Plasticity and lineage commitment of individual TH1 cells are determined by stable T-bet expression quantities

T helper 1 (TH1) cell identity is defined by the expression of the lineage-specifying transcription factor T-bet. Here, we examine the influence of T-bet expression heterogeneity on subset plasticity by leveraging cell sorting of distinct in vivo-differentiated TH1 cells based on their quantitative expression of T-bet and interferon-γ. Heterogeneous T-bet expression states were regulated by virus-induced type I interferons and were stably maintained even after secondary viral infection. Exposed to alternative differentiation signals, the sorted subpopulations exhibited graded levels of plasticity, particularly toward the TH2 lineage: T-bet quantities were inversely correlated with the ability to express the TH2 lineage-specifying transcription factor GATA-3 and TH2 cytokines. Reprogramed TH1 cells acquired graded mixed TH1 + TH2 phenotypes with a hybrid epigenetic landscape. Continuous presence of T-bet in differentiated TH1 cells was essential to ensure TH1 cell stability. Thus, innate cytokine signals regulate TH1 cell plasticity via an individual cell-intrinsic rheostat to enable T cell subset adaptation to subsequent challenges.

Principles and therapeutic applications of adaptive immunity

Adaptive immunity provides protection against infectious and malignant diseases. These effects are mediated by lymphocytes that sense and respond with targeted precision to perturbations induced by pathogens and tissue damage. Here, we review key principles underlying adaptive immunity orchestrated by distinct T cell and B cell populations and their extensions to disease therapies. We discuss the intracellular and intercellular processes shaping antigen specificity and recognition in immune activation and lymphocyte functions in mediating effector and memory responses. We also describe how lymphocytes balance protective immunity against autoimmunity and immunopathology, including during immune tolerance, response to chronic antigen stimulation, and adaptation to non-lymphoid tissues in coordinating tissue immunity and homeostasis. Finally, we discuss extracellular signals and cell-intrinsic programs underpinning adaptive immunity and conclude by summarizing key advances in vaccination and engineering adaptive immune responses for therapeutic interventions. A deeper understanding of these principles holds promise for uncovering new means to improve human health.

T-helper cells flexibility: the possibility of reprogramming T cells fate

Various disciplines cooperate to find novel approaches to cure impaired body functions by repairing, replacing, or regenerating cells, tissues, or organs. The possibility that a stable differentiated cell can reprogram itself opens the door to new therapeutic strategies against a multitude of diseases caused by the loss or dysfunction of essential, irreparable, and specific cells. One approach to cell therapy is to induce reprogramming of adult cells into other functionally active cells. Understanding the factors that cause or contribute to T cell plasticity is not only of clinical importance but also expands the knowledge of the factors that induce cells to differentiate and improves the understanding of normal developmental biology. The present review focuses on the advances in the conversion of peripheral CD4+ T cells, the conditions of their reprogramming, and the methods proposed to control such cell differentiation.

Th2 single-cell heterogeneity and clonal distribution at distant sites in helminth-infected mice

Th2 cells provide effector functions in type 2 immune responses to helminths and allergens. Despite knowledge about molecular mechanisms of Th2 cell differentiation, there is little information on Th2 cell heterogeneity and clonal distribution between organs. To address this, we performed combined single-cell transcriptome and T-cell receptor (TCR) clonotype analysis on murine Th2 cells in mesenteric lymph nodes (MLNs) and lung after infection with Nippostrongylus brasiliensis (Nb) as a human hookworm infection model. We find organ-specific expression profiles, but also populations with conserved migration or effector/resident memory signatures that unexpectedly cluster with potentially regulatory Il10^posFoxp3^neg cells. A substantial MLN subpopulation with an interferon response signature suggests a role for interferon signaling in Th2 differentiation or diversification. Further RNA-inferred developmental directions indicate proliferation as a hub for differentiation decisions. Although the TCR repertoire is highly heterogeneous, we identified expanded clones and CDR3 motifs. Clonal relatedness between distant organs confirmed effective exchange of Th2 effector cells, although locally expanded clones dominated the response. We further cloned an Nb-specific TCR from an expanded clone in the lung effector cluster and describe surface markers that distinguish transcriptionally defined clusters. These results provide insights in Th2 cell subset diversity and clonal relatedness in distant organs.

The Conundrum of Lung Disease and Drug Hypersensitivity-like Reactions in Systemic Juvenile Idiopathic Arthritis

An unusual form of lung disease has begun to affect some children with systemic juvenile idiopathic arthritis (JIA), coincident with increasing utilization of interleukin-1 (IL-1) and IL-6 antagonists. Many children with systemic JIA-associated lung disease (SJIA-LD) have a history of clinical and laboratory features resembling drug reaction with eosinophilia and systemic symptoms (DRESS), a presentation now convincingly associated with HLA-DRB1*15. Treatment of DRESS typically requires drug discontinuation, a daunting prospect for clinicians and families who rely upon these agents. Here we review SJIA-LD and its associated DRESS-like phenotype. We suggest an alternative explanation, the cytokine plasticity hypothesis, proposing that IL-1 and IL-6 blockers modulate the milieu in which T cells develop, leading to a pathologic immune response triggered through exposure to common microbes, or to other exogenous or endogenous antigens, rather than to the drugs themselves. This hypothesis differs from DRESS in mechanism but also in clinical implications, predicting that control of pathogenic T cells could permit continued use of IL-1 and IL-6 antagonists in some individuals. The spectrum posed by these two hypotheses provides a conceptual framework that will guide investigation into the pathogenesis of SJIA-LD and may open up new therapeutic avenues for patients with systemic JIA.

Role of rare immune cells in common variable immunodeficiency

Common variable immunodeficiency disorder (CVID) is a heterogeneous disorder and the most common symptomatic antibody deficiency disease characterized with hypogammaglobulinemia and a broad range of clinical manifestations. Multiple genetic, epigenetic, and immunological defects are involved in the pathogenesis of CVID. These immunological defects include abnormalities in the number and/or function of B lymphocytes, T lymphocytes, and other rare immune cells. Although some immune cells have a relatively lower proportion among total immune subsets in the human body, they could have important roles in the pathogenesis of immunological disorders like CVID. To the best of our knowledge, this is the first review that described the role of rare immune cells in the pathogenesis and clinical presentations of CVID.

CD4+ T-Cell Plasticity in Non-Infectious Retinal Inflammatory Disease

Non-infectious uveitis (NIU) is a potentially sight-threatening disease. Effector CD4+ T cells, especially interferon-γ-(IFNγ) producing Th1 cells and interleukin-17-(IL-17) producing Th17 cells, are the major immunopathogenic cells, as demonstrated by adoptive transfer of disease in a model of experimental autoimmune uveitis (EAU). CD4+FoxP3+CD25+ regulatory T cells (Tregs) were known to suppress function of effector CD4+ T cells and contribute to resolution of disease. It has been recently reported that some CD4+ T-cell subsets demonstrate shared phenotypes with another CD4+ T-cell subset, offering the potential for dual function. For example, Th17/Th1 (co-expressing IFNγ and IL-17) cells and Th17/Treg (co-expressing IL-17 and FoxP3) cells have been identified in NIU and EAU. In this review, we have investigated the evidence as to whether these 'plastic CD4+ T cells' are functionally active in uveitis. We conclude that Th17/Th1 cells are generated locally, are resistant to the immunosuppressive effects of steroids, and contribute to early development of EAU. Th17/Treg cells produce IL-17, not IL-10, and act similar to Th17 cells. These cells were considered pathogenic in uveitis. Future studies are needed to better clarify their function, and in the future, these cell subsets may in need to be taken into consideration for designing treatment strategies for disease.

Re-Programming Autoreactive T Cells Into T-Regulatory Type 1 Cells for the Treatment of Autoimmunity

Systemic delivery of peptide-major histocompatibility complex (pMHC) class II-based nanomedicines can re-program cognate autoantigen-experienced CD4+ T cells into disease-suppressing T-regulatory type 1 (TR1)-like cells. In turn, these TR1-like cells trigger the formation of complex regulatory cell networks that can effectively suppress organ-specific autoimmunity without impairing normal immunity. In this review, we summarize our current understanding of the transcriptional, phenotypic and functional make up of TR1-like cells as described in the literature. The true identity and direct precursors of these cells remain unclear, in particular whether TR1-like cells comprise a single terminally-differentiated lymphocyte population with distinct transcriptional and epigenetic features, or a collection of phenotypically different subsets sharing key regulatory properties. We propose that detailed transcriptional and epigenetic characterization of homogeneous pools of TR1-like cells will unravel this conundrum.

Functionally specialized human CD4+ T-cell subsets express physicochemically distinct TCRs

The organizational integrity of the adaptive immune system is determined by functionally discrete subsets of CD4⁺ T cells, but it has remained unclear to what extent lineage choice is influenced by clonotypically expressed T-cell receptors (TCRs). To address this issue, we used a high-throughput approach to profile the αβ TCR repertoires of human naive and effector/memory CD4⁺ T-cell subsets, irrespective of antigen specificity. Highly conserved physicochemical and recombinatorial features were encoded on a subset-specific basis in the effector/memory compartment. Clonal tracking further identified forbidden and permitted transition pathways, mapping effector/memory subsets related by interconversion or ontogeny. Public sequences were largely confined to particular effector/memory subsets, including regulatory T cells (Tregs), which also displayed hardwired repertoire features in the naive compartment. Accordingly, these cumulative repertoire portraits establish a link between clonotype fate decisions in the complex world of CD4⁺ T cells and the intrinsic properties of somatically rearranged TCRs.

Immunophenotyping in pemphigus reveals a TH17/TFH17 cell-dominated immune response promoting desmoglein1/3-specific autoantibody production

BACKGROUND

T_H2 cells were thought to be a pivotal factor for initiation of the autoimmune blistering disease pemphigus. However, the role of other T-cell subsets in pemphigus pathogenesis remained unclear.

OBJECTIVE

We aimed to characterize the exact phenotype of T cells responsible for the development of pemphigus.

METHODS

Whole transcriptome shotgun sequencing was performed to determine differential gene expression in pemphigus lesions and skin of healthy individuals. The cutaneous cytokine signature was further evaluated by real-time quantitative PCR. In peripheral blood, the distribution of T_H cell and folliclular helper (T_FH) cell subsets was analyzed by flow cytometry. Finally, the capacity of T_H and T_FH cell subsets to induce desmoglein (Dsg)-specific autoantibodies by memory B cells was evaluated in coculture experiments.

RESULTS

Transcriptome analysis of skin samples identified an IL-17A-dominated immune signature in patients with pemphigus, and Kyoto Encyclopedia of Genes and Genomes pathway analysis confirmed the dominance of the IL-17A signaling pathway. Increased expression of IL17A and associated cytokines was also detected by real-time quantitative PCR comparing lesional with perilesional or healthy skin. Interestingly, utilization of flow cytometry showed that patients with active pemphigus had elevated levels of circulating IL-17⁺_, T_H17, T_FH17, and T_FH17.1 cells. Notably, levels of T_H17 and T_FH17 cells correlated with levels of Dsg-specific CD19⁺CD27⁺ memory B cells, and patients with acute pemphigus showed higher levels of Dsg3-autoreactive T_FH17 cells. Coculture experiments revealed T_FH17 cells as primarily responsible for inducing Dsg-specific autoantibody production by B cells.

CONCLUSION

Our findings show that T_FH17 cells are critically involved in the pathogenesis of pemphigus and offer novel targets for therapeutic intervention.

The outstanding antitumor capacity of CD4+ T helper lymphocytes

Over the past decades, tumor-resident immune cells have been extensively studied to dissect their biological functions and clinical roles. Tumor-infiltrating CD8⁺ T cells, because of their cytotoxic and killing ability, have been under the spotlight for a long time, whereas CD4⁺ T cells are considered just a supporting actor in the field of cancer immunotherapy. Until recently, accumulating evidence has demonstrated the ability of CD4⁺ T cells in eradicating solid tumors, and their functions in mediating antitumor immunity have been investigated in various orientations. In this review, we highlight the pivotal role of CD4⁺ T cells in eliciting vigorous antitumor immune responses, summarize key signaling axes and molecular networks behind these antitumor functions, and also propose possible targets and promising strategies which might translate into more efficient immunotherapies against human cancers.

Relationship between chemokines and T lymphocytes in the context of respiratory allergies (Review)

Allergic diseases have been classified in the last decades using various theories. The main classes of the newest classification in allergic respiratory diseases focus on the characterization of the endotype (which takes into account biomarkers related to determinant pathophysiological mechanisms) and of the phenotype (based on the description of the disease). Th2, Th1 and Th17 lymphocytes and the type of inflammatory response mediated by them represent the basis for Th2 and non-Th2 endotype classification. In addition, new lymphocytes were also used to characterize allergic diseases: Th9 lymphocytes, Th22 lymphocytes, T follicular helper cells (T_FH) lymphocytes and invariant natural killer T (iNKT) lymphocytes. In the last decade, a growing body of evidence focused on chemokines, chemoattractant cytokines, which seems to have an important contribution to the pathogenesis of this pathology. This review presents the interactions between chemokines and Th lymphocytes in the context of Th2/non-Th2 endotype classification of respiratory allergies.

Immunity to Soil-Transmitted Helminths: Evidence From the Field and Laboratory Models

Infection with soil-transmitted helminths (STH) remains a major burden on global health and agriculture. Our understanding of the immunological mechanisms that govern whether an individual is resistant or susceptible to infection is derived primarily from model infections in rodents. Typically, experimental infections employ an artificially high, single bolus of parasites that leads to rapid expulsion of the primary infection and robust immunity to subsequent challenges. However, immunity in natura is generated slowly, and is only partially effective, with individuals in endemic areas retaining low-level infections throughout their lives. Therefore, there is a gap between traditional model STH systems and observations in the field. Here, we review the immune response to traditional model STH infections in the laboratory. We compare these data to studies of natural infection in humans and rodents in endemic areas, highlighting crucial differences between experimental and natural infection. We then detail the literature to date on the use of "trickle" infections to experimentally model the kinetics of natural infection.

Microbiota-Propelled T Helper 17 Cells in Inflammatory Diseases and Cancer

Technologies allowing genetic sequencing of the human microbiome are opening new realms to discovery. The host microbiota substantially impacts immune responses both in immune-mediated inflammatory diseases (IMIDs) and in tumors affecting tissues beyond skin and mucosae. However, a mechanistic link between host microbiota and cancer or IMIDs has not been well established. Here, we propose T helper 17 (T_H17) lymphocytes as the connecting factor between host microbiota and rheumatoid or psoriatic arthritides, multiple sclerosis, breast or ovarian cancer, and multiple myeloma. We theorize that similar mechanisms favor the expansion of gut-borne T_H17 cells and their deployment at the site of inflammation in extraborder IMIDs and tumors, where T_H17 cells are driving forces. Thus, from a pathogenic standpoint, tumors may share mechanistic routes with IMIDs. A review of similarities and divergences in microbiota-T_H17 cell interactions in IMIDs and cancer sheds light on previously ignored pathways in either one of the two groups of pathologies and identifies novel therapeutic avenues.

The impact of microRNAs on alterations of gene regulatory networks in allergic diseases

Allergic diseases including asthma are worldwide on the rise and contribute significantly to health expenditures. Allergic diseases are prototypic diseases with a strong gene by environment interaction component and epigenetic mechanisms might mediate the effects of the environment on the disease phenotype. MicroRNAs, small non-coding RNAs (miRNAs), regulate gene expression post-transcriptionally. Functional single-stranded miRNAs are generated in multiple steps of enzymatic processing from their precursors and mature miRNAs are included into the RNA-induced silencing complex (RISC). They imperfectly base-pair with the 3'UTR region of targeted genes leading to translational repression or mRNA decay. The cellular context and microenvironment as well the isoform of the mRNA control the dynamics and complexity of the regulatory circuits induced by miRNAs that regulate cell fate decisions and function. MiR-21, miR-146a/b and miR-155 are among the best understood miRNAs of the immune system and implicated in different diseases including allergic diseases. MiRNAs are implicated in the induction of the allergy reinforcing the Th2 phenotype (miR-19a, miR-24, miR-27), while other miRNAs promote regulatory T cells associated with allergen tolerance or unresponsiveness. In the current chapter we describe in detail the biogenesis and regulatory function of miRNAs and summarize current knowledge on miRNAs in allergic diseases and allergy relevant cell fate decisions focusing mainly on immune cells. Furthermore, we evoke the principles of regulatory loops and feedback mechanisms involving miRNAs on examples with relevance for allergic diseases. Finally, we show the potential of miRNAs and exosomes containing miRNAs present in several biological fluids that can be exploited with non-invasive procedures for diagnostic and potentially therapeutic purposes.

Distinct and shared gene expression for human innate versus adaptive helper lymphoid cells

Innate lymphoid cells (ILCs) are the latest identified innate immune cell family. Given their similarity in transcription factor expression and cytokine secretion profiles, ILCs have been considered as the innate phenocopy of CD4 Th cells. Here, we explored the transcriptome of circulating human ILC subsets as opposed to CD4 Th cell subsets. We describe transcriptomic differences between total ILCs and total CD4 Th cells, as well as between paired innate and adaptive cell subsets (ILC1 vs. Th1; ILC2 vs. Th2; and ILC3 vs. Th17 cells). In particular, we observed differences in expression of genes involved in cell trafficking such as CCR1, CCR6 and CXCR3, innate activation and inhibitory functions, including CD119, 2B4, TIGIT, and CTLA‐4, and neuropeptide receptors, such as VIPR2. Moreover, we report for the first time on distinct expression of long noncoding RNAs (lncRNAs) in innate vs. adaptive cells, arguing for a potential role of lncRNA in shaping human ILC biology. Altogether, our results point for unique, rather than redundant gene organization in ILCs compared to CD4 Th cells, in regard to kinetics, fine‐tuning and spatial organization of the immune response.

Succinate Coenzyme A Ligase Beta-Like Protein from Trichinella spiralis Suppresses the Immune Functions of Rat PBMCs in Vitro and Inhibits the Secretions of Interleukin-17 in Vivo

Succinate Coenzyme A ligase beta-like protein (SUCLA-β) is a subunit of Succinyl-coenzyme A synthetase, which is involved in substrate synergism, unusual kinetic reaction in which the presence of SUCLA-β for one partial reaction stimulates another partial reaction. Trichinella spiralis is a parasitic nematode, which may hinder the development of autoimmune diseases. Immunomodulatory effects of SUCLA-β from Trichinella spiralis in the parasite-host interaction are unidentified. In this study the gene encoding T. spiralis SUCLA-β was cloned and expressed. Binding activities of recombinant T. spiralis SUCLA-β (rTs-SUCLA-β) to rat peripheral blood mononuclear cells (PBMCs) were checked by immunofluorescence assay (IFA) and the immuno-regulatory effects of rTs-SUCLA-β on cell migration, cell proliferation, nitric oxide (NO) production and apoptosis were observed by co-incubation of rTs-SUCLA-β with rat PBMCs in vitro, while cytokine secretions in rTs-SUCLA-β treated rats were evaluated in vivo. Furthermore, phagocytosis of monocytes was detected by flow cytometry and effects of rTs-SUCLA-β-induced protective immunity on T. spiralis adult worms and muscle larva were evaluated in rats. The IFA results revealed that rTs-SUCLA-β could bind to rat PBMCs. Treatment of PBMCs with rTs-SUCLA-β significantly decreased the monocyte phagocytosis, cell migration and cell proliferation, while NO production and apoptosis of PBMCs were unaffected. Results of the in vivo study showed that the IL-17 secretion decreased significantly after rTs-SUCLA-β administration in rats, while no significant effects were observed on the secretions of IFN-γ, IL-9, TGF-β and IL-4. Moreover, significant reduction of T. spiralis muscle larvae burden and significant increase in anti-rTs-SUCLA-β immunoglobulin level of IgG, IgG1 and IgG2a was observed in rTs-SUCLA-β-administered rats. The results indicated that rTs-SUCLA-β may be a potential target for controlling T. spiralis infection by suppressing the immune functions of the rat PBMCs and by reducing the parasite burden. Additionally it may also contribute to the treatment of autoimmune diseases and graft rejection by suppressing IL-17 immune response in the host.

Epigenetic mechanisms regulating T-cell responses

During the last decade, advances in sequencing technologies allowed production of a wealth of information on epigenetic modifications in T cells. Epigenome maps, in combination with mechanistic studies, have demonstrated that T cells undergo extensive epigenome remodeling in response to signals, which has a strong effect on phenotypic stability and function of lymphocytes. In this review we focus on DNA methylation, histone modifications, and chromatin structure as important epigenetic mechanisms involved in controlling T-cell responses. In particular, we discuss epigenetic processes in light of the development, activation, and differentiation of CD4⁺ T helper (T_H), regulatory T, and CD8⁺ T cells. As central aspects of the adaptive immune system, we review mechanisms that ensure molecular memory, stability, plasticity, and exhaustion of T cells. We further discuss the effect of the tissue environment on imprinting T-cell epigenomes with potential implications for immunotherapy.

Shared Transcriptional Control of Innate Lymphoid Cell and Dendritic Cell Development

Innate immunity and adaptive immunity consist of highly specialized immune lineages that depend on transcription factors for both function and development. In this review, we dissect the similarities between two innate lineages, innate lymphoid cells (ILCs) and dendritic cells (DCs), and an adaptive immune lineage, T cells. ILCs, DCs, and T cells make up four functional immune modules and interact in concert to produce a specified immune response. These three immune lineages also share transcriptional networks governing the development of each lineage, and we discuss the similarities between ILCs and DCs in this review.

Helper T cell differentiation

CD4+ T helper cells are key regulators of host health and disease. In the original model, specialized subsets of T helper cells are generated following activation through lineage-specifying cytokines and transcriptional programs, but recent studies have revealed increasing complexities for CD4+ T-cell differentiation. Here, we first discuss CD4+ T-cell differentiation from a historical perspective by highlighting the major studies that defined the distinct subsets of T helper cells. We next describe the mechanisms underlying CD4+ T-cell differentiation, including cytokine-induced signaling and transcriptional networks. We then review current and emerging topics of differentiation, including the plasticity and heterogeneity of T cells, the tissue-specific effects, and the influence of cellular metabolism on cell fate decisions. Importantly, recent advances in cutting-edge approaches, especially systems biology tools, have contributed to new concepts and mechanisms underlying T-cell differentiation and will likely continue to advance this important research area of adaptive immunity.

Trogocytosis-Mediated Intracellular Signaling in CD4+ T Cells Drives TH2-Associated Effector Cytokine Production and Differentiation

CD4⁺ T cells have been observed to acquire APC-derived membrane and membrane-associated molecules through trogocytosis in diverse immune settings. Despite this, the consequences of trogocytosis on the recipient T cell remain largely unknown. We previously reported that trogocytosed molecules on CD4⁺ T cells engage their respective surface receptors, leading to sustained TCR signaling and survival after APC removal. Using peptide-pulsed bone marrow-derived dendritic cells and transfected murine fibroblasts expressing antigenic MHC:peptide complexes as APC, we show that trogocytosis-positive CD4⁺ T cells display effector cytokines and transcription factor expression consistent with a T_H2 phenotype. In vitro-polarized T_H2 cells were found to be more efficient at performing trogocytosis than T_H1 or nonpolarized CD4⁺ cells, whereas subsequent trogocytosis-mediated signaling induced T_H2 differentiation in polarized T_H1 and nonpolarized cells. Trogocytosis-positive CD4⁺ T cells generated in vivo also display a T_H2 phenotype in both TCR-transgenic and wild-type models. These findings suggest that trogocytosis-mediated signaling impacts CD4⁺ T cell differentiation and effector cytokine production and may play a role in augmenting or shaping a T_H2-dominant immune response.

What Cytokines Can Tell Us About the Pathogenesis of Breast Implant-Associated Anaplastic Large Cell Lymphoma (BIA-ALCL)

Cytokines, their receptors, and downstream signaling partners, especially JAK1/2 and STAT3, are key biomarkers in lymphoproliferative disorders including systemic anaplastic large cell lymphoma (ALCL). Here we review their role in breast implant-associated anaplastic large cell lymphoma (BIA-ALCL). Early results suggest that, in addition to CD30, IL-9, IL-10, and IL-13 can distinguish malignant from benign seromas. IL-6 is increased in both benign and malignant seromas. IFNγ may identify a subset of BIA-ALCL with a different clinical course. Immunohistochemical detection of nuclear transcription factors-which regulate cytokine signaling-and phosphorylated janus kinases/signal transducers and activators of transcription can inform the identification and malignant potential of CD30+ cells. The innate immune response is the first line of defense against microbes suspected to initiate BIA-ALCL. Innate lymphoid cells are grouped according to the cytokines they produce and could potentially be identified as precursors to BIA-ALCL. Cytokines modulate the tumor microenvironment and hence the pathology of BIA-ALCL such as the influx of eosinophils and capsular fibrosis mediated by IL-13. The plasticity of T cells and innate immune cells theoretically can enable therapeutic manipulations toward a less aggressive phenotype. Cytokine receptors targeted in clinical trials of inflammatory and autoimmune disorders could afford opportunities for immunotherapy of BIA-ALCL.

Commensal-specific T cell plasticity promotes rapid tissue adaptation to injury

Barrier tissues are primary targets of environmental stressors and are home to the largest number of antigen-experienced lymphocytes in the body, including commensal-specific T cells. We found that skin-resident commensal-specific T cells harbor a paradoxical program characterized by a type 17 program associated with a poised type 2 state. Thus, in the context of injury and exposure to inflammatory mediators such as interleukin-18, these cells rapidly release type 2 cytokines, thereby acquiring contextual functions. Such acquisition of a type 2 effector program promotes tissue repair. Aberrant type 2 responses can also be unleashed in the context of local defects in immunoregulation. Thus, commensal-specific T cells co-opt tissue residency and cell-intrinsic flexibility as a means to promote both local immunity and tissue adaptation to injury.

RAS P21 Protein Activator 3 (RASA3) Specifically Promotes Pathogenic T Helper 17 Cell Generation by Repressing T-Helper-2-Cell-Biased Programs

Pathogenic Th17 (pTh17) cells drive inflammation and immune-pathology, but whether pTh17 cells are a Th17 cell subset whose generation is under specific molecular control remains unaddressed. We found that Ras p21 protein activator 3 (RASA3) was highly expressed by pTh17 cells relative to non-pTh17 cells and was required specifically for pTh17 generation in vitro and in vivo. Mice conditionally deficient for Rasa3 in T cells showed less pathology during experimental autoimmune encephalomyelitis. Rasa3-deficient T cells acquired a Th2 cell-biased program that dominantly trans-suppressed pTh17 cell generation via interleukin 4 production. The Th2 cell bias of Rasa3-deficient T cells was due to aberrantly elevated transcription factor IRF4 expression. RASA3 promoted proteasome-mediated IRF4 protein degradation by facilitating interaction of IRF4 with E3-ubiquitin ligase Cbl-b. Therefore, a RASA3-IRF4-Cbl-b pathway specifically directs pTh17 cell generation by balancing reciprocal Th17-Th2 cell programs. These findings indicate that a distinct molecular program directs pTh17 cell generation and reveals targets for treating pTh17 cell-related pathology and diseases.

Manipulation of the balance between Th2 and Th2/1 hybrid cells affects parasite nematode fitness in mice

T-helper type 2 (Th2) responses are central to the control of helminth infections, but sensitive to opposing cytokine signals favoring Th1 priming. We previously reported on GATA-3⁺ T-bet⁺ Th2/1 hybrid cell differentiation in helminth mono-infections, resulting in a substantial proportion of cells coproducing IFN-γ next to Th2 cytokines. Here, we demonstrate Th2/1 cells as the major source of parasite-specific IFN-γ production in acute and chronic infections with the enteric nematode Heligmosomoides polygyrus. Th2/1 cells differentiated from naive precursors and accumulated in spleen and intestine of infected mice, resulting in increased systemic and mucosal IFN-γ production. IFN-γ supplementation early during infection supported Th2/1 differentiation, associated with elevated parasite fecundity and the maintenance of high worm burdens in the chronic stage of infection, whereas mice lacking IFN-γ signals generated poor Th2/1 responses and restricted parasite fecundity more efficiently. These findings suggest that Th2/1 hybrid responses take part in immune regulation during helminth infection and restrain effective anti-helminth immunity.

Role of Cytokine Combinations on CD4+ T Cell Differentiation, Partial Polarization, and Plasticity: Continuous Network Modeling Approach

Purpose: We put forward a theoretical and dynamical approach for the semi-quantitative analysis of CD4+ T cell differentiation, the process by which cells with different functions are derived from activated CD4+ T naïve lymphocytes in the presence of particular cytokine microenvironments. We explore the system-level mechanisms that underlie CD4+ T plasticity-the conversion of polarized cells to phenotypes different from those originally induced. Methods: In this paper, we extend a previous study based on a Boolean network to a continuous framework. The network includes transcription factors, signaling pathways, as well as autocrine and exogenous cytokines, with interaction rules derived using fuzzy logic. Results: This approach allows us to assess the effect of relative differences in the concentrations and combinations of exogenous and endogenous cytokines, as well as of the expression levels of diverse transcription factors. We found either abrupt or gradual differentiation patterns between observed phenotypes depending on critical concentrations of single or multiple environmental cytokines. Plastic changes induced by environmental cytokines were observed in conditions of partial phenotype polarization in the T helper 1 to T helper 2 transition. On the other hand, the T helper 17 to induced regulatory T-cells transition was highly dependent on cytokine concentrations, with TGFβ playing a prime role. Conclusion: The present approach is useful to further understand the system-level mechanisms underlying observed patterns of CD4+ T differentiation and response to changing immunological challenges.

CD28 Costimulation of T Helper 1 Cells Enhances Cytokine Release In Vivo

Compared to naive T cells, differentiated T cells are thought to be less dependent on CD28 costimulation for full activation. To revisit the role of CD28 costimulation in mouse T cell recall responses, we adoptively transferred in vitro generated OT-II T helper (Th) 1 cells into C57BL/6 mice (Thy1.2⁺) and then either blocked CD28–ligand interactions with Fab fragments of the anti-CD28 monoclonal antibody (mAb) E18 or deleted CD28 expression using inducible CD28 knock-out OT-II mice as T cell donors. After injection of ovalbumin protein in adjuvant into the recipient mice we observed that systemic interferon (IFN)γ release strongly depended on CD28 costimulation of the Th1 cells, while secondary clonal expansion was not reduced in the absence of CD28 costimulation. For human memory CD4⁺ T cell responses we also noted that cytokine release was reduced upon inhibition of CD28 costimulation. Together, our data highlight the so far underestimated role of CD28 costimulation for the reactivation of fully differentiated CD4⁺ T cells.

Epigenetic regulation of T-helper cell differentiation, memory, and plasticity in allergic asthma

An estimated 300 million people currently suffer from asthma, which causes approximately 250 000 deaths a year. Allergen-specific T-helper (Th) cells produce cytokines that induce many of the hallmark features of asthma including airways hyperreactivity, eosinophilic and neutrophilic inflammation, mucus hypersecretion, and airway remodeling. Cytokine-producing Th subsets including Th1 (IFN-γ), Th2 (IL-4, IL-5, IL-13), Th9 (IL-9), Th17 (IL-17), Th22 (IL-22), and T regulatory (IL-10) cells have all been suggested to play a role in the development of asthma. Th differentiation involves genetic regulation of gene expression through the concerted action of cytokines, transcription factors, and epigenetic regulators. We describe how Th differentiation and plasticity is regulated by epigenetic histone and DNA modifications, with a focus on the regulation of histone methylation by members of the polycomb and trithorax complexes. In addition, we outline environmental influences that could influence epigenetic regulation of Th cells and discuss the potential to regulate Th plasticity and function through drugs targeting the epigenetic machinery. It is also becoming apparent that epigenetic regulation of allergen-specific memory Th cells may be important in the development and persistence of chronic allergies. Finally, we describe how epigenetic modifiers regulate cytokine memory in Th cells and describe recently identified hybrid, plastic, and pathogenic memory Th subsets the context of allergic asthma.

TH17 cell plasticity: The role of dendritic cells and molecular mechanisms

Upon interaction with dendritic cells (DCs), naïve CD4 T cells differentiate into distinct subsets and orchestrate the development of a physiological immune response. When uncontrolled by cellular and molecular mechanisms, CD4 T cells can also lead to immune mediated inflammatory diseases (IMIDs). Initially, these distinct CD4 T-cell subsets were defined according to the expression of a limited number of cytokines. Later it was revealed that CD4 T cells can acquire much more complex functional phenotypes than previously thought. Experimental data showed that the CD4 T-cell subset T_H17 can secrete IFN-γ and IL-4, which are signature molecules of other T-cell subsets. Furthermore, some T_H17 cells can also explore an anti-inflammatory fate and participate in the resolution of the immune response. A more flexible theory has therefore evolved with the scope to better represent the plastic biology of CD4 T cells. In this context, several aspects still remain unclear. The goal of this review is to discuss the role of extrinsic and intrinsic cellular and molecular mechanisms, which can drive the plasticity of T_H17 cells. In particular, we will outline the role of DCs and the function of transcriptional factors in shaping the fate of T_H17 cells towards either a pathogenic or a regulatory phenotype. Finally, we will discuss whether T_H17 cell plasticity could be a target for new therapies for IMIDs. We indeed envision that when the cellular and molecular mechanisms controlling T_H17 plasticity are known, new therapies, which aim to reset the immune system, will be developed. This will be achieved by either selectively depleting only the pathogenic T_H17 cells or, if possible, re converting these cells from pathogenic to regulatory. This will overcome the challenge posed by the immune suppressive side effects caused by the current therapies, which impair the function of CD4 cells or delete all of them, to the detriment of the patient.

Helminth Modulation of Lung Inflammation

Parasitic helminths must establish chronic infections to complete their life cycle and therefore are potent modulators of multiple facets of host physiology. Parasitic helminths have coevolved with humans to become arguably master selectors of our immune system, whereby they have impacted on the selection of genes with beneficial mutations for both host and parasite. While helminth infections of humans are a significant health burden, studies have shown that helminths or helminth products can alter susceptibility to unrelated infectious or inflammatory diseases. This has generated interest in the use of helminth infections or molecules as therapeutics. In this review, we focus on the impact of helminth infections on pulmonary immunity, especially with regard to homeostatic lung function, pulmonary viral and bacterial (co)infections, and asthma.

Basic Aspects of T Helper Cell Differentiation

CD4+ T helper cells orchestrate the immune response and play a pivotal role during infection, chronic inflammatory, autoimmune diseases, and carcinogenesis. CD4+ T helper cells can be subdivided into different subsets, which are characterized by a specific network of transcriptional regulators and unique cytokine profiles: Th17 cells express RORγt that in turn promotes the transcription of Il17a, Il17f; Th1 cells, expresses T-bet and produces IFN-γ, IL-2, and TNF-α; Th2 cells express GATA-3 and secrete IL-4, IL-5, and IL-13. The two most studied regulatory T cell subtypes are Foxp3+ regulatory T cells, which can be generated either in the thymus (tTreg) or induced in peripheral lymphoid organs (pTregs) and type 1 regulatory T cells (Tr1), which are induced in the periphery. These T helper cell subsets can be differentiated from naïve T cells. In addition, recent findings indicate that some T helper cell subsets can emerge from other T helper cells, suggesting a certain degree of plastiticy. Here we report basic aspects of T helper cell differentiation and function while underlining some still open questions.

A cellular and molecular view of T helper 17 cell plasticity in autoimmunity

Since the original identification of the T helper 17 (Th17) subset in 2005, it has become evident that these cells do not only contribute to host defence against pathogens, such as bacteria and fungi, but that they are also critically involved in the pathogenesis of many autoimmune diseases. In contrast to the classic Th1 and Th2 cells, which represent rather stably polarized subsets, Th17 cells display remarkable heterogeneity and plasticity. This has been attributed to the characteristics of the key transcription factor that guides Th17 differentiation, retinoic acid receptor-related orphan nuclear receptor gamma (RORγ). Unlike the 'master regulators' T-bet and GATA3 that orchestrate Th1 and Th2 differentiation, respectively, RORγ controls transcription at relatively few loci in Th17 cells. Moreover, its expression is not stabilized by positive feedback loops but rather influenced by environmental cues, allowing for substantial functional plasticity. Importantly, a subset of IL-17/IFNγ double-producing Th17 cells was identified in both human and mouse models. Evidence is accumulating that these IL-17/IFNγ double-producing cells are pathogenic drivers in autoimmune diseases, including rheumatoid arthritis, multiple sclerosis and inflammatory bowel disease. In addition, IL-17/IFNγ double-producing cells have been identified in disorders in which the role of autoimmunity remains unclear, such as sarcoidosis. The observed plasticity of Th17 cells towards the Th1 phenotype can be explained by extensive epigenetic priming of the IFNG locus in Th17 cells. In fact, Th17 cells display an IFNG chromatin landscape that is remarkably similar to that of Th1 cells. On the other hand, pathogenic capabilities of Th17 cells can be restrained by stimulating IL-10 production and transdifferentiation into IL-10 producing T regulatory type 1 (Tr1) cells. In this review, we discuss recent advances in our knowledge on the cellular and molecular mechanisms involved in Th17 differentiation, heterogeneity and plasticity. We focus on transcriptional regulation of the Th17 expression program, the epigenetic dynamics involved, and how genetic variants associated with autoimmunity may affect immune responses through distal gene regulatory elements. Finally, the implications of Th17 cell plasticity for the pathogenesis and treatment of human autoimmune diseases will be discussed.

Reverse plasticity: TGF-β and IL-6 induce Th1-to-Th17-cell transdifferentiation in the gut

Th17 cells are a heterogeneous population of pro-inflammatory T cells that have been shown to mediate immune responses against intestinal bacteria. Th17 cells are highly plastic and can transdifferentiate to Th1/17 cells or unconventional Th1 cells, which are highly pathogenic in animal models of immune-mediated diseases such as inflammatory bowel diseases. A recent European Journal of Immunology article by Liu et al. (Eur. J. Immunol. 2015. 45:1010-1018) showed, surprisingly, that Th1 cells have a similar plasticity, and could transdifferentiate to Th17 cells. Thus, IFN-γ-producing Th1 effector cells specific for an intestinal microbial antigen were shown to acquire IL-17-producing capacities in the gut in a mouse model of colitis, and in response to TGF-β and IL-6 in vitro. TGF-β induced Runx1, and together with IL-6 was shown to render the ROR-γt and IL-17 promoters in Th1 cells accessible for Runx1 binding. In this commentary, we discuss how this unexpected plasticity of Th1 cells challenges our view on the generation of Th1/17 cells with the capacity to co-produce IL-17 and IFN-γ, and consider possible implications of this Th1-to-Th17-cell conversion for therapies of inflammatory bowel diseases and protective immune responses against intracellular pathogens.

Recombinant Miro domain-containing protein of Haemonchus contortus (rMiro-1) activates goat peripheral blood mononuclear cells in vitro

In our previous proteomics study, we identified Miro domain-containing protein (Miro-1), an excretory and secretory product of the pole worm, Haemonchus contortus, binds to goat peripheral blood mononuclear cells (PBMCs) in vivo. However, our understanding of the role of Miro-1and its potential immune impact on goat PBMCs is limited. The aim of the present study was to evaluate the effects of Miro-1 on functions of goat PBMCs in vitro. Recombinant protein (rMiro-1) was expressed in a prokaryote and incubated with goat PBMCs. Western blot analysis showed that rMiro-1 is successfully recognized by goat sera infected with H. contortus. Immunofluorescence analysis using rat antibodies against rMiro-1 indicated that this protein binds to goat PBMCs in vitro. Treatment of goat PBMCs/monocytes with various concentrations of rMiro-1 resulted in the upregulation of IL-2, IL-4, and IL-17, which in turn promoted cell proliferation, migration, the release of NO in PBMCs, and enhancement of phagocytosis of monocytes. These findings suggested that rMiro-1 stimulates PBMCs activity.

Th2/1 Hybrid Cells Occurring in Murine and Human Strongyloidiasis Share Effector Functions of Th1 Cells

Infections by the soil-transmitted threadworm Strongyloides stercoralis affect 30–100 million people worldwide, predominantly in tropic and sub-tropic regions. Here we assessed the T helper cell phenotypes in threadworm-infected patients and experimental murine infections with focus on CD4⁺ T cells co-expressing markers of Th2 and Th1 differentiation. We show that mice infected with the close relative S. ratti generate strong Th2 responses characterized by the expansion of CD4⁺ GATA-3⁺ cells expressing IL-4/-5/-13 in blood, spleen, gut-draining lymph nodes, lung and gut tissue. In addition to conventional Th2 cells, significantly increased frequencies of GATA-3⁺T-bet⁺ Th2/1-hybrid cells were detected in all organs and co-expressed Th2- and Th1-cytokines at intermediate levels. Assessing the phenotype of blood-derived CD4⁺ T cells from South Indian patients infected with S. stercoralis and local uninfected control donors we found that GATA-3 expressing Th2 cells were significantly increased in the patient cohort, coinciding with elevated eosinophil and IgE/IgG4 levels. A fraction of IL-4⁺CD4⁺ T cells simultaneously expressed IFN-γ hence displaying a Th2/1 hybrid phenotype. In accordance with murine Th2/1 cells, human Th2/1 cells expressed intermediate levels of Th2 cytokines. Contrasting their murine counterparts, human Th2/1 hybrids were marked by high levels of IFN-γ and rather low GATA-3 expression. Assessing the effector function of murine Th2/1 cells in vitro we found that Th2/1 cells were qualified for driving the classical activation of macrophages. Furthermore, Th2/1 cells shared innate, cytokine-driven effector functions with Th1 cells. Hence, the key findings of our study are that T helper cells with combined characteristics of Th2 and Th1 cells are integral to immune responses of helminth-infected mice, but also occur in helminth-infected humans and we suggest that Th2/1 cells are poised for the instruction of balanced immune responses during nematode infections.

Ubiquitin Ligases and Deubiquitinating Enzymes in CD4+ T Cell Effector Fate Choice and Function

The human body is exposed to potentially pathogenic microorganisms at barrier sites such as the skin, lungs, and gastrointestinal tract. To mount an effective response against these pathogens, the immune system must recruit the right cells with effector responses that are appropriate for the task at hand. Several types of CD4(+) T cells can be recruited, including Th cells (Th1, Th2, and Th17), T follicular helper cells, and regulatory T cells. These cells help to maintain normal immune homeostasis in the face of constantly changing microbes in the environment. Because these cells differentiate from a common progenitor, the composition of their intracellular milieu of proteins changes to appropriately guide their effector function. One underappreciated process that impacts the levels and functions of effector fate-determining factors is ubiquitylation. This review details our current understanding of how ubiquitylation regulates CD4(+) T cell effector identity and function.

Harnessing the plasticity of CD4(+) T cells to treat immune-mediated disease

CD4(+) T cells differentiate and acquire distinct functions to combat specific pathogens but can also adapt their functions in response to changing circumstances. Although this phenotypic plasticity can be potentially deleterious, driving immune pathology, it also provides important benefits that have led to its evolutionary preservation. Here, we review CD4(+) T cell plasticity by examining the molecular mechanisms that regulate it - from the extracellular cues that initiate and drive cells towards varying phenotypes, to the cytosolic signalling cascades that decipher these cues and transmit them into the cell and to the nucleus, where these signals imprint specific gene expression programmes. By understanding how this functional flexibility is achieved, we may open doors to new therapeutic approaches that harness this property of T cells.

Selenoprotein Expression in Macrophages Is Critical for Optimal Clearance of Parasitic Helminth Nippostrongylus brasiliensis

The plasticity of macrophages is evident in helminthic parasite infections, providing protection from inflammation. Previously we demonstrated that the micronutrient selenium induces a phenotypic switch in macrophage activation from a classically activated (pro-inflammatory; M1/CAM) toward an alternatively activated (anti-inflammatory; M2/AAM) phenotype, where cyclooxygenase (COX)-dependent cyclopentenone prostaglandin J2 (15d-PGJ2) plays a key role. Here, we hypothesize that dietary selenium modulates macrophage polarization toward an AAM phenotype to assist in the increasing clearance of adult Nippostrongylus brasiliensis, a gastrointestinal nematode parasite. Mice on a selenium-adequate (0.08 ppm) diet significantly augmented intestinal AAM presence while decreasing adult worms and fecal egg production when compared with infection of mice on selenium-deficient (<0.01 ppm) diet. Further increase in dietary selenium to supraphysiological levels (0.4 ppm) had very little or no impact on worm expulsion. Normal adult worm clearance and enhanced AAM marker expression were observed in the selenium-supplemented Trsp(fl/fl)Cre(WT) mice that express selenoproteins driven by tRNA(Sec) (Trsp), whereas N. brasiliensis-infected Trsp(fl/fl)Cre(LysM) selenium-supplemented mice showed a decreased clearance, with lowered intestinal expression of several AAM markers. Inhibition of the COX pathway with indomethacin resulted in delayed worm expulsion in selenium-adequate mice. This was rescued with 15d-PGJ2, which partially recapitulated the effect of selenium supplementation on fecal egg output in addition to increasing markers of AAMs in the small intestine. Antagonism of PPARγ blocked the effect of selenium. These results suggest that optimal expression of selenoproteins and selenium-dependent production of COX-derived endogenous prostanoids, such as Δ(12)-PGJ2 and 15d-PGJ2, may regulate AAM activation to enhance anti-helminthic parasite responses.

Nanoscale Relationship Between CD4 and CD25 of T Cells Visualized with NSOM/QD-Based Dual-Color Imaging System

In this study, by using of near-field scanning optical microscopy (NSOM)/immune-labeling quantum dot (QD)-based dual-color imaging system, we achieved the direct visualization of nanoscale profiles for distribution and organization of CD4 and CD25 molecules in T cells. A novel and interesting finding was that though CD25 clustering as nanodomains were observed on the surface of CD4(+)CD25(high) regulatory T cells, these CD25 nanodomains were not co-localized with CD4 nanodomains. This result presented that the formation of these CD25 nanodomains on the surface of CD4(+)CD25(high) T cells were not associated with the response of T cell receptor (TCR)/CD3-dependent signal transduction. In contrast, on the surface of CD4(+)CD25(low) T cells, CD25 molecules distributed randomly without forming nanodomains while CD4 clustering as nanodomains can be observed; on the surface of CD8(+)CD25(+) T cells, CD25 clustering as nanodomains and co-localization with CD8 nanodomains were observed. Collectively, above these results exhibited that TCR/CD3-based microdomains were indeed required for TCR/CD3-mediated T cells activation and enhanced the immune activity of CD4(+)CD25(low) T cells or CD8(+)CD25(+) T cells. In particular, it was found that the formation of CD25 nanodomains and their segregation from TCR/CD3 microdomains were the intrinsic capability of CD4(+)CD25(high) T cells, suggesting this specific imaging feature of CD25 should be greatly associated with the regulatory activity of CD4(+)CD25(high) T cells. Importantly, this novel NSOM/QD-based dual-color imaging system will provide a useful tool for the research of distribution-function relationship of cell-surface molecules.

Chronic obstructive pulmonary disease induced by exposure to biomass smoke is associated with a Th2 cytokine production profile

Smoking and exposure to biomass smoke induce the release of pro-inflammatory mediators and the activation of T helper cells. The resulting inflammatory response contributes to the development of COPD. Clinical heterogeneity exists among COPD patients, particularly between patients with disease associated with tobacco smoking (TS-COPD) and those exposed to biomass smoke (BE-COPD). The aim of this study was to identify whether exposure to tobacco and biomass smokes promotes different Th responses that contribute to clinical variability. The study only included women. The frequency of Th17 cells in patients with TS-COPD was significantly higher than in patients with BE-COPD and healthy controls (HC). In contrast, patients with BE-COPD had higher levels of Th2 cells than TS-COPD and HC. In accordance, IL-4 serum concentration was higher in BE-COPD than in TS-COPD. Our data indicates that the different responses induced by these two irritants may underlie the clinical heterogeneity between TS- and BE-COPD patients.

Along the Axis between Type 1 and Type 2 Immunity; Principles Conserved in Evolution from Fish to Mammals

A phenomenon already discovered more than 25 years ago is the possibility of naïve helper T cells to polarize into TH1 or TH2 populations. In a simplified model, these polarizations occur at opposite ends of an "immune 1-2 axis" (i1-i2 axis) of possible conditions. Additional polarizations of helper/regulatory T cells were discovered later, such as for example TH17 and Treg phenotypes; although these polarizations are not selected by the axis-end conditions, they are affected by i1-i2 axis factors, and may retain more potential for change than the relatively stable TH1 and TH2 phenotypes. I1-i2 axis conditions are also relevant for polarizations of other types of leukocytes, such as for example macrophages. Tissue milieus with "type 1 immunity" ("i1") are biased towards cell-mediated cytotoxicity, while the term "type 2 immunity" ("i2") is used for a variety of conditions which have in common that they inhibit type 1 immunity. The immune milieus of some tissues, like the gills in fish and the uterus in pregnant mammals, probably are skewed towards type 2 immunity. An i2-skewed milieu is also created by many tumors, which allows them to escape eradication by type 1 immunity. In this review we compare a number of i1-i2 axis factors between fish and mammals, and conclude that several principles of the i1-i2 axis system seem to be ancient and shared between all classes of jawed vertebrates. Furthermore, the present study is the first to identify a canonical TH2 cytokine locus in a bony fish, namely spotted gar, in the sense that it includes RAD50 and bona fide genes of both IL-4/13 and IL-3/ IL-5/GM-CSF families.

Avidity of human T cell receptor engineered CD4(+) T cells drives T-helper differentiation fate

The role of the T cell receptor (TCR) in antigen recognition and activation of T lymphocytes is well established. However, how the TCR affects T-helper differentiation/skewing is less well understood, particularly for human CD4(+) (CD4) T cell subsets. Here we investigate the role of TCR specific antigen avidity in differentiation and maintenance of human Th1, Th2 and Th17 subsets. Two human TCRs, both specific for the same peptide antigen but with different avidities, were cloned and expressed in human CD4 T cells. These TCR engineered cells were then stimulated with specific antigen in unskewed and T-helper skewed conditions. We show that TCR avidity can control the percentage of IL-4 and IFN-γ co-expression in unskewed TCR engineered cells, that effector function can be maintained in a TCR avidity-dependent manner in skewed TCR engineered cells, and that increased TCR avidity can accelerate Th1 skewing of TCR engineered cells.

IFNγ and IL-12 Restrict Th2 Responses during Helminth/Plasmodium Co-Infection and Promote IFNγ from Th2 Cells

Parasitic helminths establish chronic infections in mammalian hosts. Helminth/Plasmodium co-infections occur frequently in endemic areas. However, it is unclear whether Plasmodium infections compromise anti-helminth immunity, contributing to the chronicity of infection. Immunity to Plasmodium or helminths requires divergent CD4⁺ T cell-driven responses, dominated by IFNγ or IL-4, respectively. Recent literature has indicated that Th cells, including Th2 cells, have phenotypic plasticity with the ability to produce non-lineage associated cytokines. Whether such plasticity occurs during co-infection is unclear. In this study, we observed reduced anti-helminth Th2 cell responses and compromised anti-helminth immunity during Heligmosomoides polygyrus and Plasmodium chabaudi co-infection. Using newly established triple cytokine reporter mice (Il4^gfpIfng^yfpIl17a^FP635), we demonstrated that Il4^gfp+ Th2 cells purified from in vitro cultures or isolated ex vivo from helminth-infected mice up-regulated IFNγ following adoptive transfer into Rag1^–/– mice infected with P. chabaudi. Functionally, Th2 cells that up-regulated IFNγ were transcriptionally re-wired and protected recipient mice from high parasitemia. Mechanistically, TCR stimulation and responsiveness to IL-12 and IFNγ, but not type I IFN, was required for optimal IFNγ production by Th2 cells. Finally, blockade of IL-12 and IFNγ during co-infection partially preserved anti-helminth Th2 responses. In summary, this study demonstrates that Th2 cells retain substantial plasticity with the ability to produce IFNγ during Plasmodium infection. Consequently, co-infection with Plasmodium spp. may contribute to the chronicity of helminth infection by reducing anti-helminth Th2 cells and converting them into IFNγ-secreting cells.

Approximately a third of the world’s population is burdened with chronic intestinal parasitic helminth infections, causing significant morbidities. Identifying the factors that contribute to the chronicity of infection is therefore essential. Co-infection with other pathogens, which is extremely common in helminth endemic areas, may contribute to the chronicity of helminth infections. In this study, we used a mouse model to test whether the immune responses to an intestinal helminth were impaired following malaria co-infection. These two pathogens induce very different immune responses, which, until recently, were thought to be opposing and non-interchangeable. This study identified that the immune cells required for anti-helminth responses are capable of changing their phenotype and providing protection against malaria. By identifying and blocking the factors that drive this change in phenotype, we can preserve anti-helminth immune responses during co-infection. Our studies provide fresh insight into how immune responses are altered during helminth and malaria co-infection.

Th17 cells transdifferentiate into regulatory T cells during resolution of inflammation

Inflammation is a beneficial host response to infection but can contribute to inflammatory disease if unregulated. The Th17 lineage of T helper (Th) cells can cause severe human inflammatory diseases. These cells exhibit both instability (they can cease to express their signature cytokine, IL-17A) and plasticity (they can start expressing cytokines typical of other lineages) upon in vitro re-stimulation. However, technical limitations have prevented the transcriptional profiling of pre- and post-conversion Th17 cells ex vivo during immune responses. Thus, it is unknown whether Th17 cell plasticity merely reflects change in expression of a few cytokines, or if Th17 cells physiologically undergo global genetic reprogramming driving their conversion from one T helper cell type to another, a process known as transdifferentiation. Furthermore, although Th17 cell instability/plasticity has been associated with pathogenicity, it is unknown whether this could present a therapeutic opportunity, whereby formerly pathogenic Th17 cells could adopt an anti-inflammatory fate. Here we used two new fate-mapping mouse models to track Th17 cells during immune responses to show that CD4(+) T cells that formerly expressed IL-17A go on to acquire an anti-inflammatory phenotype. The transdifferentiation of Th17 into regulatory T cells was illustrated by a change in their signature transcriptional profile and the acquisition of potent regulatory capacity. Comparisons of the transcriptional profiles of pre- and post-conversion Th17 cells also revealed a role for canonical TGF-β signalling and consequently for the aryl hydrocarbon receptor (AhR) in conversion. Thus, Th17 cells transdifferentiate into regulatory cells, and contribute to the resolution of inflammation. Our data suggest that Th17 cell instability and plasticity is a therapeutic opportunity for inflammatory diseases.

Long Intergenic Non-Coding RNAs: Novel Drivers of Human Lymphocyte Differentiation

Upon recognition of a foreign antigen, CD4(+) naïve T lymphocytes proliferate and differentiate into subsets with distinct functions. This process is fundamental for the effective immune system function, as CD4(+) T cells orchestrate both the innate and adaptive immune response. Traditionally, this differentiation event has been regarded as the acquisition of an irreversible cell fate so that memory and effector CD4(+) T subsets were considered terminally differentiated cells or lineages. Consequently, these lineages are conventionally defined thanks to their prototypical set of cytokines and transcription factors. However, recent findings suggest that CD4(+) T lymphocytes possess a remarkable phenotypic plasticity, as they can often re-direct their functional program depending on the milieu they encounter. Therefore, new questions are now compelling such as which are the molecular determinants underlying plasticity and stability and how the balance between these two opposite forces drives the cell fate. As already mentioned, in some cases, the mere expression of cytokines and master regulators could not fully explain lymphocytes plasticity. We should consider other layers of regulation, including epigenetic factors such as the modulation of chromatin state or the transcription of non-coding RNAs, whose high cell-specificity give a hint on their involvement in cell fate determination. In this review, we will focus on the recent advances in understanding CD4(+) T lymphocytes subsets specification from an epigenetic point of view. In particular, we will emphasize the emerging importance of non-coding RNAs as key players in these differentiation events. We will also present here new data from our laboratory highlighting the contribution of long non-coding RNAs in driving human CD4(+) T lymphocytes differentiation.

TGF-β converts Th1 cells into Th17 cells through stimulation of Runx1 expression

Differentiated CD4(+) T cells preserve plasticity under various conditions. However, the stability of Th1 cells is unclear, as is whether Th1 cells can convert into Th17 cells and thereby contribute to the generation of IFN-γ(+) IL-17(+) CD4(+) T cells, the number of which correlates with severity of colitis. We investigated whether IFN-γ(+) Th1 cells can convert into Th17 cells under intestinal inflammation and the mechanisms involved. IFN-γ(Thy1.1+) Th1 cells were generated by culturing naïve CD4(+) T cells from IFN-γ(Thy1.1) CBir1 TCR-Tg reporter mice, whose TCR is specific for an immunodominant microbiota antigen, CBir1 flagellin, under Th1 polarizing conditions. IFN-γ(Thy1.1+) Th1 cells induced colitis in Rag(-/-) mice after adoptive transfer and converted into IL-17(+) Th17, but not Foxp3(+) Treg cells in the inflamed intestines. TGF-β and IL-6, but not IL-1β and IL-23, regulated Th1 conversion into Th17 cells. TGF-β induction of transcriptional factor Runx1 is crucial for the conversion, since silencing Runx1 by siRNA inhibited Th1 conversion into Th17 cells. Furthermore, TGF-β enhanced histone H3K9 acetylation but inhibited H3K9 trimethylation of Runx1- and ROR-γt-binding sites on il-17 or rorc gene in Th1 cells. We conclude that Th1 cells convert into Th17 cells under inflammatory conditions in intestines, which is possibly mediated by TGF-β induction of Runx1.

The Differentiation of CD4(+) T-Helper Cell Subsets in the Context of Helminth Parasite Infection

Helminths are credited with being the major selective force driving the evolution of the so-called “type 2” immune responses in vertebrate animals, with their size and infection strategies presenting unique challenges to the immune system. Originally, type 2 immune responses were defined by the presence and activities of the CD4⁺ T-helper 2 subset producing the canonical cytokines IL-4, IL-5, and IL-13. This picture is now being challenged by the discovery of a more complex pattern of CD4⁺ T-helper cell subsets that appear during infection, including Tregs, Th17, Tfh, and more recently, Th22, Th9, and ThGM. In addition, a clearer view of the mechanisms by which helminths and their products selectively prime the CD4⁺ T-cell subsets is emerging. In this review, we have focused on recent data concerning the selective priming, differentiation, and functional role of CD4⁺ T-helper cell subsets in the context of helminth infection. We argue for a re-evaluation of the original Th2 paradigm and discuss how the observed plasticity of the T-helper subsets may enable the parasitized host to achieve an appropriate compromise between elimination, tissue repair, containment, and pathology.

An animated landscape representation of CD4+ T-cell differentiation, variability, and plasticity: insights into the behavior of populations versus cells

Recent advances in understanding CD4(+) T-cell differentiation suggest that previous models of a few distinct, stable effector phenotypes were too simplistic. Although several well-characterized phenotypes are still recognized, some states display plasticity, and intermediate phenotypes exist. As a framework for reexamining these concepts, we use Waddington's landscape paradigm, augmented with explicit consideration of stochastic variations. Our animation program "LAVA" visualizes T-cell differentiation as cells moving across a landscape of hills and valleys, leading to attractor basins representing stable or semistable differentiation states. The model illustrates several principles, including: (i) cell populations may behave more predictably than individual cells; (ii) analogous to reticulate evolution, differentiation may proceed through a network of interconnected states, rather than a single well-defined pathway; (iii) relatively minor changes in the barriers between attractor basins can change the stability or plasticity of a population; (iv) intrapopulation variability of gene expression may be an important regulator of differentiation, rather than inconsequential noise; (v) the behavior of some populations may be defined mainly by the behavior of outlier cells. While not a quantitative representation of actual differentiation, our model is intended to provoke discussion of T-cell differentiation pathways, particularly highlighting a probabilistic view of transitions between states.