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 effects of interleukin-21 in the biology of transplant rejection

Interleukin-21 (IL-21) is a cytokine that plays a crucial role in regulating immune responses, affecting various immune cell types, including T cells, B cells, natural killer (NK) cells, and dendritic cells. IL-21 is primarily produced by CD4+ T cells, particularly follicular helper T (Tfh) cells and Th17 cells, and has been shown to be extensively involved in regulating both innate and adaptive immunity. IL-21 is particularly significant in the differentiation, proliferation, and effector functions of T cells and B cells. In the context of organ transplantation, IL-21 contributes to the promotion of acute transplant rejection and the development of chronic rejection, which is primarily antibody-mediated. This review summarizes relevant studies on IL-21 and discusses its multifaceted roles in transplant immune rejection, providing insights into therapeutic strategies for either inhibiting graft rejection or promoting tolerance. It also explores the feasibility of blocking the IL-21 signaling pathway within current immunosuppressive regimens, aiming to provide further clinical references.

Contribution of interleukins in the regulation of teleost fish immunity: A review from the perspective of regulating macrophages

Interleukins (ILs) are potent secreted regulators of a wide range of cell types and cellular activities, particularly in the immune system. They are able to participate in intercellular communication in homeostasis and disease, thereby exerting immune functions. Macrophages serve as the innate immune cells of vertebrates and play a pivotal role in defending against and eliminating external pathogens. In mammals, the immune response mounted by macrophages is intricately linked to ILs. Given the fact that teleost fish have evolved an innate immune system that closely resembles those of mammals, particularly in terms of the functionality of macrophages, raises the intriguing possibility that the regulatory function of ILs in macrophage-mediated immunity might be evolutionarily conserved across both mammal and teleost fish lineages. Consequently, from the perspective of interleukin regulation of macrophages, this review outlines the relationship between ILs and macrophages in teleost fish, and elucidates the regulatory role of ILs of immune cell function in teleost fish, thereby contributing to our understanding of the key role of these cytokines in the prevention and control of aquaculture diseases.

IL-21 drives skin and lung inflammation and fibrosis in a model for systemic sclerosis

BACKGROUND

Systemic sclerosis (SSc) is an autoimmune disease characterized by vasculopathy, abnormal inflammation, and fibrosis of the skin and internal organs, notably the skin and lungs, significantly impairing quality of life. There is currently no cure for SSc, and its etiology remains largely unknown, presenting a primary barrier to effective treatment. We investigated the role of interleukin-21 (IL-21) in the pathogenesis of SSc.

METHODS

We assessed the expression levels of fibrosis-related genes in human dermal fibroblasts exposed to IL-21 and TGF beta. We also induced SSc in wild-type C57BL/6 mice and IL-21 knockout (KO) mice with a C57BL/6 background using bleomycin (Bleomycin). Histological analyses were conducted on skin and lung tissues from these mice. The distribution and expression levels of fibrosis-related proteins in the tissues were examined via immunohistochemistry and quantitative real-time PCR. Furthermore, we measured the frequency of Th1, Th2, and Th17 cells among splenocytes through flow cytometry.

RESULTS

IL-21 activation led to STAT3 phosphorylation more than TGF beta in dermal fibroblasts. In IL-21 KO mice with BLM-induced SSc, skin thickness and lung fibrosis were reduced. The absence of IL-21 in these mice resulted in suppressed expression of fibrosis-related genes, including Col1a1, Col1a2, Col3a1, CTGF, α-SMA, STAT3, and TGFβ, in the skin and lungs. It also led to a decreased frequency of Th1, Th2, and Th17 cells, as well as a lower Th17/Treg ratio among splenocytes, factors known to contribute to the development of SSc.

CONCLUSIONS

IL-21 contributes to the development of SSc by promoting the expression of fibrosis-related genes and modulating the levels of CD4+ T cells.

Differentiation and Regulation of Bovine Th2 Cells In Vitro

Bovine Th2 cells have usually been characterized by IL4 mRNA expression, but it is unclear whether their IL4 protein expression corresponds to transcription. We found that grass-fed healthy beef cattle, which had been regularly exposed to parasites on the grass, had a low frequency of IL4+ Th2 cells during flow cytometry, similar to animals grown in feedlots. To assess the distribution of IL4+ CD4+ T cells across tissues, samples from the blood, spleen, abomasal (draining), and inguinal lymph nodes were examined, which revealed limited IL4 protein detection in the CD4+ T cells across the examined tissues. To determine if bovine CD4+ T cells may develop into Th2 cells, naïve cells were stimulated with anti-bovine CD3 under a Th2 differentiation kit in vitro. The cells produced primarily IFNγ proteins, with only a small fraction (<10%) co-expressing IL4 proteins. Quantitative PCR confirmed elevated IFNγ transcription but no significant change in IL4 transcription. Surprisingly, GATA3, the master regulator of IL4, was highest in naïve CD4+ T cells but was considerably reduced following differentiation. To determine if the differentiated cells were true Th2 cells, an unbiased proteomic assay was carried out. The assay identified 4212 proteins, 422 of which were differently expressed compared to those in naïve cells. Based on these differential proteins, Th2-related upstream components were predicted, including CD3, CD28, IL4, and IL33, demonstrating typical Th2 differentiation. To boost IL4 expression, T cell receptor (TCR) stimulation strength was reduced by lowering anti-CD3 concentrations. Consequently, weak TCR stimulation essentially abolished Th2 expansion and survival. In addition, extra recombinant bovine IL4 (rbIL4) was added during Th2 differentiation, but, despite enhanced expansion, the IL4 level remained unaltered. These findings suggest that, while bovine CD4+ T cells can respond to Th2 differentiation stimuli, the bovine IL4 pathway is not regulated in the same way as in mice and humans. Furthermore, Ostertagia ostertagi (OO) extract, a gastrointestinal nematode in cattle, inhibited signaling via CD3, CD28, IL4, and TLRs/MYD88, indicating that external pathogens can influence bovine Th2 differentiation. In conclusion, though bovine CD4+ T cells can respond to IL4-driven differentiation, IL4 expression is not a defining feature of differentiated bovine Th2 cells.

Enhanced attenuation of chikungunya vaccines expressing antiviral cytokines

Alphaviruses are vector-borne, medically relevant, positive-stranded RNA viruses that cause disease in animals and humans worldwide. Of this group, chikungunya virus (CHIKV) is the most significant human pathogen, responsible for generating millions of infections leading to severe febrile illness and debilitating chronic joint pain. Currently, there are limited treatments to protect against alphavirus disease; thus, there is a tremendous need to generate safe and effective vaccines. Live-attenuated vaccines (LAVs) are cost-effective and potent immunization strategies capable of generating long-term protection in a single dose. However, LAVs often produce systemic viral replication, which can lead to unwanted post-vaccination side effects and pose a risk of reversion to a pathogenic phenotype and transmission to mosquitoes. Here, we utilized a chimeric infectious clone of CHIKV engineered with the domain C of the E2 gene of Semliki Forest virus (SFV) to express IFNγ and IL-21-two potent antiviral and immunomodulatory cytokines-in order to improve the LAV's attenuation while maintaining immunogenicity. The IFNγ- and IL-21-expressing vaccine candidates were stable during passage and significantly attenuated post-vaccination, as mice experienced reduced footpad swelling with minimal systemic replication and dissemination capacity compared to the parental vaccine. Additionally, these candidates provided complete protection to mice challenged with WT CHIKV. Our dual attenuation strategy represents an innovative way to generate safe and effective alphavirus vaccines that could be applied to other viruses.

Biological effects of IL-21 on immune cells and its potential for cancer treatment

Interleukin-21 (IL-21), a member of the IL-2 cytokine family, is one of the most important effector and messenger molecules in the immune system. Produced by various immune cells, IL-21 has pleiotropic effects on innate and adaptive immune responses via regulation of natural killer, T, and B cells. An anti-tumor role of IL-21 has also been reported in the literature, as it may support cell proliferation or on the contrary induce growth arrest or apoptosis of the tumor cell. Anti-tumor effect of IL-21 enhances when combined with other agents that target tumor cells, immune regulatory circuits, or other immune-enhancing molecules. Therefore, understanding the biology of IL-21 in the tumor microenvironment (TME) and reducing its systemic toxic and side effects is crucial to ensure the maximum benefits of anti-tumor treatment strategies. In this review, we provide a comprehensive overview on the biological functions, roles in tumors, and the recent advances in preclinical and clinical research of IL-21 in tumor immunotherapy.

Single-cell multi-omics analysis of COVID-19 patients with pre-existing autoimmune diseases shows aberrant immune responses to infection

In COVID-19, hyperinflammatory and dysregulated immune responses contribute to severity. Patients with pre-existing autoimmune conditions can therefore be at increased risk of severe COVID-19 and/or associated sequelae, yet SARS-CoV-2 infection in this group has been little studied. Here, we performed single-cell analysis of peripheral blood mononuclear cells from patients with three major autoimmune diseases (rheumatoid arthritis, psoriasis, or multiple sclerosis) during SARS-CoV-2 infection. We observed compositional differences between the autoimmune disease groups coupled with altered patterns of gene expression, transcription factor activity, and cell-cell communication that substantially shape the immune response under SARS-CoV-2 infection. While enrichment of HLA-DRlow CD14+ monocytes was observed in all three autoimmune disease groups, type-I interferon signaling as well as inflammatory T cell and monocyte responses varied widely between the three groups of patients. Our results reveal disturbed immune responses to SARS-CoV-2 in patients with pre-existing autoimmunity, highlighting important considerations for disease treatment and follow-up.

Isthmin-1 attenuates allergic Asthma by stimulating adiponectin expression and alveolar macrophage efferocytosis in mice

BACKGROUND

Allergic asthma is a common respiratory disease that significantly impacts human health. Through in silico analysis of human lung RNASeq, we found that asthmatic lungs display lower levels of Isthmin-1 (ISM1) expression than healthy lungs. ISM1 is an endogenous anti-inflammatory protein that is highly expressed in mouse lungs and bronchial epithelial cells, playing a crucial role in maintaining lung homeostasis. However, how ISM1 influences asthma remains unclear. This study aims to investigate the potential involvement of ISM1 in allergic airway inflammation and uncover the underlying mechanisms.

METHODS

We investigated the pivotal role of ISM1 in airway inflammation using an ISM1 knockout mouse line (ISM1-/-) and challenged them with house dust mite (HDM) extract to induce allergic-like airway/lung inflammation. To examine the impact of ISM1 deficiency, we analyzed the infiltration of immune cells into the lungs and cytokine levels in bronchoalveolar lavage fluid (BALF) using flow cytometry and multiplex ELISA, respectively. Furthermore, we examined the therapeutic potential of ISM1 by administering recombinant ISM1 (rISM1) via the intratracheal route to rescue the effects of ISM1 reduction in HDM-challenged mice. RNA-Seq, western blot, and fluorescence microscopy techniques were subsequently used to elucidate the underlying mechanisms.

RESULTS

ISM1-/- mice showed a pronounced worsening of allergic airway inflammation and hyperresponsiveness upon HDM challenge. The heightened inflammation in ISM1-/- mice correlated with enhanced lung cell necroptosis, as indicated by higher pMLKL expression. Intratracheal delivery of rISM1 significantly reduced the number of eosinophils in BALF and goblet cell hyperplasia. Mechanistically, ISM1 stimulates adiponectin secretion by type 2 alveolar epithelial cells partially through the GRP78 receptor and enhances adiponectin-facilitated apoptotic cell clearance via alveolar macrophage efferocytosis. Reduced adiponectin expression under ISM1 deficiency also contributed to intensified necroptosis, prolonged inflammation, and heightened severity of airway hyperresponsiveness.

CONCLUSIONS

This study revealed for the first time that ISM1 functions to restrain airway hyperresponsiveness to HDM-triggered allergic-like airway/lung inflammation in mice, consistent with its persistent downregulation in human asthma. Direct administration of rISM1 into the airway alleviates airway inflammation and promotes immune cell clearance, likely by stimulating airway adiponectin production. These findings suggest that ISM1 has therapeutic potential for allergic asthma.

Release from persistent T cell receptor engagement and blockade of aryl hydrocarbon receptor activity enhance IL-6-dependent mouse follicular helper T-like cell differentiation in vitro

Follicular helper T (Tfh) cells are crucial for humoral immunity. Dysregulation of Tfh cell differentiation can cause infectious, allergic, and autoimmune diseases. To elucidate the molecular mechanisms underlying Tfh cell differentiation, we attempted to establish an in vitro mouse model of Tfh cell differentiation in the absence of other cell types. Various cytokines and cell surface molecules are suggested to contribute to the differentiation. We found that stimulating naïve CD4+ T cells with immobilized antibodies to CD3, ICOS, and LFA-1 in the presence of soluble anti-CD28 antibody, IL-6, and antibodies that block IL-2 signaling for 3 days induced the expression of Bcl6 and Rorc(γt), master regulator genes of Tfh and Th17 cells, respectively. TGF-β significantly enhanced cell proliferation and Bcl6 and Rorc(γt) expression. An additional 2 days of culture without immobilized antibodies selectively downregulated Rorc(γt) expression. These cells produced IL-21 and promoted B cells to produce IgG antibodies. Adding the aryl hydrocarbon receptor (AhR) antagonist CH-223191 to the T cell culture further downregulated Rorc(γt) expression without significantly affecting Bcl6 expression, and upregulated expression of a key Tfh marker, CXCR5. Although their CXCR5 expression levels were still not high, the CH-223191-treated cells showed chemotactic activity towards the CXCR5 ligand CXCL13. On the other hand, AhR agonists upregulated Rorc(γt) expression and downregulated CXCR5 expression. These findings suggest that AhR activity and the duration of T cell receptor stimulation contribute to regulating the balance between Tfh and Th17 cell differentiation. Although this in vitro system needs to be further improved, it may be useful for elucidating the mechanisms of Tfh cell differentiation as well as for screening physiological or pharmacological factors that affect Tfh cell differentiation including CXCR5 expression.

Heterogeneity of Islet-Infiltrating IL-21+ CD4 T Cells in a Mouse Model of Type 1 Diabetes

IL-21 is essential for type 1 diabetes (T1D) development in the NOD mouse model. IL-21-expressing CD4 T cells are present in pancreatic islets where they contribute to T1D progression. However, little is known about their phenotype and differentiation states. To fill this gap, we generated, to our knowledge, a novel IL-21 reporter NOD strain to further characterize IL-21+ CD4 T cells in T1D. IL-21+ CD4 T cells accumulate in pancreatic islets and recognize β cell Ags. Single-cell RNA sequencing revealed that CD4 T effector cells in islets actively express IL-21 and they are highly diabetogenic despite expressing multiple inhibitory molecules, including PD-1 and LAG3. Islet IL-21+ CD4 T cells segregate into four phenotypically and transcriptionally distinct differentiation states, that is, less differentiated early effectors, T follicular helper (Tfh)-like cells, and two Th1 subsets. Trajectory analysis predicts that early effectors differentiate into both Tfh-like and terminal Th1 cells. We further demonstrated that intrinsic IL-27 signaling controls the differentiation of islet IL-21+ CD4 T cells, contributing to their helper function. Collectively, our study reveals the heterogeneity of islet-infiltrating IL-21+ CD4 T cells and indicates that both Tfh-like and Th1 subsets produce IL-21 throughout their differentiation process, highlighting the important sources of IL-21 in T1D pathogenesis.

Early Phase Increase in Serum TIMP-1 in Patients with Acute Encephalopathy with Biphasic Seizures and Late Reduced Diffusion

BACKGROUND

Acute encephalopathy with biphasic seizures and late reduced diffusion (AESD) is the most frequent subtype of acute encephalopathy syndrome among Japanese children. Exanthem subitum is the most common causative infectious disease of AESD. We herein retrospectively analyzed serum and cerebrospinal fluid (CSF) concentrations of matrix metalloproteinase-9 (MMP-9), tissue inhibitor matrix metalloproteinase-1 (TIMP-1), and seven cytokines in patients with AESD or prolonged febrile seizure (FS) to assess the pathophysiology of AESD and detect biomarkers for diagnosing AESD in the early phase.

METHODS

Serum and CSF samples were obtained from 17 patients with AESD (1st seizure phase group, n = 7; 2nd seizure phase group, n = 10) and 8 with FS. The concentrations of MMP-9, TIMP-1, and seven cytokines were measured by enzyme-linked immunosorbent assays or cytometric bead arrays.

RESULTS

Serum concentrations of TIMP-1 were significantly higher in the 1st seizure phase group than in the 2nd seizure phase group. No significant differences were observed in serum concentrations of MMP-9 or the MMP-9/TIMP-1 ratio.

CONCLUSIONS

The MMP-9-independent increase in circulating TIMP-1 concentrations observed in the present study may be associated with the pathophysiology of AESD in the 1st seizure phase.

Enhancement of intestinal mucosal immunity and immune response to the foot-and-mouth disease vaccine by oral administration of danggui buxue decoction

This study investigated the effect of Danggui Buxue decoction (DBD) on the immunity of an O-type foot-and-mouth disease (FMD) vaccine and intestinal mucosal immunity. SPF KM mice were continuously and orally administered DBD for 5 d and then inoculated with an O-type FMD vaccine. The contents of a specific IgG antibody and its isotypes IgG1, IgG2a, IgG2b, and IgG3 in serum and SIgA in duodenal mucosa were determined by ELISA at 1 and 3 W after the 2^nd immunization. qRT-PCR was used to detect mRNA expression levels of IL-4, IL-10, IFN-γ, and IL-33 in the spleen, and mRNA expression levels of J-chain, pIgR, BAFF, APRIL, IL-10, IFN-γ and IL-33 in the duodenum. The results showed that compared with the control group, oral administration of DBD significantly increased levels of the anti-FMD virus (FMDV)-specific antibodies IgG, IgG1, and IgG2a in the serum of O-type FMD vaccine-immunized mice 1 W after the 2^nd immunization (P < 0.05), upregulated mRNA expression levels of spleen lymphocyte cytokines IL-4 and IL-33 (P < 0.05), promoted the secretion of SIgA in duodenal mucosa (P < 0.05). The mRNA expression levels of J-chain, pIgR, BAFF, APRIL, IL-10, and IL-33 in duodenal tissues were upregulated (P < 0.05). This study indicates that DBD has a good promotion effect on the O-type FMD vaccine and the potential to be an oral immune booster.

The Role of T Cells in Systemic Sclerosis: An Update

Systemic sclerosis (SSc) is a chronic disease characterized by microvasculopathy, autoantibodies (autoAbs), and fibrosis. The pathogenesis of the disease is incompletely understood. Microvasculopathy and autoAbs appear very early in the disease process. AutoAbs, such as those directed against DNA topoisomerase I (Topo I), are disease specific and associated with disease manifestations, and indicate activation of the adaptive immune system. B cells are involved in fibrosis in SSc. T cells are also involved in disease pathogenesis. T cells show signs of antigen-induced activation; T cells of TH2 type are increased and produce profibrotic cytokines interleukin (IL)-4, IL-13, and IL-31; CD4+ cytotoxic T lymphocytes are increased in skin lesions, and cause fibrosis and endothelial cell apoptosis; circulating T follicular helper (TFH) cells are increased in SSc produce IL-21 and promote plasmablast antibody production. On the other hand, regulatory T cells are impaired in SSc. These findings provide strong circumstantial evidence for T cell implication in SSc pathogenesis and encourage new T cell-directed therapeutic strategies for the disease.

T Cell Roles and Activity in Chronic Sclerosing Sialadenitis as IgG4-Related Disease: Current Concepts in Immunopathogenesis

IgG4-related disease is a multiorgan immunological fibroinflammatory disorder characterized by lymphoplasmacytic infiltration and fibrosis in multiple organs accompanied by high serum IgG4 levels. The salivary glands are the most common organs involved in this disease. Recently, chronic sclerosing sialadenitis affecting salivary glands, formerly known as Küttner's tumor, and Mikulicz's disease have been classified as a class of IgG4-related diseases. The etiopathobiology of IgG4-related disease is not fully understood. It has recently been hypothesized that the inflammatory and fibrotic process and the increased serum IgG4⁺ levels in IgG4-related disease are the result of an interaction between B cells and T helper cells, suggesting that T cells may play a key role in the pathogenesis of this disease. The aim of this review is to discuss the proposed roles of different T cell subsets in the pathogenesis of IgG4-related disease focusing on their roles in immunopathogenesis of IgG4-related sialadenitis.

Reprogramming the tumor microenvironment by genome editing for precision cancer therapy

The tumor microenvironment (TME) is essential for immune escape by tumor cells. It plays essential roles in tumor development and metastasis. The clinical outcomes of tumors are often closely related to individual differences in the patient TME. Therefore, reprogramming TME cells and their intercellular communication is an attractive and promising strategy for cancer therapy. TME cells consist of immune and nonimmune cells. These cells need to be manipulated precisely and safely to improve cancer therapy. Furthermore, it is encouraging that this field has rapidly developed in recent years with the advent and development of gene editing technologies. In this review, we briefly introduce gene editing technologies and systematically summarize their applications in the TME for precision cancer therapy, including the reprogramming of TME cells and their intercellular communication. TME cell reprogramming can regulate cell differentiation, proliferation, and function. Moreover, reprogramming the intercellular communication of TME cells can optimize immune infiltration and the specific recognition of tumor cells by immune cells. Thus, gene editing will pave the way for further breakthroughs in precision cancer therapy.

From inflammatory bowel disease to colorectal cancer: what's the role of miRNAs?

Inflammatory Bowel Disease (IBD) is a chronic inflammatory disease with relapse and remission periods. Ulcerative colitis and Crohn's disease are two major forms of the disease. IBD imposes a lot of sufferings on the patient and has many consequences; however, the most important is the increased risk of colorectal cancer, especially in patients with Ulcerative colitis. This risk is increased with increasing the duration of disease, thus preventing the progression of IBD to cancer is very important. Therefore, it is necessary to know the details of events contributed to the progression of IBD to cancer. In recent years, the importance of miRNAs as small molecules with 20-22 nucleotides has been recognized in pathophysiology of many diseases, in which IBD and colorectal cancer have not been excluded. As a result, the effectiveness of these small molecules as therapeutic target is hopefully confirmed. This paper has reviewed the related studies and findings about the role of miRNAs in the course of events that promote the progression of IBD to colorectal carcinoma, as well as a review about the effectiveness of some of these miRNAs as therapeutic targets.

Characterization of snakehead (Channa argus) interleukin-21: Involvement in immune defense against two pathogenic bacteria, in leukocyte proliferation, and in activation of JAK-STAT signaling pathway

Interleukin-21 (IL-21), a crucial immune regulatory molecule, belongs to the common γ-chain family of type I cytokines, and exerts pleiotropic effects on multiple immune cell types in mammals. However, the characteristics and functions of fish IL-21 remain unclear. To further investigate the molecular mechanism of IL-21 in teleosts, we first cloned and identified the IL-21 gene (designated shIL-21) of the snakehead (Channa argus). The full-length open reading frame of shIL-21 is 438 bp in length, and encodes a predicted protein of 145 amino acid residues. A sequence analysis showed that shIL-21 has the typical structural characteristics of other IL-21 proteins, containing four α-helices and four conserved cysteine residues. In a phylogenetic analysis, shIL-21 clustered within a subgroup of IL-21 proteins from other teleost species and shared its closest evolutionary relationship with that of Lates calcarifer. The expression analysis showed that shIL-21 was ubiquitously expressed in all the healthy snakehead tissues tested, albeit at different levels. After infection with Nocardia seriolae or Aeromonas schubertii, the relative expression of shIL-21 was mainly upregulated in the head kidney and spleen in vivo. Similarly, after stimulation with the three pathogen analogues lipoteichoic acid, lipopolysaccharides, and polyinosinic-polycytidylic acid, the expression of shIL-21 was also induced in head kidney leukocytes in vitro. A recombinant shIL-21 protein was expressed and purified, and promoted the proliferation of head kidney leukocytes, induced the expression of genes encoding critical signaling molecules in the Janus kinase (JAK) and signal transducer and activator of transcription (STAT) pathway, including JAK1, JAK3, STAT1, and STAT3, and induced the expression of endogenous shIL-21 and genes encoding several key proinflammatory cytokines (tumor necrosis factor-α, interferon-γ, and IL-1β). Taken together, these preliminary findings suggest that shIL-21 is involved in the immune defense against bacterial infection, in leukocyte proliferation, and in the activation of the JAK-STAT pathway. They thus extend the functional studies of IL-21 in teleosts.

High-dimensional analysis defines multicytokine T-cell subsets and supports a role for IL-21 in atopic dermatitis

BACKGROUND

Flow cytometry is a well-accepted approach for immune profiling; however, its value is restricted by the limited number of markers that can be analyzed simultaneously. Mass cytometry/CyTOF offers broad-scale immune characterization integrating large number of parameters. While partial blood phenotyping was reported in atopic dermatitis (AD), patients' comprehensive profiling, critical for leveraging new targeted treatments, is not available. IL-21 may be involved in inflammatory skin diseases but its role in AD is not well established.

METHODS

We studied T-cell polarization in the blood of 20 moderate-to-severe AD and 15 controls. Using CyTOF and an unsupervised analysis, we measured the frequencies and mean metal intensities of activated polar CD4⁺ /CD8⁺ T-cell subsets. Immunohistochemistry, immunofluorescence, and qRT-PCR were used to analyze skin samples.

RESULTS

Examining 24 surface, intracellular markers, and transcription factors, we identified six CD4⁺ and five CD8⁺ T-cell metaclusters. A CD4⁺ skin-homing IL-13⁺ monocytokine and a novel IL-13⁺ IL-21⁺ multicytokine metaclusters were increased in AD vs. controls (p < .01). While IL-13 signature characterized both clusters, levels were significantly higher in the IL-21⁺ group. Both clusters correlated with AD severity (r = 0.49, p = .029). Manual gating corroborated these results and identified additional multicytokine subsets in AD. Immunohistochemistry and immunofluorescence, validated by mRNA expression, displayed significantly increasedIL-21 counts and colocalization with IL-13/IL-4R in AD skin.

CONCLUSION

A multicytokine signature characterizes moderate-to-severe AD, possibly explaining partial therapeutic responses to one cytokine targeting, particularly in severe patients. Prominent IL-21 signature in blood and skin hints for a potential pathogenic role of IL-21 in AD.

Th17-Related Cytokines as Potential Discriminatory Markers between Neuromyelitis Optica (Devic's Disease) and Multiple Sclerosis-A Review

Multiple sclerosis (MS) and Devic’s disease (NMO; neuromyelitis optica) are autoimmune, inflammatory diseases of the central nervous system (CNS), the etiology of which remains unclear. It is a serious limitation in the treatment of these diseases. The resemblance of the clinical pictures of these two conditions generates a partial possibility of introducing similar treatment, but on the other hand, a high risk of misdiagnosis. Therefore, a better understanding and comparative characterization of the immunopathogenic mechanisms of each of these diseases are essential to improve their discriminatory diagnosis and more effective treatment. In this review, special attention is given to Th17 cells and Th17-related cytokines in the context of their potential usefulness as discriminatory markers for MS and NMO. The discussed results emphasize the role of Th17 immune response in both MS and NMO pathogenesis, which, however, cannot be considered without taking into account the broader perspective of immune response mechanisms.

IL-21/IL-21R Signaling Aggravated Respiratory Inflammation Induced by Intracellular Bacteria through Regulation of CD4+ T Cell Subset Responses

The IL-21/IL-21R interaction plays an important role in a variety of immune diseases; however, the roles and mechanisms in intracellular bacterial infection are not fully understood. In this study, we explored the effect of IL-21/IL-21R on chlamydial respiratory tract infection using a chlamydial respiratory infection model. The results showed that the mRNA expression of IL-21 and IL-21R was increased in Chlamydia muridarum-infected mice, which suggested that IL-21 and IL-21R were involved in host defense against C. muridarum lung infection. IL-21R^-/- mice exhibited less body weight loss, a lower bacterial burden, and milder pathological changes in the lungs than wild-type (WT) mice during C. muridarum lung infection. The absolute number and activity of CD4⁺ T cells and the strength of Th1/Th17 responses in IL-21R^-/- mice were significantly higher than those in WT mice after C. muridarum lung infection, but the Th2 response was weaker. Consistently, IL-21R^-/- mice showed higher mRNA expression of Th1 transcription factors (T-bet/STAT4), IL-12p40, a Th17 transcription factor (STAT3), and IL-23. The mRNA expression of Th2 transcription factors (GATA3/STAT6), IL-4, IL-10, and TGF-β in IL-21R^-/- mice was significantly lower than that in WT mice. Furthermore, the administration of recombinant mouse IL-21 aggravated chlamydial lung infection in C57BL/6 mice and reduced Th1 and Th17 responses following C. muridarum lung infection. These findings demonstrate that IL-21/IL-21R may aggravate chlamydial lung infection by inhibiting Th1 and Th17 responses.

The effect of inflammatory factors and their inhibitors on the hematopoietic stem cells fate

Inflammatory cytokines exert different effects on hematopoietic stem cells (HSCs), lead to the development of various cell lineages in bone marrow (BM) and are thus a differentiation axis for HSCs. The content used in this article has been obtained by searching PubMed database and Google Scholar search engine of English-language articles (1995-2020) using "Hematopoietic stem cell," "Inflammatory cytokine," "Homeostasis," and "Myelopoiesis." Inflammatory cytokines are involved in the differentiation and proliferation of hematopoietic progenitors to compensate for cellular death due to inflammation. Since each of these cytokines differentiates HSCs into a specific cell line, the difference in the effect of these cytokines on the fate of HSC progenitors can be predicted. Inhibitors of these cytokines can also control the inflammatory process as well as the cells involved in leukemic conditions. In general, inflammatory signaling can specify the dominant cell line in BM to counteract inflammation and leukemic condition via stimulating or inhibiting hematopoietic progenitors. Therefore, detection of the effects of inflammatory cytokines on the differentiation of HSCs can be an appropriate approach to check inflammatory and leukemic conditions and the suppression of these cytokines by their inhibitors allows for control of homeostasis in stressful conditions.

Splicing variants of grass carp (Ctenopharyngodon idellus) IL-21: Functions in IgM+ B cell proliferation and IgM secretion

In mammals, interleukin 21 (IL-21) is a type I four-helical bundle cytokine produced by activated T cells that has pleiotropic functions on immune cells. Although IL-21 has been discovered in fish, the splicing variants of this cytokine and their functions on B cells are unclear. In this study, based on the original transcript of grass carp IL-21 (named gcIL-21sv1 in this study), two alternative splicing variants, named gcIL-21sv2 and gcIL-21sv3, were cloned and characterized. The protein sequences of gcIL-21sv1 and gcIL-21sv2 consist of four α-helixes, and only the six amino acid residues at the C-terminal are different. Unlike gcIL-21sv1 and gcIL-21sv2, gcIL-21sv3 lacks the C-terminal region. The expression analysis showed that gcIL-21sv1, gcIL-21sv2, and gcIL-21sv3 were constitutively expressed in all the tested tissues, and their expression could be significantly up-regulated by LPS and Poly (I:C) in head kidney leukocytes (HKLs), with the fold change of gcIL-21sv1 being higher than that of gcIL-21sv2 and gcIL-21sv3. Recombinant gcIL-21sv1 and gcIL-21sv2, but not gcIL-21sv3, could induce the proliferation of IgM⁺ B cells and the secretion of IgM, with the activity of gcIL-21sv1 being stronger than that of gcIL-21sv2, indicating that the C-terminal region plays important roles in the function of gcIL-21. Taken together, this study found that, like IL-21 in human and mouse, IL-21 splicing variants also exist in fish, and the regulatory activities of these variants in humoral immunity are differ, suggesting that grass carp may balance the immune response mediated by IL-21 through alternative splicing.

The Cellular and Molecular Bases of Allergy, Inflammation and Tissue Fibrosis in Patients with IgG4-related Disease

IgG4-related disease (IgG4-RD) is a spectrum of complex fibroinflammatory disorder with protean manifestations mimicking malignant neoplasms, infectious or non-infectious inflammatory process. The histopathologic features of IgG4-RD include lymphoplasmacytic infiltration, storiform fibrosis and obliterative phlebitis together with increased in situ infiltration of IgG4 bearing-plasma cells which account for more than 40% of all IgG-producing B cells. IgG4-RD can also be diagnosed based on an elevated serum IgG4 level of more than 110 mg/dL (normal < 86.5 mg/mL in adult) in conjunction with protean clinical manifestations in various organs such as pancreato–hepatobiliary inflammation with/without salivary/lacrimal gland enlargement. In the present review, we briefly discuss the role of genetic predisposition, environmental factors and candidate autoantibodies in the pathogenesis of IgG4-RD. Then, we discuss in detail the immunological paradox of IgG4 antibody, the mechanism of modified Th2 response for IgG4 rather than IgE antibody production and the controversial issues in the allergic reactions of IgG4-RD. Finally, we extensively review the implications of different immune-related cells, cytokines/chemokines/growth factors and Toll-like as well as NOD-like receptors in the pathogenesis of tissue fibro-inflammatory reactions. Our proposals for the future investigations and prospective therapeutic strategies for IgG4-RD are shown in the last part.

CD2 Immunobiology

The glycoprotein CD2 is a costimulatory receptor expressed mainly on T and NK cells that binds to LFA3, a cell surface protein expressed on e.g., antigen-presenting cells. CD2 has an important role in the formation and organization of the immunological synapse that is formed between T cells and antigen-presenting cells upon cell-cell conjugation and associated intracellular signaling. CD2 expression is upregulated on memory T cells as well as activated T cells and plays an important role in activation of memory T cells despite the coexistence of several other costimulatory pathways. Anti-CD2 monoclonal antibodies have been shown to induce immune modulatory effects in vitro and clinical studies have proven the safety and efficacy of CD2-targeting biologics. Investigators have highlighted that the lack of attention to the CD2/LFA3 costimulatory pathway is a missed opportunity. Overall, CD2 is an attractive target for monoclonal antibodies intended for treatment of pathologies characterized by undesired T cell activation and offers an avenue to more selectively target memory T cells while favoring immune regulation.

Identification of a super-functional Tfh-like subpopulation in murine lupus by pattern perception

Dysregulated cytokine expression by T cells plays a pivotal role in the pathogenesis of autoimmune diseases. However, the identification of the corresponding pathogenic subpopulations is a challenge, since a distinction between physiological variation and a new quality in the expression of protein markers requires combinatorial evaluation. Here, we were able to identify a super-functional follicular helper T cell (Tfh)-like subpopulation in lupus-prone NZBxW mice with our binning approach "pattern recognition of immune cells (PRI)". PRI uncovered a subpopulation of IL-21⁺ IFN-γ^high PD-1^low CD40L^high CXCR5^- Bcl-6^- T cells specifically expanded in diseased mice. In addition, these cells express high levels of TNF-α and IL-2, and provide B cell help for IgG production in an IL-21 and CD40L dependent manner. This super-functional T cell subset might be a superior driver of autoimmune processes due to a polyfunctional and high cytokine expression combined with Tfh-like properties.

Treg Heterogeneity, Function, and Homeostasis

T-regulatory cells (Tregs) represent a unique subpopulation of helper T-cells by maintaining immune equilibrium using various mechanisms. The role of T-cell receptors (TCR) in providing homeostasis and activation of conventional T-cells is well-known; however, for Tregs, this area is understudied. In the last two decades, evidence has accumulated to confirm the importance of the TCR in Treg homeostasis and antigen-specific immune response regulation. In this review, we describe the current view of Treg subset heterogeneity, homeostasis and function in the context of TCR involvement. Recent studies of the TCR repertoire of Tregs, combined with single-cell gene expression analysis, revealed the importance of TCR specificity in shaping Treg phenotype diversity, their functions and homeostatic maintenance in various tissues. We propose that Tregs, like conventional T-helper cells, act to a great extent in an antigen-specific manner, which is provided by a specific distribution of Tregs in niches.

Highly Selective Cleavage of TH2-Promoting Cytokines by the Human and the Mouse Mast Cell Tryptases, Indicating a Potent Negative Feedback Loop on TH2 Immunity

Mast cells (MC) are resident tissue cells found primarily at the interphase between tissues and the environment. These evolutionary old cells store large amounts of proteases within cytoplasmic granules, and one of the most abundant of these proteases is tryptase. To look deeper into the question of their in vivo targets, we have analyzed the activity of the human MC tryptase on 69 different human cytokines and chemokines, and the activity of the mouse tryptase (mMCP-6) on 56 mouse cytokines and chemokines. These enzymes were found to be remarkably restrictive in their cleavage of these potential targets. Only five were efficiently cleaved by the human tryptase: TSLP, IL-21, MCP3, MIP-3b, and eotaxin. This strict specificity indicates a regulatory function of these proteases and not primarily as unspecific degrading enzymes. We recently showed that the human MC chymase also had a relatively strict specificity, indicating that both of these proteases have regulatory functions. One of the most interesting regulatory functions may involve controlling excessive TH2-mediated inflammation by cleaving several of the most important TH2-promoting inflammatory cytokines, including IL-18, IL-33, TSLP, IL-15, and IL-21, indicating a potent negative feedback loop on TH2 immunity.

Interleukin 21 Receptor/Ligand Interaction Is Linked to Disease Progression in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) displays a marked fibro-inflammatory microenvironment in which infiltrated immune cells fail to eliminate the tumor cells and often—rather paradoxically—promote tumor progression. Of special interest are tumor-promoting T cells that assume a Th17-like phenotype because their presence in PDAC tissue is associated with a poor prognosis. In that context, the role of IL-21, a major cytokine released by Th17-like cells, was assessed. In all tissue samples (n = 264) IL-21⁺ immune cells were detected by immunohistochemistry and high density of those cells was associated with poor prognosis. In the majority of patients (221/264), tumor cells expressed the receptor for IL-21 (IL-21R) and also a downstream target of IL-21, Blimp-1 (199/264). Blimp-1 expression closely correlated with IL-21R expression and multivariate analysis revealed that expression of both IL-21R and Blimp-1 was associated with shorter survival time of the patients. In vitro data using pancreatic tumor cells lines provided a possible explanation: IL-21 activated ERK and STAT3 pathways and upregulated Blimp-1. Moreover, IL-21 increased invasion of tumor cell lines in a Blimp-1-dependent manner. As an in vivo correlate, an avian xenograft model was used. Here again Blimp-1 expression was significantly upregulated in IL-21 stimulated tumor cells. In summary, our data showed an association of IL-21⁺ immune cell infiltration and IL-21 receptor expression in PDAC with poor survival, most likely due to an IL-21-mediated promotion of tumor cell invasion and enhanced colony formation, supporting the notion of the tumor-promoting abilities of the tumor microenvironment.

Gene expression profile of human T cells following a single stimulation of peripheral blood mononuclear cells with anti-CD3 antibodies

Background

Anti-CD3 immunotherapy was initially approved for clinical use for renal transplantation rejection prevention. Subsequently, new generations of anti-CD3 antibodies have entered clinical trials for a broader spectrum of therapeutic applications, including cancer and autoimmune diseases. Despite their extensive use, little is known about the exact mechanism of these molecules, except that they are able to activate T cells, inducing an overall immunoregulatory and tolerogenic behavior. To better understand the effects of anti-CD3 antibodies on human T cells, PBMCs were stimulated, and then, we performed RNA-seq assays of enriched T cells to assess changes in their gene expression profiles. In this study, three different anti-CD3 antibodies were used for the stimulation: two recombinant antibody fragments, namely, a humanized and a chimeric FvFc molecule, and the prototype mouse mAb OKT3.

Results

Gene Ontology categories and individual immunoregulatory markers were compared, suggesting a similarity in modulated gene sets, mainly those for immunoregulatory and inflammatory terms. Upregulation of interleukin receptors, such as IL2RA, IL1R, IL12RB2, IL18R1, IL21R and IL23R, and of inhibitory molecules, such as FOXP3, CTLA4, TNFRSF18, LAG3 and PDCD1, were also observed, suggesting an inhibitory and exhausted phenotype.

Conclusions

We used a deep transcriptome sequencing method for comparing three anti-CD3 antibodies in terms of Gene Ontology enrichment and immunological marker expression. The present data showed that both recombinant antibodies induced a compatible expression profile, suggesting that they might be candidates for a closer evaluation with respect to their therapeutic value. Moreover, the proposed methodology is amenable to be more generally applied for molecular comparison of cell receptor dependent antibody therapy.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5967-8) contains supplementary material, which is available to authorized users.

Clinical significance and immunobiology of IL-21 in autoimmunity

Interleukin-21 (IL-21), an autocrine cytokine predominantly produced by follicular helper T (Tfh) and T helper 17 (Th17) cells, has been proven to play an important role in the immune system, for example, by promoting proliferation and the development of Tfh and Th17 cells, balancing helper T cell subsets, inducing B cell generation and differentiation into plasma cells, and enhancing the production of immunoglobulin. These effects are mainly mediated by activation of the JAK/STAT, MAPK and PI3K pathways. Some IL-21 target genes, such as B lymphocyte induced maturation protein-1 (Blimp-1), suppressor of cytokine signaling (SOCS), CXCR5 and Bcl-6, play important roles in the immune response. Therefore, IL-21 has been linked to autoimmune diseases. Indeed, IL-21 levels are increased in the peripheral blood and tissues of patients with systematic lupus erythematosus (SLE), rheumatoid arthritis (RA), type 1 diabetes (T1D), immune thrombocytopenia (ITP), primary Sjogren's syndrome (pSS), autoimmune thyroid disease (AITD) and psoriasis. This increased IL-21 even positively associates with Tfh cells, plasma cells, autoantibodies and disease activity in SLE and RA. Additionally, IL-21 has been utilized as a therapeutic target in SLE, RA, T1D and psoriatic mouse models. Profoundly, clinical trials have shown safety and improvement in RA patients. However, tolerance and long-term pharmacodynamics effects with low bioavailability have been found in SLE patients. Therefore, this review aims to summarize the latest progress on IL-21 function and its signaling pathway and discuss the role of IL-21 in the pathogenesis of and therapy for autoimmune diseases, with the hope of providing potential therapeutic and diagnostic strategies for clinical use.

Multilayer regulation of CD4 T cell subset differentiation in the era of single cell genomics

CD4 T cells are major immune cell types that mediate effector responses appropriate for diverse incoming threats. These cells have been categorized into different subsets based on how they are induced, expression of specific master transcription factors, and the resulting effector cell phenotypes as defined by expression of signature cytokines. However, recent studies assessing the expression of gene modules in single CD4 T cells, rather than expression of one or a few signature genes, have provided a more complex picture in which the canonical model does not fit as cleanly as proposed. Here, we review the concepts of lineage commitment, plasticity and functional heterogeneity in the context of this greater complexity. We then apply our current understanding of CD4 T cell subsets to discuss outstanding questions regarding follicular helper T cells and follicular regulatory T cells with respect to their shared features with other known CD4 T cell subsets.

The Making of Hematopoiesis: Developmental Ancestry and Environmental Nurture

Evidence from studies of the behaviour of stem and progenitor cells and of the influence of cytokines on their fate determination, has recently led to a revised view of the process by which hematopoietic stem cells and their progeny give rise to the many different types of blood and immune cells. The new scenario abandons the classical view of a rigidly demarcated lineage tree and replaces it with a much more continuum-like view of the spectrum of fate options open to hematopoietic stem cells and their progeny. This is in contrast to previous lineage diagrams, which envisaged stem cells progressing stepwise through a series of fairly-precisely described intermediate progenitors in order to close down alternative developmental options. Instead, stem and progenitor cells retain some capacity to step sideways and adopt alternative, closely related, fates, even after they have “made a lineage choice.” The stem and progenitor cells are more inherently versatile than previously thought and perhaps sensitive to lineage guidance by environmental cues. Here we examine the evidence that supports these views and reconsider the meaning of cell lineages in the context of a continuum model of stem cell fate determination and environmental modulation.

Neutralizing FGF4 protein in conditioned medium of IL-21-silenced HCT116 cells restores the migratory activity of the colorectal cancer cells

The interleukin-21 (IL-21) protein was found to be expressed at an elevated level in clinical samples of colorectal cancer patients without or with a parasitic infection that were collected from Sudan in our previous study. The IL-21 gene in HT29 and HCT116 cells was then correlated to cell proliferation and cell migration, as well as the cellular mechanisms associated with gene expressions in our present study. Our results demonstrated that silencing the IL-21 gene in HCT116 cells increased the cytotoxic level and fibroblast growth factor-4 (FGF4) mRNA expression in the cancer cells. Moreover, specific gene silencing reduced the migration of cancer cells compared to non-silenced cancer cells. These events were not observed in IL-21-silenced HT29 cells. Neutralizing FGF4 in conditioned medium of IL-21-silenced HCT116 cells further increased the cytotoxic level and restored the migratory activity of HCT116 cells in the culture compared to silencing the IL-21 gene alone in the cancer cells. Our results indicate the importance of both silencing the IL-21 gene and co-expression of the FGF4 protein in HCT116 cells, which pave the way for the discovery of important factors to be used as biomarkers for the design of drugs or cost-effective supplements to effectively treat the patients having infectious disease and HCT116 cells of colorectal cancer simultaneously in the future.

IL-21 alleviates allergic asthma in DOCK8-knockout mice

Patients with DOCK8 deficiency are at increased susceptibility to develop allergic diseases such as food allergy and asthma. Here, we aimed to analyze the pathogenesis of asthma in DOCK8-deficient patients. In our mouse model, DOCK8-knockout (KO) mice sensitized with low-dose OVA were challenged with 1.5% OVA to induce allergic asthma. As compared to that in WT mice, remarkable airway hyperresponsiveness was observed in KO mice. Increased inflammatory cells and eosinophils infiltrated in airway lumen in KO mice especially around bronchi. KO mice showed higher levels of serum IgE and OVA-specific IgE and significantly elevated IgE-producing B cells in blood and in spleen. Surprisingly, nasal administration with rmIL-21 significantly reduced the airway hyperresponsiveness, inflammatory infiltration, as well as the serum IgE and IgE-producing B cells. DOCK8-knockout mice are susceptible to low-dose OVA induced allergic airway inflammation and airway hyperresponsiveness. Supplementary nasal administration of rmIL-21 alleviates allergic asthma in this mouse model.

IL-17 and related cytokines involved in systemic sclerosis: Perspectives

Systemic sclerosis (SSc) is a multisystemic, complex, and rare disease of connective tissue, with high morbidity and mortality, and without specific treatment. The disease is characterized by three main principles: vascular disease, autoantibody production and inflammation, and fibrosis. Since it is well defined that SSc is characterized by elevated production of TGF-β, IL-6, and IL-1, all of them cytokines related to Th17 differentiation, the hypothesis is that this disease may be strongly related to a polarization of the immune response towards the Th17 pathway. Considering the importance of a better understanding of the pathophysiology of Th17 pathway in SSc, this article aims to propose an update for a better understanding of current knowledge on main cytokines secreted by the Th17 cells (IL-17 A, IL-21, and IL-22) and the future prospects in the current disease.

T Helper Cells in the Immunopathogenesis of Systemic Sclerosis – Current Trends

Systemic sclerosis (SSc) is a chronic progressive autoimmune disease characterized by skin and multiorgan involvement with alterations in both the innate and adaptive immunities. The hallmark of the disease is widespread fibrosis engaging the skin and multiple internal organs, as well as the musculoskeletal system. There is mounting evidence that T cells are key players in the pathogenesis of scleroderma. The current review discusses the role of the different T helper (Th) lymphocyte subsets in the processes of inflammation and fibrosis, characteristics for the pathogenesis of the disease. Cytokines produced by Th cell populations have a major effect on endothelial cells and fibroblasts in the context of favoring/inhibiting the vasculopathy and the fibrosis spread. The Th2 pro-fibrotic cytokines IL-4 and IL-13 have been shown to induce collagen synthesis by fibroblasts, whereas IFN-γ demonstrates an inhibitory effect. Increased Th17 cells are present in the scleroderma skin infiltrates. The combination of IL-17, IFN-γ and TGF-β levels in CD45RO and CD45RA cells from patients with SSc is useful to distinguish between the limited and the diffuse phenotype of the disease. There are accumulating data for functional and numerical alterations in the Tregs in SSc. High levels of TNF-α which might reduce the suppressive ability of Tregs have been described. According to some studies, the number of Tregs in scleroderma skin biopsies has been decreased against the normal absolute number of Tregs in peripheral blood of the same patients, which suggests suppressed immunomodulatory response. Other studies reported increased frequency of Tregs in peripheral blood of patients with systemic sclerosis and established a correlation with disease activity. The main immunological challenge remains the identification of the trigger of the autoimmune response in SSc, the causes for preferential Th2-type cell responses and the immunological differences between the diffuse and the limited cutaneous form of the disease.

CREM Alpha Enhances IL-21 Production in T Cells In Vivo and In Vitro

The cAMP-responsive element modulator alpha (CREMα) plays a role in autoimmunity and, in particular, in systemic lupus erythematosus. CREMα negatively regulates IL-2 transcription and activates IL-17 expression by direct transcriptional mechanisms. To understand the role of CREM in autoimmunity, we recently generated a mouse with a transgenic overexpression of CREMα selectively in T cells. This mouse is characterized by enhanced IL-17 and IL-21 expression. We, herein, dissect the transcriptional mechanisms of enhanced IL-21 transcription in these mice. T cells of CREMα transgenic mice display an enhanced binding of CREMα to the CD3ζ chain promoter resulting in decreased CD3ζ chain expression. This is accompanied by a decreased excitation threshold and enhanced Ca²⁺ influx, which is known to induce IL-21 expression via NFATc2 activation. However, CREMα directly binds to cAMP-response element (CRE) half-site within the Il-21 promoter, which results in enhanced promoter activity shown by promoter reporter assays. CREMα-induced IL-21 transcription is not abrogated in the presence of cyclosporine A but depends on an intact CRE site within the IL-21 promoter, which suggests that CREM largely enhances IL-21 expression by direct transcriptional regulation. IL-21 transcription is critical for IL-17 generation in these mice, since IL-21 receptor blockade downregulates IL-17 transcription to wild-type levels. Finally, this is of functional relevance since CREMα transgenic mice display enhanced disease activity in dextran sodium sulfate-induced colitis accompanied by higher local IL-21 expression. Thus, we describe two novel mechanisms of CREMα-dependent IL-21 transcription. Since T cells of systemic lupus erythematosus patients are characterized by enhanced IL-21 transcription, this might also be of functional relevance in humans.

IL-21/IL-21R signaling suppresses intestinal inflammation induced by DSS through regulation of Th responses in lamina propria in mice

Serum level of IL-21 is increased in patients with inflammatory bowel diseases (IBD), suggesting that IL-21/IL-21 receptor (IL-21R) signaling may be involved in the pathogenesis of IBD. However, the role of IL-21/IL-21 receptor signaling plays in the pathogenesis of IBD is not very clear. In this study, using IL-21R.KO mice, we tested the role of IL-21/IL-21R signaling in the regulation of T helper cell responses during intestinal inflammation. Here we found that IL-21R.KO mice were more susceptible to DSS-induced colitis as compared with C57BL/6 mice. The spontaneous inflammatory cytokines released by macrophages in LP of colon were significantly increased, and Th2, Th17 and Treg responses were down-regulated markedly. However, Th1 responses were significantly up-regulated in IL-21R.KO mice. Meanwhile, the population of CD8(+)CD44(+)IFN-γ(+) T cells was markedly elevated in LP of inflammatory intestine of IL-21RKO mice. In vivo, after disease onset, DSS-induced intestinal inflammation was ameliorated in C57BL/6 mice treated with rIL-21. Our results demonstrate that IL-21/IL-21R signaling contributes to protection against DSS-induced acute colitis through suppression of Th1 and activation of Th2, Th17 and Treg responses in mice. Therefore, therapeutic manipulation of IL-21/IL-21R activity may allow improved immunotherapy for IBD and other inflammatory diseases associated with Th cell responses.

Interleukin 21 - its potential role in the therapy of B-cell lymphomas

Interleukin-21 (IL-21), a member of IL-2 cytokine family, has pleotropic biological effects on lymphoid and myeloid cells. During the past 15 years, since the discovery of IL-21, great advances have been made regarding its biological activity and the mechanisms controlling IL-21-mediated cellular responses, especially in hematological malignancies. Preclinical studies have shown that IL-21R is expressed on healthy and neoplastic B-cells and exogenous IL-21 can induce direct apoptosis of IL-21R expressing B-cell non-Hodgkin lymphomas (NHL), making it a potentially attractive anti-lymphoma therapy. However, in some hematological malignancies such as multiple myeloma, Hodgkin lymphoma and Burkitt lymphoma, IL-21 can induce proliferation of neoplastic B-cells. In NHL, the underlying mechanism of cell death was found to be different between the various subtypes, including activation of different JAK/STAT signal transduction pathways or other factors. Immunomodulatory effects of IL-21 have also been reported to contribute to its anti-tumor effects as described by earlier studies in solid tumors and B-cell associated malignancies. These effects are predominantly mediated by IL-21's ability to activate cytolytic activities by NK-cells and CD4⁺/CD8⁺ T-cells. In this review, we provide an overview of IL-21's effects in NHL, results from clinical trials utilizing IL-21, and propose how IL-21 can be therapeutically exploited for treating these lymphomas.

IL-21 and T Cell Differentiation: Consider the Context

Accumulating studies demonstrate that IL-21 modulates the differentiation of various CD4 and CD8 T cell subsets and provide insights into the underlying cellular and molecular processes that are influenced by this cytokine. Intriguingly, the effects of IL-21 on T cells can be complex and vary depending on the experimental system used. We review our current understanding of the roles of IL-21 in the generation of phenotypically distinct CD4 and CD8 T cell populations and discuss the potential environmental cues, cellular factors, and molecular mediators that impact the actions of IL-21. We propose that IL-21 acts in a context-dependent manner to accentuate T cell subset development.

The adaptor protein insulin receptor substrate 2 inhibits alternative macrophage activation and allergic lung inflammation

Insulin receptor substrate 2 (IRS2) is an adaptor protein that becomes tyrosine-phosphorylated in response to the cytokines interleukin-4 (IL-4) and IL-13, which results in activation of the phosphoinositide 3-kinase (PI3K)-Akt pathway. IL-4 and IL-13 contribute to allergic lung inflammation. To examine the role of IRS2 in allergic disease, we evaluated the responses of IRS2-deficient (IRS2(-/-)) mice. Unexpectedly, loss of IRS2 resulted in a substantial increase in the expression of a subset of genes associated with the generation of alternatively activated macrophages (AAMs) in response to IL-4 or IL-13 in vitro. AAMs secrete factors that enhance allergic responses and promote airway remodeling. Moreover, compared to IRS2(+/+) mice, IRS2(+/-) and IRS2(-/-) mice developed enhanced pulmonary inflammation, accumulated eosinophils and AAMs, and exhibited airway and vascular remodeling upon allergen stimulation, responses that partially depended on macrophage-intrinsic IRS2 signaling. Both in unstimulated and IL-4-stimulated macrophages, lack of IRS2 enhanced phosphorylation of Akt and ribosomal S6 protein. Thus, we identified a critical inhibitory loop downstream of IRS2, demonstrating an unanticipated and previously unrecognized role for IRS2 in suppressing allergic lung inflammation and remodeling.

Electronic Sorting of Immune Cell Subpopulations Based on Highly Plastic Genes

Immune cells are highly heterogeneous and plastic with regard to gene expression and cell phenotype. In this study, we categorized genes into those with low and high gene plasticity, and those categories revealed different functions and applications. We proposed that highly plastic genes could be suited for the labeling of immune cell subpopulations; thus, novel immune cell subpopulations could be identified by gene plasticity analysis. For this purpose, we systematically analyzed highly plastic genes in human and mouse immune cells. In total, 1,379 human and 883 mouse genes were identified as being extremely plastic. We also expanded our previous immunoinformatic method, electronic sorting, which surveys big data to perform virtual analysis. This approach used correlation analysis and took dosage changes into account, which allowed us to identify the differentially expressed genes. A test with human CD4(+) T cells supported the method's feasibility, effectiveness, and predictability. For example, with the use of human nonregulatory T cells, we found that FOXP3(hi)CD4(+) T cells were highly expressive of certain known molecules, such as CD25 and CTLA4, and that this process of investigation did not require isolating or inducing these immune cells in vitro. Therefore, the sorting process helped us to discover the potential signature genes or marker molecules and to conduct functional evaluations for immune cell subpopulations. Finally, in human CD4(+) T cells, 747 potential immune cell subpopulations and their candidate signature genes were identified, which provides a useful resource for big data-driven knowledge discoveries.

Phosphate substitution in an AlOOH - TLR4 adjuvant system (SPA08) modulates the immunogenicity of Serovar E MOMP from Chlamydia trachomatis

Chlamydia trachomatis is one of the most common sexually transmitted pathogens and the development of an effective vaccine is highly desirable. The Major Outer Membrane Protein (MOMP) is one of the most abundant and immunogenic chlamydial proteins. Here we investigated the effects of phosphate substitution on the physicochemical and immunochemical properties of an experimental vaccine composed of serovar E recombinant MOMP (rMOMP) and a proprietary adjuvant system SPA08, consisting of aluminum oxyhydroxide (AlOOH) containing the TLR4 agonist E6020. An increase in phosphate substitution in the AlOOH component of the adjuvant markedly decreased the adsorptive coefficient and adsorptive capacity for both Ser E rMOMP and E6020. In vaccine formulations used for immunizations, phosphate substitution induced a decrease in the % adsorption of Ser E rMOMP without affecting the % adsorption of E6020. Immunogenicity studies in CD1 mice showed that an increase in phosphate substitution of the SPA08 adjuvant resulted in an increase in Ser E rMOMP-specific serum total IgG and IgG1 but not IgG2a titers. The degree of phosphate substitution in SPA08 also significantly increased in vitro neutralization concomitant with a decrease in proinflammatory cytokines secreted by Ser E rMOMP-restimulated splenocytes. Taken together, the results of these studies suggest that the degree of phosphate substitution in AlOOH greatly affects the adsorption of E6020 and Ser E rMOMP to AlOOH resulting in significant effects on vaccine-induced cellular and humoral responses.

New insights into CD4(+) T cell abnormalities in systemic sclerosis

Systemic sclerosis (SSc) is an autoimmune connective tissue disease that is characterized by vasculopathy and excessive deposition of extracellular matrix, which causes fibrosis of the skin and internal organs and eventually leads to multiorgan dysfunction. Studies have shown that CD4(+) T cell activation is a key factor in the pathogenesis of scleroderma because activated T cells can release various cytokines, resulting in inflammation, microvascular damage and fibrosis. T helper cell 17 (Th17) and regulatory T (Treg) cell activities are a hallmark SSc, as Th17-type cytokines can induce both inflammation and fibrosis. More recently, several studies have reported new T cell subsets, including Th9 and Th22 cells, along with their respective cytokines in the peripheral blood, serum and skin lesions of individuals with SSc. Herein, we review recent data on various CD4(+) T helper cell subsets in SSc, and discuss potential roles of these cells in promoting inflammation and fibrosis.

IFN-γ and IL-21 Double Producing T Cells Are Bcl6-Independent and Survive into the Memory Phase in Plasmodium chabaudi Infection

CD4 T cells are required to fight malaria infection by promoting both phagocytic activity and B cell responses for parasite clearance. In Plasmodium chabaudi infection, one specific CD4 T cell subset generates anti-parasitic IFN-γ and the antibody-promoting cytokine, IL-21. To determine the lineage of these multifunctional T cells, we followed IFN-γ⁺ effector T cells (Teff) into the memory phase using Ifng-reporter mice. While Ifng⁺ Teff expanded, the level of the Th1 lineage-determining transcription factor T-bet only peaked briefly. Ifng⁺ Teff also co-express ICOS, the B cell area homing molecule CXCR5, and other Tfh lineage-associated molecules including Bcl6, the transcription factor required for germinal center (GC) T follicular helper cells (Tfh) differentiation. Because Bcl6 and T-bet co-localize to the nucleus of Ifng⁺ Teff, we hypothesized that Bcl6 controls the Tfh-like phenotype of Ifng⁺ Teff cells in P. chabaudi infection. We first transferred Bcl6-deficient T cells into wildtype hosts. Bcl6-deficient T cells did not develop into GC Tfh, but they still generated CXCR5⁺IFN-γ⁺IL-21⁺IL-10⁺ Teff, suggesting that this predominant population is not of the Tfh-lineage. IL-10 deficient mice, which have increased IFN-γ and T-bet expression, demonstrated expansion of both IFN-γ⁺IL-21⁺CXCR5⁺ cells and IFN-γ⁺ GC Tfh cells, suggesting a Th1 lineage for the former. In the memory phase, all Ifng⁺ T cells produced IL-21, but only a small percentage of highly proliferative Ifng⁺ T cells maintained a T-bet^hi phenotype. In chronic malaria infection, serum IFN-γ correlates with increased protection, and our observation suggests Ifng⁺ T cells are maintained by cellular division. In summary, we found that Ifng⁺ T cells are not strictly Tfh derived during malaria infection. T cells provide the host with a survival advantage when facing this well-equipped pathogen, therefore, understanding the lineage of pivotal T cell players will aid in the rational design of an effective malaria vaccine.

Human IL-21+IFN-γ+CD4+ T cells in nasal polyps are regulated by IL-12

In the previous study, we found that the levels of IL-21 in nasal polyps (NPs) were significantly increased and associated with polyp size and recurrence. However, it is unclear that the cell source of IL-21 and the regulation of IL-21 in NP tissues. In the present study, we isolated the lymphocytes from NP tissues, uncinate tissues and peripheral blood of patients with NPs. The cells were analyzed for cell surface markers, cytokines and transcriptional factors by flow cytometry. The results indicated that CD4⁺ T cells were the major IL-21-exprssing cells in NP tissues and the majority of IL-21 producing CD4⁺ T cells co-expressed IFN-γ or IL-17A. IL-21⁺IFN-γ⁺CD4⁺ T cells in NP tissues exhibited the features of both Tfh and Th1 cells which co-expressed significantly higher amount of CXCR5, ICOS, PD-1, Bcl-6 and T-bet than did IL-21⁺IFN-γ⁻CD4⁺ T cells (p < 0.05). Treatment of the lymphocytes from NP tissues with IL-12 enhanced the production of IL-21 and IFN-γ, especially the frequency of IL-21⁺IFN⁻γ⁺CD4⁺ T cells (p < 0.05). The blockade of IL-12 inhibited the production of IL-21 and IFN-γ (p < 0.05). These findings indicated that IL-12 positively enhanced the generation of IL-21⁺IFN-γ⁺CD4⁺ T cells having the features of both Tfh and Th1 cells in NP tissues.