Effector T cell plasticity: flexibility in the face of changing circumstances. Nat Immunol. 2010;11:674-680. [PMID: 20644573 DOI: 10.1038/ni.1899]

Expanding roles for CD4 T cells and their subpopulations in tumor immunity and therapy

The importance of CD4 T cells in orchestrating the immune system and their role in inducing effective T cell-mediated therapies for the treatment of patients with select established malignancies are undisputable. Through a complex and balanced array of direct and indirect mechanisms of cellular activation and regulation, this functionally diverse family of lymphocytes can potentially promote tumor eradication, long-term tumor immunity, and aid in establishing and/or rebalancing immune cell homeostasis through interaction with other immune cell populations within the highly dynamic tumor environment. However, recent studies have uncovered additional functions and roles for CD4 T cells, some of which are independent of other lymphocytes, that can not only influence and contribute to tumor immunity but paradoxically promote tumor growth and progression. Here, we review the recent advances in our understanding of the various CD4 T cell lineages and their signature cytokines in disease progression and/or regression. We discuss their direct and indirect mechanistic interplay among themselves and with other responding cells of the antitumor response, their potential roles and abilities for "plasticity" and memory cell generation within the hostile tumor environment, and their potentials in cancer treatment and immunotherapy.

Does a quorum sensing mechanism direct the behavior of immune cells?

Quorum sensing is a decision-making process used by decentralized groups such as colonies of bacteria to trigger a coordinated behavior. The existence of decentralized coordinated behavior has also been suggested in the immune system. In this paper, we explore the possibility for quorum sensing mechanisms in the immune response. Cytokines are good candidates as inducer of quorum sensing effects on migration, proliferation and differentiation of immune cells. The existence of a quorum sensing mechanism should be explored experimentally. It may provide new perspectives into immune responses and could lead to new therapeutic strategies.

Cellular and molecular mechanisms involved in the establishment of HIV-1 latency

Latently infected cells represent the major barrier to either a sterilizing or a functional HIV-1 cure. Multiple approaches to reactivation and depletion of the latent reservoir have been attempted clinically, but full depletion of this compartment remains a long-term goal. Compared to the mechanisms involved in the maintenance of HIV-1 latency and the pathways leading to viral reactivation, less is known about the establishment of latent infection. This review focuses on how HIV-1 latency is established at the cellular and molecular levels. We first discuss how latent infection can be established following infection of an activated CD4 T-cell that undergoes a transition to a resting memory state and also how direct infection of a resting CD4 T-cell can lead to latency. Various animal, primary cell, and cell line models also provide insights into this process and are discussed with respect to the routes of infection that result in latency. A number of molecular mechanisms that are active at both transcriptional and post-transcriptional levels have been associated with HIV-1 latency. Many, but not all of these, help to drive the establishment of latent infection, and we review the evidence in favor of or against each mechanism specifically with regard to the establishment of latency. We also discuss the role of immediate silent integration of viral DNA versus silencing of initially active infections. Finally, we discuss potential approaches aimed at limiting the establishment of latent infection.

The Th17 pathway and inflammatory diseases of the intestines, lungs, and skin

The recent discovery of a new CD4+ T cell subset, Th17, has transformed our understanding of the pathogenetic basis of an increasing number of chronic immune-mediated diseases. Particularly in tissues that interface with the microbial environment-such as the intestinal and respiratory tracts and the skin-where most of the Th17 cells in the body reside, dysregulated immunity to self (or the extended self, the diverse microbiota that normally colonize these tissues) can result in chronic inflammatory disease. In this review, we focus on recent advances in the biology of the Th17 pathway and on genome-wide association studies that implicate this immune pathway in human disease involving these tissues.

Plasticity within the αβ⁺CD4⁺ T-cell lineage: when, how and what for?

Following thymic output, αβ⁺CD4⁺ T cells become activated in the periphery when they encounter peptide-major histocompatibility complex. A combination of cytokine and co-stimulatory signals instructs the differentiation of T cells into various lineages and subsequent expansion and contraction during an appropriate and protective immune response. Our understanding of the events leading to T-cell lineage commitment has been dominated by a single fate model describing the commitment of T cells to one of several helper (T(H)), follicular helper (T(FH)) or regulatory (T(REG)) phenotypes. Although a single lineage-committed and dedicated T cell may best execute a single function, the view of a single fate for T cells has recently been challenged. A relatively new paradigm in αβ⁺CD4⁺ T-cell biology indicates that T cells are much more flexible than previously appreciated, with the ability to change between helper phenotypes, between helper and follicular helper, or, most extremely, between helper and regulatory functions. In this review, we comprehensively summarize the recent literature identifying when T(H) or T(REG) cell plasticity occurs, provide potential mechanisms of plasticity and ask if T-cell plasticity is beneficial or detrimental to immunity.

Self double-stranded (ds)DNA induces IL-1β production from human monocytes by activating NLRP3 inflammasome in the presence of anti-dsDNA antibodies

The pathogenic hallmark of systemic lupus erythematosus is the autoimmune response against self nuclear Ags, including dsDNA. The increased expression of the proinflammatory cytokine IL-1β has been found in the cutaneous lesion and PBMCs from lupus patients, suggesting a potential involvement of this cytokine in the pathogenesis of lupus. IL-1β is produced primarily by innate immune cells such as monocytes and can promote a Th17 cell response, which is increased in lupus. IL-1β production requires cleaving pro-IL-β into IL-1β by the caspase-1-associated multiprotein complex called inflammasomes. In this study we show that self dsDNA induces IL-1β production from human monocytes dependent on serum or purified IgG containing anti-dsDNA Abs by activating the nucleotide-binding oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome. Reactive oxygen species (ROS) and K(+) efflux were involved in this activation. Knocking down the NLRP3 or inhibiting caspase-1, ROS, and K(+) efflux decreased IL-1β production. Supernatants from monocytes treated with a combination of self dsDNA and anti-dsDNA Ab(+) serum promoted IL-17 production from CD4(+) T cells in an IL-1β-dependent manner. These findings provide new insights in lupus pathogenesis by demonstrating that self dsDNA together with its autoantibodies induces IL-1β production from human monocytes by activating the NLRP3 inflammasome through inducing ROS synthesis and K(+) efflux, leading to the increased Th17 cell response.

The dynamic lives of T cells: new approaches and themes

Activated T cells have classically been thought to progress unidirectionally through discrete phenotypic states and differentiate into static lineages. It is increasingly evident, however, that T cells exhibit much more complex and flexible dynamic behaviors than initially appreciated, and that these behaviors influence the efficacy of T cell responses to immunological challenges. In this review, we discuss how new technologies for monitoring the dynamics of T cells are enhancing the resolution of the fine phenotypic and functional heterogeneity within populations of T cells and revealing how individual T cells transition among a continuum of states. Such insights into the dynamic properties of T cells should improve immune monitoring and inform strategies for therapeutic interventions.

B lymphocyte-induced maturation protein-1 contributes to intestinal mucosa homeostasis by limiting the number of IL-17-producing CD4+ T cells

The transcription factor B lymphocyte-induced maturation protein-1 (Blimp-1) plays important roles in embryonic development and immunity. Blimp-1 is required for the differentiation of plasma cells, and mice with T cell-specific deletion of Blimp-1 (Blimp-1CKO mice) develop a fatal inflammatory response in the colon. Previous work demonstrated that lack of Blimp-1 in CD4(+) and CD8(+) T cells leads to intrinsic functional defects, but little is known about the functional role of Blimp-1 in regulating differentiation of Th cells in vivo and their contribution to the chronic intestinal inflammation observed in the Blimp1CKO mice. In this study, we show that Blimp-1 is required to restrain the production of the inflammatory cytokine IL-17 by Th cells in vivo. Blimp-1CKO mice have greater numbers of IL-17-producing TCRβ(+)CD4(+)cells in lymphoid organs and in the intestinal mucosa. The increase in IL-17-producing cells was not restored to normal levels in wild-type and Blimp-1CKO-mixed bone marrow chimeric mice, suggesting an intrinsic role for Blimp-1 in constraining the production of IL-17 in vivo. The observation that Blimp-1-deficient CD4(+) T cells are more prone to differentiate into IL-17(+)/IFN-γ(+) cells and cause severe colitis when transferred to Rag1-deficient mice provides further evidence that Blimp-1 represses IL-17 production. Analysis of Blimp-1 expression at the single cell level during Th differentiation reveals that Blimp-1 expression is induced in Th1 and Th2 but repressed by TGF-β in Th17 cells. Collectively, the results described here establish a new role for Blimp-1 in regulating IL-17 production in vivo.

Dynamics of intraocular IFN-γ, IL-17 and IL-10-producing cell populations during relapsing and monophasic rat experimental autoimmune uveitis

A major limitation of most animal models of autoimmune diseases is that they do not reproduce the chronic or relapsing-remitting pattern characteristic of many human autoimmune diseases. This problem has been overcome in our rat models of experimentally induced monophasic or relapsing-remitting autoimmune uveitis (EAU), which depend on the inducing antigen peptides from retinal S-Antigen (monophasic EAU) or interphotoreceptor retinoid-binding protein (relapsing EAU). These models enable us to compare autoreactive and regulatory T cell populations. Intraocular, but not peripheral T cells differ in their cytokine profiles (IFN-γ, IL-17 and IL-10) at distinct time points during monophasic or relapsing EAU. Only intraocular T cells concomitantly produced IFN-γ, IL-17 and/or IL-10. Monophasic EAU presented rising numbers of cells expressing IFN-γ and IL-17 (Th1/Th17) and cells expressing IL-10 or Foxp3. During relapsing uveitis an increase of intraocular IFN-γ+ cells and a concomitant decrease of IL-17+ cells was detected, while IL-10+ populations remained stable. Foxp3+ cells and cells expressing IL-10, even in combination with IFN-γ or IL-17, increased during the resolution of monophasic EAU, suggesting a regulatory role for these T cells. In general, cells producing multiple cytokines increased in monophasic and decreased in relapsing EAU. The distinct appearance of certain intraocular populations with characteristics of regulatory cells points to a differential influence of the ocular environment on T cells that induce acute and monophasic or relapsing disease. Here we provide evidence that different autoantigens can elicit distinct and differently regulated immune responses. IFN-γ, but not IL-17 seems to be the key player in relapsing-remitting uveitis, as shown by increased, synchronized relapses after intraocular application of IFN-γ. We demonstrated dynamic changes of the cytokine pattern during monophasic and relapsing-remitting disease with strongly increasing IL-10 expression in intraocular T cells during monophasic uveitis.

[Development, competition and plasticity of the T-lymph cells in inflammatory bowel disease]

The hypothesis of helper T (T(h))1/T(h)2 cytokine balance was often invoked to explain the development of inflammatory diseases, including inflammatory bowel diseases (IBD). Recently, a newly identified class of regulatory T cells (Tregs), which suppress inflammation and helper T(Th)17 cells, which produce Th17 family cytokines has been recognized as an essential subpopulation in the development of almost all kinds of human and animal inflammatory diseases. T cell subsets can act as terminally differentiated lineages, but they have been increasingly noted to demonstrated plasticity, depending on their surrounding such as intestinal microbiota. Th17 cells and Th1 cells coordinate to play a critical role in the formation of inflammatory bowel diseases. We showed Th1 and Th17 cells are competitive in lymphopenic mice, and that their orchestration results in a merged clinical phenotype of the two types of murine colitis. We also showed that Th17 and Th17/Th1 cells become colitogenic alternative Th1 cells via Th17, Th17/Th1, and Th1-like cells, independently of classical Th1 cells. Treg cells suppress this pathway, resulting in accumulation of Th17 and Th17/Th1 cells. Here we review T cell development including their plasticity and recent advances in the study of such Treg cells and Th17 cells in the pathogenesis of IBD.

T-follicular helper cells survive as long-term memory cells

T-follicular helper (TFH) cells represent the subpopulation of CD4(+) T cells that provides help for antigen-specific B cells in the GC response. They are generated from naïve T cells during an immune response and are imprinted by their master transcription factor Bcl-6. It has been a long-standing question if TFH cells contribute to the CD4(+) memory pool after the GC response has been terminated. To answer this question, we sorted antigen-specific TFH and non-TFH effector cells from an ongoing GC response and transferred them into naïve mice. Without further signals via the TCR, transferred cells rapidly contracted with a small population of both TFH and non-TFH cells surviving as memory cells in peripheral lymphoid organs for at least 4 weeks in the absence of antigen. TFH cells strongly downregulated their signature genes Bcl-6, CXCR5, and PD-1 in the memory phase. Upon rechallenge with antigen they rapidly upregulated these markers again. An enhanced potential to produce IL-21, paired with higher expression of CXCR5 and lower expression of CCR7, should enable TFH memory cells to provide more efficient help for antigen-specific B cells than their non-TFH counterparts.

Distinctive features of classic and nonclassic (Th17 derived) human Th1 cells

T helper17 (Th17) lymphocytes represent a third arm of the CD4(+) T-cell effector responses, in addition to Th1 and Th2 cells. Th17 cells have been found to exhibit high plasticity because they rapidly shift into the Th1 phenotype in inflammatory sites. In humans, Th1 cells derived from Th17 cells express CD161, whereas classic Th1 cells do not; these Th17-derived Th1 cells have been termed nonclassic Th1 cells. In this study, we examined similarities and differences between classic and nonclassic human Th1 cells by assessing a panel of T-cell clones, as well as CD161(+) or CD161(-) CD4(+) T cells derived ex vivo from the circulation of healthy subjects or the synovial fluid of patients with juvenile idiopathic arthritis. The results show that nonclassic Th1 cells can be identified based on CD161 expression, as well as the consistent expression of retinoic acid orphan receptor C, IL-17 receptor E, CCR6, and IL-4-induced gene 1, which are all virtually absent in classic Th1 cells. The possibility to distinguish these two-cell subsets by using such a panel of markers may allow the opportunity to better establish the respective pathogenic roles of classic and nonclassic (Th17 derived) Th1 cells in different chronic inflammatory disorders.

Altered AKT1 and MAPK1 gene expression on peripheral blood mononuclear cells and correlation with T-helper-transcription factors in systemic lupus erythematosus patients

Kinases have been implicated in the immunopathological mechanisms of Systemic Lupus Erythematosus (SLE). v-akt murine-thymoma viral-oncogene-homolog 1 (AKT1) and mitogen-activated-protein-kinase 1 (MAPK1) gene expressions in peripheral mononuclear cells from thirteen SLE patients with inactive or mild disease were evaluated using quantitative real-time reverse-transcription polymerase-chain-reaction and analyzed whether there was any correlation with T-helper (Th) transcription factors (TF) gene expression, cytokines, and S100A8/S100A9-(Calprotectin). Age- and gender-matched thirteen healthy controls were examined. AKT1 and MAPK1 expressions were upregulated in SLE patients and correlated with Th17-(Retinoic acid-related orphan receptor (ROR)-C), T-regulatory-(Treg)-(Transforming Growth Factor Beta (TGFB)-2), and Th2-(interleukin (IL)-5)-related genes. MAPK1 expression correlated with Th1-(IL-12A, T-box TF-(T-bet)), Th2-(GATA binding protein-(GATA)-3), and IL-10 expressions. IL-10 expression was increased and correlated with plasma Tumor Necrosis Factor (TNF)-α and Th0-(IL-2), Th1-(IL-12A, T-bet), GATA3, Treg-(Forkhead/winged-helix transcription factor- (FOXP)-3), and IL-6 expressions. FOXP3 expression, FOXP3/RORC, and FOXP3/GATA3 expression ratios were increased. Plasma IL-1β, IL-12(p70), Interferon-(IFN)-γ, and IL-6 cytokines were augmented. Plasma IL-1β, IL-6, IL-2, IFN-γ, TNF-α, IL-10, and IL-13 correlated with C-reactive protein, respectively. Increased Calprotectin correlated with neutrophils. Conclusion, SLE patients presented a systemic immunoinflammatory activity, augmented AKT1 and MAPK1 expressions, proinflammatory cytokines, and Calprotectin, together with increased expression of Treg-related genes, suggesting a regulatory feedback opposing the inflammatory activity.

Master regulators or lineage-specifying? Changing views on CD4+ T cell transcription factors

There is an emerging body of research demonstrating that the co-expression of key lineage-specifying transcription factors, commonly referred to as 'master regulators', affects the functional capabilities and flexibility of CD4(+) T cell subsets. Here, we discuss how the natural co-expression of these lineage-specifying transcription factors has challenged the concept that the expression of a single 'master regulator' strictly establishes an absolute CD4(+) T cell phenotype. Instead, it is becoming clear that the interplay between the lineage-specifying (or lineage-defining) transcription factors, including T-bet, GATA3, RORγt, BCL-6 and FOXP3, contributes to the fate and flexibility of CD4(+) T cell subtypes. This in turn has led to the realization that CD4(+) T cell phenotypes are more diverse than previously recognized.

SOCS3 deficiency promotes M1 macrophage polarization and inflammation

Macrophages participate in both the amplification of inflammation at the time of injury and downregulation of the inflammatory response to avoid excess tissue damage. These divergent functions of macrophages are dictated by their microenvironment, especially cytokines, which promote a spectrum of macrophage phenotypes. The M1 proinflammatory phenotype is induced by LPS, IFN-γ, and GM-CSF, and IL-4, IL-13, and M-CSF induce anti-inflammatory M2 macrophages. Suppressors of cytokine signaling (SOCS) proteins function as feedback inhibitors of the JAK/STAT signaling pathway, and they can terminate innate and adaptive immune responses. In this study, we have evaluated the influence of SOCS3 on macrophage polarization and function. Macrophages obtained from LysMCre-SOCS3(fl/fl) mice, which lack SOCS3 in myeloid lineage cells, exhibit enhanced and prolonged activation of the JAK/STAT pathway compared with macrophages from SOCS3(fl/fl) mice. Furthermore, SOCS3-deficient macrophages have higher levels of the M1 genes IL-1β, IL-6, IL-12, IL-23, and inducible NO synthase owing to enhanced transcriptional activation and chromatin modifications. SOCS3-deficient M1 macrophages also have a stronger capacity to induce Th1 and Th17 cell differentiation than M1 macrophages from SOCS3(fl/fl) mice. Lastly, LPS-induced sepsis is exacerbated in LysMCre-SOCS3(fl/fl) mice and is associated with enhanced STAT1/3 activation and increased plasma levels of M1 cytokines/chemokines such as IL-1β, TNF-α, IL-6, CCL3, CCL4, and CXCL11. These findings collectively indicate that SOCS3 is involved in repressing the M1 proinflammatory phenotype, thereby deactivating inflammatory responses in macrophages.

The dual roles of inflammatory cytokines and chemokines in the regulation of autoimmune diseases and their clinical implications

Cytokines and chemokines are secreted, small cell-signaling protein molecules, whose receptors are expressed on immune cells. These factors play a critical role in immune cell differentiation, migration, and polarization into functional subtypes and in directing their biological functions. Much attention has been devoted to exploring the role of key inflammatory cytokines and promigratory chemokines in autoimmune, autoinflammatory, and allergic diseases, leading to development of therapeutic strategies that are based on their targeted neutralization. Recent studies, including those coming from our groups, show that several major proinflammatory cytokines and chemokines, including IFN-γ, IL-2, CCL2, and CXCL12, may also function as anti-inflammatory mediators and therefore, may have potential as anti-inflammatory drugs. Likewise, major anti-inflammatory mediators, such as TGF-β, may under certain conditions, in combination with other cytokines, exhibit proinflammatory function and direct the polarization of the highly inflammatory CD4(+) Th17 cells. We show here that the biological function of pro- and anti-inflammatory cytokines is dependent on three key parameters: the local concentration of a given cytokine, the stage of disease in which it is administered, and its combination with other cytokines. The therapeutic implications of these findings are discussed, including two very recent studies summarizing clinical trials, in which low-dose administration of IL-2 was used to successfully suppress HCV and GVHD.

Characterization of CD4+ T cell subsets in allergy

Allergen specific T(H)2 cells are a key component of allergic disease, but their characterization has been hindered by technical limitations and lack of epitope data. Knowledge about the factors that drive the differentiation of naïve T cells into allergy-promoting T(H)2 cells and the influence of allergen specific immunotherapy on the phenotype and function of allergen-specific T cells have also been limited. Recent advances indicate that innate and adaptive immune factors drive the development of diverse subsets of allergen-specific T cells. While allergen-specific T cells are present even in non-allergic subjects, highly differentiated T(H)2 cells are present only in allergic subjects and their disappearance correlates with successful immunotherapy. Therefore, elimination of pathogenic T(H)2 cells is an essential step in tolerance induction.

IL-13-producing Th1 and Th17 cells characterize adaptive responses to both self and foreign antigens

In helper T cells, IL-13 is traditionally considered a Th2-type cytokine that is coexpressed with IL-4. Using mouse models of immunization and autoimmunity, we demonstrate that IL-13 is frequently uncoupled from IL-4, and that it can be produced by both IFN-γ(+) Th1 cells and IL-17(+) Th17 cells. We report that these IL-13-producing Th1 and Th17 cells are distinct from classical IL-4(+) Th2 cells and that they are relatively common, appearing in the context of both protective and pathogenic T-cell responses. We also demonstrate that IL-13 and Th2-type cytokines can have important consequences in Th1- and Th17-dominated settings, such as lymphopenia-induced autoimmune disease, where they can be either pro- or anti-inflammatory, depending on whether they act on innate or adaptive immune cells. Taken together, our studies indicate that IL-13 production is more widespread than previously appreciated and that blocking this cytokine may have therapeutic benefits even in settings where traditional IL-4-driven Th2-type responses are not evident.

DNA methylation: a promising landscape for immune system-related diseases

During hematopoiesis, a unique hematopoietic stem cell (HSC) from the bone marrow gives rise to a subset of mature blood cells that directs all the immune responses. Recent studies have shown that this well-defined, hierarchical process is regulated in part by epigenetic mechanisms. Changes in the DNA methylation profile have a critical role in the division of these stem cells into the myeloid and lymphoid lineages and in the establishment of a specific phenotype and functionality in each terminally differentiated cell type. In this review, we describe how the DNA methylation patterns are modified during hematopoietic differentiation and what their role is in cell plasticity and immune function. An in-depth knowledge of these epigenetic mechanisms will help clarify how cell type-specific gene programs are established, and how they can be leveraged in the development of novel strategies for treating immune system-related pathologies.

Metabolic characterization of Leishmania major infection in activated and nonactivated macrophages

Infection with Leishmania spp. can lead to a range of symptoms in the affected individual, depending on underlying immune-metabolic processes. The macrophage activation state hereby plays a key role. Whereas the l-arginine pathway has been described in detail as the main biochemical process responsible for either nitric oxide mediated parasite killing (classical activation) or amplification of parasite replication (alternative activation), we were interested in a wider characterization of metabolic events in vitro. We therefore assessed cell growth medium, parasite extract, and intra- and extracellular metabolome of activated and nonactivated macrophages, in presence and absence of Leishmania major. A metabolic profiling approach was applied combining ¹H NMR spectroscopy with multi- and univariate data treatment. Metabolic changes were observed along both conditional axes, that is, infection state and macrophage activation, whereby significantly higher levels of potential parasite end products were found in parasite exposed samples including succinate, acetate, and alanine, compared to uninfected macrophages. The different macrophage activation states were mainly discriminated by varying glucose consumption. The presented profiling approach allowed us to obtain a metabolic snapshot of the individual biological compartments in the assessed macrophage culture experiments and represents a valuable read out system for further multiple compartment in vitro studies.

New pathways of protective and pathological host defense to mycobacteria

Recent studies have uncovered new mechanisms by which the human immune system attempts to control infection and how pathogens elude these mechanisms. Mycobacterial infections are prime examples of chronic battle fields between host and pathogens. The study of tuberculosis and related mycobacterial infectious diseases such as leprosy have greatly aided in deciphering mechanisms of immune mediated protection and pathology in humans. Here we review recent insights into the role of newly discovered T cell subsets including Th17, Tregs and nonclassically restricted T cells in adaptive immunity to mycobacteria. The role of newly discovered innate immune mechanisms in tuberculosis and leprosy along with recent results from 'unbiased' genome-wide and functional genetic approaches, are deciphering critical host pathways in human infectious disease.

Immunophenotyping of circulating T helper cells argues for multiple functions and plasticity of T cells in vivo in humans--possible role in asthma

Background

The immune process driving eosinophilic and non-eosinophilic asthma is likely driven by different subsets of T helper (Th) cells. Recently, in vitro studies and animal studies suggest that Th cell subsets displays plasticity by changing their transcription factor or by expressing multiple transcription factors. Our aim was to determine whether individuals with asthma and elevated circulating eosinophils express signs of different regulatory immune mechanisms compared with asthmatics with low blood eosinophils and non-asthmatic control subjects. In addition, determine the relationship between eosinophilia and circulating Th cell subsets.

Methodology/Principal findings

Participants were selected from a random epidemiological cohort, the West Sweden Asthma Study. Immunophenotypes of fresh peripheral blood cells obtained from stable asthmatics, with and without elevated eosinophilic inflammation (EOS high and EOS low respectively) and control subjects, were determined by flow cytometry. No differences in the number of Th1 (T-bet), Th2 (GATA-3), Th17 (RORγt) or Treg (FOXP3) cells were observed between the groups when analysing each subset separately. However, in all groups, each of the Th subsets showed expression of additional canonical transcription factors T-bet, GATA-3, RORγt and FOXP3. Furthermore, by in vitro stimulation with anti-CD3/anti-CD28 there was a significant increase of single expressing GATA-3⁺ and co-expressing T-bet⁺GATA-3⁺ cells in the EOS high asthmatics in comparison with control subjects. In addition, T-bet⁻GATA-3⁺RORγt⁺FOXP3⁺ were decreased in comparison to the EOS low asthmatics. Finally, in a group of control subjects we found that the majority of proliferating Th cells (CD4⁺CD25⁺Ki67⁺) expressed three or four transcription factors.

Conclusions

The ability of human Th cells to express several regulatory transcription factors suggests that these cells may display plasticity in vivo.

Local cytokine profiles of patients with cervical intraepithelial and invasive neoplasia

Several studies have suggested that patients with cervical intraepithelial and invasive neoplasia have reduced levels of Th1 cytokines, and increased levels of Th2 cytokines. Thus, the aim of this study was to delineate the immunological profile associated with lesion progression. Biopsies were obtained from 28 patients with low grade cervical intraepithelial lesions (LSILs), 53 patients with high grade cervical intraepithelial lesions (HSILs), 25 patients with invasive cancer (CA), and 20 healthy controls. Levels of IFN-γ, TNF-α, IL-2, IL-4, IL-10, IL-12, TGF-β1 and TGF-β2 were then assayed by RT-PCR and ELISA for each biopsy sample. For LSILs, higher levels of Th1 cytokines were detected, while HSILs were associated with a Th2 cytokine profile. In contrast, CA tissues were associated with the strongest expression of a Treg cytokine profile. In conclusion the most important contribution of these work is identification of the Treg cytokine profile in HPV progression lesions and in combination, these results suggested that tumor progression is dependent on suppression of cellular immunity.

A simple theoretical framework for understanding heterogeneous differentiation of CD4+ T cells

BACKGROUND

CD4+ T cells have several subsets of functional phenotypes, which play critical yet diverse roles in the immune system. Pathogen-driven differentiation of these subsets of cells is often heterogeneous in terms of the induced phenotypic diversity. In vitro recapitulation of heterogeneous differentiation under homogeneous experimental conditions indicates some highly regulated mechanisms by which multiple phenotypes of CD4+ T cells can be generated from a single population of naïve CD4+ T cells. Therefore, conceptual understanding of induced heterogeneous differentiation will shed light on the mechanisms controlling the response of populations of CD4+ T cells under physiological conditions.

RESULTS

We present a simple theoretical framework to show how heterogeneous differentiation in a two-master-regulator paradigm can be governed by a signaling network motif common to all subsets of CD4+ T cells. With this motif, a population of naïve CD4+ T cells can integrate the signals from their environment to generate a functionally diverse population with robust commitment of individual cells. Notably, two positive feedback loops in this network motif govern three bistable switches, which in turn, give rise to three types of heterogeneous differentiated states, depending upon particular combinations of input signals. We provide three prototype models illustrating how to use this framework to explain experimental observations and make specific testable predictions.

CONCLUSIONS

The process in which several types of T helper cells are generated simultaneously to mount complex immune responses upon pathogenic challenges can be highly regulated, and a simple signaling network motif can be responsible for generating all possible types of heterogeneous populations with respect to a pair of master regulators controlling CD4+ T cell differentiation. The framework provides a mathematical basis for understanding the decision-making mechanisms of CD4+ T cells, and it can be helpful for interpreting experimental results. Mathematical models based on the framework make specific testable predictions that may improve our understanding of this differentiation system.

Defining the human T helper 17 cell phenotype

T helper (Th) 17 cells represent a third effector arm of CD4 T cells and complement the function of the Th1 and Th2 cell lineages. Here, we provide an overview of the transcription factors, cytokines, chemokines, and cytokine and chemokine receptors that characterize the Th17 cell phenotype. Data relevant for human Th17 cells are emphasized, with a focus on the function of two markers that have recently been associated with human Th17 cells, CD161 and interleukin-4-induced gene 1 (IL4I1). Also considered is the basis of Th17 cell plasticity towards the Th1 lineage, and we suggest that this plasticity together with the limited expansion of Th17 cells in response to T cell receptor (TCR) triggering accounts for the rarity of human Th17 cells in inflamed tissues.

Stem-cell-like qualities of immune memory; CD4+ T cells join the party

Similar to hematopoietic stem cells, memory lymphocytes self-renew, while their clonally expanded effector progeny differentiate to fight infection and tumors. Recently, Muranski et al. (2011) report in Immunity that a subset of Th17 effector cells function as memory cells and retain stem cell properties.

Definition of IFN-γ-related pathways critical for chemically-induced systemic autoimmunity

IFN-γ is essential for idiopathic and murine mercury-induced systemic autoimmunity (mHgIA), and heterozygous IFN-γ(+/-) mice also exhibit reduced disease. This suggests that blocking specific IFN-γ-related pathways that may only partially inhibit IFN-γ production or function will also suppress autoimmunity. To test this hypothesis, mice deficient in genes regulating IFN-γ expression (Casp1, Nlrp3, Il12a, Il12b, Stat4) or function (Ifngr1, Irf1) were examined for mHgIA susceptibility. Absence of either Ifngr1 or Irf1 resulted in a striking reduction of disease, while deficiency of genes promoting IFN-γ expression had modest to no effect. Furthermore, both Irf1- and Ifng-deficiency only modestly reduced the expansion of CD44(hi) and CD44(hi)CD55(lo) CD4(+) T cells, indicating that they are not absolutely required for T cell activation. Thus, there is substantial redundancy in genes that regulate IFN-γ expression in contrast to those that mediate later signaling events. These findings have implications for the therapeutic targeting of IFN-γ pathways in systemic autoimmunity.

IL-17/IL-17 receptor system in autoimmune disease: mechanisms and therapeutic potential

IL-17 (interleukin-17), a hallmark cytokine of Th17 (T-helper 17) cells, plays critical roles in host defence against bacterial and fungal infections, as well as in the pathogenesis of autoimmune diseases. The present review focuses on current knowledge of the regulation, functional mechanisms and targeting strategies of IL-17 in the context of inflammatory autoimmune diseases. Evidence shows that IL-17 is highly up-regulated at sites of inflammatory tissues of autoimmune diseases and amplifies the inflammation through synergy with other cytokines, such as TNF (tumour necrosis factor) α. Although IL-17 was originally thought to be produced mainly by Th17 cells, a newly defined T-cell subset with a specific differentiation programme and tight regulation, several other cell types (especially innate immune cells) are also found as important sources for IL-17 production. Although IL-17 activates common downstream signalling, including NF-κB (nuclear factor κB), MAPKs (mitogen-activated protein kinases), C/EBPs (CCAAT/enhancer-binding proteins) and mRNA stability, the immediate receptor signalling has been shown to be quite unique and tightly regulated. Mouse genetic studies have demonstrated a critical role for IL-17 in the pathogenesis of variety of inflammatory autoimmune diseases, such as RA (rheumatoid arthritis) and MS (multiple sclerosis). Importantly, promising results have been shown in initial clinical trials of monoclonal antibodies against IL-17 or its receptor (IL-17R) to block IL-17-mediated function in treating autoimmune patients with psoriasis, RA and MS. Therefore targeting IL-17/IL-17R, IL-17-producing pathways or IL-17-mediated signalling pathways can be considered for future therapy in autoimmune diseases.

Deficiency of lymphotoxin-α does not exacerbate high-fat diet-induced obesity but does enhance inflammation in mice

Lymphotoxin-α (LTα) is secreted by lymphocytes and acts through tumor necrosis factor-α receptors and the LTβ receptor. Our goals were to determine whether LT has a role in obesity and investigate whether LT contributes to the link between obesity and adipose tissue lymphocyte accumulation. LT deficient (LT(-/-)) and wild-type (WT) mice were fed standard pelleted rodent chow or a high-fat/high-sucrose diet (HFHS) for 13 wk. Body weight, body composition, and food intake were measured. Glucose tolerance was assessed. Systemic and adipose tissue inflammatory statuses were evaluated by quantifying plasma adipokine levels and tissue macrophage and T cell-specific gene expression in abdominal fat. LT(-/-) mice were smaller (20%) and leaner (25%) than WT controls after 13 wk of HFHS diet feeding. LT(-/-) mice showed improved glucose tolerance, suggesting that, in WT mice, LT may impair glucose metabolism. Surprisingly, adipose tissue from rodent chow- and HFHS-fed LT(-/-) mice exhibited increased T lymphocyte and macrophage infiltration compared with WT mice. Despite the fact that LT(-/-) mice exhibited an enhanced inflammatory status at the systemic and tissue level even when fed rodent chow, they were protected from enhanced diet-induced obesity and insulin resistance. Thus, LT contributes to body weight and adiposity and is required to modulate the accumulation of immune cells in adipose tissue.

Synchronization of dendritic cell activation and antigen exposure is required for the induction of Th1/Th17 responses

The dendritic cell (DC) targeting/activation patterns required to elicit Th1/Th17 responses remain undefined. One postulated requirement was that of a physical linkage between Ags and immunomodulators. Accordingly, the separate same-site administration of Ag85B-ESAT-6 (hybrid-1 protein; H1), a mycobacterial fusion Ag, and the CAF01 liposome-based adjuvant induced similar Ab and weak Th2 responses as those of coformulated H1/CAF01 but failed to elicit Th1/Th17 responses. Yet, this separate same-site injection generated the same type and number of activated Ag(+)/adjuvant(+) DCs in the draining lymph nodes (LN) as that of protective H1/CAF01 immunization. Thus, targeting/activating the same DC population by Ag and adjuvant is not sufficient to elicit Th1/Th17 responses. To identify the determinants of Th1/Th17 adjuvanticity, in vivo tracking experiments using fluorescently labeled Ag and adjuvant identified that a separate same-site administration elicits an additional early Ag(+)/adjuvant(-) DC population with a nonactivated phenotype, resulting from the earlier targeting of LN DCs by H1 than by CAF01 molecules. This asynchronous targeting pattern was mimicked by the injection of free H1 prior to or with, but not after, H1/CAF01 or H1/CpG/ aluminum hydroxide immunization. The injection of soluble OVA similarly prevented the induction of Th1 responses by OVA/CAF01. Using adoptively transferred OT-2 cells, we show that the Ag targeting of LN DCs prior to their activation generates nonactivated Ag-pulsed DCs that recruit Ag-specific T cells, trigger their initial proliferation, but interfere with Th1 induction in a dose-dependent manner. Thus, the synchronization of DC targeting and activation is a critical determinant for Th1/Th17 adjuvanticity.

Genome-scale profiling reveals a subset of genes regulated by DNA methylation that program somatic T-cell phenotypes in humans

The aim of this study was to investigate the dynamics and relationship between DNA methylation and gene expression during early T-cell development. Mononuclear cells were collected at birth and at 12 months from 60 infants and were either activated with anti-CD3 for 24 h or cultured in media alone, and the CD4+ T-cell subset purified. DNA and RNA were co-harvested and DNA methylation was measured in 450 000 CpG sites in parallel with expression measurements taken from 25 000 genes. In unstimulated cells, we found that a subset of 1188 differentially methylated loci were associated with a change in expression in 599 genes (adjusted P value<0.01, β-fold >0.1). These genes were enriched in reprogramming regions of the genome known to control pluripotency. In contrast, over 630 genes were induced following low-level T-cell activation, but this was not associated with any significant change in DNA methylation. We conclude that DNA methylation is dynamic during early T-cell development, and has a role in the consolidation of T-cell-specific gene expression. During the early phase of clonal expansion, DNA methylation is stable and therefore appears to be of limited importance in short-term T-cell responsiveness.

Duel of the fates: the role of transcriptional circuits and noise in CD4+ cells

CD4+ T cells play key roles in orchestrating adaptive immune responses, and are a popular model for mammalian cell differentiation. While immune regulation would seem to require exactly adjusted mRNA and protein expression levels of key factors, there is little evidence that this is strictly the case. Stochastic gene expression and plasticity of cell types contrast the apparent need for precision. Recent work has provided insight into the magnitude of molecular noise, as well as the relationship between noise, transcriptional circuits and epigenetic modifications in a variety of cell types. These processes and their interplay will also govern gene expression patterns in the different CD4+ cell types, and the determination of their cellular fates.

Active Hexose Correlated Compound promotes T helper (Th) 17 and 1 cell responses via inducing IL-1β production from monocytes in humans

The differentiation of T helper (Th) cells is critically dependent on cytokine milieu. The innate immune monocytes produce IL-1β which can affect the development of Th17 and Th1 cells that predominantly produce IL-17 and IFN-γ, respectively. Oligosaccharides from microorganisms, crops and mushrooms can stimulate innate immune cells. Active Hexose Correlated Compound (AHCC) that contains a large amount of oligosaccharides is a natural extract prepared from the mycelium of the edible Basidiomycete fungus. This compound is reported to modulate immune responses against pathogens although the mechanisms for this effect are largely unknown. Here we show that AHCC could induce high levels of IL-1β production from human monocytes. Furthermore, AHCC-treated monocytes increased the production of IL-17 and IFN-γ from autologous CD4(+) T cells, which was blocked by adding IL-1 receptor antagonist. These finding provide new insight into how food supplements like AHCC could enhance human immunity by modulating monocytes and Th cells.

Regulation of CD4+ T-cell polarization by suppressor of cytokine signalling proteins

Suppressors of cytokine signalling (SOCS) proteins are induced in responses to many stimuli and by binding to cytokine receptors and associated janus kinase (JAK) proteins, directly regulate the activation of the signal transducers and activators of transcription (STATs). STAT proteins regulate the expression of many genes required for the differentiation of various CD4(+) T helper cell lineages, and there is now accumulating evidence that SOCS also play essential roles in the regulation and maintenance of CD4(+) T-cell polarization. As it is now clear that CD4(+) T cells are more plastic than initially thought, it is of particular importance to understand the molecular mechanisms regulating CD4(+) T-cell differentiation. Here we review the current understanding of how STATs and SOCS act in concert to influence the polarization of CD4(+) T cells and highlight the relevance of this in disease.

Type17 T-cells in central nervous system autoimmunity and tumors

Interleukin-17 (IL-17) producing Type17 T-cells, specifically T-helper (Th)17 cells reactive to central nervous system (CNS) autoantigens, manifest a higher migratory capability to the CNS parenchyma compared with other T-cell subpopulations due to their ability to penetrate the blood brain barrier (BBB). In the field of cancer immunotherapy, there are now a number of cell therapy approaches including early studies using T-cells transduced with chimeric antigen receptors in hematologic malignancy, suggesting that the use of T-cells or genetically modified T-cells could have a significant role in effective cancer therapy. However, the successful application of this strategy in solid tumors, such as CNS tumors, requires careful consideration of critical factors to improve the tumor-homing of T-cells. The current review is dedicated to discuss recent findings on the role of Type17 T-cells in CNS autoimmunity and cancer. The insight gained from these findings may lead to the development of novel therapeutic and prophylactic strategies for CNS autoimmunity and tumors.

The molecular basis of the memory T cell response: differential gene expression and its epigenetic regulation

How the immune system remembers a previous encounter with a pathogen and responds more efficiently to a subsequent encounter has been one of the central enigmas for immunologists for over a century. The identification of pathogen-specific memory lymphocytes that arise after an infection provided a cellular basis for immunological memory. But the molecular mechanisms of immunological memory remain only partially understood. The emerging evidence suggests that epigenetic changes have a key role in controlling the distinct transcriptional profiles of memory lymphocytes and thus in shaping their function. In this Review, we summarize the recent progress that has been made in assessing the differential gene expression and chromatin modifications in memory CD4(+) and CD8(+) T cells, and we present our current understanding of the molecular basis of memory T cell function.

Bcl6 and Maf cooperate to instruct human follicular helper CD4 T cell differentiation

Follicular helper CD4 T (Tfh) cells provide B cells with signals that are important for the generation of high-affinity Abs and immunological memory and, therefore, are critical for the protective immunity elicited by most human vaccines. Transcriptional regulators of human Tfh cell differentiation are poorly understood. In this article, we demonstrate that Bcl6 controls specific gene modules for human Tfh cell differentiation. The introduction of Bcl6 expression in primary human CD4 T cells resulted in the regulation of a core set of migration genes that enable trafficking to germinal centers: CXCR4, CXCR5, CCR7, and EBI2. Bcl6 expression also induced a module of protein expression critical for T-B interactions, including SAP, CD40L, PD-1, ICOS, and CXCL13. This constitutes direct evidence for Bcl6 control of most of these functions and includes three genes known to be loci of severe human genetic immunodeficiencies (CD40L, SH2D1A, and ICOS). Introduction of Bcl6 did not alter the expression of IL-21 or IL-4, the primary cytokines of human Tfh cells. We show in this article that introduction of Maf (c-Maf) does induce the capacity to express IL-21. Surprisingly, Maf also induced CXCR5 expression. Coexpression of Bcl6 and Maf revealed that Bcl6 and Maf cooperate in the induction of CXCR4, PD-1, and ICOS. Altogether, these findings reveal that Bcl6 and Maf collaborate to orchestrate a suite of genes that define core characteristics of human Tfh cell biology.

Signal transducer and activator of transcription-3/suppressor of cytokine signaling-3 (STAT3/SOCS3) axis in myeloid cells regulates neuroinflammation

Suppressor of cytokine signaling (SOCS) proteins are feedback inhibitors of the JAK/STAT pathway. SOCS3 has a crucial role in inhibiting STAT3 activation, cytokine signaling, and inflammatory gene expression in macrophages/microglia. To determine the role of SOCS3 in myeloid cells in neuroinflammation, mice with conditional SOCS3 deletion in myeloid cells (LysMCre-SOCS3(fl/fl)) were tested for experimental autoimmune encephalomyelitis (EAE). The myeloid-specific SOCS3-deficient mice are vulnerable to myelin oligodendrocyte glycoprotein (MOG)-induced EAE, with a severe, nonresolving atypical form of disease. In vivo, enhanced infiltration of inflammatory cells and demyelination is prominent in the cerebellum of myeloid-specific SOCS3-deficient mice, as is enhanced STAT3 signaling and expression of inflammatory cytokines/chemokines and an immune response dominated by Th1 and Th17 cells. In vitro, SOCS3-deficient macrophages exhibit heightened STAT3 activation and are polarized toward the classical M1 phenotype. SOCS3-deficient M1 macrophages provide the microenvironment to polarize Th1 and Th17 cells and induce neuronal death. Furthermore, adoptive transfer of M2 macrophages into myeloid SOCS3-deficient mice leads to delayed onset and reduced severity of atypical EAE by decreasing STAT3 activation, Th1/Th17 cells, and proinflammatory mediators in the cerebellum. These findings indicate that myeloid cell SOCS3 provides protection from EAE through deactivation of neuroinflammatory responses.

Molecular mechanisms that control the expression and activity of Bcl-6 in TH1 cells to regulate flexibility with a TFH-like gene profile

The transcription factors T-bet and Bcl-6 are required for the establishment of a T helper type 1 cell (T(H)1 cell) and follicular helper T cell (T(FH) cell) gene-expression profile, respectively. Here we found that high concentrations of interleukin 2 (IL-2) inhibited Bcl-6 expression in polarized T(H)1 cells. Mechanistically, the low concentrations of Bcl-6 normally found in effector T(H)1 cells did not repress its target genes because a T-bet-Bcl-6 complex masked the Bcl-6 DNA-binding domain. T(H)1 cells increased their Bcl-6/T-bet ratio in response to limiting IL-2 conditions, which allowed excess Bcl-6 to repress its direct target Prdm1 (which encodes the transcriptional repressor Blimp-1). The Bcl-6-dependent repression of Blimp-1 effectively induced a partial T(FH) profile because Blimp-1 directly repressed a subset of T(FH) signature genes, including Cxcr5. Thus, IL-2-signaling regulates the Bcl-6-Blimp-1 axis in T(H)1 cells to maintain flexibility with a T(FH) cell-like gene profile.

A key role for NF-κB transcription factor c-Rel in T-lymphocyte-differentiation and effector functions

The transcription factors of the Rel/NF-κB family function as key regulators of innate and adoptive immunity. Tightly and temporally controlled activation of NF-κB-signalling pathways ensures prevention of harmful immune cell dysregulation, whereas a loss of control leads to pathological conditions such as severe inflammation, autoimmune disease, and inflammation-associated oncogenesis. Five family members have been identified in mammals: RelA (p65), c-Rel, RelB, and the precursor proteins NF-κB1 (p105) and NF-κB2 (p100), that are processed into p50 and p52, respectively. While RelA-containing dimers are present in most cell types, c-Rel complexes are predominately found in cells of hematopoietic origin. In T-cell lymphocytes, certain genes essential for immune function such as Il2 and Foxp3 are directly regulated by c-Rel. Additionally, c-Rel-dependent IL-12 and IL-23 transcription by macrophages and dendritic cells is crucial for T-cell differentiation and effector functions. Accordingly, c-Rel expression in T cells and antigen-presenting cells (APCs) controls a delicate balance between tolerance and immunity. This review gives a selective overview on recent progress in understanding of diverse roles of c-Rel in regulating adaptive immunity.

Therapeutic targeting of the IL-12/23 pathways: generation and characterization of ustekinumab

Preclinical and clinical studies conducted in the mid-1990s reported strong association and causality between the T-cell helper (T(H)) 1 inductor cytokine interleukin (IL)-12 and numerous immune-mediated disorders, which spurred the development of therapeutic agents targeting IL-12 function. One of the first to enter the clinic, ustekinumab, is a human monoclonal antibody (mAb) that binds to the p40 subunit of IL-12. Subsequent to the generation of ustekinumab, it was discovered that IL-23 also contains the p40 subunit. Thus, although ustekinumab was designed to target IL-12, it also modulates IL-23, a cytokine important to the development and/or maintenance of T(H)17 cells. Clinical observations established that IL-12/23p40 is integral to the pathologies of psoriasis, psoriatic arthritis and Crohn's disease. The molecular and cellular evaluations conducted in ustekinumab clinical programs have provided numerous insights into the pathologic processes of these disorders, illustrating how a novel molecular entity can contribute to our understanding of disease. The individual contributions of these cytokines to specific pathologies require investigation and clinical evaluation of the role of IL-12- and IL-23-specific inhibitors.

T-cell biology in aging, with a focus on lung disease

T cells are essential for defending hosts against microorganisms and malignancy as well as for regulating the development of immune-mediated inflammatory diseases like autoimmunity. Alterations in T-cell immunity occur with aging, affecting the function and proportions of T-cell subsets. Probably, the most noticeable age-associated change in T-cell immunity is an alteration in the frequency of naive and memory CD4+ and CD8+ T cells. In fact, the frequency of naive CD4+ and CD8+ T cells decreases with aging, whereas the frequency of memory CD4+ and CD8+ T cells increases. Also, changes in T-cell proliferation, cytokine production, memory response, and cytotoxicity as well as in regulatory T-cell number and function have been reported with aging. Such alterations could contribute to the development of infections, malignancies, and inflammatory diseases that rise with aging. Of interest, T cells are closely involved in the development of inflammatory airway and lung diseases including asthma and chronic obstructive pulmonary disease, which are prevalent in the elderly people. In addition, T cells play a major role in defending host against influenza virus infection, a serious medical problem with high morbidity and mortality in the elderly people. Thus, it is conceivable that altered T-cell immunity may account in part for the development of such respiratory problems with aging. Here, we will review the recent advances in T-cell immunity and its alteration with aging and discuss the potential effects of such changes on the lung.