Interleukin 21 prevents antigen-induced IgE production by inhibiting germ line C(epsilon) transcription of IL-4-stimulated B cells

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.

Biology of IgE production: IgE cell differentiation and the memory of IgE responses

The generation of long-lived plasma cells and memory B cells producing high-affinity antibodies depends on the maturation of B cell responses in germinal centers. These processes are essential for long-lasting antibody-mediated protection against infections. IgE antibodies are important for defense against parasites and toxins and can also mediate anti-tumor immunity. However, high-affinity IgE is also the main culprit responsible for the manifestations of allergic disease, including life-threatening anaphylaxisAnaphylaxis . Thus, generation of high-affinity IgE must be tightly regulated. Recent studies of IgE B cell biology have unveiled two mechanisms that limit high-affinity IgE memory responses: First, B cells that have recently switched to IgE production are programmed to rapidly differentiate into plasma cells,Plasma cells and second, IgE germinal centerGerminal center cells are transient and highly apoptotic. Opposing these processes, we now know that germinal center-derived IgG B cells can switch to IgE production, effectively becoming IgE-producing plasma cells. In this chapter, we will discuss the unique molecular and cellular pathways involved in the generation of IgE antibodies.

Central nervous system infiltrates are characterized by features of ongoing B cell-related immune activity in MP4-induced experimental autoimmune encephalomyelitis

In multiple sclerosis (MS) lymphoid follicle-like aggregates have been reported in the meninges of patients. Here we investigated the functional relevance of B cell infiltration into the central nervous system (CNS) in MP4-induced experimental autoimmune encephalomyelitis (EAE), a B cell-dependent mouse model of MS. In chronic EAE, B cell aggregates were characterized by the presence of CXCL13(+) and germinal center CD10(+) B cells. Germline transcripts were expressed in the CNS and particularly related to TH17-associated isotypes. We also observed B cells with restricted VH gene usage that differed from clones found in the spleen. Finally, we detected CNS-restricted spreading of the antigen-specific B cell response towards a myelin and a neuronal autoantigen. These data imply the development of autonomous B cell-mediated autoimmunity in the CNS in EAE - a concept that might also apply to MS itself.

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.

A brief history of T cell help to B cells

In celebration of the 50th anniversary of the discovery of B cells, I take a look back at the history of T cell help to B cells, which was discovered 47 years ago. In addition, I summarize and categorize the distinct molecules that are expressed by CD4(+) T cells that constitute 'help' to B cells, and particularly the molecules expressed by T follicular helper (TFH) cells, which are the specialized providers of help to B cells.

Hydroxypropyl-β-cyclodextrin spikes local inflammation that induces Th2 cell and T follicular helper cell responses to the coadministered antigen

Cyclodextrins are commonly used as a safe excipient to enhance the solubility and bioavailability of hydrophobic pharmaceutical agents. Their efficacies and mechanisms as drug-delivery systems have been investigated for decades, but their immunological properties have not been examined. In this study, we reprofiled hydroxypropyl-β-cyclodextrin (HP-β-CD) as a vaccine adjuvant and found that it acts as a potent and unique adjuvant. HP-β-CD triggered the innate immune response at the injection site, was trapped by MARCO(+) macrophages, increased Ag uptake by dendritic cells, and facilitated the generation of T follicular helper cells in the draining lymph nodes. It significantly enhanced Ag-specific Th2 and IgG Ab responses as potently as did the conventional adjuvant, aluminum salt (alum), whereas its ability to induce Ag-specific IgE was less than that of alum. At the injection site, HP-β-CD induced the temporary release of host dsDNA, a damage-associated molecular pattern. DNase-treated mice, MyD88-deficient mice, and TBK1-deficient mice showed significantly reduced Ab responses after immunization with this adjuvant. Finally, we demonstrated that HP-β-CD-adjuvanted influenza hemagglutinin split vaccine protected against a lethal challenge with a clinically isolated pandemic H1N1 influenza virus, and the adjuvant effect of HP-β-CD was demonstrated in cynomolgus macaques. Our results suggest that HP-β-CD acts as a potent MyD88- and TBK1-dependent T follicular helper cell adjuvant and is readily applicable to various vaccines.

Activation of invariant natural killer T cells in regional lymph nodes as new antigen-specific immunotherapy via induction of interleukin-21 and interferon-γ

Invariant natural killer T (iNKT) cells play important immunoregulatory functions in allergen-induced airway hyperresponsiveness and inflammation. To clarify the role of iNKT cells in allergic rhinitis (AR), we generated bone marrow-derived dendritic cells (BMDCs), which were pulsed by ovalbumin (OVA) and α-galactosylceramide (OVA/α-GalCer-BMDCs) and administered into the oral submucosa of OVA-sensitized mice before nasal challenge. Nasal symptoms, level of OVA-specific immunoglobulin (IgE), and T helper type 2 (Th2) cytokine production in cervical lymph nodes (CLNs) were significantly ameliorated in wild-type (WT) mice treated with OVA/α-GalCer-BMDCs, but not in WT mice treated with OVA-BMDCs. These anti-allergic effects were not observed in Jα18(-/-) recipients that lack iNKT cells, even after similar treatment with OVA/α-GalCer-BMDCs in an adoptive transfer study with CD4(+) T cells and B cells from OVA-sensitized WT mice. In WT recipients of OVA/α-GalCer-BMDCs, the number of interleukin (IL)-21-producing iNKT cells increased significantly and the Th1/Th2 balance shifted towards the Th1 dominant state. Treatment with anti-IL-21 and anti-interferon (IFN)-γ antibodies abrogated these anti-allergic effects in mice treated with α-GalCer/OVA-BMDCs. These results suggest that activation of iNKT cells in regional lymph nodes induces anti-allergic effects through production of IL-21 or IFN-γ, and that these effects are enhanced by simultaneous stimulation with antigen. Thus, iNKT cells might be a useful target in development of new treatment strategies for AR.

Functional interleukin-21 polymorphism is a protective factor of diffuse large B-cell lymphoma

Interleukin-21 (IL-21) is a recently discovered cytokine and plays critical roles in antitumor immune responses. Diffuse large B-cell lymphoma (DLBCL) is the most common type of non-Hodgkin lymphoma. In this study, we investigated the association between IL-21 genetic polymorphisms and the susceptibility to DLBCL, and the possible functions of these polymorphisms. Two IL-21 polymorphisms, rs907715G/A and rs2221903A/G, were examined in 212 DLBCL patients and 232 healthy controls. Data showed that percentages of rs907715GA and AA genotypes were significantly lower in patients than in controls (odds ratio [OR]=0.60, 95% confidence interval [CI]: 0.40-0.90, p=0.014; OR=0.31, 95% CI: 0.17-0.56, p<0.001, respectively). Frequency of the rs2221903A/G polymorphism did not reveal any significant differences between patients and healthy donors. Further analyses demonstrated a significantly decreased number of rs907715AA genotype in patients with advanced Ann Arbor stages (III+IV). Moreover, we investigated the correlation between IL-21 polymorphisms and serum level of IL-21. Results showed that subjects carrying rs907715AA had significantly increased level of IL-21 than those with GG genotype or GA genotype. These data suggest that rs907715G/A polymorphism may act as a protective factor of DLBCL and might affect the 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.

Interleukin-21: a double-edged sword with therapeutic potential

Interleukin-21 is a cytokine with broad pleiotropic actions that affect the differentiation and function of lymphoid and myeloid cells. Since its discovery in 2000, a tremendous amount has been learned about its biological actions and the molecular mechanisms controlling IL-21-mediated cellular responses. IL-21 regulates both innate and adaptive immune responses, and it not only has key roles in antitumour and antiviral responses but also exerts major effects on inflammatory responses that promote the development of autoimmune diseases and inflammatory disorders. Numerous studies have shown that enhancing or inhibiting the action of IL-21 has therapeutic effects in animal models of a wide range of diseases, and various clinical trials are underway. The current challenge is to understand how to specifically modulate the actions of IL-21 in the context of each specific immune response or pathological situation. In this Review, we provide an overview of the basic biology of IL-21 and discuss how this information has been - and can be - exploited therapeutically.

Early-onset inflammatory bowel disease and common variable immunodeficiency-like disease caused by IL-21 deficiency

BACKGROUND

Alterations of immune homeostasis in the gut can result in development of inflammatory bowel disease (IBD). Recently, Mendelian forms of IBD have been discovered, as exemplified by deficiency of IL-10 or its receptor subunits. In addition, other types of primary immunodeficiency disorders might be associated with intestinal inflammation as one of their leading clinical presentations.

OBJECTIVE

We investigated a large consanguineous family with 3 children who presented with early-onset IBD within the first year of life, leading to death in infancy in 2 of them.

METHODS

Homozygosity mapping combined with exome sequencing was performed to identify the molecular cause of the disorder. Functional experiments were performed to assess the effect of IL-21 on the immune system.

RESULTS

A homozygous mutation in IL21 was discovered that showed perfect segregation with the disease. Deficiency of IL-21 resulted in reduced numbers of circulating CD19(+) B cells, including IgM(+) naive and class-switched IgG memory B cells, with a concomitant increase in transitional B-cell numbers. In vitro assays demonstrated that mutant IL-21(Leu49Pro) did not induce signal transducer and activator of transcription 3 phosphorylation and immunoglobulin class-switch recombination.

CONCLUSION

Our study uncovers IL-21 deficiency as a novel cause of early-onset IBD in human subjects accompanied by defects in B-cell development similar to those found in patients with common variable immunodeficiency. IBD might mask an underlying primary immunodeficiency, as illustrated here with IL-21 deficiency.

Regulatory constraints in the generation and differentiation of IgE-expressing B cells

B cells expressing antibodies of the immunoglobulin E (IgE) isotype are rare, yet are heavily implicated in the pathogenesis of allergies and asthma. This review discusses recent methodological advances that permit sensitive probing of IgE-expressing (IgE(+)) B cells in vivo and have accordingly clarified the basic behavior and fate of IgE(+) B cells during immune responses in mouse models. IgE antibody secreting plasma cells can arise from extrafollicular foci, germinal centers, and memory B cells. However, compared to B cells expressing other isotypes, IgE(+) B cells are susceptible to multiple additional regulatory constraints that restrict the size of the IgE(+) B cell pool at each stage, coordinately limiting the overall magnitude, affinity, and duration of the IgE antibody response.

The emerging role of interleukin-21 in allergic diseases (Review)

Interleukin (IL)-21 is a newly discovered member of the type I cytokine family. Since its discovery in 2000, IL-21 has been the focus of extensive investigation, due to its homology to IL-2, IL-4 and IL-15 and its pleiotropic effects on innate and adaptive immune responses. An increasing amount of experimental evidence supports a role for IL-21 in the pathogenesis of several allergic diseases, such as allergic rhinitis, atopic dermatitis (AD) and atopic asthma. In this review, we aimed to discuss the biological characteristics of IL-21 and summarize the current progress on the role of IL-21 in the regulation of allergic inflammation.

T helper subsets in Sjögren's syndrome and IgG4-related dacryoadenitis and sialoadenitis: a critical review

IgG4-related disease (IgG4-RD) is a systemic disease characterized by the elevation of serum IgG4 and infiltration of IgG4-positive plasma cells in multiple target organs, including the pancreas, kidney, biliary tract and salivary glands. In contrast, Mikulicz's disease (MD) has been considered a subtype of Sjögren's syndrome (SS) based on histopathological similarities. However, it is now recognized that MD is an IgG4-RD distinguishable from SS and called as IgG4-related dacryoadenitis and sialoadenitis (IgG4-DS). Regarding immunological aspects, it is generally accepted that CD4+ T helper (Th) cells play a crucial role in the pathogenesis of SS. Since it is well known that IgG4 is induced by Th2 cytokines such as interleukin (IL)-4 and IL-13, IgG4-DS is speculated to be a unique inflammatory disorder characterized by Th2 immune reactions. However, the involvement of Th cells in the pathogenesis of IgG4-DS remains to be clarified. Exploring the role of Th cell subsets in IgG4-DS is a highly promising field of investigation. In this review, we focus on the selective localization and respective functions of Th cell subsets and discuss the differences between SS and IgG4-DS to clarify the pathogenic mechanisms of these diseases.

Alteration of circulating miRNAs in SSc: miR-30b regulates the expression of PDGF receptor β

OBJECTIVE

Although several miRNAs have been shown to regulate autoimmune pathogenesis by affecting lymphocyte function, the roles of miRNAs in the pathogenesis of SSc remain unclear. Therefore the purpose of this study was to identify miRNAs that play a role in the pathogenesis of SSc by quantitative PCR screening of serum miRNAs.

METHODS

Ninety-five miRNAs that were predicted to target SSc-related genes [IL-4, TGF-β, CTGF, PDGF-B, PDGF receptor (PDGFR) α/β and COL1A2) by in silico analyses were selected. The expression of these miRNAs in sera of SSc patients and healthy controls was measured by quantitative PCR. Involvement of miR-30b, which was most strongly down-regulated in SSc patients, in the regulation of PDGFR-β expression was examined by transfection experiments and 3'-untranslated region (3'-UTR) target luciferase assays. The expression of miR-30b in skin was evaluated in a bleomycin-induced dermal fibrosis model in mice and in SSc patients.

RESULTS

Nineteen of 95 miRNAs were significantly decreased in the sera of SSc patients. Among them, miR-30b was most strongly down-regulated in SSc patients (P = 0.00006) and the levels of miR-30b were inversely correlated with modified Rodnan skin scores. Transfection of a miR-30b mimic repressed PDGFR-β expression in dermal fibroblasts and the activity of a luciferase reporter containing 3'-UTR of PDGFR-β. Moreover, the expression of miR-30b was down-regulated in bleomycin-treated sclerotic skin and in affected skin in SSc patients.

CONCLUSION

Down-regulation of miR-30b might be involved in the pathogenesis of SSc.

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.

Interleukin-6 receptor blockade selectively reduces IL-21 production by CD4 T cells and IgG4 autoantibodies in rheumatoid arthritis

Interleukin-6 (IL-6) levels are known to be increased in patients with rheumatoid arthritis (RA). Tocilizumab, a monoclonal antibody to the IL-6 receptor (IL-6R), reduces disease activity in RA, although its mechanisms of action remain unclear. Since IL-6 regulates cytokine production by CD4 T cells during activation, we investigated whether treatment with tocilizumab altered the phenotype and cytokine production by CD4 T cells in patients with rheumatoid arthritis. We show here that tocilizumab treatment does not change the production of cytokines by naïve CD4 T cells. However, tocilizumab treatment causes a selective decrease of IL-21 production by memory/activated CD4 T cells. Since IL-21 is known to promote plasma cell differentiation, we examined the effect of tocilizumab on the production of autoantibodies. We show that there is a decrease in the levels of IgG4 anti-CCP antibodies, but there is no effect on IgG1 anti-CCP antibodies. In addition, we show that IL-21 is a powerful inducer of IgG4 production by B cells. Thus, IL-6 contributes to the presence of IgG4-specific anti-CCP autoantibodies in RA patients, likely through its effect on IL-21 production by CD4 T cells, and IL-6R blockade down-regulates this pathway.

Current concepts of IgE regulation and impact of genetic determinants

Immunoglobulin E (IgE) mediated immune responses seem to be directed against parasites and neoplasms, but are best known for their involvement in allergies. The IgE network is tightly controlled at different levels as outlined in this review. Genetic determinants were suspected to influence IgE regulation and IgE levels considerably for many years. Linkage and candidate gene studies suggested a number of loci and genes to correlate with total serum IgE levels, and recently genome-wide association studies (GWAS) provided the power to identify genetic determinants for total serum IgE levels: 1q23 (FCER1A), 5q31 (RAD50, IL13, IL4), 12q13 (STAT6), 6p21.3 (HLA-DRB1) and 16p12 (IL4R, IL21R). In this review, we analyse the potential role of these GWAS hits in the IgE network and suggest mechanisms of how genes and genetic variants in these loci may influence IgE regulation.

LINE-1 retroelements complexed and inhibited by activation induced cytidine deaminase

LINE-1 (abbreviated L1) is a major class of retroelements in humans and mice. If unrestricted, retroelements accumulate in the cytoplasm and insert their DNA into the host genome, with the potential to cause autoimmune disease and cancer. Retroviruses and other retroelements are inhibited by proteins of the APOBEC family, of which activation-induced cytidine deaminase (AID) is a member. Although AID is mainly known for being a DNA mutator shaping the antibody repertoire in B lymphocytes, we found that AID also restricts de novo L1 integrations in B- and non-B-cell lines. It does so by decreasing the protein level of open reading frame 1 (ORF1) of both exogenous and endogenous L1. In activated B lymphocytes, AID deficiency increased L1 mRNA 1.6-fold and murine leukemia virus (MLV) mRNA 2.7-fold. In cell lines and activated B lymphocytes, AID forms cytoplasmic high-molecular-mass complexes with L1 mRNA, which may contribute to L1 restriction. Because AID-deficient activated B lymphocytes do not express ORF1 protein, we suggest that ORF1 protein expression is inhibited by additional restriction factors in these cells. The greater increase in MLV compared to L1 mRNA in AID-deficient activated B lymphocytes may indicate less strict surveillance of retrovirus.

The role of the T follicular helper cells in allergic disease

T follicular helper (Tfh) cells were discovered just over a decade ago as germinal centre T cells that help B cells make antibodies. Included in this role is affinity maturation and isotype switching. It is here that their functions become less clear. Tfh cells principally produce IL-21 which inhibits class switching to IgE. Recent studies have questioned whether the germinal centre is the main site of IgE class switching or IgE affinity maturation. In this review, I will examine the evidence that these cells are responsible for regulating IgE class switching and the relationship between Tfh cells and T helper 2 (Th2) effector cells.

Interleukin-6: from an inflammatory marker to a target for inflammatory diseases

The incidence and diversity of chronic inflammatory diseases is increasing worldwide. However, the complexity of clinical symptoms has made it difficult to develop therapies that provide a substantial improvement for extended periods of time in a wide range of patient groups. Thus, there is a need for new therapies that target inflammatory responses without compromising immune defense. Interleukin (IL)-6, one of the first identified cytokines, has recently been recognized as a potential target in inflammatory disease. Here, I discuss how this cytokine has evolved from being a marker of inflammation to a successful target to control inflammation. I will summarize the results from the recent clinical studies using IL-6 receptor blockade, and describe potential mechanisms by which IL-6 can contribute to the progression of inflammatory diseases.

Liposome-based polymer complex as a novel adjuvant: enhancement of specific antibody production and isotype switch

The aim of vaccination is to induce appropriate immunity against pathogens. Antibody-mediated immunity is critical for protection against many virus diseases, although it is becoming more evident that coordinated, multifunctional immune responses lead to the most effective defense. Specific antibody (Ab) isotypes are more efficient at protecting against pathogen invasion in different locations in the body. For example, compared to other Ab isotypes, immunoglobulin (Ig) A provides more protection at mucosal areas. In this study, we developed a cationic lipopolymer (liposome-polyethylene glycol-polyethyleneimine complex [LPPC]) adjuvant that strongly adsorbs antigens or immunomodulators onto its surface to enhance or switch immune responses. The results demonstrate that LPPC enhances uptake ability, surface marker expression, proinflammatory cytokine release, and antigen presentation in mouse phagocytes. In contrast to Freund’s adjuvant, LPPC preferentially activates Th1- immunity against antigens in vivo. With lipopolysaccharides or CpG oligodeoxynucleotides, LPPC dramatically enhances the IgA or IgG2A proportion of total Ig, even in hosts that have developed Th2 immunities and high IgG1 serum titers. Taken together, the results demonstrate that the LPPC adjuvant not only increases the immunogenicity of antigens but also modulates host immunity to produce an appropriate Ab isotype by combining with immunomodulators.

What is unique about the IgE response?

IgE antibodies are involved in allergic reactions. High affinity IgE antibodies can cause anaphylaxis when cross-linked by minute amounts of antigen. The issue of how the IgE response is initiated and maintained is addressed in this review. A model has been proposed by which IgE(+) cells expressing antibodies that bind with high affinity to their antigens are generated through an IgG1 intermediate, which goes through affinity maturation in germinal centers (GC) before undergoing sequential switching to IgE. Mice deficient in IgG1 produce IgE at almost normal levels, but the IgE antibodies produced in IgG1-deficient mice lack the antigen-binding strength and the somatic mutations associated with affinity maturation. A GFP reporter strain, which expresses a modified IgE molecule, was recently developed and was utilized to challenge the sequential switching model. Several molecules that are highly expressed in GC can antagonize class switching to IgE in GC antagonize partially class switching to IgE; in addition, GC IgE(+) cells are gradually lost from GC as the immune response progresses, as shown with another recently developed, Venus-expressing IgE reporter mouse strain. In contrast, as a population, IgG1 cells thrive in the GC environment. Membrane IgE-expressing plasmablasts and plasma cells (PC) were recognized as a major component of the IgE response in secondary lymphoid organs. The swift development of IgE cells toward the PC fate, together with the affinity maturation of the IgE response via an IgG intermediate, represent the most salient features of the IgE immune responses, which make them distinct from IgG responses.

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.

Effect of IL-15 on IgG versus IgE antibody-secreting cells in vitro

Immunoglobulin E (IgE) antibodies are major contributors to the pathology of atopic and allergic diseases as well as to immune response to helminth infections. Development of an adequate immunoglobulin G (IgG) immune response against infectious agents and vaccine antigens is considered in most cases as crucial for protection from disease. In vivo and in vitro production of IgE and IgG depends on cytokines and other soluble factors. Recently it has been shown that IgG antibody secreting cells (ASCs) can be generated by in vitro maturation of blood cells with Interleukin- (IL-)15 and CpG DNA or other stimulation cocktails, while IgE-ASCs develop upon cultivation with anti-CD40 and IL-4. In the present study we employed an enzyme linked immunospot assay (ELISPOT) to assess the capacity of individuals to develop into either IgE-ASCs or IgG-ASCs upon stimulation with different combinations of stimulation cocktails in order to investigate the influence of cytokines that are dysregulated in IgE-mediated immune reactions on ASC generation. Furthermore, we modified the method to assess IgG- and IgE-ASCs specific for two model antigens causing allergic rhinitis in humans. We demonstrate that IL-15, which is important for development of IgG-ASCs, decreases the number of IgE-ASCs when added to media commonly used for in vitro development of IgE-ASCs. We show that our method is suitable for the detection of specific and non-specific IgE-ASCs and IgG-ASCs and allows the investigation of the interplay between IgG-ASCs and IgE-ASCs in different populations.

Interleukins, from 1 to 37, and interferon-γ: receptors, functions, and roles in diseases

Advancing our understanding of mechanisms of immune regulation in allergy, asthma, autoimmune diseases, tumor development, organ transplantation, and chronic infections could lead to effective and targeted therapies. Subsets of immune and inflammatory cells interact via ILs and IFNs; reciprocal regulation and counter balance among T(h) and regulatory T cells, as well as subsets of B cells, offer opportunities for immune interventions. Here, we review current knowledge about ILs 1 to 37 and IFN-γ. Our understanding of the effects of ILs has greatly increased since the discoveries of monocyte IL (called IL-1) and lymphocyte IL (called IL-2); more than 40 cytokines are now designated as ILs. Studies of transgenic or knockout mice with altered expression of these cytokines or their receptors and analyses of mutations and polymorphisms in human genes that encode these products have provided important information about IL and IFN functions. We discuss their signaling pathways, cellular sources, targets, roles in immune regulation and cellular networks, roles in allergy and asthma, and roles in defense against infections.

IL-21 reduces immediate hypersensitivity reactions in mouse skin by suppressing mast cell activation or IgE production

IL-21 regulates activation, proliferation, and differentiation of various immune cells. We have previously shown that exogenous IL-21 administration reduces allergic reactions in mouse models of anaphylaxis and allergic rhinitis. However, the effects of IL-21 in allergic cutaneous reactions remain unclear. In this study, we examined the effects of IL-21 in a mouse model of the IgE-mediated cutaneous immediate hypersensitivity reaction (IHR). We also investigated the mechanism of IL-21-induced regulation of allergic cutaneous reactions. Mice were sensitized by intraperitoneal ovalbumin (OVA) injection and challenged by injecting OVA intradermally into the ears, with intraperitoneal administration of recombinant murine (rm)IL-21 during the sensitization period or after completion of sensitization. After challenge, IL-21-untreated allergic mice developed biphasic responses characterized by early-phase and late-phase reactions. The biphasic reactions were significantly reduced by rmIL-21 treatment during sensitization or after completion of sensitization. Administration of rmIL-21 during sensitization reduced the cutaneous IHR by suppressing allergen-specific IgE production. In contrast, administration of rmIL-21 after completion of sensitization did not decrease serum levels of allergen-specific IgE, but significantly suppressed mast cell degranulation in skin. These results suggest that the regulatory effects of IL-21 on the cutaneous IHR involve suppression of allergen-specific IgE production or mast cell degranulation.

B and T lymphocyte attenuator suppresses IL-21 production from follicular Th cells and subsequent humoral immune responses

We recently showed that mice lacking B and T lymphocyte attenuator (BTLA), a third inhibitory coreceptor expressed on B cells and T cells, exhibit an increased Ag-specific IgG response and gradually develop hyper-gamma-globulinemia and autoantibody production. Recent studies revealed that follicular Th (Tfh) cells, which are non-Th1, non-Th2 effector T cells that express CXCR5 and provide help for B cells to produce Ig, also express BTLA. However, the role of BTLA in Tfh cell function remains unknown. In this study, we examined the regulatory role of BTLA in the development and function of Tfh cells. We found that CXCR5(+) Tfh cells expressed higher levels of BTLA than did CXCR5(-) conventional CD4(+) T cells. We also found that adoptive transfer of BTLA(-/-) CD4(+) T cells, stimulated under Tfh cell-inducing conditions (Tfh-like cells), to wild-type (WT) mice induced more Ag-specific IgG2a and IgG2b production compared with that of WT Tfh-like cells. By contrast, another adoptive-transfer experiment using BTLA(-/-) mice as recipients showed that the expression of BTLA on B cells was not involved in the regulation of Tfh-like cell-mediated Ag-specific IgG responses. Moreover, the development of IL-21-producing CXCR5(+) Tfh-like cells was significantly increased in BTLA(-/-) CD4(+) T cells compared with WT CD4(+) T cells. Furthermore, Tfh-like cell-mediated IgG responses were abolished when IL-21R(-/-) mice were used as recipients. These results suggest that BTLA signaling suppresses IL-21 production from Tfh cells and subsequent Tfh cell-mediated IgG responses.

Block copolymers have differing adjuvant effects on the primary immune response elicited by genetic immunization and on further induced allergy

Block copolymers were recently used to promote gene delivery in various tissues. Using a plasmid encoding a food allergen, bovine beta-lactoglobulin (BLG), we studied the effects of block copolymers on gene expression levels and primary immune response and on further induced allergy. Block copolymers (i.e., Tetronic 304, 908, and 1107) and various quantities of DNA were injected into the tibialis muscles of BALB/c mice. The BLG levels in injected muscle and the BLG-specific induced immune response were analyzed after injection. DNA-immunized mice were further experimentally sensitized with BLG, and the effects of block copolymer and DNA doses on allergic sensitization and elicitation were compared. Tetronic 304 induced a 12-fold increase in BLG production, while Tetronic 1107 increased the duration of BLG expression. Different Th1 primary specific immune responses were observed, either strong humoral and cellular (304), only cellular (1107), or weak cellular and humoral (908) responses. After BLG sensitization, increased BLG-specific IgG2a production was observed in all groups of mice independently of the presence and nature of the block copolymer. Increased BLG-specific IgG1 production was also detected after sensitization, except with Tetronic 1107. Compared with naked DNA, Tetronic 304 was the only block polymer that decreased BLG-specific IgE concentrations. However, after allergen challenge, Tetronic 1107 was the only block copolymer to reduce eosinophils and Th2 cytokines in bronchoalveolar lavage (BAL) fluid. Tetronic 304 amplified local inflammation. Each block copolymer elicited a different immune response, although always Th1 specific, in BALB/c mice.

IL-21: roles in immunopathology and cancer therapy

Cytokines are secreted signalling molecules with decisive effects on haematopoiesis, innate and adaptive immunity, and immunopathology. Interleukin (IL)-21 is a novel cytokine produced by activated CD4(+) T cells and natural killer T (NKT) cells. IL-21 is part of a family of cytokines which include IL-2, -4, -7, -9 and -15 that all share the common IL-2 receptor gamma chain (gamma(c)) in their individual receptor complexes. IL-21 receptor (IL-21R) is widely expressed on both myeloid and lymphoid cell lineages and IL-21 actions include co-stimulation of B cell differentiation and immunoglobulin (Ig) production, co-mitogen of T cells, and stimulation of NK and CD8(+) T cell cytotoxic function. Initially, IL-21 was recognized for its anti-tumour effects in several preclinical tumour models, warranting its currently ongoing clinical development as a cancer immunotherapeutic. More recently, IL-21 has been associated with the development of a panel of autoimmune and inflammatory diseases, where neutralization of IL-21 has been suggested as a potential new therapy. In this review, we will cover the latest discoveries of IL-21 as a cancer therapy and its implications in immunopathologies.

IL-21 contributes to JAK3/STAT3 activation and promotes cell growth in ALK-positive anaplastic large cell lymphoma

Interleukin (IL)-21 has been reported to both stimulate cell growth and promote survival in benign lymphoid cells and several types of hematopoietic neoplasms. It induces JAK3/STAT3 signaling, a biologically important cellular pathway activated in most cases of anaplastic lymphoma kinase (ALK)-expressing anaplastic large cell lymphoma (ALK(+)ALCL). Therefore, we hypothesize that IL-21 may contribute to JAK3/STAT3 activation and cell growth in ALK(+)ALCL. By reverse transcription-PCR, we found consistent expression of IL-21 receptor (IL-21R) in all ALK(+)ALCL cell lines and frozen tumors examined. IL-21 was also consistently expressed in ALK(+)ALCL tumors, although its mRNA was detectable in only one of three cell lines tested. By immunohistochemistry, we examined 10 paraffin-embedded ALK(+)ALCL tumors; all cases were positive for both IL-21 and IL-21R in these neoplastic cells. IL-21 signaling is biologically significant in ALK(+)ALCL since the addition of recombinant IL-21 enhanced the activation of JAK3/STAT3 and significantly increased cell growth in ALK(+)ALCL cell lines. However, small interfering RNA down-regulation of IL-21R significantly decreased both STAT3 activation and cell growth. IL-21R expression is not linked to nucleophosmin-ALK since forced expression of nucleophosmin-ALK and small interfering RNA down-regulation of nucleophosmin-ALK did not significantly change the expression of either IL-21R or IL-21. Our findings thus support the enhancement of JAK3/STAT3 activation and cell growth in ALK(+)ALCL via IL-21 signaling. These results further support the concept that constitutive activation of STAT3 in these tumors is multifactorial.

IL-6 is required for airway mucus production induced by inhaled fungal allergens

Allergic asthma is caused by inhaled allergens and is characterized by airway eosinophilia, as well as mucus hypersecretion, which can lead to airflow obstruction. Despite the association of increased IL-6 levels with human atopic asthma, the contribution of IL-6 to the development of allergic airway inflammation triggered by inhaled allergens remains unclear. In this study, we examined the role of IL-6 in a mouse model of allergic airway inflammation induced by direct airway exposure to extracts of Aspergillus fumigatus, a common allergen in humans. We show that inhaled A. fumigatus extracts rapidly trigger the production of IL-6 in the airways. IL-6 appears to be dispensable for the recruitment of eosinophils to the lung during the development of allergic airway inflammation. However, IL-6 is essential for mucus hypersecretion by airway epithelial cells triggered in response to inhaled A. fumigatus Ags. Impaired mucus production caused by IL-6 deficiency correlates with a severe reduction in the levels of IL-13, a major inducer of mucin glycoproteins. Thus, IL-6 is a key regulator of specific hallmark features of allergic airway inflammation and it could be a potential target for pulmonary diseases that are associated with goblet cell metaplasia and mucus hypersecretion.

Clinical and biological efficacy of recombinant human interleukin-21 in patients with stage IV malignant melanoma without prior treatment: a phase IIa trial

PURPOSE

Human interleukin-21 (IL-21) is a class I cytokine that mediates activation of CD8(+) T cells, natural killer (NK) cells, and other cell types. We report final clinical and biological results of a phase II study of recombinant human IL-21 (rIL-21) in patients with metastatic melanoma.

EXPERIMENTAL DESIGN

Open-label, single-arm, two-stage trial.

ELIGIBILITY CRITERIA

unresectable metastatic melanoma, measurable disease by Response Evaluation Criteria in Solid Tumors, no prior systemic therapy (adjuvant IFN permitted), adequate major organ function, good performance status, no significant autoimmune disease, and life expectancy at least 4 months.

PRIMARY OBJECTIVE

antitumor efficacy (response rate).

SECONDARY OBJECTIVES

safety, blood biomarkers, and generation of anti-rIL-21 antibodies. rIL-21 (30 microg/kg/dose) was administered by intravenous bolus injection in 8-week cycles (5 dosing days followed by 9 days of rest for 6 weeks and then 2 weeks off treatment).

RESULTS

Stage I of the study comprised 14 patients. One confirmed complete response (CR) was observed, and as per protocol, 10 more patients were accrued to stage II (total n = 24: 10 female and 14 male). Best tumor response included one confirmed CR and one confirmed partial response, both with lung metastases. Treatment was overall well tolerated. Biomarker analyses showed increases in serum soluble CD25, frequencies of CD25(+) NK and CD8(+) T cells, and mRNA for IFN-gamma, perforin, and granzyme B in CD8(+) T and NK cells.

CONCLUSIONS

rIL-21 administered at 30 microg/kg/d in 5-day cycles every second week is biologically active and well tolerated in patients with metastatic melanoma. Confirmed responses, including one CR, were observed.

IL-21 ensures TGF-beta 1-induced IgA isotype expression in mouse Peyer's patches

It is well established that TGF-beta1 induces IgA and IgG2b class-switching recombination in murine B cells. In the present study, we assessed the activity of IL-21 along with TGF-beta1 in Ig synthesis by murine spleen B cells. IL-21 showed antiproliferative activity on LPS-activated splenic B cells, comparable with that of TGF-beta1. IL-21 alone had little effect on IgA secretion and decreased other isotypes. Likewise, IL-21 also did not alter the TGF-beta1-induced IgA synthesis and concurrently diminished the syntheses of IgM and IgG2a, which were repressed by TGF-beta1. Unexpectedly, IL-21 inhibited the TGF-beta1-induced IgG2b production. This IL-21 effect was examined using B cells from IL-21R knockout mice, where the IgA production profile was paralleled by that seen in wild-type B cells. However, the inhibitory effect of IL-21 on TGF-beta1-induced IgG2b synthesis was not seen in the IL-21R(-/-) mouse, suggesting that IL-21 causes TGF-beta1-stimulated B cells to decrease IgG2b synthesis. Expression patterns of Ig germ-line alpha(GL alpha)/GL gamma 2b transcripts under the influence of TGF-beta1 and IL-21 were paralleled by IgA/IgG2b secretion. This was also observed in the activities of GL(alpha) and GL(gamma 2b) promoters. These results indicate that IL-21 decreases IgG2b secretion mainly through inhibition of GL(gamma 2b) transcription and is ultimately associated with selective IgA secretion induced by TGF-beta1. Our results showed that IL-21 was expressed in greater magnitude in Peyer's patches (PP) than in spleen. These results suggest that IL-21 has an important effect on selective IgA(+) B cell commitment in PP.

Primary immune deficiencies with aberrant IgE production

IgE antibodies play a central role in the pathogenesis of atopic diseases and in host immunity against parasitic infections. IgE has potent activities on mast cells and basophils. IgE class switching is a very tightly controlled process, and serum IgE levels are very low compared with other immunoglobulin isotypes. Transcription factors that activate or inhibit the IgE gene promoter, as well as T(H)1 and T(H)2 cytokines are important in the regulation of IgE levels. Hyper-IgE syndrome; Wiskott-Aldrich syndrome; immunodysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX); Omenn syndrome; and atypical complete DiGeorge syndrome are primary immune deficiencies that are associated with elevated serum IgE levels. Increased IgE levels in IPEX, Wiskott-Aldrich syndrome and Omenn syndrome are likely related to increased T(H)2 cytokine production caused by decreased a number or function of CD4(+)CD25(+)forkhead box protein P3(+) regulatory T cells. The link between signal transducer and activator of transcription 3 mutations and elevated serum IgE levels in hyper-IgE syndrome is unclear. Insight into IgE regulation provided by the study of primary immune deficiencies with elevated IgE has important implications for allergic diseases.

Th17 cytokines and their emerging roles in inflammation and autoimmunity

T-helper 17 (Th17) cells are a new lineage of CD4(+) T cells that are characterized by their production of interleukin-17A (IL-17A). Recent studies show that these cells can also express IL-17F, IL-22, and IL-21. IL-17A and IL-17F can form a heterodimeric cytokine, which mediates biological activities, at least in part, through shared receptors with IL-17A and IL-17F homodimers. The cytokines made by Th17 cells represent three distinct gene families, highlighting the unique biology of these cells. Accumulating data support a role for Th17 cells and these cytokines in inflammatory processes and in animal models of autoimmunity or inflammation. Emerging data in clinical trials support our understanding of the importance of Th17 cells in inflammatory disease. Future clinical studies will allow us to evaluate the role of each cytokine independently in contributing to human diseases with immune-mediated pathologies and to design optimal cytokine-targeted therapies for these diseases.

STAT3 is required for IL-21–induced secretion of IgE from human naive B cells

The production of immunoglobulin E (IgE) is tightly regulated. This is evidenced by the fact that it comprises less than 0.0001% of serum Ig, and aberrant production causes atopic conditions, including allergy, rhinitis, and anaphylaxis. Interleukin-4 (IL-4) is a well-characterized inducer of IgE by human and murine B cells, whereas interferon-γ can antagonize this effect. IL-21 has also been recognized for its ability to suppress IL-4–induced IgE production by murine B cells. Here, we identified IL-21 as an inducer of IgE production by CD40L-stimulated human naive B cells. Furthermore, there was a striking synergy between IL-4 and IL-21 on inducing IgE secretion by CD40L-stimulated human B cells, such that the levels detected under these conditions exceeded those induced by IL-4 or IL-21 alone by more than 10-fold. IL-21 induced activation of STAT3 and analysis of B cells from patients with loss-of-function STAT3 mutations revealed that the ability of IL-21 to induce IgE secretion, and augment that driven by IL-4, was STAT3-dependent. These findings highlight a fundamental difference between the regulation of IgE production by human and murine B cells and have implications for the dysregulated production of IgE in conditions characterized by extremely high levels of serum IgE.

Interleukin-21: basic biology and implications for cancer and autoimmunity

Interleukin-21 (IL-21), a potent immunomodulatory four-alpha-helical-bundle type I cytokine, is produced by NKT and CD4(+) T cells and has pleiotropic effects on both innate and adaptive immune responses. These actions include positive effects such as enhanced proliferation of lymphoid cells, increased cytotoxicity of CD8(+) T cells and natural killer (NK) cells, and differentiation of B cells into plasma cells. Conversely, IL-21 also has direct inhibitory effects on the antigen-presenting function of dendritic cells and can be proapoptotic for B cells and NK cells. IL-21 is also produced by Th17 cells and is a critical regulator of Th17 development. The regulatory activity of IL-21 is modulated by the differentiation state of its target cells as well as by other cytokines or costimulatory molecules. IL-21 has potent antitumor activity but is also associated with the development of autoimmune disease. IL-21 transcription is dependent on a calcium signal and NFAT sites, and IL-21 requires Stat3 for its signaling. The key to harnessing the power of IL-21 will depend on better understanding its range of biological actions, its mechanism of action, and the molecular basis of regulation of expression of IL-21 and its receptor.

The Yin and Yang of interleukin-21 in allergy, autoimmunity and cancer

IL-21 is a type I cytokine that like IL-2, IL-4, IL-7, IL-9, and IL-15 shares the common cytokine receptor gamma chain, gamma(c). IL-21 is produced by activated CD4(+) T cells, NKT cells, and Th17 cells and has pleiotropic actions on a range of lymphoid lineages. IL-21 regulates immunoglobulin production and drives B cell terminal differentiation into plasma cells, cooperatively expands CD8(+) T cells and drives Th17 differentiation, has inhibitory effects on antigen presentation by dendritic cells, and can be pro-apoptotic for B and NK cells. Moreover, IL-21 has potent anti-tumor effects and is implicated in the development of autoimmune diseases. Regulating IL-21 actions in vivo therefore has clinical potential for a range of diseases and is an area of active investigation.

T follicular helper (TFH) cells in normal and dysregulated immune responses

T cell help for antibody production is a fundamental aspect of immune responses. Only recently has a better understanding of the cellular and molecular mechanisms for T cell help emerged. A subset of T cells, termed T follicular helper cells (T(FH) cells), provides a helper function to B cells and represents one of the most numerous and important subsets of effector T cells in lymphoid tissues. T(FH) cells are distinguishable from Th1 and Th2 cells by several criteria, including chemokine receptor expression (CXCR5), location/migration (B cell follicles), and function (B cell help). Central to the function of CD4(+) T cells is IL-21, a "helper" cytokine produced by T(FH) cells that potently stimulates the differentiation of B cells into Ab-forming cells through IL-21R. Consequently, dysregulation of T(FH) cell function, and over- or under-expression of T(FH) cell-associated molecules such as ICOS or IL-21, most likely contributes to the pathogenesis of certain autoimmune diseases or immunodeficiencies.