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Foxp3-expressing regulatory T (Treg) cells represent the most highly immunosuppressive cell in the tumor microenvironment (TME) that halts effective anti-tumor immunity. Osteopontin (Opn), an extracellular matrix (ECM) glycophosphoprotein, plays key roles in many types of immune-related diseases and is associated with cancer aggressiveness when expressed by tumor cells. However, its role in Foxp3Treg heterogeneity, function, and stability in the TME is poorly defined. We generated mice with a Foxp3-specific deletion of Opn and assessed the ability of Opn-deficient Tregs to suppress inflammation. As these mice aged, they developed a scurfy-like syndrome characterized by aberrant and excessive activation of effector T cells. We evaluated and further confirmed the reduced suppressive capacity of Opn-deficient Tregs in an in vivo suppression assay of colitis. We also found that mice with Opn-deficient Foxp3 + Tregs have enhanced anti-tumor immunity and reduced tumor burden, associated with an unstable Treg phenotype, paralleled by reduced Foxp3 expression in tumor-infiltrating lymphocytes. Finally, we observed reduced Foxp3 and Helios expression in Opn-deficient Tregs compared to wild-type controls after in vitro activation. Our findings indicate that targeting Opn in Tregs reveals vigorous and effective ways of promoting Treg instability and dysfunction in the TME, facilitating anti-tumor immunity.

Type I interferon (IFN) production by plasmacytoid dendritic cells (pDCs) has been mainly studied in the context of Toll-like receptor (TLR) activation. In the current report, we reveal that, in the absence of TLR activation, the integrin-binding SLAYGLR motif of secreted osteopontin (sOpn) induces IFN-β production in murine pDCs. This process is mediated by α4β1 integrin, indicating that integrin triggering may act as a subtle danger signal leading to IFN-β induction. The SLAYGLR-mediated α4 integrin/IFN-β axis is MyD88 independent and operates via a PI3K/mTOR/IRF3 pathway. Consequently, SLAYGLR-treated pDCs produce increased levels of type I IFNs following TLR stimulation. Intratumoral administration of SLAYGLR induces accumulation of IFN-β-expressing pDCs and efficiently suppresses melanoma tumor growth. In this process, pDCs are crucial. Finally, SLAYGLR enhances pDC development from bone marrow progenitors. These findings open new questions on the roles of sOpn and integrin α4 during homeostasis and inflammation. The newly identified integrin/IFN-β axis may be implicated in a wide array of immune responses., (© 2022 Simoes et al.)

In the context of inflammation, osteopontin (Opn) is known to promote effector responses, facilitating a proinflammatory environment; however, its role during antigenic tolerance induction is unknown. Using a mouse model of asthma, we investigated the role of Opn during antigenic tolerance induction and its effects on associated regulatory cellular populations prior to disease initiation. Our experiments demonstrate that Opn drives protective antigenic tolerance by inducing accumulation of IFN-β-producing plasmacytoid dendritic cells, as well as regulatory T cells, in mediastinal lymph nodes. We also show that, in the absence of TLR triggers, recombinant Opn, and particularly its SLAYGLR motif, directly induces IFN-β expression in Ag-primed plasmacytoid dendritic cells, which renders them extra protective against induction of allergic airway disease upon transfer into recipient mice. Lastly, we show that blockade of type I IFNR prevents antigenic tolerance induction against experimental allergic asthma. Overall, we unveil a new role for Opn in setting up a tolerogenic milieu boosting antigenic tolerance induction, thus leading to prevention of allergic airway inflammation. Our results provide insight for the future design of immunotherapies against allergic asthma., (Copyright © 2018 by The American Association of Immunologists, Inc.)

Multiple sclerosis (MS), an autoimmune disease of the CNS, is mediated by autoreactive Th cells. A previous study showed that the neurosteroid dehydroepiandrosterone (DHEA), when administered preclinically, could suppress progression of relapsing-remitting experimental autoimmune encephalomyelitis (EAE). However, the effects of DHEA on human or murine pathogenic immune cells, such as Th17, were unknown. In addition, effects of this neurosteroid on symptomatic disease, as well as the receptors involved, had not been investigated. In this study, we show that DHEA suppressed peripheral responses from patients with MS and reversed established paralysis and CNS inflammation in four different EAE models, including the 2D2 TCR-transgenic mouse model. DHEA directly inhibited human and murine Th17 cells, inducing IL-10-producing regulatory T cells. Administration of DHEA in symptomatic mice induced regulatory CD4(+) T cells that were suppressive in an IL-10-dependent manner. Expression of the estrogen receptor β by CD4(+) T cells was necessary for DHEA-mediated EAE amelioration, as well as for direct downregulation of Th17 responses. TGF-β1 as well as aryl hydrocarbon receptor activation was necessary for the expansion of IL-10-producing T cells by DHEA. Thus, our studies demonstrate that compounds that inhibit pathogenic Th17 responses and expand functional regulatory cells could serve as therapeutic agents for autoimmune diseases, such as MS., (Copyright © 2016 by The American Association of Immunologists, Inc.)

The development of therapies for multiple sclerosis targeting pathogenic T cell responses remains imperative. Previous studies have shown that estrogen receptor (ER) β ligands could inhibit experimental autoimmune encephalomyelitis. However, the effects of ERβ-specific ligands on human or murine pathogenic immune cells, such as Th17, were not investigated. In this article, we show that the synthetic ERβ-specific ligand 4-(2-phenyl-5,7-bis[trifluoromethyl]pyrazolo[1,5-a]pyrimidin-3-yl)phenol (PHTPP) reversed established paralysis and CNS inflammation, characterized by a dramatic suppression of pathogenic Th responses as well as induction of IL-10-producing regulatory CD4(+) T cell subsets in vivo. Moreover, administration of PHTPP in symptomatic mice induced regulatory CD4(+) T cells that were suppressive in vivo. PHTPP-mediated experimental autoimmune encephalomyelitis amelioration was canceled in mice with ERβ-deficient CD4(+) T cells only, indicating that expression of ERβ by these cells is crucial for the observed therapeutic effect. Importantly, synthetic ERβ-specific ligands acting directly on CD4(+) T cells suppressed human and mouse Th17 cells, downregulating Th17 cell signature gene expression and expanding IL-10-producing T cells among them. TGF-β1 and aryl hydrocarbon receptor activation enhanced the ERβ ligand-mediated expansion of IL-10-producing T cells among Th17 cells. In addition, these ERβ-specific ligands promoted the induction and maintenance of Foxp3(+) T regulatory cells, as well as their in vitro suppressive function. Thus, ERβ-specific ligands targeting pathogenic Th17 cells and inducing functional regulatory cells represent a promising subset of therapeutic agents for multiple sclerosis., (Copyright © 2016 by The American Association of Immunologists, Inc.)

T cell Ig and ITIM domain receptor (TIGIT), expressed on T, NK, and regulatory T cells, is known as an inhibitory molecule that limits autoimmunity, antiviral and antitumor immunity. In this report, we demonstrate that TIGIT enhances Th2 immunity. TIGIT expression was upregulated in activated Th2 cells from mice with experimental allergic disease and in Th2 polarization cultures. In addition, its high-affinity ligand CD155 was upregulated in mediastinal lymph node dendritic cells from allergic mice. In an in vitro setting, we observed that Tigit expression in Th2 cells and its interaction with CD155 expressed in dendritic cells were important during the development of Th2 responses. In addition, blockade of TIGIT inhibited Th2, but had no effect on either Th1 or Th17 polarization. In vivo blockade of TIGIT suppressed hallmarks of allergic airway disease, such as lung eosinophilia, goblet cell hyperplasia, Ag-specific Th2 responses, and IgE production, and reduced numbers of T follicular helper and effector Th2 cells. Thus, TIGIT is critical for Th2 immunity and can be used as a therapeutic target, especially in light of recent findings showing TIGIT locus hypomethylation in T cells from pediatric patients with allergic asthma., (Copyright © 2016 by The American Association of Immunologists, Inc.)

Intestinal CD103(-) dendritic cells (DCs) are pathogenic for colitis. Unveiling molecular mechanisms that render these cells proinflammatory is important for the design of specific immunotherapies. In this report, we demonstrated that mesenteric lymph node CD103(-) DCs express, among other proinflammatory cytokines, high levels of osteopontin (Opn) during experimental colitis. Opn expression by CD103(-) DCs was crucial for their immune profile and pathogenicity, including induction of T helper (Th) 1 and Th17 cell responses. Adoptive transfer of Opn-deficient CD103(-) DCs resulted in attenuated colitis in comparison to transfer of WT CD103(-) DCs, whereas transgenic CD103(-) DCs that overexpress Opn were highly pathogenic in vivo. Neutralization of secreted Opn expressed exclusively by CD103(-) DCs restrained disease severity. Also, Opn deficiency resulted in milder disease, whereas systemic neutralization of secreted Opn was therapeutic. We determined a specific domain of the Opn protein responsible for its CD103(-) DC-mediated proinflammatory effect. We demonstrated that disrupting the interaction of this Opn domain with integrin α9, overexpressed on colitic CD103(-) DCs, suppressed the inflammatory potential of these cells in vitro and in vivo. These results add unique insight into the biology of CD103(-) DCs and their function during inflammatory bowel disease.

It is known that non-cachectic patients with chronic obstructive pulmonary disease (COPD) respond well to pulmonary rehabilitation, but whether cachectic COPD patients are capable of adaptive responses is both important and unknown. 10 cachectic and 19 non-cachectic COPD patients undertook high-intensity cycling training, at the same relative intensity, for 45 min x day(-1), 3 days x week(-1) for 10 weeks. Before and after rehabilitation vastus lateralis muscle biopsies were analysed morphologically and for the expression of muscle remodelling factors (insulin-like growth factor (IGF)-I, myogenic differentiation factor D (MyoD), tumour necrosis factor (TNF)-alpha, nuclear factor (NF)-kappaB and myostatin) and key components of ubiquitin-mediated proteolytic systems (muscle ring finger protein (MURF)-1 and Atrogin-1). Rehabilitation improved peak work-rate and the 6-min walk distance similarly in non-cachectic (18+/-3% and 42+/-13 m, respectively) and cachectic (16+/-2% and 53+/-16 m, respectively) patients, but quality of life only improved in non-cachectic COPD. Mean muscle fibre cross-sectional area increased in both groups, but significantly less in cachectic (7+/-2%) than in non-cachectic (11+/-2%) patients. Both groups equally decreased the proportion of type IIb fibres and increased muscle capillary/fibre ratio. IGF-I mRNA expression increased in both groups, but IGF-I protein levels increased more in non-cachectic COPD. MyoD was upregulated, whereas myostatin was downregulated at the mRNA and protein level only in non-cachectic patients. Whilst rehabilitation had no effect on TNF-alpha expression, it decreased the activation of the transcription factor NF-kappaB in both groups by the same amount. Atrogin-1 and MURF-1 expression were increased in cachectic COPD, but it was decreased in non-cachectic patients. Cachectic COPD patients partially retain the capacity for peripheral muscle remodelling in response to rehabilitation and are able to increase exercise capacity as much as those without cachexia, even if they exhibit both quantitative and qualitative differences in the type of muscle fibre remodelling in response to exercise training.

Activin-A is a pleiotropic cytokine that participates in developmental, inflammatory, and tissue repair processes. Still, its effects on T helper (Th) cell-mediated immunity, critical for allergic and autoimmune diseases, are elusive. We provide evidence that endogenously produced activin-A suppresses antigen-specific Th2 responses and protects against airway hyperresponsiveness and allergic airway disease in mice. Importantly, we reveal that activin-A exerts suppressive function through induction of antigen-specific regulatory T cells that suppress Th2 responses in vitro and upon transfer in vivo. In fact, activin-A also suppresses Th1-driven responses, pointing to a broader immunoregulatory function. Blockade of interleukin 10 and transforming growth factor beta1 reverses activin-A-induced suppression. Remarkably, transfer of activin-A-induced antigen-specific regulatory T cells confers protection against allergic airway disease. This beneficial effect is associated with dramatically decreased maturation of draining lymph node dendritic cells. Therapeutic administration of recombinant activin-A during pulmonary allergen challenge suppresses Th2 responses and protects from allergic disease. Finally, we demonstrate that immune cells infiltrating the lungs from individuals with active allergic asthma, and thus nonregulated inflammatory response, exhibit significantly decreased expression of activin-A's responsive elements. Our results uncover activin-A as a novel suppressive factor for Th immunity and a critical controller of allergic airway disease.