Interleukin-21 stimulates antigen uptake, protease activity, survival and induction of CD4+ T cell proliferation by murine macrophages

The identification and expression of an interleukin-21 receptor in large yellow croaker (Larimichthys crocea)

BACKGROUND

We identified a homologue of IL-21R (LcIL-21R) in large yellow croaker (Larimichthys crocea, Lc). Our investigation focused on understanding the molecular structural features and immune function of LcIL-21R.

METHODS

We cloned the LcIL-21R gene from the genome of Larimichthys crocea by RT‒PCR, and the molecular and structural characteristics of LcIL-21R were analyzed by a series of protein analysis tools. We used real-time PCR to investigate the tissue distribution of LcIL-21R, and LcIL-21R gene expression regulation was also measured in head kidney leukocytes under trivalent bacterial vaccine or poly (I:C) stimulation.

RESULTS

The open reading frame (ORF) of the LcIL-21R gene is 1629 bp long and encodes a precursor protein of 542 amino acids (aa), with a 23-aa signal peptide and a 519-aa mature peptide containing four putative N-glycosylation sites. LcIL-21R has two fibronectin type III (FNIII)-like domains (D1 and D2), a transmembrane domain, and a cytoplasmic region. A conserved WSXWS motif was also found in the D2 domain. The predicted structure of the extracellular region of LcIL-21R (LcIL-21R-Ex) is highly similar to that of human IL-21R. LcIL-21R was constitutively expressed in all tissues examined, and LcIL-21R mRNA levels were increased in the head kidney and spleen upon inactivated trivalent bacterial vaccine or poly(I:C) stimulation.

CONCLUSIONS

Our results suggest that LcIL-21R shares structural and functional properties with IL-21Rs found in other vertebrates, indicating its potential involvement in the IL-21-mediated immune response to pathogenic infections. These findings contribute to our understanding of the evolutionary conservation of IL-21 signaling and its role in the immune system.

The Biological Functions and Intestinal Inflammation Regulation of IL-21 in Grass Carp (Ctenopharyngodon idella) during Infection with Aeromonas hydrophila

Interleukin (IL) 21 is a pleiotropic cytokine that plays an important role in regulating innate and adaptive immune responses. In fish, the biological functions and cell source of IL-21 remain largely unknown. In this study, we performed qRT-PCR, Western blotting and immunofluorescent microscopy to examine the expression of IL-21 at the mRNA and protein levels. We found that il21 expression was induced in the primary head kidney leukocytes of grass carp (Ctenopharyngodon idella) by heat-inactivated Aeromonas hydrophila (A. hydrophila) and LPS and in tissues after infection with A. hydrophila. Recombinant IL-21 protein produced in the CHO-S cells was effective in elevating the expression of antibacterial genes, including β-defensin and lysozyme, and, interestingly, inhibited the NF-κB signaling pathway. Furthermore, we investigated the response of the IL-21 expressing cells to A. hydrophila infection. Immunofluorescent assay showed that IL-21 protein was detected in the CD3γ/δ T cells and was markedly accumulated in the anterior, middle and posterior intestine. Collectively, the results indicate that IL-21 plays an important role in regulating the intestinal inflammation induced by bacterial infection in grass carp.

IL-21 impairs pro-inflammatory activity of M1-like macrophages exerting anti-inflammatory effects on rheumatoid arthritis

Objective：Macrophages are the main source of inflammatory mediators and play important roles in the pathogenesis of rheumatoid arthritis (RA). Interleukin-21 (IL-21) regulates both innate and adaptive immune responses and exerts major effects on inflammatory responses that promote the development of RA. However, its effect on macrophage polarisation remains unclear.Methods：CD14⁺ monocytes of the peripheral blood of Human healthy donors (HD) and RA, and macrophages of RA synovial fluid (RA-SF MΦs) were isolated. IL-21 receptor (IL-21R) was detected by flow cytometry. Cytokine production by MΦs from different sources pre-treated with IL-21 and/or LPS was measured by real-time polymerase chain reaction (RT-PCR) and ELISA. CD14⁺ monocytes were differentiated into M1-like and M2-like macrophages via stimulation with GM-CSF, interferon-γ (IFN-γ), and LPS or M-CSF, IL-4, and IL-13, respectively. To determine the effect of IL-21 on macrophage polarisation, macrophage phenotypes, gene expression, and cytokine secretion were detected by flow cytometry, RT-PCR, and ELISA. TLR4 and ERK1/2 were determined by western blotting.Results：IL-21 exerted different effects on LPS-mediated inflammatory responses in various derived MΦs, and inhibited macrophages polarisation to M1-like macrophages and promote their polarisation to M2-like macrophages in HD and RA. Moreover, IL-21 inhibited LPS-mediated secretion of inflammatory cytokines, probably by downregulating the ERK1/2, in RA-SF MΦs.Conclusion：For the first time, we indicated that IL-21 inhibits LPS-mediated cytokine production in RA-SF MΦs, and impairs pro-inflammatory activity of M1-like macrophages, hereby exerting anti-inflammatory effects on RA. Thus, IL-21 might not be an appropriate therapeutic target for RA.

The Number of Donor-Specific IL-21 Producing Cells Before and After Transplantation Predicts Kidney Graft Rejection

Interleukin (IL)-21 supports induction and expansion of CD8⁺ T cells, and can also regulate the differentiation of B cells into antibody-producing plasma cells. We questioned whether the number of circulating donor-specific IL-21 producing cells (pc) can predict kidney transplant rejection, and evaluated this in two different patient cohorts. The first analysis was done on pre-transplantation samples of 35 kidney transplant recipients of whom 15 patients developed an early acute rejection. The second study concerned peripheral blood mononuclear cell (PBMC) samples from 46 patients obtained at 6 months after kidney transplantation of whom 13 developed late rejection. Significantly higher frequencies of donor-specific IL-21 pc were found by Elispot assay in both patients who developed early and late rejection compared to those without rejection. In addition, low frequencies of donor-specific IL-21 pc were associated with higher rejection-free survival. Moreover, low pre-transplant donor-specific IL-21 pc numbers were associated with the absence of anti-HLA antibodies. Donor-reactive IL-21 was mainly produced by CD4⁺ T cells, including CD4⁺ follicular T helper cells. In conclusion, the number of donor-specific IL-21 pc is associated with an increased risk of both early and late rejection, giving it the potential to be a new biomarker in kidney transplantation.

Biological activities of interleukin (IL)-21 in human monocytes and macrophages

The biological roles of interleukin (IL)-21 in human monocytes and macrophages have been neglected. We previously demonstrated that IL-21 induce phagocytosis and established that Syk is a new molecular target of IL-21. Herein, we found that IL-21 is not chemoattractant for immature THP-1 and primary monocytes but can increase the capacity of THP-1 cells (not primary monocytes) to adhere onto a cell substratum by a Syk-dependent mechanism without altering the expression of a panel of cell surface molecules. Unlike THP- 1 and monocytes, IL-21 can increase metalloproteinase (MMP)-9 secretion and activity in monocyte-derived macrophages (HMDM), as assessed by western blot and zymography experiments, respectively. We reported that IL-21 did not increase the production of IL-6 and the chemokines MIP-1α and GRO-α in HMDM. Therefore, IL-21 can increase functions other that phagocytosis, but this cytokine does not have a large spectrum of biological activities in monocytes and macrophages.

Mechanism involved in interleukin-21-induced phagocytosis in human monocytes and macrophages

The interleukin (IL)-21/IL-21 receptor (R) is a promising system to be exploited for the development of therapeutic strategies. Although the biological activities of IL-21 and its cell signalling events have been largely studied in immunocytes, its interaction with human monocytes and macrophages have been neglected. Previously, we reported that IL-21 enhances Fc gamma receptor (FcRγ)-mediated phagocytosis in human monocytes and in human monocyte-derived macrophages (HMDM) and identified Syk as a novel molecular target of IL-21. Here, we elucidate further how IL-21 promotes phagocytosis in these cells. Unlike its ability to enhance phagocytosis of opsonized sheep red blood cells (SRBCs), IL-21 did not promote phagocytosis of Escherichia coli and zymosan by monocytes and did not alter the cell surface expression of CD16, CD32 and CD64. In HMDM, IL-21 was found to enhance phagocytosis of zymosan. In addition, we found that IL-21 activates p38, protein kinase B (Akt), signal transducer and activator of transcription (STAT)-1 and STAT-3 in monocytes and HMDM. Using a pharmacological approach, we demonstrate that IL-21 enhances phagocytosis by activating some mitogen-activated protein kinases (MAPKs) and phosphoinositide 3-kinase (PI3K)-Akt and Janus kinase (JAK)-STAT pathways. These results obtained in human monocytes and macrophages have to be considered for a better exploitation of the IL-21/IL-21R system for therapeutic purposes.

CD4 T cell differentiation in type 1 diabetes

Susceptibility to type 1 diabetes is associated strongly with human leucocyte antigen (HLA) genes, implicating T cells in disease pathogenesis. In humans, CD8 T cells predominantly infiltrate the islets, yet their activation and propagation probably requires CD4 T cell help. CD4 T cells can select from several differentiation fates following activation, and this choice has profound consequences for their subsequent cytokine production and migratory potential. In turn, these features dictate which other immune cell types T cells interact with and influence, thereby determining downstream effector functions. Obtaining an accurate picture of the type of CD4 T cell differentiation associated with a particular immune-mediated disease therefore constitutes an important clue when planning intervention strategies. Early models of T cell differentiation focused on the dichotomy between T helper type 1 (Th1) and Th2 responses, with type 1 diabetes (T1D) being viewed mainly as a Th1-mediated pathology. However, several additional fate choices have emerged in recent years, including Th17 cells and follicular helper T cells. Here we revisit the issue of T cell differentiation in autoimmune diabetes, highlighting new evidence from both mouse models and patient samples. We assess the strengths and the weaknesses of the Th1 paradigm, review the data on interleukin (IL)-17 production in type 1 diabetes and discuss emerging evidence for the roles of IL-21 and follicular helper T cells in this disease setting. A better understanding of the phenotype of CD4 T cells in T1D will undoubtedly inform biomarker development, improve patient stratification and potentially reveal new targets for therapeutic intervention.

Intratumoral Delivery of IL-21 Overcomes Anti-Her2/Neu Resistance through Shifting Tumor-Associated Macrophages from M2 to M1 Phenotype

Tumor resistance is a major hurdle to anti-Her2/neu Ab-based cancer therapy. Current strategies to overcome tumor resistance focus on tumor cell-intrinsic resistance. However, the extrinsic mechanisms, especially the tumor microenvironment, also play important roles in modulating the therapeutic response and resistance of the Ab. In this study, we demonstrate that tumor progression is highly associated with TAMs with immune-suppressive M2 phenotypes, and deletion of TAMs markedly enhanced the therapeutic effects of anti-Her2/neu Ab in a HER2/neu-dependent breast cancer cell TUBO model. Tumor local delivery of IL-21 can skew TAM polarization away from the M2 phenotype to a tumor-inhibiting M1 phenotype, which rapidly stimulates T cell responses against tumor and dramatically promotes the therapeutic effect of anti-Her2 Ab. Skewing of TAM polarization by IL-21 relies substantially on direct action of IL-21 on TAMs rather than stimulation of T and NK cells. Thus, our findings identify the abundant TAMs as a major extrinsic barrier for anti-Her2/neu Ab therapy and present a novel approach to combat this extrinsic resistance by tumor local delivery of IL-21 to skew TAM polarization. This study offers a therapeutic strategy to modulate the tumor microenvironment to overcome tumor-extrinsic resistance.

Interleukin-21 and T follicular helper cells in HIV infection: research focus and future perspectives

Interleukin (IL)-21 is a member of the γ chain-receptor cytokine family along with IL-2, IL-4, IL-7, IL-9, and IL-15. The effects of IL-21 are pleiotropic, owing to the broad cellular distribution of the IL-21 receptor. IL-21 is secreted by activated CD4 T cells and natural killer T cells. Within CD4 T cells, its secretion is restricted mainly to T follicular helper (Tfh) cells and Th17 cells to a lesser extent. Our research focus has been on the role of IL-21 and more recently of Tfh in immunopathogenesis of HIV infection. This review focuses on first the influence of IL-21 in regulation of T cell, B cell, and NK cell responses and its immunotherapeutic potential in viral infections and as a vaccine adjuvant. Second, we discuss the pivotal role of Tfh in generation of antibody responses in HIV-infected persons in studies using influenza vaccines as a probe. Lastly, we review data supporting ability of HIV to infect Tfh and the role of these cells as reservoirs for HIV and their contribution to viral persistence.

IL-21 modulates release of proinflammatory cytokines in LPS-stimulated macrophages through distinct signaling pathways

The aim of this study was to investigate the anti-inflammatory effect of IL-21 on LPS-induced mouse peritoneal macrophages. The results showed that IL-21 significantly inhibited LPS-induced mRNA expression of IL-1β, TNF-α, and IL-6 in macrophages, but not of IFN-γ, IL-10, CCL5, or CXCL2. ELISA analysis showed that IL-21 also suppressed LPS-induced production of TNF-α and IL-6 in culture supernatants. Western blot analysis showed that IL-21 clearly inhibited ERK and IκBα phosphorylation and NF-κB translocation in LPS-stimulated macrophages, but it increased STAT3 phosphorylation. Flow cytometric and Western blot analysis showed that IL-21 decreased M1 macrophages surface markers expression of CD86, iNOS, and TLR4 in LPS-stimulated cells. All results suggested that IL-21 decreases IL-6 and TNF-α production via inhibiting the phosphorylation of ERK and translocation of NF-κB and promotes a shift from the M1 to M2 macrophage phenotype by decreasing the expression of CD86, iNOS, and TLR4 and by increasing STAT3 phosphorylation in LPS-stimulated cells.

Interleukin-21 receptor signalling is important for innate immune protection against HSV-2 infections

Interleukin (IL) -21 is produced by Natural Killer T (NKT) cells and CD4(+) T cells and is produced in response to virus infections, where IL-21 has been shown to be essential in adaptive immune responses. Cells from the innate immune system such as Natural Killer (NK) cells and macrophages are also important in immune protection against virus. These cells express the IL-21 receptor (IL-21R) and respond to IL-21 with increased cytotoxicity and cytokine production. Currently, however it is not known whether IL-21 plays a significant role in innate immune responses to virus infections. The purpose of this study was to investigate the role of IL-21 and IL-21R in the innate immune response to a virus infection. We used C57BL/6 wild type (WT) and IL-21R knock out (KO) mice in a murine vaginal Herpes Simplex Virus type 2 (HSV-2) infection model to show that IL-21 - IL-21R signalling is indeed important in innate immune responses against HSV-2. We found that the IL-21R was expressed in the vaginal epithelium in uninfected (u.i) WT mice, and expression increased early after HSV-2 infection. IL-21R KO mice exhibited increased vaginal viral titers on day 2 and 3 post infection (p.i.) and subsequently developed significantly higher disease scores and a lower survival rate compared to WT mice. In addition, WT mice infected with HSV-2 receiving intra-vaginal pre-treatment with murine recombinant IL-21 (mIL-21) had decreased vaginal viral titers on day 2 p.i., significantly lower disease scores, and a higher survival rate compared to infected untreated WT controls. Collectively our data demonstrate the novel finding that the IL-21R plays a critical role in regulating innate immune responses against HSV-2 infection.

The role of interleukin-21 in HIV infection

Interleukin (IL)-21 is one of a group of cytokines including IL-2, IL-4, IL-7, IL-9 and IL-15 whose receptor complexes share the common γ chain (γ(c)). Secretion of IL-21 is restricted mainly to T follicular helper (TFH) CD4 T cell subset with contributions from Th17, natural killer (NK) T cells, but the effects of IL-21 are pleiotropic, owing to the broad cellular distribution of the IL-21 receptor. The role of IL-21 in sustaining and regulating T cell, B cell and NK cell responses during chronic viral infections has recently come into focus. This chapter reviews current knowledge about the biology of IL-21 in the context of HIV infection.

Functional characterization of a nonmammalian IL-21: rainbow trout Oncorhynchus mykiss IL-21 upregulates the expression of the Th cell signature cytokines IFN-gamma, IL-10, and IL-22

In mammals, IL-21 is a common γ chain cytokine produced by activated CD4(+) T cells and NKT cells that acts on multiple lineages of cells. Although IL-21 has also been discovered in birds, amphibians, and fish, to date, no functional studies have been reported for any nonmammalian IL-21 molecule. We have sequenced an IL-21 gene (tIL-21) in rainbow trout, which has a six-exon/five-intron structure, is expressed in immune tissues, and is induced by bacterial and viral infection and the T cell stimulant PHA. In contrast to mammals, calcium ionophore and PMA act synergistically to induce tIL-21. Recombinant tIL-21 (rtIL-21) induced a rapid and long-lasting (4-72 h) induction of expression of IFN-γ, IL-10, and IL-22, signature cytokines for Th1-, Th2-, and Th17-type responses, respectively, in head kidney leukocytes. However, rtIL-21 had little effects on the expression of other cytokines studied. rtIL-21 maintained the expression of CD8α, CD8β, and IgM at a late stage of stimulation when their expression was significantly decreased in controls and increased the expression of the Th cell markers CD4, T-bet, and GATA3. Intraperitoneal injection of rtIL-21 confirmed the in vitro bioactivity and increased the expression of IFN-γ, IL-10, IL-21, IL-22, CD8, and IgM. Inhibition experiments revealed that the activation of JAK/STAT3, Akt1/2, and PI3K pathways were responsible for rtIL-21 action. This study helps to clarify the role of IL-21 in lower vertebrates for the first time, to our knowledge, and suggests IL-21 is a likely key regulator of T and B cell function in fish.

Interleukin-21: a multifunctional regulator of immunity to infections

Interleukin-21 (IL-21) is a cytokine that has broad effects on both innate and adaptive immune responses. The roles of IL-21 in determining immunity to infections are currently being defined, and notably, it has been shown that IL-21 is most critical for sustaining T cell responses during chronic viral infections. This article discusses our current understanding of the immunobiology of IL-21, as well as its known and potential roles in influencing immunity to infections.

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.

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.

IRF4 is essential for IL-21-mediated induction, amplification, and stabilization of the Th17 phenotype

Differentiation of murine T-helper (Th) 17 cells is induced by antigenic stimulation and the sequential action of the cytokines IL-6, IL-21, and IL-23, along with TGFbeta. Current dogma proposes that IL-6 induces IL-21, which, in a STAT3-dependent manner, amplifies its own transcription, contributes to IL-17 production, and, moreover, promotes the expression of the IL-23 receptor. This, in turn, prepares cells for IL-23-mediated stabilization of the Th17 phenotype. Here we demonstrate that these effects of IL-21 on Th17 differentiation are completely dependent on IFN regulatory factor 4 (IRF4). After culturing in the presence of IL-21 plus TGFbeta, IRF4-deficient (Irf4(-/-)) Th cells showed a profound intrinsic defect in IL-17 production and in the autocrine IL-21 loop. Likewise, the levels of IL-23 receptor and the lineage-specific orphan nuclear receptors RORalpha and RORgammat were diminished, whereas the T regulatory (Treg) transcription factor forkhead box P3 (Foxp3) was strongly up-regulated, consistent with the reciprocal relationship between Th17 and Treg development. Despite this loss of IL-21 functions, IL-21-induced STAT3 activation was unimpaired and induced normal Socs3 expression. Forced expression of Foxp3 in WT cells inhibited IL-21-mediated IL-17 production, suggesting that the increase in Foxp3 contributes to the Irf4(-/-) phenotype. Additionally, the low levels of RORalpha and RORgammat are also partially responsible, because simultaneous overexpression of both proteins restored IL-17 production in Irf4(-/-) cells to some extent. These data highlight IRF4 as a decisive factor during the IL-21-mediated steps of Th17 development by influencing the balance of Foxp3, RORalpha, and RORgammat.

Liver transcriptome profiles associated with strain-specific Ehrlichia chaffeensis-induced hepatitis in SCID mice

Infection of humans with Ehrlichia chaffeensis, the etiologic agent of human monocytic ehrlichiosis, can cause hepatitis of various levels of severity. When the three human isolates of E. chaffeensis, each belonging to a different genogroup, are inoculated into severe combined immunodeficiency mice, the order of severity of clinical signs and bacterial burden detected in the liver is as follows (from greatest to least severity and highest to lowest burden): strain Wakulla, followed by strain Liberty, followed by strain Arkansas. In this article, we used microarray analysis to define transcriptional profiles characteristic of the histopathological features in the mouse liver. Cytokine and chemokine profiles and their receptor profiles were strikingly different among the three strains of E. chaffeensis: gamma interferon, CCL5, CXCL1, CXCL2, CXCL7, CXCL9, interleukin 2 receptor gamma (IL2Rgamma), IL21R, CCR2, and CXCR6 were highly upregulated with strain Arkansas; and tumor necrosis factor (TNF), CCL2, CCL3, CCL5, CCL6, CCL12, CCL20, CXCL2, CXCL7, CXCL9, CXCL13, TNF receptor superfamily 9 (TNFRSF9), TNFRSF13beta, IL1R2, IL2Rgamma, IL20Rbeta, IL21R, CCR1, CCR2, and CXCR4 were highly upregulated with strain Wakulla. With strain Liberty, only CXCL13 was highly upregulated, and IL13Ralpha2 was downregulated. In livers infected with the Arkansas strain, monocytes/macrophages and NK cells were enriched in the granulomas and an increase in NK cell marker mRNAs was detected. Livers infected with the Wakulla strain displayed infiltration of significantly more neutrophils and an increase in neutrophil marker mRNAs. Genes commonly upregulated in liver tissue infected with the three strains are other host innate immune and inflammatory response genes, including those encoding several acute-phase proteins. Genes downregulated commonly are related to host physiologic functions. The results suggest that marked modulation of host cytokine and chemokine profiles by E. chaffeensis strains underlies the distinct host liver disease.