IL-21 promotes CD8+ CTL activity via the transcription factor T-bet.

CD8(+) T cells are fundamental for immune-mediated clearance of viral infections and contribute to immune pathology in autoimmune diseases such as type 1 diabetes. To execute these functions, CD8(+) T cells must differentiate into CTLs, a process that is precisely regulated by a variety of cytokines, costimulatory molecules, and transcription factors. IL-21 is an IL-2 family cytokine and a growth factor for multiple lymphocyte effector lineages, including cytotoxic CD8(+) T cells. Recent studies demonstrate that loss of IL-21 signaling results in reduced viral clearance in models of lymphocytic choriomeningitis virus infection, and also protection from type 1 diabetes in the NOD model. This is most likely the result of impaired CD8(+) CTL function in the absence of IL-21 signaling. Currently, the mechanisms by which IL-21 promotes CTL differentiation in CD8(+) T cells remain unclear, particularly the identity of the relevant transcription factor(s). We show that IL-21 promotes CTL function in vitro and killing of pancreatic islets in vivo via the use of transgenic mice expressing IL-21 in pancreatic ß cells. We demonstrate that IL-21 induces the expression of the transcription factor T-bet in CD8(+) T cells, predominantly via STAT1, and that T-bet is required for the induction of cytolytic molecules, including perforin and granzyme B in response to IL-21. Finally, we show that IL-21-induced CTL function is T-bet dependent, as T-bet deficiency results in defective IL-21-dependent cytotoxicity in CD8(+) T cells in vitro and in vivo. Thus, IL-21 drives CD8(+) CTL differentiation via the actions of the transcription factor T-bet.

The zinc finger protein ZBTB20 regulates transcription of fructose-1,6-bisphosphatase 1 and ß cell function in mice.

BACKGROUND & AIMS: Fructose-1,6-bisphosphatase (FBP)-1 is a gluconeogenic enzyme that regulates glucose metabolism and insulin secretion in ß cells, but little is known about how its transcription is controlled. The zinc finger protein ZBTB20 regulates glucose homeostasis, so we investigated its effects on expression of FBP-1. METHODS: We analyzed gene expression using real-time reverse-transcription polymerase chain reaction, immunoblotting, and immunohistochemistry. We generated mice with ß cell-specific disruption of Zbtb20 using Cre/LoxP technology. Expression of Zbtb20 in ß cells was reduced using small interfering RNAs, and promoter occupancy and transcriptional regulation were analyzed by chromatin immunoprecipitation and reporter assays. RESULTS: ZBTB20 was expressed at high levels by ß cells and other endocrine cells in islets of normal mice; expression levels were reduced in islets from diabetic db/db mice. Mice with ß cell-specific knockout of Zbtb20 had normal development of ß cells but had hyperglycemia, hypoinsulinemia, glucose intolerance, and impaired glucose-stimulated insulin secretion. Islets isolated from these mice had impaired glucose metabolism, adenosine triphosphate production, and insulin secretion after glucose stimulation in vitro, although insulin secretion returned to normal levels in the presence of KCl. ZBTB20 knockdown with small interfering RNAs impaired glucose-stimulated insulin secretion in the ß cell line MIN6. Expression of Fbp1 was up-regulated in ß cells with ZBTB20 knockout or knockdown; impairments to glucose-stimulated insulin secretion were restored by inhibition of FBPase activity. ZBTB20 was recruited to the Fbp1 promoter and repressed its transcription in ß cells. CONCLUSIONS: The transcription factor ZBTB20 regulates ß cell function and glucose homeostasis in mice. It might be a therapeutic target for type 2 diabetes mellitus.

NIP45 controls the magnitude of the type 2 T helper cell response.

Nuclear factor of activated T cell (NFAT) transcription factors are key regulators of gene transcription within immune cells. The NFAT-interacting protein, (NIP45), augments NFAT-driven IL-4 expression by a mechanism that relies on arginine methylation. To establish the function of NIP45 in vivo, we generated mice with a targeted deletion of the gene encoding this cofactor. NIP45-deficient T helper cells displayed profound defects in the expression of NFAT-regulated cytokine genes, including IL-4. Whereas NIP45 deficiency does not interfere with T helper cell NFAT activation or lineage-specific transcription-factor expression, NIP45 acts as an enhancer for the assembly of protein arginine methyltransferase 1 and the protein arginine methyltransferase 1-linked histone 4 arginine 3 methylation with the IL-4 promoter. Our study reveals an essential role for NIP45 in promoting robust cytokine expression in vivo, which is required for the efficient handling of parasites. We propose that NIP45 acts as a molecular rheostat serving to amplify the type-2 immune response.

IL-21R is essential for epicutaneous sensitization and allergic skin inflammation in humans and mice.

Atopic dermatitis (AD) is a common allergic inflammatory skin disease caused by a combination of intense pruritus, scratching, and epicutaneous (e.c.) sensitization with allergens. To explore the roles of IL-21 and IL-21 receptor (IL-21R) in AD, we examined skin lesions from patients with AD and used a mouse model of allergic skin inflammation. IL-21 and IL-21R expression was upregulated in acute skin lesions of AD patients and in mouse skin subjected to tape stripping, a surrogate for scratching. The importance of this finding was highlighted by the fact that both Il21r-/- mice and WT mice treated with soluble IL-21R-IgG2aFc fusion protein failed to develop skin inflammation after e.c. sensitization of tape-stripped skin. Adoptively transferred OVA-specific WT CD4+ T cells accumulated poorly in draining LNs (DLNs) of e.c. sensitized Il21r-/- mice. This was likely caused by both DC-intrinsic and nonintrinsic effects, because trafficking of skin DCs to DLNs was defective in Il21r-/- mice and, to a lesser extent, in WT mice reconstituted with Il21r-/- BM. More insight into this defect was provided by the observation that skin DCs from tape-stripped WT mice, but not Il21r-/- mice, upregulated CCR7 and migrated toward CCR7 ligands. Treatment of epidermal and dermal cells with IL-21 activated MMP2, which has been implicated in trafficking of skin DCs. These results suggest an important role for IL-21R in the mobilization of skin DCs to DLNs and the subsequent allergic response to e.c. introduced antigen.

PDLIM2 suppresses human T-cell leukemia virus type I Tax-mediated tumorigenesis by targeting Tax into the nuclear matrix for proteasomal degradation.

The mechanisms by which the human T-cell leukemia virus type I (HTLV-I) Tax oncoprotein deregulates cellular signaling for oncogenesis have been extensively studied, but how Tax itself is regulated remains largely unknown. Here we report that Tax was negatively regulated by PDLIM2, which promoted Tax K48-linked polyubiquitination. In addition, PDLIM2 recruited Tax from its functional sites into the nuclear matrix where the polyubiquitinated Tax was degraded by the proteasome. Consistently, PDLIM2 suppressed Tax-mediated signaling activation, cell transformation, and oncogenesis both in vitro and in animal. Notably, PDLIM2 expression was down-regulated in HTLV-I-transformed T cells, and PDLIM2 reconstitution reversed the tumorigenicity of the malignant cells. These studies indicate that the counterbalance between HTLV-I/Tax and PDLIM2 may determine the outcome of HTLV-I infection. These studies also suggest a potential therapeutic strategy for cancers and other diseases associated with HTLV-I infection and/or PDLIM2 deregulation.

Essential role of NKT cells producing IL-4 and IL-13 in the development of allergen-induced airway hyperreactivity.

Using natural killer T (NKT) cell-deficient mice, we show here that allergen-induced airway hyperreactivity (AHR), a cardinal feature of asthma, does not develop in the absence of V(alpha)14i NKT cells. The failure of NKT cell-deficient mice to develop AHR is not due to an inability of these mice to produce type 2 T-helper (Th2) responses because NKT cell-deficient mice that are immunized subcutaneously at non-mucosal sites produce normal Th2-biased responses. The failure to develop AHR can be reversed by the adoptive transfer of tetramer-purified NKT cells producing interleukin (IL)-4 and IL-13 to Ja281(-/-) mice, which lack the invariant T-cell receptor (TCR) of NKT cells, or by the administration to Cd1d(-/-) mice of recombinant IL-13, which directly affects airway smooth muscle cells. Thus, pulmonary V(alpha)14i NKT cells crucially regulate the development of asthma and Th2-biased respiratory immunity against nominal exogenous antigens. Therapies that target V(alpha)14i NKT cells may be clinically effective in limiting the development of AHR and asthma.

Zinc finger protein ZBTB20 is a key repressor of alpha-fetoprotein gene transcription in liver.

The alpha-fetoprotein (AFP) gene is highly activated in fetal liver but is dramatically repressed shortly after birth. The mechanisms that underlie AFP transcriptional repression in postpartum liver are not well understood. AFP enhancer, repressor region, and promoter are implicated to be involved in AFP postnatal repression, but the major transcriptional repressor remains undefined. We previously identified a zinc finger protein gene ZBTB20. To determine its physiological functions in vivo, we have generated hepatocyte-specific ZBTB20 knockout mice by the Cre/loxP approach and demonstrated here that ZBTB20 ablation in liver led to dramatic derepression of the AFP gene in entire liver throughout adult life, although the hepatocytes were normally under nonproliferating status. Furthermore, we found that ZBTB20 was a transcriptional repressor capable of specifically inhibiting AFP promoter-driven transcriptional activity. Liver chromatin immunoprecipitation and mobility shift assays showed that ZBTB20 bound to AFP promoter directly. ZBTB20 was developmentally activated in liver after birth and inversely correlated with its AFP gene expression, suggesting that activated ZBTB20 expression in liver mediated AFP gene repression. Our data point to ZBTB20 as a key regulator governing AFP gene transcription and postulate a new model for the postnatal gene repression of AFP in liver.

Interleukin 21 is a T helper (Th) cell 2 cytokine that specifically inhibits the differentiation of naive Th cells into interferon gamma-producing Th1 cells.

The cytokine potential of developing T helper (Th) cells is directly shaped both positively and negatively by the cytokines expressed by the effector Th cell subsets. Here we find that the recently identified cytokine, interleukin (IL)-21, is preferentially expressed by Th2 cells when compared with Th1 cells generated in vitro and in vivo. Exposure of naive Th precursors to IL-21 inhibits interferon (IFN)-gamma production from developing Th1 cells. The repression of IFN-gamma production is specific in that the expression of other Th1 and Th2 cytokines is unaffected. IL-21 decreases the IL-12 responsiveness of developing Th cells by specifically reducing both signal transducer and activator of transcription 4 protein and mRNA expression. These results suggest that Th2 cell-derived IL-21 regulates the development of IFN-gamma-producing Th1 cells which could serve to amplify a Th2 response.

Regulation and function of the interleukin 13 receptor alpha 2 during a T helper cell type 2-dominant immune response.

Highly polarized type 2 cytokine responses can be harmful and even lethal to the host if they are too vigorous or persist too long. Therefore, it is important to elucidate the mechanisms that down-regulate these reactions. Interleukin (IL)-13 has emerged as a central mediator of T helper cell (Th)2-dominant immune responses, exhibiting a diverse array of functional activities including regulation of airway hyperreactivity, resistance to nematode parasites, and tissue remodeling and fibrosis. Here, we show that IL-13 receptor (R)alpha2 is a critical down-regulatory factor of IL-13-mediated tissue fibrosis induced by the parasitic helminth Schistosoma mansoni. IL-13Ralpha2 expression was induced after the onset of the fibrotic response, IL-10, IL-13, and Stat6 dependent, and inhibited by the Th1-inducing adjuvant IL-12. Strikingly, schistosome-infected C57BL/6 and BALB/c IL-13Ralpha2-deficient mice showed a marked exacerbation in hepatic fibrosis, despite displaying no change in granuloma size, tissue eosinophilia, or mastocytosis. Fibrosis increased despite the fact that IL-13 levels decreased significantly in the liver and serum. Importantly, pathology was prevented when IL-13Ralpha2-deficient mice were treated with a soluble IL-13Ralpha2-Fc construct, formally demonstrating that their exacerbated fibrotic response was due to heightened IL-13 activity. Together, these studies illustrate the central role played by the IL-13Ralpha2 in the down-regulation of a chronic and pathogenic Th2-mediated immune response.

Enhanced interleukin (IL)-13 responses in mice lacking IL-13 receptor alpha 2.

Interleukin (IL)-13 has recently been shown to play important and unique roles in asthma, parasite immunity, and tumor recurrence. At least two distinct receptor components, IL-4 receptor (R)alpha and IL-13Ralpha1, mediate the diverse actions of IL-13. We have recently described an additional high affinity receptor for IL-13, IL-13Ralpha2, whose function in IL-13 signaling is unknown. To better appreciate the functional importance of IL-13Ralpha2, mice deficient in IL-13Ralpha2 were generated by gene targeting. Serum immunoglobulin E levels were increased in IL-13Ralpha2-/- mice despite the fact that serum IL-13 was absent and immune interferon gamma production increased compared with wild-type mice. IL-13Ralpha2-deficient mice display increased bone marrow macrophage progenitor frequency and decreased tissue macrophage nitric oxide and IL-12 production in response to lipopolysaccharide. These results are consistent with a phenotype of enhanced IL-13 responsiveness and demonstrate a role for endogenous IL-13 and IL-13Ralpha2 in regulating immune responses in wild-type mice.

The IL-21 receptor augments Th2 effector function and alternative macrophage activation.

The IL-21 receptor (IL-21R) shows significant homology with the IL-4R, and CD4+ Th2 cells are an important source of IL-21. Here we examined whether the IL-21R regulates the development of Th2 responses in vivo. To do this, we infected IL-21R-/- mice with the Th2-inducing pathogens Schistosoma mansoni and Nippostrongylus brasiliensis and examined the influence of IL-21R deficiency on the development of Th2-dependent pathology. We showed that granulomatous inflammation and liver fibrosis were significantly reduced in S. mansoni-infected IL-21R-/- mice and in IL-21R+/+ mice treated with soluble IL-21R-Fc (sIL-21R-Fc). The impaired granulomatous response was also associated with a marked reduction in Th2 cytokine expression and function, as evidenced by the attenuated IL-4, IL-13, AMCase, Ym1, and FIZZ1 (also referred to as RELMalpha) responses in the tissues. A similarly impaired Th2 response was observed following N. brasiliensis infection. In vitro, IL-21 significantly augmented IL-4Ralpha and IL-13Ralpha1 expression in macrophages, resulting in increased FIZZ1 mRNA and arginase-1 activity following stimulation with IL-4 and IL-13. As such, these data identify the IL-21R as an important amplifier of alternative macrophage activation. Collectively, these results illustrate an essential function for the IL-21R in the development of pathogen-induced Th2 responses, which may have relevance in therapies for both inflammatory and chronic fibrotic diseases.

Contribution of IL-12R mediated feedback loop to Th1 cell differentiation.

T helper 1 (Th1) cell fate is induced by overlapping signaling pathways, whose kinetic principles and regulatory motifs are largely unknown. We identified a simple positive feedback loop in the STAT4 signaling pathway, whereby activation by IL-12 leads to the increased expression in IL-12 receptor. A computational analysis shows that this feedback loop synergizes with the one mediated by the IFN-gamma secreted by differentiating cells, when the induction of Th1 cell fate is weak. Positive feedback loops are often utilized to enhance phenotypic differentiation. This effect was confirmed by experiments showing that stochastic fluctuations in the expression of IL-12 receptor gene were amplified, leading to two discrete levels of expression in a cell population.

Stat6 and IRS-2 cooperate in interleukin 4 (IL-4)-induced proliferation and differentiation but are dispensable for IL-4-dependent rescue from apoptosis.

Stat6 and IRS-2 are two important signaling proteins that associate with the cytoplasmic tail of the interleukin 4 (IL-4) receptor. Data from numerous in vitro experiments have led to a model for IL-4 signal transduction in which the Stat6 signaling pathway is responsible for the IL-4 induced changes in gene expression and differentiation events, while the IRS-2 signaling pathway provides mitogenic and antiapoptotic signals. In order to determine the relative contributions of these signaling molecules in primary lymphocytes, we have examined IL-4 responses in T cells from mice deficient for either Stat6 or IRS-2 as well as from mice doubly deficient for both genes. Both IRS-2 and, especially, Stat6 are shown to be critically involved in IL-4-induced proliferation of T cells, presumably through the cooperative regulation of the Cdk inhibitor p27kip1. Like Stat6-deficient Th cells, IRS-2-deficient cells are also compromised in their ability to secrete Th2 cytokines, revealing a previously unrecognized role for IRS-2 in Th2 cell development. Although Stat6 and/or IRS-2 expression is required for IL-4-induced proliferative and differentiative responses, both signaling proteins are dispensable for the antiapoptotic effect of IL-4. However, treatment of lymphocytes with a protein tyrosine phosphatase inhibitor is able to block the antiapoptotic effect of IL-4 specifically in Stat6- or IRS-2-deficient cells and not in wild-type cells. Our results suggest that Stat6 and IRS-2 cooperate in promoting both IL-4-induced proliferative and differentiating responses, while an additional signaling mediator that depends on protein tyrosine phosphatase activity contributes to the antiapoptotic activities of IL-4 in primary T cells.

ZBTB20 is required for anterior pituitary development and lactotrope specification.

The anterior pituitary harbours five distinct hormone-producing cell types, and their cellular differentiation is a highly regulated and coordinated process. Here we show that ZBTB20 is essential for anterior pituitary development and lactotrope specification in mice. In anterior pituitary, ZBTB20 is highly expressed by all the mature endocrine cell types, and to some less extent by somatolactotropes, the precursors of prolactin (PRL)-producing lactotropes. Disruption of Zbtb20 leads to anterior pituitary hypoplasia, hypopituitary dwarfism and a complete loss of mature lactotropes. In ZBTB20-null mice, although lactotrope lineage commitment is normally initiated, somatolactotropes exhibit profound defects in lineage specification and expansion. Furthermore, endogenous ZBTB20 protein binds to Prl promoter, and its knockdown decreases PRL expression and secretion in a lactotrope cell line MMQ. In addition, ZBTB20 overexpression enhances the transcriptional activity of Prl promoter in vitro. In conclusion, our findings point to ZBTB20 as a critical regulator of anterior pituitary development and lactotrope specification.

PDLIM2 restricts Th1 and Th17 differentiation and prevents autoimmune disease.

BACKGROUND: PDLIM2 is essential for the termination of the inflammatory transcription factors NF-κB and STAT but is dispensable for the development of immune cells and immune tissues/organs. Currently, it remains unknown whether and how PDLIM2 is involved in physiologic and pathogenic processes. RESULTS: Here we report that naive PDLIM2 deficient CD4+ T cells were prone to differentiate into Th1 and Th17 cells. PDLIM2 deficiency, however, had no obvious effect on lineage commitment towards Th2 or Treg cells. Notably, PDLIM2 deficient mice exhibited increased susceptibility to experimental autoimmune encephalitis (EAE), a Th1 and/or Th17 cell-mediated inflammatory disease model of multiple sclerosis (MS). Mechanistic studies further indicate that PDLIM2 was required for restricting expression of Th1 and Th17 cytokines, which was in accordance with the role of PDLIM2 in the termination of NF-κB and STAT activation. CONCLUSION: These findings suggest that PDLIM2 is a key modulator of T-cell-mediated immune responses that may be targeted for the therapy of human autoimmune diseases.

PDLIM2 inhibits T helper 17 cell development and granulomatous inflammation through degradation of STAT3.

Granuloma formation is an important host defense mechanism against intracellular bacteria; however, uncontrolled granulomatous inflammation is pathologic. T helper 17 (TH17) cells are thought to have a pathogenic role in autoimmune and inflammatory diseases, including in granulomas. Here, we report that the PDZ-LIM domain protein PDLIM2 inhibited TH17 cell development and granulomatous responses by acting as a nuclear ubiquitin E3 ligase that targeted signal transducer and activator of transcription 3 (STAT3), a transcription factor critical for the commitment of naïve CD4+ T cells to the TH17 lineage. PDLIM2 promoted the polyubiquitination and proteasomal degradation of STAT3, thereby disrupting STAT3-mediated gene activation. Deficiency in PDLIM2 resulted in the accumulation of STAT3 in the nucleus, enhanced the extent of TH17 cell differentiation, and exacerbated granuloma formation. This study delineates an essential role for PDLIM2 in inhibiting TH17 cell-mediated inflammatory responses by suppressing STAT3 signaling and provides a potential therapeutic target for the treatment of autoimmune diseases.

DNA methylation-dependent repression of PDZ-LIM domain-containing protein 2 in colon cancer and its role as a potential therapeutic target.

Constitutive activation of the nuclear factor-kappaB (NF-kappaB) transcription factor plays a key role in chronic colonic inflammation and colon tumorigenesis. However, the mechanisms by which the tightly regulated NF-kappaB pathway becomes constitutively activated during colonic pathogenesis remain obscure. Here, we report that PDLIM2, an essential terminator of NF-kappaB activation, is repressed in various human colorectal cancer cell lines, suggesting one important mechanism for the constitutive activation of NF-kappaB. Indeed, expression of exogenous PDLIM2 inhibited constitutive NF-kappaB activation in these colorectal cancer cells. Importantly, the PDLIM2 expression was sufficient to suppress in vitro anchorage-independent growth and in vivo tumor formation of these malignant cells. We have further shown that the PDLIM2 repression involves promoter methylation. Accordingly, treatment of the colorectal tumor cell lines with the DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine restored PDLIM2 expression and resulted in growth arrest. These studies thus provide new mechanistic insights into colon tumorigenesis by identifying a novel tumor suppressor role for PDLIM2.

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.

Identification of the small protein rich in arginine and glycine (SRAG): a newly identified nucleolar protein that can regulate cell proliferation.

The characterization of new proteins will aid in our explanation of normal biology and disease. Toward that goal, we describe the initial characterization of the small protein rich in arginine and glycine (SRAG). Human and mouse SRAG are 248/249-amino acid arginine- and glycine-rich proteins that are widely expressed in tissues and cell lines. Two SRAG isoforms, SRAG-5 and SRAG-3, which are truncations of full-length SRAG, were also identified. Although all SRAG proteins reside in the nucleus, they were also found within the nucleolus. Localization within the nucleolus was regulated by the N terminus of the protein. Our initial studies indicated that SRAG can interact with RNA. Full-length SRAG protein levels were highest in resting cells and were reduced in proliferating cells. The reduction in SRAG protein that occurs in proliferating cells was mapped with inhibitors to the G(2)/M phase of the cell cycle. As expected, the overexpression of SRAG reduced the percentage of cells in the G(2)/M phase and increased cell death. In sum, we have identified a new and intriguing member of the nucleolar proteome.

Interleukin-21 is required for the development of type 1 diabetes in NOD mice.

OBJECTIVE: Interleukin (IL)-21 is a type 1 cytokine that has been implicated in the pathogenesis of type 1 diabetes via the unique biology of the nonobese diabetic (NOD) mouse strain. The aim of this study was to investigate a causal role for IL-21 in type 1 diabetes. RESEARCH DESIGN AND METHODS: We generated IL-21R-deficient NOD mice and C57Bl/6 mice expressing IL-21 in pancreatic beta-cells, allowing the determination of the role of insufficient and excessive IL-21 signaling in type 1 diabetes. RESULTS: Deficiency in IL-21R expression renders NOD mice resistant to insulitis, production of insulin autoantibodies, and onset of type 1 diabetes. The lymphoid compartment in IL-21R-/- NOD is normal and does not contain an increased regulatory T-cell fraction or diminished effector cytokine responses. However, we observed a clear defect in autoreactive effector T-cells in IL-21R-/- NOD by transfer experiments. Conversely, overexpression of IL-21 in pancreatic beta-cells induced inflammatory cytokine and chemokines, including IL-17A, IL17F, IFN-gamma, monocyte chemoattractant protein (MCP)-1, MCP-2, and interferon-inducible protein-10 in the pancreas. The ensuing leukocytic infiltration in the islets resulted in destruction of beta-cells and spontaneous type 1 diabetes in the normally diabetes-resistant C57Bl/6 and NOD x C57Bl/6 backgrounds. CONCLUSIONS: This work provides demonstration of the essential prodiabetogenic activities of IL-21 on diverse genetic backgrounds (NOD and C57BL/6) and indicates that IL-21 blockade could be a promising strategy for interventions in human type 1 diabetes.