Hypoxia decreases the T helper cell-suppressive capacity of synovial fibroblasts by downregulating IDO1-mediated tryptophan metabolism.

OBJECTIVE: The development of RA is linked to local infiltration of immune cells and to changes in the phenotype of synovial fibroblasts. Synovial fibroblasts possess the capacity to suppress T cell responses through indoleamine 2, 3-dioxygenase 1 (IDO1)-mediated tryptophan metabolism. However, synovial fibroblasts from RA patients are restricted in this immune-modulatory function. Moreover, hypoxic conditions are detected within synovial tissues of RA patients, with oxygen tensions of only 3.2% O2. This study aims at investigating the effects of hypoxia on the interaction between T cells and synovial fibroblasts, particularly on the T cell-suppressive capacities of synovial fibroblasts. METHODS: Synovial fibroblasts were cultured with Th cells under normoxic and hypoxic conditions (3% O2). Th cell proliferation was detected by flow cytometry. Tryptophan and kynurenine amounts were measured by HPLC. IDO1 expression and signal transducer and activator of transcription 1 (STAT1) phosphorylation were quantified by real-time PCR or western blot, and cytokine secretion by ELISA. RESULTS: Hypoxic conditions strongly diminished the Th cell-suppressive capacities of both OA synovial fibroblasts and RA synovial fibroblasts. Accordingly, IDO1 mRNA and protein expression, STAT1 phosphorylation and tryptophan metabolism were greatly reduced in OA synovial fibroblasts by hypoxia. MMP-3, IL-6, IL-10 and IFNγ secretion were significantly decreased under hypoxia in synovial fibroblast-Th cell co-cultures, while IL-17A levels were elevated. Supplementation with IFNγ, a well-known inducer of IDO1 expression, could rescue neither IDO1 expression nor Th cell suppression under hypoxic conditions. CONCLUSION: Hypoxia strongly affected the crosstalk between synovial fibroblasts and Th cells. By reducing the efficiency of synovial fibroblasts to restrict Th cell proliferation and by increasing the expression of IL-17A, hypoxia might have implications on the pathophysiology of RA.

Synovial Fibroblasts Selectively Suppress Th1 Cell Responses through IDO1-Mediated Tryptophan Catabolism.

The development of rheumatoid arthritis (RA) is linked to functional changes in synovial fibroblasts (SF) and local infiltration of T lymphocytes. Fibroblasts possess the capacity to suppress T cell responses, although the molecular mechanisms of this suppression remain incompletely understood. In this study, we aimed to define the mechanisms by which noninflammatory SF modulate Th cell responses and to determine the immunosuppressive efficacy of RASF. Hence, the influence of SF from osteoarthritis or RA patients on total Th cells or different Th cell subsets of healthy donors was analyzed in vitro. We show that SF strongly suppressed the proliferation of Th cells and the secretion of IFN-γ in a cell contact-independent manner. In cocultures of SF and Th cells, tryptophan was completely depleted within a few days, resulting in eukaryotic initiation factor 2α phosphorylation, TCRζ-chain downregulation, and proliferation arrest. Blocking IDO1 activity completely restored Th cell proliferation, but not IFN-γ production. Interestingly, only the proliferation of Th1 cells, but not of Th2 or Th17 cells, was affected. Finally, RASF had a significantly lower IDO1 expression and a weaker Th cell suppressive capacity compared with osteoarthritis SF. We postulate that the suppression of Th cell growth by SF through tryptophan catabolism may play an important role in preventing inappropriate Th cell responses under normal conditions. However, expansion of Th17 cells that do not induce IDO1-mediated suppression and the reduced capacity of RASF to restrict Th cell proliferation through tryptophan metabolism may support the initiation and propagation of synovitis in RA patients.

Activated human B cells induce inflammatory fibroblasts with cartilage-destructive properties and become functionally suppressed in return.

BACKGROUND: Cross-talk between synovial fibroblasts (SF) and immune cells is suggested to play a crucial role in inflammation and chronification of rheumatoid arthritis (RA). The contribution of B cells in this process is poorly defined. METHODS: Here, primary B cells from healthy donors were polyclonally activated and cocultured with SF of non-synovitic origin from patients with osteoarthritis. RESULTS: In B-SF cocultures the concentrations of interleukin 6 (IL-6) and IL-8 increased manifold compared with single cultures even under physical separation and remained stable for several days after B-cell removal. Intracellular staining confirmed SF as key producers of IL-6 and IL-8, and B cells as main producers of tumour necrosis factor alpha (TNFα) and IL-1ß. Blocking experiments with a combination of anti-TNFα-antibodies and rIL-1RA significantly reduced SF cytokine production by up to 90%, suggesting that B-cell-derived TNFα and IL-1ß were crucial mediators of SF activation. Interestingly, B-cell cytokine production, CD25 expression and proliferation decreased in cocultures by at least 50%, demonstrating a negative regulatory loop towards the activated B cells. Inhibition of activin receptor-like kinase 5, a crucial component of the tumour growth factor ß (TGFß) signalling pathway, partly restored B-cell proliferation, suggesting a contribution of SF-derived TGFß in B-cell suppression. Besides cytokines, B-cell-activated SF also upregulated secretion of matrix metalloproteases such as MMP-3, thereby acquiring potential tissue destructive properties. This was confirmed by their invasion into human cartilage in the severe combined immunodeficiency mouse fibroblast invasion model in vivo. CONCLUSIONS: Interaction with activated B cells leads to conversion of non-arthritic SF into SF with a proinflammatory and aggressive RA-like phenotype, thereby suggesting a new, so far unrecognised role for B cells in RA pathogenesis.

Role of the cholinergic antiinflammatory pathway in murine autoimmune myocarditis.

RATIONALE: This study was performed to gain insights into novel therapeutic approaches for the treatment of autoimmune myocarditis. OBJECTIVE: Chemical stimulation of the efferent arm of the vagus nerve through activation of nicotinic acetylcholine receptor subtype-7α (α7-nAChR) has been shown to be protective in several models of inflammatory diseases. In the present study, we investigated the potentially protective effect of vagus nerve stimulation on myocarditis. METHODS AND RESULTS: A/J mice were immunized with cardiac troponin I (TnI) to induce autoimmune myocarditis. Mice were exposed to drinking water that contained nicotine in different concentrations and for different time periods (for 3 days at 12.5 mg/L; 3 days at 125 mg/L; 21 days at 12.5 mg/L; and 21 days at 125 mg/L after first immunization). TnI-immunized mice with no pharmacological treatment showed extensive myocardial inflammation and fibrosis and significantly elevated levels of interleukin-6 and tumor necrosis factor-α. Furthermore, elevated levels of mRNA transcripts of proinflammatory chemokines (monocyte chemoattractant protein-1, macrophage inflammatory protein-1ß, and RANTES) and chemokine receptors (CCR1, CCR2, and CCR5) were found. Oral nicotine administration reduced inflammation within the myocardium, decreased the production of interleukin-6 and tumor necrosis factor-α, and downregulated the expression of monocyte chemoattractant protein-1, macrophage inflammatory protein-1ß, RANTES, CCR1, CCR2, and CCR5. In addition, nicotine treatment resulted in decreased expression of matrix metalloproteinase-14, natriuretic peptide precursor B, tissue inhibitor of metalloproteinase-1, and osteopontin, proteins that are commonly involved in heart failure. Finally, we found that nicotine reduced levels of pSTAT3 (phosphorylated signal transducer and activator of transcription 3) protein expression within the myocardium. Neostigmine treatment did not affect the progression of myocarditis. CONCLUSIONS: We showed that activation of the cholinergic antiinflammatory pathway with nicotine reduces inflammation in autoimmune myocarditis. Our results may open new possibilities in the therapeutic management of autoimmune myocarditis.

Identification of a human Th1-like IFNγ-secreting Treg subtype deriving from effector T cells.

Characteristics and function of effector T-cells with regulatory properties (induced Treg, "iTreg") in humans are ill defined. Here we report that a proportion of activated, initially CD4(+)CD25(-)CD127(+) effector T-cells from human peripheral blood can convert into T-cells with regulatory activity while concomitantly secreting IFNγ. Upon short-term culture in vitro these cells expressed a panel of common Treg markers, including FOXP3, CD25, GITR, HLA-DR and CTLA-4 in parallel with the Th1-specific transcription factor T-bet. Despite their own IFNγ secretion they effectively suppressed IFNγ secretion in effector T cells in parallel with inhibition of their proliferation. Highly purified IFNγ(+)iTreg shared many functional properties with nTreg: Their suppressive activity was antigen-independent, contact-mediated and cytokine-independent. Of note, in contrast to nTreg an inhibitor of TGF-ß1 signalling promoted the proliferation of IFNγ(+)iTreg, without abrogating their suppressive function. In addition in vivo in tonsils of patients with chronic tonsillitis an IFNγ-secreting subpopulation of the CD4(+)CD25(-)CD127(+)CD45RA(-) memory T helper cell population was detected, which exhibited regulatory properties as well. Our results support the existence of Th1-like adaptive Tregs in humans that express a robust regulatory phenotype, comparable to nTreg and at the same time share characteristics of Th1 cells. According to our in vitro data IFNγ(+)iTreg can emerge from activated effector T cells and downregulate Th1-mediated immune responses, supporting the hypothesis of effector T cell plasticity as a means for proper initiation and self regulation of inflammatory processes. This report characterizes a new subpopulation of human adaptive regulatory T-cells that derive from effector Th-cells and concomitantly express Th1-specific T-bet and IFNγ with Foxp3.

Effect of JAK Inhibition on the Induction of Proinflammatory HLA-DR+CD90+ Rheumatoid Arthritis Synovial Fibroblasts by Interferon-γ.

OBJECTIVE: Findings from recent transcriptome analyses of the synovium of patients with rheumatoid arthritis (RA) have revealed that 15-fold expanded HLA-DR+CD90+ synovial fibroblasts potentially act as key mediators of inflammation. The reasons for the expansion of HLA-DR+CD90+ synovial fibroblasts are unclear, but genetic signatures indicate that interferon-γ (IFNγ) plays a central role in the generation of this fibroblast subset. The present study was undertaken to investigate the generation, function and therapeutically intended blockage of HLA-DR+CD90+ synovial fibroblasts. METHODS: We combined functional assays using primary human materials and focused bioinformatic analyses of mass cytometry and transcriptomics patient data sets. RESULTS: We detected enriched and activated Fcγ receptor type IIIa-positive (CD16+) NK cells in the synovial tissue from patients with active RA. Soluble immune complexes were recognized by CD16 in a newly described reporter cell model, a mechanism that could be contributing to the activation of natural killer (NK) cells in RA. In vitro, NK cell-derived IFNγ induced HLA-DR on CD90+ synovial fibroblasts, leading to an inflammatory, cytokine-secreting HLA-DR+CD90+ phenotype. HLA-DR+CD90+ synovial fibroblasts consecutively activated CD4+ T cells upon receptor crosslinking via superantigens. HLA-DR+CD90+ synovial fibroblasts also activated CD4+ T cells in the absence of superantigens, an effect that was initiated by NK cell-derived IFNγ and that was 4 times stronger in patients with RA compared to patients with osteoarthritis. Finally, JAK inhibition in synovial fibroblasts prevented HLA-DR induction and blocked proinflammatory signals to T cells. CONCLUSION: The HLA-DR+CD90+ phenotype represents an activation state of synovial fibroblasts during the process of inflammation in RA that can be induced by IFNγ, likely generated from infiltrating leukocytes such as activated NK cells. The induction of these proinflammatory, interleukin-6-producing, and likely antigen-presenting synovial fibroblasts can be targeted by JAK inhibition.

Targeting of Janus Kinases Limits Pro-Inflammatory but Also Immunosuppressive Circuits in the Crosstalk between Synovial Fibroblasts and Lymphocytes.

Crosstalk between synovial fibroblasts (SF) and immune cells plays a central role in the development of rheumatoid arthritis (RA). Janus kinase inhibitors (JAKi) have proven efficacy in the treatment of RA, although clinical responses are heterogeneous. Currently, little is known regarding how JAKi affect pro- and anti-inflammatory circuits in the bidirectional interplay between SF and immune cells. Here, we examined the effects of tofacitinib, baricitinib and upadacitinib on crosstalk between SF and T or B lymphocytes in vitro and compared them with those of biologic disease modifying anti-rheumatic drugs (bDMARDs). JAKi dose-dependently suppressed cytokine secretion of T helper (Th) cells and decreased interleukin (IL)-6 and matrix metalloproteinase (MMP)3 secretion of SF stimulated by Th cells. Importantly, JAK inhibition attenuated the enhanced memory response of chronically stimulated SF. Vice versa, JAKi reduced the indoleamine-2,3-dioxygenase (IDO)1-mediated suppression of T cell-proliferation by SF. Remarkably, certain bDMARDs were as efficient as JAKi in suppressing the IL-6 and MMP3 secretion of SF stimulated by Th (adalimumab, secukinumab) or B cells (canakinumab) and combining bDMARDs with JAKi had synergistic effects. In conclusion, JAKi limit pro-inflammatory circuits in the crosstalk between SF and lymphocytes; however, they also weaken the immunosuppressive functions of SF. Both effects were dose-dependent and may contribute to heterogeneity in clinical response to treatment.

Proinflammatory T cell polarization is already present in patients with early knee osteoarthritis.

BACKGROUND: Investigating the pathophysiological mechanisms of early osteoarthritis (OA) is of utmost interest since this stage holds the strongest promise for therapeutic interventions. The aims of this study were to analyze if synovial inflammation is already present in early OA and to characterize the involved cell populations, by investigating synovial fluid (SF) and synovial membrane (SM) of early OA patients for the presence and polarization status of CD4 T cells. METHODS: A quantitative analysis of CD4+ T cell infiltration in SF and SM compared to peripheral blood (PB) was performed in patients with early stages of OA. We further investigated intracellular staining (ICS), surface marker, and chemokine receptor expression profiles of CD4+ T cells in SF, SM, and PB, as well as cytokine expression in native SF and PB. Matched samples of SF, SM, and PB were harvested from 40 patients with early OA at the time of surgery. Early OA was confirmed by independent surgeons intraoperatively. Samples were analyzed by flow cytometry for surface markers and cytokines, which are preferentially expressed by distinct T cell subsets (Th1, Th2, Th17, regulatory T cells). Furthermore, we analyzed native SF and PB supernatants using MACSPlex for multiple cytokine expression profiles. RESULTS: SF and SM showed a distinct infiltration of CD4+ T lymphocytes, with significantly increased expression of chemokine receptors CXCR3/CCR5, cytokine IFN-γ (preferentially expressed by Th1 cells), and CD161 (preferentially expressed by IL-17 producing Th17 cells) compared to PB. Furthermore, the percentage of CD4+ T cells polarized to Treg was significantly increased in SM compared to SF and PB. No significant differences were observed for CCR3 and CCR4 (preferentially expressed by Th2 cells), although IL-4 values were significantly higher in SM and SF compared to PB. Cytokine analysis showed comparable results between PB and SF, with only IL-6 being significantly increased in SF. CONCLUSIONS: Early OA joints show already significant inflammation through CD4+ T cell infiltration, with predominant Th1 cell polarization. Inflammation seems to be driven by direct proinflammatory cell interaction. Cytokine signaling seems to be negligible at the site of inflammation in early OA, with only IL-6 being significantly increased in SF compared to PB.

Increase of aerobic glycolysis mediated by activated T helper cells drives synovial fibroblasts towards an inflammatory phenotype: new targets for therapy?

BACKGROUND: A dysregulated glucose metabolism in synovial fibroblasts (SF) has been associated with their aggressive phenotype in rheumatoid arthritis (RA). Even though T helper (Th) cells are key effector cells in the propagation and exacerbation of synovitis in RA, little is known about their influence on the metabolism of SF. Thus, this study investigates the effect of Th cells on the glucose metabolism and phenotype of SF and how this is influenced by the blockade of cytokines, janus kinases (JAKs) and glycolysis. METHODS: SF from patients with RA or osteoarthritis (OA) were cultured in the presence of a stable glucose isotopomer ([U-13C]-glucose) and stimulated with the conditioned media of activated Th cells (ThCM). Glucose consumption and lactate production were measured by proton nuclear magnetic resonance (1H NMR) spectroscopy. Cytokine secretion was quantified by ELISA. The expression of glycolytic enzymes was analysed by PCR, western blot and immunofluorescence. JAKs were blocked using either baricitinib or tofacitinib and glycolysis by using either 3-bromopyruvate or FX11. RESULTS: Quiescent RASF produced significantly higher levels of lactate, interleukin (IL)-6 and matrix metalloproteinase (MMP) 3 than OASF. Stimulation by ThCM clearly changed the metabolic profile of both RASF and OASF by inducing a shift towards aerobic glycolysis with strongly increased lactate production together with a rise in IL-6 and MMP3 secretion. Interestingly, chronic stimulation of OASF by ThCM triggered an inflammatory phenotype with significantly increased glycolytic activity compared to unstimulated, singly stimulated or re-stimulated OASF. Finally, in contrast to cytokine-neutralizing biologics, inhibition of JAKs or glycolytic enzymes both significantly reduced lactate production and cytokine secretion by Th cell-stimulated SF. CONCLUSIONS: Soluble mediators released by Th cells drive SF towards a glycolytic and pro-inflammatory phenotype. Targeting of JAKs or glycolytic enzymes both potently modulate SF's glucose metabolism and decrease the release of IL-6 and MMP3. Thus, manipulation of glycolytic pathways could represent a new therapeutic strategy to decrease the pro-inflammatory phenotype of SF.

Mimicry of pre-B cell receptor signaling by activation of the tyrosine kinase Blk.

During B lymphoid ontogeny, assembly of the pre-B cell receptor (BCR) is a principal developmental checkpoint at which several Src-related kinases may play redundant roles. Here the Src-related kinase Blk is shown to effect functions associated with the pre-BCR. B lymphoid expression of an active Blk mutant caused proliferation of B progenitor cells and enhanced responsiveness of these cells to interleukin 7. In mice lacking a functional pre-BCR, active Blk supported maturation beyond the pro-B cell stage, suppressed VH to DJH rearrangement, relieved selection for productive heavy chain rearrangement, and stimulated kappa rearrangement. These alterations were accompanied by tyrosine phosphorylation of immunoglobulin beta and Syk, as well as changes in gene expression consistent with developmental maturation. Thus, sustained activation of Blk induces responses normally associated with the pre-BCR.

Induction of CD4+ T-cell anergy and apoptosis by activated human B cells.

B cells are well-known mediators of humoral immunity and serve as costimulators in the generation of T cell-mediated responses. In several mouse models, however, it was observed that B cells can also down-regulate immune reactions, suggesting a dual role for B cells. Due to this discrepancy and so far limited data, we directly tested the effects of primary human B cells on activated CD4(+) T helper cells in vitro. We found that under optimal costimulation large, activated CD25(+) B cells but not small CD25(-) B cells induced temporary T-cell anergy, determined by cell division arrest and down-regulation of cytokine production. In addition, large CD25(+) B cells directly induced CD95-independent apoptosis in a subpopulation of activated T cells. Suppression required direct B-T-cell contact and was not transferable from T to T cell, excluding potential involvement of regulatory T cells. Moreover, inhibitory effects involved an IL-2-dependent mechanism, since decreasing concentrations of IL-2 led to a shift from inhibitory toward costimulatory effects triggered by B cells. We conclude that activated CD25(+) B cells are able to costimulate or down-regulate T-cell responses, depending on activation status and environmental conditions that might also influence their pathophysiological impact.

T Helper Cell Infiltration in Osteoarthritis-Related Knee Pain and Disability.

Despite the growing body of literature demonstrating a crucial role of T helper cell (Th) responses in the pathogenesis of osteoarthritis (OA), only few clinical studies have assessed interactions between Th cells and OA-related symptoms. Yet, the inclusion of clinical data in the interpretation of cellular analyses of Th cell infiltration is essential to reveal the mechanisms underlying the complex pathophysiology of OA pain and disability. Thus, the aim of the study was to analyze the infiltration pattern of Th cells in systemic (peripheral blood) and joint-derived (synovial membrane and fluid) samples from patients with knee OA in relation to OA-induced pain and disability. Therefore, radiographic OA severity, knee pain and function of 47 OA patients undergoing knee arthroplasty were evaluated prior to surgery. In parallel, samples of peripheral blood (PB), synovial membrane (SM) and synovial fluid (SF) were harvested and analyzed for different Th subsets using flow cytometry. According to surface marker expression Th cells (CD3+ CD4+ CD8-) were assigned to the Th subsets Th1 (CXCR3+, CCR5+), Th2 (CCR3+, CCR4+) and Th17 (CD161+, CCR6+). Interestingly, infiltration of the SM with all Th subtypes (Th1, Th2, Th17) significantly correlated with OA-induced disability. Most importantly, synovial CCR5+ and CCR3+ Th cell infiltration was associated with OA-related knee pain and disability. Furthermore, higher percentage rates of CXCR3+ Th cells in all tissue samples (PB, SM, SF) showed significant associations with OA severity. In contrast, increasing percentage rates of CD161+ Th cells in SM samples corresponded to a better functional outcome. In conclusion, the current study provides an extensive profile of the Th cell infiltration pattern in PB, SF and SM from patients with clinically relevant knee OA. Th cell infiltration of the SM might play a crucial role not only in the pathogenesis of OA but also in the development of OA-related knee pain and disability.

Activation of natural killer cells by rituximab in granulomatosis with polyangiitis.

OBJECTIVE: In the last few years, anti-CD20 antibody rituximab profoundly changed the therapeutic landscape of granulomatosis with polyangiitis (GPA). Here, we investigated whether natural killer (NK) cells may play a role in rituximab's mechanism of action in GPA. METHODS: B cell depletion, NK cell degranulation, and the expression of CD69 and CD16 on NK cells were measured in a series of in vitro experiments using peripheral blood mononuclear cells (PBMCs). In vivo activation of NK cells was investigated in patients receiving rituximab infusions. Cells were analyzed by seven-color flow cytometry. RESULTS: NK cells from GPA patients were activated by immobilized rituximab. Also soluble rituximab activated NK cells, provided that B cells were present. NK cells degranulated and expressed the activation marker CD69 while CD16 expression was decreased. This activation of NK cells by soluble rituximab was accompanied by a reduction of B cells. The next-generation anti-CD20 antibody obinutuzumab showed stronger effects compared to rituximab on both the reduction of B cells and the activation of NK cells. Finally, we found that rituximab led to the activation of NK cells in vivo, provided that B cells were not depleted due to prior rituximab infusions. CONCLUSION: B cell-bound rituximab activates NK cells in GPA. While NK cells therefore participate in rituximab's mechanism of action in humans, their potential may be more efficiently exploited, e.g., by Fc engineering of therapeutic antibodies.

Peripheral blood natural killer cell percentages in granulomatosis with polyangiitis correlate with disease inactivity and stage.

INTRODUCTION: The role of CD3-CD56+ natural killer (NK) cells in granulomatosis with polyangiitis (GPA) is poorly understood. Recently, it has been shown that peripheral blood NK cells can kill renal microvascular endothelial cells, suggesting a pathogenic role of NK cells in this disease. So far, subset distribution, phenotype, and function of peripheral blood NK cells in relation to GPA disease activity have not been elucidated. Moreover, it is not known whether NK cells infiltrate GPA tissue lesions. METHODS: Paraffin sections of GPA granulomas and controls were stained with anti-CD56 and anti-CD3 antibodies. Peripheral blood lymphocyte subsets were analyzed by flow cytometry. NK cell degranulation was analyzed using cocultures of patient PBMCs with target cells and surface expression of CD107a. Clinical data were extracted from medical records. Statistical analysis was performed in an exploratory way. RESULTS: CD56+ cells were not detectable in active granulomatous GPA lesions but were found frequently in granulomas from tuberculosis and sarcoidosis patients. In GPA, the proportion of NK cells among peripheral blood lymphocytes correlated negatively with the Birmingham Vasculitis Activity Score (BVAS) (n = 28). Accordingly, NK cell percentages correlated positively with the duration of remission (n = 28) and were significantly higher in inactive GPA (BVAS = 0, n = 17) than in active GPA, healthy controls (n = 29), and inactive control diseases (n = 12). The highest NK cell percentages were found in patients with long-term remission and tapered immunosuppressive therapy. NK cell percentages >18.5% of peripheral blood lymphocytes (n = 12/28) determined GPA inactivity with a specificity of 100%. The differentiation into CD56(dim) and CD56(bright) NK cell subsets was unchanged in GPA (n = 28), irrespective of disease activity. Similar surface expression of the activating NK cell-receptors (NKp30, NKp46, and NKG2D) was determined. Like in healthy controls, GPA NK cells degranulated in the presence of NK cell receptor ligand bearing epithelial and lymphatic target cells. CONCLUSIONS: NK cells were not detectable in GPA granulomas. Peripheral blood NK cell percentages positively correlate with the suppression of GPA activity and could serve as a biomarker for GPA activity. Peripheral blood NK cells in GPA patients are mature NK cells with preserved immune recognition.

Impaired suppressive capacity of activation-induced regulatory B cells in systemic lupus erythematosus.

OBJECTIVE: B cells with immunoregulatory properties (Breg cells) have been described in mice, but their role in the control of human immune responses is not well defined. We recently identified a human population of activated FSC(high) B cells that exhibited regulatory activity toward T helper cells. The aim of the present study was to test such induced Breg (iBreg) cells in patients with autoimmune disease. METHODS: Purified CD19+FSC(high) B cells derived from patients with systemic lupus erythematosus (SLE) or from healthy donors, which were activated via their B cell receptor, were cocultured with CD3-stimulated CD4+ T helper cells from SLE patients or healthy donors. (3) H-thymidine incorporation, flow cytometry, and enzyme-linked immunosorbent assay (ELISA) were used to analyze proliferation, cytokine secretion, and surface marker expression. RESULTS: Although under costimulatory conditions, FSC(high) SLE B cells supported the proliferation of healthy donor T cells to a similar extent as donor B cells, their regulatory function was significantly diminished in B cell suppressor assays. Similar effects were seen when SLE T cells were used, confirming that SLE T cells were equally susceptible to iBreg cell signals as healthy donor T cells and that SLE iBreg cell defects were independent of T cell origin. B cell viability and expression of surface markers (CD25, CD80, and B7-H1) or cytokines (interleukin-6 [IL-6], tumor necrosis factor α, and IL-10) were comparable in the two B cell populations. There was no correlation between the extent of iBreg cell-induced inhibition and disease activity. CD19+FSC(high) B cells from patients with another systemic autoimmune disease, granulomatosis with polyangiitis (Wegener's) (GPA), exhibited no regulatory defects, which suggests that the iBreg cell defects were SLE-specific and not a general consequence of autoimmunity or inflammation. CONCLUSION: Induced Breg cells from SLE patients, but not GPA patients, are less effective in the control of T helper cell proliferation, which supports the reported skewed B cell repertoire in SLE. The malfunctioning SLE iBreg cells might allow the overstimulation of immune responses and contribute to the initiation and/or perpetuation of disease.

CD4⁺CD25⁺/highCD127low/⁻ regulatory T cells are enriched in rheumatoid arthritis and osteoarthritis joints--analysis of frequency and phenotype in synovial membrane, synovial fluid and peripheral blood.

INTRODUCTION: CD4⁺CD25⁺/highCD127low/⁻ regulatory T cells (Tregs) play a crucial role in maintaining peripheral tolerance. Data about the frequency of Tregs in rheumatoid arthritis (RA) are contradictory and based on the analysis of peripheral blood (PB) and synovial fluid (SF). Because Tregs exert their anti-inflammatory activity in a contact-dependent manner, the analysis of synovial membrane (SM) is crucial. Published reports regarding this matter are lacking, so we investigated the distribution and phenotype of Tregs in concurrent samples of SM, SF and PB of RA patients in comparison to those of osteoarthritis (OA) patients. METHODS: Treg frequency in a total of 40 patients (18 RA and 22 OA) matched for age and sex was assessed by flow cytometry. Functional status was assessed by analysis of cell surface markers representative of activation, memory and regulation. RESULTS: CD4⁺ T cells infiltrate the SM to higher frequencies in RA joints than in OA joints (P = 0.0336). In both groups, Tregs accumulate more within the SF and SM than concurrently in PB (P < 0.0001). Relative Treg frequencies were comparable in all compartments of RA and OA, but Treg concentration was significantly higher in the SM of RA patients (P = 0.025). Both PB and SM Tregs displayed a memory phenotype (CD45RO⁺RA⁻), but significantly differed in activation status (CD69 and CD62L) and markers associated with Treg function (CD152, CD154, CD274, CD279 and GITR) with only minor differences between RA and OA. CONCLUSIONS: Treg enrichment into the joint compartment is not specific to inflammatory arthritis, as we found that it was similarly enriched in OA. RA pathophysiology might not be due to a Treg deficiency, because Treg concentration in SM was significantly higher in RA. Synovial Tregs represent a distinct phenotype and are activated effector memory cells (CD62L⁻CD69⁺), whereas peripheral Tregs are resting central memory cells (CD62L⁺CD69⁻).

Leflunomide induces apoptosis in fludarabine-resistant and clinically refractory CLL cells.

PURPOSE: Environmental conditions in lymph node proliferation centers protect chronic lymphocytic leukemia (CLL) cells from apoptotic triggers. This situation can be mimicked by in vitro stimulation with CD40 ligand (CD40L) and interleukin 4 (IL-4). Our study investigates the impact of the drug leflunomide to overcome apoptosis resistance of CLL cells. EXPERIMENTAL DESIGN: CLL cells were stimulated with CD40L and IL-4 and treated with fludarabine and the leflunomide metabolite A771726. RESULTS: Resistance to fludarabine-mediated apoptosis was induced by CD40 activation alone stimulating high levels of BCL-XL and MCL1 protein expression. Apoptosis resistance was further enhanced by a complementary Janus-activated kinase (JAK)/STAT signal induced by IL-4. In contrast, CLL proliferation required both a CD40 and a JAK/STAT signal and could be completely blocked by pan-JAK inhibition. Leflunomide (A771726) antagonized CD40L/IL-4-induced proliferation at very low concentrations (3 µg/mL) reported to inhibit dihydroorotate dehydrogenase. At a concentration of 10 µg/mL, A771726 additionally attenuated STAT3/6 phosphorylation, whereas apoptosis of CD40L/IL-4-activated ("resistant") CLL cells was achieved with higher concentrations (IC(50): 80 µg/mL). Apoptosis was also effectively induced by A771726 in clinically refractory CLL cells with and without a defective p53 pathway. Induction of apoptosis involved inhibition of NF-κB activity and loss of BCL-XL and MCL1 expression. In combination with fludarabine, A771726 synergistically induced apoptosis (IC(50): 56 µg/mL). CONCLUSION: We thus show that A771726 overcomes CD40L/IL-4-mediated resistance to fludarabine in CLL cells of untreated as well as clinically refractory CLL cells. We present a possible novel therapeutic principle for attacking chemoresistant CLL cells.

Reduced CD4+,CD25- T cell sensitivity to the suppressive function of CD4+,CD25high,CD127 -/low regulatory T cells in patients with active systemic lupus erythematosus.

OBJECTIVE: CD4+,CD25high regulatory T (Treg) cells play a crucial role in the maintenance of self tolerance and prevention of organ-specific autoimmunity. The presence of many in vivo-preactivated CD4+,CD25++ T cells in patients with systemic lupus erythematosus (SLE) poses a difficulty in discriminating CD25++ activated T cells from CD25high Treg cells. To overcome this problem, we analyzed the phenotype and function of CD4+,CD25high,CD127(-/low) natural Treg (nTreg) cells isolated from the peripheral blood of patients with SLE. METHODS: CD4+,CD25high,CD127(-/low) nTreg cells and CD4+,CD25- responder T (Tresp) cells from patients with SLE and normal donors were separated by fluorescence-activated cell sorting. Cell proliferation was quantified by 3H-thymidine incorporation, and immunophenotyping of the cells was done using FACScan. RESULTS: Comparable percentages of CD4+,CD25high,FoxP3+ T cells were observed in patients with SLE and normal donors. Proliferation of SLE nTreg cells sorted into the subset CD4+,CD25high,CD127(-/low) was significantly decreased compared with that of SLE nTreg cells sorted into the subset CD4+,CD25high (mean +/- SEM 2,223 +/- 351 counts per minute versus 9,104 +/- 1,720 cpm, respectively), while in normal donors, these values were 802 +/- 177 cpm and 2,028 +/- 548 cpm, respectively, confirming that effector cell contamination was reduced. Notably, the suppressive activity of nTreg cells was intact in all groups. However, CD4+,CD25- Tresp cells isolated from patients with active SLE were significantly less sensitive than those from patients with inactive SLE to the suppressive function of autologous or normal donor CD4+,CD25high,CD127(-/low) nTreg cells. Furthermore, a significant inverse correlation was observed between the extent of T cell regulation in suppressor assays and the level of lupus disease activity. CONCLUSION: This study is the first to show that, in human SLE, impaired sensitivity of Tresp cells to the suppressive effects of a comparably functional, highly purified nTreg cell population leads to a defective suppression of T cell proliferation in active SLE. Studies aiming to define the mechanisms leading to Tresp cell resistance might help in the development of highly specific, alternative immunotherapeutic tools for the control of systemic autoimmune diseases such as SLE.

Interleukin-4 supports interleukin-12-induced proliferation and interferon-gamma secretion in human activated lymphoblasts and T helper type 1 cells.

Interleukin-12 (IL-12) and IL-4 are known to differentially promote T helper (Th) cell differentiation. While IL-12 induces interferon-gamma (IFN-gamma) production and maturation of Th1 cells, IL-4 is thought to antagonize IL-12 and to favour Th2 development. Here we studied the combined action of various concentrations of common gamma-chain (gamma(c)-chain) cytokines, including IL-4 and the Th1 cytokine IL-12, in human activated lymphoblasts and Th1 cells. IL-4 and IL-7 potentiated IL-12-induced proliferation at every concentration tested (1-10 ng/ml) without increasing rescue from apoptosis, indicating that proliferation was directly affected by these cytokine combinations. With regards to cytokine secretion, IL-2 together with IL-12 initiated tumour necrosis factor-alpha synthesis, enhanced IFN-gamma production, and shedding of soluble IL-2 receptor alpha as expected. Importantly, combining IL-4 with IL-12 also enhanced IFN-gamma secretion in lymphoblasts and a Th1 cell line. Investigating signal transduction in lymphoblasts induced by these cytokines, we found that not only IL-2 but also IL-4 enhances signal transducer and activator of transcription 3 (STAT3) tyrosine phosphorylation by IL-12. Tyrosine phosphorylations of janus kinase 2 (JAK-2), tyrosine kinase 2 (TYK2), extracellular signal-regulated kinase (ERK) and STAT4, STAT5 and STAT6 were not potentiated by combinations of these cytokines, suggesting specificity for increased STAT3 phosphorylation. In conclusion, two otherwise antagonizing cytokines co-operate in activated human lymphoblasts and Th1 cells, possibly via STAT3 as a converging signal. These data demonstrate that IL-4 can directly enhance human Th1 cell function independently of its known actions on antigen-presenting cells. These findings should be of importance for the design of cytokine-targeted therapies of human Th-cell-driven diseases.