Joint cytokine quantification in two rodent arthritis models: kinetics of expression, correlation of mRNA and protein levels and response to prednisolone treatment

Biomarker quantification in disease tissues from animal models of rheumatoid arthritis (RA) can help to provide insights into the mechanisms of action of novel therapeutic agents. In this study we validated the kinetics of IL-1beta, TNF-alpha and IL-6 mRNA and protein expression levels in joints from DBA/1OlaHsd murine collagen-induced arthritis (CIA) and Lewis rat Streptococcal cell wall (SCW)-induced arthritis by real-time polymerase chain reaction (PCR) TaqMan and Enzyme-linked immunosorbent assay (ELISA). Prednisolone was used as a reference to investigate any correlation between clinical response and cytokine levels at selected time-points. To our knowledge this is the first report showing a close pattern of expression between mRNA and protein for IL-1beta and IL-6, but not for TNF-alpha, in these two models of RA. The kinetics of expression for these biomarkers suggested that the optimal sampling time-points to study the effect of compounds on both inflammation and cytokine levels were day 4 postonset in CIA and day 3 after i.v challenge in SCW-induced arthritis. Prednisolone reduced joint swelling through a mechanism associated with a reduction in IL-1beta and IL-6 protein and mRNA expression levels. At the investigated time points, protein levels for TNF-alpha in arthritic joints were lower than the lower limit of detection of the ELISA, whereas mRNA levels for this cytokine were reliably detected. These observations suggest that RT-PCR TaqMan is a sensitive technique that can be successfully applied to the quantification of mRNA levels in rodent joints from experimental arthritis models providing insights into mechanisms of action of novel anti-inflammatory drugs.

Interleukin 17 induces cartilage collagen breakdown: novel synergistic effects in combination with proinflammatory cytokines

OBJECTIVE

To investigate whether interleukin 17 (IL17), derived specifically from T cells, can promote type II collagen release from cartilage. The ability of IL17 to synergise with other proinflammatory mediators to induce collagen release from cartilage, and what effect anti-inflammatory agents had on this process, was also assessed.

METHODS

IL17 alone, or in combination with IL1, IL6, oncostatin M (OSM), or tumour necrosis factor alpha (TNFalpha), was added to bovine nasal cartilage explant cultures. Proteoglycan and collagen release were determined. Collagenolytic activity was determined by bioassay. Chondroprotective effects of IL4, IL13, transforming growth factor beta1 (TGFbeta1) and insulin-like growth factor-1 (IGF1) were assessed by inclusion in the explant cultures.

RESULTS

IL17 alone stimulated a dose dependent release of proteoglycan and type II collagen from bovine nasal cartilage explants. Suboptimal doses of IL17 synergised potently with TNFalpha, IL1, OSM, and IL6 to promote collagen degradation. This collagen release was completely inhibited by tissue inhibitor of metalloproteinase-1 and BB-94 (a synthetic metalloproteinase inhibitor), and was significantly reduced by IL4, IL13, TGFbeta1, and IGF1. In IL17 treated chondrocytes, mRNA expression for matrix metalloproteinase (MMP)-1, MMP-3, and MMP-13 was detected. Moreover, a synergistic induction of these MMPs was seen when IL17 was combined with other proinflammatory cytokines.

CONCLUSIONS

IL17 can, alone and synergistically in combination with other proinflammatory cytokines, promote chondrocyte mediated MMP dependent type II collagen release from cartilage. Because levels of all these proinflammatory cytokines are raised in rheumatoid synovial fluids, this study suggests that IL17 may act as a potent upstream mediator of cartilage collagen breakdown in inflammatory joint diseases.

Amelioration of arthritis in two murine models using antibodies to oncostatin M

OBJECTIVE

Oncostatin M (OSM) is a member of the interleukin-6 cytokine family, with well-documented effects on cell growth and differentiation. OSM also has proinflammatory and cartilage degradative properties. The aim of this study was to investigate the significance of OSM in arthritis pathology using a neutralizing antibody in arthritis models.

METHODS

Collagen-induced arthritis (CIA) was established in male DBA/1 mice. Reverse transcriptase-polymerase chain reaction was used to detect OSM messenger RNA (mRNA) message levels in arthritic joints. Neutralizing anti-OSM antibody or control immunoglobulin was administered on days 1 and 3 after disease onset. Animals were assessed for clinical arthritis for 2 weeks, followed by a histologic analysis of paws. Pristane-induced arthritis (PIA) was produced in male CBA mice dosed with anti-OSM or control immunoglobulin immediately before disease onset. Mice with PIA were assessed for clinical arthritis over a period of 100 days.

RESULTS

Levels of mRNA for OSM, but not GAPDH, were elevated in arthritic joints of mice with CIA compared with those of normal controls. Mice with CIA treated with anti-OSM antibody showed significant amelioration of both the clinical severity (P < 0.01) and the number of affected paws (P < 0.01) compared with control animals. Histologic analysis confirmed these clinical findings, revealing a marked reduction in cellular infiltration of synovium and cartilage damage. In the PIA model, the incidence of arthritis was 65% in the control group compared with 0% in the anti-OSM-treated animals.

CONCLUSION

These results demonstrate a key role for endogenously produced OSM as a potent mediator of joint pathology, and suggest that OSM might be a potentially important, novel therapeutic target for treatment of established rheumatoid arthritis.

Synergistic effects of glycoprotein 130 binding cytokines in combination with interleukin-1 on cartilage collagen breakdown

OBJECTIVE

To determine whether other glycoprotein 130 (gp130) binding cytokines can mimic the effects of oncostatin M (OSM) in acting synergistically with interleukin-1alpha (IL-1alpha) to induce cartilage collagen breakdown and collagenase expression, and to determine which receptors mediate these effects.

METHODS

The release of collagen and proteoglycan was assessed in bovine and human cartilage explant cultures. Messenger RNA (mRNA) and protein production from immortalized human chondrocytes (T/C28a4) was analyzed by Northern blotting and specific enzyme-linked immunosorbent assays. Collagenase activity was measured by bioassay. Cell surface receptors were detected by flow cytometry.

RESULTS

OSM in combination with IL-1alpha caused a rapid synergistic induction of matrix metalloproteinase 1 mRNA, which was sustained over a 72-hour period. Flow cytometric analyses detected both the OSM-specific receptor and the gp130 receptor at the chondrocyte cell surface, but failed to detect the leukemia inhibitory factor receptor (LIFR). Cartilage degradation assays revealed that, of the gp130 binding cytokines, only OSM and IL-6, in the presence of its soluble receptor (sIL-6R), were able to act synergistically with IL-1alpha to promote collagen release.

CONCLUSION

This study demonstrates that IL-6 can mimic OSM in synergizing with IL-1alpha to induce chondrocyte-mediated cartilage collagen breakdown and collagenase production. In order to have this effect, IL-6 requires the presence of its soluble receptor. The apparent absence of LIFR explains why other gp130 binding cytokines do not act in synergy with IL-1alpha. Since OSM, IL-6, and sIL-6R levels have all been shown to be elevated in the rheumatoid joint, our findings suggest that these cytokines may be key mediators of cartilage collagen catabolism in the inflammatory arthritides.

96-Well plate assays for measuring collagenase activity using (3)H-acetylated collagen

We describe two alternative assays for measuring collagenolytic activity using (3)H-acetylated collagen. Both assays have been developed for the 96-well plate format and measure the amount of radiolabeled collagen fragments released into the supernatant from an insoluble (3)H-acetylated collagen fibril preparation. The first method separates digested solubilized fragments from the intact fibril by sedimentation of the undigested collagen by centrifugation. The second method achieves this separation by filtration of the supernatant through the membrane of a 96-well filtration plate which retains the undigested collagen fibril. Both methods give linear dose- and time-dependent responses of collagenase activity > or = 70% of total collagen lysis. In addition, both assays can be simply modified to measure tissue inhibitors of metalloproteinases (TIMPs) inhibitory activity, which is also linear between 20 and 75% of total collagen lysis with the amount of TIMP added.

A lack of evidence for down-modulation of CD3 zeta expression in colorectal carcinoma and pregnancy using multiple detection methods

Loss of the T cell receptor-associated CD3 zeta chain has been proposed as a possible mechanism of the acquired immunosuppression in both tumour-bearing hosts, and in symptomatic patients with HIV infection. However, other reports suggest that the zeta-chain loss may in part be caused by protease activity of contaminating phagocytes ex vivo. Using flow cytometry and Western blot analysis on highly purified T cells, and ensuring adequate addition of protease inhibitors, we have studied the expression of CD3zeta on peripheral blood T cells from patients with colorectal carcinoma, and compared these with normal controls, and pregnant donors, as a further example of an immunocompromised state. Immunohistochemistry was performed on tumour sections from patients with colorectal carcinoma to measure CD3zeta expression in tumour infiltrating T cells, and compared with normal mucosa and tonsil. Using these three approaches, our data provide no evidence for downregulation of CD3zeta chain expression either in colorectal carcinoma or pregnancy and suggest that this explanation is unlikely to fully account for the reduced T cell function associated with these conditions in all patients.

The role of oncostatin M in animal and human connective tissue collagen turnover and its localization within the rheumatoid joint

OBJECTIVE

To study the interaction of interleukin-1alpha (IL-1alpha) and oncostatin M (OSM) in promoting cartilage collagen destruction.

METHODS

Bovine, porcine, and human cartilage and human chondrocytes were studied in culture. The levels of collagenase (matrix metalloproteinase 1 [MMP-1]) and tissue inhibitor of metalloproteinases 1 (TIMP-1) were measured by bioassay and enzyme-linked immunosorbent assay (ELISA). The levels of OSM in rheumatoid synovial fluid were measured by ELISA.

RESULTS

When combined with OSM, IL-1alpha, IL-1beta, and tumor necrosis factor alpha released proteoglycan and collagen from cartilage. OSM was the only member of the IL-6 family to have this effect. Human tendon also responded to IL-1alpha and OSM. OSM increased the production of MMP-1 and TIMP-1 but when combined with IL-1alpha, synergistically promoted MMP-1 production in human chondrocytes and synovial fibroblasts. High levels of OSM were found in human rheumatoid synovial fluids, and confocal microscopy showed that OSM was produced by macrophages in rheumatoid synovial tissue.

CONCLUSION

These results highlight an important new mechanism by which there is irreversible loss of collagen from cartilage.

T-cell response to mycobacterial proteins: a comparative study of tuberculous and control immunoblots of Mycobacterium tuberculosis and M. bovis BCG

OBJECTIVE

To evaluate and compare the lymphoproliferative response of human peripheral blood mononuclear cells (PBMC) to fractionated soluble extracts of Mycobacterium tuberculosis H37Rv (MTSE) and M. bovis bacille Calmette-Guérin (BCG) (MBSE), and thereby determine responses that correlate to infection, and to contrast antibody and T-cell responses.

DESIGN

Membrane blots of SDS-PAGE fractionated M. tuberculosis H37Rv and M. bovis BCG were employed for antibody immunoblotting and T-cell proliferative responses using sera and PBMC from seven tuberculous and seven BCG vaccinated control subjects.

RESULTS

The profiles of responses contrasted rather interestingly, with antibody and T-cells responding more to higher and lower molecular weight fractions respectively. T-cells responding to antigens in the 59-88 kDa region discriminated between tuberculous and BCG vaccinated controls (P < 0.05) even though the differences were more toward the 70-75 kDa fractions within the region in question. Responses to smaller molecular weight fractions of both MTSE and MBSE were high in direct contrast to antibody responses. Additionally, responses to MBSE in these regions were generally higher than for MTSE in vaccinated controls. The reverse was the case with tuberculous subjects where responses to MTSE were generally higher, though not sufficiently significant in enough of the tuberculous subjects to be considered discriminatory.

CONCLUSION

T-cell proliferative responses to mycobacterial antigens in the 59-88 kDa region, and particularly antigens in the 70-75 kDa region, can be an indication of infection with M. tuberculosis, as well as the basis for discriminating between active disease and vaccination with BCG.

IL-8-induced signal transduction in T lymphocytes involves receptor-mediated activation of phospholipases C and D

We have characterized the IL-8-induced signal transduction processes in T lymphocytes. A basal level of IL-8 receptor expression was shown on mixed PBL, as identified by using phycoerythrin (PE)-coupled IL-8, and this expression was increased following IL-2 stimulation. Scatchard analysis of T cells revealed competitive binding of IL-8 with a Kd of 0.55 nM, with approximately 1200 receptors per cell, on freshly isolated T cells. After 24 h in culture following purification, reverse transcriptase PCR (RT-PCR) analyses show the mRNA for only the type B IL-8R on these cultured T lymphocytes and the cell line MOLT-4. Stimulation of T lymphocytes or T cell clones with IL-8 led to generation of inositol trisphosphate and calcium flux. In addition, when T cells were prelabeled with [3H]oleic acid, IL-8 caused a long lasting, time- and dose-related increase in [3H]phosphatidylethanol (PtE), indicating activation of phospholipase D (PLD). By contrast, this IL-8-dependent PLD activity was undetectable in IL-8-stimulated neutrophils. PLD activation appeared to be downstream of protein kinase C, because several inhibitors abrogated the increase in [3H]PtE, whereas guanosine-5'-O-(3-thiotriphosphate (GTP(gamma)S) and inositol trisphosphorothioate (IP3S3) both increased the generation of [3H]PtE. Together, these results demonstrate that the IL-8RB receptor is sufficient to mediate phospholipase C (PLC) and PLD activation in T lymphocytes, but not in neutrophils, and indicate an important difference in receptor usage and signal transduction pathways between IL-8-stimulated lymphocytes and neutrophils.

IL-8-induced signal transduction in T lymphocytes involves receptor-mediated activation of phospholipases C and D

We have characterized the IL-8-induced signal transduction processes in T lymphocytes. A basal level of IL-8 receptor expression was shown on mixed PBL, as identified by using phycoerythrin (PE)-coupled IL-8, and this expression was increased following IL-2 stimulation. Scatchard analysis of T cells revealed competitive binding of IL-8 with a Kd of 0.55 nM, with approximately 1200 receptors per cell, on freshly isolated T cells. After 24 h in culture following purification, reverse transcriptase PCR (RT-PCR) analyses show the mRNA for only the type B IL-8R on these cultured T lymphocytes and the cell line MOLT-4. Stimulation of T lymphocytes or T cell clones with IL-8 led to generation of inositol trisphosphate and calcium flux. In addition, when T cells were prelabeled with [3H]oleic acid, IL-8 caused a long lasting, time- and dose-related increase in [3H]phosphatidylethanol (PtE), indicating activation of phospholipase D (PLD). By contrast, this IL-8-dependent PLD activity was undetectable in IL-8-stimulated neutrophils. PLD activation appeared to be downstream of protein kinase C, because several inhibitors abrogated the increase in [3H]PtE, whereas guanosine-5'-O-(3-thiotriphosphate (GTP(gamma)S) and inositol trisphosphorothioate (IP3S3) both increased the generation of [3H]PtE. Together, these results demonstrate that the IL-8RB receptor is sufficient to mediate phospholipase C (PLC) and PLD activation in T lymphocytes, but not in neutrophils, and indicate an important difference in receptor usage and signal transduction pathways between IL-8-stimulated lymphocytes and neutrophils.

A longitudinal study of peripheral blood mononuclear cell proliferative responses to bacterial antigens in reactive arthritis

Reactive arthritis (ReA) is a sterile inflammatory arthritis which usually occurs after an enteric or genitourinary infection. In recent years it has been recognized that synovial fluid mononuclear cells from an affected joint demonstrate marked proliferative responses if incubated with preparations of the organism triggering the arthritis; peripheral blood mononuclear cell (PBMC) responses are typically much smaller. One interpretation of this finding is that recognition of the triggering organism is enhanced within the joint compared to peripheral blood, but it could also be argued that the PBMC responses are actually depressed during acute arthritis. We have examined this possibility in a longitudinal study of PBMC proliferative responses in patients with ReA. In this study we have demonstrated that PBMC proliferative responses to the triggering organism were indeed depressed during acute ReA, and showed a significant increase after recovery from the arthritis. These findings also applied to PBMC recognition of the recall antigen PPD, and to the response to IL-2.

MHC restriction of synovial fluid lymphocyte responses to the triggering organism in reactive arthritis. Absence of a class I-restricted response

Synovial fluid mononuclear cells (SFMC) from patients with reactive arthritis (ReA) show marked proliferative responses to preparations of the organism triggering the arthritis. Initial studies with MHC-specific MoAbs have indicated that a significant element of these proliferative responses is mediated by class II MHC-restricted CD4+ T cells. It is imperative to establish the presence or absence of a class I-restricted response, for two reasons. Firstly, the association of ReA with the MHC class I molecule, HLA B27, raises the possibility of there being a B27-restricted response to the triggering organism. Secondly, a number of the organisms associated with ReA are intracellular pathogens, whose antigens might be expected to be presented by class I MHC molecules. In an effort to identify a class I MHC-restricted pathogen-specific response in the SFMC of ReA patients, we have assessed the proliferative responses of SFMC depleted of CD4+ T cells. Responses were grossly diminished by CD4+ T cell depletion. We also investigated Chlamydia-specific cytotoxicity in the SFMC of patients with sexually acquired ReA in a system using productive chlamydial infection to produce both targets and effectors. Significant antigen specific cytotoxicity was not seen. These experiments do not provide evidence to support the existence of pathogen-specific responses by CD8+, class I-restricted synovial fluid T cells in ReA.

Epitope specificity and MHC restriction of rheumatoid arthritis synovial T cell clones which recognize a mycobacterial 65 kDa heat shock protein

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.

Isolation of Yersinia-specific T cell clones from the synovial membrane and synovial fluid of a patient with reactive arthritis

Synovial fluid (SF) mononuclear cells from patients with reactive arthritis (ReA) proliferate in vitro when challenged with ReA-associated bacteria, the maximal response being for the organism causing the triggering infection. We report the results of a study of the antigenic specificity of synovial T lymphocytes from an HLA-B27 positive ReA patient whose SF mononuclear cells responded preferentially to Yersinia antigens. This is the first report of the isolation of Yersinia-specific T cell clones from synovial membrane (obtained by closed-needle synovial biopsy). We present a detailed analysis of these clones, together with others obtained from the SF.

Recognition of a mycobacteria-specific epitope in the 65-kD heat-shock protein by synovial fluid-derived T cell clones

Adjuvant arthritis in rats is induced by a T cell clone specific for amino acids 180-188 of the mycobacterial 65-kD heat-shock protein, and synovial T cell responses to this same Ag have been noted in human arthritis. We have isolated 65-kD Ag-specific T cell clones from synovial fluid mononuclear cells of a patient with acute arthritis, which, unlike the corresponding PBMC, showed a marked proliferative response to the 65-kD Ag. Using synthetic peptides corresponding to the whole sequence of the 65-kD Ag, all the clones were shown to recognize an epitope present in the first NH2-terminal peptide (amino acids 1-15), with no response to the adjacent peptide (amino acids 6-22) or to any other peptide. The complete dominance of this epitope in the response to the 65-kD Ag was shown by documenting responses to the peptide in PBMC obtained after recovery from the arthritis. This epitope, like that recognized by the rat arthritogenic T cell clone, is in a portion of the 65-kD sequence that is not conserved between bacteria and eukaryotes, so that in this case, joint inflammation could not be attributed to bacteria-induced T cell clones cross-reacting with the self 65-kD Ag.

Synovial fluid antigen-presenting cells unmask peripheral blood T cell responses to bacterial antigens in inflammatory arthritis

We and others have previously shown that synovial fluid (SF) mononuclear cells (MC) from patients with both reactive arthritis and other inflammatory arthritides proliferate in vitro in response to bacteria clinically associated with the triggering of reactive arthritis. In all cases, such SFMC responses are greater than the corresponding peripheral blood (PB) MC responses, often markedly so, and the mechanism for this is unclear. We have investigated this phenomenon by comparing the relative abilities of irradiated non-T cells derived from PB and SF to support autologous T cell responses to ReA-associated bacteria. Seven patients whose SFMC had been shown previously to respond to bacteria were studied. We demonstrate antigen-specific responses of PB T cells to bacteria in the presence of SF non-T cells which are in marked contrast to the minimal responses of either unfractionated PBMC or PB T cells reconstituted with PB non-T cells. We also show that PB, but not SF T cells respond strongly to autologous SF non-T cells in the absence of antigen or mitogen. These findings demonstrate that SF antigen-presenting cells (APC) are potent activators of PB T cells. We conclude that the contrasting responses of SFMC and PBMC to bacterial antigens may be accounted for at least in part by an enhanced ability of SF APC to support T cell proliferative responses.

In vitro responses to a 65-kilodalton mycobacterial protein by synovial T cells from inflammatory arthritis patients

Bacterial Ag, especially those of mycobacteria, have been implicated in the pathogenesis of experimental inflammatory arthritis in rodents, while in man, reactive arthritis has a clear temporal relationship to infection with particular bacteria. To investigate the role of immune responses to bacterial Ag in inflammatory arthritis, we have examined the proliferative responses of paired synovial fluid and PBMC when stimulated with 1) suspensions of irradiated or heat-killed bacteria associated with reactive arthritis (ReA), 2) purified protein derivative, 3) a recombinant 65-kDa heat shock protein of Mycobacterium leprae. The 65-kDa Ag was stimulatory to synovial fluid mononuclear cells, but not PBMC, from patients with different arthropathies, including most of those with ReA, but also some with rheumatoid arthritis. Furthermore, the magnitude of these responses correlated more closely with responses to ReA-associated bacteria (such as Salmonella), than with responses to the mycobacterial Ag represented in purified protein derivative. These results suggest that the 65-kDa molecule, which is common to a wide range of bacteria, may be an important immunogen for the T cell-mediated immune responses within the joint in different clinically defined inflammatory arthropathies.

In vitro responses to a 65-kilodalton mycobacterial protein by synovial T cells from inflammatory arthritis patients

Bacterial Ag, especially those of mycobacteria, have been implicated in the pathogenesis of experimental inflammatory arthritis in rodents, while in man, reactive arthritis has a clear temporal relationship to infection with particular bacteria. To investigate the role of immune responses to bacterial Ag in inflammatory arthritis, we have examined the proliferative responses of paired synovial fluid and PBMC when stimulated with 1) suspensions of irradiated or heat-killed bacteria associated with reactive arthritis (ReA), 2) purified protein derivative, 3) a recombinant 65-kDa heat shock protein of Mycobacterium leprae. The 65-kDa Ag was stimulatory to synovial fluid mononuclear cells, but not PBMC, from patients with different arthropathies, including most of those with ReA, but also some with rheumatoid arthritis. Furthermore, the magnitude of these responses correlated more closely with responses to ReA-associated bacteria (such as Salmonella), than with responses to the mycobacterial Ag represented in purified protein derivative. These results suggest that the 65-kDa molecule, which is common to a wide range of bacteria, may be an important immunogen for the T cell-mediated immune responses within the joint in different clinically defined inflammatory arthropathies.

Synovial T lymphocyte recognition of organisms that trigger reactive arthritis

Reactive arthritis (ReA) is believed to be "triggered' by infection with certain bacteria. When the proliferative responses of mononuclear cells (MC) obtained from the synovial fluid (SF) of ReA patients were examined, it was found that they responded maximally to the specific organism responsible for the preceding infection. The response was shown to be due to Class II MHC-restricted T cells by inhibition experiments using cyclosporin A and monoclonal antibodies. Significant SFMC responses to additional organisms associated with ReA were also recorded; since there was no serological evidence of preceding infection by these organisms, this finding suggests that these bacteria share common T cell-recognized antigenic epitopes. The corresponding responses by peripheral blood mononuclear cells (PBMC) were much lower and often barely detectable, whereas their responses to PHA were consistently higher than those of SFMC. These results, combined with evidence that bacterial antigens localize in the joint, indicate that a bacteria-specific, T-cell-mediated response may play a central role in the pathogenesis of ReA.