IL-9 induces differentiation of TH17 cells and enhances function of FoxP3+ natural regulatory T cells

The development of T helper (T_H)17 and regulatory T (T_reg) cells is reciprocally regulated by cytokines. Transforming growth factor (TGF)-β alone induces FoxP3⁺ T_reg cells, but together with IL-6 or IL-21 induces T_H17 cells. Here we demonstrate that IL-9 is a key molecule that affects differentiation of T_H17 cells and T_reg function. IL-9 predominantly produced by T_H17 cells, synergizes with TGF-β1 to differentiate naïve CD4⁺ T cells into T_H17 cells, while IL-9 secretion by T_H17 cells is regulated by IL-23. Interestingly, IL-9 enhances the suppressive functions of FoxP3⁺ CD4⁺ T_reg cells in vitro, and absence of IL-9 signaling weakens the suppressive activity of nT_regs in vivo, leading to an increase in effector cells and worsening of experimental autoimmune encephalomyelitis. The mechanism of IL-9 effects on T_H17 and T_regs is through activation of STAT3 and STAT5 signaling. Our findings highlight a role of IL-9 as a regulator of pathogenic versus protective mechanisms of immune responses.     

A critical role for IL-21 receptor signaling in the pathogenesis of systemic lupus erythematosus in BXSB-Yaa mice

Interleukin 21 (IL-21) is a pleiotropic cytokine produced by CD4 T cells that affects the differentiation and function of T, B, and NK cells by binding to a receptor consisting of the common cytokine receptor γ chain and the IL-21 receptor (IL-21R). IL-21, a product associated with IL-17-producing CD4 T cells (T_H17) and follicular CD4 T helper cells (T_FH), has been implicated in autoimmune disorders including the severe systemic lupus erythematosus (SLE)-like disease characteristic of BXSB-Yaa mice. To determine whether IL-21 plays a significant role in this disease, we compared IL-21R-deficient and -competent BXSB-Yaa mice for multiple parameters of SLE. The deficient mice showed none of the abnormalities characteristic of SLE in IL-21R-competent Yaa mice, including hypergammaglobulinemia, autoantibody production, reduced frequencies of marginal zone B cells and monocytosis, renal disease, and premature morbidity. IL-21 production associated with this autoimmune disease was not a product of T_H17 cells and was not limited to conventional CXCR5⁺ T_FH but instead was produced broadly by ICOS⁺ CD4⁺ splenic T cells. IL-21 arising from an abnormal population of CD4 T cells is thus central to the development of this lethal disease, and, more generally, could play an important role in human SLE and related autoimmune disorders.     

Characterization of the HCMV-Specific CD4 T Cell Responses that Are Associated with Protective Immunity

Most humans become infected with human cytomegalovirus (HCMV). Typically, the immune system controls the infection, but the virus persists and can reactivate in states of immunodeficiency. While substantial information is available on the contribution of CD8 T cells and antibodies to anti-HCMV immunity, studies of the T_H1, T_H2, and T_H17 subsets have been limited by the low frequency of HCMV-specific CD4 T cells in peripheral blood mononuclear cell (PBMC). Using the enzyme-linked Immunospot^® assay (ELISPOT) that excels in low frequency measurements, we have established these in a sizable cohort of healthy HCMV controllers. Cytokine recall responses were seen in all seropositive donors. Specifically, interferon (IFN)-γ and/or interleukin (IL)-17 were seen in isolation or with IL-4 in all test subjects. IL-4 recall did not occur in isolation. While the ratios of T_H1, T_H2, and T_H17 cells exhibited substantial variations between different individuals these ratios and the frequencies were relatively stable when tested in samples drawn up to five years apart. IFN-γ and IL-2 co-expressing polyfunctional cells were seen in most subjects. Around half of the HCMV-specific CD4 cells were in a reversible state of exhaustion. The data provided here established the T_H1, T_H2, and T_H17 characteristic of the CD4 cells that convey immune protection for successful immune surveillance against which reactivity can be compared when the immune surveillance of HCMV fails.     

Increased levels of circulating Th17 cells in quiescent versus active Crohn's disease

Background and aimsTh17 cells, a subset of CD4 + T cells that produce interleukin (IL)-17A, IL-17F, IL-21, IL-22, IL-26, and the chemokine CCL20 are critically involved in the mucosal inflammation observed in Crohn's disease (CD). However, their role as mediators of inflammation in CD has been questioned by a recent clinical trial in which anti-IL-17A (secukinumab) treatment was ineffective. Besides being pro-inflammatory, Th17-related cytokines mediate mucosal protective functions. We aimed to investigate the role of Th17 cells in CD inflammation.MethodsBlood samples from 26 patients with active CD and 10 healthy controls (HC) were analyzed for levels of IL-17A-, IL-21- and IL-22-producing CD45RO+CD4 + T cells using multicolor flow cytometry. Samples were analyzed before and during adalimumab treatment to compare intra-individual changes during active and quiescent disease.ResultsCD patients had statistically significantly higher levels of IL-17-A-, IL-21- and IL-22-producing CD45RO+CD4 + T cells in both active and quiescent disease compared with HC. Baseline levels of IL-21 and IL-22 producing CD45RO+CD4 + T cells correlated inversely with mucosal inflammation estimated by fecal calprotectin. Patients who responded to adalimumab treatment demonstrated a 2- to 3-fold increase in levels of IL-17A- and IL-21-producing CD45RO+CD4 + T cells in quiescent disease compared with active disease.ConclusionOur data support the involvement of Th17 cells and IL-21- and IL-22-producing CD45RO+CD4 + T cells in CD. Because patients had higher levels in quiescent disease compared with active CD, we question whether Th17 cells are promoters of inflammation. Instead, Th17 cells may counterbalance inflammation and maintain gut homeostasis.     

Plasma Exchange Downregulates Activated Monocytes and Restores Regulatory T Cells in Kawasaki Disease

In Kawasaki disease (KD), the effect of plasma exchange (PE) on immune cells has not been fully elucidated. Therefore, we examined the changes in the number of CD14⁺ CD16⁺ activated monocytes, regulatory T (T_reg), and T‐helper type 17 (Th17) cells in KD patients treated with PE. The percentage of total monocytes and subclasses of lymphocytes, including CD4⁺ and CD8⁺ T cells, and CD19⁺ B cells, showed no significant difference before and after PE. However, the percentage of CD14⁺ CD16⁺ monocytes in total leukocytes decreased significantly after PE (1.1% ± 1.5% vs. 2.1% ± 2.3%, P < 0.05). Furthermore, while the percentage of Th17 cells in CD4⁺ T cells did not change, the percentage of T_reg cells in CD4⁺ T cells increased significantly after PE (11.1% ± 5.1% vs. 8.0% ± 4.4%, P < 0.05). Therefore, PE downregulates activated monocytes and upregulates T_reg cells toward normal levels and thus attenuates inflammation in KD.     

Physiopathologie de la maladie de Behçet

Although the precise pathogenesis and etiology of Behçet's disease (BD) still remains unknown, current evidence suggests that inflammatory reaction in BD arises from disruption of homeostasis in genetically susceptible individuals, resulting in altered innate and adaptive immunity responses, pathogenic T cell activation in the peripheral blood, and in inflammatory sites. Association with HLA-B51 is known as the strongest genetic susceptibility factor for BD. Recent GWAS (genome-wide association studies) have confirmed this relationship, and reported new susceptibility genes (IL-10, IL-23R, IL-12RB2) for the disease. A triggering infectious agent could operate through molecular mimicry, and the disease could subsequently be perpetuated by an abnormal immune response to an auto-antigen in the absence of ongoing infection. Several potential bacteria have been investigated but the most commonly implicated microorganism is Streptococcus sanguis. Recent data have showed that the T cell homeostasis perturbation consisted mainly of Th1 and Th17 expansions, while regulatory T cell response was suppressed. Cytokine such as IL-17, IL-23 and IL-21 play a significant role in the pathogenesis of BD. Inflammatory cells within BD inflammatory lesions include mostly neutrophils, CD4⁺ T cells, and cytotoxic cells. Lastly, endothelium dysfunction has been clearly established. This improved understanding of the pathophysiology of BD will certainly lead to the development of new therapeutic agents, potentially more effective than current therapy. In this review, we have studied the etiopathogenesis of BD in the light of recent advances.     

Dendritic cell SIRT1–HIF1α axis programs the differentiation of CD4+ T cells through IL-12 and TGF-β1

The differentiation of naive CD4⁺ T cells into distinct lineages plays critical roles in mediating adaptive immunity or maintaining immune tolerance. In addition to being a first line of defense, the innate immune system also actively instructs adaptive immunity through antigen presentation and immunoregulatory cytokine production. Here we found that sirtuin 1 (SIRT1), a type III histone deacetylase, plays an essential role in mediating proinflammatory signaling in dendritic cells (DCs), consequentially modulating the balance of proinflammatory T helper type 1 (T_H1) cells and antiinflammatory Foxp3⁺ regulatory T cells (T_reg cells). Genetic deletion of SIRT1 in DCs restrained the generation of T_reg cells while driving T_H1 development, resulting in an enhanced T-cell–mediated inflammation against microbial responses. Beyond this finding, SIRT1 signaled through a hypoxia-inducible factor-1 alpha (HIF1α)-dependent pathway, orchestrating the reciprocal T_H1 and T_reg lineage commitment through DC-derived IL-12 and TGF-β1. Our studies implicates a DC-based SIRT1–HIF1α metabolic checkpoint in controlling T-cell lineage specification.CD4⁺ T cells are essential components of the adaptive immune system that regulate immune responses against foreign antigen. Upon antigen recognition, naive CD4⁺ T cells undergo activation and expansion, and, depending on inflammatory contexts and cytokine milieus, differentiate into functional and phenotypic T helper (T_H) subsets characterized by distinct cytokine production profile and function (1–3). T_H1 cells produce IFN-γ and elicit cellular immunity in responding to intracellular pathogens; T_H2 cells produce IL-4 and IL-5 and promote humoral immunity in responding to extracellular bacteria and helminthes; and T_H17 cells produce IL-17 and mediate antifungal defense and inflammation (4, 5). Additionally, regulatory T cells, often known as “induced regulatory T cells” (iT_reg cells), which act in synergy with naturally occurring T_reg cells (nT_reg cells), produce IL-10 and TGF-β1 and dampen immune responses elicited from T_H1, T_H2, and T_H17 (6–9).Dendritic cells (DCs), an essential component in the innate immune system, play a critical role in initiating front-line primary immune responses and directing subsequent pathogen-specific adaptive immune responses (2). In addition to presenting antigens and modulating cell surface costimulatory molecules, DC-derived cytokines and chemokines can result in either a proinflammatory or antiinflammatory environment, engaging distinct T-cell differentiation programs on naive CD4⁺ T cells (1, 10–16). For example, DC-producing IL-12 can support T_H1 development, whereas DC-producing IL-10 or TGF-β1 can support T_reg development. Recent studies from us and others have shown that innate signaling in DCs mediated by G protein-coupled receptor S1P1, the mitogen-activated kinases (MAPKs), and Wnt–β-catenin plays important roles in stimulating adaptive immune responses through directing native CD4⁺ T-cell differentiation (17–20). However, other critical signaling components in DCs that may play a role in shaping T-cell lineage engagement remain to be identified.SIRT1 is a mammalian homolog of the yeast NAD⁺-dependent protein deacetylase Sirt2, and plays a role in a variety of essential biological processes, including cell cycle progression, apoptosis, cell survival, gene silencing, heterochromatin formation, tumorigenesis, metabolism, and development (21, 22). SIRT1 has also been implicated in regulating immune responses. In T cells, SIRT1 is required to maintain T-cell tolerance (23, 24) and also play a role in inhibiting the function of T_reg cells in allograft survival (25). In myeloid cells, SIRT1 limits the inflammatory process by inhibiting the expression of proinflammatory cytokines (26, 27), while promoting DC maturation and T_H2 response in airway allergy (28). However, whether SIRT1 is involved in bridging the innate immune signal to adaptive immune response remains unexplored.Here, we found that SIRT1 plays a critical role in determining the T-cell lineage fate by directing DC-derived cytokine production, which links innate and adaptive immune modulation. Largely through a HIF1α–dependent signaling pathway, SIRT1 is required for the reciprocal production of IL-12 and TGF-β1 production in DCs as well as the expression of IL-12Rβ2 and TGF-βR2 in responding T cells, resulting in a differential lineage engagement of T_H1 and iT_reg in the microbial-induced inflammation.     

Adjuvants et formulations de l’immunothérapie spécifique par voie sublinguale

Sublingual immunotherapy (SLIT) is a non-invasive and efficacious treatment for type I respiratory allergies. To identify candidate adjuvants and galenic formulations capable of inducing tolerance by the sublingual route, an initial screening was carried out using in vitro cocultures of human monocyte-derived dendritic cells and naïve CD4⁺ T cells. Selected molecules were subsequently tested in a murine asthma model of sublingual immunotherapy in BALB/c mice sensitized to ovalbumin. In this model, we evaluated bronchial hyperreactivity (measured by whole-body plethysmography), pulmonary inflammation (evaluated histologically), and type 2 humoral and cellular immune responses monitored by Elisa and Elispot techniques in mice sensitized with either soluble or with adjuvant-formulated ovalbumin. Four categories of adjuvant known to increase IL-10 +/− IFNγ production by naïve CD4⁺ T cells (Treg/Th1) were found to enhance SLIT efficacy in vivo in these mice. These adjuvants were: vitamin D3/dexamethasone, Lactobacillus plantarum, the TLR2 agonist Pam3CSK4, and the TLR4 synthetic ligand OM-294-BA-MP. In addition, sublingual administration of ovalbumin combined with mucoadhesive maize-derived maltodextrin increased sublingual tolerance induction by targeting oral dendritic cells and ovalbumin-specific T cells in cervical and submaxillary lymph nodes. In conclusion, better understanding of specific immune responses to allergen at the level of the sublingual mucosa may lead to the development of new sublingual vaccines. In the future, such vaccines would incorporate Th1/Treg adjuvants, as well as mucoadhesive galenic formulations that target dendritic cells in the sublingual mucosa.     

In differentiated CD4+ T Cells, interleukin 4 production is cytokine-autonomous, whereas interferon γ production is cytokine-dependent

CD4⁺ T cells from T cell receptor transgenic mice that have been vigorously primed to be interleukin (IL)-4 producers (T_H2 cells) are capable of producing IL-4 even if restimulated in the absence of IL-4 and in the presence of IL-12. T cells vigorously primed in the absence of IL-4 (T_H1 cells) fail to produce IL-4 even if restimulated under conditions that would cause a naive T cell to produce IL-4. In contrast, interferon γ (IFN-γ) production is highly cytokine-regulated. T cells primed in the presence of IL-4 develop into IFN-γ producers if IFN-γ is included in the priming culture and if the cells are challenged in the presence of IL-12, presumably reflecting the role of IFN-γ in inducing responsiveness to IL-12. Cells primed in the absence of IL-4 become highly responsive to IL-12 if IFN-γ is included in the priming culture, and these cells are excellent IFN-γ producers upon challenge; IL-12 considerably enhances their production of IFN-γ. If cells are primed in the absence of IL-4 and IFN-γ, they show very weak responsiveness to IL-12 as determined by STAT-4 activation. However, these cells acquire IL-12 responsiveness if cultured with IFN-γ for a period as short as 4 hr. Thereafter, they produce large amounts of IFN-γ upon challenge with antigen in the presence of IL-12. These results indicate that in primed CD4⁺ T cells, IL-4 production is largely cytokine-autonomous, whereas IFN-γ production is highly cytokine-regulated.     

A commensal symbiotic factor derived from Bacteroides fragilis promotes human CD39+Foxp3+ T cells and Treg function

Polysaccharide A (PSA) derived from the human commensal Bacteroides fragilis is a symbiosis factor that stimulates immunologic development within mammalian hosts. PSA rebalances skewed systemic T helper responses and promotes T regulatory cells (T_regs). However, PSA-mediated induction of Foxp3 in humans has not been reported. In mice, PSA-generated Foxp3⁺ T_regs dampen Th17 activity thereby facilitating bacterial intestinal colonization while the increased presence and function of these regulatory cells may guard against pathological organ-specific inflammation in hosts. We herein demonstrate that PSA induces expression of Foxp3 along with CD39 among naïve CD4 T cells in vitro while promoting IL-10 secretion. PSA-activated dendritic cells are essential for the mediation of this regulatory response. When cultured with isolated Foxp3⁺ T_regs, PSA enriched Foxp3 expression, enhanced the frequency of CD39⁺HLA-DR⁺ cells, and increased suppressive function as measured by decreased TNFα expression by LPS-stimulated monocytes. Our findings are the first to demonstrate in vitro induction of human CD4⁺Foxp3⁺ T cells and enhanced suppressive function of circulating Foxp3⁺ T_regs by a human commensal bacterial symbiotic factor. Use of PSA for the treatment of human autoimmune diseases, in particular multiple sclerosis and inflammatory bowel disease, may represent a new paradigm in the approach to treating autoimmune disease.     

Lymphocytes T CD8+ : implications dans l’asthme

CD8⁺ T lymphocytes include several T cell populations with various functional properties: CD8⁺αβ T cells that produce cytokines (Tc1, Tc2), cytotoxic T cells, CD8⁺ NKT cells, and CD8⁺γδ. Their role in asthma has been assessed in a limited number of studies which are reviewed here. Evidence from animal models indicates that conventional CD8⁺αβ T cells are protective or enhance the immunoallergic immune response. While Tc2 is always an amplifier in immune reactions, the role of Tc1 is still controversial. Cytotoxic T cells, producing perforin and expressing CX3CR1⁺, are found in excess in asthma, notably during exacerbations. Bronchial infiltration by CD8⁺ T cells is associated with reduced FEV₁ in both asthma and COPD; it is also correlated with asthma mortality. During exacerbations, viruses, allergens, and/or pollutants induce CD8⁺ lymphocytes that are able to increase asthmatic inflammation, probably non-specifically, via the involvement of these bystander CD8⁺ cells. The role of the nonconventional CD8⁺γδ T cells, intermediate between innate and adaptive immunity, is likewise controversial and depends on the models studied. They recognize nonpeptidic antigens and are said to be involved in occupational asthma caused by low molecular weight agents. In conclusion, all the CD8⁺ T cell populations are implicated in asthmatic inflammation. They are involved in exacerbations of asthma and its severity. As their activation is less sensitive to corticosteroids than CD4⁺ T cells, targeting CD8⁺ T cells appears to be an important therapeutic target in severe corticosteroid-dependent asthma.     

Control of type 1 diabetes by CD4+Foxp3+ regulatory T cells: lessons from mouse models and implications for human disease

In recent years, there has been a revival of the concept of CD4⁺ regulatory T (T_reg) cells as being a central control point in various immune responses, including autoimmune responses and immunity to transplants, allergens, tumours and infectious microbes. The current literature suggests that T_reg cells are diverse in their phenotype and mechanism(s) of action, and as such, may constitute a myriad of naturally occurring and induced T cell precursors with variable degrees of regulatory potential. In this review, we summarize research from various laboratories, including our own, showing that CD4⁺Foxp3⁺ T_reg cells are critical in the control of type 1 diabetes (T1D) in mouse models and humans. In this review, we also discuss cellular and molecular determinants that impact CD4⁺Foxp3⁺ T_reg cell development and function and consequential resistance to organ‐specific autoimmune disease. Recent advances in the use of CD4⁺Foxp3⁺ T_reg cellular therapy to promote immunological tolerance in the absence of long‐term generalized immunosuppression are also presented. Copyright © 2009 John Wiley & Sons, Ltd.     

Persistent effects of early infant diet and associated microbiota on the juvenile immune system

Early infant diet has significant impacts on the gut microbiota and developing immune system. We previously showed that breast-fed and formula-fed rhesus macaques develop significantly different gut microbial communities, which in turn are associated with different immune systems in infancy. Breast-fed animals manifested greater T cell activation and proliferation and harbored robust pools of T helper 17 (T_H17) cells. These differences were sustained throughout the first year of life. Here we examine groups of juvenile macaques (approximately 3 to 5 y old), which were breast-fed or formula-fed in infancy. We demonstrate that juveniles breast-fed in infancy maintain immunologic differences into the fifth year of life, principally in CD8⁺ memory T cell activation. Additionally, long-term correlation networks show that breast-fed animals maintain persistent relationships between immune subsets that are not seen in formula-fed animals. These findings demonstrate that infant feeding practices have continued influence on immunity for up to 3 to 5 y after birth and also reveal mechanisms for microbial modulation of the immune system.