Interleukin 21 and its receptor are involved in NK cell expansion and regulation of lymphocyte function

The common gamma chain cytokine interleukin-21 is expressed by activated lymphocytes from two macropod marsupials, Macropus eugenii and Onychogalea fraenata

In mammals, interleukin-21 is a member of the common gamma chain cytokine family that also includes IL-2, IL-4, IL-7, IL-9 and IL-15. IL-21 has pleiotropic effects on both myeloid and lymphoid immune cells and as a consequence, the biological actions of IL-21 are broad: regulating both innate and adaptive immune responses and playing a pivotal role in antiviral, inflammatory and antitumour cellular responses. While IL-21 genes have been characterized in mammals, birds, fish and amphibians, there are no reports for any marsupial species to date. We characterized the expressed IL-21 gene from immune tissues of two macropod species, the tammar wallaby (Macropus eugenii), a model macropod, and the closely related endangered bridled nailtail wallaby (Onychogalea fraenata). The open reading frame of macropod IL-21 is 462 nucleotides in length and encodes a 153-mer putative protein that has 46% identity with human IL-21. Despite the somewhat low amino acid conservation with other mammals, structural elements and residues essential for IL-21 conformation and receptor association were conserved in the macropod IL-21 predicted peptides. The detection of IL-21 gene expression in T-cell-enriched tissues, combined with analysis of the promotor region of the tammar wallaby gene, suggests that macropod IL-21 is expressed in stimulated T cells but is not readily detected in other cells and tissues. The similarity of gene expression profile and functionally important amino acid residues to eutherian IL-21 makes it unlikely that the differences in B- and T-cell responses that are reported for some marsupial species are due to a lack of important functional residues or IL-21 gene expression in this group of mammals.

IL-21-Induced MHC Class II+ NK Cells Promote the Expansion of Human Uncommitted CD4+ Central Memory T Cells in a Macrophage Migration Inhibitory Factor-Dependent Manner

NK cells are critical for innate immunity-mediated protection. The main roles of NK cells rely on their cytotoxic functions or depend on the tuning of Th1 adaptive immunity by IFN-γ. However, the precise influence of inflammatory cytokines on NK cell and CD4 T lymphocyte interactions was never investigated. In this study, we provide evidence that IL-21, a cytokine produced during chronic inflammation or infectious diseases, promotes the differentiation of a specific subset of NK cells coexpressing CD86 and HLA-DR and lacking NKp44. More importantly, IL-21-propagated HLA-DR(+) NK cells produce macrophage migration inhibitory factor and provide costimulatory signaling during naive CD4(+) T cell priming inducing the differentiation of uncommitted central memory T cells. Central memory T cells expanded in the presence of HLA-DR(+) NK cells are CXCR3(+)CCR6(-)CCR4(-)CXCR5(-) and produce IL-2, as well as low levels of TNF-α. Costimulation of CD4(+) T cells by HLA-DR(+) NK cells prevents the acquisition of effector memory phenotype induced by IL-2. Moreover, we identified this population of NK HLA-DR(+) macrophage migration inhibitory factor(+) cells in inflammatory human appendix. Collectively, these results demonstrate a novel function for IL-21 in tuning NK and CD4(+) T cell interactions promoting a specific expansion of central memory lymphocytes.

Advances of the interleukin-21 signaling pathway in immunity and angiogenesis

Interleukin-21 (IL-21) and its receptor (IL-21R) are broadly expressed on human B cells, activated T cells and other myeloid cells. IL-21 cooperates with IL-6 and transforming growth factor-β to regulate T-cell differentiation. IL-21-mediated human B cell and dendritic cells differentiation requires signal transducer and activator of transcription 3 (STAT3), and also induces B-cell apoptosis dependents on the Toll-like receptor signal. Recently, in vitro and in vivo experiments showed that IL-21/IL-21R regulate angiogenesis through STAT3. IL-21 signaling pathways are complex due to its cooperation with other transcriptional factors, such as interferon regulatory factor 4 and granulocyte-macrophage colony-stimulating factor. The Janus kinase-STAT pathway has been the most extensively studied. With the increase in the understanding of IL-21 biology in the context of each specific disease or pathological condition, IL-21 could be a new therapeutic target for immune-related disease.

Impaired coronary microcirculation in type 2 diabetic patients is associated with elevated circulating regulatory T cells and reduced number of IL-21R⁺ T cells

Background

Low-grade systemic inflammation is considered to participate in the progression of type 2 diabetes (T2D) and in diabetic complications.

Methods

To determine if circulating leukocytes were abnormally regulated in T2D patients, 8-color flow-cytometry (FACS) analysis was performed in a cross-sectional study of 37 T2D patients and 16 controls. Data obtained from the FACS analysis were compared to coronary flow reserve (CFR), assessed by Rb⁸²-PET-imaging, to uncover inflammatory signatures associated with impaired CFR.

Results

Presence of T2D was associated with T cell attenuation characterized by reduced overall T cell, Th17, IL-21R⁺, Treg’s and TLR4⁺ T cells, while the monocyte population showed enhanced TLR4 expression. Further, our data revealed reduced M1-like CD11c expression in T2D which was associated with impaired CFR. In contrast, we show, for the first time in T2D, increased TLR4 expression on CD8 T cells, increased Treg cell number and Treg maturation and reduced IL-21R expression on CD8 T cells to be functionally associated with impaired CFR.

Conclusions

Our demonstration that HbA1c inversely correlates to several T cell populations suggests that T cells may play disease modulating roles in T2D. Further, the novel association between impaired CFR and regulatory T cells and IL-21R⁺ T cells imply an intricate balance in maintaining tissue homeostasis in vascular diabetic complications.

Electronic supplementary material

The online version of this article (doi:10.1186/s12933-016-0378-5) contains supplementary material, which is available to authorized users.

Prognostic value of plasma biomarkers in patients with acute coronary syndrome: a review of advances in the past decade

Acute coronary syndrome (ACS), especially myocardial infarction, commonly known as a heart attack, is a serious life-threatening cardiovascular disease. Despite dramatic therapeutic advances, there have still been more than 20% patients with ACS suffering recurrent adverse cardiovascular events 3 years after disease onset. Therefore, the aim to prevent cardiac death caused by the heart attack remains challenging. Plasma biomarkers, originally developed to complement clinical assessment and electrocardiographic examination for the diagnosis of ACS, have been reported to play important prognostic roles in predicting adverse outcomes. These biomarkers mirror different pathophysiological mechanisms in association with ACS. In this review, we focus on advances of prognostic biomarkers in the past decade for short- and long-term risk assessment and management of patients with ACS.

Transient CD4+ T Cell Depletion Results in Delayed Development of Functional Vaccine-Elicited Antibody Responses

We have recently demonstrated that CD4(+)T cell help is required at the time of adenovirus (Ad) vector immunization for the development of functional CD8(+)T cell responses, but the temporal requirement for CD4(+)T cell help for the induction of antibody responses remains unclear. Here we demonstrate that induction of antibody responses in C57BL/6 mice can occur at a time displaced from the time of Ad vector immunization by depletion of CD4(+)T cells. Transient depletion of CD4(+)T cells at the time of immunization delays the development of antigen-specific antibody responses but does not permanently impair their development or induce tolerance against the transgene. Upon CD4(+)T cell recovery, transgene-specific serum IgG antibody titers develop and reach a concentration equivalent to that in undepleted control animals. These delayed antibody responses exhibit no functional defects with regard to isotype, functional avidity, expansion after boosting immunization, or the capacity to neutralize a simian immunodeficiency virus (SIV) Env-expressing pseudovirus. The development of this delayed transgene-specific antibody response is temporally linked to the expansion of de novo antigen-specific CD4(+)T cell responses, which develop after transient depletion of CD4(+)T cells. These data demonstrate that functional vaccine-elicited antibody responses can be induced even if CD4(+)T cell help is provided at a time markedly separated from the time of vaccination.

IMPORTANCE

CD4(+)T cells have a critical role in providing positive help signals to B cells, which promote robust antibody responses. The paradigm is that helper signals must be provided immediately upon antigen exposure, and their absence results in tolerance against the antigen. Here we demonstrate that, in contrast to the current model that the absence of CD4(+)T cell help at priming results in long-term antibody nonresponsiveness, antibody responses can be induced by adenovirus vector immunization or alum-adjuvanted protein immunization even if CD4(+)T cell help is not provided until >1 month after immunization. These data demonstrate that the time when CD4(+)T cell help signals must be provided is more dynamic and flexible than previously appreciated. These data suggest that augmentation of CD4(+)T cell helper function even after the time of vaccination can enhance vaccine-elicited antibody responses and thereby potentially enhance the immunogenicity of vaccines in immunocompromised individuals.

Genetic Association Between IL-21 Polymorphisms and Cryptorchidism in a Chinese Han Population

AIMS

Increasing evidence suggests an association between interleukin gene polymorphisms and cryptorchidism. To investigate the relationship between IL-21 gene polymorphisms and cryptorchidism susceptibility, a comprehensive genetic association study in a Chinese Han population was conducted.

METHODS AND RESULTS

A total of 328 men were enrolled in a case-control study (116 cases and 212 healthy controls). Three SNPs (rs907715, rs2055979, and rs12508721) of the IL-21 gene were genotyped using the TaqMan(®) genotyping assay. For the rs2055979 C>A polymorphism, A allele carriers had significantly decreased cryptorchidism susceptibility (p = 0.021, odds ratios [OR] = 0.58, 95% confidence intervals [CI] = 0.37-0.93) in a dominant model (AA+CA vs. CC), a codominant model (AC vs. CC; p = 0.029, OR = 0.52, 95% CI = 0.31-0.85), and an overdominant model (AC vs. CC/AA; p = 0.0087, OR = 0.53, 95% CI = 0.33-0.86). However, no associations were identified for the rs907715 C>T and rs12508721 C>A polymorphisms. In the haplotype analyses, the C-C-T haplotype of rs907715-rs2055979-rs12508721 significantly increased the risk of cryptorchidism (p < 0.0001, OR = 5.251, 95% CI = 2.528-10.906).

CONCLUSIONS

The rs2055979 C>A polymorphism of the IL-21 gene is associated with cryptorchidism susceptibility, and the C allele increases the risk of cryptorchidism in a Chinese Han population.

Multiple genomic signatures of selection in goats and sheep indigenous to a hot arid environment

Goats and sheep are versatile domesticates that have been integrated into diverse environments and production systems. Natural and artificial selection have shaped the variation in the two species, but natural selection has played the major role among indigenous flocks. To investigate signals of natural selection, we analyzed genotype data generated using the caprine and ovine 50K SNP BeadChips from Barki goats and sheep that are indigenous to a hot arid environment in Egypt's Coastal Zone of the Western Desert. We identify several candidate regions under selection that spanned 119 genes. A majority of the genes were involved in multiple signaling and signal transduction pathways in a wide variety of cellular and biochemical processes. In particular, selection signatures spanning several genes that directly or indirectly influenced traits for adaptation to hot arid environments, such as thermo-tolerance (melanogenesis) (FGF2, GNAI3, PLCB1), body size and development (BMP2, BMP4, GJA3, GJB2), energy and digestive metabolism (MYH, TRHDE, ALDH1A3), and nervous and autoimmune response (GRIA1, IL2, IL7, IL21, IL1R1) were identified. We also identified eight common candidate genes under selection in the two species and a shared selection signature that spanned a conserved syntenic segment to bovine chromosome 12 on caprine and ovine chromosomes 12 and 10, respectively, providing, most likely, the evidence for selection in a common environment in two different but closely related species. Our study highlights the importance of indigenous livestock as model organisms for investigating selection sweeps and genome-wide association mapping.

A Context-Dependent Role for IL-21 in Modulating the Differentiation, Distribution, and Abundance of Effector and Memory CD8 T Cell Subsets

The activation of naive CD8 T cells typically results in the formation of effector cells (TE) as well as phenotypically distinct memory cells that are retained over time. Memory CD8 T cells can be further subdivided into central memory, effector memory (TEM), and tissue-resident memory (TRM) subsets, which cooperate to confer immunological protection. Using mixed bone marrow chimeras and adoptive transfer studies in which CD8 T cells either do or do not express IL-21R, we discovered that under homeostatic or lymphopenic conditions IL-21 acts directly on CD8 T cells to favor the accumulation of TE/TEM populations. The inability to perceive IL-21 signals under competitive conditions also resulted in lower levels of TRM phenotype cells and reduced expression of granzyme B in the small intestine. IL-21 differentially promoted the expression of the chemokine receptor CX3CR1 and the integrin α4β7 on CD8 T cells primed in vitro and on circulating CD8 T cells in the mixed bone marrow chimeras. The requirement for IL-21 to establish CD8 TE/TEM and TRM subsets was overcome by acute lymphocytic choriomeningitis virus infection; nevertheless, memory virus-specific CD8 T cells remained dependent on IL-21 for optimal accumulation in lymphopenic environments. Overall, this study reveals a context-dependent role for IL-21 in sustaining effector phenotype CD8 T cells and influencing their migratory properties, accumulation, and functions.

Mycobacterium tuberculosis-Specific IL-21+IFN-γ+CD4+ T Cells Are Regulated by IL-12

In the current study of Mycobacterium tuberculosis (MTB)-specific T and B cells, we found that MTB-specific peptides from early secreted antigenic target-6 (ESAT-6) and culture filtrate protein-10 (CFP-10) induced the expression of IL-21 predominantly in CD4⁺ T cells. A fraction of IL-21-expressing CD4⁺ T cells simultaneously expressed Th1 cytokines but did not secrete Th2 or Th17 cytokines, suggesting that MTB-specific IL-21-expressing CD4⁺ T cells were different from Th1, Th2 and Th17 subpopulations. The majority of MTB-specific IL-21-expressing CD4⁺ T cells co-expressed IFN-γ and IL-21⁺IFN-γ⁺CD4⁺ T cells exhibited obviously polyfunctionality. In addition, MTB-specific IL-21-expressing CD4⁺ T cells displayed a CD45RO⁺CD62L^lowCCR7^lowCD40L^highICOS^high phenotype. Bcl-6-expression was significantly higher in IL-21-expressing CD4⁺ T cells than IL-21^-CD4⁺ T cells. Moreover, IL-12 could up-regulate MTB-specific IL-21 expression, especially the frequency of IL-21⁺IFN-γ⁺CD4⁺ T cells. Taken together, our results demonstrated that MTB-specific IL-21⁺IFN-γ⁺CD4⁺ T cells from local sites of tuberculosis (TB) infection could be enhanced by IL-12, which have the features of both Tfh and Th1 cells and may have an important role in local immune responses against TB infection.

Improved Treatment of Breast Cancer with Anti-HER2 Therapy Requires Interleukin-21 Signaling in CD8+ T Cells

The HER2/ErbB2 monoclonal antibody (mAb) trastuzumab is combined with chemotherapy as a standard-of-care for newly diagnosed HER2(+) breast cancer patients, but some patients treated with this combination therapy experience early relapse. Our analysis of data from a clinical trial evaluating the efficacy of chemotherapy plus/minus trastuzumab suggested that the magnitude of trastuzumab benefit on distant disease-free survival was higher for increasing expression of the IL21 receptor (IL21R). Therefore, we investigated a possible role for IL21 signaling in promoting HER2 mAb therapeutic efficacy. We found that IL21R-deficient mice and wild-type mice treated with a neutralizing anti-IL21 mAb were less susceptible to trastuzumab-like anti-ErbB2 therapy. Furthermore, IL21R expression on CD8(+) T cells, but not on natural killer cells, was required for optimal anti-ErbB2 mAb efficacy, and IL21 expression was enhanced in tumor-infiltrating CD4(+) T lymphocytes after anti-ErbB2 therapy. Finally, we found that administering recombinant IL21 in combination with anti-ErbB2 therapy was therapeutic against primary tumors and experimental metastases in mice. Collectively, our findings suggest that elevating IL21 signaling may enhance trastuzumab efficacy, thus constituting a novel candidate strategy to overcome trastuzumab resistance and improve patient survival. Cancer

The emerging role of aryl hydrocarbon receptor in the activation and differentiation of Th17 cells

The aryl hydrocarbon receptor (AHR) is a cytoplasmic transcription factor, which plays an essential role in the xenobiotic metabolism in a wide variety of cells. The AHR gene is evolutionarily conserved and it has a central role not only in the differentiation and maturation of many tissues, but also in the toxicological metabolism of the cell by the activation of metabolizing enzymes. Several lines of evidence support that both AHR agonists and antagonists have profound immunological effects; and recently, the AHR has been implicated in antibacterial host defense. According to recent studies, the AHR is essential for the differentiation and activation of T helper 17 (Th17) cells. It is well known that Th17 cells have a central role in the development of inflammation, which is crucial in the defense against pathogens. In addition, Th17 cells play a major role in the pathogenesis of several autoimmune diseases such as rheumatoid arthritis. Therefore, the AHR may provide connection between the environmental chemicals, the immune regulation, and autoimmunity. In the present review, we summarize the role of the AHR in the Th17 cell functions.

Construction and Functional Characterization of a Fusion Protein Interleukin-21/Immunoglobulin for Long-Term In Vivo Biodisponibility

Interleukin (IL)-21 has been intensively studied for use in therapy of autoimmune diseases, cancers, and chronic viruses due to its immunomodulatory properties, especially on CD4(+) and CD8(+) T cells and natural killer (NK) cells. The objective of this study was to produce an optimized form of IL-21 with improved stability. Plasmids encoding the murine IL-21 alone (pIL-21) or IL-21 genetically fused to portions from mouse IgG3 (pIL-21/Ig) were constructed, and the efficiency of expression, protein kinetics, biodisponibility, and function were analyzed. The genetic constructions of pIL-21 and pIL-21/Ig were transfected into HEK 293 cells, and significant levels of functional IL-21 were obtained. The amino acid of murine IL-21 and IgG3 cloned showed 100% identity with correspondent published sequences. At 24 h of incubation, increased levels of IL-21 were detected in the supernatants of pIL-21. At 72 h of culture, the levels of IL-21 in the supernatant of cells transfected with pIL-21/Ig were significantly higher than those secreted by pIL-21-transfected cells. Furthermore, the data showed that our chimeric IL-21/Ig present improved systemic disponibility in BALB/c mice and conserved the intrinsic ability to increase the frequency of CD4(+) T cells, NKT cells, and CD8(+) T cells.

Ex Vivo Expansion of Human NK Cells Using K562 Engineered to Express Membrane Bound IL21

Natural killer (NK) cells have gained significant attention for adoptive immunotherapy of cancer due to their well-documented antitumor function. In order to evaluate the therapeutic efficacy of NK cell adoptive immunotherapy in preclinical models with a potential for clinical translation, there is a need for a reliable platform for ex vivo expansion of NK cells. Numerous methods are reported in literature using cytokines and feeder cells to activate and expand human NK cells, and many of these methods are limited by low-fold expansion, cytokine dependency of expanded NK cells or expansion-related senescence. In this chapter, a robust NK cell expansion protocol is described using K562 cell line gene modified to express membrane bound IL21 (K562 mb.IL21). We had previously demonstrated that this platform enables the highest fold expansion of NK cells reported in the literature to date (>47,000-folds in 21 days), and produces highly activated and pure NK cells without signs of senescence, as determined by telomere shortening.

Therapeutic utility of the newly discovered properties of interleukin-21

Since its discovery in 2000, interleukin-21 (IL-21) has been shown to display a broad spectrum of pleiotropic actions including the regulation of development, differentiation and function of lymphoid-myeloid cells. More specifically, IL-21 modulates the effector functions of T, B and NK cells, which not only have key roles in antitumoral and antiviral immunity but also in exerting major effects on inflammatory responses promoting the development of autoimmune diseases. Recent studies have unveiled an unexpected role for IL-21 in immune regulation and de novo T-cell development. While highlighting its critical role in immunity, this review will mainly focus on recent advances in IL-21 biology and how such newly discovered properties could potentially be exploited therapeutically in the establishment of future clinical trials.

IL-21 Promotes Pulmonary Fibrosis through the Induction of Profibrotic CD8+ T Cells

Type 2 effector production of IL-13, a demonstrated requirement in models of fibrosis, is routinely ascribed to CD4(+) Th2 cells. We now demonstrate a major role for CD8(+) T cells in a murine model of sterile lung injury. These pulmonary CD8(+) T cells differentiate into IL-13-producing Tc2 cells and play a major role in a bleomycin-induced model of fibrosis. Differentiation of these Tc2 cells in the lung requires IL-21, and bleomycin treated IL-21- and IL-21R-deficient mice develop inflammation but not fibrosis. Moreover, IL-21R-expressing CD8(+) cells are sufficient to reconstitute the fibrotic response in IL-21R-deficient mice. We further show that the combination of IL-4 and IL-21 skews naive CD8(+) T cells to produce IL-21, which, in turn, acts in an autocrine manner to support robust IL-13 production. Our data reveal a novel pathway involved in the onset and regulation of pulmonary fibrosis and identify Tc2 cells as key mediators of fibrogenesis.

FcγRIIIa-Syk Co-signal Modulates CD4+ T-cell Response and Up-regulates Toll-like Receptor (TLR) Expression

CD4(+) T-cells in systemic lupus erythematosus (SLE) patients show altered T-cell receptor signaling, which utilizes Fc-receptor γ-chain FcRγ-Syk. A role for FcγRIIIa activation from immune complex (IC) ligation and sublytic terminal complement complex (C5b-9) in CD4(+) T-cell responses is not investigated. In this study, we show that the ICs present in SLE patients by ligating to FcγRIIIa on CD4(+) T-cells phosphorylate Syk and provide a co-stimulatory signal to CD4(+) T-cells in the absence of CD28 signal. This led to the development of pathogenic IL-17A(+) and IFN-γ(high) CD4(+) T-cells in vitro. Cytokines IL-1β, IL-6, TGF-β1, and IL-23 were the only requirement for the development of both populations. SLE patients CD4(+) T-cells that expressed CD25, CD69, and CD98 bound to ICs showed pSyk and produced IFN-γ and IL-17A. This FcγRIIIa-mediated co-signal differentially up-regulated the expression of IFN pathway genes compared with CD28 co-signal. FcγRIIIa-pSyk up-regulated several toll-like receptor genes as well as the HMGB1 and MyD88 gene transcripts. ICs co-localized with these toll-like receptor pathway proteins. These results suggest a role for the FcγRIIIa-pSyk signal in modulating adaptive immune responses.

Common gamma chain cytokines in combinatorial immune strategies against cancer

Common γ chain (γC) cytokines, namely IL-2, IL-4, IL-7, IL-9, IL-15, and IL-21 are important for the proliferation, differentiation, and survival of lymphocytes that display antitumor activity, thus stimulating considerable interest for the use of cytokines in cancer immunotherapy. In this review, we will focus on the γC cytokines that demonstrate the greatest potential for immunotherapy, IL-2, IL-7, IL-15, and IL-21. We will briefly cover their biological function, potential applications in cancer therapy, and update on their use in combinatorial immune strategies for eradicating tumors and hematopoietic malignancies.

Interleukin-21-Producing CD4(+) T Cells Promote Type 2 Immunity to House Dust Mites

Asthma is a T helper 2 (Th2)-cell-mediated disease; however, recent findings implicate Th17 and innate lymphoid cells also in regulating airway inflammation. Herein, we have demonstrated profound interleukin-21 (IL-21) production after house dust mite (HDM)-driven asthma by using T cell receptor (TCR) transgenic mice reactive to Dermatophagoides pteronyssinus 1 and an IL-21GFP reporter mouse. IL-21-producing cells in the mediastinal lymph node (mLN) bore characteristics of T follicular helper (Tfh) cells, whereas IL-21(+) cells in the lung did not express CXCR5 (a chemokine receptor expressed by Tfh cells) and were distinct from effector Th2 or Th17 cells. Il21r(-/-) mice developed reduced type 2 responses and the IL-21 receptor (IL-21R) enhanced Th2 cell function in a cell-intrinsic manner. Finally, administration of recombinant IL-21 and IL-25 synergistically promoted airway eosinophilia primarily via effects on CD4(+) lymphocytes. This highlights an important Th2-cell-amplifying function of IL-21-producing CD4(+) T cells in allergic airway inflammation.

IL-21 and IL-21 receptor in the immunopathogenesis of multiple sclerosis

Cytokines are considered important factors in the modulation of various immune responses. Among them, interleukin (IL)-21 is one of the major immune modulators, adjusting various immune responses by affecting various immune cells. It has been suggested that IL-21 may enhance autoimmunity through different mechanisms, such as development and activation of helper T (TH)-17 and follicular helper T (TFH) cells, activation of natural killer (NK) cells, enhancing B-cell differentiation and antibody secretion and suppression of regulatory T (Treg) cells. Moreover, IL-21 has also been suggested to be an inducer of autoimmunity when following treatment of MS patients with some therapeutics such as alemtuzumab. This review will seek to clarify the precise role of IL-21/IL-21R in the pathogenesis of MS and, in its animal model, experimental autoimmune encephalomyelitis (EAE).

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.

Chemokine Receptor Expression on Normal Blood CD56(+) NK-Cells Elucidates Cell Partners That Comigrate during the Innate and Adaptive Immune Responses and Identifies a Transitional NK-Cell Population

Studies of chemokine receptors (CKR) in natural killer- (NK-) cells have already been published, but only a few gave detailed information on its differential expression on blood NK-cell subsets. We report on the expression of the inflammatory and homeostatic CKR on normal blood CD56(+low) CD16(+) and CD56(+high)  CD16(-/+low) NK-cells. Conventional CD56(+low) and CD56(+high) NK-cells present in the normal PB do express CKR for inflammatory cytokines, although with different patterns CD56(+low) NK-cells are mainly CXCR1/CXCR2(+) and CXCR3/CCR5(-/+), whereas mostly CD56(+high) NK-cells are CXCR1/CXCR2(-) and CXCR3/CCR5(+). Both NK-cell subsets have variable CXCR4 expression and are CCR4(-) and CCR6(-). The CKR repertoire of the CD56(+low) NK-cells approaches to that of neutrophils, whereas the CKR repertoire of the CD56(+high) NK-cells mimics that of Th1(+) T cells, suggesting that these cells are prepared to migrate into inflamed tissues at different phases of the immune response. In addition, we describe a subpopulation of NK-cells with intermediate levels of CD56 expression, which we named CD56(+int) NK-cells. These NK-cells are CXCR3/CCR5(+), they have intermediate levels of expression of CD16, CD62L, CD94, and CD122, and they are CD57(-) and CD158a(-). In view of their phenotypic features, we hypothesize that they correspond to a transitional stage, between the well-known CD56(+high) and CD56(+low) NK-cells populations.

IL-21-Expressing Mesenchymal Stem Cells Prevent Lethal B-Cell Lymphoma Through Efficient Delivery of IL-21, Which Redirects the Immune System to Target the Tumor

Interleukin (IL)-21, a proinflammatory cytokine, has been developed as an immunotherapeutic approach due to its effects on various lymphocytes, including natural killer (NK) cells and T cells; however, the clinical success in cancer patients has been limited. Recently, mesenchymal stem cells (MSCs) have emerged as vehicles for cancer gene therapy due to their inherent migratory abilities toward tumors. In the present study, we hypothesized that MSCs, genetically modified to express high levels of IL-21 (IL-21/MSCs), can enhance antitumor responses through localized delivery of IL-21. For tumor induction, BALB/c mice were injected intravenously with syngeneic A20 B-cell lymphoma cells to develop a disseminated B-cell lymphoma model. Then, 6 days following tumor induction, the tumor-bearing mice were treated with IL-21/MSCs weekly, four times. Systemic infusion of A20 cells led to hind-leg paralysis as well as severe liver metastasis in the control group. The IL-21/MSC-treated group showed delayed tumor incidence as well as improved survival, whereas the MSC- and recombinant adenovirus-expressing IL-21 (rAD/IL-21)-treated groups did not show significant differences from the untreated mice. These therapeutic effects were associated with high levels of IL-21 delivered to the liver, which prevented the formation of tumor nodules. Furthermore, the infusion of IL-21/MSCs led to induction of effector T and NK cells, while potently inhibiting immune suppressor cells. Our findings demonstrate that IL-21-expressing MSCs have the therapeutic potential to induce potent antitumor effects against disseminated B-cell lymphoma through localized IL-21 delivery and induction of systemic antitumor immunity.

Direct and immune-mediated cytotoxicity of interleukin-21 contributes to antitumor effects in mantle cell lymphoma

Mantle cell lymphoma (MCL) is a distinct subtype of non-Hodgkin lymphoma characterized by overexpression of cyclin D1 in 95% of patients. MCL patients experience frequent relapses resulting in median survival of 3 to 5 years, requiring more efficient therapeutic regimens. Interleukin (IL)-21, a member of the IL-2 cytokine family, possesses potent antitumor activity against a variety of cancers not expressing the IL-21 receptor (IL-21R) through immune activation. Previously, we established that IL-21 exerts direct cytotoxicity on IL-21R-expressing diffuse large B-cell lymphoma cells. Herein, we demonstrate that IL-21 possesses potent cytotoxicity against MCL cell lines and primary tumors. We identify that IL-21-induced direct cytotoxicity is mediated through signal transducer and activator of transcription 3-dependent cMyc upregulation, resulting in activation of Bax and inhibition of Bcl-2 and Bcl-XL. IL-21-mediated cMyc upregulation is only observed in IL-21-sensitive cells. Further, we demonstrate that IL-21 leads to natural killer (NK)-cell-dependent lysis of MCL cell lines that were resistant to direct cytotoxicity. In vivo treatment with IL-21 results in complete FC-muMCL1 tumor regression in syngeneic mice via NK- and T-cell-dependent mechanisms. Together, these data indicate that IL-21 has potent antitumor activity against MCL cells via direct cytotoxic and indirect, immune-mediated effects.

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.

A conserved sugar bridge connected to the WSXWS motif has an important role for transport of IL-21R to the plasma membrane

Interleukin-21 (IL-21) is a class I cytokine that belongs to the γc-subfamily of cytokines and regulates immune responses. It signals through a heterodimeric receptor complex composed of the IL-21R1 and γc-receptor chains. A characteristic feature of class I cytokine receptors is the presence of a consensus motif WSXWS (WS motif) in the membrane proximal fibronectin type III domain (FNIII) of these receptors. We recently described the structure of the IL-21R:IL-21 complex and showed that the first tryptophan of the WS motif of IL-21R is mannosylated and involved in formation of a sugar bridge that connects the two FNIII domains of the receptor. Furthermore, a mutation within the WS motif of IL-21R was recently shown to cause a novel kind of primary immunodeficiency syndrome (PID). Here, we report the structure of IL-21R alone, which shows that the sugar bridge forms independently of whether IL-21R binds IL-21 or not, and we furthermore investigate the role of this bridge in the export of IL-21R and γC to the plasma membrane. Thus, we provide a molecular explanation for how mutations in the WS motif may cause PIDs.

Tumor-Elicited Inflammation and Colorectal Cancer

The link between chronic inflammation and cancer has long been suspected, due to the pioneering work of Rudolf Virchow over 150 years ago. Yet the causal relationship between inflammation and cancer was only deciphered in the past decade or so, using animal models of various cancers. Up to 20% of all human cancers result from chronic inflammation and persistent infections. Proinflammatory cytokines and tumor-infiltrating myeloid and immune cells play critical roles in almost every developmental stages of inflammation-induced cancers, from initiation, promotion, and progression to malignant metastasis. However, even in cancers with no preceding inflammation, inflammatory cells infiltrate tumor stroma and contribute to cancer development. Such "tumor-elicited inflammation" further emphasizes the importance of inflammation in different types of cancers, including that of the colon. In this review, we summarize our current knowledge of the function and induction mechanisms of inflammatory cytokines during colorectal cancer development, and hope to provide insight into the development of novel anticancer therapies by modulating tumor-elicited inflammation.

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.

Addition of interleukin-21 for expansion of T-cells for adoptive immunotherapy of murine melanoma

We previously demonstrated that interleukin (IL)-7/15 was superior to IL-2 for expansion of T cells in vitro for adoptive immunotherapy. We sought to ascertain whether IL-21 would further improve yield and therapeutic efficacy of T cells in culture. Naïve T cell receptor (TcR) transgenic splenocytes or antigen-sensitized lymph node cells were harvested from PMEL-1 mice and exposed to bryostatin-1 and ionomycin (B/I) for 18 h. Cells were then cultured in IL-2, IL-21, IL-7/15 or IL-7/15/21 for six days. Harvested cells were analyzed by flow cytometry and used to treat C57Bl/6 mice injected intravenously with B16 melanoma. Lungs were harvested and metastases counted 14 days after treatment. Culturing lymphocytes in IL-7/15/21 increased expansion compared to IL-2 or IL-7/15. IL-21 and IL-7/15/21 increased CD8+ cells compared to IL-2 or IL-7/15. IL-21 preferentially expanded a CD8+CD44−CD62L+ T “naïve” population, whereas IL-7/15/21 increased CD8+CD44+CD62Lhigh central-memory T cells. T cells grown in IL-7/15/21 were more effective at reducing metastases than IL-2. The addition of IL-21 to IL-7/15 induced greater expansion of lymphocytes in culture and increased the yield of CD8+ T central-memory cells vs. IL-7/15 alone. This may have significant impact on future clinical trials of adoptive immunotherapy, particularly for generating adequate numbers of lymphocytes for treatment.

IL-21: a pleiotropic cytokine with potential applications in oncology

Interleukin- (IL-) 21 is a pleiotropic cytokine that regulates the activity of both innate and specific immunity. Indeed, it costimulates T and natural killer (NK) cell proliferation and function and regulates B cell survival and differentiation and the function of dendritic cells. In addition, IL-21 exerts divergent effects on different lymphoid cell leukemia and lymphomas, as it may support cell proliferation or on the contrary induce growth arrest or apoptosis of the neoplastic lymphoid cells. Several preclinical studies showed that IL-21 has antitumor activity in different tumor models, through mechanism involving the activation of NK and T or B cell responses. Moreover, IL-21's antitumor activity can be potentiated by its combination with other immune-enhancing molecules, monoclonal antibodies recognizing tumor antigens, chemotherapy, or molecular targeted agents. Clinical phase I-II studies of IL-21 in cancer patients showed immune stimulatory properties, acceptable toxicity profile, and antitumor effects in a fraction of patients. In view of its tolerability, IL-21 is also suitable for combinational therapeutic regimens with other agents. This review will summarize the biological functions of IL-21, and address its role in lymphoid malignancies and preclinical and clinical studies of cancer immunotherapy.

Interleukin-21 gene polymorphisms and chronic hepatitis B infection in a Chinese population

AIM: To investigate the relationship between interleukin-21 (IL21) gene polymorphisms and chronic hepatitis B virus (HBV) infection in a Chinese population.

METHODS: In this case-control study, 366 Chinese HBV-infected patients were recruited and divided into hepatocellular carcinoma (HCC; n = 94) and non-HCC (n = 272) groups at The First Affiliated Hospital of Sun Yat-Sen University, from April 2009 to December 2012. In the non-HCC group, the patients were classified into three clinical subsets, 76 patients had chronic hepatitis B, 101 were HBV carriers and 95 patients had HBV-related cirrhosis. Two hundred eight unrelated healthy controls were also included. Genomic DNA was extracted from peripheral blood. Single nucleotide polymorphisms (SNPs) rs13143866, rs2221903, and rs907715 were subsequently genotyped using the SNaPshot SNP technique.

RESULTS: There were no significant differences in allele and genotype frequencies of SNPs rs13143866, rs2221903, and rs907715 between chronic HBV-infected patients and control subjects. Furthermore, no significant differences were found in the frequencies of all alleles and genotypes between the HCC group and the non-HCC group. However, in the subgroup analysis, IL21 rs13143866 genotype AA frequency in the HBV carrier group was higher than in controls (OR = 6.280, 95%CI: 1.238-31.854; P = 0.019), and the effect of the recessive model (AA vs GG + GA, OR = 6.505, 95%CI: 1.289-32.828) was observed in the HBV carrier group. IL21 rs2221903 genotype TC frequency in the HBV carrier group was higher than in controls (OR = 1.809, 95%CI: 1.043-3.139; P = 0.035). In the haplotype analysis, the ATA haplotype (rs13143866, rs2221903, and rs907715) of IL21 was more frequent in the HCC group than in the non-HCC group (0.165 vs 0.104, P = 0.044; OR = 1.700, 95%CI: 1.010-2.863).

CONCLUSION: Genotypes rs13143866 AA and rs2221903 TC are risk factors for carrying HBV; ATA haplotype increases the risk of HBV-related HCC onset in a Chinese population.

Effector CD8 T cell immunity in microsporidial infection: a lone defense mechanism

Microsporidia is a group of pathogens, which can pose severe risks to the immunocompromised population such as HIV-infected individuals. The expertise to diagnose these pathogens is limited and therefore their prevalence is believed to be much higher than what is currently known. In a mouse model of infections, it has been reported that CD8 T cells are the primary effector cells responsible for protecting the infected host. As the infection is acquired via per-oral route, CD8 T cells in the gut compartment apparently act as a first line of defense against the pathogens. Thus, generation of a robust CD8 T cell response that exhibits polyfunctional ability is critical for host survival. In this review, we describe the effector CD8 T cells generated during microsporidial infection and underline the factors that may be essential for the elicitation of protective immunity against this understudied but significant pathogen. Overall, this review will highlight the necessity for a better understanding of the development of the CD8 T cell response in gut associated lymphoid tissue (GALT) and provide some insights into therapies that may be used to restore defective CD8 T cell functionality in an immunocompromised situation.

Defective PTEN regulation contributes to B cell hyperresponsiveness in systemic lupus erythematosus

PTEN regulates normal signaling through the B cell receptor (BCR). In systemic lupus erythematosus (SLE), enhanced BCR signaling contributes to increased B cell activity, but the role of PTEN in human SLE has remained unclear. We performed fluorescence-activated cell sorting analysis in B cells from SLE patients and found that all SLE B cell subsets, except for memory B cells, showed decreased expression of PTEN compared with B cells from healthy controls. Moreover, the level of PTEN expression was inversely correlated with disease activity. We then explored the mechanisms governing PTEN regulation in SLE B cells. Notably, in normal but not SLE B cells, interleukin-21 (IL-21) induced PTEN expression and suppressed Akt phosphorylation induced by anti-immunoglobulin M and CD40L stimulation. However, this deficit was not primarily at the signaling or the transcriptional level, because IL-21-induced STAT3 (signal transducer and activator of transcription 3) phosphorylation was intact and IL-21 up-regulated PTEN mRNA in SLE B cells. Therefore, we examined the expression of candidate microRNAs (miRs) that could regulate PTEN: SLE B cells were found to express increased levels of miR-7, miR-21, and miR-22. These miRs down-regulated the expression of PTEN, and IL-21 stimulation increased the expression of miR-7 and miR-22 in both normal and SLE B cells. Indeed, a miR-7 antagomir corrected PTEN-related abnormalities in SLE B cells in a manner dependent on PTEN. Therefore, defective miR-7 regulation of PTEN contributes to B cell hyperresponsiveness in SLE and could be a new target of therapeutic intervention.

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.

Advances in IL-21 biology - enhancing our understanding of human disease

Cytokines play critical roles in regulating the development and function of immune cells. Cytokines function by binding specific multimeric receptor complexes and activating intracellular signaling pathways that often involve JAKs and STATs. In addition to contributing to immunity, when production of cytokines is perturbed, they can contribute to disease. IL-21 is a pleiotropic cytokine produced predominantly by CD4(+) T cells and NKT cells. Gene-targeting studies in mice and in vitro analyses of human and murine lymphocytes have revealed central roles of IL-21 in regulating effector functions of T cells, NK cells and B cells. However, recent discoveries of loss-of function mutations in IL21 or IL21R in humans have unveiled unexpected roles for IL-21 in immune regulation. This review will focus on recent advances in IL-21 biology that have highlighted its critical role in normal immunity and how dysregulated IL-21 production can lead to immunodeficiency and autoimmune conditions.

The role of soluble common gamma chain in autoimmune disease

The common gamma chain (γc) is the central signaling unit for a number of cytokine receptors collectively known as the γc cytokine receptor family. γc is critical for ligand binding and signaling by γc cytokines. γc cytokine signaling had been thought to be mainly regulated by cytokine-specific receptor α chain expression levels with little or no effect by γc surface levels because γc expression was presumed to remain unchanged during T-cell activation and development. The extent of γc cytokine responses is thought to be regulated by cytokine specific receptor subunits and not by the γc receptor. In contrast to this prevailing view, we have recently reported that γc itself actively regulates γc cytokine responses. Interestingly, γc exerted its regulatory effects not only as a conventional membrane receptor protein but also as a secreted protein whose expression was upregulated upon T-cell stimulation. Here we will review how a soluble form of γc, which is generated by alternative splicing, regulates γc cytokine signaling and plays a role in controlling immune activation related to autoimmune disease.

Extending the lifespan and efficacies of immune cells used in adoptive transfer for cancer immunotherapies-A review

Cells used in adoptive cell-transfer immunotherapies against cancer include dendritic cells (DCs), natural-killer cells, and CD8⁺ T-cells. These cells may have limited efficacy due to their lifespan, activity, and immunosuppressive effects of tumor cells. Therefore, increasing longevity and activity of these cells may boost their efficacy. Four cytokines that can extend immune effector-cell longevity are IL-2, IL-7, IL-21, and IL-15. This review will discuss current knowledge on effector-cell lifespans and the mechanisms by which IL-2, IL-7, IL-15, and IL-21 can extend effector-cell longevity. We will also discuss how lifespan and efficacy of these cells can be regulated to allow optimal clinical benefits.

CD4+ T cell-derived IL-21 and deprivation of CD40 signaling favor the in vivo development of granzyme B-expressing regulatory B cells in HIV patients

IL-21 can induce both plasma cells and regulatory B cells. In this article, we demonstrate that untreated HIV patients display CD4(+) T cells with enhanced IL-21 expression and high in vivo frequencies of regulatory B cells overexpressing the serine protease granzyme B. Granzyme B-expressing regulatory B cells (GraB cells) cells from HIV patients exhibit increased expression of CD5, CD43, CD86, and CD147 but do not produce IL-10. The main functional characteristic of their regulatory activity is direct granzyme B-dependent degradation of the TCR-ζ-chain, resulting in significantly decreased proliferative T cell responses. Although Th cells from HIV patients secrete IL-21 in a Nef-dependent manner, they barely express CD40L. When culturing such IL-21(+)CD40L(-) Th cells with B cells, the former directly induce B cell differentiation into GraB cells. In contrast, the addition of soluble CD40L multimers to T cell/B cell cultures redirects B cell differentiation toward plasma cells, indicating that CD40L determines the direction of IL-21-dependent B cell differentiation. As proof of principle, we confirmed this mechanism in a patient lacking intact CD40 signaling due to a NEMO mutation. The majority of peripheral B cells from this patient were GraB cells and strongly suppressed T cell proliferation. In conclusion, GraB cells represent potent regulatory B cells in humans that are phenotypically and functionally distinct from B10 cells and occur in early HIV infection. GraB cells may contribute significantly to immune dysfunction in HIV patients, and may also explain ineffective Ab responses after vaccination. The use of soluble CD40L multimers may help to improve vaccination responses in HIV patients.

The plasmacytoid dendritic cell as the Swiss army knife of the immune system: molecular regulation of its multifaceted functions

Plasmacytoid dendritic cells (pDC) have been regarded as the "professional type I IFN-producing cells" of the immune system following viral recognition that relies on the expression of TLR7 and TLR9. Furthermore, pDC link the innate and adaptive immune systems via cytokine production and Ag presentation. More recently, their ability to induce tolerance and cytotoxicity has been added to their "immune skills." Such a broad range of actions, resembling the diverse functional features of a Swiss army knife, requires strong and prompt molecular regulation to prevent detrimental effects, including autoimmune pathogenesis or tumor escape. Over the last decades, we and other investigators have started to unravel some aspects of the signaling pathways that regulate the various functions of human pDC. In this article, we review aspects of the molecular regulatory mechanisms to control pDC function in light of their multifaceted roles during immunity, autoimmunity, and cancer.

IL-21 receptor signalling partially mediates Th2-mediated allergic airway responses

BACKGROUND

Interleukin-21 (IL-21) has been implicated in the development of Th2-mediated immune responses; however, the exact role it plays in allergic diseases is not well understood.

OBJECTIVE

To elucidate the contribution of IL-21 receptor signalling to Th2-dependent immune responses in the lung.

METHODS

We compared allergic airway responses in wild-type BALB/c and Il21r-deficient mice exposed to local airway challenge with house dust mite (HDM).

RESULTS

We demonstrate that IL-21R-deficiency reduces HDM-driven airway hyperresponsiveness (AHR) with only partial effects on airway inflammation. Concomitant with the reduction in AHR in Il21r-deficient mice, significant suppression was observed in protein levels of the Th2 cytokines IL-4, and IL-13. In contrast, IL-21R-deficiency was associated with an increase in PBS- and allergen-driven IgE levels, while IgG1 and IgG2a levels were decreased. Moreover, our results suggest that IL-21 may contribute to AHR through its ability to both directly induce Th2 cell survival and to impair regulatory T-cell suppression of Th2 cytokine production. Importantly, we show that IL-21-positive cells are increased in the bronchial mucosa of asthmatics compared with non-asthmatics.

CONCLUSION

These results suggest that IL-21 plays an important role in the allergic diathesis by enhancing Th2 cytokine production through multiple mechanisms including the suppression of Treg inhibitory effects on Th2 cell cytokine production.