The role of Interleukin-21 in autoimmune Diseases: Mechanisms, therapeutic Implications, and future directions.

IL-21 is a multifunctional cytokine that regulates the functional activity of various immune cells. Initial studies have shown that IL-21 can influence the differentiation, proliferation and function of T and B cells, as well as promote the maturation and increase the cytotoxicity of CD8 + T cells and NK cells. During humoral immune responses, IL-21 has significant effects on B cell activation, differentiation and apoptosis. In addition, IL-21 promotes the differentiation of both naive and memory B cells, ultimately leading to the activation of plasma cells. The function of IL-21 in the immune system is complex, as it has the ability to either stimulate or inhibit immune responses. in addition, IL-21 facilitates the differentiation of naive and memory B cells into plasma cells. The functionality of IL-21 in the immune system is diverse, as it has the ability to stimulate or inhibit immune responses. This cytokine has been implicated in several diseases including cancer, allergies and autoimmune diseases. Research has suggested that this cytokine is involved in the development of autoimmune diseases such as systemic lupus erythematosus and rheumatoid arthritis. Several studies have suggested that inhibition of IL-21 has a therapeutic effect on autoimmune diseases. Therefore, targeting both the cytokine's receptor and IL-21 in autoimmune diseases may be an effective approach to reduce the severity of the disease or to treat it. This review will examine the biological effects of IL-21 on various immune cells and the role of the cytokine in autoimmune diseases.

Association between Interleukin-21 and Interleukin-21 receptor gene polymorphisms with susceptibility to chronic hepatitis B virus infection and HBV spontaneous clearance in Iranian population.

Hepatitis B virus (HBV) infection is a major public health concern due to the infection often leads to chronic infection, liver cirrhosis and also liver cancer. The host immune response to HBV infection and also genetic background play significant role in outcome of infection. Single nucleotide polymorphisms (SNPs) are the most important kind of variation in genetic sequences that caused by point mutations. As cytokines have major roles in viral infections, it seems that cytokine gene polymorphisms are independently associated with response to viral infections. Interleukin 21 (IL-21) plays an influential role in both innate and adaptive immune responses. Its specific receptor, IL-21R, produced and located on the surface of T, B and natural killer (NK) cells and is critical for the proliferation and differentiation of these immune effector cells. Many studies confirmed that the IL-21 involved in response to viral infections. We aimed to investigate the association of G/T IL-21 (rs2055979) and C/T IL-21R (rs3093390) gene polymorphisms with chronic hepatitis B virus infection and HBV spontaneous clearance in Iranian population. METHODS: In this study, blood samples were gathered from 320 patients with chronic HBV and 310 healthy controls and also 120 HBV spontaneous clearance individuals. Following genomic DNA extraction, genotypes of the selected SNPs determined by PCR and restriction fragment length polymorphism (RFLP) method. The results were analyzed by SPSS software using Chi-square, Logistic Regression, ANOVA and Independent Samples t-Test. RESULTS: According to our results, in IL-21R (rs3093390 C/T) gene polymorphism, allele frequency of T is statistically different in the HBV spontaneous clearance group compared to chronic HBV cases. But there is no significant difference between G/T IL-21 (rs2055979) and C/T IL-21R (rs3093390) genotypes distribution in three groups. Also we found that higher serum aspartate transaminase (AST) level in HBV spontaneous clearance group is significantly associated with TT genotype of IL-21 (rs2055979) compared to GG genotype (P value = 0.006). DISCUSSION: Our results showed that T allele frequency in IL-21R (rs3093390 C/T) gene polymorphism could consider as a host genetic factor for HBV spontaneous clearance. Probably we can serve it as a potential prognostic genetic marker for spontaneous clearance of HBV infection.

Interleukin-21 receptor signalling is not critically required for imiquimod-induced psoriasiform dermatitis in mice.

Psoriasis is largely mediated by interleukin (IL)-23/T helper (Th) 17 axis, and IL-21 is a pleiotropic cytokine expressed by Th17 cells. Despite previously reported possible pathogenic roles of IL-21 in human psoriasis, we found that IL-21 receptor (IL-21R) signalling was not crucial for imiquimod-induced psoriatic inflammation, using IL-21R-/- mice. The severity of imiquimod-induced psoriatic manifestation and pro-inflammatory Th17 cytokine levels, IL-17A-producing γδ T cells and CD4+ T cells, and in vitro IL-17A production by γδ T cells after IL-23 stimulation was comparable between wild-type and IL-21R-/- mice. Collectively, IL-21R signalling was not critically involved in IMQ-induced psoriatic inflammation despite an increased IL-21 expression in the IMQ-treated mouse skin. Our data may represent the significant differences between human psoriasis and murine psoriasis model, and further studies using other models will be required to elucidate the role of IL-21 in psoriasis pathogenesis.

Contribution of enhanced engagement of antigen presentation machinery to the clinical immunogenicity of a human interleukin (IL)-21 receptor-blocking therapeutic antibody.

Reliable risk assessment for biotherapeutics requires accurate evaluation of risk factors associated with immunogenicity. Immunogenicity risk assessment tools were developed and applied to investigate the immunogenicity of a fully human therapeutic monoclonal antibody, ATR-107 [anti-interleukin (IL)-21 receptor] that elicited anti-drug antibodies (ADA) in 76% of healthy subjects in a Phase 1 study. Because the ATR-107 target is expressed on dendritic cells (DCs), the immunogenicity risk related to engagement with DC and antigen presentation pathways was studied. Despite the presence of IL-21R on DCs, ATR-107 did not bind to the DCs more extensively than the control therapeutic antibody (PF-1) that had elicited low clinical ADA incidence. However, ATR-107, but not the control therapeutic antibody, was translocated to the DC late endosomes, co-localized with intracellular antigen-D related (HLA-DR) molecules and presented a dominant T cell epitope overlapping the complementarity determining region 2 (CDR2) of the light chain. ATR-107 induced increased DC activation exemplified by up-regulation of DC surface expression of CD86, CD274 (PD-L1) and CD40, increased expansion of activated DC populations expressing CD86(hi), CD40(hi), CD83(hi), programmed death ligand 1 (PD-L1)(hi), HLA-DR(hi) or CCR7(hi), as well as elevated secretion of tumour necrosis factor (TNF)-α by DCs. DCs exposed to ATR-107 stimulated an autologous T cell proliferative response in human donor cells, in concert with the detection of immunoglobulin (Ig)G-type anti-ATR-107 antibody response in clinical samples. Collectively, the enhanced engagement of antigen presentation machinery by ATR-107 was suggested. The approaches and findings described in this study may be relevant to identifying lower immunogenicity risk targets and therapeutic molecules.

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

BACKGROUND: The capacity of CD8(+) T cells to control infections and mediate antitumor immunity requires the development and survival of effector and memory cells. IL-21 has emerged as a potent inducer of CD8(+) T-cell effector function and memory development in mouse models of infectious disease. However, the role of IL-21 and associated signaling pathways in protective CD8(+) T-cell immunity in human subjects is unknown. OBJECTIVE: We sought to determine which signaling pathways mediate the effects of IL-21 on human CD8(+) T cells and whether defects in these pathways contribute to disease pathogenesis in patients with primary immunodeficiencies caused by mutations in components of the IL-21 signaling cascade. METHODS: Human primary immunodeficiencies resulting from monogenic mutations provide a unique opportunity to assess the requirement for particular molecules in regulating human lymphocyte function. Lymphocytes from patients with loss-of-function mutations in signal transducer and activator of transcription 1 (STAT1), STAT3, or IL-21 receptor (IL21R) were used to assess the respective roles of these genes in human CD8(+) T-cell differentiation in vivo and in vitro. RESULTS: Mutations in STAT3 and IL21R, but not STAT1, led to a decrease in multiple memory CD8(+) T-cell subsets in vivo, indicating that STAT3 signaling, possibly downstream of IL-21R, regulates the memory cell pool. Furthermore, STAT3 was important for inducing the lytic machinery in IL-21-stimulated naive CD8(+) T cells. However, this defect was overcome by T-cell receptor engagement. CONCLUSION: The IL-21R/STAT3 pathway is required for many aspects of human CD8(+) T-cell behavior but in some cases can be compensated by other signals. This helps explain the relatively mild susceptibility to viral disease observed in STAT3- and IL-21R-deficient subjects.

Tonsillar Microbiome-Derived Lantibiotics Induce Structural Changes of IL-6 and IL-21 Receptors and Modulate Host Immunity.

Emerging evidence emphasizes the functional impacts of host microbiome on the etiopathogenesis of autoimmune diseases, including rheumatoid arthritis (RA). However, there are limited mechanistic insights into the contribution of microbial biomolecules especially microbial peptides toward modulating immune homeostasis. Here, by mining the metagenomics data of tonsillar microbiome, a deficiency of the encoding genes of lantibiotic peptides salivaricins in RA patients is identified, which shows strong correlation with circulating immune cells. Evidence is provided that the salivaricins exert immunomodulatory effects in inhibiting T follicular helper (Tfh) cell differentiation and interleukin-21 (IL-21) production. Mechanically, salivaricins directly bind to and induce conformational changes of IL-6 and IL-21 receptors, thereby inhibiting the bindings of IL-6 and IL-21 to their receptors and suppressing the downstream signaling pathway. Finally, salivaricin administration exerts both prophylactic and therapeutic effects against experimental arthritis in a murine model of RA. Together, these results provide a mechanism link of microbial peptides-mediated immunomodulation.

Targeting Cbx3/HP1γ Induces LEF-1 and IL-21R to Promote Tumor-Infiltrating CD8 T-Cell Persistence.

Immune checkpoint blockade (ICB) relieves CD8+ T-cell exhaustion in most mutated tumors, and TCF-1 is implicated in converting progenitor exhausted cells to functional effector cells. However, identifying mechanisms that can prevent functional senescence and potentiate CD8+ T-cell persistence for ICB non-responsive and resistant tumors remains elusive. We demonstrate that targeting Cbx3/HP1γ in CD8+ T cells augments transcription initiation and chromatin remodeling leading to increased transcriptional activity at Lef1 and Il21r. LEF-1 and IL-21R are necessary for Cbx3/HP1γ-deficient CD8+ effector T cells to persist and control ovarian cancer, melanoma, and neuroblastoma in preclinical models. The enhanced persistence of Cbx3/HP1γ-deficient CD8+ T cells facilitates remodeling of the tumor chemokine/receptor landscape ensuring their optimal invasion at the expense of CD4+ Tregs. Thus, CD8+ T cells heightened effector function consequent to Cbx3/HP1γ deficiency may be distinct from functional reactivation by ICB, implicating Cbx3/HP1γ as a viable cancer T-cell-based therapy target for ICB resistant, non-responsive solid tumors.

Short Communication: Nonprogressive HIV-1 Infection Is Associated with Expansion of IL-21R Expressing Class-Switched Memory B Cells.

HIV perturbs the functionality of B cells resulting in defective humoral responses. As efficient humoral immune responses are important in controlling HIV-disease progression, we characterized the memory B cell population for its subsets and their activation (CD38 expression) and functional [interleukin (IL)-21R expression] profile in individuals with nonprogressive [long-term nonprogressors (LTNPs), N = 16] and progressive HIV disease (progressors, N = 16) along with 10 HIV uninfected healthy controls (HCs). The frequencies of total memory B cells were similar in HCs and HIV-infected individuals, whereas the frequencies of unswitched memory B (UMB) cells and CD38+ UMB cells were significantly higher in progressors than LTNPs and HCs (p < .03). LTNPs showed higher frequencies of class-switched memory B (SMB) cells and IL-21R expressing SMB cells than seen in progressors (p = .019), which were similar to that seen in HCs. The %UMB cells correlated inversely (p = .0002, r = -0.6053) and %SMB cells correlated positively (p = .0005, r = 0.5804) with CD4 count. IL-21/IL-21R interaction is required for class switching of B cells and differentiation into antibody-secreting plasma cells. The higher expression of IL-21R on class SMB cells from LTNPs might be resulting in efficient plasma cell differentiation and the functional humoral immune response that might be responsible for mounting efficient antibody response against the encountered infections. The more insights in this area might be required to further understand the role of IL-21R expressing class SMB cells in HIV infection.

IL-21 receptor signaling is essential for control of hepatocellular carcinoma growth and immunological memory for tumor challenge.

Hepatocellular carcinoma (HCC) is a typical inflammation-associated cancer. IL-21 regulates both innate and adaptive immune responses and has key roles in antitumor and antiviral responses. However, the role of IL-21 in HCC development is poorly defined. In the current study, we explored the role of IL-21R signaling in HCC growth by using IL-21R knockout mice and HCC mouse models. We discovered that IL-21R signaling deficiency promoted HCC growth in tumor-bearing mice. We showed that IL-21R deletion reduced T cells infiltration and activation as well as their function but increased the accumulation of myeloid-derived suppressor cells in tumor tissues to enhance HCC growth. Furthermore, loss of IL-21R signaling in tumor-bearing mice resulted in an imbalance of the systemic immune system characterized by decreased antitumor immune cells and increased immunosuppressive cells in the spleen and lymph nodes. In addition, we revealed that IL-21R signaling is critical for the expansion of antitumor immune cells in the memory immune response to tumor rechallenge. Finally, we showed that the transcriptional levels of IL-21 in the peritumoral region and IL-21R within the tumor are associated with survival and recurrence of HCC patients. In conclusion, our study demonstrates that IL-21R signaling is essential for controlling the development of HCC and immunological memory response to tumor challenge.

A Critical Role for IL-21 Receptor Signaling in the Coxsackievirus B3-Induced Myocarditis.

To determine whether IL-21 receptor signaling plays a significant role in promoting Tfh cell-mediated cardiac injury in viral myocarditis (VMC), we compared IL-21R-deficient mice for some parameters of VMC. Balb/c and IL-21R-/- mice were infected with CVB3. Frequencies of splenic Tfh cells were determined by flow cytometric analysis, and productions of anti-adenine nucleotide translocator (ANT) autoantibodies were detected by enzyme-linked immunosorbent assay. To determine the effects of IL-21R signal on the proliferation of B cells, lymphocytes from spleens of the IL-21R-/- and Balb/c mice infected by CVB3 were tagged with carboxyfluorescein succinimidyl ester (CFSE) and then were stimulated with lipopolysaccharides plus IL-21 or anti-IL-21 neutralizing antibody for 3 days. The proliferation of B cells was analyzed by flow cytometry. Anti-ANT antibodies in the supernatants were detected by ELISA. Results showed that IL-21R-/- mice developed significantly less inflammation of the myocardium than Balb/c mice. Numbers of the Tfh cells and levels of anti-ANT antibody were decreased in IL-21R-/- mice, indicating IL-21 signaling plays a role on the Tfh cell response. The percentage of CD19+CFSE+ B cells decreased in IL-21R-/- mice compared to VMC mice. And anti-ANT antibodies were detected at lower levels in cultured supernatant from IL-21R-/- mice than in those from VMC mice. These data suggest that IL-21R signal may contribute to anti-ANT antibody production and expansion of B cells in VMC mice.

IL-21 Receptor Antagonist Inhibits Differentiation of B Cells toward Plasmablasts upon Alloantigen Stimulation.

Interaction between T follicular helper (Tfh) cells and B cells is complex and involves various pathways, including the production of IL-21 by the Tfh cells. Secretion of IL-21 results in B cell differentiation toward immunoglobulin-producing plasmablasts. In patients after kidney transplantation, the formation of alloantibodies produced by donor antigen-activated B cells are a major cause of organ failure. In this allogeneic response, the role of IL-21-producing Tfh cells that regulate B cell differentiation is unknown. Here, we tested, in an alloantigen-driven setting, whether Tfh cell help signals control B cell differentiation with its dependency on IL-21. Pre-transplantation patient PBMCs were sorted into pure CD4posCXCR5pos Tfh cells and CD19posCD27pos memory B cells and stimulated with donor antigen in the presence or absence of an IL-21 receptor (IL-21R) antagonist (αIL-21R). Donor antigen stimulation initiated expression of the activation markers inducible co-stimulator (ICOS) and programmed death 1 (PD-1) on Tfh cells and a shift toward a mixed Tfh2 and Tfh17 phenotype. The memory B cells underwent class switch recombination and differentiated toward IgM- and IgG-producing plasmablasts. In the presence of αIL-21R, a dose-dependent inhibition of STAT3 phosphorylation was measured in both T and B cells. Blockade of the IL-21R did not have an effect on PD-1 and ICOS expression on Tfh cells but significantly inhibited B cell differentiation. The proportion of plasmablasts decreased by 78% in the presence of αIL-21R. Moreover, secreted IgM and IgG2 levels were significantly lower in the presence of αIL-21R. In conclusion, our results demonstrate that IL-21 produced by alloantigen-activated Tfh cells controls B cell differentiation toward antibody producing plasmablasts. The IL-21R might, therefore, be a useful target in organ transplantation to prevent antigen-driven immune responses leading to graft failure.

Activation of the FcgammaReceptorIIIa on human natural killer cells leads to increased expression of functional interleukin-21 receptor.

Natural killer (NK) cells are innate immune effector cells that play a crucial role in immune surveillance and the destruction of cancer cells. NK cells express a low-affinity receptor for the Fc or constant region of immunoglobulin G (FcγRIIIa) and multiple cytokine receptors that respond to antibody-coated targets and cytokines in the tumor microenvironment. In the present work, microarray gene expression analysis revealed that the IL-21 receptor (IL-21R) was strongly upregulated following FcR stimulation. The IL-21R was found to be upregulated on FcR-stimulated NK cells at the transcript level as determined by reverse transcription polymerase chain reaction (RT-PCR). Immunoblot analysis revealed that protein expression of the IL-21R peaked at 8 h post-stimulation of the FcR. Inhibition of the mitogen-activated protein kinase (MAPK) pathway downstream of the FcR blocked the induction of IL-21R expression. Increased expression of the IL-21R sensitized NK cells to IL-21 stimulation, as treatment of FcR-stimulated NK cells led to significantly increased phosphorylation of STAT1 and STAT3, as measured by intracellular flow cytometry and immunoblot analysis. Following FcR-stimulation, IL-21-activated NK cells were better able to mediate the lysis of trastuzumab-coated human epidermal growth factor receptor 2 (HER2+) SK-BR-3 tumor cells as compared to control-treated cells. Likewise, IL-21-induced NK cell secretion of IFNγ following exposure to antibody-coated tumor cells was enhanced following FcR-stimulation. The analysis of NK cells from patients receiving trastuzumab therapy for HER2+ cancer exhibited increased levels of the IL-21R following the administration of antibody suggesting that the presence of monoclonal antibody-coated tumor cells in vivo can stimulate the increased expression of IL-21R on NK cells.

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

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

The Biological Effects of IL-21 Signaling on B-Cell-Mediated Responses in Organ Transplantation.

Antibody-mediated rejection has emerged as one of the major issues limiting the success of organ transplantation. It exerts a highly negative impact on graft function and outcome, and effective treatment is lacking. The triggers for antibody development, and the mechanisms leading to graft dysfunction and failure, are incompletely understood. The production of antibodies is dependent on instructions from various immunocytes including CD4 T-helper cells that secrete interleukin (IL)-21 and interact with antigen-specific B-cells via costimulatory molecules. In this article, we discuss the role of IL-21 in the activation and differentiation of B-cells and consider the mechanisms of IL-21 and B-cell interaction. An improved understanding of the biological mechanisms involved in antibody-mediated complications after organ transplantation could lead to the development of novel therapeutic strategies, which control humoral alloreactivity, potentially preventing and treating graft-threatening antibody-mediated rejection.

Interleukin 21 and Its Receptor Play a Role in Proliferation, Migration and Invasion of Breast Cancer Cells.

Interleukin 21 (IL21) is a cytokine produced predominantly by cluster of differentiation 4 (CD4+) T-cells and natural killer T-cells. There exists evidence that IL21 is implicated in various immunological processes through its specific receptor (IL21R). However, the participation of IL21 in the pathogenesis of solid tumors is not fully conclusive. In the present study, we demonstrated that there was differential expression of IL21R in breast cancer cells using reverse transcription-polymerase chain reaction (RT-PCR), western blotting and sequence analysis. The expression of IL21R was stronger in MDA-231 cells, weaker in MCF7 but negative in ZR-75.1 cells. The invasion and migratory capacity of IL21R+ MDA-231 cells was enhanced by IL21 in a dose-dependent manner. After IL21R was knocked-down by siRNA gene silencing, the response of MDA-231 to treatment with IL21 was attenuated. We found that siRNA silencing of IL21R also spontaneously suppressed cell proliferation. However, IL21 had no additional effect on the proliferation of MDA-231 cells. We also found that IL21R was involved in signaling pathways of matrix metalloproteinases (MMPs), that are crucial for spreading and migration of metastatic MDA231 cells. In conclusion, we unveiled the roles of IL21R in breast cancer cells, which enhances our knowledge on immunological regulation of cancer cells through the axis of IL21 and its receptor.

IL-21 as a therapeutic target in inflammatory disorders.

INTRODUCTION: IL-21, a cytokine produced by activated CD4(+) cells, activated natural killer T cells and T helper cells in the germinal centers, is involved in the control of the function of both immune and parenchymal cells. AREAS COVERED: IL-21 is overproduced in many chronic inflammatory disorders, including inflammatory bowel diseases, psoriasis, rheumatoid arthritis, type I diabetes and systemic lupus erythematosus, and studies in experimental models indicate that IL-21 plays an important role in sustaining tissue-damaging immune responses in such pathologies. However, genetic deficiency of IL-21 associates with inflammatory bowel diseases and blockade of IL-21 in the early phases exacerbates the disease progression in some models of rheumatoid arthritis and systemic lupus erythematosus, thus suggesting a dual role of IL-21 in the control of immune-mediated diseases. IL-21 can exert additional protective functions for the host as it promotes cytotoxic responses against tumors and viruses. EXPERT OPINION: We here review the available data on the role of IL-21 in chronic inflammatory diseases and discuss the therapeutic benefit of IL-21 inhibitors in such diseases as well as the potential risks of such treatments.

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

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