Induction of a distinct CD8 Tnc17 subset by transforming growth factor-beta and interleukin-6

Role of autoreactive Tc17 cells in the pathogenesis of experimental autoimmune encephalomyelitis

Background

The pathogenesis of multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE—an animal model of MS) is primarily mediated by T cells. However, recent studies have only focused on interleukin (IL)‐17‐secreting CD4+ T‐helper cells, also known as Th17 cells. This study aimed to compare Th17 cells and IL‐17‐secreting CD8+ T‐cytotoxic cells (Tc17) in the context of MS/EAE.

Methods

Female C57BL/6 mice were immunized with myelin oligodendrocyte glycoprotein peptides 35–55 (MOG35–55), pertussis toxin, and complete Freund's adjuvant to establish the EAE animal model. T cells were isolated from the spleen (12–14 days postimmunization). CD4+ and CD8+ T cells were purified using isolation kit and then differentiated into Th17 and Tc17, respectively, using MOG35–55 and IL‐23. The secretion levels of interferon‐γ (IFN‐γ) and IL‐17 were measured via enzyme‐linked immunosorbent assay using cultured CD4+ and CD8+ T cell supernatants. The pathogenicity of Tc17 and Th17 cells was assessed through adoptive transfer (tEAE), with the clinical course assessed using an EAE score (0–5). Hematoxylin and eosin as well as Luxol fast blue staining were used to examine the spinal cord. Purified CD8+ CD3+ and CD4+ CD3+ cells differentiated into Tc17 and Th17 cells, respectively, were stimulated with MOG35–55 peptide for proliferation assays.

Results

The results showed that Tc17 cells (15,951 ± 1985 vs. 55,709 ± 4196 cpm; p < 0.050) exhibited a weaker response to highest dose (20 μg/mL) MOG35–55 than Th17 cells. However, this response was not dependent on Th17 cells. After the 48 h stimulation, at the highest dose (20 μg/mL) of MOG35–55. Tc17 cells secreted lower levels of IFN‐γ (280.00 ± 15.00 vs. 556.67 ± 15.28 pg/mL, p < 0.050) and IL‐17 (102.67 ± 5.86 pg/mL vs. 288.33 ± 12.58 pg/mL; p < 0.050) than Th17 cells. Similar patterns were observed for IFN‐γ secretion at 96 and 144 h. Furthermore, Tc17 cell‐induced tEAE mice exhibited similar EAE scores to Th17 cell‐induced tEAE mice and also showed similar inflammation and demyelination.

Conclusion

The degree of pathogenicity of Tc17 cells in EAE is lower than that of Th17 cells. Future investigation on different immune cells and EAE models is warranted to determine the mechanisms underlying MS.

Friend or Foe - Tc17 cell generation and current evidence for their importance in human disease

The term Tc17 cells refers to interleukin 17 (IL-17)-producing CD8+ T cells. While IL-17 is an important mediator of mucosal defense, it is also centrally involved in driving the inflammatory response in immune-mediated diseases, such as psoriasis, multiple sclerosis, and inflammatory bowel disease. In this review, we aim to gather the current knowledge on the phenotypic and transcriptional profile, the in vitro and in vivo generation of Tc17 cells, and the evidence pointing towards a relevant role of Tc17 cells in human diseases such as infectious diseases, cancer, and immune-mediated diseases.

Celastrol pretreatment attenuates concanavalin A-induced hepatitis in mice by suppressing interleukin-6/STAT3-interleukin-17 signaling

BACKGROUND AND AIM

Celastrol is extracted from Tripterygium wilfordii Hook F. It has been reported to have protective effects against various liver diseases and immune regulation of autoimmune diseases. However, little is known about whether celastrol protects against immune-mediated hepatitis. This study aimed to investigate the effect of celastrol on liver injury induced by concanavalin A (ConA) and the potential mechanisms.

METHODS

Intravenous administration of ConA was applied to induce acute liver injury in mice with or without pretreatment of celastrol. The effects of celastrol on ConA-induced liver injury were further demonstrated by biochemical and histopathological assessments, immunoblotting, and flow cytometry analysis.

RESULTS

Both biochemical and histopathological observations showed that pretreatment of celastrol significantly ameliorated liver injury induced by ConA. Moreover, the hepatocyte apoptosis and inflammatory responses induced by ConA were also improved in celastrol-pretreated mice. Further studies revealed that these improvements were characterized as the celastrol-mediated suppression of total interleukin (IL)-17 from liver mononuclear cells in ConA-treated mice. Flow cytometry analysis suggested that celastrol specifically decreased IL-17 production by CD4⁺ T cells but not by CD8⁺ T cells. Fundamentally, pretreatment with celastrol inhibited both the IL-6 produced by F4/80⁺ macrophages and the IL-6 receptor on Th17 cells in the liver, which further led to the downregulated activation of STAT3, thus accounting for blocked Th17 signaling.

CONCLUSIONS

Celastrol may exhibit immune regulatory effects by regulating IL-6/STAT3-IL-17 signaling in ConA-induced hepatitis, which suggested new potentials for celastrol to be applied in treating immune-mediated liver diseases.

Tc17 cells in autoimmune diseases

ABSTRACT

Multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE), a pathologically similar disease used to model MS in rodents, are typical CD4+ T cell-dominated autoimmune diseases. CD4+ interleukin (IL)17+ T cells (Th17 cells) have been well studied and have shown that they play a critical role in the pathogenesis of MS/EAE. However, studies have suggested that CD8+IL17+ T cells (Tc17 cells) have a similar phenotype and cytokine and transcription factor profiles to those of Th17 cells and have been found to be crucial in the pathogenesis of autoimmune diseases, including MS/EAE, psoriasis, type I diabetes, rheumatoid arthritis, and systemic lupus erythematosus. However, the evidence for this is indirect and insufficient. Therefore, we searched for related publications and attempted to summarize the current knowledge on the role of Tc17 cells in the pathogenesis of MS/EAE, as well as in the pathogenesis of other autoimmune diseases, and to find out whether Tc17 cells or Th17 cells play a more critical role in autoimmune disease, especially in MS and EAE pathogenesis, or whether the interaction between these two cell types plays a critical role in the development of the disease.

IL-17A/F enable cholangiocytes to restrict T cell-driven experimental cholangitis by upregulating PD-L1 expression

BACKGROUND & AIMS

IL-17A-producing T cells are present in autoimmune cholestatic liver diseases; however, little is known about the contribution of IL-17 to periductal immune responses. Herein, we investigated the role of IL-17 produced by antigen-specific CD8⁺ T cells in a mouse model of cholangitis and in vitro in human cholangiocyte organoids.

METHODS

K14-OVAp mice express a major histocompatibility complex I-restricted ovalbumin (OVA) peptide sequence (SIINFEKL) on cholangiocytes. Cholangitis was induced by the adoptive transfer of transgenic OVA-specific ovalbumin transgene (OT)-1 CD8⁺ T cells that either had OT-1^wt or lacked IL-17A/F (OT-1^IL17ko). The response of mouse and human cholangiocytes/organoids to IL-17A was assessed in vitro.

RESULTS

Transfer of OVA-specific OT-1^IL17ko cells significantly aggravated periductal inflammation in K14-OVAp recipient mice compared with transfer of OT-1^wt T cells. OT-1^IL17ko T cells were highly activated in the liver and displayed increased cytotoxicity and proliferation. IL-17A/F produced by transferred OT-1^wt CD8⁺ T cells induced upregulation of the inhibitory molecule programmed cell death ligand 1 (PD-L1) on cholangiocytes, restricting cholangitis by limiting cytotoxicity and proliferation of transferred cells. In contrast, OT-1^IL17ko T cells failed to induce PD-L1 on cholangiocytes, resulting in uncontrolled expansion of cytotoxic CD8⁺ T cells and aggravated cholangitis. Blockade of PD-L1 after transfer of OT-1^wt T cells with anti-PD-L1 antibody also resulted in aggravated cholangitis. Using human cholangiocyte organoids, we were able to confirm that IL-17A induces PD-L1 expression in cholangiocytes.

CONCLUSIONS

We demonstrate that by upregulating PD-L1 on cholangiocytes, IL-17 has an important role in restricting cholangitis and protecting against CD8⁺ T cell-mediated inflammatory bile duct injury. Caution should be exercised when targeting IL-17 for the treatment of cholangitis.

LAY SUMMARY

IL-17 is assumed to be a driver of inflammation in several autoimmune diseases, such as psoriasis. IL-17 is also present in inflammatory diseases of the bile duct, but its role in these conditions is not clear, as the effects of IL-17 depend on the context of its expression. Herein, we investigated the role of IL-17 in an experimental autoimmune cholangitis mouse model, and we identified an important protective effect of IL-17 on cholangiocytes, enabling them to downregulate bile duct inflammation via checkpoint inhibitor PD-L1.

The Roles of CD8+ T Cell Subsets in Antitumor Immunity

Effector CD8⁺ T cells are typically thought to be a homogenous group of cytotoxic cells that produce interferon-(IFN) γ. However, recent findings have challenged this notion because multiple subsets of CD8⁺ T cells have been described, each with distinct effector functions and cytotoxic potential. These subsets, referred to as the Tc subsets, have also been detected in tumor microenvironments (TMEs), where they potentially influence the antitumor response and patient outcomes. In this review, we highlight the prevalence and roles of Tc subsets in the TME. We also discuss their therapeutic applications in the context of adoptive immunotherapy to treat cancer.

Inhibition of the transcription factor ROR-γ reduces pathogenic Th17 cells in acetylcholine receptor antibody positive myasthenia gravis

IL-17 producing CD4 T cells (Th17) cells increase significantly with disease severity in myasthenia gravis (MG) patients. To suppress the generation of Th17 cells, we examined the effect of inhibiting retinoic acid receptor-related-orphan-receptor-C (RORγ), a Th17-specific transcription factor critical for differentiation. RORγ inhibition profoundly reduced Th17 cell frequencies, including IFN-γ and IL-17 co-producing pathogenic Th17 cells. Other T helper subsets were not affected. In parallel, CD8 T cell subsets producing IL-17 and IL-17/IFN-γ were increased in MG patients and inhibited by the RORγ inhibitor. These findings provide rationale for exploration of targeted Th17 therapies, including ROR-γ inhibitors, to treat MG patients.

Decreased Frequencies of Th17 and Tc17 Cells in Patients Infected with Avian Influenza A (H7N9) Virus

The outbreak of avian influenza A (H7N9) virus infection, with a high mortality rate, has caused concern worldwide. Although interleukin-17- (IL-17-) secreting CD4⁺ T (Th17) and CD8⁺ T (Tc17) cells have been proven to play crucial roles in influenza virus infection, the changes and roles of Th17 and Tc17 cells in immune responses to H7N9 infection remain controversial. In this study, we found that the frequencies of Th17 and Tc17 cells among human peripheral blood mononuclear cells (PBMCs) as well as IL-17A protein and mRNA levels were markedly decreased in patients with acute H7N9 virus infection. A positive correlation was found between the serum IL-17A level and the frequency of these two cell groups. In vitro infection experiments revealed decreased Th17 and Tc17 cell frequency and IL-17A levels at various time points postinfection. In addition, Th17 cells were the predominant sources of IL-17A in PBMCs of patients infected with H7N9 virus. Taken together, our results indicate immune disorder in acute H7N9 infection and a restored Th17 and Tc17 cell frequency might serve as a biomarker for predicting recovery in patients infected with this virus.

Chicken IL-17A is expressed in αβ and γδ T cell subsets and binds to a receptor present on macrophages, and T cells

IL-17A as important cytokine in host defense has been analysed intensively and various homologous have been identified. To further gain insight into the functional properties of chicken (gg) IL-17A its expression profile was analysed by intracellular cytokine staining. In splenocytes and peripheral blood mononuclear cells gg IL-17A was detected in subsets of CD4⁺ T cells and γδ T cells. In contrast the gg IL-17A producing populations in intestinal intraepithelial lymphocytes were characterized as either CD3⁺CD25⁺ cells or γδ T cells. Furthermore, using FLAG tagged gg IL-17A, binding to its receptor was demonstrated on the macrophage cell line HD11. In peripheral blood IL-17A binding activity was found on αβ and γδ T cell subsets, monocytes and a distinct population of CD25^high cells. Treatment of HD11 cells with gg IL-17A induced IL-6 mRNA expression and nitric oxide production. These results demonstrate the presence of a αβ T helper₁₇ cell subset and IL-17 producing γδ T cells in the chicken.

A STAT3-dependent transcriptional circuitry inhibits cytotoxic gene expression in T cells

CD8⁺ T cells are preprogrammed for cytotoxic differentiation in the thymus as they acquire expression of the transcription factor Runx3. However, a subset of effector CD8⁺ T cells (Tc17) produce IL-17 and fail to express cytotoxic genes. Here, we show that the transcription factors directing IL-17 production, STAT3 and RORγt, inhibit cytotoxicity despite persistent Runx3 expression. Cytotoxic gene repression did not require the transcription factor Thpok, which in CD4⁺ T cells restrains Runx3 functions and cytotoxicity; and STAT3 restrained cytotoxic gene expression in CD8⁺ T cells responding to viral infection in vivo. STAT3-induced RORγt represses cytotoxic genes by inhibiting the functions but not the expression of the "cytotoxic" transcription factors T-bet and Eomesodermin. Thus, the transcriptional circuitry directing IL-17 expression inhibits cytotoxic functions. However, by allowing expression of activators of the cytotoxic program, this inhibitory mechanism contributes to the instability of IL-17-producing T cells.

Human Gingiva-Derived Mesenchymal Stem Cells Ameliorate Streptozoticin-induced T1DM in mice via Suppression of T effector cells and Up-regulating Treg Subsets

There is yet no cure for type 1 diabetes (T1DM) so far. A significant body of evidence has demonstrated that bone marrow-derived mesenchymal stem cells (BMSCs) showed great potential in controlling T1DM. But there exists much difficulty in using BMSCs as a clinical therapy. We here test whether a new population of mesenchymal stem cells from human gingiva (GMSCs), which has many advantages over BMSCs, can delay or prevent progress of T1DM. GMSCs were adoptively transferred to multiple low-dose streptozotocin (STZ)-induced T1DM. Blood glucose levels and disease severities were analyzed. T cells subsets in blood, spleen and lymph nodes were detected dynamically by flow cytometry. GMSC distribution was dynamically analyzed. We found that infusion of GMSCs but not fibroblast cells significantly controlled blood glucose levels, delayed diabetes onset, ameliorated pathology scores in pancreas, and down-regulated production of IL-17 and IFN-γ in CD4+ and CD8+ T cells in spleens, pancreatic lymph nodes (pLN) and other lymph nodes. GMSCs also up-regulated the levels of CD4+ Treg induced in the periphery. Mechanismly, GMSCs could migrate to pancreas and local lymph node and function through CD39/CD73 pathway to regulate effector T cells. Thus, GMSCs show a potential promise in treating T1DM in the clinic.

The paradox of Th17 cell functions in tumor immunity

Immune system acts as a host defensive mechanism protecting against attacking pathogens and transformed cells, including cancer cells. Th17 cells are a specific subset of T helper lymphocytes determined by high secretion of IL-17 and other inflammatory cytokines. Th17 cells increase tumor progression by activating angiogenesis and immunosuppressive activities. They can also mediate antitumor immune responses through recruiting immune cells into tumors, stimulating effector CD8+ T cells, or surprisingly by altering toward Th1 phenotype and producing IFN-γ, so Th17 cells are supposed as a double-edged sword in cancer. A comprehensive approach to indicating the activity of Th17 cells in tumor progression could help in the planning of new therapeutic approaches specially targeting Th17 cells in cancer.

Generation of glycosylphosphatidylinositol linked chicken IL-17 to generate specific monoclonal antibodies applicable for intracellular cytokine staining

Interleukin 17 (IL-17) cytokines play a crucial role in host defense and inflammatory diseases. Of the six mammalian IL-17 members five are described in the chicken (gg) genome. A novel method that attached cytokines to the surface of cells via a GPI linker was established to generate two chicken IL-17A and one chicken IL-17F specific mab. Recombinant gg IL-17A and gg IL-17F that showed dimerization in Western blot were used to verify the antibodies specificity. The mab could detect gg IL-17 by intracellular cytokine staining as demonstrated on cells expressing recombinant IL-17. Furthermore IL-17A and lower amounts of IL-17F were detectable in CD4 positive T cells of stimulated splenocytes. In conclusion, we have generated novel tools to analyze chicken IL-17 in more detail and demonstrated that the surface expression of cytokines is a reliable method to generate specific mab applicable for intracellular cytokine staining.

Loss of Tff1 Promotes Pro-Inflammatory Phenotype with Increase in the Levels of RORγt+ T Lymphocytes and Il-17 in Mouse Gastric Neoplasia

Background: TFF1 deficiency induces a mucosal pro-inflammatory phenotype that contributes to gastric tumorigenesis in mouse and human. Methods: We utilized the Tff1-KO mouse model to assess the impact of TFF1 loss on immune cells infiltration in the stomach. We used single cell suspension, flow cytometry, immunohistochemistry, and quantitative PCR (qPCR) assays. Results: The Tff1-KO gastric mucosa demonstrated high chronic inflammatory scores (score: 3-4) at age 2 months, which exacerbated at age 8 months (score: 4-6). We next used single-cell suspensions for flow cytometry analysis of total leukocytes (CD45+ cells), total T lymphocytes (CD45+CD3+cells), T cell subsets (CD4+, CD8+, and CD3+CD4-CD8-cells), and monocytes/macrophages (CD45+F4/80+cells). The results demonstrated an age-dependent (2 → 8 month age) significant increase of leukocytes (p<0.05), T cells (p<0.05), and monocytes/macrophages (p<0.001) in the gastric mucosa of the Tff1-KO mice, as compared to Tff1-WT. A similar increase was observed in blood samples (p<0.05). Using ionomycin to activate CD4⁺ splenocytes, the results indicated that Tff1-KO CD4⁺ splenocytes secreted higher levels of IL-17A (p<0.05 at 2 and p<0.001 at 8 months) and IL-17F (p<0.05 at 2 and 8 months) than Tff1-WT splenocytes. Conversely, Tff1-KO CD8⁺-cells secreted less IL-17F, but comparable levels of IL-17A. In addition, we detected a significant upregulation of Il-17 mRNA expression in gastric tissues in the Tff1-KO, as compared to Tff1-WT (p<0.001). Conclusions: The results identify TFF1 loss as a major pro-inflammatory step that modulates the tumor microenvironment and immune cell infiltration in the stomach. Furthermore, the data suggest that the increase of IL-17A and IL-17F in Th17 cells, derived from CD4⁺ T cells, reflects the chronic inflammation in gastric mucosa, whereas the absence of change of IL-17A and decrease of IL-17F in CD8⁺Tc17 cells suggest loss of cytotoxic function of CD8⁺Tc17 cells during gastric tumorigenesis of the Tff1-KO mice.

IL-17A levels in systemic lupus erythematosus associated with inflammatory markers and lower rates of malignancy and heart damage: Evidence for a dual role

OBJECTIVE

The interleukin 17 (IL-17) cytokine family is involved in a number of chronic inflammatory diseases. In spite of contradictory findings and a lack of causality in clinical studies, IL-17 inhibition for systemic lupus erythematosus (SLE) has regained attention as a potential therapeutic pathway, after demonstrating disease-modifying capabilities in ankylosing spondylitis. We investigated the clinical associations of interleukin 17 A (IL-17A) in patients with SLE.

MATERIAL AND METHODS

A cross-sectional study was performed involving SLE patients (n=102; age: 49 years; 86% female) recruited from a regional registry. IL-17A levels were determined by immunoassay, disease activity by Systemic Lupus Erythematosus Disease Activity Index-2K (SLEDAI-2K), and cumulative damage by Systemic Lupus International Collaborative Clinics Damage Index (SDI) scores. Non-parametric techniques were used to examine the association between IL-17A and disease activity and autoantibody profiles were compared with healthy controls (n=31): principal component analysis (PCA) was used to determine the interplay of immune cells across disease states and damage development in SLE patients.

RESULTS

SLE patients had higher IgG levels, lower T-cell and B-cell counts, but median IL-17A levels did not differ from the controls (28.4 vs. 28.4 pg/mL, p=0.9). In SLE patients, IL-17A did not correlate with SLEDAI-2K or SDI, but was inversely related with age (correlation coefficients, Rs.=-0.29, p<0.05), systolic blood pressure (Rs.=-0.31, p<0.05), years of smoking (Rs.=-0.43, p<0.05), cumulative heart (Rs.=-0.22, p<0.05), and malignancy damage (Rs.=-0.18, p<0.05). Serological correlations for IL-17A existed with immunoglobulin G (IgG) levels (Rs.=0.21, p<0.05), high sensitivity C-reactive protein (hs-CRP) levels (Rs.=0.28, p<0.05), proteinuria (Rs.=0.64, p<0.05), and pre-albumin (Rs.=-0.22, p<0.05). Longitudinal data showed only modest fluctuation in IL-17A levels, independent of SLEDAI-2K.

CONCLUSION

These results suggest that IL-17A, while participating in inflammation, may also serve a protective purpose in SLE patients.

Pro-Tumor and Anti-Tumor Functions of IL-17 and of TH17 Cells in Tumor Microenvironment

The current review reveals the seven subclasses of CD4+ T helper cells, i.e. Th1, Th2, Th9, Th17, Th22, regulatory T cells and Tfh, the cytokines produced by them and their role in tumor microenvironment. Main attention was paid to IL-17 and Th17 cells. IL-17-producing cells were described, among which were Treg17 cells and Tc17 cells. The transcription factors, engaged in the activation of Th17 cell differentiation were reviewed. It was shown that Th17 cells might possess regulatory functions in tumor microenvironments that directs toward immunosuppression. The reciprocity between Treg and Th17 cells is realized when the production of a large amount of TGF-β in tumors causes Treg cell differentiation, and the addition of IL-6 shifts the differentiation of naïve T cells to Th17 cells. The main pro-tumor role of IL-17 is the promotion of tumor angiogenesis through stimulation of fibroblasts and endothelial cells. The antitumor functions of IL-17 are associated with enhancement of cytotoxic activity of tumor specific CTL cells and with angiogenesis that provide channels through which immune cells might invade tumor and promote antitumor immunity.

Dextran sulfate sodium-induced acute experimental colitis in C57BL/6 mice is mitigated by selenium

BACKGROUND

Sodium selenite has been shown to have a protective role in experimental colitis. Th1 and Th17 responses are involved in the pathogenesis of dextran sulfate sodium (DSS)-induced colitis and inflammatory bowel disease. This study investigated whether sodium selenite can suppress Th1/Th17-mediated experimental colitis.

METHODS

Mice were administered sodium selenite (2μg/g body weight) by gavage daily for 30days. Beginning on day 21, mice were administered 2.5% oral DSS for 9days. The mice were sacrificed on day 31. Survival rates, clinical symptoms, colon lengths, and histological changes were determined.

RESULTS

Pretreatment with sodium selenite (2μg/g body weight) improved survival rates, colon shortening, body weight loss, disease activity index, and histopathological score in mice with DSS-induced colitis. Pretreatment with sodium selenite restored interleukin-10 and Foxp3 excretion, as well as reducing the levels of interferon-γ and interleukin-17A.

CONCLUSIONS

Pretreatment with sodium selenite showed therapeutic potential for preventing colitis in mice. This effect may be mediated by the immunomodulation of regulatory T cells, expressing anti-inflammatory genes that suppress Th1 and Th17 responses.

IL-17+ CD8+ T cells: Differentiation, phenotype and role in inflammatory disease

•

IL-17A (IL-17) is produced by multiple cell subsets, including CD8+ T cells.

•

The presence of IL-17+ CD8+ T cells in human inflammatory diseases suggests these cells may contribute to immunopathology.

•

Increased knowledge of human IL-17+ CD8+ T cells will enhance our overall understanding of their role in human disease.

The pro-inflammatory cytokine interleukin-17A (IL-17) has been the subject of research by many groups worldwide. IL-17 expression is often associated with a specific subset of CD4+ T cells (the so-called Th17 cells); however various other immune cell subsets can also synthesise and express IL-17, including CD8+ T cells. Here we review recent data regarding the presence of IL-17+ CD8+ T cells (also known as Tc17 cells) in human inflammatory disease, discuss current knowledge regarding the culture conditions required for the differentiation of these cells in humans and mice, and describe key phenotypic and functional features. Collectively, this information may shed light on the potential pathogenic role that IL-17+ CD8+ T cells may play in human inflammatory disease.

TGF-β and IL-21 cooperatively stimulate activated CD8(+) T cells to differentiate into Tc17 cells

TGF-β together with IL-21 or IL-6 can drive the differentiation of naïve CD8(+) T cells into IL-17-producing CD8(+) T cells. These IL-17-producing CD8(+) T cells are termed Tc17 cells. Tc17 cells preserve plasticity under various conditions in vitro and in vivo. IFN-γ-producing CD8(+) T cells are termed Tc1 cells. However, Tc1 cells are considered relatively stable. In the present study, we show that the combination of TGF-β plus IL-21, but not IL-6, converts Tc1 cells into Tc17 cells; this conversion is associated with elevated RORα, RORγt, and Batf mRNA levels. These results indicate that Tc1 cells are skewed to the Tc17 cell phenotype under TGF-β plus IL-21-polarizing conditions. Furthermore, IL-6R is expressed on naïve, but not activated, CD8(+) T cells. In contrast, IL-21R is expressed on both naïve and activated CD8(+) T cells. Thus, differential expression profiles of IL-6R and IL-21R on naïve and activated CD8(+) T cells may be one mechanism by which TGF-β plus IL-21, but not IL-6, can drive activated CD8(+) T cells to differentiate into IL-17-producing cells. Taken together, these results provide a novel viewpoint for the plasticity of Tc1 cells.

IL-10 Modulates Th17 Pathogenicity during Autoimmune Diseases

The immune system is essential for host defense against pathogen infections; however dysregulated immune response may lead to inflammatory or autoimmune diseases. Elevated activation of both innate immune cells and T cells such as Th17 cells are linked to many autoimmune diseases, including Multiple Sclerosis (MS), arthritis and inflammatory bowel disease (IBD). To keep immune homeostasis, the immune system develops a number of negative feedback mechanisms, such as the production of anti-inflammatory cytokine IL-10, to dampen excessive production of inflammatory cytokines and uncontrolled activation of immune cells. Our recent studies uncover a novel immunoregulatory function of interferon (IFN) pathways on the innate and antigen-specific immune response. Our results show that IFNα/β induced IL-10 production from macrophages and Th17 cells, which in turn negatively regulated Th17 function in autoimmune diseases such as Experimental Allergic Encephalomyelitis (EAE), an animal model of human MS. In a chronic colitis model resembling human IBD, we also found that IL-10 inhibited inflammasome/IL-1 pathway, and the pathogenicity of Th17 cells, leading to reduced chronic intestinal inflammation. Results from our and other studies further suggest that IL-10 produced by both macrophages and regulatory T cells may shift Th17 into more regulatory phenotypes, leading to reduced inflammatory response.

Dynamic regulation of effector IFN-γ-producing and IL-17-producing T cell subsets in the development of acute graft-versus-host disease

Graft-versus-host disease (GVHD) as the predominant complication of allogeneic hematopoietic stem cell transplantation remains to be fully understood. It is known that the cytokines produced by allogeneic reactive effector CD4+ and CD8+ T cells are involved in GVHD. However, the regulation and coordination of IFN-γ-producing and IL-17-producing effector T cells remain unclear. The present study aimed to investigate the dynamic changes of alloantigen-specific effector CD4+ T and CD8+ T cell subsets by flow cytometry, which produce inflammatory cytokines involved in the multistep GVHD pathogenesis progress. The results demonstrated that IL-17-producing CD8+ T (Tc17) cells and IFN-γ+CD8+ T (Tc1) cells were detected in the early stage of GVHD. The differentiation of CD4+ T cells into Th1 cell (IFN-γ+CD4+ T) and Th17 (IL-17+CD4+ T) cells was later than that of the Tc1 and Tc17 cells. The effector CD4+ T and CD8+ T cell subsets either became exhausted or became memory cells, exhibiting a CD62L-CD44+ phenotype following marked expansion during GVHD. Furthermore, T cell-associated type I (IL-2 and IFN-γ) and type II (IL-4 and IL-10) classical cytokines exhibited coordinated dynamic regulation. It was concluded that the differentiation of cytokine-producing Tc1 and Tc17 cells may be the key step in the initiation of GVHD, whereas CD4+ effector Th1 and Th17 cells are considered to be pathophysiological factors leading to the continuous aggravation of GVHD.

IL-17A-producing T cells and associated cytokines are involved in the progression of gastric cancer

Interleukin-17A-producing T cells (IL-17A+ T) (IL-17A+CD4+ Th17, IL-17A+CD8+ Tc17 and IL-17A+ γδT17 cells) and associated cytokines (IL-17A, IL-23 and IL-1β) play crucial roles in inflammation-associated diseases, such as infection, autoimmunity and tumors. Th17 cells promote human gastric cancer (GC), although the source of intracellular IL‑17A and the roles of Tc17 and γδT17 cells remain poorly understood. In this study, the frequencies of circulating Th17 and γδT17 cells in patients with GC were found to be significantly increased compared to those in healthy donors; however, Tc17 cells were decreased in these patients, and a negative relationship was found between the frequencies of Th17 and Tc17 cells. Moreover, the cytokine IL‑17A was found to be produced mainly by Th17 cells in human peripheral blood. Similarly, serum cytokine levels and relative mRNA expression levels of IL‑17A, IL‑23 and IL‑1β were significantly increased in patients with GC, and the frequency of Th17 cells was closely associated with serum IL‑17A concentrations in patients with GC. Additionally, Th17 cells and associated cytokines were present at significantly different levels during the progression and metastasis of GC, as were Tc17 and γδT17 cells. Taken together, these findings suggest that IL-17A+ T cells and associated cytokines might play crucial roles in human GC progression and metastasis and thus represent potential targets for treatment.

Down-regulation of expression of retinoid acid-related orphan receptor C (RORC) in systemic lupus erythematosus

CONTEXT

Retinoic acid-related orphan receptor C (RORC), the key factor orchestrating the transcription of genes encoding interleukin 17, plays a critical role in the regulation of inflammatory responses.

OBJECTIVE

The objective of this study was to analyze the expression of RORC in the peripheral blood of patients with systemic lupus erythematosus (SLE) for a better understanding of the pathogenesis of SLE especially in relation to disease activity and clinical and biochemical findings.

METHODS

The study included 24 patients with SLE and a control group of 18 healthy gender- and age-matched individuals. Evaluation of the level of expression of RORC mRNA was performed by real-time polymerase chain reaction.

RESULTS

The results showed that patients with SLE had lower RORC gene expression levels compared with healthy subjects that were not correlated with disease activity. The down-regulation of RORC was significantly lower in patients with lupus nephritis in remission than active lupus nephritis and nonrenal patients.

CONCLUSIONS

The findings suggest that RORC plays a significant role in the dysregulated immune response associated with SLE. Deciphering the intricate regulatory network and the target genes of RORC will help unravel new specific treatments for SLE.

CCL2/CCR2-dependent recruitment of Th17 cells but not Tc17 cells to the lung in a murine asthma model

BACKGROUND

Interleukin (IL)-17 has been implicated in the pathogenesis of asthma and the progression of airway inflammation. Here, we used a model of allergic asthma and found that the frequencies of IL-17-secreting T helper (Th)17 and CD8 (Tc)17 cells were both significantly increased, as was the expression of the CC chemokine receptor (CCR2) on the surface of these cells. CC chemokine ligand 2 (CCL2) has been shown to mediate the activation and recruitment of inflammatory cells in asthma, which are also skewed after ovalbumin (OVA) challenge. However, the role of CCL2 on Th17 cells and Tc17 cells in asthma has not been illuminated.

METHODS

Mice that were sensitized and challenged with OVA received anti-CCL2 antibody (Ab; 5 μg/day intratracheally) or CCR2 antagonist (RS504393, 2 mg/kg/day intraperitoneally) prior to the challenge. Some mice received an isotype control Ab or vehicle alone. We then assessed the effects of allergic asthma and anti-CCL2 Ab or CCR2 antagonist treatment on the levels of IL-17 and CCL2, the Th17 and Tc17 cell frequencies and lung tissue inflammation.

RESULTS

We demonstrated that CCL2 and IL-17 levels and the frequency of Th17 and Tc17 cells in lung tissues and bronchoalveolar lavage fluid increased in the asthma group compared with the normal control mice. Blocking the CCL2/CCR2 axis greatly reduced the Th17 but not the Tc17 cell frequency, and revealed a suppressive effect on airway inflammation.

CONCLUSION

These findings indicate a role for the CCL2/CCR2 axis in mediating Th17 but not Tc17 cell migration during acute allergic airway inflammation.

Nonapoptotic and extracellular activity of granzyme B mediates resistance to regulatory T cell (Treg) suppression by HLA-DR-CD25hiCD127lo Tregs in multiple sclerosis and in response to IL-6

In autoimmune patients, regulatory T cells (Tregs) are increasingly found to be unable to suppress patient-derived T cells, an outcome referred to as Treg resistance. In this study, we show that CD4 T cells from patients with multiple sclerosis resist suppression by patient-derived or healthy donor-derived ex vivo Tregs. Importantly, we report that granzyme B (GzmB) contributes to this Treg resistance via a novel, apoptosis-independent mechanism. We show that memory CD4(+)CD127(lo)FOXP3(+) Treg subsets do not express GzmB, whereas activated, nonregulatory CD4 T cells isolated from patients with multiple sclerosis express higher levels of GzmB than do cells from healthy donors. In contrast to the intracellular GzmB that mediates apoptosis, GzmB can be found in extracellular fluids where it is hypothesized to regulate other cellular processes. In this study, we show that providing extracellular GzmB strongly inhibits Treg suppression, without altering Treg viability. However, when GzmB and GzmB-specific inhibitor are both provided to the cocultures, Treg suppression occurs. Thus, these data suggest that a novel activity of extracellular GzmB is to regulate Treg suppression. Additionally, we find that the suppression-abrogating cytokine IL-6 augments GzmB expression by human CD4 T cells, and it inhibits Treg suppression via this nonapoptotic GzmB-mediated mechanism. Lastly, in examining the mechanism whereby GzmB inhibits Treg function, we show that extracellular GzmB reduces Treg expression of CD39 and programmed death ligand 1. Collectively, these data indicate that extracellular GzmB plays an unexpected, nonapoptotic role in regulating Treg suppression and suggest that inactivation of specifically the extracellular activity of GzmB may be an efficacious therapeutic in autoimmunity.

Th22 cells in allergic disease

During the last decade, the field of T cell immunology started to confuse the scientific community. More and more subtypes of T helper cells and their counterparts in the innate immune system are described. We are just at the beginning to understand which specific function the distinct subtypes fulfill. Th22 cells are terminally differentiated and very specialized T helper cells characterized by the secretion of their signature cytokine IL-22 and lack of IL-4, IL-17 and IFN-γ. The main function of Th22 cells is to protect epithelial barrier organs such as skin and lung, but also to modulate inflamed and injured tissue. This review summarizes our current knowledge on Th22 cells and their function in allergic disease.

Cite this as Eyerich K, Eyerich S. Th22 cells in allergic disease. Allergo J Int 2015;24:1–7 DOI: 10.1007/s40629-015-0039-3

IL-17A-producing CD8(+)T cells as therapeutic targets in autoimmunity

INTRODUCTION

The involvement of IL-17-producing CD8(+)T cells (TC17) in various conditions, such as infection, cancer and autoimmune inflammation, has been documented in both humans and mice; however, TC17 cells have received only marginal attention.

AREAS COVERED

Here, we provide an overview of the cytokines, chemokines, and cytokine and chemokine receptors that characterize the murine and human TC17 cell phenotype. We also discuss signaling pathways, molecular interactions, and transcriptional and epigenetic events that contribute to TC17 differentiation and acquisition of effector functions. Heterogeneity and inherent phenotypic instability of TC17 cells were shown both in humans and murine models. Aberrant expression of TC17 cells was observed in many autoimmune conditions. Moreover, functional analysis demonstrated in vivo plasticity of TC17 cells may be a key feature of TC17 cell biology in autoimmune diseases.

EXPERT OPINION

Due to its important roles in inflammation and autoimmunity, TC17 cell pathway may have promise as a potential therapeutic target for autoimmune diseases. The strategies include the suppression of TC17 cell generation and migration and the blockade of TC17 cell instability and heterogeneity. TMP778 may open an avenue to novel therapeutic strategies.

SLAM-SAP signaling promotes differentiation of IL-17-producing T cells and progression of experimental autoimmune encephalomyelitis

IL-17 plays critical roles in host defenses, combating bacterial and fungal infections, as well as the pathogenesis of autoimmune diseases such as experimental autoimmune encephalomyelitis (EAE). The signaling adaptor SAP is essential for normal immune homeostasis and mutations within SH2D1A, the locus encoding this protein, result in serious and sometimes fatal syndromes, including X-linked lymphoproliferative disease and severe cases of common variable immunodeficiency. However, the precise cellular basis of how SAP deficiency contributes to immune dysfunction remains incompletely understood. In this study, we found that CD4 and CD8 T cells lacking SAP had a diminished capacity to differentiate into IL-17-producing Th17 and T cytotoxic (Tc17) cells relative to wild-type lymphocytes. The use of costimulating SLAM Abs was found to augment the differentiation of IL-17-secreting effectors in wild-type but not Sh2d1a(-/-) splenic T cells under IL-17-polarizing conditions. In addition, SAP's regulation of IL-17-secreting T cells was shown to be a T cell-intrinsic role, as purified naive Sh2d1a(-/-) CD4 and CD8 T cells were inherently defective at converting into Th17 and Tc17 cells in vitro and in vivo. Furthermore, Sh2d1a(-/-) mice were protected from EAE and exhibited greatly decreased numbers of CNS-infiltrating Th17 and Tc17 effector T cells and reduced disease severity. Collectively, these results suggest that SLAM-SAP signaling drives the differentiation and function of Th17 and Tc17 cells in vitro and in vivo and contributes to the pathogenesis of autoimmunity in EAE.

Tc17 Cells in Immunity and Systemic Autoimmunity

Tc17 cells-a subset of CD8(+)T cells-have recently been identified that are characterized by the production of interleukin (IL)-17. Cytokines IL-6 and transforming growth factor-beta 1 (TGF-β1) and transcription factors signaling transducers and activators of transcription (STAT)3, retinoic acid receptor-related orphan nuclear receptor gamma (RORγt), and interferon regulatory factor (IRF)4 are necessary for differentiation of Tc17 cells, controlling expression of molecules essential for Tc17 cell trafficking and function. Current human researches have determined the significance of CD161 expression as either a marker of Tc17 cells or as an effector and regulator of Tc17 cell function. Noncytotoxic Tc17 cells possess a high plasticity to convert into IFN-γ producing cells, which exhibit strong cytotoxic activity. The importance of in vivo plasticity of Tc17 cells for the induction of autoimmune diseases has been demonstrated and Tc17 cells potentially represent novel therapeutic targets in autoimmune diseases. The involvement of interleukin (IL)-17-producing CD8(+)T cells (Tc17) in various conditions, such as infection, cancer, and autoimmune inflammation, has been documented in both humans and mice; however, Tc17 cells have received only marginal attention. Here, we provide an overview of the cytokines and chemokines that characterize the murine and human Tc17 cells. Moreover, we discuss signaling pathways, molecular interactions, and transcriptional events that contribute to Tc17 differentiation and acquisition of effector functions. Also considered is the basis of Tc17 cell plasticity toward the Tc1 lineage, and we suggest that in vivo plasticity of Tc17 cells may be a key feature of Tc17 cell biology in autoimmune diseases. Furthermore, current human researches have revealed that Tc17 cells are different than that in mice because all of them express CD161 and exclusively originate from CD161 precursors present in umbilical cord blood. Finally, we focus on the recent evidence for long-lived Tc17 memory cell populations in mouse models and humans, and their functional roles in mediating disease memory. Hopefully, the information obtained will benefit for developing novel therapeutic strategies.

Brodalumab: an evidence-based review of its potential in the treatment of moderate-to-severe psoriasis

Advances in knowledge regarding the pathogenesis of psoriasis have allowed the development of a new class of agents known as biologic drugs. Data confirm that T helper (Th)17 and interleukin (IL)-17 signaling has a crucial role in the pathogenesis of the disease. High levels of IL-17 and Th17-related cytokines have been reported in psoriasis, leading to the suggestion of agents targeting IL-17 as a potential therapeutic strategy in psoriasis. Brodalumab is a human monoclonal antibody that targets IL-17 receptor A, blocking the effects of IL-17A, IL-17F, and IL-17E. Data from Phase I and Phase II clinical trials indicate that brodalumab has a favorable safety and tolerability profile, with strong clinical activity, suggesting that it is a potential tool for use in the treatment of moderate-to-severe psoriasis.

CTLA-4 (CD152) enhances the Tc17 differentiation program

Although CD8(+) T cells that produce IL-17 (Tc17 cells) have been linked to host defense, Tc17 cells show reduced cytotoxic activity, which is the characteristic function of CD8(+) T cells. Here, we show that CTLA-4 enhances the frequency of IL-17 in CD8(+) T cells, indicating that CTLA-4 (CD152) specifically promotes Tc17 differentiation. Simultaneous stimulation of CTLA-4(+/+) and CTLA-4(-/-) T cells in cocultures and agonistic CTLA-4 stimulation unambiguously revealed a cell-intrinsic mechanism for IL-17 control by CTLA-4. The quality of CTLA-4-induced Tc17 cells was tested in vivo, utilizing infection with the facultative intracellular bacterium Listeria monocytogenes (LM). Unlike CTLA-4(+/+) Tc17 cells, CTLA-4(-/-) were nearly as efficient as Tc1 CTLA-4(+/+) cells in LM clearance. Additionally, adoptively transferred CTLA-4(-/-) Tc17 cells expressed granzyme B after rechallenge, and produced Tc1 cytokines such as IFN-γ and TNF-α, which strongly correlate with bacterial clearance. CTLA-4(+/+) Tc17 cells demonstrated a high-quality Tc17 differentiation program ex vivo, which was also evident in isolated IL-17-secreting Tc17 cells, with CTLA-4-mediated enhanced upregulation of Tc17-related molecules such as IL-17A, RORγt, and IRF-4. Our results show that CTLA-4 promotes Tc17 differentiation that results in robust Tc17 responses. Its inactivation might therefore represent a central therapeutic target to enhance clearance of infection.

Impaired balance of T helper 17/T regulatory cells in carbon tetrachloride-induced liver fibrosis in mice

AIM: To investigate the effect of T helper (Th) 17/T regulatory (Treg) cells on hepatic fibrosis in mice and its possible mechanism.

METHODS: Hepatic fibrosis was induced by intraperitoneal injection of carbon tetrachloride. Hepatic pathological changes were observed by hematoxylin and eosin staining; the protein levels of interleukin (IL)-6, transforming growth factor (TGF)-β and α-smooth muscle actin (SMA) in liver tissue were determined by Western blotting; and the frequency of Th17 and Treg cells in the liver was estimated by flow cytometry. In addition, hepatic stellate cells were isolated from healthy mouse liver and co-cultured with Th17 or Treg cells. Immunofluorescence staining and Western blotting were performed to determine the change in HSC activation.

RESULTS: In the model group, there were different degrees of fibroplasia, degeneration and necrosis. The protein levels of IL-6, TGF-β and α-SMA in liver tissue were significantly higher than those in the control group at 12 wk (P < 0.05). Compared with the control group, the frequency of Th17 cells in the model group was increased but the frequency of Treg cells decreased gradually. Furthermore, at 4, 8 and 12 wk, there were significant differences in the number of Th17 cells (0.52% ± 0.16%, 1.46% ± 0.24%, and 2.60% ± 0.41%, respectively, P < 0.05) and Treg cells (2.99% ± 0.40%, 2.16% ± 0.50%, and 1.49% ± 0.34%, respectively, P < 0.05). In vitro, Th17 cells promoted, whereas Treg cells inhibited the expression of α-SMA, both in a dose-dependent manner, compared with the control group.

CONCLUSION: Th17/Treg imbalance exists in mice with liver fibrosis, which potentially promotes liver fibrosis via HSC activation.

Leptin-cytokine crosstalk in breast cancer

Despite accumulating evidence suggesting a positive correlation between leptin levels, obesity, post-menopause and breast cancer incidence, our current knowledge on the mechanisms involved in these relationships is still incomplete. Since the cloning of leptin in 1994 and its receptor (OB-R) 1 year later by Friedman's laboratory (Zhang et al., 1994) and Tartaglia et al. (Tartaglia et al., 1995), respectively, more than 22,000 papers related to leptin functions in several biological systems have been published (Pubmed, 2012). The ob gene product, leptin, is an important circulating signal for the regulation of body weight. Additionally, leptin plays critical roles in the regulation of glucose homeostasis, reproduction, growth and the immune response. Supporting evidence for leptin roles in cancer has been shown in more than 1000 published papers, with almost 300 papers related to breast cancer (Pubmed, 2012). Specific leptin-induced signaling pathways are involved in the increased levels of inflammatory, mitogenic and pro-angiogenic factors in breast cancer. In obesity, a mild inflammatory condition, deregulated secretion of proinflammatory cytokines and adipokines such as IL-1, IL-6, TNF-α and leptin from adipose tissue, inflammatory and cancer cells could contribute to the onset and progression of cancer. We used an in silico software program, Pathway Studio 9, and found 4587 references citing these various interactions. Functional crosstalk between leptin, IL-1 and Notch signaling (NILCO) found in breast cancer cells could represent the integration of developmental, proinflammatory and pro-angiogenic signals critical for leptin-induced breast cancer cell proliferation/migration, tumor angiogenesis and breast cancer stem cells (BCSCs). Remarkably, the inhibition of leptin signaling via leptin peptide receptor antagonists (LPrAs) significantly reduced the establishment and growth of syngeneic, xenograft and carcinogen-induced breast cancer and, simultaneously decreased the levels of VEGF/VEGFR2, IL-1 and Notch. Inhibition of leptin-cytokine crosstalk might serve as a preventative or adjuvant measure to target breast cancer, particularly in obese women. This review is intended to present an update analysis of leptin actions in breast cancer, highlighting its crosstalk to inflammatory cytokines and growth factors essential for tumor development, angiogenesis and potential role in BCSC.

The multifaceted role of Th17 lymphocytes and their associated cytokines in cancer

While the role of T helper 17 lymphocytes (Th17) in the pathogenesis of autoimmune diseases and in infectious immunity has been relatively well defined, the impact of these cells and their associated cytokines on cancer development is still under debate. Although multiple reports have indicated that Th17 can promote anticancer immunity, others have argued that these cells may exhibit tumor-promoting properties. This dichotomy in the function of Th17 lymphocytes in cancer may be related to the versatile nature of these cells, being capable of differentiating into either proinflammatory Th1 or suppressive FoxP3-expressing Treg cells or hybrid T cell subsets depending on the underlying environmental conditions. In the current review, we examine the role of Th17 lymphocytes and Th17-associated cytokines in cancer and discuss how factors that control their final lineage commitment decision may influence the balance between their tumor-promoting versus tumor-suppressing properties.

Dendritic Cell-Induced Th1 and Th17 Cell Differentiation for Cancer Therapy

The success of cellular immunotherapies against cancer requires the generation of activated CD4⁺ and CD8⁺ T-cells. The type of T-cell response generated (e.g., Th1 or Th2) will determine the efficacy of the therapy, and it is generally assumed that a type-1 response is needed for optimal cancer treatment. IL-17 producing T-cells (Th17/Tc17) play an important role in autoimmune diseases, but their function in cancer is more controversial. While some studies have shown a pro-cancerous role for IL-17, other studies have shown an anti-tumor function. The induction of polarized T-cell responses can be regulated by dendritic cells (DCs). DCs are key regulators of the immune system with the ability to affect both innate and adaptive immune responses. These properties have led many researchers to study the use of ex vivo manipulated DCs for the treatment of various diseases, such as cancer and autoimmune diseases. While Th1/Tc1 cells are traditionally used for their potent anti-tumor responses, mounting evidence suggests Th17/Tc17 cells should be utilized by themselves or for the induction of optimal Th1 responses. It is therefore important to understand the factors involved in the induction of both type-1 and type-17 T-cell responses by DCs.

Constitutive induction of intestinal Tc17 cells in the absence of hematopoietic cell-specific MHC class II expression

The enteric pathogen Citrobacter rodentium induces a mucosal IL-17 response in CD4(+) T helper (Th17) cells that is dependent on the Nod-like receptors Nod1 and Nod2. Here, we sought to determine whether this early Th17 response required antigen presentation by major histocompatibility complex class II (MHCII) for full induction. At early phases of C. rodentium infection, we observed that the intestinal mucosal Th17 response was fully blunted in irradiated mice reconstituted with MHCII-deficient (MHCII(-/-) →WT) hematopoietic cells. Surprisingly, we also observed a substantial increase in the relative frequency of IL-17(+) CD8(+) CD4(-) TCR-β(+) cells (Tc17 cells) and FOXP3(+) CD8(+) CD4(-) TCR-β(+) cells in the lamina propria and intraepithelial lymphocyte compartment of MHCII(-/-) →WT mice compared with that in WT→WT counterparts. Moreover, MHCII(-/-) →WT mice displayed increased susceptibility, increased bacterial translocation to deeper organs, and more severe colonic histopathology after infection with C. rodentium. Finally, a similar phenotype was observed in mice deficient for CIITA, a transcriptional regulator of MHCII expression. Together, these results indicate that MHCII is required to mount early mucosal Th17 responses to an enteric pathogen, and that MHCII regulates the induction of atypical CD8(+) T-cell subsets, such as Tc17 cells and FOXP3(+) CD8(+) cells, in vivo.

IL-17 in the rheumatologist's line of sight

Over the past decades, the identification of several new cytokines, including interleukin (IL)-17 and IL-23, and of new T helper cell subsets, including Th17 cells, has changed the vision of immunological processes. The IL-17/Th17 pathway plays a critical role during the development of inflammation and autoimmunity, and targeting this pathway has become an attractive strategy for a number of diseases. This review aims to describe the effects of IL-17 in the joint and its roles in the development of autoimmune and inflammatory arthritis. Furthermore, biotherapies targeting directly or indirectly IL-17 in inflammatory rheumatisms will be developed.

Induction of apoptosis-resistant and TGF-β-insensitive murine CD8(+) cytotoxic T lymphocytes specific for HIV-1 gp160

Although TGF-β and IL-6 would turn CD8(+) T cells to differentiate into non-cytotoxic state, these treated cells were converted to cytolytic phenotypes after re-exposure to their antigenic epitope in vitro. Here, using spleen cells from TCR transgenic mice expressing TCRαβ genes of clone RT1 recognizing an epitope peptide (P18-I10: RGPGRAFVTI) of HIV-1 gp160, we generated CD8(+) cytotoxic T lymphocytes (CTLs) activated by re-exposure to P18-I10 after primarily cultured with TGF-β and IL-6 in vitro to examine their effector function. The CTLs, having strong cytotoxic activity in vitro, were not only resistant to Fas-FasL mediated apoptosis, but also insensitive to the suppression of their cytotoxicity by re-exposure to TGF-β in vitro. Moreover, adoptive transfer experiments indicated that the CTLs are capable of eliminating recombinant vaccinia virus expressing HIV-1 gp160 in vivo. Taken together, our data suggest that TGF-β and IL-6 may play pivotal roles in inducing apoptosis-resistant and TGF-β-insensitive CTLs in vitro.

Downregulation of Hlx closely related to the decreased expressions of T-bet and Runx3 in patients with gastric cancer may be associated with a pathological event leading to the imbalance of Th1/Th2

T-bet plays an important role in immunoregulation; it induces the differentiation of Th1 together with the homeobox transcription factor gene Hlx. Recent studies show that T-bet and Th1-associated factors are critical in regulating tumor development. However, the contributions of Hlx in the occurrence and development of cancer remain unknown. In this study, the Hlx, T-bet, Runx3, and IFN-γ were measured in PBMC from patients with gastric cancer and the correlation between Hlx and T-bet or IFN-γ was assessed. The expression levels of Hlx, T-bet, and IFN-γwere significantly decreased, and there was a positive correlation between Hlx and T-bet or IFN-γ. In addition, the Runx3 expression was also downregulated with the lower T-bet mRNA level. These results suggested that the decreased Hlx expression was closely associated with T-bet and Runx3 downregulations and may contribute to the development of gastric cancer.

CD4+ T cells disarm or delete cytotoxic T lymphocytes under IL-17-polarizing conditions

Previous studies have shown that TGF-β acts cooperatively with IL-6 to elicit a high frequency of IL-17-secreting CD4(+) T cells (termed Th17) and an elevated CD8(+)IL-17(+) T cell population (termed Tc17). These CD8(+) cells fail to behave like most cytotoxic T lymphocytes that express IFN-γ and granzyme B, but they exhibit a noncytotoxic phenotype. Although a significant increase in the number of these Tc17 cells was found in tumors, their role and interaction with other cell types remain unclear. In this study, we demonstrate that the presence of CD4(+)CD25(-) T cells, but not the CD4(+)CD25(+) (regulatory T [Treg]) cell population, significantly reduced the elicitation of Tc17 cells, possibly as a result of the induction of apoptotic signals. Importantly, these signals may be derived from soluble mediators, and the addition of anti-IL-2 restored the reduction of Tc17 cells in the presence of CD4(+)CD25(-) T cells. Finally, the elicited Tc17 and Treg cells exhibited a close association in patients with head and neck cancer, indicating that the surrounding Treg cells might maintain the survival of the Tc17 cells. Taken together, these results reveal an intriguing mechanism in which Tc17 cells are controlled by a finely tuned collaboration between the different types of CD4(+) T cells in distinct tumor microenvironments.

The development of IL-17/IFN-γ-double producing CTLs from Tc17 cells is driven by epigenetic suppression of Socs3 gene promoter

The plasticity of T lymphocytes induced by epigenetic modifications of gene promoters may play a pivotal role in controlling their effector functions, which are sometimes causally associated with immune disorders. IL -17-producing T cells, which induce type 17 immune responses, are newly identified pathogenic effector cells. The type 1 signature cytokine IFN-γ strongly inhibits their differentiation, indicating a mutually exclusive relationship between type 17- and type 1-immune responses. However, many reports indicate the presence of a unique IL-17/IFN-γ-double producing T-cell subset in various inflammatory settings, although the mechanisms responsible for their development and their precise functions remain unclear. Here, we demonstrate that IL-12 permits the conversion of mouse IL-17-producing CD8(+) T (Tc17) cells to IL-17/IFN-γ-double producing CD8(+) T (Tc17/IFN-γ) cells, and that this conversion is due to repressive epigenetic modifications of Socs3 gene promoters. Moreover, we show that SOCS3 strongly regulates the capability of Tc17 cells to produce IL-17, in addition to regulating the expression of the type 17-master regulator RORγt. These findings elucidate the mechanisms underlying the conversion of Tc17 cells into Tc17/IFN-γ cells. As these cells are known to have potent antitumor activities, manipulation of these conversion mechanisms for therapeutic tumor immunity may be possible.

Use of praziquantel as an adjuvant enhances protection and Tc-17 responses to killed H5N1 virus vaccine in mice

Background

H5N1 is a highly pathogenic influenza A virus, which can cause severe illness or even death in humans. Although the widely used killed vaccines are able to provide some protection against infection via neutralizing antibodies, cytotoxic T-lymphocyte responses that are thought to eradicate viral infections are lacking.

Methodology/Principal Findings

Aiming to promote cytotoxic responses against H5N1 infection, we extended our previous finding that praziquantel (PZQ) can act as an adjuvant to induce IL-17-producing CD8⁺ T cells (Tc17). We found that a single immunization of 57BL/6 mice with killed viral vaccine plus PZQ induced antigen-specific Tc17 cells, some of which also secreted IFN-γ. The induced Tc17 had cytolytic activities. Induction of these cells was impaired in CD8 knockout (KO) or IFN-γ KO mice, and was even lower in IL-17 KO mice. Importantly, the inoculation of killed vaccine with PZQ significantly reduced virus loads in the lung tissues and prolonged survival. Protection against H5N1 virus infection was obtained by adoptively transferring PZQ-primed wild type CD8⁺ T cells and this was more effective than transfer of activated IFN-γ KO or IL-17 KO CD8⁺ T cells.

Conclusions/Significance

Our results demonstrated that adding PZQ to killed H5N1 vaccine could promote broad Tc17-mediated cytotoxic T lymphocyte activity, resulting in improved control of highly pathogenic avian influenza virus infection.

Transforming growth factor-β protein inversely regulates in vivo differentiation of interleukin-17 (IL-17)-producing CD4+ and CD8+ T cells

TGF-β is a pleiotropic cytokine that predominantly exerts inhibitory functions in the immune system. Unexpectedly, the in vitro differentiation of both Th17 and Tc17 cells requires TGF-β. However, animals that are impaired in TGF-β signaling (TGF-βRIIDN mice) display multiorgan autoimmune disorders. Here we show that CD4⁺ T cells from TGF-βRIIDN mice are resistant to Th17 cell differentiation and, paradoxically, that CD8⁺ T cells from these animals spontaneously acquire an IL-17-producing phenotype. Neutralization of IL-17 or depletion of CD8⁺ T cells dramatically inhibited inflammation in TGF-βRIIDN mice. Therefore, the absence of TGF-β triggers spontaneous differentiation of IL-17-producing CD8⁺ T cells, suggesting that the in vivo and in vitro conditions that promote the differentiation of IL-17-producing CD8⁺ T cells are distinct.

IL-17-expressing cells as a potential therapeutic target for treatment of immunological disorders

IL-17 is a multifunctional cytokine produced by activated CD4+ and CD8+ lymphocytes as well as stimulated unconventional Tγδ and natural killer T cells. IL-17 induces expression of chemokines, proinflammatory cytokines and metalloproteinases, thereby stimulating the inflammation and chemotaxis of neutrophils. Elevation of proinflammatory cytokines is associated with asthma and autoimmune disorders, such as multiple sclerosis, rheumatoid arthritis and psoriasis. Although the role of IL-17 in these disorders is not always easy to define, extensive research has demonstrated an aggravating influence of IL-17 in some animal models. Thus, the development of therapeutics to reduce IL-17 levels is a promising strategy for ameliorating inflammatory diseases. This review briefly summarizes recent knowledge about stimulants and intracellular signaling pathways that induce development and maturation of IL-17-expressing cells. Its positive and negative roles on disease progression and its importance in vaccine-induced memory are also discussed. Finally, recent literature describing potential therapeutic approaches for targeting IL-17 is presented.

Cytokines and effector T cell subsets causing autoimmune CNS disease

Although experimental autoimmune encephalomyelitis (EAE) is limited in its potency to reproduce the entirety of clinical and histopathologic features of multiple sclerosis (MS), this model has been successfully used to prove that MS like autoimmunity in the CNS is orchestrated by autoantigen specific T cells. EAE was also very useful to refute the idea that IFN-γ producing T helper type 1 (Th1) cells were the sole players within the pathogenic T cell response. Rather, "new" T cell lineages such as IL-17 producing Th17 cells or IL-9 producing Th9 cells have been first discovered in the context of EAE. Here, we will summarize new concepts of early and late T cell plasticity and the cytokine network that shapes T helper cell responses and lesion development in CNS specific autoimmunity.