IL-27 supports germinal center function by enhancing IL-21 production and the function of T follicular helper cells

Complement factor B inhibitor LNP023 mediates the effect and mechanism of AMPK/mTOR on autophagy and oxidative stress in lupus nephritis

This study investigated the impact of LNP023 on the AMPK/mTOR signaling pathway in lupus nephritis (LN) and its effects on autophagy and oxidative stress. A mouse model of LN was established, and renal injury was confirmed by assessing various LN markers, including antinuclear antibody, ds-DNA, anti-Sm antibody, and others. Mice were treated with LNP023, the AMPK activator AICAR, or the AMPK inhibitor dorsomorphin. Renal injury and fibrosis were evaluated using HE and Masson staining. Expression levels of AMPK, mTOR, LC3, Beclin1, and p62 were assessed by immunohistochemistry and Western blot. Oxidative stress and inflammatory markers were measured by polymerase chain reaction and enzyme-linked immunosorbent assay. LN mice exhibited low AMPK/p-AMPK and high mTOR/p-mTOR levels, alongside significant renal injury, fibrosis, reduced autophagy, and elevated oxidative stress. LNP023 treatment improved these parameters, with enhanced effects when combined with AICAR. Conversely, dorsomorphin reversed LNP023's therapeutic benefits. The complement factor B inhibitor LNP023 promotes kidney health in LN mice by mediating the AMPK/mTOR pathway, promoting autophagy, and attenuating oxidative stress.

The role of antibody glycosylation in autoimmune and alloimmune kidney diseases

Immunoglobulin glycosylation is a pivotal mechanism that drives the diversification of antibody functions. The composition of the IgG glycome is influenced by environmental factors, genetic traits and inflammatory contexts. Differential IgG glycosylation has been shown to intricately modulate IgG effector functions and has a role in the initiation and progression of various diseases. Analysis of IgG glycosylation is therefore a promising tool for predicting disease severity. Several autoimmune and alloimmune disorders, including critical and potentially life-threatening conditions such as systemic lupus erythematosus, anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis and antibody-mediated kidney graft rejection, are driven by immunoglobulin. In certain IgG-driven kidney diseases, including primary membranous nephropathy, IgA nephropathy and lupus nephritis, particular glycome characteristics can enhance in situ complement activation and the recruitment of innate immune cells, resulting in more severe kidney damage. Hypofucosylation, hypogalactosylation and hyposialylation are the most common IgG glycosylation traits identified in these diseases. Modulating IgG glycosylation could therefore be a promising therapeutic strategy for regulating the immune mechanisms that underlie IgG-driven kidney diseases and potentially reduce the burden of immunosuppressive drugs in affected patients.

Immune interplay from circulation to local lesion in pemphigus pathogenesis

Pemphigus, a potentially lethal autoimmune skin disease, is mediated by desmoglein-specific antibodies, manifesting cutaneous and mucosal blisters and erosions. The interaction between multiple immune counterparts contributes to the progress of pemphigus. Currently, the emergence of bioinformatic analysis enables investigators to gain a global picture of the pemphigus immune network, based on the exhaustive pedigree annotation of multiple subsets. T helper subsets dominate the landscape as mentioned previously, and innate immune cells have been involved as well. Of particular interests is which phenotype of T cells orchestrates the autoimmune process and chronic inflammation in a certain condition. In this review, the circulatory and peripheral immune cells and cytokine components constituting the immune microenvironment are separately discussed to provide a perspective on pemphigus pathogenesis, with particular reference to insights provided by the bioinformation technique.

RACK1 enhances STAT3 stability and promotes T follicular helper cell development and function during blood-stage Plasmodium infection in mice

CD4+ T cells are central mediators of protective immunity to blood-stage malaria, particularly for their capacity in orchestrating germinal center reaction and generating parasite-specific high-affinity antibodies. T follicular helper (Tfh) cells are predominant CD4+ effector T cell subset implicated in these processes, yet the factors and detailed mechanisms that assist Tfh cell development and function during Plasmodium infection are largely undefined. Here we provide evidence that receptor for activated C kinase 1 (RACK1), an adaptor protein of various intracellular signals, is not only important for CD4+ T cell expansion as previously implied but also plays a prominent role in Tfh cell differentiation and function during blood-stage Plasmodium yoelii 17XNL infection. Consequently, RACK1 in CD4+ T cells contributes significantly to germinal center formation, parasite-specific IgG production, and host resistance to the infection. Mechanistic exploration detects specific interaction of RACK1 with STAT3 in P. yoelii 17XNL-responsive CD4+ T cells, ablation of RACK1 leads to defective STAT3 phosphorylation, accompanied by substantially lower amount of STAT3 protein in CD4+ T cells, whereas retroviral overexpression of RACK1 or STAT3 in RACK1-deficient CD4+ T cells greatly restores STAT3 activity and Bcl-6 expression under the Tfh polarization condition. Further analyses suggest RACK1 positively regulates STAT3 stability by inhibiting the ubiquitin-proteasomal degradation process, thus promoting optimal STAT3 activity and Bcl-6 induction during Tfh cell differentiation. These findings uncover a novel mechanism by which RACK1 participates in posttranslational regulation of STAT3, Tfh cell differentiation, and subsequent development of anti-Plasmodium humoral immunity.

IL-27 promotes pathogenic T cells in a mouse model of Sjögren's disease

Sjögren's disease (SjD) is a chronic autoimmune disease characterized by focal lymphocytic inflammation in lacrimal and salivary glands. We recently identified IL-27 as a requisite signal for the spontaneous SjD-like manifestations in nonobese diabetic (NOD) mice. Here, we define T cell-intrinsic effects of IL-27 in lacrimal gland disease in NOD mice. IL-27 receptor was required by both CD4 T effector (Te) cells and CD8 T cells to mediate focal inflammation. Intrinsic IL-27 signaling was associated with PD-1 and ICOS expressing T follicular helper (Tfh)-like CD4 Te cells within lacrimal glands, including subsets defined by CD73 or CD39 expression. CD8 T cells capable of IL-27 signaling also expressed PD-1 with subsets expressing ICOS and CD73 demonstrating a T follicular cytotoxic (Tfc)-like cell phenotype and others expressing a CD39hi exhausted-like phenotype. These findings suggest IL-27 is a key early signal driving a follicular-type response in lacrimal gland inflammation in NOD mice.

IL-27 expression regulation and its effects on adaptive immunity against viruses

IL-27, a member of the IL-6/IL-12 cytokine superfamily, is primarily secreted by antigen presenting cells, specifically by dendric cells, macrophages and B cells. IL-27 has antiviral activities and modulates both innate and adaptive immune responses against viruses. The role of IL-27 in the setting of viral infections is not well defined and both pro-inflammatory and anti-inflammatory functions have been described. Here, we discuss the latest advancements in the role of IL-27 in several viral infection models of human disease. We highlight important aspects of IL-27 expression regulation, the critical cell sources at different stages of the infection and their impact in cell mediated immunity. Lastly, we discuss the need to better define the antiviral and modulatory (pro-inflammatory vs anti-inflammatory) properties of IL-27 in the context of human chronic viral infections.

Interleukin 27, like interferons, activates JAK-STAT signaling and promotes pro-inflammatory and antiviral states that interfere with dengue and chikungunya viruses replication in human macrophages

Interferons (IFNs) are a family of cytokines that activate the JAK-STAT signaling pathway to induce an antiviral state in cells. Interleukin 27 (IL-27) is a member of the IL-6 and/or IL-12 family that elicits both pro- and anti-inflammatory responses. Recent studies have reported that IL-27 also induces a robust antiviral response against diverse viruses, both in vitro and in vivo, suggesting that IFNs and IL-27 share many similarities at the functional level. However, it is still unknown how similar or different IFN- and IL-27-dependent signaling pathways are. To address this question, we conducted a comparative analysis of the transcriptomic profiles of human monocyte-derived macrophages (MDMs) exposed to IL-27 and those exposed to recombinant human IFN-α, IFN-γ, and IFN-λ. We utilized bioinformatics approaches to identify common differentially expressed genes between the different transcriptomes. To verify the accuracy of this approach, we used RT-qPCR, ELISA, flow cytometry, and microarrays data. We found that IFNs and IL-27 induce transcriptional changes in several genes, including those involved in JAK-STAT signaling, and induce shared pro-inflammatory and antiviral pathways in MDMs, leading to the common and unique expression of inflammatory factors and IFN-stimulated genes (ISGs)Importantly, the ability of IL-27 to induce those responses is independent of IFN induction and cellular lineage. Additionally, functional analysis demonstrated that like IFNs, IL-27-mediated response reduced chikungunya and dengue viruses replication in MDMs. In summary, IL-27 exhibits properties similar to those of all three types of human IFN, including the ability to stimulate a protective antiviral response. Given this similarity, we propose that IL-27 could be classified as a distinct type of IFN, possibly categorized as IFN-pi (IFN-π), the type V IFN (IFN-V).

An updated advancement of bifunctional IL-27 in inflammatory autoimmune diseases

Interleukin-27 (IL-27) is a member of the IL-12 family. The gene encoding IL-27 is located at chromosome 16p11. IL-27 is considered as a heterodimeric cytokine, which consists of Epstein-Barr virus (EBV)-induced gene 3 (Ebi3) and IL-27p28. Based on the function of IL-27, it binds to receptor IL-27rα or gp130 and then regulates downstream cascade. To date, findings show that the expression of IL-27 is abnormal in different inflammatory autoimmune diseases (including systemic lupus erythematosus, rheumatoid arthritis, Sjogren syndrome, Behcet's disease, inflammatory bowel disease, multiple sclerosis, systemic sclerosis, type 1 diabetes, Vogt-Koyanagi-Harada, and ankylosing spondylitis). Moreover, in vivo and in vitro studies demonstrated that IL-27 is significantly in3volved in the development of these diseases by regulating innate and adaptive immune responses, playing either an anti-inflammatory or a pro-inflammatory role. In this review, we comprehensively summarized information about IL-27 and autoimmunity based on available evidence. It is hoped that targeting IL-27 will hold great promise in the treatment of inflammatory autoimmune disorders in the future.

IL-27 regulates the differentiation of follicular helper NKT cells via metabolic adaptation of mitochondria

Invariant natural killer T (iNKT) cells are innate-like T lymphocytes that express an invariant T cell receptor α chain and contribute to bridging innate and acquired immunity with rapid production of large amounts of cytokines after stimulation. Among effecter subsets of iNKT cells, follicular helper NKT (NKTFH) cells are specialized to help B cells. However, the mechanisms of NKTFH cell differentiation remain to be elucidated. In this report, we studied the mechanism of NKTFH cell differentiation induced by pneumococcal surface protein A and α-galactosylceramide (P/A) vaccination. We found that Gr-1+ cells helped iNKT cell proliferation and NKTFH cell differentiation in the spleen by producing interleukin-27 (IL-27) in the early phase after vaccination. The neutralization of IL-27 impaired NKTFH cell differentiation, which resulted in compromised antibody production and diminished protection against Streptococcus pneumoniae infection by the P/A vaccine. Our data indicated that Gr-1+ cell-derived IL-27 stimulated mitochondrial metabolism, meeting the energic demand required for iNKT cells to differentiate into NKTFH cells. Interestingly, Gr-1+ cell-derived IL-27 was induced by iNKT cells via interferon-γ production. Collectively, our findings suggest that optimizing the metabolism of iNKT cells was essential for acquiring specific effector functions, and they provide beneficial knowledge on iNKT cell-mediated vaccination-mediated therapeutic strategies.

Tertiary lymphoid structures in autoimmune diseases

Tertiary lymphoid structures (TLSs) are organized lymphoid-like aggregations in non-lymphoid tissues. Tissues with chronic and persistent inflammation infiltration may drive and form ectopic germinal center-like structures, which are very common in autoimmune diseases, chronic infections, and tumor microenvironments. However, the mechanisms governing the formation of TLSs are still being explored. At present, it is not clear whether the formation of TLSs is associated with local uncontrolled immune inflammatory responses. While TLSs suggest a good prognosis in tumors, the opposite is true in autoimmune diseases. This review article will discuss the current views on initiating and maintaining TLSs and the potential therapeutic target in autoimmune diseases.

The dichotomic role of single cytokines: Fine-tuning immune responses

Cytokines are known for their pleiotropic effects. They can be classified by their function as pro-inflammatory, such as tumor necrosis factor (TNF), interleukin (IL) 1 and IL-12, or anti-inflammatory, like IL-10, IL-35 and transforming growth factor β (TGF-β). Though this type of classification is an important simplification for the understanding of the general cytokine's role, it can be misleading. Here, we discuss recent studies that show a dichotomic role of the so-called pro and anti-inflammatory cytokines, highlighting that their function can be dependent on the microenvironment and their concentrations. Furthermore, we discuss how the back-and-forth interplay between cytokines and immunometabolism can influence the dichotomic role of inflammatory responses as an important target to complement cytokine-based therapies.

Statins in Graves Orbitopathy: A New Therapeutic Tool

PURPOSE

Graves orbitopathy (GO) is the most common extrathyroidal manifestation of Graves disease. Although its pathogenesis is not fully elucidated, GO is commonly considered an autoimmune disease due to loss of self-tolerance against autoantigens shared by thyroid epithelial cells and orbital fibroblasts. High-dose intravenous glucocorticoids (ivGCs) are the most used treatment for moderate-to-severe, active GO, but the addition of other immunomodulating treatments can improve the efficacy of ivGCs. Among the various risk factors that can affect the occurrence of GO, cholesterol may be worthy of interest. Since 2015 the role of cholesterol and cholesterol-lowering medications has been investigated. The purpose of this review is to discuss this topic, thereby offering new therapeutic opportunities for patients with GO.

METHODS

We searched PubMed for studies published between January 1, 1980 and June 1, 2023, using the search terms "Graves orbitopathy," "thyroid eye disease," "Graves ophthalmopathy," "thyroid ophthalmopathy," "thyroid-associated ophthalmopathy," "endocrine ophthalmopathy," "cholesterol," "lipids," "statins," "low-density lipoprotein," "atorvastatin," and "cholesterol-lowering drugs." Only English-language articles were included.

RESULTS

A correlation between low-density lipoprotein cholesterol and the risk of GO development has been reported. Furthermore, low-density lipoprotein cholesterol has been proposed as a risk factor that can affect the course of GO and the response to ivGCs. The protective role of cholesterol-lowering medications in preventing GO has been also investigated. Statin treatment was found to have potential benefits in reducing the risk of GO in patients with Graves disease. Given these findings, measurement of low-density lipoprotein cholesterol and treatment of hypercholesterolemia in patients with moderate-to-severe, active GO may be considered before starting ivGCs administration. Recently, a randomized clinical trial aimed at investigating the effects of statins in GO suggested that the addition of oral atorvastatin to ivGCs improves the overall outcome of moderate-to-severe, active GO in hypercholesterolemic patients given ivGCs.

CONCLUSIONS

Overall, statins seem to have a preventive and therapeutic role in moderate-to-severe active GO. Their efficacy can be related to cholesterol-lowering activity, pleiotropic actions, and interaction with methylprednisolone.

Are comorbidities associated with the cytokine/chemokine profile of persistent apical periodontitis?

OBJECTIVES

This study aimed to identify disease-related markers in persistent apical periodontitis (PAP) biopsies and examine whether these were associated with comorbidities like rheumatoid arthritis (RA) and cardiovascular diseases (CVD).

MATERIALS AND METHOD

The levels of the cytokines/chemokines GM-CSF, IFN-γ, IL-2, IL-6, IL-9, IL-10, IL-13, IL-15, IL-17E/IL-25, IL-21, IL-23, IL-27, IL-28A/IFN -λ2, IL-33, MIP-3α/CCL20, and TNF-α were determined in lesions from patients with PAP (n = 20) and compared to healthy bone samples (n = 20).

RESULTS

We identified eleven cytokines to be differently expressed, and among them, IL-2, IL-6, IL-17E, IL-21, and IL-27 appeared to drive the discrepancy between the disease and healthy groups. The levels of T follicular helper (Tfh) cell promoting cytokines (IL-21, IL-6, IL-27) were enhanced while T helper (Th) 1 cell promoting cytokine (IL-2), Th2 cell promoting cytokine (IL-13), and Th17 cell promoting cytokine (IL-17E) were reduced in the PAP group. The data also indicate that Tfh cell differentiation (IL-21), along with Th1 (GM-CSF, IFNγ), Th2 (IL-13), and Th17 (GM-CSF) cell differentiation, might be increased in the subpopulation of patients suffering from RA, whereas no differences were found in patients with CVD.

CONCLUSIONS

Levels of cytokines/chemokines in PAP were identified, and cluster analyzes indicated that these markers may be associated with the differentiation of different T cell populations. Patients with PAP and RA comorbidities showed elevated levels of markers reinforcing this association.

CLINICAL RELEVANCE

Molecular analyses of PAP may result in identification of prognostic markers.

Dysregulated IFN-γ signals promote autoimmunity in STAT1 gain-of-function syndrome

Heterozygous signal transducer and activator of transcription 1 (STAT1) gain-of-function (GOF) mutations promote a clinical syndrome of immune dysregulation characterized by recurrent infections and predisposition to humoral autoimmunity. To gain insights into immune characteristics of STAT1-driven inflammation, we performed deep immunophenotyping of pediatric patients with STAT1 GOF syndrome and age-matched controls. Affected individuals exhibited dysregulated CD4⁺ T cell and B cell activation, including expansion of T_H1-skewed CXCR3⁺ populations that correlated with serum autoantibody titers. To dissect underlying immune mechanisms, we generated Stat1 GOF transgenic mice (Stat1^GOF mice) and confirmed the development of spontaneous humoral autoimmunity that recapitulated the human phenotype. Despite clinical resemblance to human regulatory T cell (T_reg) deficiency, Stat1^GOF mice and humans with STAT1 GOF syndrome exhibited normal T_reg development and function. In contrast, STAT1 GOF autoimmunity was characterized by adaptive immune activation driven by dysregulated STAT1-dependent signals downstream of the type 1 and type 2 interferon (IFN) receptors. However, in contrast to the prevailing type 1 IFN-centric model for STAT1 GOF autoimmunity, Stat1^GOF mice lacking the type 1 IFN receptor were only partially protected from STAT1-driven systemic inflammation, whereas loss of type 2 IFN (IFN-γ) signals abrogated autoimmunity. Last, germline STAT1 GOF alleles are thought to enhance transcriptional activity by increasing total STAT1 protein, but the underlying biochemical mechanisms have not been defined. We showed that IFN-γ receptor deletion normalized total STAT1 expression across immune lineages, highlighting IFN-γ as the critical driver of feedforward STAT1 elevation in STAT1 GOF syndrome.

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.

PEGylated Gold Nanoparticles Target Age-Associated B Cells In Vivo

Engineered gold nanoparticles (GNPs) have become a useful tool in various therapeutic and diagnostic applications. Uncertainty remains regarding the possible impact of GNPs on the immune system. In this regard, we investigated the interactions of polymer-coated GNPs with B cells and their functions in mice. Surprisingly, we observed that polymer-coated GNPs mainly interact with the recently identified subpopulation of B lymphocytes named age-associated B cells (ABCs). Importantly, we also showed that GNPs did not affect cell viability or the percentages of other B cell populations in different organs. Furthermore, GNPs did not activate B cell innate-like immune responses in any of the tested conditions, nor did they impair adaptive B cell responses in immunized mice. Together, these data provide an important contribution to the otherwise limited knowledge about GNP interference with B cell immune function, and demonstrate that GNPs represent a safe tool to target ABCs in vivo for potential clinical applications.

Characteristics and Roles of T Follicular Helper Cells in SARS-CoV-2 Vaccine Response

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination is critical to controlling the coronavirus disease 2019 (COVID-19) pandemic. However, a weak response to the vaccine and insufficient persistence of specific antibodies may threaten the global impact of mass vaccination campaigns. This study summarizes the internal factors of the body that affect the effectiveness of the SARS-CoV-2 vaccine. T follicular helper (Tfh) cells support germinal center B cells to produce vaccine-specific immunoglobulins. A reduction in the Tfh cell number and a shift in the subset phenotypes caused by multiple factors may impair the production and persistence of high-affinity antibodies. Besides efficacy differences caused by the different types of vaccines, the factors that affect vaccine effectiveness by intervening in the Tfh cell response also include age-related defects, the polarity of the body microenvironment, repeated immunization, immunodeficiency, and immunosuppressive treatments. Assessing the phenotypic distribution and activation levels of Tfh cell subsets after vaccination is helpful in predicting vaccine responses and may identify potential targets for improving vaccine effectiveness.

Meta-Analysis of Two Human RNA-seq Datasets to Determine Periodontitis Diagnostic Biomarkers and Drug Target Candidates

Periodontitis is a chronic inflammatory oral disease that affects approximately 42% of adults 30 years of age or older in the United States. In response to microbial dysbiosis within the periodontal pockets surrounding teeth, the host immune system generates an inflammatory environment in which soft tissue and alveolar bone destruction occur. The objective of this study was to identify diagnostic biomarkers and the mechanistic drivers of inflammation in periodontitis to identify drugs that may be repurposed to treat chronic inflammation. A meta-analysis comprised of two independent RNA-seq datasets was performed. RNA-seq analysis, signal pathway impact analysis, protein-protein interaction analysis, and drug target analysis were performed to identify the critical pathways and key players that initiate inflammation in periodontitis as well as to predict potential drug targets. Seventy-eight differentially expressed genes, 10 significantly impacted signaling pathways, and 10 hub proteins in periodontal gingival tissue were identified. The top 10 drugs that may be repurposed for treating periodontitis were then predicted from the gene expression and pathway data. The efficacy of these drugs in treating periodontitis has yet to be investigated. However, this analysis indicates that these drugs may serve as potential therapeutics to treat inflammation in gingival tissue affected by periodontitis.

Fatty Acid Metabolism and T Cells in Multiple Sclerosis

Cellular metabolic remodeling is intrinsically linked to the development, activation, differentiation, function, and survival of T cells. T cells transition from a catabolic, naïve state to an anabolic effector state upon T cell activation. Subsequently, specialization of T cells into T helper (Th) subsets, including regulatory T cells (Treg), requires fine-tuning of metabolic programs that better support and optimize T cell functions for that particular environment. Increasingly, studies have shown that changes in nutrient availability at both the cellular and organismal level during disease states can alter T cell function, highlighting the importance of better characterizing metabolic-immune axes in both physiological and disease settings. In support of these data, a growing body of evidence is emerging that shows specific lipid species are capable of altering the inflammatory functional phenotypes of T cells. In this review we summarize the metabolic programs shown to support naïve and effector T cells, and those driving Th subsets. We then discuss changes to lipid profiles in patients with multiple sclerosis, and focus on how the presence of specific lipid species can alter cellular metabolism and function of T cells.

Providing a Helping Hand: Metabolic Regulation of T Follicular Helper Cells and Their Association With Disease

T follicular helper (Tfh) cells provide support to B cells upon arrival in the germinal center, and thus are critical for the generation of a robust adaptive immune response. Tfh express specific transcription factors and cellular receptors including Bcl6, CXCR5, PD-1, and ICOS, which are critical for homing and overall function. Generally, the induction of an immune response is tightly regulated. However, deviation during this process can result in harmful autoimmunity or the inability to successfully clear pathogens. Recently, it has been shown that Tfh differentiation, activation, and proliferation may be linked with the cellular metabolic state. In this review we will highlight recent discoveries in Tfh differentiation and explore how these cells contribute to functional immunity in disease, including autoimmune-related disorders, cancer, and of particular emphasis, during infection.

Synergistic Effects of Toll-Like Receptor 1/2 and Toll-Like Receptor 3 Signaling Triggering Interleukin 27 Gene Expression in Chikungunya Virus-Infected Macrophages

Chikungunya virus (CHIKV) is the etiological agent of chikungunya fever (CHIKF), a self-limiting disease characterized by myalgia and severe acute or chronic arthralgia. CHIKF is associated with immunopathology and high levels of pro-inflammatory factors. CHIKV is known to have a wide range of tropism in human cell types, including keratinocytes, fibroblasts, endothelial cells, monocytes, and macrophages. Previously, we reported that CHIKV-infected monocytes-derived macrophages (MDMs) express high levels of interleukin 27 (IL27), a heterodimeric cytokine consisting of IL27p28 and EBI3 subunits, that triggers JAK-STAT signaling and promotes pro-inflammatory and antiviral response, in interferon (IFN)-independent manner. Based on the transcriptomic analysis, we now report that induction of IL27-dependent pro-inflammatory and antiviral response in CHIKV-infected MDMs relies on two signaling pathways: an early signal dependent on recognition of CHIKV-PAMPs by TLR1/2-MyD88 to activate NF-κB-complex that induces the expression of EBI3 mRNA; and second signaling dependent on the recognition of intermediates of CHIKV replication (such as dsRNA) by TLR3-TRIF, to activate IRF1 and the induction of IL27p28 mRNA expression. Both signaling pathways were required to produce a functional IL27 protein involved in the induction of ISGs, including antiviral proteins, cytokines, CC- and CXC- chemokines in an IFN-independent manner in MDMs. Furthermore, we reported that activation of TLR4 by LPS, both in human MDMs and murine BMDM, results in the induction of both subunits of IL27 that trigger strong IL27-dependent pro-inflammatory and antiviral response independent of IFNs signaling. Our findings are a significant contribution to the understanding of molecular and cellular mechanisms of CHIKV infection.

B cell-derived IL-27 promotes control of persistent LCMV infection

Recent studies have identified a critical role for B cell-produced cytokines in regulating both humoral and cellular immunity. Here, we show that B cells are an essential source of interleukin-27 (IL-27) during persistent lymphocytic choriomeningitis virus (LCMV) clone 13 (Cl-13) infection. By using conditional knockout mouse models with specific IL-27p28 deletion in B cells, we observed that B cell-derived IL-27 promotes survival of virus-specific CD4 T cells and supports functions of T follicular helper (Tfh) cells. Mechanistically, B cell-derived IL-27 promotes CD4 T cell function, antibody class switch, and the ability to control persistent LCMV infection. Deletion of IL-27ra in T cells demonstrated that T cell-intrinsic IL-27R signaling is essential for viral control, optimal CD4 T cell responses, and antibody class switch during persistent LCMV infection. Collectively, our findings identify a cellular mechanism whereby B cell-derived IL-27 drives antiviral immunity and antibody responses through IL-27 signaling on T cells to promote control of LCMV Cl-13 infection.

Assessment of the Impact of Cytokines on TFH, TREG, and TFR Cell Populations After Influenza Infection

Within the last several years, great strides have been made in understanding the molecular and cellular mechanisms that control the generation of T follicular helper (T_FH), T regulatory (T_REG), and T follicular regulatory (T_FR) cells. As a result, it is now clear that cytokines play a critical role in regulating the development and function of these CD4⁺ T cell subsets. One of the critical limitations when studying the effect of individual cytokines in these populations is differentiating between the intrinsic and extrinsic effects of these cytokines in vivo. Here we describe how to utilize mixed bone marrow chimeras in combination with MHC class II tetramers to characterize the direct role played by cytokines on controlling the development, function, and maintenance of T_FH, T_REG, and T_FR cells in vivo.

Costimulation molecules differentially regulate the ERK-Zfp831 axis to shape T follicular helper cell differentiation

T follicular helper (Tfh) cells play essential roles in regulating humoral immunity, especially germinal center reactions. However, how CD4⁺ T cells integrate the antigenic and costimulatory signals in Tfh cell development is still poorly understood. Here, we found that phorbol 12-myristate 13-acetate (PMA) + ionomycin (P+I) stimulation, together with interleukin-6 (IL-6), potently induce Tfh cell-like transcriptomic programs in vitro. The ERK kinase pathway was attenuated under P+I stimulation; ERK2 inhibition enhanced Tfh cell development in vitro and in vivo. We observed that inducible T cell costimulator (ICOS), but not CD28, lacked the ability to activate ERK, which was important in sustaining Tfh cell development. The transcription factor Zfp831, whose expression was repressed by ERK, promoted Tfh cell differentiation by directly upregulating the expression of the transcription factors Bcl6 and Tcf7. We have hence identified an ERK-Zfp831 axis, regulated by costimulation signaling, in critical regulation of Tfh cell development.

AIRE-overexpressing BMDCs suppress TFH cells through ICOSL to prevent and attenuate autoimmune diabetes in NOD mice

The strong genetic association between autoimmune regulator (AIRE) and autoimmune diseases indicates its critical role in immune tolerance. AIRE deficiency is thought to promote the development of follicular helper T (TFH) cells, which are considered to be essential in B cell proliferation. Excessive TFH cell generation is a key step towards the development of autoimmune diseases, including type 1 diabetes. However, the potential mechanism by which AIRE contributes to the generation and function of the TFH cell population has remained elusive. We show that AIRE reduced TFH cell generation by inhibiting the expression of inducible costimulatory ligand (ICOSL), interleukin (IL)-6 and IL-27 in dendritic cells (DCs). To understand the precise impact of AIRE-overexpressing bone marrow-derived DCs (AIRE-BMDCs) on type 1 diabetes progression and the associated molecular mechanisms, we transferred AIRE-BMDCs to recipient NOD mice and found that transplantation of AIRE-BMDCs can prevent or delay the onset of diabetes, attenuate diabetes after the establishment of overt hyperglycaemia, and lead to the inhibition of autoreactive pathological TFH cells and germinal centre (GC) B cells. To further determine the potential mechanism underlying this TFH cell depletion, BMDCs were cotransferred with recombinant mouse ICOSL (ICOSLG protein). We demonstrated that NOD mice were more susceptible to diabetes when they received AIRE-BMDCs and ICOSLG than when they received only mock-vehicle BMDCs (GFP-BMDCs). In addition, we did not observe the reversal of diabetes in any mice subjected to this cotransfer system. A single cycle of ICOSLG treatment temporarily promoted TFH cell proliferation and GC development. Our results reveal a mechanistic role of AIRE-BMDCs in the initiation of TFH cell differentiation, and the AIRE-mediated decrease in ICOSL expression in BMDCs plays a critical role. The effect of decreased ICOSL expression in type 1 diabetes will guide the design and evaluation of parallel studies in patients.

T follicular helper cells: Their development and importance in the context of helminthiasis

The development of T follicular helper cells (Tfh) is a multifactorial process that occurs in multiple stages. After their activation the Tfh cells interact with the B cells to complete their differentiation. During this process, the Tfh cells begin to express canonical molecules such as the transcription factor B-cell lymphoma 6 protein, the CXC chemokine receptors type 5, and the inducible T-cell costimulator, as well as secreting other molecules such as IL-21. This whole process is regulated positively and negatively by several factors so that the best response is offered in the face of diseases of various origins, among them helminthiasis. In this context, the role of circulating Tfh, IL-4 and IgG subtypes is essential for an effective response against these pathogens. In this review, the migration process and the differentiation of Tfh, the regulation, their cell subtypes and the role of Tfh in the context of helminth infections will be addressed.

The dual role of IL-27 in CD4+T cells

Interleukin-27 (IL-27), a member of the IL-6/IL-12 family, has diverse regulatory functions in various immune responses, and is recognised as a potent agonist and antagonist of CD4+T cells in different contexts. However, this dual role and underlying mechanisms have not been completely defined. In the present review, we summarise the dual role of IL-27 in CD4+T cells. In particular, we aimed to decipher its mechanism to better understand the context-dependent function of IL-27 in CD4+T cells. Furthermore, we propose a possible mechanism for the dual role of IL-27. This may be helpful for the development of appropriate IL-27 treatments in various clinical settings.

Emerging roles for IL-6 family cytokines as positive and negative regulators of ectopic lymphoid structures

IL-6 family cytokines display broad effects in haematopoietic and non-haematopoietic cells that regulate immune homeostasis, host defence, haematopoiesis, development, reproduction and wound healing. Dysregulation of these activities places this cytokine family as important mediators of autoimmunity, chronic inflammation and cancer. In this regard, ectopic lymphoid structures (ELS) are a pathological hallmark of many tissues affected by chronic disease. These inducible lymphoid aggregates form compartmentalised T cell and B cell zones, germinal centres, follicular dendritic cell networks and high endothelial venules, which are defining qualities of peripheral lymphoid organs. Accordingly, ELS can support local antigen-specific responses to self-antigens, alloantigens, pathogens and tumours. ELS often correlate with severe disease progression in autoimmune conditions, while tumour-associated ELS are associated with enhanced anti-tumour immunity and a favourable prognosis in cancer. Here, we discuss emerging roles for IL-6 family cytokines as regulators of ELS development, maintenance and activity and consider how modulation of these activities has the potential to aid the successful treatment of autoimmune conditions and cancers where ELS feature.

Predictive Ability of Serum IL-27 Level for Assessing Activity of Antineutrophil Cytoplasmic Antibody-Associated Vasculitis

Serum interleukin- (IL-) 27 level has been reported to increase in patients with several autoimmune diseases; however, its significance in patients with antineutrophil cytoplasmic antibody- (ANCA-) associated vasculitis (AAV) is unknown. In this study, we investigated the associations between serum IL-27, laboratory features, and activity of AAV and evaluate the predictive ability of serum IL-27 level for disease activity. This study included 77 AAV patients, and we collected clinical and laboratory data at blood sampling. Inflammation-related variables included white blood cell, neutrophil, lymphocyte and platelet counts, serum albumin, erythrocyte sedimentation rate, and C-reactive protein levels. Serum IL-27 and IL-18 levels were measured from stored sera using Human Magnetic Luminex® assay. High disease activity of AAV was defined as the highest tertile of Birmingham vasculitis activity score (BVAS) (≥11). The mean age of the enrolled patients was 59.9 years, and 38 (49.4%) were diagnosed as microscopic polyangiitis. In the multivariable analysis, serum albumin (β = −0.419) and serum IL-27 level (β = 0.221) were significantly associated with BVAS. Furthermore, patients with renal manifestation exhibited higher serum IL-27 (mean 308.7 pg/mL vs. 105.8 pg/mL) and IL-18 levels (mean 376.7 pg/mL vs. 270.4 pg/mL) than those without. On applying the optimal cut-off of serum IL-27 level for predicting high activity, AAV patients with serum IL − 27 level ≥ 300.8 pg/mL had a significantly higher risk for having high disease activity than those with serum IL − 27 level < 300.8 pg/mL (relative risk 3.380, 95% confidence interval 1.223, 9.345, P = 0.016). These results suggest that serum IL-27 level is associated with the cross-sectional activity and the presence of renal manifestation and could be used to predict high disease activity in patients with AAV.

α2-3 Sialic acid binding and uptake by human monocyte-derived dendritic cells alters metabolism and cytokine release and initiates tolerizing T cell programming

Dendritic cells (DCs) are key in the initiation of the adaptive T cell responses to tailor adequate immunity that corresponds to the type of pathogen encountered. Oppositely, DCs control the resolution phase of inflammation and are able to induce tolerance after receiving anti-inflammatory cytokines or upon encounter of self-associated molecular patterns, such as α2-3 linked sialic acid (α2-3sia).

Objective: We here investigated whether α2-3sia, that bind immune inhibitory Siglec receptors, would alter signaling and reprogramming of LPS-stimulated human monocyte-derived DCs (moDCs).

Methods and Results: Transcriptomic analysis of moDCs stimulated with α2-3sia-conjugated dendrimers revealed differentially expressed genes related to metabolic pathways, cytokines, and T cell differentiation. An increase in genes involved in ATPase regulator activity, oxidoreductase activity, and glycogen metabolic processes was detected. Metabolic extracellular flux analysis confirmed a more energetic moDC phenotype upon α2-3sia binding as evidenced by an increase in both glycolysis and mitochondrial oxidative phosphorylation. TH1 differentiation promoting genes IFNL and IL27, were significantly downregulated in the presence of α2-3sia. Functional assays confirmed that α2-3sia binding to moDCs induced phosphorylation of Siglec-9, reduced production of inflammatory cytokines IL-12 and IL-6, and increased IL-10. Surprisingly, α2-3sia-differentiated moDCs promoted FoxP3+CD25+/-CD127- regulatory T cell differentiation and decreased FoxP3-CD25-CD127- effector T cell proliferation.

Conclusions: In conclusion, we demonstrate that α2-3sia binding to moDCs, phosphorylates Siglec-9, alters metabolic pathways, cytokine signaling, and T cell differentiation processes in moDCs and promotes regulatory T cells. The sialic acid-Siglec axis on DCs is therefore, a novel target to induce tolerance and to explore for immunotherapeutic interventions aimed to restore inflammatory processes.

A review of signaling and transcriptional control in T follicular helper cell differentiation

T follicular helper (Tfh) cells are a critical component of adaptive immunity and assist in optimal Ab-mediated defense. Multiple effector functions of Tfh support germinal center B cell survival, Ab class switching, and plasma cell maturation. In the past 2 decades, the phenotype and functional characteristics of GC Tfh have been clarified allowing for robust studies of the Th subset including activation signals and environmental cues controlling Tfh differentiation and migration during an immune response. A unique, 2-step differentiation process of Tfh has been proposed but the mechanisms underlying transition between unstable Tfh precursors and functional mature Tfh remain elusive. Likewise, newly identified transcriptional regulators of Tfh development have not yet been incorporated into our understanding of how these cells might function in disease. Here, we review the signals and downstream transcription factors that shape Tfh differentiation including what is known about the epigenetic processes that maintain Tfh identity. It is proposed that further evaluation of the stepwise differentiation pattern of Tfh will yield greater insights into how these cells become dysregulated in autoimmunity.

IL-21-Deficient T Follicular Helper Cells Support B Cell Responses Through IL-27 in Patients With Chronic Hepatitis B

Chronic Hepatitis B (CHB) affects over 350 million people worldwide. Current treatment does result in reduced complications; however, a cure (development of antibodies to the S antigen) is not achieved, requiring life-long therapy. Humoral responses contribute to viral elimination by secreting neutralizing antibodies; though, effective induction of humoral immunity require CD4T cell differentiation into T follicular helper (T_FH) cells that support B cell response through interleukin-21 (IL-21). In CHB, mechanism of T_FH-B interactions is seldom described. During CHB, T_FH cells are defective in producing IL-21 in response to hepatitis B surface antigen (HBsAg). However, regardless of low IL-21, T_FH cells efficiently support B cell responses by producing interleukin-27 (IL-27), which directs the formation of plasmablasts and plasma cells from memory and naïve B cells by enhancing B lymphocyte-induced maturation protein-1. IL-27 not only improved total antibody production but HBsAg-specific IgG and IgM secretion that are essential for viral clearance. Importantly, IL-27+T_FH cells were significantly associated with HBV DNA reduction. Therefore, these findings imply a novel mechanism of T_FH mediated B cell help in CHB and suggest that IL-27 effectively compensate the function of IL-21 by supporting T_FH-B cell function, required for protective antibody response and may contribute to viral clearance by providing potential target for achieving a functional cure.

Functional differentiation and regulation of follicular T helper cells in inflammation and autoimmunity

Follicular T helper (T_FH ) cells are specialized T cells that support B cells, which are essential for humoral immunity. T_FH cells express the transcription factor B-cell lymphoma 6 (Bcl-6), chemokine (C-X-C motif) receptor (CXCR) 5, the surface receptors programmed cell death protein 1 (PD-1) and inducible T-cell costimulator (ICOS), the cytokine IL-21 and other molecules. The activation, proliferation and differentiation of T_FH cells are closely related to dynamic changes in cellular metabolism. In this review, we summarize the progress made in understanding the development and functional differentiation of T_FH cells. Specifically, we focus on the regulatory mechanisms of T_FH cell functional differentiation, including regulatory signalling pathways and the metabolic regulatory mechanisms of T_FH cells. In addition, T_FH cells are closely related to immune-associated diseases, including infections, autoimmune diseases and cancers.

IL-27, a pleiotropic cytokine for fine-tuning the immune response in cancer

Interleukin (IL)-27, a member of the IL-6/IL-12 family, has an important role in modulating inflammation in partnership with innate and adaptive immune cells. IL-27 binding to IL-27R starts downstream signaling based on the target cells. It can instigate inflammation by inducing CD4⁺ T cell proliferation, Th1 polarization, cytotoxic T cell activation, generation of the natural killer cell, and macrophage and dendritic cell activation. However, by inducing programmed cell death and suppression of effector cells, IL-27 can suppress inflammation and return the immune response to hemostasis. Altogether, IL-27 displays multifaceted dual functions, which may result in either pro- or anti-inflammatory effects. Recent investigations indicated the antitumor activity of IL-27 via inducing Th1, and CTL responses and generating NK cells. On the other hand, IL-27 also can promote tumor cells' proliferation, survival, and angiogenesis. In the present review, we'll discuss recent advances concerning the role of IL-27 in inflammatory diseases such as infections, autoimmune diseases with a focus on cancer.

The role of B7 family members in the generation of Immunoglobulin

Ig is a Y-shaped protein produced by plasma cells and exerts multiple functions in humoral immunity. There are five groups of Igs including IgA, IgD, IgE, IgG, and IgM, which differ in their heavy chain class. The primary function of Igs includes the neutralization of extrinsic pathogens, agglutination of foreign cells for phagocytosis, precipitation of soluble antigens in serum, and complement fixation. The B cells activated by antigen(s) can differentiate into antibody-producing cells that are called plasma cells and usually matured in the germinal center (GC). Follicular T helper (Tfh) cells crosstalk with antigen-presenting cells and play a crucial role in the development of the GC. Moreover, Tfh cells regulate trafficking through the GC to allow formative interaction with GC B cells that ultimately results in affinity maturation, B-cell memory, and Ig class switching. The B7 family is a series of number of structurally related membrane proteins that bind with a specific receptor to deliver costimulatory or co-inhibitory signals that regulate the activation of T cells in GC. Here, we review and summarize the recent advance of the effects of B7 family members on Ig production and relative diseases.

Impaired Interleukin-27-Mediated Control of CD4+ T Cell Function Impact on Ectopic Lymphoid Structure Formation in Patients With Sjögren's Syndrome

OBJECTIVE

Ectopic lymphoid structures (ELS) develop at sites of infection, autoimmunity, and cancer. In patients with Sjögren's syndrome (SS), ELS support autoreactive B cell activation and lymphomagenesis. Interleukin-27 (IL-27) is a key regulator of adaptive immunity and limits Th17 cell-driven pathology. We undertook this study to elucidate the role of IL-27 in ELS formation and function in autoimmunity using a murine model of sialadenitis and in patients with SS.

METHODS

ELS formation was induced in wild-type and Il27ra-/- mice via salivary gland (SG) cannulation of a replication-deficient adenovirus in the presence or absence of IL-17A neutralization. In SG biopsy samples, IL-27-producing cells were identified by multicolor immunofluorescence microscopy. Lesional and circulating IL-27 levels were determined by gene expression and enzyme-linked immunosorbent assay. The in vitro effect of IL-27 on T cells was assessed using fluorescence-activated cell sorting and cytokine release.

RESULTS

In experimental sialadenitis, Il27ra-/- mice had larger and more hyperactive ELS (focus score; P < 0.001), increased autoimmunity, and an expanded Th17 response (P < 0.001), compared to wild-type mice. IL-17 blockade in Il27ra-/- mice suppressed the aberrant ELS response (B and T cell reduction against control; P < 0.01). SS patients displayed increased circulating IL-27 levels (P < 0.01), and in SG biopsy samples, IL-27 was expressed by DC-LAMP+ dendritic cells in association with CD3+ T cells. Remarkably, in SS T cells (but not in T cells from patients with rheumatoid arthritis or healthy controls), IL-27-mediated suppression of IL-17 secretion was severely impaired and associated with an aberrant interferon-γ release upon IL-27 stimulation.

CONCLUSION

Our data indicate that the physiologic ability of IL-27 to limit the magnitude and function of ELS through control of Th17 cell expansion is severely impaired in SS patients, highlighting a defective immunoregulatory checkpoint in this condition.

T Cell Immunity to Bacterial Pathogens: Mechanisms of Immune Control and Bacterial Evasion

The human body frequently encounters harmful bacterial pathogens and employs immune defense mechanisms designed to counteract such pathogenic assault. In the adaptive immune system, major histocompatibility complex (MHC)-restricted αβ T cells, along with unconventional αβ or γδ T cells, respond to bacterial antigens to orchestrate persisting protective immune responses and generate immunological memory. Research in the past ten years accelerated our knowledge of how T cells recognize bacterial antigens and how many bacterial species have evolved mechanisms to evade host antimicrobial immune responses. Such escape mechanisms act to corrupt the crosstalk between innate and adaptive immunity, potentially tipping the balance of host immune responses toward pathological rather than protective. This review examines the latest developments in our knowledge of how T cell immunity responds to bacterial pathogens and evaluates some of the mechanisms that pathogenic bacteria use to evade such T cell immunosurveillance, to promote virulence and survival in the host.

Interleukin-27 Functional Duality Balances Leishmania Infectivity and Pathogenesis

IL-27 is a cytokine that exerts diverse effects on the cells of innate and adaptive immune systems. Chiefly expressed in macrophages and dendritic cells during the early phase of Leishmania infection, IL-27 contributes to the protection against L. major infection but suppresses the protective Th1 response against L. donovani, L. infantum, L. amazonensis and L. braziliensis infections, suggesting its functional duality. During the late stage of Leishmania infection, IL-27 limits the immunopathogenic reactions and tissue damages. Herein, we analyze the mechanism of the functional duality of IL-27 in the resistance or susceptibility to Leishmania infection, prompting IL-27 for anti-Leishmanial therapy.

IL-27: An endogenous constitutive repressor of human monocytes

Interleukin (IL)-27 is a pleiotropic cytokine that initially was described as being pro-inflammatory and an inducer of T helper (Th)1 cells. In contrast, it has also been described as an anti-inflammatory cytokine in that it suppresses pro-inflammatory Th17 cells and induces anti-inflammatory IL-10 producing T regulatory (Tr)1 cells. While the majority of studies have been focused on the effects of IL-27 on T cells, human antigen-presenting cells express high levels of the IL-27 receptor ex vivo, in addition to being the major producer of IL-27. We report here that human monocytes are repressed by endogenous IL-27, in that the addition of an anti-IL-27 neutralizing antibody increases the production of pro-inflammatory cytokines ex vivo. We observed that neutralizing monocyte-derived IL-27 leads to increased IL-17A production by CD4+ T cells and a down-regulation of the IL-17 modulating ectonucleotidase CD39 on monocytes. The locus that contains the IL27 gene has been linked to susceptibility for type 1 diabetes (T1D). Interestingly, ex vivo monocytes from subjects with T1D produce more IL-27 suggesting this upregulation of IL-27 acts as a negative feedback loop to attempt to counterbalance the pro-inflammatory immune response in the disease state. In summary, we provide evidence that IL-27 is an endogenous regulator of human monocytes and has consequences on CD4+ T cell phenotype, particularly Th17 cells.

The Impact of Malaria Parasites on Dendritic Cell-T Cell Interaction

Malaria is caused by apicomplexan parasites of the genus Plasmodium. While infection continues to pose a risk for the majority of the global population, the burden of disease mainly resides in Sub-Saharan Africa. Although immunity develops against disease, this requires years of persistent exposure and is not associated with protection against infection. Repeat infections occur due to the parasite's ability to disrupt or evade the host immune responses. However, despite many years of study, the mechanisms of this disruption remain unclear. Previous studies have demonstrated a parasite-induced failure in dendritic cell (DCs) function affecting the generation of helper T cell responses. These T cells fail to help B cell responses, reducing the production of antibodies that are necessary to control malaria infection. This review focuses on our current understanding of the effect of Plasmodium parasite on DC function, DC-T cell interaction, and T cell activation. A better understanding of how parasites disrupt DC-T cell interactions will lead to new targets and approaches to reinstate adaptive immune responses and enhance parasite immunity.

Regulation of the germinal center and humoral immunity by interleukin-21

Here we review the critical and non-redundant functions of IL-21 in regulating humoral immune responses. We particularly focus on studies in natura—from individuals from inborn errors of immunity that impact on IL-21 production and/or function.

Cytokines play critical roles in regulating the development, survival, differentiation, and function of immune cells. Cytokines exert their function by binding specific receptor complexes on the surface of immune cells and activating intracellular signaling pathways, thereby resulting in induction of specific transcription factors and regulated expression of target genes. While the function of cytokines is often fundamental for the generation of robust and effective immunity following infection or vaccination, aberrant production or function of cytokines can underpin immunopathology. IL-21 is a pleiotropic cytokine produced predominantly by CD4⁺ T cells. Gene-targeting studies in mice, in vitro analyses of human and murine lymphocytes, and the recent discoveries and analyses of humans with germline loss-of-function mutations in IL21 or IL21R have revealed diverse roles of IL-21 in immune regulation and effector function. This review will focus on recent advances in IL-21 biology that have highlighted its critical role in T cell–dependent B cell activation, germinal center reactions, and humoral immunity and how impaired responses to, or production of, IL-21 can lead to immune dysregulation.

T Helper Plasticity Is Orchestrated by STAT3, Bcl6, and Blimp-1 Balancing Pathology and Protection in Malaria

Hybrid Th1/Tfh cells (IFN-γ⁺IL-21⁺CXCR5⁺) predominate in response to several persistent infections. In Plasmodium chabaudi infection, IFN-γ⁺ T cells control parasitemia, whereas antibody and IL-21⁺Bcl6⁺ T cells effect final clearance, suggesting an evolutionary driver for the hybrid population. We found that CD4-intrinsic Bcl6, Blimp-1, and STAT3 coordinately regulate expression of the Th1 master regulator T-bet, supporting plasticity of CD4 T cells. Bcl6 and Blimp-1 regulate CXCR5 levels, and T-bet, IL-27Rα, and STAT3 modulate cytokines in hybrid Th1/Tfh cells. Infected mice with STAT3 knockout (KO) T cells produced less antibody and more Th1-like IFN-γ⁺IL-21⁻CXCR5^lo effector and memory cells and were protected from re-infection. Conversely, T-bet KO mice had reduced Th1-bias upon re-infection and prolonged secondary parasitemia. Therefore, each feature of the CD4 T cell population phenotype is uniquely regulated in this persistent infection, and the cytokine profile of memory T cells can be modified to enhance the effectiveness of the secondary response.

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Plasmodium infection induces a CXCR5⁺IFN-γ⁺IL-21⁺ hybrid Th1/Tfh cell subset

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STAT3/WSX-1, T-bet, Bcl6, and Blimp-1 regulate different aspects of Th1/Tfh phenotype

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T cell-intrinsic STAT3 regulates degree of Th1 commitment of hybrid Th1/Tfh

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Shifting the plastic response toward Th1-like cells promotes resistance from reinfection

Pristane/Hypoxia (PriHx) Mouse as a Novel Model of Pulmonary Hypertension Reflecting Inflammation and Fibrosis

BACKGROUND

Pulmonary arterial hypertension (PAH), particularly connective tissue disease-associated PAH (CTD-PAH), is a progressive disease and novel therapeutic agents based on the specific molecular pathogenesis are desired. In the pathogenesis of CTD-PAH, inflammation, immune cell abnormality, and fibrosis play important roles. However, the existing mouse pulmonary hypertension (PH) models do not reflect these features enough. The relationship between inflammation and hypoxia is still unclear.Methods and Results:Intraperitoneal administration of pristane, a kind of mineral oil, and exposure to chronic hypoxia were combined, and this model is referred to as pristane/hypoxia (PriHx) mice. Hemodynamic and histological analyses showed that the PriHx mice showed a more severe phenotype of PH than pristane or hypoxia alone. Immunohistological and flow cytometric analyses revealed infiltration of immune cells, including hemosiderin-laden macrophages and activated CD4⁺helper T lymphocytes in the lungs of PriHx mice. Pristane administration exacerbated lung fibrosis and elevated the expression of fibrosis-related genes. Inflammation-related genes such asIl6andCxcl2were also upregulated in the lungs of PriHx mice, and interleukin (IL)-6 blockade by monoclonal anti-IL-6 receptor antibody MR16-1 ameliorated PH of PriHx mice.

CONCLUSIONS

A PriHx model, a novel mouse model of PH reflecting the pathological features of CTD-PAH, was developed through a combination of pristane administration and exposure to chronic hypoxia.

The contribution from interleukin-27 towards rheumatoid inflammation: insights from gene expression

We aimed to assess expression of genes encoding the heterodimeric IL-27 cytokine and constituent subunits of the Il-27 receptor in rheumatoid arthritis (RA), including in extra-articular, subcutaneous rheumatoid nodules. Comparing between nodules and joint synovia, significantly elevated expression of IL27A within nodules, and comparable IL27B expression, identified nodules as a significant source of IL-27 in RA. T-lymphocytes were the main source of IL27RA transcript, and IL27RA expression correlated with a number of plasma cytokines, as well as tissue TNF expression in both nodules and RA synovia. In synovia, correlations between IL27A, IL27RA IL17A and CD21L expression, and significantly elevated expression of the genes encoding IL-27, associated the presence of IL-27 with B cell-dominated synovial inflammation. Impact from nodule derived IL-27 on systemic or synovial inflammation in RA remains unknown and further study of these implications is required. Our study raises questions regarding the appropriate circumstances for the blockade or administration of IL-27 as a potential therapeutic adjunct in RA.

IgG Fc sialylation is regulated during the germinal center reaction following immunization with different adjuvants

BACKGROUND

Effector functions of IgG Abs are regulated by their Fc N-glycosylation pattern. IgG Fc glycans that lack galactose and terminal sialic acid residues correlate with the severity of inflammatory (auto)immune disorders and have also been linked to protection against viral infection and discussed in the context of vaccine-induced protection. In contrast, sialylated IgG Abs have shown immunosuppressive effects.

OBJECTIVE

We sought to investigate IgG glycosylation programming during the germinal center (GC) reaction following immunization of mice with a foreign protein antigen and different adjuvants.

METHODS

Mice were analyzed for GC T-cell, B-cell, and plasma cell responses, as well as for antigen-specific serum IgG subclass titers and Fc glycosylation patterns.

RESULTS

Different adjuvants induce distinct IgG⁺ GC B-cell responses with specific transcriptomes and expression levels of the α2,6-sialyltransferase responsible for IgG sialylation that correspond to distinct serum IgG Fc glycosylation patterns. Low IgG Fc sialylation programming in GC B cells was overall highly dependent on the Foxp3^- follicular helper T (T_FH) cell-inducing cytokine IL-6, here in particular induced by water-in-oil adjuvants and Mycobacterium tuberculosis. Furthermore, low IgG Fc sialylation programming was dependent on adjuvants that induced IL-27 receptor-dependent IFN-γ⁺ T_FH1 cells, IL-6/IL-23-dependent IL-17A⁺ T_FH17 cells, and high ratios of T_FH cells to Foxp3⁺ follicular regulatory T cells. Here, the 2 latter were dependent on M tuberculosis and its cord factor.

CONCLUSION

This study's findings regarding adjuvant-dependent GC responses and IgG glycosylation programming may aid in the development of novel vaccination strategies to induce IgG Abs with both high affinity and defined Fc glycosylation patterns in the GC.

Antigen presentation by dendritic cells and their instruction of CD4+ T helper cell responses

Dendritic cells are powerful antigen-presenting cells that are essential for the priming of T cell responses. In addition to providing T-cell-receptor ligands and co-stimulatory molecules for naive T cell activation and expansion, dendritic cells are thought to also provide signals for the differentiation of CD4+ T cells into effector T cell populations. The mechanisms by which dendritic cells are able to adapt and respond to the great variety of infectious stimuli they are confronted with, and prime an appropriate CD4+ T cell response, are only partly understood. It is known that in the steady-state dendritic cells are highly heterogenous both in phenotype and transcriptional profile, and that this variability is dependent on developmental lineage, maturation stage, and the tissue environment in which dendritic cells are located. Exposure to infectious agents interfaces with this pre-existing heterogeneity by providing ligands for pattern-recognition and toll-like receptors that are variably expressed on different dendritic cell subsets, and elicit production of cytokines and chemokines to support innate cell activation and drive T cell differentiation. Here we review current information on dendritic cell biology, their heterogeneity, and the properties of different dendritic cell subsets. We then consider the signals required for the development of different types of Th immune responses, and the cellular and molecular evidence implicating different subsets of dendritic cells in providing such signals. We outline how dendritic cell subsets tailor their response according to the infectious agent, and how such transcriptional plasticity enables them to drive different types of immune responses.

Rejuvenating conventional dendritic cells and T follicular helper cell formation after vaccination

Germinal centres (GCs) are T follicular helper cell (Tfh)-dependent structures that form in response to vaccination, producing long-lived antibody secreting plasma cells and memory B cells that protect against subsequent infection. With advancing age the GC and Tfh cell response declines, resulting in impaired humoral immunity. We sought to discover what underpins the poor Tfh cell response in ageing and whether it is possible to correct it. Here, we demonstrate that older people and aged mice have impaired Tfh cell differentiation upon vaccination. This deficit is preceded by poor activation of conventional dendritic cells type 2 (cDC2) due to reduced type 1 interferon signalling. Importantly, the Tfh and cDC2 cell response can be boosted in aged mice by treatment with a TLR7 agonist. This demonstrates that age-associated defects in the cDC2 and Tfh cell response are not irreversible and can be enhanced to improve vaccine responses in older individuals.

Interleukin-27 Enforces Regulatory T Cell Functions to Prevent Graft-versus-Host Disease

Graft-versus-host disease (GvHD) remains a significant complication of allogeneic hematopoietic cell transplantation (HCT), associated with significant morbidity and mortality. GvHD is characterized by dysregulated immune responses and resulting tissue damage of target organs. Recent investigations have focused on Foxp3⁺ regulatory T cells (Tregs) as a therapeutic tool, based on its regulatory functions in GvHD pathogenesis and their instrumental role in mitigating GvHD severity while preserving graft-versus-leukemia (GvL) activity. There are several challenges to its clinical application, including their paucity, impaired suppressive activity, and instability in vivo. Herein, we report that IL-27 pre-stimulation enhances suppressive functions of both mouse and human Tregs. In a complete MHC mismatched murine bone marrow transplant model, IL-27 pre-stimulated polyclonal iTregs diminish acute (a)GvHD lethality, while preserving the GvL effect. Allo-antigen specificity further improves suppressive functions when combined with IL-27 pre-stimulation. In a xenogeneic (human to mouse) GvHD model, IL-27 pre-stimulated human iTregs are superior in protecting recipients from GvHD. Lastly, we compared gene expression profiles of circulating Tregs isolated from HCT recipients with and without aGvHD and found that Tregs from aGvHD patients express distinct gene signatures enriched in immune activation and inflammation. Therefore, these results highlight a novel function of IL-27 in enforcing Treg functions to prevent aGvHD mediated lethality, proposing the hypothesis that dysregulated Treg functions may account for the potential mechanisms underlying GvHD development.

Dysregulation of T Follicular Helper Cells in Lupus

Although multiple and overlapping mechanisms are ultimately responsible for the immunopathology observed in patients with systemic lupus erythematosus, autoreactive Abs secreted by autoreactive plasma cells (PCs) are considered to play a critical role in disease progression and immunopathology. Given that PCs derive from the germinal centers (GC), long-term dysregulated GC reactions are often associated with the development of spontaneous autoantibody responses and immunopathology in systemic lupus erythematosus patients. In this review, we summarize the emerging evidence concerning the roles of T follicular helper cells in regulating pathogenic GC and autoreactive PC responses in lupus.