Interplay Between Effector Th17 and Regulatory T Cells

Introduction  Over two decades ago, T helper cells were classified into its functional subsets. Soon after the classical observation of Mosmann et al., immunologists agreed to accept the Th1/Th2 paradigm of the T helper subsets. Each subset is not only characterized by its specific cytokines pattern and effector functions but also by their properties to counter regulate each other’s functions. This classification helped to understand the complex principles of T helper cell biology and allowed us to comprehend different immune reactions in context of Th1 and Th2 subsets. Discussion  Although Th1 subsets thought to be the crucial player for most of the organ-specific autoimmune diseases like multiple sclerosis and type-1 diabetes but the loss of Th1 dominant cytokine, IFN-γ did not prevent the development of autoimmunity which raised the possibility of involvement of other Th subsets, different from Th1 cells in the induction of autoimmunity. Conclusion  Recently, a new subset of Th cells that predominantly produce IL-17 and induce autoimmunity has been discovered, and it is believed that this subset may be the major cell type involved in orchestrating tissue inflammation and autoimmunity. Recent data propose that the differentiation factors of Th17 cells reveal a link with induction of Foxp3⁺ regulatory T cells. Here, we review the interplay between Th17 and Foxp3⁺ T-reg cells and Tr1 cells during autoimmune inflammatory reaction.     

Elevated circulating Th17 and follicular helper CD4+ T cells in patients with rheumatoid arthritis

It remains not fully elucidated the potential functions of Th17 cells and follicular helper T (Tfh) cells and secreting cytokines in the pathogenesis of rheumatoid arthritis (RA) and their association with disease activity. In this study, the frequencies of Th17 and Tfh cells were determined by flow cytometry, and the levels of interleukin (IL)‐17, IL‐21, and IL‐22 were measured by ELISA in RA patients with different disease activities. The dynamic changes of cell subsets were also detected in response to disease‐modify antirheumatic drugs (DMARDs) therapy. The percentages of CD3⁺CD4⁺IL‐17A⁺ (Th17) cells and CD3⁺CD4⁺CXCR5⁺ICOS^high (Tfh) cells, as well as the concentrations of IL‐17, IL‐21, and IL‐22 were significantly elevated in RA patients than those in healthy individuals. Furthermore, Tfh cells, IL‐21, and IL‐22 in the serum was positively correlated with the values of disease activity score. Concentrations of IL‐21 and IL‐22 in the serum were remarkably reduced following the DMARDs therapies. Our data suggested that Th17 cells, Tfh cells as well as the secreting cytokines may be involved in the pathogenesis of RA. The frequency of circulating Tfh cells and the productions of IL‐21 and IL‐22 were associated with the disease activity of RA patients, and might be potential therapeutic targets for treatment of RA.     

Activation of Peripheral Th17 Lymphocytes in Patients with Asthma

A recently identified interleukin (IL)-17-producing T-helper (Th) lymphocyte subset, which comprises Th17 cells producing hallmark cytokines IL-17A, IL-17F and IL-22, is involved in chronic inflammatory diseases. Elevated gene and protein expressions of IL-17 are manifested in allergic asthma. We further characterized the activation of Th17 cells in asthmatic patients. Peripheral blood mononuclear cells (PBMC) were purified from 31 asthmatic patients and 20 sex- and age-matched control subjects. The number of IL-17A secreting cells in peripheral blood was enumerated by enzyme-linked immunosorbent spot assay. Cell surface expression of Th17-related chemokine receptor CCR6, and plasma level of IL-17A, IL-17F and IL-22, and ex vivo production of IL-17A and IL-22 were measured by flow cytometry and enzyme-linked immunosorbent assay, respectively. The number of peripheral Th17 lymphocytes, expression of CCR6 on Th cells, and ex vivo IL-23, anti-CD3 and anti-CD28 induced production of IL-22 by PBMC were significantly elevated in asthmatic patients compared with control subjects (all p < 0.01). This clinical study further confirmed increased number of peripheral Th17 lymphocytes and cell surface expression of CCR6 receptors on Th cells in asthmatic patients. Pro-inflammatory cytokine IL-23 can exacerbate disease severity by activating pathogenic Th17 lymphocytes to release downstream inflammatory cytokine IL-22 in asthma.     

Resolution of Th/Tc17-driven inflammation during anti-TNFα treatment of rheumatoid arthritis reveals a unique immune biomarker profiling pattern

Rheumatoid arthritis (RA) is a chronic multisystem disease with a complex immunopathology. Its inflammatory state is dominated by pro-inflammatory cytokines such as TNFα and activated Th1/Th17. Only proportion of patients achieve clinical remission despite potent biologics targeting these pathways. This study investigated the resolution of inflammation in RA patients (naïve for biologics) receiving TNFα inhibitors (TNFi) and evaluated the biological mechanisms behind treatment response and assessed them using clinical scoring systems. The majority showed a good clinical response after six months (6M) and a significant drop in DAS28-CRP (P ≤ .002), CDAI (P ≤ .0001) and RheumXpert (P ≤ .0001). Before treatment, the patients demonstrated a chronic innate and adaptive inflammatory state. The improved clinical condition was reflected with a decrease in Th17/Tc17 (P ≤ .05) and an increase in Tregs after 6M (P ≤ .05). Using a logistic regression model on serum data, IL-6, IL-18, IL-21, IL-22, IFNγ and TNFα were identified as the main contributing biomarkers in the chronic inflammatory state of RA. A specific test score (STS) was defined and converted to a single cytokine composite test score (CCTS), which showed the disease outcome on a scale 0-100, providing sensitivity and specificity of ≥90%. Thus, the immunological complexity in RA is driven by a complex interplay of pro-inflammatory cytokines and effector T-cell response dominated by Th17/Tc17. In addition, the resolution of inflammation could be linked to a partially Treg-driven homeostatic innate immune response. Therefore, a more complex therapeutic approach against the above markers might be of value to obtain full clinical remission in the future.     

The Role of Th17/Tc17 Peripheral Blood T cells in Psoriasis and Their Positive Therapeutic Response

It is known that NB‐UVB therapy can suppress a broad range of immune cells, but the additional effect of bathing in geothermal seawater still remains unclear. To study the influence of treatment on the expression of circulating immune cells contributing to the pathogenesis of psoriasis, six patients with psoriasis were treated with bathing in geothermal seawater two times daily combined with NB‐UVB five times/week for 2 weeks and six patients were treated with NB‐UVB therapy three times/week for 8 weeks. Disease severity (Psoriasis Area and Severity Index, PASI), chemokines, inflammatory cytokines, T cells and Toll‐like receptors in the blood and skin samples were evaluated on enrolment (W0) and at 1 (W1), 3 (W3) and 8 (W8) weeks. Compared with healthy controls, psoriasis patients with active disease had significantly higher proportion of peripheral CLA+ T cells expressing CCR10 and CD103 and T cells with both Th1/Tc1 (CD4+/CD8+ IFN‐γ+ or TNF‐α+ cells) and Th17/Tc17 (CD4+CD45R0+IL‐23R+, CD4+/CD8+ IL‐17A+ or IL‐22+ cells) phenotypes. Both treatments gave a significant clinical effect; however, bathing in geothermal seawater combined with NB‐UVB therapy was more effective than NB‐UVB therapy alone. This clinical improvement was reflected by a reduction in circulating CLA+ peripheral blood T cells and by a decreased Th1/Th17 and Tc1/Tc17 inflammatory response. These findings suggest that the inflammatory response in psoriasis is predominantly driven by both CD4+ and CD8+ skin‐homing tissue retaining T cells of the Th17/Tc17 lineages.     

Pathogenic T helper type 17 cells contribute to type 1 diabetes independently of interleukin‐22

We have shown that pathogenic T helper type 17 (Th17) cells differentiated from naive CD4⁺ T cells of BDC2·5 T cell receptor transgenic non‐obese diabetic (NOD) mice by interleukin (IL)‐23 plus IL‐6 produce IL‐17, IL‐22 and induce type 1 diabetes (T1D). Neutralizing interferon (IFN)‐γ during the polarization process leads to a significant increase in IL‐22 production by these Th17 cells. We also isolated IL‐22‐producing Th17 cells from the pancreas of wild‐type diabetic NOD mice. IL‐27 also blocked IL‐22 production from diabetogenic Th17 cells. To determine the functional role of IL‐22 produced by pathogenic Th17 cells in T1D we neutralized IL‐22 in vivo by using anti‐IL‐22 monoclonal antibody. We found that blocking IL‐22 did not alter significantly adoptive transfer of disease by pathogenic Th17 cells. Therefore, IL‐22 is not required for T1D pathogenesis. The IL‐22Rα receptor for IL‐22 however, increased in the pancreas of NOD mice during disease progression and based upon our and other studies we suggest that IL‐22 may have a regenerative and protective role in the pancreatic islets.     

NK cells modulate the lung dendritic cell‐mediated Th1/Th17 immunity during intracellular bacterial infection

The impact of the interaction between NK cells and lung dendritic cells (LDCs) on the outcome of respiratory infections is poorly understood. In this study, we investigated the effect and mechanism of NK cells on the function of LDCs during intracellular bacterial lung infection of Chlamydia muridarum in mice. We found that the naive mice receiving LDCs from C. muridarum‐infected NK‐cell‐depleted mice (NK‐LDCs) showed more serious body weight loss, bacterial burden, and pathology upon chlamydial challenge when compared with the recipients of LDCs from infected sham‐treated mice (NK+LDCs). Cytokine analysis of the local tissues of the former compared with the latter exhibited lower levels of Th1 (IFN‐γ) and Th17 (IL‐17), but higher levels of Th2 (IL‐4), cytokines. Consistently, NK‐LDCs were less efficient in directing C. muridarum‐specific Th1 and Th17 responses than NK+LDCs when cocultured with CD4⁺ T cells. In NK cell/LDC coculture experiments, the blockade of NKG2D receptor reduced the production of IL‐12p70, IL‐6, and IL‐23 by LDCs. The neutralization of IFN‐γ in the culture decreased the production of IL‐12p70 by LDCs, whereas the blockade of TNF‐α resulted in diminished IL‐6 production. Our findings demonstrate that NK cells modulate LDC function to elicit Th1/Th17 immunity during intracellular bacterial infection.     

IL-13-producing Th1 and Th17 cells characterize adaptive responses to both self and foreign antigens

In helper T cells, IL‐13 is traditionally considered a Th2‐type cytokine that is coexpressed with IL‐4. Using mouse models of immunization and autoimmunity, we demonstrate that IL‐13 is frequently uncoupled from IL‐4, and that it can be produced by both IFN‐γ⁺ Th1 cells and IL‐17⁺ Th17 cells. We report that these IL‐13‐producing Th1 and Th17 cells are distinct from classical IL‐4⁺ Th2 cells and that they are relatively common, appearing in the context of both protective and pathogenic T‐cell responses. We also demonstrate that IL‐13 and Th2‐type cytokines can have important consequences in Th1‐ and Th17‐dominated settings, such as lymphopenia‐induced autoimmune disease, where they can be either pro‐ or anti‐inflammatory, depending on whether they act on innate or adaptive immune cells. Taken together, our studies indicate that IL‐13 production is more widespread than previously appreciated and that blocking this cytokine may have therapeutic benefits even in settings where traditional IL‐4‐driven Th2‐type responses are not evident.     

Emodin Prolongs Recipient Survival Time After Orthotopic Liver Transplantation in Rats by Polarizing the Th1/Th2 Paradigm to Th2

Advances in immunosuppressive drugs have improved the short‐term survival of liver transplantation. However, drug toxicities have been a serious problem in patients after long‐term administration. Therefore, it is necessary to develop a novel immunosuppressant with low‐toxicity. We investigated the immunosuppressive effects of Emodin on acute graft rejection following liver transplantation in rats. The recipient rats of orthotopic liver transplantation were divided into groups as follows: isograft+NS group, allograft+NS group, and allograft+emodin group. The survival time of the recipients in each group was recorded. Histopathological changes in the liver, as well as serum concentrations of IL‐2, TNF‐α, and IL‐10 and their expressions in liver tissue were determined. Our results showed that Emodin treatment prolonged liver allograft survival time and inhibited histopathologic changes of acute graft rejection. The rejection activity index in groups isograft+NS, allograft+NS, and allograft+emodin were 1.52 ± 0.37, 6.95 ± 0.75, and 4.23 ± 0.51, respectively (P < 0.01, isograft+NS group vs. allograft+emodin group and allograft+NS group vs. allograft+emodin group). The serum levels of IL‐2 and TNF‐α were down‐regulated but that of IL‐10 was up‐regulated by Emodin. Serum levels of IL‐2 and TNF‐α were higher in allograft+NS group than the allograft+emodin group, but that of IL‐10 showed opposite effects (P < 0.05 or 0.01). Changes in the expression of these cytokines in transplanted liver tissue were consistent with changes in serum concentrations. These results demonstrate that Emodin has therapeutic potentials for alleviating acute rejection following liver transplantation in rats and prolonging liver allograft survival. The mechanisms underlying this effect may be associated with polarizing the Th1/Th2 paradigm to Th2. Anat Rec, 2011. © 2011 Wiley‐Liss, Inc.     

Blockade of tumour necrosis factor‐α in experimental autoimmune encephalomyelitis reveals differential effects on the antigen‐specific immune response and central nervous system histopathology

In various autoimmune diseases, anti‐tumour necrosis factor (TNF)‐α treatment has been shown to reduce both clinical disease severity and T helper type 1 (Th1)1/Th17 responses. In experimental autoimmune encephalomyelitis (EAE), however, the role of TNF‐α has remained unclear. Here, C57BL/6 mice were immunized with myelin oligodendrocyte glycoprotein (MOG) peptide 35–55 and treated with anti‐TNF‐α, control antibody or vehicle. The clinical disease course, incidence and severity were assessed. On day 20 after immunization the antigen‐specific Th1/Th17 response was evaluated by enzyme‐linked immunospot (ELISPOT) in spleen and central nervous system (CNS). Also, the extent of spinal cord histopathology was analysed on semi‐ and ultrathin sections. Our results demonstrate that anti‐TNF‐α treatment reduced the incidence and delayed the onset of EAE, but had no effect on disease severity once EAE had been established. Whereas anti‐TNF‐α treatment induced an increase in splenic Th1/Th17 responses, there was no effect on the number of antigen‐specific Th1/Th17 cells in the spinal cord. Accordingly, the degree of CNS histopathology was comparable in control and anti‐TNF‐α‐treated mice. In conclusion, while the anti‐TNF‐α treatment had neither immunosuppressive effects on the Th1/Th17 response in the CNS nor histoprotective properties in EAE, it enhanced the myelin‐specific T cell response in the immune periphery.     

CD4+ T-cell subsets in transplantation

The identification of T-helper 9 (Th9), Th17, Th22 cells as distinct subsets of CD4⁺ T cells has extended the Th1/Th2 paradigm in the adaptive immunity. In the past decade, many studies in animal models and clinical transplantation have demonstrated that interleukin-17 (IL-17) is involved in allograft rejection. It appears that Th17 cells together with Th1 and Th2 cells play an important role in mediating allograft rejection. Here, we summarize our current knowledge on the contribution of Th1, Th2, Th9, Th17, Th22, and follicular T-helper (Tfh) cells in allograft rejection. We also discuss the regulation of CD4⁺ T-cell subsets by CD4⁺Foxp3⁺ regulatory T cells (Tregs) in the context of transplantation tolerance.     

Tim‐3 regulates inflammatory cytokine expression and Th17 cell response induced by monocytes from patients with chronic hepatitis B

Tim‐3 is expressed on monocytes/macrophages and is involved in the regulation of inflammatory responses. The aim of this study was to determine the effect of Tim‐3 on inflammatory response triggered by peripheral monocytes from patients with chronic hepatitis B (CHB). Tim‐3 expression on peripheral monocytes and frequency of Th17 cells in peripheral blood mononuclear cells (PBMCs) derived from CHB patients were detected. Followed by lipopolysaccharides (LPS) activation of circulating monocytes from CHB patients, expression of inflammatory cytokines including TNF‐α，IL‐1β and IL‐6 were examined in the presence and absence of Galectin‐9 which is the ligand for Tim‐3. Subsequently, after purified CD4+T cells were cocultured with LPS‐activated monocytes from CHB patients in the presence of anti‐Tim‐3 antibody, percentage of Th17 cells and production of IL‐17 were measured. Tim‐3 expression was significantly upregulated and closely correlated to the frequency of Th17 cells in patients with CHB. Expression of TNF‐α，IL‐1β and IL‐6 increased significantly in monocytes stimulated with LPS and Galectin‐9, compared to LPS stimulation alone. LPS‐activated monocytes from CHB patients could drive differentiation of memory CD4+T cells to Th17 cells. However, under the blockade of Tim‐3 signalling by anti‐Tim‐3 antibody, percentage of Th17 cells and production of IL‐17 decreased significantly. Our results demonstrate that upregulated expression of Tim‐3 on circulating monocytes accelerates inflammatory response by promoting production of inflammatory cytokines and Th17 responses in CHB.     

Soluble flagellin coimmunization attenuates Th1 priming to Salmonella and clearance by modulating dendritic cell activation and cytokine production

Soluble flagellin (sFliC) from Salmonella Typhimurium (STm) can induce a Th2 response to itself and coadministered antigens through ligation of TLR5. These properties suggest that sFliC could potentially modulate responses to Th1 antigens like live STm if both antigens are given concurrently. After coimmunization of mice with sFliC and STm there was a reduction in Th1 T cells (T‐bet⁺IFN‐γ⁺ CD4 T cells) compared to STm alone and there was impaired clearance of STm. In contrast, there was no significant defect in the early extrafollicular B‐cell response to STm. These effects are dependent upon TLR5 and flagellin expression by STm. The mechanism for these effects is not related to IL‐4 induced to sFliC but rather to the effects of sFliC coimmunization on DCs. After coimmunization with STm and sFliC, splenic DCs had a lower expression of costimulatory molecules and profoundly altered kinetics of IL‐12 and TNFα expression. Ex vivo experiments using in vivo conditioned DCs confirmed the effects of sFliC were due to altered DC function during a critical window in the coordinated interplay between DCs and naïve T cells. This has marked implications for understanding how limits in Th1 priming can be achieved during infection‐induced, Th1‐mediated inflammation.     

Indirect co‐cultures of healthy mesenchymal stem cells restore the physiological phenotypical profile of psoriatic mesenchymal stem cells

Psoriasis microenvironment, characterized by an imbalance between T helper type 1 (Th1)/Th17 and Th2 cytokines and also influences the mesenchymal stem cells (MSCs) phenotypical profile. MSCs from healthy donors (H‐MSCs) can exert a strong paracrine effect by secreting active soluble factors, able to modulate the inflammation in the microenvironment. To evaluate the influence of H‐MSCs on MSCs from psoriatic patients (PsO‐MSCs), H‐MSCs and PsO‐MSCs were isolated and characterized. Indirect co‐culture of H‐MSCs with PsO‐MSCs was performed; effects on proliferation and expression of cytokines linked to Th1/Th17 and Th2 pathways were assayed before and after co‐culture. The results show that before co‐culture, proliferation of PsO‐MSCs was significantly higher than H‐MSCs (P < 0·05) and the levels of secreted cytokines confirmed the imbalance of Th1/Th17 versus the Th2 axis. After co‐culture of H‐MSCs with PsO‐MSCs, healthy MSCs seem to exert a ‘positive’ influence on PsO‐MSCs, driving the inflammatory phenotypical profile of PsO‐MSCs towards a physiological pattern. The proliferation rate decreased towards values nearer to those observed in H‐MSCs and the secretion of the cytokines that mostly identified the inflammatory microenvironment that characterized psoriasis, such as interleukin (IL)‐6, IL‐12, IL‐13, IL‐17A, tumour necrosis factor (TNF)‐α and granulocyte–macrophage colony‐stimulating factor (G‐CSF), is significantly lower in co‐cultured PsO‐MSCs than in individually cultured PSO‐MSCs (P at least < 0·05). In conclusion, our preliminary results seem to provide an intriguing molecular explanation for the ever‐increasing evidence of therapeutic efficacy of allogeneic MSCs infusion in psoriatic patients.     

Anti‐tumour necrosis factor treatment increases circulating T helper type 17 cells similarly in different types of inflammatory arthritis

We investigated changes in circulating T helper type 17 (Th17) cells following anti‐tumour necrosis factor (TNF) in rheumatoid arthritis (RA), ankylosing spondylitis (AS) and psoriatic arthritis (PsA) patients. Peripheral blood mononuclear cells (PBMC) were isolated from 25 RA, 15 AS and eight PsA patients at baseline 4 and 12 weeks after treatment, and Th17 cell frequencies were analysed using interleukin (IL)‐17 enzyme‐linked immunospot (ELISPOT) and flow cytometry. A significant increase in IL‐17‐producing cells was observed by ELISPOT in RA and AS patients at 12 weeks. Flow cytometry confirmed significant increases in CD4⁺IL‐17⁺ cells at 12 weeks in RA and AS and 4 weeks in PsA patients. Anti‐TNF treatment increases circulating Th17 cells in three different diseases.     

Leptin deficiency impairs maturation of dendritic cells and enhances induction of regulatory T and Th17 cells

Leptin is an adipose‐secreted hormone that plays an important role in both metabolism and immunity. Leptin has been shown to induce Th1‐cell polarization and inhibit Th2‐cell responses. Additionally, leptin induces Th17‐cell responses, inhibits regulatory T (Treg) cells and modulates autoimmune diseases. Here, we investigated whether leptin mediates its activity on T cells by influencing dendritic cells (DCs) to promote Th17 and Treg‐cell immune responses in mice. We observed that leptin deficiency (i) reduced the expression of DC maturation markers, (ii) decreased DC production of IL‐12, TNF‐α, and IL‐6, (iii) increased DC production of TGF‐β, and (iv) limited the capacity of DCs to induce syngeneic CD4⁺ T‐cell proliferation. As a consequence of this unique phenotype, DCs generated under leptin‐free conditions induced Treg or T_H17 cells more efficiently than DCs generated in the presence of leptin. These data indicate important roles for leptin in DC homeostasis and the initiation and maintenance of inflammatory and regulatory immune responses by DCs.     

Lipoarabinomannan‐specific TNF‐α and IFN‐γ as markers of protective immunity against tuberculosis: a cohort study in an endemic setting

Lipoarabinomannan (LAM) is a virulent factor used for entry and survival of Mycobacterium tuberculosis (Mtb) in macrophages. Although the role of LAM for the diagnosis of tuberculosis (TB) has been extensively investigated, its cytokine response during natural Mtb infection in humans is largely unknown. In this study, LAM‐specific IFN‐γ, TNF‐α, and IL‐10 levels following whole blood assay were measured in untreated pulmonary TB patients, their contacts and community controls at baseline. In treated patients and contacts, cytokines were also measured at 6 and 12 months. At entry, 52.8% and 74.8% of controls and contacts were QFT‐GIT positive, respectively. At baseline, untreated TB patients and contacts had significantly lower IFN‐γ and TNF‐α response compared to community controls (p < 0.0001). Besides, untreated patients had significantly higher TNF‐α and IL‐10 response compared to their contacts (p < 0.0001). At 6 months, contacts and treated TB patients had significantly increased INF‐γ and TNF‐α response (p < 0.0001). In TB patients, IFN‐γ increased 10‐fold following chemotherapy suggesting its potential role for treatment monitoring. The data suggests that LAM might have an anti‐inflammatory effect during clinical TB and early Mtb infection. The data also suggests that LAM‐induced IFN‐γ and TNF‐α could be used as biomarkers of protective immunity.