Jacques Urbain

CD4+ CD25+ Regulatory T Cells Control T Helper Cell Type 1 Responses to Foreign Antigens Induced by Mature Dendritic Cells In Vivo

Recent evidence suggests that in addition to their well known stimulatory properties, dendritic cells (DCs) may play a major role in peripheral tolerance. It is still unclear whether a distinct subtype or activation status of DC exists that promotes the differentiation of suppressor rather than effector T cells from naive precursors. In this work, we tested whether the naturally occurring CD4+ CD25+ regulatory T cells (Treg) may control immune responses induced by DCs in vivo. We characterized the immune response induced by adoptive transfer of antigen-pulsed mature DCs into mice depleted or not of CD25+ cells. We found that the development of major histocompatibility complex class I and II–restricted interferon γ–producing cells was consistently enhanced in the absence of Treg. By contrast, T helper cell (Th)2 priming was down-regulated in the same conditions. This regulation was independent of interleukin 10 production by DCs. Of note, splenic DCs incubated in vitro with Toll-like receptor ligands (lipopolysaccharide or CpG) activated immune responses that remained sensitive to Treg function. Our data further show that mature DCs induced higher cytotoxic activity in CD25-depleted recipients as compared with untreated hosts. We conclude that Treg naturally exert a negative feedback mechanism on Th1-type responses induced by mature DCs in vivo.

Cytokines Regulate the Capacity of CD8α+ and CD8α− Dendritic Cells to Prime Th1/Th2 Cells In Vivo

Prior studies have shown that subclasses of dendritic cells (DC) direct the development of distinct Th populations in rodents and in humans. In the mouse, we have recently shown that administration of Ag-pulsed CD8α− DC induces a Th2-type response, whereas injection of CD8α+ DC leads to Th1 differentiation. To define the DC-derived factors involved in the polarization of Th responses, we injected either subset purified from mice genetically deficient for IFN-γ, IL-4, IL-12, or IL-10 into wild-type animals. In this work, we report that DC-derived IL-12 and IFN-γ are required for Th1 priming by CD8α+ DC, whereas IL-10 is required for optimal development of Th2 cells by CD8α− DC. The level of IL-12 produced by the DC appears to determine the Th1/Th2 balance in vivo. We further show that the function of DC subsets displays some flexibility. Treatment of DC with IL-10 in vitro induces a selective decrease in the viability of CD8α+ DC. Conversely, incubation with IFN-γ down-regulates the Th2-promoting capacities of CD8α− DC and increases the Th1-skewing properties of both subsets.

Role of CD8alpha+ and CD8alpha- dendritic cells in the induction of primary immune responses in vivo.

Data from adoptive transfer of mature dendritic cells (DC) indicate that they are responsible for the induction of primary immunity. Two subclasses of DC have been recently identified in spleen that differ in their phenotype and in certain regulatory features. In vitro, both subsets have the capacity to activate naive T cells, although CD8α+ DC have been shown to induce T cell apoptosis and to stimulate lower levels of cytokines compared with CD8α− DC. The objective of this study was to analyze the function of these distinct DC types in vivo. Our results show that both subsets, pulsed extracorporeally with antigen and injected in the footpads of syngeneic mice, sensitize an antigen‐specific T cell primary response. However, CD8α+ cells trigger the development of Th1‐type cells, whereas CD8α− DC induce a Th2‐type response. These observations suggest that the Th1/Th2 balance in vivo is regulated by the antigen‐presenting‐cells of the primary immune responses. J. Leukoc. Biol. 66: 242–246; 1999.

Towards a logical analysis of the immune response.

We present a new way to conceive, formalize and analyse models of the immune network. The models proposed are minimal ones, based essentially on the well-established negative feedback loop between helper and suppressor T cells. The occurrence of T-T interactions in both helper and suppressor circuits. These T-T interactions are represented here by autocatalytic feedback loops on TH and TS. The fact that immature B cells are sensitive to negative signaling, as was originally suggested by Lederberg (1959). There is a functional inactivation of immature B cells encountering antigen or anti-idiotypic antibody. This prevents further differentiation to a stage where the B cells become fully responsive. We describe the role of a logical method in the generation and analysis of the models, and the complementarity between this logical method and the more classical description by continuous differential equations. Logical analysis and numerical simulations of the differential equations show that the emerging model accounts for, the occurrence of multiple steady states (a virgin state, a memory state and a non-responsive state) in the absence of antigen, the kinetics of primary and secondary responses, high dose paralysis, low dose of paralysis. Its fit with real situations is surprisingly good for a model of this simplicity. Nevertheless, we give it as an example of what can now be done in the field rather than as a stable model.

Dendritic cells fused with mastocytoma cells elicit therapeutic antitumor immunity

Characterization of the spontaneous immune response that frequently occurs in tumor‐bearing animals, as well as immunization using dendritic cells pulsed with tumor antigens, suggests that a limiting factor of the tumor‐specific immune response may be a defect in the co‐stimulatory signal that is required for optimal activation of T cells. In this work, we describe a new approach to improve the antigen‐presenting capacity of tumor cells, which does not require a source of purified tumor‐associated antigen. We fused P815 mastocytoma cells with bone marrow‐derived dendritic cells. We obtained one hybrid that displayed the phenotypic and functional properties of dendritic cells and expressed mRNA coding for the tumor‐associated antigen P815 A/B. Injections of irradiated hybrid cells prevented the growth of pre‐implanted mastocytoma and induced long‐lasting tumor resistance. Int. J. Cancer76:250–258, 1998.© 1998 Wiley‐Liss, Inc.

TLR4 and Toll-IL-1 Receptor Domain-Containing Adapter-Inducing IFN-β, but Not MyD88, Regulate Escherichia coli-Induced Dendritic Cell Maturation and Apoptosis In Vivo

Dendritic cells (DC) are short-lived, professional APCs that play a central role in the generation of adaptive immune responses. Induction of efficient immune responses is dependent on how long DCs survive in the host. Therefore, the regulation of DC apoptosis in vivo during infection remains an important question that requires further investigation. The impact of Escherichia coli bacteremia on DCs has never been analyzed. We show here that i.v. or i.p. administration of live or heat-killed E. coli in mice induces splenic DC migration, maturation, and apoptosis. We further characterize which TLR and Toll-IL-1R (TIR)-containing adaptor molecules regulate these processes in vivo. In this model, DC maturation is impaired in TLR2−/−, TLR4−/− and TIR domain-containing adapter-inducing IFN-β (TRIF)−/− mice. In contrast, DC apoptosis is reduced only in TLR4−/− and TRIF−/− mice. As expected, DC apoptosis induced by the TLR4 ligand LPS is also abolished in these mice. Injection of the TLR9 ligand CpG-oligodeoxynucleotide (synthetic bacterial DNA) induces DC migration and maturation, but only modest DC apoptosis when compared with LPS and E. coli. Together, these results suggest that E. coli bacteremia directly impacts on DC maturation and survival in vivo through a TLR4-TRIF-dependent signaling pathway.

Regulation of T helper cell differentiation in vivo by soluble and membrane proteins provided by antigen-presenting cells.

The aim of this study was to test whether the nature of the antigen‐presenting cell (APC) can influence the Th1 / Th2 balance in vivo. Our data show that dendritic cells (DC), pulsed extra corporeally with antigen, induced the development of cells secreting IL‐2, IFN‐γ and IL‐4 upon antigen rechallenge in vitro. Priming with peritoneal macrophages sensitized cells that produced IL‐4 but not IFN‐γ. To identify the factors involved in T helper development, mice were primed with APC with or without treatment with neutralizing antibodies to co‐stimulatory molecules or cytokines. Our results indicate that priming with DC or macrophages is strictly dependent on the CD28‐CTLA4/ B7 interaction. Of note, CD86 provides the initial signal to induce naive T cells to become IL‐4 producers, whereas CD80 is a more neutral differentiation signal. IL‐12, released by the DC, appears as a potent and obligatory inducer of differentiation for IFN‐γ‐producing cells. IL‐6, although produced by both APC populations, is necessary to direct activation of the Th2‐type response by macrophages but not by DC.

CD4+ CD25+ regulatory T cells control the magnitude of T-dependent humoral immune responses to exogenous antigens.

CD4+CD25+ T reg cells are critical for peripheral tolerance and prevention of autoimmunity. Here we show that CD4+CD25+ T reg also regulate the magnitude of humoral responses against a panel of T‐dependent antigens of foreign origin during both primary and secondary immune responses. Depletion of CD4+CD25+ T cells leads to increased antigen‐specific antibody production and affinity maturation but does not affect T‐independent B cell responses, suggesting that CD4+CD25+ T reg exert a feedback mechanism on non‐self antigen‐specific antibody secretion by dampening the T cell help for B cell activation. Moreover, we show that CD4+CD25+ T reg also suppress in vitro B cell immunoglobulin production by inhibiting CD4+CD25– T cell help delivery, and that blockade of TGF‐β activity abolishes this suppression.

Hyper IgE in stimulatory graft‐ versus‐host disease: role of interleukin‐4

Intravenous injection of 2 × 108 DBA/2 spleen cells into adult intact (C57BL/6 x DBA/2) Fl mice results in a stimulatory graft‐versus‐host reaction (GVHR) linked to the recognition by donor CD4+ T cells of Ia alloantigens on host B cells. In the experiments presented here, we found that this GVHR is associated with a major increase in IgE serum levels which was already present 7 days after the cell transfer. At 6 weeks, mean IgE levels were more than 200‐fold above the control values. Host B cells were responsible for the hypersecretion of IgE in stimulatory GVHR since it was also observed when the DBA/2 donor inoculum was depleted of B cells but not when the Fl recipients were irradiated. The induction of IgE secretion required donor CD4+ T cells as treatment of the donor inoculum with lytic anti‐CD4 monoclonal antibody (MoAb) completely prevented the occurrence of the hyper IgE whereas depletion of CD8+ cells had no influence on this parameter. The role played by interleukin‐4 (IL‐4) in this model was analysed in vivo by the administration of the 11B11 anti‐IL‐4 rat MoAb (total dose 36 mg) during the first 12 days following induction of stimulatory GVHR by 8 × 107 DBA/2 spleen cells. This treatment completely prevented the development of hyper IgE whereas the administration of a control rat MoAb had no significant effect. We conclude that stimulatory GVHR in mice is associated with a major increase in serum IgE which is mediated by IL‐4.

T Cell-Dependent Maturation of Dendritic Cells in Response to Bacterial Superantigens

Dendritic cells (DC) express a set of germline-encoded transmembrane Toll-like receptors that recognize shared microbial products, such as Escherichia coli LPS, termed pathogen-associated molecular patterns. Analysis of the in vivo response to pathogen-associated molecular patterns has uncovered their ability to induce the migration and the maturation of DC, favoring thus the delivery of Ag and costimulatory signals to naive T cells in vivo. Bacterial superantigens constitute a particular class of pathogen-derived molecules known to induce a potent inflammatory response in vivo, secondary to the activation of a large repertoire of T cells. We demonstrate in this work that Staphylococcal superantigens induce migration and maturation of DC populations in vivo. However, in contrast to LPS, superantigens failed to induce DC maturation in RAG or MHC class II-deficient mice, suggesting that T cell activation was a prerequisite for DC maturation. This conclusion was further supported by the finding that T cell activation induced by 1) mitogenic anti-CD3 mAbs, 2) allo-MHC determinants, or 3) nominal Ag in a TCR-transgenic model induces DC maturation in vivo. These studies also revealed that DC that matured in response to T cell mitogens display, comparatively to LPS, a distinctive phenotype characterized by high expression of the MHC class II, CD40, and CD205 markers, but only moderate (CD86) to minimal (CD80) expression of CD28/CTLA4 ligands. This work demonstrates that activation of a sufficient number of naive T cells in vivo constitutes a novel form of immune danger, functionally linked to DC maturation.