Jocelyne Demengeot

Regulatory T Cells Selectively Express Toll-like Receptors and Are Activated by Lipopolysaccharide

Regulatory CD4 T cells (Treg) control inflammatory reactions to commensal bacteria and opportunist pathogens. Activation of Treg functions during these processes might be mediated by host-derived proinflammatory molecules or directly by bacterial products. We tested the hypothesis that engagement of germline-encoded receptors expressed by Treg participate in the triggering of their function. We report that the subset of CD4 cells known to exert regulatory functions in vivo (CD45RBlow CD25+) selectively express Toll-like receptors (TLR)-4, -5, -7, and -8. Exposure of CD4+ CD25+ cells to the TLR-4 ligand lipopolysaccharide (LPS) induces up-regulation of several activation markers and enhances their survival/proliferation. This proliferative response does not require antigen-presenting cells and is augmented by T cell receptor triggering and interleukin 2 stimulation. Most importantly, LPS treatment increases CD4+ CD25+ cell suppressor efficiency by 10-fold and reveals suppressive activity in the CD4+ CD45RBlow CD25− subset that when tested ex-vivo, scores negative. Moreover, LPS-activated Treg efficiently control naive CD4 T cell–dependent wasting disease. These findings provide the first evidence that Treg respond directly to proinflammatory bacterial products, a mechanism that likely contributes to the control of inflammatory responses.

Specificity requirements for selection and effector functions of CD25+4+ regulatory T cells in anti-myelin basic protein T cell receptor transgenic mice

CD25+4+ regulatory T cells (Treg) play an indispensable role in preventing autoimmunity. Little is known, however, about the antigen specificities required for their development and effector functions. Mice transgenic for an anti-myelin basic protein (MBP) T cell antigen receptor (TCR) spontaneously develop experimental autoimmune encephalomyelitis (EAE) when deficient for the RAG-1 gene (T/R−), whereas RAG-1-competent transgenic animals (T/R+) remain healthy, protected by CD4+ Treg-expressing endogenous TCRs. We have now investigated the role and specificity of CD25+4+ Treg in this system. The results show that T/R+ animals contain MBP-specific suppressive CD25+4+ cells, whereas T/R− do not. Adoptive transfer of CD25+4+ cells from nontransgenic or T/R+ donors into T/R− mice prevented the development of EAE. Surprisingly, transfer of nontransgenic CD25+4+ cells purified from T/R+ donors conferred only a limited protection, possibly because of their restricted repertoire diversity that we demonstrate here. Absence of transgenic CD25+4+ cells in animals deficient for endogenous TCRα chains and analyses of endogenous TCR gene expression in subsets of CD4+ cells from T/R+ mice demonstrate that development of transgenic MBP-specific CD25+4+ Treg depends on the coexpression of endogenous TCRα chains. Taken together, these results indicate that specificity to MBP is required for effector functions but is not sufficient for thymic selection/commitment of CD25+4+ Treg preventing EAE.

The immunogenicity of anti-TNF therapy in immune-mediated inflammatory diseases: a systematic review of the literature with a meta-analysis

Background Immunogenicity of aTNFs is one of the mechanisms behind treatment failure. Objective To assess the effect of anti-drug antibodies (ADA) on drug response to infliximab, adalimumab and etanercept, and the effect of immunosuppression on ADA detection, in patients with Rheumatoid Arthritis, Spondyloarthritis, Psoriasis and Inflammatory Bowel Diseases. Data sources PubMed, EMBASE, Cochrane databases, article reference lists (through August 19 2012). Study selection Out of 2082 studies, 17 were used in the meta-analysis (1RCT; 16 observational studies). Data extraction Two reviewers extracted data. Risk ratios (RR), 95% CI, using random-effect models, sensitivity analysis, meta-regressions and Eggers test were calculated. Data synthesis Of 865 patients, ADA against infliximab or adalimumab reduced drug response rate by 68% (RR=0.68, 95% CI=0.12 to 0.36), an effect attenuated by concomitant methotrexate (MTX): <74% MTX+: RR=0.23, 95% CI=0.15 to 0.36; ≥74% MTX+: RR=0.32, 95% CI=0.22 to 0.48. Anti-etanercept antibodies were not detected. Of 936 patients, concomitant MTX or azathioprine/mercaptopurine reduced ADA frequency by 47% (RR=0.53, 95% CI=0.42 to 0.67), particularly when ADA were assessed by RIA (RR=0.36, 95% CI=0.23 to 0.55) compared with ELISA (RR=0.63, 95% CI=0.53 to 0.74). Conclusions ADA reduces drug response, an effect that can be attenuated by concomitant immunosuppression, which reduces ADA frequency. Drug immunogenicity should be considered for the management of patients receiving biological therapies.

Natural Treg cells spontaneously differentiate into pathogenic helper cells in lymphopenic conditions

Induction of Forkhead‐box p3 (Foxp3) expression in developing T cells upon peptide‐MHC encountering has been proposed to define a lineage of committed Treg cells. However, sustained expression of Foxp3 is required for Treg function and what maintains Foxp3 expression in peripheral Treg remains obscure. To address this issue, we monitored natural Treg phenotype and function upon adoptive transfer into lymphocyte‐deficient mice. We first show that about 50% of Foxp3‐GFP+ Treg isolated from Foxp3gfp KI animals loose Foxp3 expression in severe lymphopenic conditions. We next evidence that the cytokine IL‐2, either produced by co‐transferred conventional T cells or administrated i.v. prevents Foxp3 downregulation. Moreover, we document that Treg that lost Foxp3 expression upon adoptive transfer produce IL‐2 are not suppressive and promote tissue infiltration and damage upon secondary transfer into alymphoid mice. Our findings that Treg convert into pathogenic Th cells in absence of IL‐2 provide new clues to the success of Treg‐based immune therapies.

Type I Interferon controls the onset and severity of autoimmune manifestations in lpr mice

Type I Interferons (IFN-I) are immunoregulatory cytokines that enhance activation and survival of many cellular components of the immune system. In the present work, we evaluated the effect of IFN-I on the development of the lymphoproliferative disorder in Fas-defective lpr mice. We report that sustained injection of polyinosinic:polycytidylic acid, a potent inducer of IFN-I, in B6 lpr mice resulted in a dramatic aggravation of the renal disease, higher titers of autoantibodies, a 10-fold increase in serum Ig and accumulation of activated lymphocytes. Moreover, introducing a null mutation for the IFN-I-Receptor gene into the lpr background resulted in dramatic decrease of immune complexes deposition in the kidney and reduced lymphadenopathy. While several recent reports correlated serum levels of IFN-alpha with disease activity in systemic Lupus erythematosus patients, our findings establish a causal link from IFN-I production to the onset and severity of another related autoimmune syndrome.

Notch1 engagement by Delta-like-1 promotes differentiation of B lymphocytes to antibody-secreting cells

Notch signaling regulates B and T lymphocyte development and T cell effector class decision. In this work, we tested whether Notch activity affects mature B cell activation and differentiation to antibody-secreting cells (ASC). We show increased frequency of ASC in cultures of splenic B cells activated with LPS or anti-CD40 when provided exogenous Notch ligand Delta-like-1 (Dll1). Our results indicate that Notch–Dll1 interaction releases a default pathway that otherwise inhibits Ig secretion upon B cell activation. Thus, Dll1 enhanced spontaneous Ig secretion by naturally activated marginal zone B and B1 cells and reversed the inhibition of ASC differentiation mediated by B cell receptor crosslinking during LPS. Moreover, suppression of Notch signaling in B cell expression of either a dominant-negative mutant form of Mastermind-like 1 or a null mutation of Notch1 not only prevented Dll1-mediated enhancement of ASC differentiation but also reduced dramatically LPS-induced Ig secretion. Finally, we show that Dll1 and Jagged-1 are differentially expressed in discrete areas of the spleen, and that the effect of Notch engagement on Ig secretion is ligand-specific. These results indicate that Notch ligands participate in the definition of the mature B cell microenvironment that influences their terminal differentiation.

Regulatory T cells: the physiology of autoreactivity in dominant tolerance and “quality control” of immune responses

Summary: Little progress has been achieved over the last 20 years on the clinical management of several conditions that relate to self‐tolerance and to the regulation of immune responses: autoimmune diseases, transplantation tolerance, tumor immunity, allergy and vaccine development in chronic infections. These failures, it is argued, are due to the inability of the prevalent “recessive tolerance” concepts to accommodate physiological autoreactivity and the regulatory potential it embodies. In this review, the advantages of “dominant tolerance” models are underlined in the light of critical evidence and in the general context of the natural autoimmune activities. The role of regulatory T cells is discussed, notably in the regulation of inflammatory reactions and, more generally, in the “quality control” of immune responses. It is anticipated that progress will be brought about by dominant tolerance approaches, and through an increased knowledge of the differentiative pathways, repertoires, mechanisms of activation and effector functions of autoreactive, regulatory T cells.

When three is not a crowd : a Crossregulation Model of the dynamics and repertoire selection of regulatory CD4+ T cells

Summary:  Regulatory CD4+ T cells, enriched in the CD25 pool of healthy individuals, mediate natural tolerance and prevent autoimmune diseases. Despite their fundamental and potential clinical significance, regulatory T (TR) cells have not yet been incorporated in a coherent theory of the immune system. This article reviews experimental evidence and theoretical arguments supporting a model of TR cell dynamics, uncovering some of its most relevant biological implications. According to this model, the persistence and expansion of TR cell populations depend strictly on specific interactions they make with antigen‐presenting cells (APCs) and conventional effector T (TE) cells. This three‐partner crossregulation imposes that TR cells feed on the specific autoimmune activities they suppress, with implications ranging from their interactions with other cells to their repertoire selection in the periphery and in the thymus, and to the relationship between these cells and the innate immune system. These implications stem from the basic prediction that the peripheral dynamics sort the CD4+ T‐cell repertoire into two subsets: a less diverse set of small clones of autoreactive effector and regulatory cells that regulate each other’s growth, and a more diverse set of barely autoreactive TE cell clones, whose expansion is limited only by APC availability. It is argued that such partitioning of the repertoire sets the ground for self–non‐self discrimination.

Protection against systemic candidiasis in mice immunized with secreted aspartic proteinase 2

Secreted aspartic proteinases (Sap) have been described as virulence factors implicated in the mechanisms of host colonization by the yeast Candida albicans in different types of candidiasis. Intraperitoneal inoculation of C. albicans into BALB/c mice rapidly leads to systemic candidiasis, with significant colonization of the kidneys measurable in the following week. In this study we assessed the potential of vaccination with C. albicans secreted aspartic proteinase 2 (Sap2) in preventing systemic candidiasis in BALB/c mice. Intradermal injection of highly purified native Sap2 protein incorporated in alum adjuvant provided efficient immune protection, as indicated by a 20‐fold decrease in the colonization of kidneys. The protective effect of Sap2 immunization with alum adjuvant was also observed in mice infected with a lethal inoculum of C. albicans. Immunization with the native Sap2 alone, as well as with a denatured recombinant form of the protein, also conferred protection, albeit to a lesser level. In all cases, protection correlated with an increase in serum antibodies to Sap2. Moreover, passive transfer of anti‐Sap2 immunoglobulin G (IgG) significantly decreased the yeast burden in kidneys of C. albicans‐infected mice. This result shows that immune protection against systemic candidiasis in mice immunized with Sap2 is antibody‐mediated. Taken together, these analyses demonstrate that Sap2 can be successfully used as a vaccination target in systemic candidiasis and reveals the potential immunomodulatory role of Sap2 on C. albicans infection.

1,25-Dihydroxyvitamin D3 Promotes Tolerogenic Dendritic Cells with Functional Migratory Properties in NOD Mice

The biologically active form of vitamin D, 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], is able to promote the generation of tolerogenic mature dendritic cells (mDCs) with an impaired ability to activate autoreactive T cells. These cells could represent a reliable tool for the promotion or restoration of Ag-specific tolerance through vaccination strategies, for example in type 1 diabetes patients. However, successful transfer of 1,25(OH)2D3-treated mDCs (1,25D3-mDCs) depends on the capacity of 1,25(OH)2D3 to imprint a similar tolerogenic profile in cells derived from diabetes-prone donors as from diabetes-resistant donors. In this study, we examined the impact of 1,25(OH)2D3 on the function and phenotype of mDCs originating from healthy (C57BL/6) and diabetes-prone (NOD) mice. We show that 1,25(OH)2D3 is able to imprint a phenotypic tolerogenic profile on DCs derived from both mouse strains. Both NOD- and C57BL/6-derived 1,25D3-mDCs decreased the proliferation and activation of autoreactive T cells in vitro, despite strain differences in the regulation of cytokine/chemokine expression. In addition, 1,25D3-mDCs from diabetes-prone mice expanded CD25+Foxp3+ regulatory T cells and induced intracellular IL-10 production by T cells in vitro. Furthermore, 1,25D3-mDCs exhibited an intact functional migratory capacity in vivo that favors homing to the liver and pancreas of adult NOD mice. More importantly, when cotransferred with activated CD4+ T cells into NOD.SCID recipients, 1,25D3-mDCs potently dampened the proliferation of autoreactive donor T cells in the pancreatic draining lymph nodes. Altogether, these results argue for the potential of 1,25D3-mDCs to restore Ag-specific immune tolerance and arrest autoimmune disease progression in vivo.