Dll4-Notch signaling in Flt3-independent dendritic cell development and autoimmunity in mice

Delta-like ligand 4 (Dll4)-Notch signaling is essential for T cell development and alternative thymic lineage decisions. How Dll4-Notch signaling affects pro-T cell fate and thymic dendritic cell (tDC) development is unknown. We found that Dll4 pharmacological blockade induces accumulation of tDCs and CD4 +CD25 +FoxP3 + regulatory T cells (T reg cells) in the thymic cortex. Both genetic inactivation models and anti-Dll4 antibody (Ab) treatment promote de novo natural T reg cell expansion by a DC-dependent mechanism that requires major histocompatibility complex II expression on DCs. Anti-Dll4 treatment converts CD4 -CD8 -c-kit +CD44 +CD25 - (DN1) T cell progenitors to immature DCs that induce ex vivo differentiation of naive CD4 + T cells into T reg cells. Induction of these tolerogenic DN1-derived tDCs and the ensuing expansion of T reg cells are Fms-like tyrosine kinase 3 (Flt3) independent, occur in the context of transcriptional up-regulation of PU.1, Irf-4, Irf-8, and CSF-1, genes critical for DC differentiation, and are abrogated in thymectomized mice. Anti-Dll4 treatment fully prevents type 1 diabetes (T1D) via a T reg cell-mediated mechanism and inhibits CD8+ T cell pancreatic islet infiltration. Furthermore, a single injection of anti-Dll4 Ab reverses established T1D. Disease remission and recurrence are correlated with increased T reg cell numbers in the pancreasdraining lymph nodes. These results identify Dll4-Notch as a novel Flt3-alternative pathway important for regulating tDC-mediated T reg cell homeostasis and autoimmunity

Etude de l'intéraction entre lymphocytes T régulateurs CD4+CD25+ et lymphocytes T effecteurs in vivo, chez la souris

Les lymphocytes T régulateurs CD4+CD25+ (LTreg) régulent les réponses immunitaires, notamment les réactions auto-immunes.Notre étude porte sur les interactions entre ces cellules et les lymphocytes T effecteurs CD4+CD25- conventionnels (LTconv),in vivo chez la souris. Nos travaux montrent que les LTreg endogènes perdent le contrôle des LTconv lorsque ceux-ci sont trèsactivés. Les LTreg de même spécificité que les LTconv arrivent par contre à les contrôler, parce qu'ils se divisentactivement. La déplétion des LTreg endogènes chez des souris NOD jeunes, et non âgées, accélèrent le diabète. Nous proposonsque l'apparition du diabète chez la souris NOD est dûe à une perte de contrôle, par les LTreg endogènes, des LTconv auto-réactifs du fait de l'inflammation croissante. Nous démontrons également qu'en présence de LTconv, les LTreg prolifèrentplus que tout seuls. Cet effet "boost" des LTconv sur les LTreg peut conférer une protection long terme face à une induction de diabète.PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Tumor emergence is sensed by self-specific CD44hi memory Tregs that create a dominant tolerogenic environment for tumors in mice

Early responses of Tregs and effector T cells (Teffs) to their first encounter with tumor cells have been poorly characterized. Here we have shown, in both implanted and in situ–induced mouse tumor models, that the appearance of tumor cells is immediately sensed by CD44hi memory Tregs that are specific for self antigens. The rapid response of these Tregs preceded and prevented activation of naive antitumor Teffs. The relative speed of the Treg versus the Teff response within the first 2–4 days determined the outcome of the antitumor immune response: tolerance or rejection. If antitumor memory Teffs were present at the time of tumor emergence, both Tregs and Teffs were recruited and activated with memory kinetics; however, the Tregs were unable to control the Teffs, which eradicated the tumor cells. This balance between effector and regulatory responses did not depend on the number of Tregs and Teffs, but rather on their memory status. Thus, in the natural setting, dominant tolerogenic immunosurveillance by self-specific memory Tregs protects tumors, just as it protects normal tissues. More generally, our results reveal that the timing of Treg and Teff engagement, determined by their memory status, is an important mode of regulation of immune responses

Pathogenic T cells have a paradoxical protective effect in murine autoimmune diabetes by boosting Tregs

CD4+CD25+Foxp3+ Tregs play a major role in prevention of autoimmune diseases. The suppressive effect of Tregs on effector T cells (Teffs), the cells that can mediate autoimmunity, has been extensively studied. However, the in vivo impact of Teff activation on Tregs during autoimmunity has not been explored. In this study, we have shown that CD4+ Teff activation strongly boosts the expansion and suppressive activity of Tregs. This helper function of CD4+ T cells, which we believe to be novel, was observed in the pancreas and draining lymph nodes in mouse recipients of islet-specific Teffs and Tregs. Its physiological impact was assessed in autoimmune diabetes. When islet-specific Teffs were transferred alone, they induced diabetes. Paradoxically, when the same Teffs were cotransferred with islet-specific Tregs, they induced disease protection by boosting Treg expansion and suppressive function. RNA microarray analyses suggested that TNF family members were involved in the Teff-mediated Treg boost. In vivo experiments showed that this Treg boost was partially dependent on TNF but not on IL-2. This feedback regulatory loop between Teffs and Tregs may be critical to preventing or limiting the development of autoimmune diseases

Regulation of innate and adaptive immunity by Notch.

Coordinated function of the innate and adaptive arms of the immune system in vertebrates is essential to promote protective immunity and to avoid immunopathology. The Notch signalling pathway, which was originally identified as a pleiotropic mediator of cell fate in invertebrates, has recently emerged as an important regulator of immune cell development and function. Notch was initially shown to be a key determinant of cell-lineage commitment in developing lymphocytes, but it is now known to control the homeostasis of several innate cell populations. Moreover, the roles of Notch in adaptive immunity have expanded to include the regulation of T cell differentiation and function. The aim of this Review is to summarize the current status of immune regulation by Notch. A better understanding of Notch function in both innate and adaptive immunity will hopefully provide multiple avenues for therapeutic intervention in disease