IL-21 Up-Regulates the Expression of Genes Associated with Innate Immunity and Th1 Response

Synergy between Common γ Chain Family Cytokines and IL-18 Potentiates Innate and Adaptive Pathways of NK Cell Activation

Studies to develop cell-based therapies for cancer and other diseases have consistently shown that purified human natural killer (NK) cells secrete cytokines and kill target cells after in vitro culture with high concentrations of cytokines. However, these assays poorly reflect the conditions that are likely to prevail in vivo in the early stages of an infection and have been carried out in a wide variety of experimental systems, which has led to contradictions within the literature. We have conducted a detailed kinetic and dose-response analysis of human NK cell responses to low concentrations of IL-12, IL-15, IL-18, IL-21, and IFN-α, alone and in combination, and their potential to synergize with IL-2. We find that very low concentrations of both innate and adaptive common γ chain cytokines synergize with equally low concentrations of IL-18 to drive rapid and potent NK cell CD25 and IFN-γ expression; IL-18 and IL-2 reciprocally sustain CD25 and IL-18Rα expression in a positive feedback loop; and IL-18 synergizes with FcγRIII (CD16) signaling to augment antibody-dependent cellular cytotoxicity. These data indicate that NK cells can be rapidly activated by very low doses of innate cytokines and that the common γ chain cytokines have overlapping but distinct functions in combination with IL-18. Importantly, synergy between multiple signaling pathways leading to rapid NK cell activation at very low cytokine concentrations has been overlooked in prior studies focusing on single cytokines or simple combinations. Moreover, although the precise common γ chain cytokines available during primary and secondary infections may differ, their synergy with both IL-18 and antigen-antibody immune complexes underscores their contribution to NK cell activation during innate and adaptive responses. IL-18 signaling potentiates NK cell effector function during innate and adaptive immune responses by synergy with IL-2, IL-15, and IL-21 and immune complexes.

Elevated expression of interleukin-21 and its correlation to T-cell subpopulation in patients with ulcerative colitis

Objective

To investigate the expression of interleukin-21 (IL-21) and its correlation to T-cell subpopulation including Th1, Tc1 and Th17 cells in Ulcerative colitis (UC).

Material and methods

We examined the expression of IL-21, IL-17 and IFN-γ in UC patients and controls by enzyme-linked immunosorbent assay (ELISA) and flow cytometry.

Results

We found that IL-21 was expressed on CD3⁺CD8^-T cells by flow cytometry. Plasma IL-21 level and the percentage of CD3⁺CD8^-IL-21⁺ T cells were significantly elevated in UC patients compared to controls. The percentage of CD3⁺CD8^-IL-17⁺ T (Th17), CD3⁺CD8^-IFN-γ⁺ T (Th1) and CD3⁺CD8⁺ IFN-γ⁺ T (Tc1) cells was also significantly increased in UC patients. Moreover, we found a significant positive correlation between CD3⁺CD8^-IL-21⁺T cells and Th17 cells.

Conclusions

Elevated IL-21 and its positive correlation to Th17 cells may play a role in the pathogenesis of UC.

IFN-γ and IL-21 Double Producing T Cells Are Bcl6-Independent and Survive into the Memory Phase in Plasmodium chabaudi Infection

CD4 T cells are required to fight malaria infection by promoting both phagocytic activity and B cell responses for parasite clearance. In Plasmodium chabaudi infection, one specific CD4 T cell subset generates anti-parasitic IFN-γ and the antibody-promoting cytokine, IL-21. To determine the lineage of these multifunctional T cells, we followed IFN-γ⁺ effector T cells (Teff) into the memory phase using Ifng-reporter mice. While Ifng⁺ Teff expanded, the level of the Th1 lineage-determining transcription factor T-bet only peaked briefly. Ifng⁺ Teff also co-express ICOS, the B cell area homing molecule CXCR5, and other Tfh lineage-associated molecules including Bcl6, the transcription factor required for germinal center (GC) T follicular helper cells (Tfh) differentiation. Because Bcl6 and T-bet co-localize to the nucleus of Ifng⁺ Teff, we hypothesized that Bcl6 controls the Tfh-like phenotype of Ifng⁺ Teff cells in P. chabaudi infection. We first transferred Bcl6-deficient T cells into wildtype hosts. Bcl6-deficient T cells did not develop into GC Tfh, but they still generated CXCR5⁺IFN-γ⁺IL-21⁺IL-10⁺ Teff, suggesting that this predominant population is not of the Tfh-lineage. IL-10 deficient mice, which have increased IFN-γ and T-bet expression, demonstrated expansion of both IFN-γ⁺IL-21⁺CXCR5⁺ cells and IFN-γ⁺ GC Tfh cells, suggesting a Th1 lineage for the former. In the memory phase, all Ifng⁺ T cells produced IL-21, but only a small percentage of highly proliferative Ifng⁺ T cells maintained a T-bet^hi phenotype. In chronic malaria infection, serum IFN-γ correlates with increased protection, and our observation suggests Ifng⁺ T cells are maintained by cellular division. In summary, we found that Ifng⁺ T cells are not strictly Tfh derived during malaria infection. T cells provide the host with a survival advantage when facing this well-equipped pathogen, therefore, understanding the lineage of pivotal T cell players will aid in the rational design of an effective malaria vaccine.

IL-21 Is Important for Induction of KLRG1+ Effector CD8 T Cells during Acute Intracellular Infection

Microsporidia, a latent opportunistic infection associated with mild inflammation, is characterized by a strong CD8 T cell response, which has been shown to be CD4 T cell dependent. In this manuscript, we demonstrate that CD4 help is provided via IL-21 production, a common γ-chain cytokine closely related to IL-2. The peak of IL-21 expression, observed during the acute infection, is associated with an elevated IL-21(+) CD4 T subset, and these cells bear a phenotypic resemblance to T follicular helper cells. We observed that, during per-oral microsporidial infection, IL-21 was critical for the generation of an optimal effector CD8 T cell immunity. Sharply decreased effector KLRG1(+) CD8 response was observed in IL-21R knockout mice, and although these cells exhibited reduced functional properties, they retained the ability to proliferate. The role of IL-21 in the generation of CD8 effectors was cell intrinsic, as stronger defects were observed in the IL-21-deficient compartment from the bone marrow chimeric mice (IL-21R knockout/wild-type). These findings are different from those reported for viral infections in which IL-21 has been primarily associated with the generation and maintenance of CD8 memory response. To the best of our knowledge, this report demonstrates a critical role for IL-21 in the generation of a primary effector CD8 T cell response to an infectious disease model.

Serum level of interleukin-21 is elevated in chronic rhinosinusitis

BACKGROUND

Chronic rhinosinusitis (CRS) is an inflammatory disease of the sinuses and mucosa with unclear pathogenesis. Interleukin (IL)-21 is mainly expressed in activated cluster of differentiation (CD)4(+) T cells and has potent regulatory effects on the immune system.

OBJECTIVE

This study is to determine whether IL-21 in the blood is correlated with CRS.

METHODS

The blood samples from CRS patients and normal controls were analyzed in correlation with clinical features. The eosinophil percentage was counted, and serum levels of total immunoglobulin E (IgE) and IL-21 were analyzed by enzyme-linked immunosorbent assay (ELISA). In addition, IL-21 and interferon (IFN)-γ secreted from stimulated peripheral blood mononuclear cells (PBMCs) were measured by ELISA, and their mRNA expression levels were analyzed by real-time quantitative polymerase chain reaction (RT-qPCR). Disease severity was scored based on computed tomography (CT) scan, nasal endoscopy, and global osteitis scoring scale (GOSS).

RESULTS

A total of 55 CRS and 37 healthy subjects were recruited. The average levels of serum total IgE were 20 kU/L in normal group, 290 kU/L in CRS with nasal polys (CRSwNP), and 187 kU/L in CRS without nasal polys (CRSsNP). IL-21 levels were 28 pg/mL in normal group, 54 pg/mL in CRSwNP, and 71 pg/mL in CRSsNP. Both IgE and IL-21 were significantly elevated in both CRS patient subgroups. However, no significant difference was found between these two patient subgroups. The serum IL-21 levels correlated well with the disease severity in the patients. In addition, the secreted IL-21 was enhanced significantly in the patient's PBMCs stimulated by phytohemagglutin (PHA).

CONCLUSION

IL-21 could be a target for diagnosis and treatment of CRS.

Human IL-21+IFN-γ+CD4+ T cells in nasal polyps are regulated by IL-12

In the previous study, we found that the levels of IL-21 in nasal polyps (NPs) were significantly increased and associated with polyp size and recurrence. However, it is unclear that the cell source of IL-21 and the regulation of IL-21 in NP tissues. In the present study, we isolated the lymphocytes from NP tissues, uncinate tissues and peripheral blood of patients with NPs. The cells were analyzed for cell surface markers, cytokines and transcriptional factors by flow cytometry. The results indicated that CD4⁺ T cells were the major IL-21-exprssing cells in NP tissues and the majority of IL-21 producing CD4⁺ T cells co-expressed IFN-γ or IL-17A. IL-21⁺IFN-γ⁺CD4⁺ T cells in NP tissues exhibited the features of both Tfh and Th1 cells which co-expressed significantly higher amount of CXCR5, ICOS, PD-1, Bcl-6 and T-bet than did IL-21⁺IFN-γ⁻CD4⁺ T cells (p < 0.05). Treatment of the lymphocytes from NP tissues with IL-12 enhanced the production of IL-21 and IFN-γ, especially the frequency of IL-21⁺IFN⁻γ⁺CD4⁺ T cells (p < 0.05). The blockade of IL-12 inhibited the production of IL-21 and IFN-γ (p < 0.05). These findings indicated that IL-12 positively enhanced the generation of IL-21⁺IFN-γ⁺CD4⁺ T cells having the features of both Tfh and Th1 cells in NP tissues.

CpG oligodeoxynucleotide CpG-685 upregulates functional interleukin-21 receptor on chronic lymphocytic leukemia B cells through an NF-κB mediated pathway

CpG oligodeoxynucleotides (ODNs) upregulate the interleukin-21 receptor (IL21R) and enhance IL-21-mediated cytotoxicity in chronic lymphocytic leukemia (CLL) B cells. We demonstrate that treatment of CLL B cells with the ODN CpG-685 leads to increased IL21R expression, and that this increased expression enhances the effects of IL-21 treatment as evidenced by increased phosphorylation of JAK1, STAT1, and STAT3, as compared to IL-21 treatment without prior CpG stimulation. Induction of IL21R by CpG-685 also enhanced IL-21-mediated cytotoxicity. The mechanism by which CpG ODNs upregulate IL21R has not been elucidated, although IL21R regulation in T cells has been shown to be linked to T cell receptor-induced Sp1 binding to the IL21R promoter. Here, we demonstrate that luciferase reporter constructs containing the Sp1 binding site have increased basal luciferase activity compared to constructs lacking the Sp1 binding site, but fail to increase luciferase activity with CpG-685 stimulation in CLL B cells. By treating CLL cells with an NF-κB inhibitor, we inhibit the CpG ODN-mediated induction of IL21R, thus demonstrating that CpG-685 upregulates IL21R through an NF-κB mediated pathway. These findings suggest an alternative mechanism for induction of IL-21 receptor in CLL B cells and provide a basis for creation of future combination therapies.

Interleukin-21 suppresses the differentiation and functions of T helper 2 cells

T helper type 2 (Th2) cells, which produce interleukin-4 (IL-4), IL-5 and IL-13, control immunity to all forms of allergic inflammatory responses. Interleukin-21 (IL-21) reduces allergic symptoms in murine models and inhibits IL-4-induced IgE secretion by B cells. However, whether or not IL-21 directly affects Th2 cells, which leads to reduced allergic symptoms, is unclear. In this study, we investigated the effects of IL-21 on the differentiation and effector functions of Th2 cells. We found that IL-21 reduced the number of differentiated Th2 cells and these Th2 cells showed a diminished Th2 cytokine production. Interleukin-21 suppressed Th2 cytokine production of already polarized Th2 cells by down-regulation of transcription factor GATA-3. It also induced apoptosis of Th2 cells with decreased anti-apoptotic factor Bcl-2. Intranasal administration of IL-21 at the beginning of ovalbumin (OVA) sensitization or before OVA challenge decreased Th2 cytokines in the bronchoalveolar lavage fluid of OVA/alum-immunized allergic mice. In addition, the inhibitory effects of IL-21 on Th2 effector functions can also be found in allergic patients. Our results demonstrate that IL-21 suppresses the development of Th2 cells and functions of polarized Th2 cells. Hence, the administration of IL-21 may be considered for use as a preventive and therapeutic approach when dealing with Th2-mediated allergic diseases.

Mucosal interleukin-21 mRNA expression level is high in patients with Helicobacter pylori and is associated with the severity of gastritis

Helicobacter pylori (H. pylori) infection is associated with gastritis and marked infiltration of the gastric mucosa by several cytokines secreting inflammatory cells. Different clinical forms of the infection may reflect distinctive patterns of cytokine expression. Interleukin (IL)-17, IL-21, IL-22, and IL-23 have been reported to be involved in H. pylori-induced gastric mucosal inflammation, but the details and relationship to different patterns of inflammation and virulence factors remain unclear. The present study was launched to analyse IL-6 expression in H. pylori-infected and uninfected gastric patients and to investigate its correlation with chronic gastritis among H. pylori-infected patients. Total RNA was extracted from the gastric antrum biopsies of 48 H. pylori-infected patients and 38 H. pylori uninfected patients. Mucosal IL-21 mRNA expression level in H. pylori-infected and uninfected gastric biopsy was determined by real-time PCR. The presence of vacA (vacuolating cytotoxin A) and cagA (cytotoxin associated gene A) virulence factors were evaluated using PCR. Interleukin-21 mRNA expression was significantly high in biopsies of H. pylori-infected patients compared to H. pylori uninfected patients, and the mucosal IL-21 mRNA level was positively correlated with the grade of chronic inflammation. There was no association between virulence factors and IL-21 mRNA expression. We believe that IL-21 might be involved in the pathogenesis of H. pylori and might be an index of the severity of chronic gastritis.

Increased IL-21/IL-21R expression and its proinflammatory effects in autoimmune thyroid disease

To determine the potential role of interleukin-21 (IL-21) / IL-21 receptor (IL-21R) in the pathogenesis of autoimmune thyroid disease (AITD) mainly known as Graves' disease (GD) and Hashimoto's thyroiditis (HT). IL-21 and IL-21R of peripheral blood samples and/or thyroid tissues from AITD patients and healthy controls were analyzed by ELISA, quantitative real-time polymerase chain reaction (qRT-PCR), flow cytometry and immunohistochemistry. In vitro, the mRNA and protein of inflammatory cytokines of cultured peripheral blood mononuclear cells (PBMCs) upon recombinant human IL-21 (rhIL-21) stimulation were detected. There was an increased serum concentration of IL-21 in untreated GD and HT patients, and IL-21(+)CD3(+)CD8(-)T cells were significantly increased in PBMCs of HT patients compared with healthy volunteers. The IL-21 mRNA expression in PBMCs increased dramatically in GD and HT patients, and marked augmentations of IL-21 and IL-21R mRNA in thyroid tissues of HT patients were observed. Immunohistochemical staining confirmed the expression of IL-21R protein in HT thyroid cells and lymphocytes. In vitro, PBMCs from GD cultured with rhIL-21 induced increased IL-17A but decreased IL-4 production, while from HT stimulated by rhIL-21 induced augmented production of IFN-γ. In conclusion, the expression of IL-21 and IL-21R were up-regulated in AITD and may be involved in the pathogenesis of the disease through augmenting aberrant immune cascade.

Involvement of interleukin-21 in the pathophysiology of aplastic anemia

OBJECTIVE

Recently enhanced T-helper type 17 (Th17) immune responses and deficient CD4(+) CD25(hi) FoxP3(+) regulatory T cells (Tregs) have been reported in acquired aplastic anemia (AA). Interleukin-21 (IL-21), a CD4(+) T-cell-derived proinflammatory cytokine, modulates the balance between Th17 cells and Tregs. However, its role in AA remains unclear.

METHODS

IL-21 gene expression was examined by quantitative real-time PCR. Cytokines in plasma and cell culture supernatants were detected by ELISA. Cytokines-producing T cells and Tregs were evaluated by flow cytometry.

RESULTS

IL-21 mRNA levels in circulating CD4(+) T cells and IL-21 levels in blood plasma were markedly increased in patients with newly diagnosed AA. Moreover, elevated IL-21-producing CD4(+) T cells were accompanied by Th17 cells accumulation and Tregs decrease, and correlated with AA activity. In vitro, IL-21 not only inhibited the expression of FoxP3, but also induced the expression of IL-17 in CD4(+) T cells of AA patients. More importantly, we found that T cells within the bone marrow (BM) of AA patients were in a heightened activation state, which may be related to IL-21.

CONCLUSION

Our data suggested a critical role of IL-21 in breaking immune homeostasis in AA by promoting Th17 cells, activating BM T cells and suppressing Tregs.

Elevated levels of Th17 cells and Th17-related cytokines are associated with disease activity in patients with inflammatory bowel disease

OBJECTIVE

Interleukin-17(IL-17)-producing T helper(Th)17 cells are considered as a new subset of cells critical to the development of inflammatory bowel disease (IBD). We aimed to investigate the distribution of Th17 cells, the expressions of Th17-related cytokines (IL-17, IL-21 and IL-22) and their association with disease activity in IBD patients.

METHODS

We collected intestinal tissue biopsies from 40 patients with active ulcerative colitis (UC), 20 patients with active Crohn's disease (CD) and 20 healthy controls. The distribution of Th17 cells and expressions of Th17-related cytokines in colonic tissues were evaluated by a standard immunohistochemical procedure. Serum IL-17, IL-21 and IL-22 levels were determined by ELISA. Pearson's and Spearman's correlation analyses were performed to analyze the correlation between the number of Th17 cells, the expressions of Th17-related cytokines and disease activity index, endoscopic and histological grading, and CRP and PLT levels, respectively.

RESULTS

Compared with healthy controls, the number of Th17 cells and the expressions of IL-17, IL-21 and IL-22 were significantly increased in active IBD patients (P < 0.05). In addition, Pearson's and Spearman's correlation analyses showed that the number of Th17 cells and the expressions of Th17-related cytokines were correlated with disease activity index, endoscopic and histological grading, CRP and PLT levels (P < 0.05).

CONCLUSIONS

Th17 cells and Th17-related cytokines (IL-17, IL-21 and IL-22) were increased in the intestinal mucosa in active IBD patients and may play an important role in disease activity and mucosal damage.

Polymorphism in interleukin 21 gene is associated with decreased susceptibility to diffuse large B cell lymphoma

Interleukin 21 (IL-21) plays a key role in innate and adaptive immunity. Polymorphisms in IL-21 gene may be greatly involved in various diseases. The aim of the study was to investigate the association between IL-21 genetic polymorphisms and the susceptibility to diffuse large B cell lymphoma (DLBCL). IL-21 -2498G/A and +78A/G polymorphisms were examined in 221 DLBCL patients and 243 healthy controls. We found that distributions of -2498GA genotype and -2498AA genotype were clearly decreased in DLBCL cases compared to healthy donors (odds ratio [OR] = 0.71, 95% confidence interval [CI] = 0.43-0.92, P = 0.021; OR = 0.36, 95 % CI = 0.15-0.48, P < 0.001; data were adjusted for age and sex). Stratification analyses revealed that patients with advanced Ann Arbor stages (III+IV) had further decreased percentage of -2498AA genotype than those with primary stages (OR = 0.31, 95% CI = 0.13-0.87, P = 0.023; data were adjusted for age and sex). In addition, we evaluated the possible effect of IL-21 polymorphisms on gene expression by examining serum level of IL-21 in patients and controls. Data revealed that subjects carrying -2498AA genotype had significantly higher serum level of IL-21 than those with GG genotype or GA genotype. These data suggest that IL-21 -2498G/A polymorphism is associated with decreased susceptibility to DLBCL and may increase serum level of IL-21.

Upregulated interleukin-21 receptor on B cells associated with the downregulation of IgE in patients with allergic rhinitis

Allergic diseases, such as allergic rhinitis, caused by an immunoglobulin E (IgE)-mediated reaction to specific allergens are a common chronic condition worldwide. Interleukin-21 (IL-21), a type I cytokine that is produced by T cells, exerts regulatory effects on a variety of immune cells. In our previous study, we found that serum levels of IL-21 were significantly decreased in patients with severe atopic dermatitis, suggesting that IL-21 might play a role in allergic reactions. In this study, we investigated the role of IL-21/IL-21 receptor (IL-21R) in patients with allergic rhinitis. Our results demonstrated that there was no difference in IL-21 serum levels between allergic rhinitis patients and controls. However, allergic patients had significantly increased expression of IL-21R on naive and memory B cells. IL-21R was upregulated through stimulation by the combination of CD40 ligand (CD40L) and IL-4. IL-21 alone neither induced nor inhibited IgE secretion from CD40L-stimulated B cells. However, IL-21 inhibited IgE secretion of B cells that were induced by the combination of CD40L and IL-4 in allergic patients. Moreover, a negative correlation between the expression of IL-21R and serum levels of IgE was found in patients with allergy. These results suggest that the role of IL-21 in an ongoing allergic reaction is to downregulate the IgE level by binding to IL-21R on B cells, which increases the expression in allergic patients.

Therapeutic potential of STAT4 in autoimmunity

INTRODUCTION

STAT4, which acts as the major signaling transducing STATs in response to IL-12, is a central mediator in generating inflammation during protective immune responses and immune-mediated diseases.

AREAS COVERED

This review summarizes that STAT4 is essential for the differentiation and function of a wide variety of immune cells, including natural killer cells, mast cells, dendritic cells and T helper cells. In addition, STAT4-mediated signaling promoted the production of autoimmune-associated components, which are implicated in the pathogenesis of autoimmune diseases, such as rheumatoid arthritis, systemic lupus erythematosus, systemic sclerosis and psoriasis.

EXPERT OPINION

Due to its crucial roles in inflammation and autoimmunity, STAT4 may have promise as an effective therapeutic target for autoimmune diseases. Understanding the molecular mechanisms driving STAT4, together with knowledge on the ability of current immunosuppressive treatment to target this process, may open an avenue to novel therapeutic options.

Effect of serum interleukin 21 on the development of coronary artery disease

There has been more and more evidence to confirm the essential role of inflammatory processes in the development of coronary artery disease (CAD). Interleukin-21 (IL-21), the most recently discovered CD132-dependent cytokine, plays a key role in regulating inflammation. The aim of the study was to understand the effect of peripheral IL-21 on the pathogenesis and progression of CAD. Serum level of IL-21 in 92 CAD patients and 73 controls was measured by the enzyme-linked immunosorbent assay. Data showed that IL-21 expression was significantly increased in CAD than in controls (p < 0.001). Interestingly, when comparing IL-21 level with different genders, male subjects revealed higher IL-21 than female subjects (p = 0.024). Also, we observed that patients with hypertension had upregulated level of serum IL-21 (p = 0.002). Moreover, serum level of IL-21 was positively correlated with total cholesterol level (p = 0.015) or low-density lipoprotein cholesterol (p = 0.0009) of CAD cases. In addition, we analyzed IL-21 level with the severity of CAD, and identified that cases with 3-vessel affected had significantly elevated level of IL-21 than those with 1-vessel or 2-vessel affected. These data suggested that serum level of IL-21 may be closely associated with the development and progression of CAD.

Distinct from its canonical effects, deletion of IL-12p40 induces cholangitis and fibrosis in interleukin-2Rα(-/-) mice

The IL-12 family modulates T cell mediated autoimmune diseases and GWAS in PBC have suggested a critical role of IL-12 and its subunits in modulating portal inflammation. We have taken advantage of an aggressive model of portal inflammation and colitis in IL-2Rα(-/-) mice to study the specific role of IL-12 and, in particular, the immunobiology of p40(-/-)IL-2Rα(-/-) mice. Colonies of IL-2Rα(+/-), IL-2Rα(-/-) and p40(-/-)IL-2Rα(-/-) mice were studied for the natural history of immunopathology in liver and colon using histology and immunohistochemistry. Further, to focus on mechanisms, liver, spleen and mesenteric lymph node flow cytometry was employed to identify specific phenotypes; cytokine analysis on inflammatory cell populations was compared between groups. Finally, Real-Time PCR was used to focus on the genes involved in hepatic fibrosis. Surprisingly, p40(-/-)IL-2Rα(-/-) mice manifest more severe portal inflammation and bile duct damage, including signs of portal hypertension and liver fibrosis, but a significant reduction in colitis. Indeed, p40(-/-)IL-2Rα(-/-) mice reveal a profound hepatic CD8(+) T cell infiltrate, whose major component are effector memory cells as well as enhanced hepatic Th1 but reduced Th17 responses. These observations were confirmed by Real-Time PCR analysis of fibrosis-related genes in the liver. Distinct from its canonical effects, IL-12p40 plays a critical role in autoimmune cholangitis, including hepatic fibrosis. These data take on striking significance for any proposed human trials that modulate the IL-12p40 pathway in human PBC.

Immunomodulatory and antitumor effects of interleukin-21 in patients with renal cell carcinoma

Interleukin (IL)-21 is a class I cytokine with sequence homology to the IL-2 cytokine superfamily. IL-21 signals through a heterodimer of a unique IL-21 receptor and the common gamma-chain cytokine receptor. Preclinical murine models suggested strong antitumor activity of IL-21 in renal cell carcinoma, melanoma and other tumor models. IL-21 antitumor activity was superior to IL-2 in these tumor models. A Phase I clinical trial of IL-21 in humans with metastatic renal cell carcinoma or melanoma began in May 2004. Clinical regressions were observed in renal cell carcinoma. Preliminary immunological and clinical findings of patients receiving IL-21 will be reviewed.

IL-21 is increased in peripheral blood of emphysema mice and promotes Th1/Tc1 cell generation in vitro

Interleukin-21 (IL-21) has been reported to be involved in many Th1-associated diseases. However, the alteration and immune regulation of IL-21 in emphysema remains unknown. In this study, we tested the levels of IFN-γ and IL-21 and the frequencies of Th1 and Tc1 in peripheral blood from cigarette smoke (CS)-exposed mice and air-exposed mice and explored the effect of IL-21 on generation of Th1 and Tc1 cells in vitro. It was found that the levels of IFN-γ and IL-21 and the frequencies of Th1, Tc1, CD4(+) IL-21(+), CD4(+) IL-21R(+), and CD8(+) IL-21R(+) T cells were much higher in CS-exposed mice. Moreover, the levels of IL-21 were correlated positively with Th1 cells and with Tc1 cells. Finally, the in vitro experiments showed that IL-21 could promote Th1/Tc1 cell generation in CS-exposed mice. These results indirectly provide evidence that IL-21 produced by CD4(+) T cells could promote Th1/Tc1 response, leading to systemic inflammation in emphysema.

Interleukin-21 receptor signalling is important for innate immune protection against HSV-2 infections

Interleukin (IL) -21 is produced by Natural Killer T (NKT) cells and CD4(+) T cells and is produced in response to virus infections, where IL-21 has been shown to be essential in adaptive immune responses. Cells from the innate immune system such as Natural Killer (NK) cells and macrophages are also important in immune protection against virus. These cells express the IL-21 receptor (IL-21R) and respond to IL-21 with increased cytotoxicity and cytokine production. Currently, however it is not known whether IL-21 plays a significant role in innate immune responses to virus infections. The purpose of this study was to investigate the role of IL-21 and IL-21R in the innate immune response to a virus infection. We used C57BL/6 wild type (WT) and IL-21R knock out (KO) mice in a murine vaginal Herpes Simplex Virus type 2 (HSV-2) infection model to show that IL-21 - IL-21R signalling is indeed important in innate immune responses against HSV-2. We found that the IL-21R was expressed in the vaginal epithelium in uninfected (u.i) WT mice, and expression increased early after HSV-2 infection. IL-21R KO mice exhibited increased vaginal viral titers on day 2 and 3 post infection (p.i.) and subsequently developed significantly higher disease scores and a lower survival rate compared to WT mice. In addition, WT mice infected with HSV-2 receiving intra-vaginal pre-treatment with murine recombinant IL-21 (mIL-21) had decreased vaginal viral titers on day 2 p.i., significantly lower disease scores, and a higher survival rate compared to infected untreated WT controls. Collectively our data demonstrate the novel finding that the IL-21R plays a critical role in regulating innate immune responses against HSV-2 infection.

IL-17 producing T cells in celiac disease: angels or devils?

Celiac disease (CD) is a very common chronic condition in human beings, affecting approximately one in 100 individuals. It is an autoimmune disease with a defined environmental trigger, the gluten contained in dietary cereals, occurring in genetically susceptible individuals. The disease has a very strong HLA association. More than 90% of CD patients have HLA-DQ2, and almost all of the remaining celiac population possesses HLA-DQ8 molecules. Th17 cells seem to participate in the disease pathogenesis producing and secreting either proinflammatory or anti-inflammatory cytokines.

Interleukin-21 up-regulates interleukin-21R expression and interferon gamma production by CD8+ cells in SHIV-infected macaques

Interleukin-21 (IL-21) is produced primarily by CD4+ T cells and regulates immunity against human/simian immunodeficiency virus (HIV/SIV) infection. Activated CD8+ cells and their secreted interferon-gamma (IFN-γ) are crucial for the control of acute HIV/SIV infection. However, whether IL-21 can regulate IFN-γ production by CD8+ cells remains controversial. Rhesus macaques (RMs, n = 8) were infected with SHIV and the levels of plasma IL-21, IFN-γ and the frequency of peripheral blood activated T cells were measured longitudinally. Following infection with SHIV, the levels of plasma IL-21 and IFN-γ increased, peaked at 17 days postinfection and declined later. Furthermore, IL-21 induced IL-21 receptor (IL-21R) and IFN-γ, perforin, but not granmyze B, expression in CD8+ cells from four selected SHIV-infected RMs. The regulatory effect of IL-21 on CD8+ cell function appeared to be associated with increased levels of STAT3, but not STAT5, phosphorylation in CD8+ cells from SHIV-infected RMs. In parallel, treatment with soluble IL-21R/Fc, an inhibitor of IL-21-induced activation of JAK1/3 and STAT3, abrogated IL-21-induced STAT3 activation and IFN-γ production in CD8+ cells from SHIV-infected RMs in vitro. Our data indicated that IL-21 was a positive regulator of IFN-γ-secreting CD8+ cells and increased the STAT3 phosphorylation, regulating T-cell immunity against acute SHIV infection in RMs. Our findings may provide a new basis for the development of immunotherapies for the control of SHIV/HIV infection.

Signal transducer and activator of transcription 3 (STAT3) mutations underlying autosomal dominant hyper-IgE syndrome impair human CD8(+) T-cell memory formation and function

BACKGROUND

The capacity of CD8(+) T cells to control infections and mediate antitumor immunity requires the development and survival of effector and memory cells. IL-21 has emerged as a potent inducer of CD8(+) T-cell effector function and memory development in mouse models of infectious disease. However, the role of IL-21 and associated signaling pathways in protective CD8(+) T-cell immunity in human subjects is unknown.

OBJECTIVE

We sought to determine which signaling pathways mediate the effects of IL-21 on human CD8(+) T cells and whether defects in these pathways contribute to disease pathogenesis in patients with primary immunodeficiencies caused by mutations in components of the IL-21 signaling cascade.

METHODS

Human primary immunodeficiencies resulting from monogenic mutations provide a unique opportunity to assess the requirement for particular molecules in regulating human lymphocyte function. Lymphocytes from patients with loss-of-function mutations in signal transducer and activator of transcription 1 (STAT1), STAT3, or IL-21 receptor (IL21R) were used to assess the respective roles of these genes in human CD8(+) T-cell differentiation in vivo and in vitro.

RESULTS

Mutations in STAT3 and IL21R, but not STAT1, led to a decrease in multiple memory CD8(+) T-cell subsets in vivo, indicating that STAT3 signaling, possibly downstream of IL-21R, regulates the memory cell pool. Furthermore, STAT3 was important for inducing the lytic machinery in IL-21-stimulated naive CD8(+) T cells. However, this defect was overcome by T-cell receptor engagement.

CONCLUSION

The IL-21R/STAT3 pathway is required for many aspects of human CD8(+) T-cell behavior but in some cases can be compensated by other signals. This helps explain the relatively mild susceptibility to viral disease observed in STAT3- and IL-21R-deficient subjects.

Endogenous IL-21 regulates pathogenic mucosal CD4 T-cell responses during enhanced RSV disease in mice

A role for interleukin-21 (IL-21) has recently been found in several diseases, but contribution to mucosal defences has not been described. In BALB/c mice infected with respiratory syncytial virus (RSV), IL-21 depletion had little effect in primary infection. However, depletion of mice during priming with recombinant vaccinia expressing RSV G protein (which primes RSV-specific T helper type 2 cells and causes lung eosinophilia during RSV infection) further exacerbated pathology during RSV challenge, with reduced viral clearance and impaired virus-specific serum antibody responses. This enhancement was accompanied by lymphocyte, neutrophil, and antigen-presenting cell recruitment to the lungs, with increased bronchoalveolar lavage interferon-γ and IL-17 levels. Adoptive transfer of splenic CD4 T cells from depleted mice into naive recipients replicated these effects, indicating that IL-21 mediates its effects via CD4 T cells. Endogenous IL-21, therefore, has potent and specific effects on mucosal antiviral responses, assisting viral clearance, regulating pulmonary T- and B-cell responses, and inhibiting IL-17 production.

Monoclonal antibody therapy of pancreatic cancer with cetuximab: potential for immune modulation

Pancreatic cancer is a devastating disease, with a median survival of around 6 months for patients with stage IV disease. The epidermal growth factor receptor (EGFR, or HER1) belongs to the erbB receptor tyrosine kinase family. HER1-mediated cell signaling has been shown to play a major role in promoting tumor proliferation, angiogenesis, metastasis, and evasion of apoptosis. Over-expression of HER1 is observed in multiple human malignancies, including colorectal, lung, breast and pancreatic cancers. In pancreatic carcinoma, over-expression of HER1 is observed in greater than 70% of patients and is associated with a poor prognosis and a significant decrease in survival. Cetuximab (Erbitux) is a chimeric monoclonal antibody (mAb) that binds to the extracellular domain of the HER1 molecule preventing ligand binding and promoting internalization and subsequent degradation of the HER1 receptor. Cetuximab has shown anti-tumor activity either alone or in combination with other agents and is currently FDA approved for use in both squamous cell carcinoma of the head and neck (SCCHN) and colorectal carcinoma. Research efforts continue to elucidate a possible role for cetuximab in the treatment of pancreatic cancer. Despite promising preclinical work, phase II and phase III clinical trials have failed to consistently show efficacy of cetuximab treatment in advanced pancreatic cancer either alone or in combination with cytotoxic agents. Alternative approaches to HER1 blockade and mAbs including immune modulation with cytokines might be necessary in order to improve the efficacy of mAbs in pancreatic cancer therapy.

Promoting immunity during chronic infection--the therapeutic potential of common gamma-chain cytokines

The continued global burden wrought by chronic infectious disease is unrelenting. Current therapies have curbed the severity of disease for patients, but Human Immunodeficiency Virus (HIV) and Hepatitis B (HBV) infection remain incurable and Mycobacterium tuberculosis (MTB) is rapidly becoming resistant to our existing antibiotics. Much attention has been given to enhancing T cell immunity through the use of certain common gamma-chain cytokines, which have proven to be essential and necessary for T cell survival and function. This article reviews the pre-clinical and clinical literature surrounding IL-2, IL-7, IL-15 and IL-21 and we comment on the potential therapeutic promise of these cytokines as adjuvant treatments for chronic infectious diseases.

Interleukin-21 (IL-21) synergizes with IL-2 to enhance T-cell receptor-induced human T-cell proliferation and counteracts IL-2/transforming growth factor-β-induced regulatory T-cell development

Interleukin-2 (IL-2) is a mainstay for current immunotherapeutic protocols but its usefulness in patients is reduced by severe toxicities and because IL-2 facilitates regulatory T (Treg) cell development. IL-21 is a type I cytokine acting as a potent T-cell co-mitogen but less efficient than IL-2 in sustaining T-cell proliferation. Using various in vitro models for T-cell receptor (TCR)-dependent human T-cell proliferation, we found that IL-21 synergized with IL-2 to make CD4(+) and CD8(+) T cells attain a level of expansion that was impossible to obtain with IL-2 alone. Synergy was mostly evident in naive CD4(+) cells. IL-2 and tumour-released transforming growth factor-β (TGF-β) are the main environmental cues that cooperate in Treg cell induction in tumour patients. Interleukin-21 hampered Treg cell expansion induced by IL-2/TGF-β combination in naive CD4(+) cells by facilitating non-Treg over Treg cell proliferation from the early phases of cell activation. Conversely, IL-21 did not modulate the conversion of naive activated CD4(+) cells into Treg cells in the absence of cell division. Treg cell reduction was related to persistent activation of Stat3, a negative regulator of Treg cells associated with down-modulation of IL-2/TGF-β-induced phosphorylation of Smad2/3, a positive regulator of Treg cells. In contrast to previous studies, IL-21 was completely ineffective in counteracting the suppressive activity of Treg cells on naive and memory, CD4(+) and CD8(+) T cells. Present data provide proof-of-concept for evaluating a combinatorial approach that would reduce the IL-2 needed to sustain T-cell proliferation efficiently, thereby reducing toxicity and controlling a tolerizing mechanism responsible for the contraction of the T-cell response.

IL-15 positively regulates IL-21 production in celiac disease mucosa

Celiac disease (CD)-associated inflammation is characterized by high interleukin- 21 (IL-21), but the mechanisms that control IL-21 production are not fully understood. Here we analyzed IL-21 cell sources and examined how IL-21 production is regulated in CD. Intraepithelial lymphocytes (IELs) and lamina propria lymphocytes (LPLs), isolated from CD patients and non-CD controls, were analyzed for cell markers, cytokines, and transcription factors by flow cytometry. IL-21 was highly produced by CD4+ and CD4+/CD8+ IELs and LPLs in active CD. IL-21-producing cells coexpressed interferon-γ (IFN-γ) and to a lesser extent T helper type 17 (Th17) cytokines. Treatment of control LPLs with IL-15, a cytokine overproduced in CD, activated Akt and STAT3 (signal transducer and activator of transcription 3), thus enhancing IL-21 synthesis. Active CD biopsies contained elevated levels of Akt, and blockade of IL-15 in those samples reduced IL-21. Similarly, neutralization of IL-15 in biopsies of inactive CD patients inhibited peptic-tryptic digest of gliadin-induced IL-21 expression. These findings indicate that in CD, IL-15 positively regulates IL-21 production.

A regulatory effect of IL-21 on T follicular helper-like cell and B cell in rheumatoid arthritis

Introduction

Interleukin (IL)-21 is a member of type I cytokine family. Recent studies indicate that IL-21 can promote T follicular helper (Tfh) cell differentiation and survival, a specialized T cell subset which provides help for B cell. It can also regulate the activation, proliferation and differentiation of human B cell and immunoglobulin (Ig) production as well as isotype switching of plasma cell. Rheumatoid arthritis (RA) is characterized by auto-antibodies overproduction such as rheumatoid factor (RF) and anti-cyclic citrullinated peptide (anti-CCP) antibody, suggesting a pivotal role of Tfh cell and B cell in the pathogenesis of RA. This study aimed to investigate whether IL-21 had a regulatory effect on Tfh cell and B cell in RA.

Methods

Serum IL-21 concentrations were measured by ELISA. The correlations between serum IL-21 levels and clinical features of RA patients were analyzed by Spearman's rank test. The percentages of Tfh-like cells, IL-21 receptor (R) expression on Tfh-like cells and B cells in peripheral blood (PB) were analyzed by flow cytometry. Peripheral blood mononuclear cells (PBMC) were stimulated by rIL-21 (100 ng/ml) in the presence or absence of anti-CD40 and/or anti-IgM, and changes of IL-21R, activation-associated surface markers (CD25, CD69 and CD40), the proliferation, apoptosis and differentiation of B cells were analyzed by flow cytometry. Production of IgG and IgM in the culture supernatants was determined by ELISA.

Results

The results showed that the serum IL-21 levels in RA patients were significantly higher than that of healthy controls (HC). IL-21 concentrations were positively correlated with 28-joint count disease activity score (DAS28) and anti-CCP antibody in RA patients with high IL-21 levels. Furthermore, the frequencies of peripheral CXCR5⁺PD-1⁺CD4⁺ Tfh-like cells markedly increased in RA patients and the percentages of Tfh-like cells were positively correlated with DAS28 and anti-CCP antibody levels. Moreover, elevated IL-21 levels were also correlated with the frequencies of Tfh-like cells. IL-21R expression on both Tfh-like cells and B cells were significantly enhanced in RA patients. In cultures vitro, exogenous IL-21 upregulated IL-21R expression and activation-associated surface markers on B cells and promoted more B cell proliferation in RA than in HC. This IL-21-mediated effect could be reversed by IL-21R-specific neutralizing antibody. Importantly, IL-21 promoted more differentiation of B cell into plasmablast and higher levels of IgG and IgM production in RA than in HC.

Conclusions

Increased serum IL-21 levels in RA patients correlate with DAS28, anti-CCP antibody and frequencies of Tfh-like cells. IL-21 supports B cell activation, proliferation and antibody secretion via IL-21R pathway. Thus, IL-21 may be involved in the pathogenesis of RA and antagonizing IL-21 could be a novel strategy for the therapy of RA.

What's the next best cytokine target in IBD?

In the gut of patients with inflammatory bowel disease (IBD), immune and nonimmune cells produce large amounts of cytokines that drive the inflammatory process leading to the tissue damage. Cytokine blockers, such as anti-tumor necrosis factor alpha (TNF-α), have been used with some success in IBD. However, not all patients respond, and the therapeutic effects wane with time, demonstrating the need for more effective and long-lasting antiinflammatory strategies. A key question is whether neutralizing other proinflammatory cytokines such as interleukin (IL)-12, IL-21, IL-27, or IL-33 will lead to a better clinical response than with anti-TNF-α antibodies. Equally, we now know that IBD-related inflammation is marked by defective production/activity of antiinflammatory cytokines, and there are strategies to correct these defects. An alternative approach is to try to target individual therapies to individual patients, to improve clinical efficacy in subsets of patients, but this has proven difficult. Here we try to evaluate the potential of each of these choices.

Kinetics of T helper subsets and associated cytokines correlate well with the clinical activity of graft-versus-host disease

Background

CD4⁺interferon (IFN)-γ⁺ T cell (Th1) and CD4⁺interleukin (IL)-4⁺ T cell (Th2) polarizations are crucial in the pathogenesis of graft-versus-host disease (GVHD). However, this hypothesis is largely based on animal experiments of Parent-into-F1 GVHD model. The causal relationship between kinetics of Th1, Th2 and associated cytokines and the clinical activity of GVHD in a real world situation remains unknown.

Methodology

Peripheral blood was collected every week prospectively from Day 0 to Day 210 (patients without GVHD) or Day 300 (patients with chronic GVHD) after allogeneic peripheral blood stem cell transplantation in consecutive 27 patients. The frequencies of Th1 and Th2 within CD4⁺ T cells were determined by flow cytometry and pplasma IFN-γ, IL-12, IL-4, and IL-10 were determined by ELISA.

Principal Findings

Kinetics of Th1, Th2 frequency, and the plasma IL-10 and IFN-γ more commonly coincided with, rather than predicted, the activity of GVHD. These markers are significantly higher when acute or chronic GVHD developed. The kinetics of IL-10 is especially correlated well with the activity of GVHD during clinical course of immunosuppressive treatment. For patients with hepatic GVHD, there is a positive correlation between plasma IL-10 levels and the severity of hepatic injury. The frequency of Th2 is also significant higher in acute GVHD and tends to be higher in chronic GVHD. Interestingly, there is a very good positive correlation between the frequency of Th1 and Th2 (r = 0.951, p<0.001). The plasma level of IL-4 and IL-12 are not associated with the activity of GVHD.

Conclusions

The frequency of Th1, Th2 within CD4⁺ T cells and plasma IL-10 and IFN-γ are good biomarkers of GVHD. Plasma IL-10 can also be used to monitor the therapeutic responsiveness. Furthermore, both Th1 and Th2 likely contribute to the pathogenesis of GVHD.

IL-10+ CTLA-4+ Th2 inhibitory cells form in a Foxp3-independent, IL-2-dependent manner from Th2 effectors during chronic inflammation

Activated Th cells influence other T cells via positive feedback circuits that expand and polarize particular types of response, but little is known about how they may also initiate negative feedback against immunopathological reactions. In this study, we demonstrate the emergence, during chronic inflammation, of GATA-3(+) Th2 inhibitory (Th2i) cells that express high levels of inhibitory proteins including IL-10, CTLA-4, and granzyme B, but do so independently of Foxp3. Whereas other Th2 effectors promote proliferation and IL-4 production by naive T cells, Th2i cells suppress proliferation and IL-4 production. We show that Th2i cells develop directly from Th2 effectors, in a manner that can be promoted by effector cytokines including IL-2, IL-10, and IL-21 ex vivo and that requires T cell activation through CD28, Card11, and IL-2 in vivo. Formation of Th2i cells may act as an inbuilt activation-induced feedback inhibition mechanism against excessive or chronic Th2 responses.

Antigen-independent induction of Tim-3 expression on human T cells by the common γ-chain cytokines IL-2, IL-7, IL-15, and IL-21 is associated with proliferation and is dependent on the phosphoinositide 3-kinase pathway

T cell Ig mucin domain-containing molecule 3 (Tim-3) is a glycoprotein found on the surface of a subset of CD8(+) and Th1 CD4(+) T cells. Elevated expression of Tim-3 on virus-specific T cells during chronic viral infections, such as HIV-1, hepatitis B virus, and hepatitis C virus, positively correlates with viral load. Tim-3(+) cytotoxic T cells are dysfunctional and are unable to secrete effector cytokines, such as IFN-γ and TNF-α. In this study, we examined potential inducers of Tim-3 on primary human T cells. Direct HIV-1 infection of CD4(+) T cells, or LPS, found to be elevated in HIV-1 infection, did not induce Tim-3 on T cells. Tim-3 was induced by the common γ-chain (γc) cytokines IL-2, IL-7, IL-15, and IL-21 but not IL-4, in an Ag-independent manner and was upregulated on primary T cells in response to TCR/CD28 costimulation, as well as γc cytokine stimulation with successive divisions. γc cytokine-induced Tim-3 was found on naive, effector, and memory subsets of T cells. Tim-3(+) primary T cells were more prone to apoptosis, particularly upon treatment with galectin-9, a Tim-3 ligand, after cytokine withdrawal. The upregulation of Tim-3 could be blocked by the addition of a PI3K inhibitor, LY 294002. Thus, Tim-3 can be induced via TCR/CD28 costimulation and/or γc cytokines, likely through the PI3K pathway.

Chronic fatigue syndrome, the immune system and viral infection

The chronic fatigue syndrome (CFS), as defined by recent criteria, is a heterogeneous disorder with a common set of symptoms that often either follows a viral infection or a period of stress. Despite many years of intense investigation there is little consensus on the presence, nature and degree of immune dysfunction in this condition. However, slightly increased parameters of inflammation and pro-inflammatory cytokines such as interleukin (IL) 1, IL6 and tumour necrosis factor (TNF) α are likely present. Additionally, impaired natural killer cell function appears evident. Alterations in T cell numbers have been described by some and not others. While the prevalence of positive serology for the common herpes viruses appears no different from healthy controls, there is some evidence of viral persistence and inadequate containment of viral replication. The ability of certain herpes viruses to impair the development of T cell memory may explain this viral persistence and the continuation of symptoms. New therapies based on this understanding are more likely to produce benefit than current methods.

Decrease in interleukin-21 in children suffering with severe atopic dermatitis

BACKGROUND

Atopic dermatitis (AD) is a kind of eczema with an inflammatory, relapsing, non-contagious, and pruritic skin disorder. It is associated with the local infiltration of T helper type 2 (Th2) cells that secrete interleukin (IL)-4 and IL-5. IL-21 is a member of IL-2 family cytokine mainly expressed by activated CD4+ T lymphocytes. Until now, there is no clinical research in the expression of IL-21 in patients with AD.

METHODS

We analyzed serum levels of total immunoglobulin E (IgE), allergen-specific IgE, and cytokines IL-4, IL-5, IFN-γ, IL-17, and IL-21 in AD cases and controls. In addition, cytokine levels in the culture supernatants of peripheral blood mononuclear cells stimulated with anti-CD3 and anti-CD28 Abs, phytohemagglutin (PHA), or pokeweed mitogen (PWM) were measured. We also assessed clinical skin severity by Scoring of Atopic Dermatitis (SCORAD) index.

RESULTS

Our results showed that serum total IgE in the case group was significantly higher than that of control group (365.449 ± 52.945 and 39.243 ± 7.605 IU/ml, respectively). Logistic regression analysis system reveals serum levels of IL-21 and IFN-γ are significantly correlated. However, IL-21 and IL-4, IL-21 and IL-5, as well as IL-21 and IL-17 showed no correlation.

CONCLUSION

A significantly decreased level of IL-21 was observed in children suffering with severe AD compared with controls, suggesting that IL-21 may play a role in AD.

Th17-related cytokines: new players in the control of chronic intestinal inflammation

Crohn's disease (CD) and ulcerative colitis (UC), the main forms of inflammatory bowel diseases (IBD) in man, are thought to be caused by an excessive and poorly controlled immune response that is directed against components of the normal microflora. The exact sequence of events by which this pathological process is triggered and maintained is not fully understood, but studies in experimental models of IBD and data emerging from recent clinical trials indicate that T cell-derived cytokines are crucial mediators of the tissue damage. Although CD and UC have been traditionally considered two typical examples of T helper (Th)1 or Th2-associated disease respectively, it is now known that CD- and UC-related inflammation is also marked by enhanced production of cytokines made by a distinct subset of Th cells, termed Th17 cells. Th17 cytokines can have both tissue-protective and inflammatory effects in the gut and there is evidence that Th17 cells can alter their cytokine program according to the stimuli received and convert into Th1-producing cells. These novel findings have contributed to advancing our understanding of mechanisms of gut tissue damage and open new avenues for development of therapeutic strategies in IBD.

No association observed between schizophrenia and non-HLA coeliac disease genes: integration with the initial MYO9B association with coeliac disease

Schizophrenia is a severe psychotic illness with a heterogeneous presentation and a devastating impact on social and occupational function. Worldwide variations in schizophrenia incidence rates suggest that local conditions may modify disease risk. The human leukocyte antigen (HLA) region has been confirmed to be associated with schizophrenia by genome-wide association studies in populations across the world. While the presence of autoimmune processes in a subgroup of schizophrenia cases is contentious, the immune system could allow environmental exposures to lead to schizophrenia by generating improper immune response. To investigate this topic, we reviewed the current evidence of the relationship between schizophrenia and coeliac disease. Based on this review, we performed genetic analysis of the MYO9B gene and the IL-2/IL-21 locus by genotyping SNPs that have been previously associated with coeliac disease or schizophrenia in 223 families, 108 unrelated individuals with schizophrenia and 120 controls. Finding no evidence for association with these two loci in our study samples, we applied meta-analytic techniques to combine our findings with previous reports. This synthesis, in light of our review of previous reports, suggests a differing developmental trajectory for schizophrenia and coeliac disease. It is possible that these two conditions do not share any functional overlap.

Interleukin-23 and T helper 17-type responses in intestinal inflammation: from cytokines to T-cell plasticity

Interleukin-23 (IL-23) plays an essential role in driving intestinal pathology in experimental models of both T-cell-dependent and innate colitis. Furthermore, genome-wide association studies have identified several single-nucleotide polymorphisms in the IL-23 receptor (IL-23R) gene that are associated with either susceptibility or resistance to inflammatory bowel disease in humans. Although initially found to support the expansion and maintenance of CD4(+) T helper 17 (Th17) cells, IL-23 is now recognized as having multiple effects on the immune response, including restraining Foxp3(+) regulatory T-cell activity and inducing the expression of Th17-type cytokines from non-T-cell sources. Here we focus on Th17 cells and their associated cytokines IL-17A, IL-17F, IL-21 and IL-22. We review studies performed in mouse models of colitis where these effector cytokines have been shown to have either a pathogenic or a tissue-protective function. We also discuss the heterogeneity found within the Th17 population and the phenomenon of plasticity of Th17 cells, in particular the ability of these lymphocytes to extinguish IL-17 expression and turn on interferon-γ production to become Th1-like 'ex-Th17' cells. Interleukin-23 has been identified as a key driver in this process, and this may be an additional mechanism by which IL-23 promotes pathology in the intestinal tract. These 'ex-Th17' cells may contribute to disease pathogenesis through their secretion of pro-inflammatory mediators.

Disruption of downstream MyD88 or TRIF Toll-like receptor signaling does not protect against cerebral ischemia

Toll-like receptor (TLR) signaling plays an important role in cerebral ischemia, but downstream signaling events, which can be organ-specific, are incompletely understood. We thereby investigated involvement of the MyD88-dependent (MyD88) and MyD88-independent (TRIF) TLR signaling pathways in 2 in vitro and 2 in vivo models of cerebral ischemia. For in vitro studies, we used a model of oxygen-glucose deprivation (OGD) followed by flow cytometric analysis to determine:1) viability of PC12 cells following knock-down with MyD88 siRNA compared to negative control siRNA and 2) viability, apoptosis and necrosis of cortical neurons from MyD88 null (-/-) , TRIF mutant, and wild type (WT) mice. In addition, in vivo, 1) We examined CA1 neuronal survival 7 days after global forebrain ischemia and 2) infarct volumes 24h after Middle Cerebral Artery Occlusion (MCAO) in all 3 types of mice. OGD: 1) There were no differences in either percent viability of PC12 cells transfected with MyD88 compared to negative control siRNA or 2) in percent viability, apoptosis and necrosis of cortical neurons from MyD88-/-,TRIF mutant and WT mice. Global ischemia: neuronal survival was similar in all 3 groups of mice. Finally, MCAO: infarct volumes were not statistically different among all 3 groups of mice: MyD88-/-, 23.9±9.9 mm(3), TRIF mutant, 26.7±5.8 mm(3) and WT, 17.9±8.4mm(3). These findings show that disruption of MyD88 or TRIF signaling does not confer protection in brain ischemia and suggests the possibility of additional or alternate downstream adaptors during TLR signaling in cerebral ischemia.

Regulation of effector and memory T-cell functions by type I interferon

Type I interferon (IFN-α/β) is comprised of a family of highly related molecules that exert potent antiviral activity by interfering with virus replication and spread. IFN-α/β secretion is tightly regulated through pathogen sensing pathways that are operative in most somatic cells. However, specialized antigen-presenting plasmacytoid dendritic cells are uniquely equipped with the capacity to secrete extremely high levels of IFN-α/β, suggesting a key role for this cytokine in priming adaptive T-cell responses. Recent studies in both mice and humans have demonstrated a role for IFN-α/β in directly influencing the fate of both CD4(+) and CD8(+) T cells during the initial phases of antigen recognition. As such, IFN-α/β, among other innate cytokines, is considered an important 'third signal' that shapes the effector and memory T-cell pool. Moreover, IFN-α/β also serves as a counter-regulator of T helper type 2 and type 17 responses, which may be important in the treatment of atopy and autoimmunity, and in the development of novel vaccine adjuvants.

IL-21 promotes skin recruitment of CD4(+) cells and drives IFN-γ-dependent epidermal hyperplasia

Psoriasis is a chronic inflammatory disorder of the skin characterized by epidermal hyperplasia and infiltration of leukocytes into the dermis and epidermis. T cell-derived cytokines, such as IFN-γ and IL-17A, play a major role in the psoriasis-associated epidermal hyperplasia, even though factors/mechanisms that regulate the production of these cytokines are not fully understood. We have recently shown that IL-21 is synthesized in excess in psoriatic skin lesions and causes epidermal hyperplasia when injected intradermally in mice. Moreover, in the human psoriasis SCID mouse model, neutralization of IL-21 reduces both skin thickening and expression of inflammatory molecules, thus supporting the pathogenic role of IL-21 in psoriasis. However, the basic mechanism by which IL-21 promotes skin pathology remains unknown. In this study, we show that CD4(+) cells accumulate early in the dermis of IL-21-treated mice and mediate the development of epidermal hyperplasia. Indeed, IL-21 fails to induce skin damage in RAG1-deficient mice and CD4(+) cell-depleted wild-type mice. The majority of CD4(+) cells infiltrating the dermis of IL-21-treated mice express IFN-γ and, to a lesser extent, IL-17A. Studies in cytokine knockout mice show that IFN-γ, but not IL-17A, is necessary for IL-21-induced epidermal hyperplasia. Finally, we demonstrate that IFN-γ-producing CD4(+) cells infiltrating the human psoriatic plaque express IL-21R, and abrogation of IL-21 signals reduces IFN-γ expression in cultures of psoriatic CD4(+) cells. Data indicate that IL-21 induces an IFN-γ-dependent pathogenic response in vivo, thus contributing to elucidate a mechanism by which IL-21 sustains skin-damaging inflammation.

Joining the immunological dots in recurrent miscarriage

While raised cellular immunity mediated by T helper (Th) 1 type cells may be harmful for the developing embryo/foetus, it is likely that Th2 type immunity may be helpful. The role of natural killer (NK) cells is presently underestimated, although they are clearly important in angiogenesis and the coordinated invasion of the decidua by the trophoblast. Deficient T regulatory cell (Treg) function is evident in women with recurrent miscarriage particularly when this occurs in early pregnancy. The role of the pro-inflammatory Th17 cells is presently unclear. However, early evidence suggests that excessive Th17 activity may promote miscarriage and preterm delivery. This may relate to the ability of these cells to produce those cytokines that encourage Th1 and NK cell activity. As such recurrent miscarriage may be caused not only by chromosomal abnormalities, autoimmunity and uterine abnormalities but also by subclinical uterine infection and inflammation which by stimulating interleukin 6 favours Th17 development over Tregs. This review examines the role of these different cells in early pregnancy and suggests a schema that may join the dots of the immunological puzzle called pregnancy. Finally, suggestions are made as to how inappropriate immunity in recurrent miscarriage may be down-regulated using currently available therapies.

Recent advances in cytokines: therapeutic implications for inflammatory bowel diseases

Inflammatory bowel diseases (IBDs) are complex and chronic disabling conditions resulting from a dysregulated dialogue between intestinal microbiota and components of both the innate and adaptive immune systems. Cytokines are essential mediators between activated immune and non-immune cells, including epithelial and mesenchymal cells. They are immunomodulatory peptides released by numerous cells and these have significant effects on immune function leading to the differentiation and survival of T cells. The physiology of IBD is becoming a very attractive field of research for development of new therapeutic agents. These include cytokines involved in intestinal immune inflammation. This review will focus on mechanisms of action of cytokines involved in IBD and new therapeutic opportunities for these diseases.