Periodontitis-associated pathogens P. gingivalis and A. actinomycetemcomitans activate human CD14(+) monocytes leading to enhanced Th17/IL-17 responses.

The Th17/IL-17 pathway is implicated in the pathogenesis of periodontitis (PD), however the mechanisms are not fully understood. We investigated the mechanism by which the periodontal pathogens Porphyromonas gingivalis (Pg) and Aggregatibacter actinomycetemcomitans (Aa) promote a Th17/IL-17 response in vitro, and studied IL-17(+) CD4(+) T-cell frequencies in gingival tissue and peripheral blood from patients with PD versus periodontally healthy controls. Addition of Pg or Aa to monocyte/CD4(+) T-cell co-cultures promoted a Th17/IL-17 response in vitro in a dose- and time-dependent manner. Pg or Aa stimulation of monocytes resulted in increased CD40, CD54 and HLA-DR expression, and enhanced TNF-α, IL-1ß, IL-6 and IL-23 production. Mechanistically, IL-17 production in Pg-stimulated co-cultures was partially dependent on IL-1ß, IL-23 and TLR2/TLR4 signalling. Increased frequencies of IL-17(+) cells were observed in gingival tissue from patients with PD compared to healthy subjects. No differences were observed in IL-17(+) CD4(+) T-cell frequencies in peripheral blood. In vitro, Pg induced significantly higher IL-17 production in anti-CD3 mAb-stimulated monocyte/CD4(+) T-cell co-cultures from patients with PD compared to healthy controls. Our data suggest that periodontal pathogens can activate monocytes, resulting in increased IL-17 production by human CD4(+) T cells, a process that appears enhanced in patients with PD.

Interaction with activated monocytes enhances cytokine expression and suppressive activity of human CD4+CD45ro+CD25+CD127(low) regulatory T cells.

OBJECTIVE: Despite the high frequency of CD4+ T cells with a regulatory phenotype (CD25+CD127(low) FoxP3+) in the joints of patients with rheumatoid arthritis (RA), inflammation persists. One possible explanation is that human Treg cells are converted into proinflammatory interleukin-17 (IL-17)-producing cells by inflammatory mediators and thereby lose their suppressive function. The aim of this study was to investigate whether activated monocytes, which are potent producers of inflammatory cytokines and are abundantly present in the rheumatic joint, induce proinflammatory cytokine expression in human Treg cells and impair their regulatory function. METHODS: The presence and phenotype of CD4+CD45RO+CD25+CD127(low) T cells (memory Treg cells) and CD14+ monocytes in the peripheral blood (PB) and synovial fluid (SF) of patients with RA were investigated by flow cytometry. Memory Treg cells obtained from healthy control subjects underwent fluorescence-activated cell sorting and then were cocultured with autologous activated monocytes and stimulated with anti-CD3 monoclonal antibodies. Intracellular cytokine expression, phenotype, and function of cells were determined by flow cytometry, enzyme-linked immunosorbent assay, and proliferation assays. RESULTS: In patients with RA, the frequencies of CD4+CD45RO+CD25+CD127(low) Treg cells and activated CD14+ monocytes were higher in SF compared with PB. In vitro-activated monocytes induced an increase in the percentage of IL-17-positive, interferon-γ (IFNγ)-positive, and tumor necrosis factor α (TNFα)-positive Treg cells as well as IL-10-positive Treg cells. The observed increase in IL-17-positive and IFNγ-positive Treg cells was driven by monocyte-derived IL-1ß, IL-6, and TNFα and was mediated by both CD14+CD16- and CD14+CD16+ monocyte subsets. Despite enhanced cytokine expression, cells maintained their CD25+FoxP3+CD39+ Treg cell phenotype and showed an enhanced capacity to suppress T cell proliferation and IL-17 production. CONCLUSION: Treg cells exposed to a proinflammatory environment show increased cytokine expression as well as enhanced suppressive activity.

FAS/FAS-L dependent killing of activated human monocytes and macrophages by CD4+CD25- responder T cells, but not CD4+CD25+ regulatory T cells.

Conclusive resolution of an immune response is critical for the prevention of autoimmunity and chronic inflammation. We report that following co-culture with autologous CD4+CD25- responder T cells, human CD14+ monocytes and monocyte-derived macrophages become activated but also significantly more prone to apoptosis than monocytes/macrophages cultured alone. In contrast, in the presence of CD4+CD25+ regulatory T cells (Tregs), monocytes and macrophages survive whilst adopting an anti-inflammatory phenotype. The induction of monocyte death requires responder T cell activation and cell-contact between responder T cells and monocytes. We demonstrate a critical role for FAS/FAS-L ligation in responder T cell-induced monocyte killing since responder T cells, but not Tregs, upregulate FAS-ligand (FAS-L) mRNA, and induce FAS expression on monocytes. Furthermore, responder T cell-induced monocyte apoptosis is blocked by neutralising FAS/FAS-L interaction, and is not observed when monocytes from an autoimmune lymphoproliferative syndrome (ALPS) patient with complete FAS-deficiency are used as target cells. Finally, we show that responder T cell-induced killing of monocytes is impaired in patients with active rheumatoid arthritis (RA). Our data suggest that resolution of inflammation in the course of a healthy immune response is aided by the unperturbed killing of monocytes with inflammatory potential by responder T cells and the induction of longer-lived, Treg-induced, anti-inflammatory monocytes.

In vivo activated monocytes from the site of inflammation in humans specifically promote Th17 responses.

Th17 cells are a recently defined subset of proinflammatory T cells that contribute to pathogen clearance and tissue inflammation by means of the production of their signature cytokine IL-17A (henceforth termed IL-17). Although the in vitro requirements for human Th17 development are reasonably well established, it is less clear what their in vivo requirements are. Here, we show that the production of IL-17 by human Th17 cells critically depends on both the activation status and the anatomical location of accessory cells. In vivo activated CD14+ monocytes were derived from the inflamed joints of patients with active rheumatoid arthritis (RA). These cells were found to spontaneously and specifically promote Th17, but not Th1 or Th2 responses, compared with resting CD14+ monocytes from the blood. Surprisingly, unlike Th17 stimulation by monocytes that were in vitro activated with lipopolysaccharide, intracellular IL-17 expression was induced by in vivo activated monocytes in a TNF-alpha- and IL-1beta-independent fashion. No role for IL-6 or IL-23 production by either in vitro or in vivo activated monocytes was found. Instead, in vivo activated monocytes promoted Th17 responses in a cell-contact dependent manner. We propose that, in humans, newly recruited memory CD4(+) T cells can be induced to produce IL-17 in nonlymphoid inflamed tissue after cell-cell interactions with activated monocytes. Our data also suggest that different pathways may be utilized for the generation of Th17 responses in situ depending on the site or route of accessory cell activation.

Identification of early neurodegenerative pathways in progressive multiple sclerosis.

Progressive multiple sclerosis (MS) is characterized by unrelenting neurodegeneration, which causes cumulative disability and is refractory to current treatments. Drug development to prevent disease progression is an urgent clinical need yet is constrained by an incomplete understanding of its complex pathogenesis. Using spatial transcriptomics and proteomics on fresh-frozen human MS brain tissue, we identified multicellular mechanisms of progressive MS pathogenesis and traced their origin in relation to spatially distributed stages of neurodegeneration. By resolving ligand-receptor interactions in local microenvironments, we discovered defunct trophic and anti-inflammatory intercellular communications within areas of early neuronal decline. Proteins associated with neuronal damage in patient samples showed mechanistic concordance with published in vivo knockdown and central nervous system (CNS) disease models, supporting their causal role and value as potential therapeutic targets in progressive MS. Our findings provide a new framework for drug development strategies, rooted in an understanding of the complex cellular and signaling dynamics in human diseased tissue that facilitate this debilitating disease.

Mouse fetal growth restriction through parental and fetal immune gene variation and intercellular communications cascade.

Fetal growth restriction (FGR) affects 5-10% of pregnancies, and can have serious consequences for both mother and child. Prevention and treatment are limited because FGR pathogenesis is poorly understood. Genetic studies implicate KIR and HLA genes in FGR, however, linkage disequilibrium, genetic influence from both parents, and challenges with investigating human pregnancies make the risk alleles and their functional effects difficult to map. Here, we demonstrate that the interaction between the maternal KIR2DL1, expressed on uterine natural killer (NK) cells, and the paternally inherited HLA-C*0501, expressed on fetal trophoblast cells, leads to FGR in a humanized mouse model. We show that the KIR2DL1 and C*0501 interaction leads to pathogenic uterine arterial remodeling and modulation of uterine NK cell function. This initial effect cascades to altered transcriptional expression and intercellular communication at the maternal-fetal interface. These findings provide mechanistic insight into specific FGR risk alleles, and provide avenues of prevention and treatment.

CD4+CD25+Foxp3+ regulatory T cells induce alternative activation of human monocytes/macrophages.

CD4(+)CD25(+)Foxp3(+) regulatory T cells (Tregs) are potent suppressors of the adaptive immune system, but their effects on innate immune cells are less well known. Here we demonstrate a previously uncharacterized function of Tregs, namely their ability to steer monocyte differentiation toward alternatively activated macrophages (AAM). AAM are cells with strong antiinflammatory potential involved in immune regulation, tissue remodeling, parasite killing, and tumor promotion. We show that, after coculture with Tregs, monocytes/macrophages display typical features of AAM, including up-regulated expression of CD206 (macrophage mannose receptor) and CD163 (hemoglobin scavenger receptor), an increased production of CCL18, and an enhanced phagocytic capacity. In addition, the monocytes/macrophages have reduced expression of HLA-DR and a strongly reduced capacity to respond to LPS in terms of proinflammatory mediator production (IL-1beta, IL-6, IL-8, MIP-1alpha, TNF-alpha), NFkappaB activation, and tyrosine phosphorylation. Mechanistic studies reveal that CD4(+)CD25(+)CD127(low)Foxp3(+) Tregs produce IL-10, IL-4, and IL-13 and that these cytokines are the critical factors involved in the suppression of the proinflammatory cytokine response. In contrast, the Treg-mediated induction of CD206 is entirely cytokine-independent, whereas the up-regulation of CD163, CCL18, and phagocytosis are (partly) dependent on IL-10 but not on IL-4/IL-13. Together these data demonstrate a previously unrecognized function of CD4(+)CD25(+)Foxp3(+) Tregs, namely their ability to induce alternative activation of monocytes/macrophages. Moreover, the data suggest that the Treg-mediated induction of AAM partly involves a novel, cytokine-independent pathway.

TNF Blockade Maintains an IL-10+ Phenotype in Human Effector CD4+ and CD8+ T Cells.

CD4+ and CD8+ effector T cell subpopulations can display regulatory potential characterized by expression of the prototypically anti-inflammatory cytokine IL-10. However, the underlying cellular mechanisms that regulate expression of IL-10 in different T cell subpopulations are not yet fully elucidated. We recently showed that TNF inhibitors (TNFi) promote IL-10 expression in human CD4+ T cells, including IL-17+ CD4+ T cells. Here, we further characterized the regulation of IL-10 expression via blockade of TNF signaling or other cytokine/co-stimulatory pathways, in human T cell subpopulations. Addition of the TNFi drug adalimumab to anti-CD3-stimulated human CD4+ T cell/monocyte cocultures led to increased percentages of IL-10+ cells in pro-inflammatory IL-17+, IFNγ+, TNFα+, GM-CSF+, and IL-4+ CD4+ T cell subpopulations. Conversely, exogenous TNFα strongly decreased IL-10+ cell frequencies. TNF blockade also regulated IL-10 expression in CD4+ T cells upon antigenic stimulation. Using time course experiments in whole peripheral blood mononuclear cell (PBMC) cultures, we show that TNF blockade maintained, rather than increased, IL-10+ cell frequencies in both CD4+ and CD8+ T cells following in vitro stimulation in a dose- and time-dependent manner. Blockade of IL-17, IFNγ, IL-6R, or CD80/CD86-mediated co-stimulation did not significantly regulate IL-10 expression within CD4+ or CD8+ T cell subpopulations. We show that TNF blockade acts directly on effector CD4+ T cells, in the absence of monocytes or CD4+ CD25highCD127low regulatory T cells and independently of IL-27, resulting in higher IL-10+ frequencies after 3 days in culture. IL-10/IL-10R blockade reduced the frequency of IL-10-expressing cells both in the presence and absence of TNF blockade. Addition of recombinant IL-10 alone was insufficient to drive an increase in IL-10+ CD4+ T cell frequencies in 3-day CD4+ T cell/monocyte cocultures, but resulted in increased IL-10 expression at later time points in whole PBMC cultures. Together, these data provide additional insights into the regulation of IL-10 expression in human T cells by TNF blockade. The maintenance of an IL-10+ phenotype across a broad range of effector T cell subsets may represent an underappreciated mechanism of action underlying this widely used therapeutic strategy.

Interleukin-10 and prostaglandin E2 have complementary but distinct suppressive effects on Toll-like receptor-mediated dendritic cell activation in ovarian carcinoma.

Dendritic cells (DC) have the potential to instigate a tumour-specific immune response, but their ability to prime naïve lymphocytes depends on their activation status. Thus, for tumour immunotherapy to be effective, the provision of appropriate DC activation stimuli such as Toll-like receptor (TLR) agonists is crucial in order to overcome immunosuppression associated with the tumour microenvironment. To address this, we investigated how ovarian carcinoma (OC)-associated ascites impedes activation of DC by TLR agonists. Our results show that ascites reduces the TLR-mediated up-regulation of CD86 and partially inhibits the production of the pro-inflammatory cytokines interleukin 6 (IL-6), IL-12 and tumour necrosis factor α (TNFα) in monocyte-derived DC from healthy controls. We further observe an impaired T cell stimulatory capacity of DC upon activation with TLR agonists in the presence of ascites, indicating that their functionality is affected by the immunosuppressive factors. We identify IL-10 and prostaglandin E2 (PGE2) as the pivotal immunosuppressive components in OC-associated ascites compromising TLR-mediated DC activation. Interestingly, IL-10 is present in both ascites from patients with malignant OC and in peritoneal fluid from patients with benign ovarian conditions and both fluids have similar ability to reduce TLR-mediated DC activation. However, depletion of IL-10 from ascites revealed that the presence of paracrine IL-10 is not crucial for ascites-mediated suppression of DC activation in response to TLR activation. Unlike IL-10, PGE2 is absent from peritoneal fluid of patients with benign conditions and selectively reduces TNFα induction in response to TLR-mediated activation in the presence of OC-associated ascites. Our study highlights PGE2 as an immunosuppressive component of the malignant OC microenvironment rendering PGE2 a potentially important target for immunotherapy in OC.

Phenotypic, Functional, and Gene Expression Profiling of Peripheral CD45RA+ and CD45RO+ CD4+CD25+CD127(low) Treg Cells in Patients With Chronic Rheumatoid Arthritis.

OBJECTIVE: Conflicting evidence exists regarding the suppressive capacity of Treg cells in the peripheral blood (PB) of patients with rheumatoid arthritis (RA). The aim of this study was to determine whether Treg cells are intrinsically defective in RA. METHODS: Using a range of assays on PB samples from patients with chronic RA and healthy controls, CD3+CD4+CD25+CD127(low) Treg cells from the CD45RO+ or CD45RA+ T cell compartments were analyzed for phenotype, cytokine expression (ex vivo and after in vitro stimulation), suppression of Teff cell proliferation and cytokine production, suppression of monocyte-derived cytokine/chemokine production, and gene expression profiles. RESULTS: No differences between RA patients and healthy controls were observed with regard to the frequency of Treg cells, ex vivo phenotype (CD4, CD25, CD127, CD39, or CD161), or proinflammatory cytokine profile (interleukin-17 [IL-17], interferon-γ [IFNγ], or tumor necrosis factor [TNF]). FoxP3 expression was slightly increased in Treg cells from RA patients. The ability of Treg cells to suppress the proliferation of T cells or the production of cytokines (IFNγ or TNF) upon coculture with autologous CD45RO+ Teff cells and monocytes was not significantly different between RA patients and healthy controls. In PB samples from some RA patients, CD45RO+ Treg cells showed an impaired ability to suppress the production of certain cytokines/chemokines (IL-1ß, IL-1 receptor antagonist, IL-7, CCL3, or CCL4) by autologous lipopolysaccharide-activated monocytes. However, this was not observed in all patients, and other cytokines/chemokines (TNF, IL-6, IL-8, IL-12, IL-15, or CCL5) were generally suppressed. Finally, gene expression profiling of CD45RA+ or CD45RO+ Treg cells from the PB revealed no statistically significant differences between RA patients and healthy controls. CONCLUSION: Our findings indicate that there is no global defect in either CD45RO+ or CD45RA+ Treg cells in the PB of patients with chronic RA.

Resolving TYK2 locus genotype-to-phenotype differences in autoimmunity.

Thousands of genetic variants have been identified, which contribute to the development of complex diseases, but determining how to elucidate their biological consequences for translation into clinical benefit is challenging. Conflicting evidence regarding the functional impact of genetic variants in the tyrosine kinase 2 (TYK2) gene, which is differentially associated with common autoimmune diseases, currently obscures the potential of TYK2 as a therapeutic target. We aimed to resolve this conflict by performing genetic meta-analysis across disorders; subsequent molecular, cellular, in vivo, and structural functional follow-up; and epidemiological studies. Our data revealed a protective homozygous effect that defined a signaling optimum between autoimmunity and immunodeficiency and identified TYK2 as a potential drug target for certain common autoimmune disorders.

Interleukin-17+CD8+ T cells are enriched in the joints of patients with psoriatic arthritis and correlate with disease activity and joint damage progression.

OBJECTIVE: Psoriatic arthritis (PsA) is associated with HLA class I genes, in contrast to the association with HLA class II in rheumatoid arthritis (RA). Since IL-17+ cells are considered important mediators of synovial inflammation, we sought to determine whether IL-17-producing CD8+ T cells may be found in the joints of patients with PsA and whether these cells might contribute to the disease process. METHODS: Mononuclear cells from paired samples of synovial fluid (SF) and peripheral blood (PB) from patients with PsA or patients with RA were stimulated ex vivo, and CD4- T cells were examined by flow cytometry for cytokine expression, cytotoxic markers, and frequencies of γ/δ or mucosal-associated invariant T cells. Clinical measures of arthritis activity (C-reactive protein [CRP] level, erythrocyte sedimentation rate [ESR], Disease Activity Score in 28 joints [DAS28]) and power Doppler ultrasound (PDUS) scores for the presence of active synovitis in the aspirated knee were recorded and assessed for correlations with immunologic markers. RESULTS: Within the CD3+ T cell compartment, both IL-17+CD4- (predominantly CD8+) and IL-17+CD4+ T cells were significantly enhanced in the SF compared to the PB of patients with PsA (P = 0.0003 and P = 0.002, respectively; n = 21), whereas in patients with RA, only IL-17+CD4+ T cells were increased in the SF compared to the PB (P = 0.008; n = 14). The frequency of IL-17+CD4- T cells in PsA SF was positively correlated with the CRP level (r = 0.52, P = 0.01), ESR (r = 0.59, P = 0.004), and DAS28 (r = 0.52, P = 0.01), and was increased in patients with erosive disease (P < 0.05). In addition, the frequency of IL-17+CD4- T cells positively correlated with the PDUS score, a marker for active synovitis (r = 0.49, P = 0.04). CONCLUSION: These results show, for the first time, that the PsA joint, but not the RA joint, is enriched for IL-17+CD8+ T cells. Moreover, the findings reveal that the levels of this T cell subset are correlated with disease activity measures and the radiographic erosion status after 2 years, suggesting a previously unrecognized contribution of these cells to the pathogenesis of PsA.

TNF-α blockade induces IL-10 expression in human CD4+ T cells.

IL-17+ CD4+ T (Th17) cells contribute to the pathogenesis of several human inflammatory diseases. Here we demonstrate that TNF inhibitor (TNFi) drugs induce the anti-inflammatory cytokine IL-10 in CD4+ T cells including IL-17+ CD4+ T cells. TNFi-mediated induction of IL-10 in IL-17+ CD4+ T cells is Treg-/Foxp3-independent, requires IL-10 and is overcome by IL-1ß. TNFi-exposed IL-17+ CD4+ T cells are molecularly and functionally distinct, with a unique gene signature characterized by expression of IL10 and IKZF3 (encoding Aiolos). We show that Aiolos binds conserved regions in the IL10 locus in IL-17+ CD4+ T cells. Furthermore, IKZF3 and IL10 expression levels correlate in primary CD4+ T cells and Aiolos overexpression is sufficient to drive IL10 in these cells. Our data demonstrate that TNF-α blockade induces IL-10 in CD4+ T cells including Th17 cells and suggest a role for the transcription factor Aiolos in the regulation of IL-10 in CD4+ T cells.

Thymosin ß4-sulfoxide attenuates inflammatory cell infiltration and promotes cardiac wound healing.

The downstream consequences of inflammation in the adult mammalian heart are formation of a non-functional scar, pathological remodelling and heart failure. In zebrafish, hydrogen peroxide released from a wound is the initial instructive chemotactic cue for the infiltration of inflammatory cells, however, the identity of a subsequent resolution signal(s), to attenuate chronic inflammation, remains unknown. Here we reveal that thymosin ß4-sulfoxide lies downstream of hydrogen peroxide in the wounded fish and triggers depletion of inflammatory macrophages at the injury site. This function is conserved in the mouse and observed after cardiac injury, where it promotes wound healing and reduced scarring. In human T-cell/CD14+ monocyte co-cultures, thymosin ß4-sulfoxide inhibits interferon-γ, and increases monocyte dispersal and cell death, likely by stimulating superoxide production. Thus, thymosin ß4-sulfoxide is a putative target for therapeutic modulation of the immune response, resolution of fibrosis and cardiac repair.

Linking power Doppler ultrasound to the presence of th17 cells in the rheumatoid arthritis joint.

BACKGROUND: Power Doppler ultrasound (PDUS) is increasingly used to assess synovitis in Rheumatoid Arthritis (RA). Prior studies have shown correlations between PDUS scores and vessel counts, but relationships with T cell immunopathology have not been described. METHODOLOGY/PRINCIPAL FINDINGS: PBMC were isolated from healthy controls (HC) or RA patients and stimulated ex vivo with PMA and ionomycin for 3 hours in the presence of Golgistop. Paired synovial fluid (SF) or synovial tissue (ST) were analysed where available. Intracellular expression of IL-17, IFNgamma, and TNFalpha by CD4+ T cells was determined by flow cytometry. Synovial blood flow was evaluated by PDUS signal at the knees, wrists and metacarpophalangeal joints of RA patients. Serum, SF and fibroblast culture supernatant levels of vascular endothelial growth factor-A (VEGF-A) were measured by ELISA. The frequency of IL17+IFNgamma-CD4+ T cells (Th17 cells) was significantly elevated in peripheral blood (PB) from RA patients vs. HC (median (IQR) 0.5 (0.28-1.59)% vs. 0.32 (0.21-0.54)%, p = 0.005). Th17 cells were further enriched (mean 6.6-fold increase) in RA SF relative to RA PB. Patients with active disease had a higher percentage of IL-17+ T cells in ST than patients in remission, suggesting a possible role for Th17 cells in active synovitis in RA. Indeed, the percentage of Th17 cells, but not Th1, in SF positively correlated with CRP (r = 0.51, p = 0.04) and local PDUS-defined synovitis (r = 0.61, p = 0.002). Furthermore, patients with high levels of IL-17+CD4+ T cells in SF had increased levels of the angiogenic factor VEGF-A in SF. Finally, IL-17, but not IFNgamma, increased VEGF-A production by RA synovial fibroblasts in vitro. CONCLUSIONS/SIGNIFICANCE: Our data demonstrate a link between the presence of pro-inflammatory Th17 cells in SF and local PDUS scores, and offer a novel immunological explanation for the observation that rapid joint damage progression occurs in patients with persistent positive PDUS signal.

Optimal induction of T helper 17 cells in humans requires T cell receptor ligation in the context of Toll-like receptor-activated monocytes.

Recently, a new lineage of CD4+ T cells has been described in the mouse that specifically secretes IL-17 [T helper (Th) 17]. This discovery has led to a revision of the hypothesis that many autoimmune diseases are predominantly a Th1 phenomenon and may instead be critically dependent on the presence of Th17 cells. Murine Th17 cells differentiate from naïve T cell precursors in the presence of TGF-beta and IL-6 or IL-21. However, given their putative importance in human autoimmunity, very little is known about the pathways that control the expression of IL-17 in humans. Here we show that the factors that determine the expression of IL-17 in human CD4+ T cells are completely different from mice. IL-6 and IL-21 were unable to induce IL-17 expression in either naïve or effector T cells, and TGF-beta actually inhibited IL-17 expression. The expression of IL-17 was maximally induced from precommitted precursors present in human peripheral blood by cell-cell contact with Toll-like receptor-activated monocytes in the context of T cell receptor ligation. Furthermore, unlike IFN-gamma, IL-17 expression was not suppressed by the presence of FOXP3+ regulatory CD4+ T cells. Taken together, these data indicate that human and mouse Th17 cells have important biological differences that may be of critical importance in the development of therapeutic interventions in diseases characterized by aberrant T cell polarization.