Osteopontin Promotes Protective Antigenic Tolerance against Experimental Allergic Airway Disease

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

Activin-A induces regulatory T cells that suppress T helper cell immune responses and protect from allergic airway disease

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 β1 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

Study of the role of cytokine osteopontin in the initiation and development of intestinal inflammation

Inflammatory bowel diseases (IBDs), including Crohn’s disease (CD) and ulcerativecolitis (UC), are caused by excessive inflammatory responses against commensal floraand other antigens present in the intestinal lumen. Alternations in intestinal dendriticcells (DCs) contribute to IBD development on humans and mice with experimentalcolitis (EC). Mesenteric lymph node (MLN) DCs are crucial mediators of colitisinduction and they are separated in two main subsets that differentially express theintegrin αΕ (CD103): CD11chighCD103+ and CD11chighCD103- DCs. Although bothDC subsets are identified in MLNs during acute colitis, which DC subset mediatescolitis initiation remains unknown.A recent study suggested the pro-inflammatory role for the cytokine osteopontin(Opn) in chronic EC. In addition, Opn is highly expressed in intestinal immune andnon-immune mucosal cells, and in the plasma of IBD patients, as well as in colon and plasma of mice with EC. Opn expressed by DCs during autoimmunity contributes tothe cellular mechanisms that mediate autoimmune diseases. Overall, Opn plays a rolein modulating DC phenotype, recruitment and function during several inflammatoryconditions. However, whether the crucial DC subset for colitis expresses Opn and thepossible significance of DC-expressed Opn is unknown.The initial scope of this thesis was aimed in the identification of the critical DC subsetfor acute colitis induction. We found that the MLN CD103- DCs exhibit proinflammatoryrole in acute colitis. We address that apart from other inflammatorycytokines, CD103- DCs expressed very high levels of Opn during colitis. We also found that Opn expression by CD103- DCs is critical for their inflammatoryproperties.By different experimental approaches, this thesis addresses that Opn expression byCD103- DCs could be solely responsible for their pro-inflammatory function. Thus,here we demonstrate for the first time that particularly Opn expression by CD103-DCs is crucial for their pro-inflammatory cytokine secretion. Opn expression boostedthe special capability of CD103- DCs to drive type 1 CD4 T-helper cell (Th1) andTh17 cell polarization that mediate colitis. Additionally this thesis proposes a noveltargeted therapeutic approach for colitis. Particularly, we show that neutralization ofalpha 9 integrin that is a ligand for Opn, and is expressed specifically on CD103- DCssurface during colitis, blocked the pro-inflammatory action of Opn.Οι ιδιοπαθείς φλεγμονώδεις νόσοι του εντέρου (ΙΦΝΕ) προκαλούνται απόυπερβολικές φλεγμονώδεις ανοσοαποκρίσεις ενάντια στην συμβιωτική μικροχλωρίδακαι σε άλλα αντιγόνα του εντερικού αυλού. Αλλαγές στα εντερικά δενδριτικάκύτταρα (ΔΚ) συμβάλλουν στην δημιουργία ΙΦΝΕ στους ανθρώπους καιπειραματικής κολίτιδας σε μύες. Τα ΔΚ των μεσεντέριων λεμφαδένων είναι βασικοίμεσολαβητές της επαγωγής της κολίτιδας και χωρίζονται σε δυο κύριους υποτύπουςμε διαφορετική έκφραση της ιντεγκρίνης αΕ (CD103): Υπάρχουν ταCD11chighCD103+ και τα CD11chighCD103- ΔΚ.Πρόσφατη μελέτη προτείνει τον προ-φλεγμονώδη ρόλο της κυτοκίνης οστεοποντίνης(Opn) στην χρόνια πειραματική κολίτιδα. Επιπροσθέτως, η Opn εκφράζεται σε πολύυψηλά επίπεδα σε κύτταρα ανοσοποιητικά και μη του εντέρου, στο πλάσμα ασθενώνμε ΙΦΝΕ, αλλά και στο κόλον και το πλάσμα μυών με κολίτιδα. Η Opn εκφράζεταικαι από τα ΔΚ συμβάλλοντας στους κυτταρικούς μηχανισμούς που διαμεσολαβούν τις αυτοάνοσες ασθένειες. Συνολικά, η Opn παίζει ρόλο στην ρύθμιση τουφαινοτύπου, της επιστράτευσης και της λειτουργιάς των ΔΚ σε διάφορες καταστάσειςφλεγμονής. Παρόλα αυτά είναι άγνωστο αν ο καίριος υπότυπος ΔΚ για την κολίτιδαεκφράζει Opn και την πιθανή σημαντικότητα αυτής της έκφρασης για την ασθένεια.Ο σκοπός της διδακτορικής διατριβής αρχικά στόχευε στην ταυτοποίηση του καίριουυπότυπου ΔΚ για την επαγωγή κολίτιδας. Αποδείξαμε πως τα CD103- ΔΚ τωνμεσεντέριων λεμφαδένων έχουν προ-φλεγμονώδη δράση στην οξεία κολίτιδα. Επίσηςορίσαμε ότι τα CD103- ΔΚ εκτός από άλλες προ-φλεγμονώδεις κυτοκίνες, εκφράζουν πολύ υψηλά επίπεδα Opn. Ακόμη βρήκαμε ότι η έκφραση Opn από τα CD103- ΔΚκαθορίζει την προ-φλεγμονώδη υπόσταση τους στην κολίτιδα.Με τη χρήση διαφορετικών πειραματικών προσεγγίσεων, σε αυτή τη διατριβήδείχνουμε ότι η έκφραση της Opn από τα CD103- ΔΚ μπορεί να είναι από μόνη τηςυπεύθυνη για την προ-φλεγμονώδη δράση τους. Αποδεικνύουμε για πρώτη φορά, ότιη έκφραση της Opn από τα CD103- ΔΚ είναι σημαντική για την έκφραση άλλων προ-φλεγμονωδών κυτοκινών από τα ίδια κύτταρα. Η έκφραση της Opn ενίσχυσε τηνικανότητα των CD103- ΔΚ να οδηγούν την διαφοροποίηση των Τ βοηθητικώνλεμφοκυττάρων Τύπου 1 (Th1) και Th17, διαμεσολαβητών της ασθένειας.Τέλος, η διατριβή προτείνει μια στοχευμένη θεραπευτική προσέγγιση: Συγκεκριμένα,χρήση αντισώματος ενάντια στην άλφα 9 ιντεγκρίνη που είναι προσδέτης της Opn,και εκφράζεται στην επιφάνεια των CD103- ΔΚ κατά την επαγωγή της κολίτιδας, εμπόδισε σημαντικά την προ-φλεγμονώδη δράση της Opn

An integrin axis induces IFN-β production in plasmacytoid dendritic cells

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

TIGIT Enhances Antigen-Specific Th2 Recall Responses and Allergic Disease

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

Osteopontin expression by CD103−dendritic cells drives intestinal inflammation

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