The IL-12-STAT4 axis in the pathogenesis of human systemic lupus erythematosus

IL-12 family cytokines and autoimmune diseases: A potential therapeutic target?

In recent years, the discovery of IL-12 family cytokines, which includes IL-12, IL-23, IL-27, IL-35, and IL-39, whose biological functions directly or indirectly affect various autoimmune diseases. In autoimmune diseases, IL-12 family cytokines are aberrantly expressed to varying degrees. These cytokines utilize shared subunits to influence T-cell activation and differentiation, thereby regulating the balance of T-cell subsets, which profoundly impacts the onset and progression of autoimmune diseases. In such conditions, IL-12 family members are aberrantly expressed to varying degrees. By exploring their immunomodulatory functions, researchers have identified varying therapeutic potentials for each member. This review examines the physiological functions of the major IL-12 family members and their interactions, discusses their roles in several autoimmune diseases, and summarizes the progress of clinical studies involving monoclonal antibodies targeting IL-12 and IL-23 subunits currently available for treatment.

Lupus and inflammatory bowel disease share a common set of microbiome features distinct from other autoimmune disorders

OBJECTIVES

This study aims to elucidate the microbial signatures associated with autoimmune diseases, particularly systemic lupus erythematosus (SLE) and inflammatory bowel disease (IBD), compared with colorectal cancer (CRC), to identify unique biomarkers and shared microbial mechanisms that could inform specific treatment protocols.

METHODS

We analysed metagenomic datasets from patient cohorts with six autoimmune conditions-SLE, IBD, multiple sclerosis, myasthenia gravis, Graves' disease and ankylosing spondylitis-contrasting these with CRC metagenomes to delineate disease-specific microbial profiles. The study focused on identifying predictive biomarkers from species profiles and functional genes, integrating protein-protein interaction analyses to explore effector-like proteins and their targets in key signalling pathways.

RESULTS

Distinct microbial signatures were identified across autoimmune disorders, with notable overlaps between SLE and IBD, suggesting shared microbial underpinnings. Significant predictive biomarkers highlighted the diverse microbial influences across these conditions. Protein-protein interaction analyses revealed interactions targeting glucocorticoid signalling, antigen presentation and interleukin-12 signalling pathways, offering insights into possible common disease mechanisms. Experimental validation confirmed interactions between the host protein glucocorticoid receptor (NR3C1) and specific gut bacteria-derived proteins, which may have therapeutic implications for inflammatory disorders like SLE and IBD.

CONCLUSIONS

Our findings underscore the gut microbiome's critical role in autoimmune diseases, offering insights into shared and distinct microbial signatures. The study highlights the potential importance of microbial biomarkers in understanding disease mechanisms and guiding treatment strategies, paving the way for novel therapeutic approaches based on microbial profiles.

TRIAL REGISTRATION NUMBER

NCT02394964.

Cordyceps protein alleviates renal injury by inhibiting T cell infiltration and Th1 cell differentiation in lupus nephritis mice

BACKGROUND

T cell infiltration and differentiation play a central part in the development of lupus nephritis (LN). Our prior research has indicated that protein, the primary active component of cordyceps (WCP), a traditional Chinese medicine, possesses properties that can enhance renal fibrosis and provide kidney protection. Nonetheless, the connection between WCP and T cell infiltration and differentiation in LN remains poorly understood.

OBJECTIVE

The objective of this research was to assess the immunomodulatory impacts of WCP in LN mice and elucidate the underlying mechanism through in vivo and in vitro investigations.

METHODS

To investigate the impact and mechanism of WCP in MRL/lpr lupus-prone mice, WCP (1.5 g/kg/d), Bailing capsules (BC, 0.75 g/kg/d), and saline in equivalent quantities were administered to the mice over a period of 8 weeks. The therapeutic effects, T cell infiltration and differentiation of WCP on MRL/lpr mice were verified through ELISA, Hematoxylin-eosin (H&E), Periodic Acid Schiff (PAS) staining, immunofluorescence, Luminex analysis and flow cytometry. The mechanism by which WCP alleviates LN was investigated using tissues of mice, T cells and Mouse Podocyte Clone-5 (MPC-5) cells by transcriptomics, Western blot (WB), and Real-time quantitative polymerase chain reaction (RT-qPCR).

RESULTS

We found that WCP improved LN in MRL/lpr mice by reducing urinary protein, creatinine, and serum auto antibodies, increasing complement 3 (C3) level, improving renal immunopathology and downregulating serum cytokines, including IFN-γ, IL-12, and RANTES. Notably, the infiltration of CD4+ and CD8+ T cells in the kidney was reduced by WCP. Similarly, the cell transwell co-culturation study showed that the WCP treated MPC-5 cells were weaker in inducing T cell migration. Consistent with this finding, our observations revealed that WCP could inhibit T cell-related chemokine expression in kidney and MPC-5 cells, as well as reduce the levels of TLR4, MYD88, phosphorylated-p38, phosphorylated-ERK, and phosphorylated-JNK. On the other hand, WCP was found to greatly inhibit the Th1 cells differentiation in vivo and in vitro. Cytokine-receptor induced Th1 cell differentiation pathway and PI3K-AKT pathway were the most enriched pathways based on differentially expressed genes (DEGs) enrichment analysis among different cell groups. Results from RT-qPCR and WB showed that WCP notably reduced the levels of IL-12, p-STAT4, IFN-γ, p-STAT1, p-PI3K, and p-AKT in T cells.

CONCLUSION

WCP demonstrated positive immunomodulatory effects on LN disease, by decreasing the T cells infiltration through TLR4/MYD88/MAPK signaling pathway and inhibiting Th1 cells differentiation via IL-12-STAT4 and IFN-γ-STAT1 pathways, in addition to the PI3K-AKT pathway.

Genetic polymorphisms in genes involved in the type I interferon system (STAT4 and IRF5): association with Asian SLE patients

Systemic lupus erythematosus (SLE) is a common autoimmune disease with a polymorphic clinical presentation involving multisystem damages with significant differences in prevalence and disease severity among different ethnic groups. Although genetic, hormonal, and environmental factors have been demonstrated to contribute a lot to SLE, the pathogenesis of SLE is still unknown. Numerous evidence revealed that gene variants within the type I interferons (IFN) signaling pathway performed the great genetic associations with autoimmune diseases including SLE. To date, through genome-wide association studies (GWAS), genetic association studies showed that more than 100 susceptibility genes have been linked to the pathogenesis of SLE, among which TYK2, STAT1, STAT4, and IRF5 are important molecules directly connected to the type I interferon signaling system. The review summarized the genetic associations and the detailed risk loci of STAT4 and IRF5 with Asian SLE patients, explored the genotype distributions associated with the main clinical manifestations of SLE, and sorted out the potential reasons for the differences in susceptibility in Asia and Europe. Moreover, the therapies targeting STAT4 and IRF5 were also evaluated in order to propose more personalized and targeted treatment plans in SLE.

Targeting T-bet expressing B cells for therapeutic interventions in autoimmunity

Apart from serving as a Th1 lineage commitment regulator, transcription factor T-bet is also expressed in other immune cell types and thus orchestrates their functions. In case of B cells, more specifically, T-bet is responsible for their isotype switching to specific IgG sub-classes (IgG2a/c in mice and IgG1/3 in humans). In various autoimmune disorders, such as systemic lupus erythematosus and/or rheumatoid arthritis, subsets of T-bet expressing B cells, known as age-associated B cells (CD19+CD11c+CD21-T-bet+) and/or double-negative B cells (CD19+IgD-CD27-T-bet+), display an expansion and seem to drive disease pathogenesis. According to data, mostly derived from mice models of autoimmunity, the targeting of these specific B-cell populations is capable of ameliorating the general health status of the autoimmune subjects. Here, in this review article, we present a variety of therapeutic approaches for both mice and humans, suffering from an autoimmune disease, and we discuss the effects of each approach on T-bet+ B cells. In general, we highlight the importance of specifically targeting T-bet+ B cells for therapeutic interventions in autoimmunity.

SOCS1 is a critical checkpoint in immune homeostasis, inflammation and tumor immunity

The Suppressor of Cytokine Signaling (SOCS) family proteins are important negative regulators of cytokine signaling. SOCS1 is the prototypical member of the SOCS family and functions in a classic negative-feedback loop to inhibit signaling in response to interferon, interleukin-12 and interleukin-2 family cytokines. These cytokines have a critical role in orchestrating our immune defence against viral pathogens and cancer. The ability of SOCS1 to limit cytokine signaling positions it as an important immune checkpoint, as evidenced by the detection of detrimental SOCS1 variants in patients with cytokine-driven inflammatory and autoimmune disease. SOCS1 has also emerged as a key checkpoint that restricts anti-tumor immunity, playing both a tumor intrinsic role and impacting the ability of various immune cells to mount an effective anti-tumor response. In this review, we describe the mechanism of SOCS1 action, focusing on the role of SOCS1 in autoimmunity and cancer, and discuss the potential for new SOCS1-directed cancer therapies that could be used to enhance adoptive immunotherapy and immune checkpoint blockade.

Modifying T cell phenotypes using TYK2 inhibitor and its implications for the treatment of systemic lupus erythematosus

OBJECTIVES

The tuning effects of JAK/TYK2 inhibitors on the imbalance between T follicular helper (Tfh) and T regulatory (Treg) cells, related to systemic lupus erythematosus (SLE) pathogenesis, were investigated using human peripheral blood samples.

METHODS

Peripheral blood mononuclear cells from untreated patients with SLE and healthy controls were analysed. Tfh1 cells were identified in nephritis tissue, and the effect of Tfh1 cells on B-cell differentiation was examined by coculturing naïve B cells with Tfh1 cells.

RESULTS

Tfh1 cell numbers were increased in the peripheral blood of patients, and activated Treg cell counts were decreased relative to Tfh1 cell counts. This imbalance in the Tfh to Treg ratio was remarkably pronounced in cases of lupus nephritis, especially in types III and IV active nephritis. Immunohistochemistry revealed Tfh1 cell infiltration in lupus nephritis tissues. Co-culture of Tfh1 cells (isolated from healthy individuals) with naïve B cells elicited greater induction of T-bet+ B cells than controls. In JAK/TYK2-dependent STAT phosphorylation assays using memory CD4+ T cells, IL-12-induced STAT1/4 phosphorylation and Tfh1 cell differentiation were inhibited by both JAK and TYK2 inhibitors. However, phosphorylation of STAT5 by IL-2 and induction of Treg cell differentiation by IL-2+TGFβ were inhibited by JAK inhibitors but not by TYK2 inhibitors, suggesting that TYK2 does not mediate the IL-2 signalling pathway.

CONCLUSIONS

Tfh1 cells can induce T-bet+ B cell production and may contribute to SLE pathogenesis-associated processes. TYK2 inhibitor may fine-tune the immune imbalance by suppressing Tfh1 differentiation and maintaining Treg cell differentiation, thereby preserving IL-2 signalling, unlike other JAK inhibitors.

Peripheral helper T cells in human diseases

Peripheral helper T cells (Tph) are a specialized subset of CD4+ T cells with the ability to help B cells and induce antibody production. Although usually located in ectopic lymphoid-like structures (ELS), inside the peripheral blood, Tph cells can also be identified. The aberrant proliferation and functions of Tph cells are commonly found in the patients with disease. In this review, first we will summarize the biological characteristics of Tph cells, such as the expression of surface molecules, transcription factors and cytokines, and discuss its B cell help functions. Tph cells also have roles in a wide range of human diseases, including autoimmune diseases, infectious diseases, malignancies etc. Therefore, there is a strong interest in targeting Tph cells to improve treat strategies of human diseases.

Circulating TIGIT±PD1+TPH, TIGIT ± PD1+TFH cells are elevated and their predicting role in systemic lupus erythematosus

It is well established that increased peripheral helper T cells (TPH) and follicular helper T cells (TFH) was found in systemic lupus erythematosus (SLE) patients. However, the expression patterns and immunomodulatory roles of TIGIT and PD1 on TPH/TFH in SLE are poorly understood. The expression patterns of TIGIT and PD1 on TPH and TFH cells were examined using flow cytometry and their expression patterns in SLE patients were then further evaluated for their correlation with auto-antibodies, disease activity and severity, B cell differentiation. Logistic regression was used to analyze the risk factors. And the receiver operating characteristic curves and logistic regression model were created to evaluate the predicting role in SLE. TIGIT±PD1+TPH, TIGIT±PD1+TFH cells in the peripheral blood of SLE patients were upregulated, whereas TIGIT+PD1-TFH was downregulated. TIGIT ± PD1+TPH, TIGIT ± PD1+TFH cells positively correlated with auto-antibodies production, disease activity and severity, whereas TIGIT+PD1-TFH cells negatively correlated. TIGIT ± PD1+TPH, TIGIT-PD1+TFH were positively correlated with the frequency of plasmablasts. Furthermore, higher TIGIT+PD1+TPH and TIGIT+PD1+TFH were shown to be risk factors for SLE, whereas TIGIT+PD1-TFH was found to be a protective factor, according to logistic regression analysis. A further logistic regression model showed that combination of TPH/TFH and routine blood indicators may has potential predicting value for SLE, with AUC of 0.957. The increased TIGIT ± PD1+TPH, increased TIGIT ± PD1+TFH, decreased TIGIT+PD1-TFH correlates with disease severity and activity, may boost our comprehending of the role of TIGIT and PD1 on TPH/TFH in SLE, and a logistic regression model based on combination of TPH/TFH and routine blood indicators shows prominent value for predicting SLE.

Interleukin-12 induces IFN-γ secretion and STAT signaling implying its potential regulation of Th1 cell response in Nile tilapia

As a pleiotropic cytokine consisting of IL-12p35 and IL-12p40, Interleukin-12 (IL-12) features in inflammation regulation and anti-bacterial immunity. While IL-12 homologs have been identified in non-mammalian species, the precise mechanisms by which IL-12 contributes to early adaptive immune responses in vertebrates remain incompletely understood. Herein, an evolutionary conserved Oreochromis niloticus IL-12 (defined as OnIL-12) was identified by synteny characterization, structural comparisons and phylogenetic pattern of IL-12p35b and IL-12p40a. IL-12p35b and IL-12p40a exhibited widespread expression in lymphoid-related tissues of tilapia, while their mRNA expression in head-kidney demonstrated a significant increase after Edwardsiella piscicida infection. Compared with other lymphocytes, recombinant OnIL-12 (rOnIL-12) displayed stronger affinity binding to T cells. Although stimulation of lymphocytes with the p35b or p40a subunit resulted in a significant induction of IFN-γ expression, rOnIL-12 showed stronger potential to promote IFN-γ expression than these subunits. rOnIL-12 not only elevated the mRNA expression level Th1 cell-associated transcription factor T-bet in lymphocytes, but also increased the proportion of CD4-1+IFN-γ+ lymphocytes. Moreover, the mRNA and phosphorylation levels of STAT1, STAT3, STAT4 and STAT5 were enhanced by rOnIL-12. These findings will offer previous evidence for further exploration into the regulatory mechanisms of Th1 cellular immunity in early vertebrates.

IL-21, Inflammatory Cytokines and Hyperpolarized CD8+ T Cells Are Central Players in Lupus Immune Pathology

Systemic lupus erythematous (SLE) is a chronic autoimmune disorder, broadly characterized by systemic inflammation along with heterogeneous clinical manifestations, severe morbidity, moribund organ failure and eventual mortality. In our study, SLE patients displayed a higher percentage of activated, inflamed and hyper-polarized CD8⁺ T cells, dysregulated CD8⁺ T cell differentiation, significantly elevated serum inflammatory cytokines and higher accumulation of cellular ROS when compared to healthy controls. Importantly, these hyper-inflammatory/hyper-polarized CD8⁺ T cells responded better to an antioxidant than to an oxidant. Terminally differentiated Tc1 cells also showed plasticity upon oxidant/antioxidant treatment, but that was in contrast to the SLE CD8⁺ T cell response. Our studies suggest that the differential phenotype and redox response of SLE CD8⁺ T cells and Tc1 cells could be attributed to their cytokine environs during their respective differentiation and eventual activation environs. The polarization of Tc1 cells with IL-21 drove hyper-cytotoxicity without hyper-polarisation suggesting that the SLE inflammatory cytokine environment could drive the extreme aberrancy in SLE CD8⁺ T cells.

CD72-semaphorin3A axis: A new regulatory pathway in systemic lupus erythematosus

CD72 is a regulatory co-receptor on B cells, with a role in the pathogenesis of systemic lupus erythematosus (SLE) in both human and animal models. Semaphorin3A (sema3A) is a secreted member of the semaphorin family that can reconstruct B cells' regulatory functions by upregulating IL-10 expression and inhibiting the pro-inflammatory activity of B and T cells in autoimmune diseases. The aim of our present study was to identify a new ligand for CD72, namely sema3A, and exploring the signal transduction pathways following its ligation in B cells. We established that CD72 functions as sema3A binding and signal-transducing receptor. These functions of CD72 are independent of neuropilin-1 (NRP-1) (the known sema3A receptor). We discovered that sema3A induces the phosphorylation of CD72 on tyrosine residues and the association of CD72 with SHP-1 and SHP-2. In addition, the binding of sema3A to CD72 on B cells inhibits the phosphorylation of STAT-4 and HDAC-1 and induces the phosphorylation of p38-MAPK and PKC-theta in B-cells derived B-lymphoblastoid (BLCL) cells, and in primary B-cells isolated from either healthy donors or SLE patients. We concluded that sema3A is a functional regulatory ligand for CD72 on B cells. The sema3A-CD72 axis is a crucial regulatory pathway in the pathogenesis of autoimmune and inflammatory diseases namely SLE, and modulation of this pathway may have a potential therapeutic value for autoimmune diseases.

Aberrant expansion of follicular helper T cell subsets in patients with systemic lupus erythematosus

Objective

Systemic lupus erythematosus (SLE) is a chronic and complex autoimmune disease characterized by multiple autoantibodies, resulting in multiple organ and tissue damages. These pathogenic autoantibodies produced by B cells are closely correlated with follicular helper T (Tfh) cell subsets that play a fundamental role in the pathogenesis of SLE. The aim of the present study was to study the phenotype and role of circulating Tfh (cTfh) cell subsets and associated B cell subpopulations in active and inactive SLE patients.

Methods

Thirty SLE outpatients and 24 healthy controls (HCs) were enrolled in this study. The frequency of cTfh cell and B cell subsets in peripheral blood mononuclear cells (PBMCs) and the plasma levels of eight cytokines were determined by flow cytometry, and plasma IL-21 levels were measured by ELISA. Meanwhile, we used MRL/lpr mice as the model of SLE to research the alterations of Tfh cells in the thymus and spleen of mice.

Results

Frequencies of CD4⁺CXCR5⁺CD45RA^-effector cTfh cells, PD1⁺cTfh, PD1⁺ICOS⁺cTfh, PD1⁺cTfh1, PD1⁺cTfh2, PD1⁺cTfh17, and PD1⁺ICOS⁺cTfh1 cells as well as plasmablasts showed significant differences among HC, active and inactive SLE patients. Moreover, cytokines typically associated with cTfh cells, including IL-6 and IL-21, were elevated in active SLE patients compared to inactive SLE patients and HCs. Additionally, a positive correlation was observed between PD1⁺ICOS⁺ cTfh or PD1⁺ICOS⁺ cTfh1 cell frequencies and plasmablasts or IL-21 levels, as well as between plasmablasts. We also found PD1⁺ICOS⁺ Tfh cells expansion in both thymus and spleen of MRL/lpr mice, accompanied by increased frequencies in B cells and plasmablasts, meanwhile, cTfh1which expressing IFN-γ was increased in the peripheral blood of MRL/lpr mice.

Conclusion

Tfh cell subsets and plasmablasts may play a fundamental role in the pathogenesis of SLE and may provide potential targets for therapeutic interventions for SLE.

Jak Inhibitors for Treatment of Autoimmune Diseases: Lessons from Systemic Sclerosis and Systemic Lupus Erythematosus

Systemic sclerosis and systemic lupus erythematosus represent two distinct autoimmune diseases belonging to the group of connective tissue disorders. Despite the great progress in the basic science, this progress has not been translated to the development of novel therapeutic approaches that can radically change the face of these diseases. The discovery of JAK kinases, which are tyrosine kinases coupled with cytokine receptors, may open a new chapter in the treatment of so far untreatable diseases. Small synthetic compounds that can block Janus kinases and interact directly with cytokine signalling may provide therapeutic potential in these diseases. In this review, we discuss the therapeutic potential of Jak kinases in light of the cytokine network that JAK kinases are able to interact with. We also provide the theoretical background for the rationale of blocking cytokines with specific JAK inhibitors.

Double Negative (DN) B cells: A connecting bridge between rheumatic diseases and COVID-19?

Double Negative (DN) B cells constitute a B cell population that lacks expression of immunoglobulin D and CD27 memory marker. These cells expand in elderly healthy individuals, but also accumulate prematurely in autoimmune and infectious diseases.

COVID-19 is a pandemic infectious disease caused by SARS-CoV-2, a coronavirus that was first observed in Wuhan, China in December 2019. In its more severe cases, COVID-19 causes severe pneumonia and acute respiratory syndrome with high morbidity and mortality.

Recent studies have revealed that the extrafollicular DN2 B cell subset, previously described in lupus patients, does also expand in severe and/or critical groups of COVID-19 patients. These DN2 cells correlate with disease severity and laboratory parameters of inflammation. However, their exact role and function in COVID-19 require to be further investigated.

In this review, we highlight the DN immune responses in both rheumatic diseases and COVID-19, and we point out the importance of clarifying DN’s role in the immunopathology of the aforementioned infection, as it could probably enable better management of rheumatic diseases during the pandemic. Of note, the symptomatology of COVID-19, as well as the potential outcome of death, have given rise to a worldwide concern and scare of exposition to SARS-CoV-2, especially among the rheumatological patients who believe to be at higher risk due to their immunological background and the immunosuppressive therapies. Nevertheless, there is no convincing evidence so far that these patients are truly at higher risk than others.

SPaRTAN, a computational framework for linking cell-surface receptors to transcriptional regulators

The identity and functions of specialized cell types are dependent on the complex interplay between signaling and transcriptional networks. Recently single-cell technologies have been developed that enable simultaneous quantitative analysis of cell-surface receptor expression with transcriptional states. To date, these datasets have not been used to systematically develop cell-context-specific maps of the interface between signaling and transcriptional regulators orchestrating cellular identity and function. We present SPaRTAN (Single-cell Proteomic and RNA based Transcription factor Activity Network), a computational method to link cell-surface receptors to transcription factors (TFs) by exploiting cellular indexing of transcriptomes and epitopes by sequencing (CITE-seq) datasets with cis-regulatory information. SPaRTAN is applied to immune cell types in the blood to predict the coupling of signaling receptors with cell context-specific TFs. Selected predictions are validated by prior knowledge and flow cytometry analyses. SPaRTAN is then used to predict the signaling coupled TF states of tumor infiltrating CD8+ T cells in malignant peritoneal and pleural mesotheliomas. SPaRTAN enhances the utility of CITE-seq datasets to uncover TF and cell-surface receptor relationships in diverse cellular states.

Interleukin-12 exacerbates symptoms in an MRL/MpJ-Faslpr mouse model of systemic lupus erythematosus

Interleukin (IL)-12 modulates the generation and function of a variety of immune cells and serves an important role in the pathogenesis of autoimmune diseases. However, the precise role of IL-12 in the pathogenesis of systemic lupus erythematosus (SLE) remains to be elucidated. In the present study, the serum levels of IL-12 in patients with SLE were determined using an ELISA. The association between serum levels of IL-12 and clinical and laboratory indices, specifically, disease activity and complement 3, were analyzed. Recombinant IL-12 or an anti-IL-12 antibody was used to treat the MRL/MpJ-Fas^lpr mouse model of systemic lupus erythematosus. The glomerulonephritis and inflammatory cell infiltration was examined to evaluate histological changes using hematoxylin and eosin and Periodic acid-Schiff staining. Serum creatinine and proteinuria were used to determine renal function. The levels of anti-double stranded DNA and anti-nuclear autoantibodies were assessed. The results demonstrated that serum levels of IL-12 were markedly increased in patients with SLE compared with controls and in lupus model mice in comparison with control mice. The serum levels of IL-12 increased with disease severity in patients with SLE. SLE-like symptoms were exacerbated in lupus model mice treated with exogenous IL-12. However, SLE-like symptoms were ameliorated in lupus model mice treated with an anti-IL-12 antibody. The present results demonstrated that IL-12 aggravated SLE and anti-IL12 antibodies ameliorated SLE. The present data suggest that blocking IL-12 may be a beneficial therapeutic strategy to halt the progression of lupus nephritis.

Age-Associated B Cells (ABCs) in the Prognosis, Diagnosis and Therapy of Systemic Lupus Erythematosus (SLE)

The term “age-associated B cells” (ABCs) refers to a heterogeneous B cell subset (CD19⁺,CD21⁻, CD11c⁺,T-bet⁺) which is expanded in the elderly, but also accumulates prematurely in patients with autoimmune disorders and/or infectious diseases. In healthy individuals, ABCs represent a low prevalence population that positively impacts immunosenescence. In autoimmunity and infections though, ABCs expand dramatically and produce high titers of antibodies, thus playing a role in the regulation of humoral responses. Despite the fact that these observations were made on both mice and humans, the functional features of ABCs and their exact role in human health and disease are still elusive. This review focuses on ABC and ABC-like sub-populations found in Systemic Lupus Erythematosus (SLE) patients (such as the double negative 2;DN2 population: CD19⁺,IgD⁻,CD27⁻, CXCR5⁻,T-bet⁺) and broaches the subject of their potential use as prognostic and/or diagnostic markers. The identification of novel biomarkers, via correlating the cell populations with the clinical profile of the patients, should enable better patient stratification and monitoring. Moreover, the necessity and importance of elucidating the role of transcription factor T-bet (TBX21) in the pathogenesis of human autoimmunity are addressed. T-bet, whose expression is upregulated in both mouse and human ABCs, is considered to play a major role in various aspects of autoimmunity, such as the production of autoreactive IgG, the enhanced antigen presentation to T cells and also the formation of spontaneous germinal centres (GC). Shedding light to its role in human disease, in conjunction with the characterisation of genes and pathways associated with the transcription factor itself, may lead to the discovery of novel druggable targets.

Shared and distinct roles of T peripheral helper and T follicular helper cells in human diseases

The interactions of CD4⁺ T cells and B cells are fundamental for the generation of protective antibody responses, as well as for the development of harmful autoimmune diseases. Recent studies of human tissues and blood samples have established a new subset of CD4⁺ B helper T cells named peripheral helper T (Tph) cells. Unlike T follicular helper (Tfh) cells, which interact with B cells within lymphoid organs, Tph cells provide help to B cells within inflamed tissues. Tph cells share many B helper-associated functions with Tfh cells and induce B cell differentiation toward antibody-producing cells. The differentiation mechanism is also partly shared between Tph and Tfh cells in humans, and both Tfh and Tph cells can be found within the same tissues, including cancer tissues. However, Tph cells display features distinct from those of Tfh cells, such as the expression of chemokine receptors associated with Tph cell localization within inflamed tissues and a low Bcl-6/Blimp1 ratio. Unlike that of Tfh cells, current evidence shows that the target of Tph cells is limited to memory B cells. In this review, we first summarize recent findings on human Tph cells and discuss how Tph and Tfh cells play shared and distinct roles in human diseases.