Expanded T cell receptor Vβ–restricted T cells from patients with sporadic inclusion body myositis are proinflammatory and cytotoxic CD28null T cells

Objective

Sporadic inclusion body myositis (IBM) is characterized by T cell infiltrates in muscle tissue, but their functional role is unclear. Systemic signs of inflammation are lacking, and the absence of beneficial effects following immunosuppression has challenged the notion of a role for the immune system. This study was undertaken to investigate the phenotype and functionality of T cells, specifically a subset of proinflammatory, cytotoxic, and apoptosis‐resistant T cells defined as CD28^null T cells, in the pathogenesis of sporadic IBM.

Methods

A cohort of 27 patients with sporadic IBM was analyzed for the frequency of circulating and muscle‐infiltrating CD28^null T cells. The T cell receptor (TCR) V_β usage was determined using flow cytometry and immunohistochemistry. Anti‐CD3–stimulated peripheral blood mononuclear cells were analyzed for intracellular interferon‐γ and cytotoxic potential by flow cytometry.

Results

We found striking accumulations of both CD8+CD28^null and CD4+CD28^null T cells, which represented the TCR V_β–expanded T cells in sporadic IBM. Such CD28^null T cells were abundant both in the inflamed muscle tissue and in the circulation. Although the specific TCR V_β expansions varied between patients, both CD8+CD28^null and CD4+CD28^null T cells consistently displayed a highly proinflammatory and cytotoxic potential.

Conclusion

Our results suggest that CD28null T cell expansions represent the previously described expanded T cell subsets in sporadic IBM, and their proinflammatory capacity and presence in both muscle tissue and the circulation may imply a role of immune activation in sporadic IBM. In addition, CD4+CD28^null T cells may exert cytotoxic effects directly on muscle fibers due to a cytotoxic potential similar to that in CD8+ T cells.

     

Impact of the CTLA‐4/CD28 axis on the processes of joint inflammation in rheumatoid arthritis

Objective

The importance of the costimulatory molecules CD28 and CTLA‐4 in the pathologic mechanism of rheumatoid arthritis (RA) has been demonstrated by genetic associations and the successful clinical application of CTLA‐4Ig for the treatment of RA. This study was undertaken to investigate the role of the CTLA‐4/CD28 axis in the local application of CTLA‐4Ig in the synovial fluid (SF) of RA patients.

Methods

Quantitative polymerase chain reaction was used to analyze the expression of proinflammatory and antiinflammatory cytokines in ex vivo fluorescence‐activated cell sorted CTLA‐4+ and CTLA‐4− T helper cells from the peripheral blood and SF of RA patients. T helper cells were also analyzed for cytokine expression in vitro after the blockade of CTLA‐4 by anti–CTLA‐4 Fab fragments or of B7 (CD80/CD86) molecules by CTLA‐4Ig.

Results

CTLA‐4+ T helper cells were unambiguously present in the SF of all RA patients examined, and they expressed increased amounts of interferon‐γ (IFNγ), interleukin‐17 (IL‐17), and IL‐10 as compared to CTLA‐4− T helper cells. The selective blockade of CTLA‐4 in T helper cells from the SF in vitro led to increased levels of IFNγ, IL‐2, and IL‐17. The concomitant blockade of CD28 and CTLA‐4 in T helper cells from RA SF by CTLA‐4Ig in vitro resulted in reduced levels of the proinflammatory cytokines IFNγ and IL‐2 and increased levels of the antiinflammatory cytokines IL‐10 and transforming growth factor β.

Conclusion

Our ex vivo and in vitro results demonstrate that the CTLA‐4/CD28 axis constitutes a drug target for not only the systemic, but potentially also the local, application of the costimulation blocking agent CTLA‐4Ig for the treatment of RA.

     

Increased intraarticular interleukin‐7 in rheumatoid arthritis patients stimulates cell contact–dependent activation of CD4+ T cells and macrophages

Objective

To determine the level of intraarticular expression of interleukin‐7 (IL‐7) in patients with rheumatoid arthritis (RA) and to investigate the mechanisms by which IL‐7 facilitates activation of CD4+ T cells and monocyte/macrophages in RA.

Methods

IL‐7 levels were measured in synovial fluid obtained from patients with RA and patients with osteoarthritis (OA). Immunohistologic analysis was used to assess the expression of IL‐7 in synovial tissue from patients with RA. Proliferation and activation markers were determined in order to measure the effect of IL‐7 on mononuclear cells, isolated CD4+ T cells, and monocyte/macrophages from the peripheral blood and synovial fluid. Cocultures of CD4+ T cells and monocytic cells in the absence or presence of a semipermeable membrane were performed to assess the extent to which IL‐7 induces its effects, either contact dependently or via soluble mediators.

Results

IL‐7 levels were increased in synovial fluid from patients with RA compared with the levels in synovial fluid from patients with OA. Macrophages, fibroblasts, and endothelial cells in the joint lining tissue expressed abundant IL‐7. In vitro, synovial fluid CD4+ T cells and macrophages were hyperresponsive to IL‐7 when compared with peripheral blood cells. Furthermore, IL‐7 enhanced cell contact–dependent activation of CD4+ T cells and monocyte/macrophages.

Conclusion

The abundant intraarticular expression of IL‐7 and the stimulation by IL‐7 of contact‐dependent activation of CD4+ T cells and monocytic cells indicate that this cytokine plays an important proinflammatory role in RA synovitis. Further identification of IL‐7–induced pathways may improve understanding of the important interactive role of CD4+ T cells and monocytic cells in RA.

     

Proinflammatory mediator–induced reversal of CD4+,CD25+ regulatory T cell–mediated suppression in rheumatoid arthritis

Objective

We previously demonstrated that CD4+,CD25+ regulatory T (Treg) cells are present in increased numbers in the synovial fluid (SF) of rheumatoid arthritis (RA) patients and display enhanced suppressive activity as compared with their peripheral blood (PB) counterparts. Despite the presence of these immunoregulatory cells in RA, chronic inflammation persists. The purpose of the present study was to investigate whether particular proinflammatory mediators that are associated with RA could abrogate CD4+,CD25+ Treg–mediated suppression.

Methods

Monocyte phenotype was determined by flow cytometry and cytokine levels by enzyme‐linked immunosorbent assay. Magnetically sorted CD4+,CD25– and CD4+,CD25+ T cells derived from the PB and SF obtained from RA patients were stimulated alone or in coculture with anti‐CD3 monoclonal antibody (mAb) and autologous antigen‐presenting cells, in the absence or presence of anti‐CD28 mAb or the proinflammatory cytokines interleukin‐6 (IL‐6), tumor necrosis factor α (TNFα), or IL‐7.

Results

Monocytes from the SF of RA patients displayed increased expression of HLA class II molecules, CD80, CD86, and CD40 as compared with PB‐derived monocytes, indicating their activated status. Mimicking this increased costimulatory potential, addition of anti‐CD28 mAb to cocultures of CD4+,CD25– and CD4+,CD25+ T cells resulted in reduced CD4+,CD25+ Treg–mediated suppression in both PB and SF. Furthermore, IL‐7 and, to a limited extent, TNFα, both of which are produced by activated monocytes and were detected in SF, abrogated the CD4+,CD25+ Treg–mediated suppression. In contrast, IL‐6 did not influence Treg‐mediated suppression.

Conclusion

Our findings suggest that the interaction of CD4+,CD25+ Treg cells with activated monocytes in the joint might lead to diminished suppressive activity of CD4+,CD25+ Treg cells in vivo, thus contributing to the chronic inflammation in RA.

     

Suppression of immune responses in collagen‐induced arthritis by a rationally designed CD80‐binding peptide agent

Objective

The CD80/CD86–CD28/CD152 costimulatory pathways transmit signals for CD4+ T cell activation and suppression and are critically involved in the pathogenesis of rheumatoid arthritis (RA). A significant number of CD4+ T cells and macrophages in the rheumatoid synovium express elevated levels of CD80, increasing the potential for costimulation in trans of naive T cells. To determine the effect of blockade of this costimulatory axis in RA, we designed novel CD80‐binding peptides and evaluated their therapeutic potential in collagen‐induced arthritis (CIA), an animal model of RA.

Methods

The conserved MYPPPY motif of CD152 adopts a polyproline type II (PPII) helical conformation in the CD80–CD152 complex. The pairing preferences of the critical residues at the CD80–CD152 interface and their propensity to form PPII helices were integrated to design peptides with optimum PPII helical content that selectively block CD80–receptor interactions. The clinical efficacy was tested in DBA/1LacJ mice that were administered the CD80 blocking agents, called CD80‐binding competitive antagonist peptides (CD80‐CAPs), at the time of immunization with bovine type II collagen or 3 weeks after immunization.

Results

A single administration of select CD80‐CAPs significantly reduced the clinical, radiologic, and histologic disease severity in CIA. Importantly, administration of CD80‐CAPs during activated immune response significantly suppressed disease development by reducing mononuclear cell infiltration in the joints and mediating peripheral deletion of activated CD4+ T cells.

Conclusion

A rationally designed CD80‐binding peptide both prevents and suppresses CIA, suggesting a potential application in RA. Apoptosis of activated CD4+ T cells following in vivo blockade suggests that the effects of CD80‐CAPs may be long‐lasting.

     

Macrophage subpopulations in rheumatoid synovium: Reduced CD163 expression in CD4+ T lymphocyte–rich microenvironments

Objective

The cell surface glycoprotein CD163 is a member of the cysteine‐rich scavenger receptor family, highly specific for leukocytes of the mononuclear phagocyte lineage. In vitro, it is induced by glucocorticoids, interleukin‐6 (IL‐6), and IL‐10 and down‐regulated by interferon‐γ (IFNγ), indicating that it has a role in antiinflammatory or other immunomodulatory pathways. We assessed CD163 expression in microenvironments within rheumatoid arthritis (RA) synovium to clarify the relationships among CD4+ T lymphocytes, IFNγ, and macrophage function in RA.

Methods

Double immunofluorescence and serial immunoenzymatic studies were performed on normal, osteoarthritic, and RA synovium and tonsil with antibodies to CD163, CD45, CD68, CD14, CD3, CD4, CD8, CD19, and IFNγ.

Results

CD163 was observed on all CD14+ cells in synovium and tonsil with the exception of cells within larger T lymphocyte clusters in synovium and within tonsillar follicles. All brightly CD14+ cells in or around vessel walls (interpreted as immigrant monocytes) were CD163+. CD163 labeled fewer cells than did CD68 in synovial intima, but all CD45+ intimal cells were CD163+. CD4+,IFNγ+ T lymphocytes in RA synovium were chiefly localized within clusters containing CD68+, CD163− cells.

Conclusion

Within RA synovium, CD163 has major advantages as a macrophage marker and does not appear to be restricted to “mature” macrophages. CD163 discriminates between synovial macrophages and synovial intimal fibroblasts, which also stain positively for CD68 in diseased tissue.

     

CD4+CD25+ regulatory T cells in rheumatoid arthritis: Differences in the presence,phenotype, and function between peripheral blood and synovial fluid

Objective

In mice, CD4+CD25+ regulatory T cells play a pivotal role in preventing autoimmunity. Regulatory T cells are also present and functional in healthy humans. We investigated the presence, phenotype, and function of CD4+CD25+ regulatory T cells in peripheral blood (PB) and synovial fluid (SF) from patients with rheumatoid arthritis (RA).

Methods

The presence and phenotype of CD4+CD25+ regulatory T cells were determined by flow cytometry. Anergy and suppressive activity were assessed by culturing CD4+CD25− and CD4+CD25+ T cells with anti‐CD3 monoclonal antibodies and antigen‐presenting cells, followed by proliferation and cytokine detection.

Results

The percentage of CD4+CD25+ T cells in RA SF was significantly increased compared with that in RA PB, and both of these percentages were higher than that in PB from controls. The cells in RA PB were similar in phenotype and function to CD4+CD25+ regulatory T cells from controls. In SF, however, ∼40–50% of CD4+CD25+ T cells expressed an activated phenotype, i.e., CD69+, class II MHC+, OX‐40+, with high levels of CTLA‐4 and glucocorticoid‐induced tumor necrosis factor receptor. These synovial CD4+CD25+ T cells displayed an increased suppressive capacity compared with blood CD4+CD25+ T cells. However, this enhanced suppressive activity was counterbalanced, because activated responder T cells from SF were less susceptible to CD4+CD25+ T cell–mediated suppression than were responder cells from PB.

Conclusion

We demonstrate that CD4+CD25+ regulatory T cells are present and functional in patients with RA, with higher numbers of regulatory T cells with increased suppressive activity found in SF compared with PB. These findings suggest a negative feedback system that is active at the site of inflammation. The balance between activated responder and regulatory T cells appears to influence the extent of immunoregulation in RA.

     

Presence of CD4+CD8+ double‐positive T cells with very high interleukin‐4 production potential in lesional skin of patients with systemic sclerosis

Objective

Fibrotic skin changes in systemic sclerosis (SSc) are preceded by the appearance of an inflammatory infiltrate rich in T cells. Since no direct comparison with T cells in normal skin has been performed previously, this study was undertaken to functionally characterize T cells in the skin of patients with early active SSc and in normal skin.

Methods

We characterized coreceptor expression, T cell receptor (TCR) usage, cytokine production, and helper and cytolytic activity of T cell lines and clones established from skin biopsy specimens from 6 SSc patients and 4 healthy individuals. Immunofluorescence analysis of skin biopsy and peripheral blood samples was performed to confirm the presence of specific subsets in vivo.

Results

A distinct subset expressing both CD4 and CD8α/β coreceptors at high levels (double‐positive [DP]) was present in T cell lines from SSc and normal skin. DP T cells actively transcribed both accessory molecules, exerted clonally distributed cytolytic and helper activity, and expressed TCR clonotypes distinct from those in CD4+ or CD8+ single‐positive (SP) T cells. In SSc skin, DP T cells produced very high levels of interleukin‐4 (IL‐4) compared with CD4+ SP T cells. Furthermore, DP T cells were directly identified in SSc skin, thus providing evidence that they are a distinct subset in vivo.

Conclusion

The present findings show that T cells with the unusual CD4+CD8+ DP phenotype are present in the skin. Their very high level of IL‐4 production in early active SSc may contribute to enhanced extracellular matrix deposition by fibroblasts.

     

Reconstitution of deficient T cell receptor ζ chain restores T cell signaling and augments T cell receptor/CD3–induced interleukin‐2 production in patients with systemic lupus erythematosus

Objective

T cells from a majority of patients with systemic lupus erythematosus (SLE) display antigen receptor–mediated signaling aberrations associated with defective T cell receptor (TCR) ζ chain, a subunit of the TCR/CD3 complex. This study was undertaken to explore the possibility that forced expression of TCR ζ chain may reverse the known signaling abnormalities and defective interleukin‐2 (IL‐2) production in SLE T cells.

Methods

Freshly isolated SLE T cells were transfected with TCR ζ chain construct in a eukaryotic expression vector at high efficiency, by a recently developed nucleoporation technique. Restoration of TCR/CD3‐mediated signaling was studied in the ζ chain–transfected cells.

Results

In SLE T cells transfected with TCR ζ chain, surface expression of TCR chain was increased and the TCR/CD3‐induced increased free intracytoplasmic calcium concentration response was normalized, as was hyperphosphorylation of cellular substrates. Simultaneously, the previously noted increased expression of the Fc receptor γ chain was diminished in SLE T cells transfected with the ζ chain expression vector, and the surface membrane clusters of cell signaling molecules were redistributed to a more continuous pattern. TCR ζ chain replacement also augmented the expression of diminished TCR/CD3‐mediated IL‐2 production in SLE T cells, associated with increased expression of the p65 subunit of nuclear factor κB in the nuclear fractions of these T cells.

Conclusion

These results suggest that reconstitution of deficient TCR ζ chain can reverse the TCR/CD3‐mediated signaling abnormalities as well as the defective IL‐2 production in T cells of patients with SLE.

     

CTLA‐4IG suppresses reactive oxygen species by preventing synovial adherent cell–induced inactivation of rap1, a ras family GTPASE mediator of oxidative stress in rheumatoid arthritis T cells

Objective

Oxidative stress contributes to the inflammatory properties of rheumatoid arthritis (RA) synovial T lymphocytes. This study was undertaken to investigate the mechanisms leading to production of reactive oxygen species (ROS) and oxidative stress in RA synovial T lymphocytes.

Methods

ROS production in T lymphocytes from the peripheral blood (PB) of healthy donors and from the PB and synovial fluid (SF) of RA patients was measured by ROS‐dependent fluorescence of 6‐carboxy‐2′,7′‐dichlorofluorescein. Rap1 GTPase activation was assessed by activation‐specific probe precipitation. Proliferation of RA PB and SF T lymphocytes was assayed by ³H‐thymidine incorporation. In some experiments, RA PB T cells were preincubated with autologous SF or with PB or SF adherent cells. Experiments were performed in the absence or presence of transwell membranes or CTLA‐4Ig fusion proteins. Short‐ and long‐term stimulations of healthy donor PB T lymphocytes were performed with inflammatory cytokines, in the absence or presence of activating anti‐CD28 antibodies.

Results

T lymphocyte ROS production and Rap1 inactivation were mediated by cell–cell contact with RA synovial adherent cells, and this correlated with T cell mitogenic hyporesponsiveness. CTLA4‐Ig blockade of synovial adherent cell signaling to CD28 T cells reversed the inhibition of Rap1 activity and prevented induction of ROS. Introduction of active RapV12 into T cells also prevented induction of ROS production. Coincubation of T cells with stimulating anti‐CD28 antibodies and inflammatory cytokines synergistically increased T cell ROS production.

Conclusion

Cell–cell contact between T cells and RA synovial adherent cells mediates Rap1 inactivation and subsequent ROS production in T lymphocytes following exposure to inflammatory cytokines. This process can be blocked by CTLA4‐Ig fusion protein.

     

MRL/Mp CD4+,CD25− T cells show reduced sensitivity to suppression by CD4+,CD25+ regulatory T cells in vitro: A novel defect of T cell regulation in systemic lupus erythematosus

Objective

To investigate the hypothesis that loss of suppression mediated by peripheral CD4+,CD25+ regulatory T cells is a hallmark of systemic lupus erythematosus (SLE).

Methods

Mice of the MRL/Mp strain were studied as a polygenic model of SLE. Following immunomagnetic selection, peripheral lymphoid CD25+ and CD25− CD4+ T cells were cultured independently or together in the presence of anti‐CD3/CD28 monoclonal antibody–coated beads. Proliferation was assessed by measuring the incorporation of tritiated thymidine.

Results

While MRL/Mp CD4+,CD25+ regulatory T cells showed only subtle abnormalities of regulatory function in vitro, syngeneic CD4+,CD25− T cells showed significantly reduced sensitivity to suppression, as determined by crossover experiments in which MRL/Mp CD4+,CD25− T cells were cultured with H‐2–matched CBA/Ca CD4+,CD25+ regulatory T cells in the presence of a polyclonal stimulus.

Conclusion

Our findings highlight a novel defect of peripheral tolerance in SLE. Identification of this defect could open new opportunities for therapeutic intervention.

     

Impaired activation‐induced cell death promotes spontaneous arthritis in antigen (cartilage proteoglycan)–specific T cell receptor–transgenic mice

Objective

To investigate whether genetic preponderance of a T cell receptor (TCR) recognizing an arthritogenic peptide of human cartilage proteoglycan (PG) is sufficient for development of arthritis.

Methods

We performed a longitudinal study using BALB/c mice expressing a TCR that recognizes the arthritogenic ATEGRVRVNSAY QDK peptide of human cartilage PG. PG‐specific TCR–transgenic (PG‐TCR–Tg) mice were inspected weekly for peripheral arthritis until 12 months of age. Peripheral joints were examined histologically, and T cell responses, T cell activation markers, serum cytokines, and autoantibodies were measured. Apoptosis and signaling studies were performed in vitro on T cells from aged PG‐TCR–Tg mice.

Results

Spontaneous arthritis developed as early as 5–6 months of age, and the incidence increased to 40–50% by 12 months of age. Progressive inflammation began with cartilage and bone erosions in the interphalangeal joints, and later expanded to the proximal joints of the front and hind paws. Spontaneous arthritis was associated with a high proportion of activated CD4+ T cells, enhanced interferon‐γ and interleukin‐17 (IL‐17) production, and elevated levels of serum autoantibodies. PG‐TCR–Tg mice lacking IL‐4 developed arthritis earlier and at a higher incidence than IL‐4–sufficient mice. Antigen‐specific activation–induced cell death was diminished in vitro in CD4+ T cells of PG‐TCR–Tg mice with spontaneous arthritis, especially in those lacking IL‐4.

Conclusion

The presence of CD4+ T cells expressing a TCR specific for an arthritogenic PG epitope is sufficient to trigger spontaneous autoimmune inflammation in the joints of BALB/c mice. IL‐4 appears to be a negative regulator of this disease, through attenuation of activation‐induced cell death.

     

Definitive engagement of cytotoxic CD8 T cells in C protein–induced myositis,a murine model of polymyositis

Objective

To substantiate a pathogenic role of cytotoxic CD8 T cells in the development of a murine polymyositis model, C protein–induced myositis (CIM).

Methods

Beta₂‐microglobulin–null mutant, perforin‐null mutant, and wild‐type (WT) C57BL/6 mice were immunized with skeletal muscle C protein fragments to provoke CIM. Regional lymph node CD8 or CD4 T cells stimulated with C protein–pulsed dendritic cells were transferred adoptively to naive mice. Inflammation and damage of the muscle tissues were evaluated histologically.

Results

The incidence of myositis development was significantly lower in β₂‐microglobulin–null and perforin‐null mutant mice compared with WT mice. Inflammation was less severe in mutant mice, and the incidence of muscle injury was reduced significantly. Adoptive transfer of lymph node T cells from mice with CIM induced myositis in naive recipient mice. The CD8 T cell–induced muscle injuries were significantly more severe than the CD4 T cell–induced muscle injuries.

Conclusion

Perforin‐mediated cytotoxicity by CD8 T cells is definitively responsible for muscle injury in CIM.

     

CD4+,CD28− T cells in rheumatoid arthritis patients combine features of the innate and adaptive immune systems

Objective

To determine whether CD4+,CD28− T cells, which are expanded in patients with rheumatoid arthritis (RA), express receptors that typically regulate the function of natural killer (NK) cells.

Methods

Expression of the NK cell surface molecules CD158, p70, CD94, CD161, and CD8α on T cell subsets was determined by multicolor flow cytometric analysis of peripheral blood mononuclear cells from 36 RA patients. Expression of CD161 on tissue‐infiltrating CD4 T cells was determined by 2‐color immunohistochemistry analysis of synovial tissue samples.

Results

Killer cell–inhibitory receptors (KIR) and killer cell–activating receptors (KAR) were exclusively expressed on CD4+,CD28− T cells, with the CD158b molecule being the most frequently detected isoform. A coordinated mechanism inducing KIR/KAR expression was suggested by similarities in the expression of CD158b on CD4 and CD8 T cells. CD4+,CD28− T cells were also positive for CD8‐αα homodimers, another characteristic shared with NK cells. Of the C‐type lectin NK cell receptors (NK receptors), CD94 was consistently absent, but CD161 was found on a CD4 T cell population that is significantly expanded in RA patients (P = 0.01). Involvement in disease of NK receptor–expressing CD4 T cells was suggested by the presence of CD4+,CD161+ T cells in follicular microstructures typical of rheumatoid synovitis.

Conclusion

Patients with RA have an expanded and unusual subset of CD4 T cells that infiltrates the tissue lesions and is characterized by a deficiency of CD28, the expression of CD8‐αα homodimers, and the expression of several types of HLA class I–recognizing NK receptors. CD4 T cells bearing NK receptors can bridge functions of the innate and adaptive immune systems, such as responsiveness to specific antigen, rapid release of interferon‐γ, cytotoxicity, independence from classic costimulatory pathways, and integration of multiple activating and inhibitory signals to control effector functions.

     

Novel role of plasmacytoid dendritic cells in humans: Induction of interleukin‐10–producing treg cells by plasmacytoid dendritic cells in patients with rheumatoid arthritis responding to therapy

Objective

Reestablishing immune tolerance and long‐term suppression of disease represent major therapeutic goals in rheumatoid arthritis (RA). Dendritic cells (DCs) likely play a central role in such regulation via the expansion and/or induction of Treg cells. The present study was undertaken to explore the contribution of DCs to the development of Treg cells in a human autoimmune disease setting.

Methods

DC subsets were characterized by flow cytometry in the peripheral blood and synovial fluid of patients with RA. Proliferation of and cytokine release by naive CD4+CD25− T cells were measured in cocultures of these cells with DCs from patients with RA and healthy controls. The suppressive capacity of DC‐polarized T cells was explored in vitro by a standard suppression assay.

Results

Only very low numbers of both plasmacytoid DCs (CD303+) and myeloid DCs (CD1c+) were present in the peripheral blood of patients with active RA. In contrast, patients with therapy‐induced remission of RA exhibited higher numbers of circulating plasmacytoid DCs. Mature plasmacytoid DCs from RA patients with low disease activity, but not those from healthy controls, expressed high levels of indoleamine 2,3‐dioxygenase and promoted the differentiation of allogeneic naive CD4+CD25− T cells into interleukin‐10–secreting Treg cells, or Tr1 cells, that showed poor proliferation in vitro. Importantly, these plasmacytoid DC–primed Treg cells potently suppressed the proliferation of autologous naive CD4+ T cells, in a dose‐dependent manner.

Conclusion

These results demonstrate, for the first time, that human plasmacytoid DCs may be educated within the rheumatoid microenvironment to acquire a tolerogenic phenotype. Modulation of the immune response by plasmacytoid DCs might provide novel immune‐based therapies in autoimmunity and transplantation.