected in affected joints, bacterial RNA from many other bacteria is also present, as was previously noted in studies of other forms of inflammatory arthropathy.

Chlamydia trachomatis (CT) causes several sexually transmitted diseases. In 2-5% of cases, CT infection leads to the development of reactive arthritis. Dendritic cells (DC) are central in T cell priming and the induction of antigen specific immunity. Here we have studied the uptake and processing of CT serovar L2 by human DC, and their ability to present CT antigens to both CD4(+) and CD8(+) T cells. We show that the entry of CT was mediated by the attachment of CT to heparan sulfates and could be inhibited by heparin. There was no inhibition of uptake by an agent which blocks micropinocytosis. Infecting DC with CT led to their activation and the production of IL-12 and TNF-alpha but not IL-10. Following invasion, CT was confined to distinct vacuoles which were visualized with anti-CT antibodies using confocal microscopy. Unlike with epithelial cells, these vacuoles did not develop into characteristic inclusion bodies. In the first 48 h, CT(+) vacuoles were negative for Lamp-1 and MHC class II. Despite no obvious co-localization between CT vacuoles and MHC loading compartments, infected DC efficiently presented CT antigens to CD4(+) T cells. Infected DC also expanded CT specific CD8(+) T cells, allowing us to generate a number of CT-reactive CD8(+) T cell clones. There is still controversy about the importance of chlamydia-specific CD8(+) T cell responses in patients with arthritis. This is largely due to the difficulties in studying CTL responses at the clonal level. The use of DC as antigen-presenting cells should enable more detailed characterization of these CTL responses.

Epstein-Barr virus (EBV)-specific cytotoxic T cell precursors, present in the circulation of previously infected (seropositive) individuals, have been reactivated in vitro by challenging with autologous EBV-transformed cells, and the reactivated populations subsequently expanded as interleukin 2 (IL2)-dependent cell lines. These lines were dominated by T cells possessing the cytotoxic/suppressor cell surface phenotype and, when tested for effector function in chromium-release assays, demonstrated potent EBV-specific, HLA-A and -B antigen-restricted cytotoxicity even when derived from seropositive donors whose initial cytotoxic response to in vitro reactivation was relatively weak. With all the lines tested from 10 seropositive donors, strong killing of autologous EBV-transformed cells was observed in the absence of any significant lysis of autologous mitogen-stimulated lymphoblasts or of a panel of EBV genome-negative cell lines sensitive to natural killing. Furthermore, the availability of IL2-expanded effectors cell populations allowed their being tested upon a wide panel of allogeneic EBV-transformed targets such that the dominant HLA-restricted reactivities within these populations could be identified. Monoclonal antibody blocking experiments confirmed that lysis of the autologous EBV-transformed cell line by IL2-expanded effectors could be specifically inhibited (a) by pretreatment of the target cells with antibodies binding to the HLA/beta 2-microglobulin complex, and (b) by pretreatment of the effector cells with the cytotoxic/suppressor T cell-specific antibody Leu 2a.