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

In vitro potency, pharmacokinetic profiles, and pharmacological activity of optimized anti-IL-21R antibodies in a mouse model of lupus

Using phage display, we generated a panel of optimized neutralizing antibodies against the human and mouse receptors for interleukin 21 (IL-21), a cytokine that is implicated in the pathogenesis of many types of autoimmune disease. Two antibodies, Ab-01 and Ab-02, which differed by only four amino acids in V(L) CDR3, showed potent inhibition of human and mouse IL-21R in cell-based assays and were evaluated for their pharmacological and pharmacodynamic properties. Ab-01, but not Ab-02, significantly reduced a biomarker of disease (anti-dsDNA antibodies) and IgG deposits in the kidney in the MRL-Fas(lpr) mouse model of lupus, suggesting that anti-IL-21R antibodies may prove useful in the treatment of lupus. Ab-01 also had a consistently higher exposure (AUC(0-infinity)) than Ab-02 following a single dose in rodents or cynomolgus monkeys (2-3-fold or 4-7-fold, respectively). Our data demonstrate that small differences in CDR3 sequences of optimized antibodies can lead to profound differences in in vitro and in vivo properties, including differences in pharmacological activity and pharmacokinetic profiles. The lack of persistent activity of Ab-02 in the MRL-Fas(lpr) mouse lupus model may have been a consequence of faster elimination, reduced potency in blocking the effects of mouse IL-21R, and more potent/earlier onset of the anti-product response relative to Ab-01.

Gamma(c) deficiency precludes CD8+ T cell memory despite formation of potent T cell effectors

Several cytokines (including IL-2, IL-7, IL-15, and IL-21) that signal through receptors sharing the common gamma chain (gamma(c)) are critical for the generation and peripheral homeostasis of naive and memory T cells. Recently, we demonstrated that effector functions fail to develop in CD4(+) T cells that differentiate in the absence of gamma(c). To assess the role of gamma(c) cytokines in cell-fate decisions that condition effector versus memory CD8(+) T cell generation, we compared the response of CD8(+) T cells from gamma(c)(+) or gamma(c)(-) P14 TCR transgenic mice after challenge with lymphocytic choriomeningitis virus. The intrinsic IL-7-dependent survival defect of gamma(c)(-) naive CD8(+) T cells was corrected by transgenic expression of human Bcl-2. We demonstrated that although gamma(c)-dependent signals are dispensable for the initial expansion and the acquisition of cytotoxic functions following antigenic stimulation, they condition the terminal proliferation and differentiation of CD8(+) effector T cells (i.e., KLRG1(high) CD127(low) short-lived effector T cells) via the transcription factor, T-bet. Moreover, the gamma(c)-dependent signals that are critical for memory T cell formation are not rescued by Bcl2 overexpression. Together, these data reveal an unexpected divergence in the requirement for gamma(c) cytokines in the differentiation of CD4(+) versus CD8(+) cytotoxic T lymphocytes.

Understanding the development and function of T follicular helper cells

A fundamental function of T helper (Th) cells is to regulate B-cell proliferation and immunoglobulin class switching, especially in the germinal centers. Th1 and Th2 lineages of CD4(+) T cells have long been considered to play an essential role in helping B cells by promoting the production immunoglobulin G2a (IgG2a) and IgG1/IgE, respectively. Recently, it has become clear that a subset CD4(+) T cells, named T follicular helper (Tfh) cells, is critical to B-cell response induction. In this review, we summarize the latest advances in our understanding of the regulation of Tfh cell differentiation, the relationship of Tfh cells to other CD4(+) T-cell lineages, and the role of Tfh cells in health and disease.

IL-10 production by CD4+ effector T cells: a mechanism for self-regulation

The development of Th1 lymphocytes is essential for cell-mediated immunity and resistance against intracellular pathogens. However, if left unregulated, the same response can cause serious damage to host tissues and lead to mortality. A number of different paracrine regulatory mechanisms involving distinct myeloid and lymphoid subpopulations have been implicated in controlling excessive secretion of inflammatory cytokines by Th1 cells. Much of this work has focused on interleukin (IL)-10, a cytokine with broad anti-inflammatory properties, one of which is to counteract the function of Th1 lymphocytes. While studying the role of IL-10 in regulating immunopathology during infection with the intracellular parasite Toxoplasma gondii, we discovered that the host-protective IL-10 derives in an autocrine manner from conventional interferon-gamma (IFN-gamma)-producing T-bet(+) Foxp3(neg) Th1 cells. In the following review, we will discuss these findings that support the general concept that production of IL-10 is an important self-regulatory function of CD4(+) T lymphocytes.

NCI First International Workshop on The Biology, Prevention, and Treatment of Relapse After Allogeneic Hematopoietic Stem Cell Transplantation: Report from the Committee on the Biology Underlying Recurrence of Malignant Disease following Allogeneic HSCT: Graft-versus-Tumor/Leukemia Reaction

The success of allogeneic hematopoietic stem cell transplantation (HSCT) depends on the infusion of benign stem cells as well as lymphocytes capable of participating in a graft-versus-tumor/leukemia (GVL) reaction. Clinical proof of concept is derived from studies showing increased relapse after the infusion of lymphocyte depleted hematopoietic grafts as well as the therapeutic efficacy of donor lymphocyte infusions without chemotherapy to treat relapse in some diseases. Despite this knowledge, relapse after allogeneic HSCT is common with rates approaching 40% in those with high-risk disease. In this review, we cover the basic biology and potential application to exploit adaptive T cell responses, minor histocompatibility antigens, contraction and suppression mechanisms that hinder immune responses, adaptive B cell responses and innate NK cell responses, all orchestrated in a GVL reaction. Optimal strategies to precisely balance immune responses to favor GVL without harmful graft-versus-host disease (GVHD) are needed to protect against relapse, treat persistent disease and improve disease-free survival after HSCT.

Dendritic cells and humoral immunity in humans

Dendritic cells (DCs) orchestrate the innate and adaptive immune systems to induce tolerance and immunity. DC plasticity and subsets are prominent determinants in the regulation of immune responses. Our recent studies suggest that humoral and cellular immunity is regulated by different myeloid DC subsets with distinct intrinsic properties in humans. Although antibody response is preferentially mediated by CD14(+) dermal DCs, cytotoxic T-cell response is preferentially mediated by Langerhans cells (LCs). Thus, mechanisms whereby DCs induce humoral and cellular immunity seem to be fundamentally distinct. In this review, we will focus on the role of DCs in the development of humoral immunity. We will also discuss the mechanisms whereby DCs induce CD4(+) T cells associated with aiding B-cell response, including T follicular helper (Tfh) cells, and why human LCs lack this ability.

Correlation of pharmacodynamic activity, pharmacokinetics, and anti-product antibody responses to anti-IL-21R antibody therapeutics following IV administration to cynomolgus monkeys

BACKGROUND

Anti-IL-21R antibodies are potential therapeutics for the treatment of autoimmune diseases. This study evaluated correlations between the pharmacodynamic (PD) activity, pharmacokinetics, and anti-product antibody responses of human anti-IL-21R antibodies Ab-01 and Ab-02 following IV administration to cynomolgus monkeys.

METHODS

The PD assay was based on the ability of recombinant human IL-21 (rhuIL-21) to induce expression of the IL-2RA gene in cynomolgus monkey whole blood samples ex vivo. Monkeys screened for responsiveness to rhuIL-21 stimulation using the PD assay, were given a single 10 mg/kg IV dosage of Ab-01, Ab-02, or a control antibody (3/group), and blood samples were evaluated for PD activity (inhibition of IL-2RA expression) for up to 148 days. Anti-IL-21R antibody concentrations and anti-product antibody responses were measured in serum using immunoassays and flow cytometry.

RESULTS

Following IV administration of Ab-01 and Ab-02 to cynomolgus monkeys, PD activity was observed as early as 5 minutes (first time point sampled). This PD activity had good correlation with the serum concentrations and anti-product antibody responses throughout the study. The mean terminal half-life (t1/2) was approximately 10.6 and 2.3 days for Ab-01 and Ab-02, respectively. PD activity was lost at approximately 5-13 weeks for Ab-01 and at approximately 2 weeks for Ab-02, when serum concentrations were relatively low. The estimated minimum concentrations needed to maintain PD activity were approximately 4-6 nM for Ab-01 and approximately 2.5 nM for Ab-02, and were consistent with the respective KD values for binding to human IL-21R. For Ab-01, there was noticeable inter-animal variability in t1/2 values (approximately 6-14 days) and the resulting PD profiles, which correlated with the onset of anti-product antibody formation. While all three Ab-01-dosed animals were positive for anti-Ab-01 antibodies, only one monkey (with the shortest t1/2 and the earliest loss of PD activity) had evidence of neutralizing anti-Ab-01 antibodies. All three Ab-02-dosed monkeys developed neutralizing anti-Ab-02 antibodies.

CONCLUSIONS

For anti-IL-21R antibodies Ab-01 and Ab-02, there was good correlation between PD activity and PK profiles following IV administration to cynomolgus monkeys. Compared with Ab-01, Ab-02 was eliminated markedly faster from the circulation, which correlated with a shorter duration of PD activity.

How are T(H)2-type immune responses initiated and amplified?

CD4(+) T helper (T(H)) cells have crucial roles in orchestrating adaptive immune responses. T(H)2 cells control immunity to extracellular parasites and all forms of allergic inflammatory responses. Although we understand the initiation of the T(H)2-type response in tissue culture in great detail, much less is known about T(H)2 cell induction in vivo. Here we discuss the involvement of allergen- and parasite product-mediated activation of epithelial cells, basophils and dendritic cells and the functions of the cytokines interleukin-4 (IL-4), IL-25, IL-33 and thymic stromal lymphopoietin in the initiation and amplification of T(H)2-type immune responses in vivo.

Biodistribution of [125I]-labeled therapeutic proteins: application in protein drug development beyond oncology

The majority of biodistribution studies of therapeutic proteins published to date focus on tumor-targeting agents. In this report we present a number of case studies that demonstrate the utility of biodistribution studies during preclinical development of biotherapeutics for non oncology indications, as well as provide a practical perspective on the methodology applied to these studies. For the commonly used classes of biologics (such as human monoclonal antibodies), biodistribution profiles may be compared to those of other therapeutics of the same class and compounds with unexpected off-target mediated uptake may be identified. Temporal biodistribution profiles may be used to address kinetics and reversibility of target- and/or off-target-mediated accumulation. In cases when circulating biotherapeutic is rapidly eliminated from circulation due to the formation of anti-product antibodies, tissue data may provide useful insight on test article exposure at the site of therapeutic action (or at the site of toxicity). Comparison of temporal biodistribution profiles between the genetically engineered and wild-type mouse strains or between the disease models and healthy animals may provide useful insight on sites and kinetics of target-mediated elimination. Finally, biodistribution studies will be a useful tool to study in vivo disposition for a variety of existing and upcoming novel classes of protein compounds.

Harnessing human dendritic cell subsets for medicine

Immunity results from a complex interplay between the antigen-non-specific innate immune system and the antigen-specific adaptive immune system. The cells and molecules of the innate system employ non-clonal recognition receptors including lectins, Toll-like receptors, NOD-like receptors, and helicases. B and T lymphocytes of the adaptive immune system employ clonal receptors recognizing antigens or their derived peptides in a highly specific manner. An essential link between innate and adaptive immunity is provided by dendritic cells (DCs). DCs can induce such contrasting states as immunity and tolerance. The recent years have brought a wealth of information on the biology of DCs revealing the complexity of this cell system. Indeed, DC plasticity and subsets are prominent determinants of the type and quality of elicited immune responses. In this article, we summarize our recent studies aimed at a better understanding of the DC system to unravel the pathophysiology of human diseases and design novel human vaccines.

Rational design of interleukin-21 antagonist through selective elimination of the gammaC binding epitope

The cytokine interleukin (IL)-21 exerts pleiotropic effects acting through innate as well as adaptive immune responses. The activities of IL-21 are mediated through binding to its cognate receptor complex composed of the IL-21 receptor private chain (IL-21Ralpha) and the common gamma-chain (gammaC), the latter being shared by IL-2, IL-4, IL-7, IL-9, and IL-15. The binding energy of the IL-21 ternary complex is predominantly provided by the high affinity interaction between IL-21 and IL-21Ralpha, whereas the interaction between IL-21 and gammaC, albeit essential for signaling, is rather weak. The design of IL-21 analogues, which have lost most or all affinity toward the signaling gammaC chain, while simultaneously maintaining a tight interaction with the private chain, would in theory represent candidates for IL-21 antagonists. We predicted the IL-21 residues, which compose the gammaC binding epitope using homology modeling and alignment with the related cytokines, IL-2 and IL-4. Next we systematically analyzed the predicted binding epitope by a mutagenesis study. Indeed two mutants, which have significantly impaired gammaC affinity with undiminished IL-21Ralpha affinity, were successfully identified. Functional studies confirmed that these two novel hIL-21 double mutants do act as hIL-21 antagonists.

Analysis of interleukin-21-induced Prdm1 gene regulation reveals functional cooperation of STAT3 and IRF4 transcription factors

Interleukin-21 (IL-21) is a pleiotropic cytokine that induces expression of transcription factor BLIMP1 (encoded by Prdm1), which regulates plasma cell differentiation and T cell homeostasis. We identified an IL-21 response element downstream of Prdm1 that binds the transcription factors STAT3 and IRF4, which are required for optimal Prdm1 expression. Genome-wide ChIP-Seq mapping of STAT3- and IRF4-binding sites showed that most regions with IL-21-induced STAT3 binding also bound IRF4 in vivo and furthermore revealed that the noncanonical TTCnnnTAA GAS motif critical in Prdm1 was broadly used for STAT3 binding. Comparing genome-wide expression array data to binding sites revealed that most IL-21-regulated genes were associated with combined STAT3-IRF4 sites rather than pure STAT3 sites. Correspondingly, ChIP-Seq analysis of Irf4(-/-) T cells showed greatly diminished STAT3 binding after IL-21 treatment, and Irf4(-/-) mice showed impaired IL-21-induced Tfh cell differentiation in vivo. These results reveal broad cooperative gene regulation by STAT3 and IRF4.

IL-21 acts directly on B cells to regulate Bcl-6 expression and germinal center responses

During T cell–dependent responses, B cells can either differentiate extrafollicularly into short-lived plasma cells or enter follicles to form germinal centers (GCs). Interactions with T follicular helper (Tfh) cells are required for GC formation and for selection of somatically mutated GC B cells. Interleukin (IL)-21 has been reported to play a role in Tfh cell formation and in B cell growth, survival, and isotype switching. To date, it is unclear whether the effect of IL-21 on GC formation is predominantly a consequence of this cytokine acting directly on the Tfh cells or if IL-21 directly influences GC B cells. We show that IL-21 acts in a B cell–intrinsic fashion to control GC B cell formation. Mixed bone marrow chimeras identified a significant B cell–autonomous effect of IL-21 receptor (R) signaling throughout all stages of the GC response. IL-21 deficiency profoundly impaired affinity maturation and reduced the proportion of IgG1⁺ GC B cells but did not affect formation of early memory B cells. IL-21R was required on GC B cells for maximal expression of Bcl-6. In contrast to the requirement for IL-21 in the follicular response to sheep red blood cells, a purely extrafollicular antibody response to Salmonella dominated by IgG2a was intact in the absence of IL-21.

The cannabinoid R+ methanandamide induces IL-6 secretion by prostate cancer PC3 cells

In the present study, we have investigated the effect of the cannabinoid R+ methanandamide (MET) in the androgen-resistant prostate cancer PC3 cells. MET induced a dose-dependent decrease in PC3 cell viability as well as a dose-dependent increase in the secretion of the cytokine IL-6. Looking deeper into the mechanisms involved, we found that MET-induced de novo synthesis of the lipid mediator ceramide that was blocked by the ceramide synthase inhibitor Fumonisin B1. Pre-incubation of cells with the cannabinoid receptor CB2 antagonist SR 144528 (SR2), but not the CB1 antagonist Rimonabant or the TRPV1 antagonist capsazepine, partially prevented the anti-proliferative effect, the ceramide accumulation, and the IL-6-induced secretion, suggesting a CB2 receptor-dependent mechanism. Fumonisin B1 did not have any effect in the IL-6 secretion increase induced by MET. However, even an incomplete down-regulation of (i.e., not a total silencing of) ceramide kinase expression by specific siRNA prevented the MET-induced IL-6 secretion. These results suggest that MET regulates ceramide metabolism in prostate PC3 cells which is involved in cell death as well as in IL-6 secretion. Our findings also suggest that CB2 agonists may offer a novel approach in the treatment of prostate cancer by decreasing cancer epithelial cell proliferation. However, the interaction of prostate cancer cells with their surrounding, and in particular with the immune system in vivo, needs to be further explored.

IL-21 enhances NK cell functions and survival in healthy and HIV-infected patients with minimal stimulation of viral replication

IL-21 plays an important role in regulating immune response and controlling chronic viral infections. Recently, we reported its decreased serum concentrations and their immunological consequences in HIV-infected persons. In this study, we have investigated how exogenous IL-21 enhances NK cell responses in these persons. We show that the cytokine receptors are expressed equally on all NK cell subsets defined by expression of CD16 and CD56; the cytokine activates STAT-3, MAPK, and Akt to enhance NK cell functions; the STAT-3 activation plays a key role in constitutive and IL-21-mediated enhancement of NK cell functions; the cytokine increases expression of antiapoptotic proteins Bcl-2 and Bcl-X(L) and enhances viability of NK cells but has no effect on their proliferation; the cytokine enhances HIV-specific ADCC, secretory, and cytotoxic functions, as well as viability of NK cells from HIV-infected persons; it exerts its biological effects on NK cells with minimal stimulation of HIV-1 replication; and the cytokine-activated NK cells inhibit viral replication in cocultured, HIV-infected, autologous CD4(+) T cells in a perforin- and LFA-1-dependent manner. These data suggest that IL-21 may serve as a valuable therapeutic tool for enhancing NK cell responses and inhibiting viral replication in HIV-infected patients.

Immune modulation with interleukin-21

Interleukin 21 (IL-21) is produced by activated CD4(+) T cells. The IL-21R shares the common receptor gamma-chain with IL-2, IL-4, IL-7, IL-9, and IL-15, is widely expressed on immune cells, and mediates a variety of effects on the immune system. IL-21 enhances the proliferation, antigen-induced activation, clonal expansion, IFN-gamma production, and cytotoxicity of NK cells and T cells. The antitumor actions of IL-21 have been variously attributed to NK cell and CD8(+) T cell cytotoxicity, CD4(+) T cell help, NKT cells, and the antiangiogenic properties induced by IFN-gamma secretion. In clinical trials IL-21 has been well tolerated and induces a unique pattern of immune activation. IL-21 is therefore an excellent candidate for use in immune therapy.

RGMA and IL21R show association with experimental inflammation and multiple sclerosis

Rat chromosome 1 harbors overlapping quantitative trait loci (QTL) for cytokine production and experimental models of inflammatory diseases. We fine-dissected this region that regulated cytokine production, myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE), anti-MOG antibodies and pristane-induced arthritis (PIA) in advanced intercross lines (AILs). Analysis in the tenth and twelfth generation of AILs resolved the region in two narrow QTL, Eae30 and Eae31. Eae30 showed linkage to MOG-EAE, anti-MOG antibodies and levels of interleukin-6 (IL-6). Eae31 showed linkage to EAE, PIA, anti-MOG antibodies and levels of tumor necrosis factor (TNF) and IL-6. Confidence intervals defined a limited set of potential candidate genes, with the most interesting being RGMA, IL21R and IL4R. We tested the association with multiple sclerosis (MS) in a Nordic case-control material. A single nucleotide polymorphism in RGMA associated with MS in males (odds ratio (OR)=1.33). Polymorphisms of RGMA also correlated with changes in the expression of interferon-gamma (IFN-gamma) and TNF in cerebrospinal fluid of MS patients. In IL21R, there was one positively associated (OR=1.14) and two protective (OR=0.87 and 0.68) haplotypes. One of the protective haplotypes correlated to lower IFN-gamma expression in peripheral blood mononuclear cells of MS patients. We conclude that RGMA and IL21R and their pathways are crucial in MS pathogenesis and warrant further studies as potential biomarkers and therapeutic targets.

IRF4 and its regulators: evolving insights into the pathogenesis of inflammatory arthritis?

Accumulating evidence from murine and human studies supports a key role for interleukin-17 (IL-17) and IL-21 in the pathogenesis of inflammatory arthritis. The pathways and molecular mechanisms that underlie the production of IL-17 and IL-21 are being rapidly elucidated. This review focuses on interferon regulatory factor 4 (IRF4), a member of the IRF family of transcription factors, which has emerged as a crucial controller of both IL-17 and IL-21 production. We first outline the complex role of IRF4 in the function of CD4(+) T cells and then discuss recent studies from our laboratory that have revealed a surprising role for components of Rho GTPase-mediated pathways in controlling the activity of IRF4. A better understanding of these novel pathways will hopefully provide new insights into mechanisms responsible for the development of inflammatory arthritis and potentially guide the design of novel therapeutic approaches.

Interleukin-21 restrains tumor growth and induces a substantial increase in the number of circulating tumor-specific T cells in a murine model of malignant melanoma

New strategies of immunotherapy are currently being evaluated, and the combination of chemo- and immunotherapy has shown promising results. The cytokine interleukin-21 (IL-21) is known to enhance immune function, and in this study we have investigated its ability to boost the efficacy of chemoimmunotherapy-cyclophosphamide and adoptive cell transfer (ACT)-in the B16-OVA/OT-I murine model of malignant melanoma. Subcutaneous B16-OVA tumors were established in C57BL/6J mice 8 days before adoptive transfer of tumor-specific OT-I T cells. In addition to cyclophosphamide and ACT, one group of mice received daily injections of murine IL-21 (mIL-21). Mice treated with mIL-21 had more tumor-specific T cells in the circulation 4 and 7 days following ACT (P=0.004 and P=0.002, respectively). Importantly, mIL-21 and ACT controlled tumor growth instantly and more effectively than ACT alone (P=0.001, day 4)-an effect that persisted up to 5 days after the last mIL-21 injection. We conclude that mIL-21 enhances chemoimmunotherapy: it amplifies the number of tumor-specific T cells in the circulation and also stunts early tumor growth.

c-Maf activates the promoter and enhancer of the IL-21 gene, and TGF-beta inhibits c-Maf-induced IL-21 production in CD4+ T cells

Previous studies have shown that IL-6 potently induces IL-21 production in CD4(+) T cells, whereas TGF-beta inhibits IL-6-induced IL-21 production in CD4(+) T cells. In this study, we addressed the mechanisms underlying the transcriptional regulation of IL-21 production in CD4(+) T cells. We found that IL-6 induced c-Maf expression in CD4(+) T cells and that the enforced expression of c-Maf induced IL-21 production in CD4(+) T cells without IL-6, IL-4/STAT6 signaling, or an autocrine effect of IL-21. Moreover, we found that c-Maf directly bound to and activated IL-21P and the CNS-2 enhancer through MARE sites. On the other hand, we also found that although TGF-beta up-regulated IL-6-induced c-Maf expression in CD4(+) T cells, TGF-beta inhibited c-Maf-induced IL-21 production in CD4(+) T cells. Finally, we found that Foxp3 bound to IL-21P and the CNS-2 enhancer and inhibited c-Maf-induced IL-21 production modestly but significantly in CD4(+) T cells. Taken together, these results suggest that c-Maf induces IL-21 production directly in CD4(+) T cells by activating IL-21P and the CNS-2 enhancer and that TGF-beta suppresses c-Maf-induced IL-21 production in CD4(+) T cells.

IL-21 imposes a type II EBV gene expression on type III and type I B cells by the repression of C- and activation of LMP-1-promoter

Epstein-Barr virus (EBV) is associated with a variety of human tumors. Although the EBV-infected normal B cells in vitro and the EBV-carrying B cell lymphomas in immunodeficient patients express the full set of latent proteins (type III latency), the majority of EBV-associated malignancies express the restricted type I (EBNA-1 only) or type II (EBNA-1 and LMPs) viral program. The mechanisms responsible for these different latent viral gene expression patterns are only partially known. IL-21 is a potent B cell activator and plasma cell differentiation-inducer cytokine produced by CD4(+) T cells. We studied its effect on EBV-carrying B cells. In type I Burkitt lymphoma (BL) cell lines and in the conditional lymphoblastoid cell line (LCL) ER/EB2-5, IL-21 potently activated STAT3 and induced the expression of LMP-1, but not EBNA-2. The IL-21-treated type I Jijoye M13 BL line ceased to proliferate, and this was paralleled by the induction of IRF4 and the down-regulation of BCL6 expression. In the type III LCLs and BL lines, IL-21 repressed the C-promoter-derived and LMP-2A mRNAs, whereas it up-regulated the expression of LMP-1 mRNAs. The IL-21-treated type III cells underwent plasma cell differentiation with the induction of Blimp-1, and high levels of Ig and Oct-2. IL-21 might be involved in the EBNA-2-independent expression of LMP-1 in EBV-carrying type II cells. In light of the fact that IL-21 is already in clinical trials for the treatment of multiple malignancies, the in vivo modulation of EBV gene expression by IL-21 might have therapeutic benefits for the EBV-carrying malignancies.

Lymphocytes in cancer development: polarization towards pro-tumor immunity

The classic view that the role of immune cells in cancer is primarily one of tumor rejection has been supplanted by a more complex view of leukocytes having both pro- and anti-tumor properties. This shift is due to the now well recognized capabilities of several myeloid cell types that foster pro-tumor programming of premalignant tissue, as well as the discovery that subsets of leukocytes also suppress development and effector functions of lymphocytes important for mediating anti-tumor immunity. In this review, we focus on the underappreciated role that T lymphocytes play in promoting tumor development. This includes, in addition to the role of T regulatory cells, a role for natural killer T cells and CD4(+) T helper cells in suppressing anti-tumor immunity and promoting cancer growth and metastasis.

Dynamics and consequences of IL-21 production in HIV-infected individuals: a longitudinal and cross-sectional study

IL-21 is a relatively newly discovered immune-enhancing cytokine that plays an essential role in controlling chronic viral infections. It is produced mainly by CD4(+) T cells, which are also the main targets of HIV-1 and are often depleted in HIV-infected individuals. Therefore, we sought to determine the dynamics of IL-21 production and its potential consequences for the survival of CD4(+) T cells and frequencies of HIV-specific CTL. For this purpose, we conducted a series of cross-sectional and longitudinal studies on different groups of HIV-infected patients and show in this study that the cytokine production is compromised early in the course of the infection. The serum cytokine concentrations correlate with CD4(+) T cell counts in the infected persons. Among different groups of HIV-infected individuals, only elite controllers maintain normal production of the cytokine. Highly active antiretroviral therapy only partially restores the production of this cytokine. Interestingly, HIV infection of human CD4(+) T cells inhibits cytokine production by decreasing the expression of c-Maf in virus-infected cells, not in uninfected bystander cells. We also show that the frequencies of IL-21-producing HIV-specific, but not human CMV-specific, Ag-experienced CD4(+) T cells are decreased in HIV-infected viremic patients. Furthermore, we demonstrate in this study that recombinant human IL-21 prevents enhanced spontaneous ex vivo death of CD4(+) T cells from HIV-infected patients. Together, our results suggest that serum IL-21 concentrations may serve as a useful biomarker for monitoring HIV disease progression and the cytokine may be considered for immunotherapy in HIV-infected patients.

IL-21 and T follicular helper cells

Upon encounter with antigen, CD4(+) T cells differentiate into effector T(h) subsets with distinctive functions that are related to their unique cytokine profiles and anatomical locations. One of the most important T(h) functions is to provide signals to developing B cells that induce specific and appropriate antibody responses. The major CD4(+) T cell subset that helps B cells is the T follicular helper (T(FH)) cell, whose expression of the chemokine receptor CXCR5 [chemokine (C-X-C motif) receptor 5] serves to localize this cell to developing germinal centers (GCs) where it provides instructive signals leading to Ig class switching and somatic mutation. T(FH) cells produce high levels of IL-21, a cytokine that is critical for GC formation and also for the generation of T(FH) cells. Although T(FH) cells have been found to produce cytokines characteristic of other T(h) subsets, they represent a distinct lineage whose development is driven by the transcription factor B-cell CLL lymphoma-6 (BCL6). Consistent with their critical role in the generation of antibody responses, dysregulated T(FH) function has been associated with the development of systemic autoimmunity. Here, we review the role of IL-21 in the regulation of normal T(FH) development and function as well as in progression of autoimmune responses.

Endogenous IL-21 restricts CD8+ T cell expansion and is not required for tumor immunity

IL-21 has antitumor activity through actions on NK cells and CD8(+) T cells, and is currently in clinical development for the treatment of cancer. However, no studies have addressed the role of endogenous IL-21 in tumor immunity. In this study, we have studied both primary and secondary immune responses in IL-21(-/-) and IL-21R(-/-) mice against several experimental tumors. We found intact immune surveillance toward methylcholanthrene-induced sarcomas in IL-21(-/-) and IL-21R(-/-) mice compared with wild-type mice and B16 melanomas showed equal growth kinetics and development of lung metastases. IL-21R(-/-) mice showed competent NK cell-mediated rejection of NKG2D ligand (Rae1beta) expressing H-2b(-) RMAS lymphomas and sustained transition to CD8(+) T cell-dependent memory against H-2b(+) RMA lymphomas. alpha-Galactosylceramide stimulation showed equal expansion and activation of NKT and NK cells and mounted a powerful antitumor response in the absence of IL-21 signaling, despite reduced expression of granzyme B in NKT, NK, and CD8(+) T cells. Surprisingly, host IL-21 significantly restricted the expansion of Ag-specific CD8(+) T cells and inhibited primary CD8(+) T cell immunity against OVA-expressing EG7 lymphomas, as well as the secondary expansion of memory CD8(+) T cells. However, host IL-21 did not alter the growth of less immunogenic MC38 colon carcinomas with dim OVA expression. Overall, our results show that endogenous IL-21/IL-21R is not required for NK, NKT, and CD8(+) T cell-mediated tumor immunity, but restricts Ag-specific CD8(+) T cell expansion and rejection of immunogenic tumors, indicating novel immunosuppressive actions of this cytokine.

Loss of parity between IL-2 and IL-21 in the NOD Idd3 locus

IL-2 and IL-21 are two cytokines with great potential to affect autoimmune infiltration of nonlymphoid tissue, and are contained within the strongest non-MHC-linked locus for type 1 diabetes (T1D) susceptibility on the nonobese diabetic (NOD) mouse (Idd3). IL-21 is necessary for the development of diabetes in the NOD mouse, but a number of important studies argue that decreased expression of IL-2 explains Idd3. In this study, we demonstrate that the amount of IL-21, but not IL-2, correlated with T1D incidence. During our analyses of the IL-2/IL-21 interval, we found that mice segregate into one of two distinct expression profiles. In the first group, which includes the C57BL/6 strain, both Il2 and Il21 were expressed at low levels. In the other group, which includes the NOD strain, Il2 and Il21 were both highly expressed. However, because NOD IL-2 mRNA was relatively unstable, IL-2 production was remarkably similar between strains. The increased production of IL-21 in NOD mice was found to result from two single nucleotide polymorphisms within the distal promoter region that conferred increased binding affinity for the transcription factor Sp1. Our findings indicate that a loss of locus parity after decreased IL-2 mRNA stability ensures that the high-expressing IL-21 allele persists in nature and provides a basis for autoimmunity.

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.

Involvement of interleukin-15 and interleukin-21, two γ-chain-related cytokines, in celiac disease

Celiac disease (CD), an enteropathy caused by dietary gluten in genetically susceptible individuals, is histologically characterized by villous atrophy, crypt cell hyperplasia, and increased number of intra-epithelial lymphocytes. The nature of CD pathogenesis remains unclear, but recent evidence indicates that both innate and adaptive immune responses are necessary for the phenotypic expression and pathologic changes characteristic of CD. Extensive studies of molecules produced by immune cells in the gut of CD patients have led to identification of two cytokines, namely interleukin (IL)-15 and IL-21, which are thought to play a major role in orchestrating the mucosal inflammatory response in CD. Here we review the current knowledge of the expression and function of IL-15 and IL-21 in CD.

A little 'help' from IL-21 during persistent viral infection

Anti-viral CD4(+) T cells are required to orchestrate and sustain the activities of the adaptive immune system during a persistent viral infection. Three recent studies suggest that CD4(+) T cells accomplish this in part through the release of IL-21.

The role of T helper type 17 cells in inflammatory arthritis

While T cells have been implicated in the pathogenesis of inflammatory arthritis for more than three decades, the focus on the T helper type 17 (Th17) subset of CD4 T cells and their secreted cytokines, such as interleukin (IL)-17, is much more recent. Proinflammatory actions of IL-17 were first identified in the 1990s, but the delineation of a distinct Th17 subset in late 2005 has sparked great interest in the role of these cells in a broad range of immune-mediated diseases. This review summarizes current understanding of the role of Th17 cells and their products in both animal models of inflammatory arthritis and human immune-driven arthritides.

In vivo antitumor efficacy of interleukin-21 in combination with chemotherapeutics

Interleukin-21 (IL-21) is a class I cytokine with antitumor properties due to enhanced proliferation and effector function of CD8(+) T cells and natural killer (NK) cells. Here we have explored the magnitude and time-course of cytostatics-induced lymphopenia in mice and investigated whether treatment with cytostatics influences the antitumor effect of IL-21 in mouse tumor models. We show that pegylated liposomal doxorubicin (PLD), irinotecan and oxaliplatin induced transient lymphopenia, whereas 5-fluorouracil (5-FU) transiently increased lymphocyte counts. B cells were more sensitive than T cells towards irinotecan and oxaliplatin. Additive antitumor effects were observed after combining IL-21 with PLD, oxaliplatin and to less extent 5-FU but not irinotecan, and larger effect was observed when IL-21 administration was postponed relative to chemotherapy, suggesting that these agents may transiently impair immune function. However, the chemotherapies did not significantly alter the levels of circulating regulatory T cells and only marginally affected the ability of CD8(+) T cells to respond to IL-21 measured as increased granzyme B mRNA. Our results show that IL-21 therapy can be successfully combined with agents from different chemotherapeutic drug classes, i.e. topoisomerase II inhibitors (PLD), anti-metabolites (5-FU) and platinum analogs (oxaliplatin) provided that IL-21 therapy is delayed relative to chemotherapy.

Immunopathogenesis of bronchial asthma

Bronchial asthma is a common immune-mediated disorder characterized by reversible airway inflammation, mucus production, and variable airflow obstruction with airway hyperresponsiveness. Allergen exposure results in the activation of numerous cells of the immune system, of which dendritic cells (DCs) and Th2 lymphocytes are of paramount importance. Although the epithelium was initially considered to function solely as a physical barrier, it is now evident that it plays a central role in the Th2-cell sensitization process due to its ability to activate DCs. Cytokines are inevitable factors in driving immune responses. To the list of numerous cytokines already known to be involved in the regulation of allergic reactions, new cytokines were added, such as TSLP, IL-25, and IL-33. IgE is also a central player in the allergic response. The activity of IgE is associated with a network of proteins, especially with its high- and low-affinity Fc receptors. Understanding the cellular and molecular mechanisms of allergic reactions helps us not only to understand the mechanisms of current treatments, but is also important for the identification of new targets for biological intervention. An IgE-specific monoclonal antibody, omalizumab, has already reached the clinic and similar biological agents will surely follow.

Local cytokine profiles in knee osteoarthritis: elevated synovial fluid interleukin-15 differentiates early from end-stage disease

OBJECTIVE

Much of what is known about the inflammatory response in the synovial membrane (SM) of patients with osteoarthritis (OA) comes from studies of synovial tissues from end-stage disease. In this study, we sought to better characterize the inflammatory infiltrate in symptomatic patients with early signs of knee OA, and to determine how inflammatory cell populations relate to the pattern of cytokine and degradative enzyme production.

METHODS

Study populations comprised patients with degenerative meniscal tears and early cartilage thinning undergoing arthroscopic procedures (early OA) and patients undergoing total knee replacement for end-stage OA. Quantitative real-time polymerase chain reaction (PCR) was used to measure expression of SM cytokines and enzymes implicated in the pathogenesis of inflammatory arthritis and OA, as well as cell lineage-specific markers. We quantified synovial fluid (SF) cytokines and enzymes by enzyme-linked immunosorbent assay (ELISA) and SM cell populations by immunohistochemistry.

RESULTS

We found increased levels of SF interleukin-15 (IL-15) protein in the early knee OA patients when compared to end-stage OA. Both SF IL-15 protein and numbers of CD8 cells within SM correlated with matrix metalloproteinase-1 (MMP-1) and three levels. TNF-alpha, IL-6 and IL-21 were also detectable in the SF of the majority of patients, and IL-15 levels were associated with IL-6 levels.

CONCLUSION

IL-15 is elevated in early knee OA, suggesting activation of an innate immune response in the SM. The association of IL-15 expression with CD8 transcripts and MMPs implicates this cytokine in OA pathogenesis and as a candidate therapeutic target.

Cytokine gene-mediated immunotherapy: current status and future perspectives

Recent understanding of the molecular events crucial in overcoming immunosuppressive tumor microenvironments and generating effective antitumor immunity provides us with the wreath opportunity to manipulate genes that have a key role in antitumor immune responses. Granulocyte-macrophage colony stimulating factor (GM-CSF) and interleukin-12 (IL-12) are two indispensable cytokines for activating dendritic cells and boosting the strong immune responses against cancer. In this review, we describe the antitumor mechanisms and clinical application of gene-modified tumor cells and dendritic cells to secrete GM-CSF or IL-12, respectively, in various preclinical and clinical settings. The principles operative in these vaccination strategies may prove applicable to other immunotherapy strategies, especially in combination with other therapeutic modalities, such as chemotherapy and targeted therapy.

Il-21 enhances NK cell activation and cytolytic activity and induces Th17 cell differentiation in inflammatory bowel disease

BACKGROUND

Interleukin-21 (IL-21) is involved in T and NK cell activation and effector response and promotes Th17 cell differentiation. Here we investigated IL-21 receptor (IL-21R) expression in inflamed mucosa of inflammatory bowel disease (IBD) and evaluated its role in the induction of NK cell cytotoxicity and activation as well as Th17 differentiation.

METHODS

Expression of IL-21R was performed by immunohistochemistry and flow cytometry. NK cell cytotoxicity was detected by a standard (51)Cr-release assay. Cytokine levels were analyzed by enzyme-linked immunosorbent assay (ELISA) and quantitative real-time polymerase chain reaction (PCR).

RESULTS

IL-21R-positive cells were significantly increased in inflamed mucosa of IBD compared with controls, and mainly expressed in freshly isolated peripheral blood (PB)- and lamina propria (LP)-CD4(+), CD8(+) T, B, and NK cells. PB-NK cells from IBD patients produced higher levels of interferon gamma (IFN-gamma) and tumor necrosis factor (TNF) than controls when stimulated with immobilized human IgG and IL-21. IL-21-primed IBD NK cells showed a more potent antitumor cytotoxicity to NK-sensitive K562 cells than controls. Moreover, PB-T and LP-T cells from IBD patients produced large amounts of proinflammatory cytokines (e.g., TNF, IFN-gamma) than controls when stimulated with IL-21 and anti-CD3. Importantly, IL-21 facilitated IBD CD4(+) T cell to differentiate into Th17 cells, characterized by increased expression of IL-17A and ROR gamma t.

CONCLUSIONS

IL-21 enhances IBD NK cell cytotoxic response, triggers T cells to produce proinflammatory cytokines, and induces IBD CD4(+) T cells to differentiate into Th17 cells, suggesting that IL-21 is involved in the pathogenesis of IBD and that blocking IL-21R signaling may have a therapeutic potential in IBD.

IL-21 induces the secretion of proinflammatory cytokines in patients with autoimmune hepatitis

AIM: To detect the expression of IL-21 receptor (IL-21R) in peripheral blood mononuclear cells (PBMCs) from patients with autoimmune hepatitis (AIH) and analyze the secretion of proinflammatory cytokines (e.g., TNF-α, IFN-γ and IL-2) in cultured PBMCs stimulated with IL-21.

METHODS: Peripheral blood samples were collected from 21 AIH patients and 25 healthy controls, respectively. The expression of IL-21Rin CD4⁺ and CD8⁺ T cells was examined by flow cytometry. After cultured PBMCs were stimulated with IL-21 and anti-CD3, the secretion of cytokines was examined by ELISA.

RESULTS: IL-21R was significantly upregulated in CD4⁺ and CD8⁺ T cells (7.66% ± 2.37% vs 3.12% ± 0.76% and 9.42% ± 2.48% vs 4.02% ± 0.89%, respectively; both P < 0.05). After stimulation with IL-21 and anti-CD3, the levels of secreted TNF-α, IFN-γ and IL-2 in PBMCs from AIH patients were significantly higher than those in PBMCs from healthy controls (P < 0.05).

CONCLUSION: IL-21R is highly expressed in T cells from AIH patients, and IL-21 is able to induce the secretion of proinflammatory cytokines, suggesting that IL-21 is involved in the process of tissue injury in AIH.

Human dendritic cells induce the differentiation of interleukin-21-producing T follicular helper-like cells through interleukin-12

T follicular helper (Tfh) cells help development of antibody responses via interleukin-21 (IL-21). Here we show that activated human dendritic cells (DCs) induced naive CD4(+) T cells to become IL-21-producing Tfh-like cells through IL-12. CD4(+) T cells primed with IL-12 induced B cells to produce immunoglobulins in a fashion dependent on IL-21 and inducible costimulator (ICOS), thus sharing fundamental characteristics with Tfh cells. The induction of Tfh-like cells by activated DCs was inhibited by neutralizing IL-12. IL-12 induced two different IL-21-producers: IL-21(+)IFN-gamma(+)T-bet(+) Th1 cells and IL-21(+)IFN-gamma(-)T-bet(-) non-Th1 cells, in a manner dependent on signal transducer and activator of transcription 4 (STAT4). IL-12 also regulated IL-21 secretion by memory CD4(+) T cells. Thus, IL-12 produced by activated DCs regulates antibody responses via developing IL-21-producing Tfh-like cells and inducing IL-21 secretion from memory CD4(+) T cells. These data suggest that the developmental pathway of Tfh cells differs between mice and humans, which have considerable implications for vaccine development.

Human B cells secrete granzyme B when recognizing viral antigens in the context of the acute phase cytokine IL-21

Human B cells are currently not known to produce the proapoptotic protease granzyme B (GrB) in physiological settings. We have discovered that BCR stimulation with either viral Ags or activating Abs in the context of the acute phase cytokine IL-21 can induce the secretion of substantial amounts of GrB by human B cells. Importantly, GrB response to viral Ags was significantly stronger in B cells from subjects recently vaccinated against the corresponding viruses as compared with unvaccinated subjects. GrB-secreting B cells featured a homogeneous CD19(+)CD20(+)CD27(-)CD38(-)IgD(-) phenotype, improved survival, and enhanced expression of costimulatory, Ag-presenting and cell-adhesion molecules. B cell-derived GrB was enzymatically active and its induction required the activation of similar signaling pathways as those in CTLs. Our findings suggest that GrB-secreting B cells support the early antiviral immune response against viruses with endosomal entry pathways, thereby counteracting overwhelming viral replication at the beginning of an infection until virus-specific T cells from draining lymph nodes arrive at the site of infection. Our data may also explain the elevated serum GrB levels found in the early phase of various viral diseases.

New insights into the regulation of T cells by gamma(c) family cytokines

Common cytokine receptor gamma-chain (gamma(c)) family cytokines have crucial roles in the development, proliferation, survival and differentiation of multiple cell lineages of both the innate and adaptive immune systems. In this Review, we focus on our current understanding of the distinct and overlapping effects of interleukin-2 (IL-2), IL-7, IL-9, IL-15 and IL-21, as well as the IL-7-related cytokine thymic stromal lymphopoietin (TSLP), on the survival and proliferation of conventional alphabeta T cells, gammadelta T cells and regulatory T cells. This knowledge potentially allows for the therapeutic manipulation of immune responses for the treatment of cancer, autoimmunity, allergic diseases and immunodeficiency, as well as for vaccine development.

A vital role for interleukin-21 in the control of a chronic viral infection

Understanding the factors that regulate the induction, quality, and longevity of antiviral T cell responses is essential for devising rational strategies to prevent or combat infections. In this study, we show that interleukin-21 (IL-21), likely produced by CD4+ T cells, directly influences the generation of polyfunctional CD8+ T cells and that the number of CD4+ T cells that produce IL-21 differs markedly between acute and chronic infections. IL-21 regulates the development of CD8+ T cell exhaustion and the ability to contain chronic lymphocytic choriomeningitis virus infection. Thus, IL-21 serves as a critical helper factor that shapes the functional quality of antiviral CD8+ T cells and is required for viral control.

IL-21 is required to control chronic viral infection

CD4+ and CD8+ T cell functions are rapidly aborted during chronic infection, preventing viral clearance. CD4+ T cell help is required throughout chronic infection so as to sustain CD8+ T cell responses; however, the necessary factor(s) provided by CD4+ T cells are currently unknown. Using a mouse model of chronic viral infection, we demonstrated that interleukin-21 (IL-21) is an essential component of CD4+ T cell help. In the absence of IL-21 signaling, despite elevated CD4+ T cell responses, CD8+ T cell responses are severely impaired. CD8+ T cells directly require IL-21 to avoid deletion, maintain immunity, and resolve persistent infection. Thus, IL-21 specifically sustains CD8+ T cell effector activity and provides a mechanism of CD4+ T cell help during chronic viral infection.

Follicular helper T cells as cognate regulators of B cell immunity

Follicular helper T (T(FH)) cells are a class of helper T cells specialized in the cognate control of antigen-specific B cell immunity. Upon first contact with antigen-primed B cells, pregerminal center effector T(FH) cells promote B cell clonal expansion, antibody isotype switch, plasma cell differentiation, and the induction of germinal centers. By contrast, within germinal centers, T(FH) cells regulate the fate of antigen-specific GC B cells expressing high-affinity variant B cell receptors to promote memory B cell and long-lived plasma cell development. Recent studies unravel multiple signals controlling T(FH) development and functional subtypes of antigen-specific T(FH) cells, including memory T(FH) cells that accelerate memory B cell responses to antigen rechallenge in vivo.

New insights into the regulation of human B-cell differentiation

B lymphocytes provide the cellular basis of the humoral immune response. All stages of this process, from B-cell activation to formation of germinal centers and differentiation into memory B cells or plasma cells, are influenced by extrinsic signals and controlled by transcriptional regulation. Compared to naïve B cells, memory B cells display a distinct expression profile, which allows for their rapid secondary responses. Indisputably, many B-cell malignancies result from aberrations in the circuitry controlling B-cell function, particularly during the germinal centre (GC) reaction. Here, we review new insights into memory B-cell subtypes, recent literature on transcription factors regulating human B-cell differentiation and further evidence for B-cell lymphomagenesis emanating from errors during GC cell reactions.

IL-21R on T cells is critical for sustained functionality and control of chronic viral infection

Chronic viral infection is often associated with the dysfunction of virus-specific T cells. Our studies using Il21r-deficient (Il21r-/-) mice now suggest that interleukin-21 (IL-21) is critical for the long-term maintenance and functionality of CD8+ T cells and the control of chronic lymphocytic choriomeningitis virus infection in mice. Cell-autonomous IL-21 receptor (IL-21R)-dependent signaling by CD8+ T cells was required for sustained cell proliferation and cytokine production during chronic infection. Il21r-/- mice showed normal CD8+ T cell expansion, effector function, memory homeostasis, and recall responses during acute and after resolved infection with several other nonpersistent viruses. These data suggest that IL-21R signaling is required for the maintenance of polyfunctional T cells during chronic viral infections and have implications for understanding the immune response to other persisting antigens, such as tumors.

Fc(epsilon)RI and FcgammaRIII/CD16 differentially regulate atopic dermatitis in mice

The high-affinity IgE receptor Fc(epsilon)RI and, in some models, the low-affinity IgG receptor Fc(epsilon)RIIII/CD16 play an essential role in allergic diseases. In human skin, they are present on APCs and effector cells recruited into the inflamed dermis. FcRgamma is a subunit shared, among other FcRs, by Fc(epsilon)RI and CD16 and is essential to their assembly and signal transduction. Using an experimental model reproducing some features of human atopic dermatitis and specific FcR-deficient mice, we have herein delineated the respective contribution of Fc(epsilon)RIand Fc(epsilon)RIII/CD16 to the pathology. We demonstrate that symptoms of atopic dermatitis are completely absent in FcRgamma-deficient animals but only partially inhibited in either Fc(epsilon)RI- or FcgammaRIII/CD16-deficient animals. Absence or attenuation of the pathology is correlated to increased skin expression of regulatory IL-10 and Foxp3. While Fc(epsilon)RI controls both Th1 and Th2 skin response, mast cell recruitment into draining lymph nodes and IgE production, CD16 regulates only Th2 skin response, as well as T cell proliferation and IgG1 production. This isotype-specific regulation by the cognate FcR is associated to a differential regulation of IL-4 and IL-21 expression in the draining lymph nodes. Fc(epsilon)RIand CD16 thus contribute to atopic dermatitis but differentially regulate immune responses associated with the disease. Targeting both IgE/Fc(epsilon)RI and IgG/CD16 interactions might represent an efficient therapeutic strategy for allergic diseases.