Search

International audience; Salmonella is an intracellular bacterium found in the gastrointestinal tract of mammalian, avian, and reptilian hosts. Mouse models have been extensively used to model in vivo distinct aspects of human Salmonella infections and have led to the identification of several host susceptibility genes. We have investigated the susceptibility of Collaborative Cross strains to intravenous infection with Salmonella enterica serovar Typhimurium as a model of human systemic invasive infection. In this model, strain CC042/GeniUnc (CC042) mice displayed extreme susceptibility with very high bacterial loads and mortality. CC042 mice showed lower spleen weights and decreased splenocyte numbers before and after infection, affecting mostly CD8+ T cells, B cells, and all myeloid cell populations, compared with control C57BL/6J mice. CC042 mice also had lower thymus weights with a reduced total number of thymocytes and double-negative and double-positive (CD4+, CD8+) thymocytes compared to C57BL/6J mice. Analysis of bone marrow-resident hematopoietic progenitors showed a strong bias against lymphoid-primed multipotent progenitors. An F2 cross between CC042 and C57BL/6N mice identified two loci on chromosome 7 (Stsl6 and Stsl7) associated with differences in bacterial loads. In the Stsl7 region, CC042 carried a loss-of-function variant, unique to this strain, in the integrin alpha L (Itgal) gene, the causative role of which was confirmed by a quantitative complementation test. Notably, Itgal loss of function increased the susceptibility to S. Typhimurium in a (C57BL/6J × CC042)F1 mouse background but not in a C57BL/6J mouse inbred background. These results further emphasize the utility of the Collaborative Cross to identify new host genetic variants controlling susceptibility to infections and improve our understanding of the function of the Itgal gene.

International audience; T cell development and selection are coordinated in the thymus by a specialized niche of diverse stromal populations1-3. Although much progress has been made over the years in identifying the functions of the different cell types of the thymic stromal compartment, there is no comprehensive characterization of their diversity and heterogeneity. Here we combined massively parallel single-cell RNA-sequencing4,5, spatial mapping, chromatin profiling and gene targeting to characterize de novo the entire stromal compartment of the mouse thymus. We identified dozens of cell states, with thymic epithelial cells (TECs) showing the highest degree of heterogeneity. Our analysis highlights four major medullary TEC (mTEC I-IV) populations, with distinct molecular functions, epigenetic landscapes and lineage regulators. Specifically, mTEC IV constitutes a new and highly divergent TEC lineage with molecular characteristics of the gut chemosensory epithelial tuft cells. Mice deficient in Pou2f3, a master regulator of tuft cells, have complete and specific depletion of mTEC IV cells, which results in increased levels of thymus-resident type-2 innate lymphoid cells. Overall, our study provides a comprehensive characterization of the thymic stroma and identifies a new tuft-like TEC population, which is critical for shaping the immune niche in the thymus.

Avian influenza virus subtype H9N2 (H9N2) and Chlamydia psittaci (C. psittaci) are frequently isolated in chickens with respiratory disease. However, their roles in co-infection remain unclear. We tested the hypothesis that C. psittaci enhances H9N2 infection through suppression of host immunity. Thus, 10-day-old SPF chickens were inoculated intra-tracheally with a high or low virulence C. psittaci strain and were simultaneously vaccinated against Newcastle disease virus (NDV). Significant decreases in body weight, NDV antibodies and immune organ indices occurred in birds with the virulent C. psittaci infection, while the ratio of CD4+/CD8+ T cells increased significantly compared to that of the lower virulence strain. A second group of birds were inoculated with C. psittaci and H9N2 simultaneously (C. psittaci+H9N2), C. psittaci 3 days prior to H9N2 (C. psittaci/H9N2), or 3 days after H9N2 (H9N2/C. psittaci), C. psittaci or H9N2 alone. Survival rates were 65%, 80% and 90% in the C. psittaci/H9N2, C. psittaci+H9N2 and H9N2/C. psittaci groups, respectively and respiratory clinical signs, lower expression of pro-inflammatory cytokines and higher pathogen loads were found in both C. psittaci/H9N2 and C. psittaci+H9N2 groups. Hence, virulent C. psittaci infection suppresses immune response by inhibiting humoral responses and altering Th1/Th2 balance, increasing mortality in H9N2 infected birds.

International audience; Misrepair of DNA double-strand breaks produced by the V(D)J recombinase (the RAG1/RAG2 proteins) at immunoglobulin (Ig) and T cell receptor (Tcr) loci has been implicated in pathogenesis of lymphoid malignancies in humans and in mice. Defects in DNA damage response factors such as ataxia telangiectasia mutated (ATM) protein and combined deficiencies in classical non-homologous end joining and p53 predispose to RAG-initiated genomic rearrangements and lymphomagenesis. Although we showed previously that RAG1/RAG2 shepherd the broken DNA ends to classical non-homologous end joining for proper repair, roles for the RAG proteins in preserving genomic stability remain poorly defined. Here we show that the RAG2 carboxy (C) terminus, although dispensable for recombination, is critical for maintaining genomic stability. Thymocytes from 'core' Rag2 homozygotes (Rag2(c/c) mice) show dramatic disruption of Tcrα/δ locus integrity. Furthermore, all Rag2(c/c) p53(-/-) mice, unlike Rag1(c/c) p53(-/-) and p53(-/-) animals, rapidly develop thymic lymphomas bearing complex chromosomal translocations, amplifications and deletions involving the Tcrα/δ and Igh loci. We also find these features in lymphomas from Atm(-/-) mice. We show that, like ATM-deficiency, core RAG2 severely destabilizes the RAG post-cleavage complex. These results reveal a novel genome guardian role for RAG2 and suggest that similar 'end release/end persistence' mechanisms underlie genomic instability and lymphomagenesis in Rag2(c/c) p53(-/-) and Atm(-/-) mice.

International audience; Intestinal CD8αα intraepithelial T lymphocytes (T-IELs) have a key role in mucosal immunity and, unlike other T cells, were proposed to differentiate locally. In apparent contradiction, these cells were also shown to originate from a wave of thymus migrants colonizing the gut in the first 3 weeks after birth. We here identify previously uncharacterized very immature CD4(-)CD8(-)CD3(-)CD44(+)CD25(int) thymocytes, which have not yet rearranged their T-cell antigen receptor (TCR), as having the capacity to leave the thymus, migrate to the blood, colonize the gut, and reconstitute CD8αα T-IEL, and show that this cell set is fully responsible for the generation of the CD8αα T-IEL pool. Thus, although the thymus may be fundamental for efficient T-cell commitment, CD8αα T-IEL' complete TCR rearrangements and TCR-αβ/γδ lineage commitment must occur in the gut. These results demonstrate a major role of the gut environment as a primary lymphoid organ.

International audience; Some gammadelta and alphabeta T lymphocytes exhibit an "innate" phenotype associated with rapid cytokine responses. The PLZF transcription factor is essential for the innate phenotype of NKT cells. This report shows that PLZF is likewise responsible for the innate, NKT-like phenotype of Vgamma1+Vdelta6.3/Vdelta6.4+ cells. TCR cross-linking induced PLZF expression in all polyclonal immature gammadelta thymocytes, suggesting that agonist selection might be required for PLZF induction. Transgenic expression of Vgamma1Vdelta6.4 TCR was sufficient to support the development of large numbers of PLZF+ T cells, further supporting the importance of the TCR for PLZF induction. Interestingly, expression of this TCR transgene led to the development of spontaneous dermatitis.

The thymus represents the “cradle” for T cell development, with thymic stroma providing multiple soluble and membrane cues to developing thymocytes. Although IL-7 is recognized as an essential factor for thymopoiesis, the “environmental niche” of thymic IL-7 activity remains poorly characterized in vivo. Using bacterial artificial chromosome transgenic mice in which YFP is under control of IL-7 promoter, we identify a subset of thymic epithelial cells (TECs) that co-express YFP and high levels of Il7 transcripts (IL-7 hi cells). IL-7 hi TECs arise during early fetal development, persist throughout life, and co-express homeostatic chemokines ( Ccl19 , Ccl25 , Cxcl12 ) and cytokines ( Il15 ) that are critical for normal thymopoiesis. In the adult thymus, IL-7 hi cells localize to the cortico-medullary junction and display traits of both cortical and medullary TECs. Interestingly, the frequency of IL-7 hi cells decreases with age, suggesting a mechanism for the age-related thymic involution that is associated with declining IL-7 levels. Our temporal-spatial analysis of IL-7-producing cells in the thymus in vivo suggests that thymic IL-7 levels are dynamically regulated under distinct physiological conditions. This IL-7 reporter mouse provides a valuable tool to further dissect the mechanisms that govern thymic IL-7 expression in vivo.

CD4+CD25+Foxp3+ regulatory T lymphocytes are crucial for maintenance of immunological tolerance to self and innocuous non-self, are known to modulate immunity to tumors and infectious agents, and can induce transplantation tolerance. Surprisingly, only a single genetic polymorphism is known to modulate regulatory T cell development in the thymus, leading to a lethal autoimmune disorder. Here we show that considerably different levels of regulatory T cells are found in thymi of distinct common laboratory mouse strains. We demonstrate that distinct levels of phenotypically and functionally identical regulatory T cells develop with similar kinetics in the studied mice, that the responsible locus acts in a thymocyte intrinsic manner, and that levels of thymic Foxp3+ regulatory T cells correlate to those found in the periphery. Using several congenic mouse-strains we mapped one of the at least two genetic loci capable of quantitatively modulating thymic regulatory T cell development to a ≤ 2.2 Mbp region telomeric to the MHC. Our data indicate that polymorphic genes closely linked to the MHC locus substantially modulate differentiation of regulatory T cells. Identification of responsible genes should help in understanding mechanisms involved in commitment to the regulatory T cell lineage as well as selection of these cells in the thymus.

Natural CD4+CD25+ regulatory T lymphocytes (Treg) are key protagonists in the induction and maintenance of peripheral T cell tolerance. Their thymic origin and biased repertoire continue to raise important questions about the signals that mediate their development. We validated analysis of MHC class II capture by developing thymocytes from thymic stroma as a tool to study quantitative and qualitative aspects of the cellular interactions involved in thymic T cell development and used it to analyze Treg differentiation in wild-type mice. Our data indicate that APCs of bone marrow origin, but, surprisingly and importantly, not thymic epithelial cells, induce significant negative selection among the very autoreactive Treg precursors. This fundamental difference between thymic development of regulatory and effector T lymphocytes leads to the development of a Treg repertoire enriched in cells specific for a selected subpopulation of self-Ags, i.e., those specifically expressed by thymic epithelial cells.

International audience; IL-7 and thymic stromal lymphopoietin (TSLP) are two major cytokines controlling murine B cell development. IL-7 has been studied extensively, but only recently has it become possible to unravel the role of TSLP in detail. We studied the biological activities of TSLP in B cell development at distinct ages in the mouse. On the one hand, TSLP is able to give rise to a measurable B1 cell compartment derived from fetal liver pro-B cells, although, as is the case for B2 cells, it does not play a prevalent role in the development of this subset. On the other hand, TSLP drives the proliferation of pro-B cells from the fetal and neonatal liver, but in the bone marrow environment, B cell precursors require pre-B cell receptor expression for TSLP responsiveness.

International audience; Deletions of interleukin 7 (IL-7) or its receptor components permit fetal but not adult B cell development in mice. Mice deficient in IL-7 receptor alpha (IL-7R alpha) had 1% the number of B cells of controls and 10% that of mice deficient in the common gamma chain. As IL-7R alpha is also a receptor for thymic stromal-derived lymphopoietin (TSLP), we assayed the ability of TSLP to support proliferation of fetal or adult precursor B cells. Only fetal-derived pro-B cells were able to respond to TSLP, although pre-B cells from both origins were TSLP-responsive. Fetal but not adult precursors generated a measurable B cell compartment in the absence of IL-7. The residual B cells found in IL-7R alpha-deficient mice required fetal liver kinase 2 (Flk-2) for their development. Thus, IL-7R alpha- and Flk-2-mediated signals account for the generation of almost all mouse B lymphocytes.

International audience; Transcription factors orchestrate T-lineage differentiation in the thymus. One critical checkpoint involves Notch1 signaling that instructs T-cell commitment at the expense of the B-lineage program. While GATA-3 is required for T-cell specification, its mechanism of action is poorly understood. We show that GATA-3 works in concert with Notch1 to commit thymic progenitors to the T-cell lineage via 2 distinct pathways. First, GATA-3 orchestrates a transcriptional “repertoire” that is required for thymocyte maturation up to and beyond the pro–T-cell stage. Second, GATA-3 critically suppresses a latent B-cell potential in pro–T cells. As such, GATA-3 is essential to sealing in Notch-induced T-cell fate in early thymocyte precursors by promoting T-cell identity through the repression of alternative developmental options.

International audience; HFE, an MHC class Ib molecule that controls iron metabolism, can be directly targeted by cytotoxic TCR αβ T lymphocytes. Transgenic DBA/2 mice expressing, in a Rag 2 KO context, an αβ TCR that directly recognizes mouse HFE (mHFE) were created to further explore the interface of HFE with the immune system. TCR-transgenic mHfe WT mice deleted mHFE-reactive T cells in the thymus, but a fraction of reprogrammed cells were able to escape deletion. In contrast, TCR-transgenic mice deprived of mHFE molecules (mHfe KO mice) or expressing a C282→Y mutated mHFE molecule - the most frequent mutation associated with human hereditary hemochromatosis - positively selected mHFE-reactive CD8(+) T lymphocytes and were not tolerant toward mHFE. By engrafting these mice with DBA/2 WT (mHFE(+)) skin, it was established, as suspected on the basis of similar engraftments performed on DBA/2 mHfe KO mice, that mHFE behaves as an autonomous skin-associated histocompatibility antigen, even for mHFE-C282→Y mutated mice. By contrast, infusion of DBA/2 mHFE(+) mice with naïve mHFE-reactive transgenic CD8(+) T lymphocytes did not induce GVHD. Thus, tolerance toward HFE in mHfe WT mice can be acquired at either thymic or peripheral levels but is disrupted in mice reproducing human familial hemochromatosis.

International audience; Erythropoietin-producing hepatocellular kinases (Eph kinases) constitute the largest family of cell membrane receptor tyrosine kinases, and their ligand ephrins are also cell surface molecules. Because of promiscuous interaction between Ephs and ephrins, there is considerable redundancy in this system, reflecting the essential roles of these molecules in the biological system through evolution. In this study, both Efnb1 and Efnb2 were null-mutated in the T cell compartment of mice through loxP-mediated gene deletion. Mice with this double conditional mutation (double KO mice) showed reduced thymus and spleen size and cellularity. There was a significant decrease in the DN4, double positive, and single positive thymocyte subpopulations and mature CD4 and CD8 cells in the periphery. dKO thymocytes and peripheral T cells failed to compete with their WT counterparts in irradiated recipients, and the T cells showed compromised ability of homeostatic expansion. dKO naive T cells were inferior in differentiating into Th1 and Th17 effectors in vitro. The dKO mice showed diminished immune response against LCMV infection. Mechanistic studies revealed that IL-6 signaling in dKO T cells was compromised, in terms of abated induction of STAT3 phosphorylation upon IL-6 stimulation. This defect likely contributed to the observed in vitro and in vivo phenotype in dKO mice. This study revealed novel roles of Efnb1 and Efnb2 in T cell development and function.

International audience; The dendritic cells (DCs) present in lymphoid and non-lymphoid organs are generated from progenitors with myeloid-restricted potential. However, in the thymus a major subset of DCs expressing CD8α and langerin (CD207) appears to stand apart from all other DCs in that it is thought to derive from progenitors with lymphoid potential. Using mice expressing a fluorescent reporter and a diphtheria toxin receptor under the control of the cd207 gene, we demonstrated that CD207(+) CD8α(+) thymic DCs do not share a common origin with T cells but originate from intrathymic precursors that express markers that are normally present on all (CD11c(+) and MHCII molecules) or on some (CD207, CD135, CD8α, CX3CR1) DC subsets. Those intrathymic myeloid-type precursors correspond to CD44(+) CD25(-) double-negative 1c (DN1c) cells and are continuously renewed from bone marrow-derived canonical DC precursors. In conclusion, our results demonstrate that the earliest intrathymic precursors of CD8α(+) thymic DCs correspond to myeloid-type DN1c cells and support the view that under physiological conditions myeloid-restricted progenitors generate the whole constellation of DCs present in the body including the thymus.

After entry into thymus, T cell progenitors migrate in the cortex and the medulla while completing their education. Recent reports have documented the dynamic and tortuous behavior of thymocytes. However, other than chemokines and/or segregated thymic substrates, the factors contributing to the dynamic patterns of thymocyte movement are poorly characterized. By combining confocal and dynamic two-photon microscopy, we demonstrate that thymocytes continuously migrate on thymic stromal cell networks. In addition to constituting “roads” for thymocytes, we observed that these networks also provide a scaffold on which dendritic cells attach themselves. These results highlight the central role of stromal microanatomy in orchestrating the multiple cellular interactions necessary for T cell migration/development within the thymus.

The mechanisms underlying tolerance to noninherited maternal Ags (NIMA) are not fully understood. In this study, we designed a double-transgenic model in which all the offspring’s CD8+ T cells corresponded to a single clone recognizing the Kb MHC class I protein. In contrast, the mother and the father of the offspring differed by the expression of a single Ag, Kb, that served as NIMA. We investigated the influence of NIMA exposure on the offspring thymic T cell selection during ontogeny and on its peripheral T cell response during adulthood. We observed that anti-Kb thymocytes were exposed to NIMA and became activated during fetal life but were not deleted. Strikingly, adult mice exposed to NIMA accepted permanently Kb+ heart allografts despite the presence of normal levels of anti-Kb TCR transgenic T cells. Transplant tolerance was associated with a lack of a proinflammatory alloreactive T cell response and an activation/expansion of T cells producing IL-4 and IL-10. In addition, we observed that tolerance to NIMA Kb was abrogated via depletion of CD4+ but not CD8+ T cells and could be transferred to naive nonexposed mice via adoptive transfer of CD4+CD25high T cell expressing Foxp3 isolated from NIMA mice.

International audience; Although the primary determinant of cell tropism is the interaction of viral envelope or capsid proteins with cellular receptors, other viral elements can strongly modulate viral replication. While the HIV-1 promoter is polymorphic for a variety of transcription factor binding sites, the impact of these polymorphisms on viral replication in vivo is not known. To address this issue, we engineered isogenic SIVmac239 chimeras harboring the core promoter/enhancer from HIV-1 clades B, C, and E. Here it is shown that the clade C and E core promoters/enhancers bear a noncanonical activator protein-1 (AP-1) binding site, absent from the corresponding clade B region. Relative ex vivo replication of chimeras was strongly dependent on the tissue culture system used. Notably, in thymic histocultures, replication of the clade C chimera was favored by IL-7 enrichment, which suggests that the clade C polymorphism in the AP-1 and NF-kappaB binding sites is involved. Simultaneous infection of rhesus macaques with the 3 chimeras revealed a strong predominance of the clade C chimera during primary infection. Thereafter, the B chimera dominated in all tissues. These data show that the clade C promoter is particularly adapted to sustain viral replication in primary viremia and that clade-specific promoter polymorphisms constitute a major determinant for viral replication.

Thymic epithelial cells (TECs) are the predominant intrathymic source of the essential thymopoietin IL-7. Whether thymocyte-TEC interactions have a role in the regulation of IL-7 expression is not known. By exploiting IL-7 reporter mice in which yellow fluorescent protein expression identifies TECs expressing high levels of IL-7 (Il7+ TECs), we show that Il7+ TECs segregate from emerging medullary TECs during thymic organogenesis. Although Il7+ TECs normally diminish with age, we found that Il7+ TECs are markedly retained in alymphoid Rag2−/−Il2rg−/− IL-7 reporter mice that manifest a profound thymopoietic arrest. Transfer of Tcra−/− or wild-type (but not Rag2−/−) hematopoietic progenitors to alymphoid IL-7 reporter recipients normalizes the frequency of Il7+ TECs and re-establishes cortical TEC/medullary TEC segregation. Although thymocyte-derived signals are often considered stimulatory for TEC maturation, our findings identify a negative feedback mechanism in which signals derived from TCRβ-selected thymocytes modulate TEC-dependent IL-7 expression.

Poly(ADP-ribose) polymerase-2 (Parp-2) belongs to a family of enzymes that catalyse poly(ADP-ribosyl)ation of proteins. Parp-2 deficiency in mice (Parp-2(-/-)) results in reduced thymic cellularity associated with increased apoptosis in thymocytes, defining Parp-2 as an important mediator of T-cell survival during thymopoiesis. To determine whether there is a link between Parp-2 and the p53 DNA-damage-dependent apoptotic response, we have generated Parp-2/p53-double-null mutant mice. We found that p53(-/-) backgrounds completely restored the survival and development of Parp-2(-/-) thymocytes. However, Parp-2-deficient thymocytes accumulated high levels of DNA double-strand breaks (DSB), independently of the p53 status, in line with a function of Parp-2 as a caretaker promoting genomic stability during thymocytes development. Although Parp-2(-/-) mice do not have spontaneous tumours, Parp-2 deficiency accelerated spontaneous tumour development in p53-null mice, mainly T-cell lymphomas. These data suggest a synergistic interaction between Parp-2 and p53 in tumour suppression through the role of Parp-2 in DNA-damage response and genome integrity surveillance, and point to the potential importance of examining human tumours for the status of both genes.

International audience; T lymphocytes depend on the thymic microenvironment for initiation of the T-cell developmental program. As the progenitors in the thymus have lost the capacity to self-renew, this process depends on the constant influx of hematopoietic progenitors that originate in the bone marrow. Nevertheless, thymic emigrants are heterogeneous and retain developmental plasticity for both the myeloid and lymphoid lineages. It is the role of the thymic microenvironment to steer these uncommitted progenitors toward a T-cell fate. Still, the thymus also generates a unique population of thymic NK cells, thus raising the question of how the T versus NK lymphoid cell fate is determined intrathymically. Many factors have been implicated in the developmental pathways in the thymus, and the processes are characterized by both subtle and not so subtle modifications in gene expression. In this review, we consider the crucial factors governing lineage determination of T cells versus NK cells from bi-potent thymic NK/T precursors. Recent reports have shed new light on the complex interactions of cytokines and transcription factors at different cell fate decision branch points in thymopoiesis. We discuss the implications of these findings and propose a model that may be applicable at this critical thymic NK/T juncture.

International audience; ZAP-70 is critical for T cell receptor (TCR) signaling. Tyrosine to phenylalanine mutations of Y315 and Y319 in ZAP-70 suggest these residues function to recruit downstream effector molecules, but mutagenesis and crystallization studies reveal that these residues also play an important role in autoinhibition ZAP-70. To address the importance of the scaffolding function, we generated a zap70 mutant mouse (YYAA mouse) with Y315 and Y319 both mutated to alanines. These YYAA mice reveal that the scaffolding function is important for normal development and function. Moreover, the YYAA mice have many similarities to a previously identified ZAP-70 mutant mouse, SKG, which harbors a distinct hypomorphic mutation. Both YYAA and SKG mice have impaired T cell development and hyporesponsiveness to TCR stimulation, markedly reduced numbers of thymic T regulatory cells and defective positive and negative selection. YYAA mice, like SKG mice, develop rheumatoid factor antibodies, but fail to develop autoimmune arthritis. Signaling differences that result from ZAP-70 mutations appear to skew the TCR repertoire in ways that differentially influence propensity to autoimmunity versus autoimmune disease susceptibility. By uncoupling the relative contribution from T regulatory cells and TCR repertoire during thymic selection, our data help to identify events that may be important, but alone are insufficient, for the development of autoimmune disease.

Signals initiated through the TCR during development can result in either survival and differentiation or cell death. High affinity signals that induce death elicit a robust yet transient activation of signaling pathways, including Erk, whereas low affinity ligands, which promote survival, generate a gradual and weaker activation of the same pathways. It was recently demonstrated that Erk localizes to distinct cellular locations in response to high and low affinity ligands. Although a requirement for Erk in positive selection is well established, its role in negative selection is controversial and, thus, the importance of Erk relocalization during development is not understood. In this study, we examined the role of Erk in negative selection using mice that are genetically deficient in both Erk1 and Erk2 in T cells. Results from three different models reveal that thymocyte deletion remains intact in the absence of Erk.

Antibody responses are critical for host protection against many pathogens. By reporting what actually occurs in vivo, two new studies provide important clues about follicular helper T cells that are dedicated to providing help to B cells.

International audience; Thymus-specific serine protease (TSSP) was initially reported as a putative protease specifically expressed in the endosomal compartment of cortical thymic epithelial cells (cTEC). As such, TSSP is potentially involved in the presentation of the self-peptides that are bound to MHC class II molecules expressed at the cTEC surface and are involved in the positive selection of CD4(+) thymocytes. We tested this hypothesis by generating mutant mice deprived of Prss16, the gene encoding TSSP. TSSP-deficient mice produced normal numbers of T cells, despite a decrease in the percentage of cTEC expressing high surface levels of MHC class II. By using sensitive transgenic models expressing MHC class II-restricted TCR transgenes (Marilyn and OT-II), we showed that the absence of TSSP markedly impaired the selection of Marilyn and OT-II CD4(+) T cells. In contrast, selection of CD8(+) T cells expressing an MHC class I-restricted TCR transgene (OT-I) was unaffected. Therefore, TSSP is involved in the positive selection of some CD4(+) T lymphocytes and likely constitutes the first serine protease to play a function in the intrathymic presentation of self-peptides bound to MHC class II complexes.

Mucosal-associated invariant T (MAIT) cells display two evolutionarily conserved features: an invariant T cell receptor (TCR)α (iTCRα) chain and restriction by the nonpolymorphic class Ib major histocompatibility complex (MHC) molecule, MHC-related molecule 1 (MR1). MR1 expression on thymus epithelial cells is not necessary for MAIT cell development but their accumulation in the gut requires MR1 expressing B cells and commensal flora. MAIT cell development is poorly known, as these cells have not been found in the thymus so far. Herein, complementary human and mouse experiments using an anti-humanVα7.2 antibody and MAIT cell-specific iTCRα and TCRβ transgenic mice in different genetic backgrounds show that MAIT cell development is a stepwise process, with an intra-thymic selection followed by peripheral expansion. Mouse MAIT cells are selected in an MR1-dependent manner both in fetal thymic organ culture and in double iTCRα and TCRβ transgenic RAG knockout mice. In the latter mice, MAIT cells do not expand in the periphery unless B cells are added back by adoptive transfer, showing that B cells are not required for the initial thymic selection step but for the peripheral accumulation. In humans, contrary to natural killer T (NKT) cells, MAIT cells display a naïve phenotype in the thymus as well as in cord blood where they are in low numbers. After birth, MAIT cells acquire a memory phenotype and expand dramatically, up to 1%–4% of blood T cells. Finally, in contrast with NKT cells, human MAIT cell development is independent of the molecular adaptor SAP. Interestingly, mouse MAIT cells display a naïve phenotype and do not express the ZBTB16 transcription factor, which, in contrast, is expressed by NKT cells and the memory human MAIT cells found in the periphery after birth. In conclusion, MAIT cells are selected by MR1 in the thymus on a non-B non-T hematopoietic cell, and acquire a memory phenotype and expand in the periphery in a process dependent both upon B cells and the bacterial flora. Thus, their development follows a unique pattern at the crossroad of NKT and γδ T cells., Author Summary White blood cells, or lymphocytes, play an important role in defending the body from infection and disease. T lymphocytes come in many varieties with diverse functions. Mucosal-associated invariant T (MAIT) cells constitute a subset of unconventional T lymphocytes, characterized by their invariant T cell receptor (TCR)α chain and their requirement for the nonpolymorphic class Ib (MHC) molecule, MR1. MAIT cells are extremely abundant in human blood and mucosae. Contrary to mainstream T cells, their development requires B cells and commensal microbial flora. To shed light on the little-understood MAIT cells, we used new tools, including an antibody that we recently developed to detect human MAIT cells, and we were able to show that MAIT cell development is a stepwise process, with an intra-thymic selection followed by peripheral expansion. We show that thymic selection is MR1 dependent but requires neither B cells nor the commensal flora, which are both necessary for the expansion in the periphery. In contrast with the other evolutionarily conserved invariant subset, the natural killer T (NKT) cells, we found that MAIT cells exit the thymus as “naïve” cells before becoming antigen-experienced memory cells and expanding in number to represent a significant 1%–4% of peripheral T cells in human blood. In mice, we found that MAIT cells remain naïve and do not expand substantially. We conclude that MAIT cell development follows a unique scheme, where, unlike NKT cells, MAIT cell selection and expansion are uncoupled events that are mediated by distinct cell types in different compartments., Mucosal-associated invariant T cells, the most abundant invariant T cell subset in humans, arise via a distinct developmental pathway that represents a hybrid of that seen for NKT and γδ T cells, two other unconventional T cell subsets.

International audience; Atopic dermatitis (AD) is often the initial step in the "atopic march," given that more than half of AD patients with moderate to severe AD develop asthma later in life. Both AD and asthma share a similar "atopy" phenotype that includes T helper type 2 inflammation with eosinophilia and hyper-IgE immunoglobulinemia, but the molecular mechanisms underlying the "atopic march" remain elusive. In the present study, we show that induced expression of thymic stromal lymphopoietin (TSLP) in mouse epidermal keratinocytes upon topical application of MC903 (a low calcemic analogue of vitamin D3) not only triggers AD as we previously reported but also aggravates experimental allergic asthma induced by ovalbumin sensitization and challenge. Our study, which provides a mouse model to study human "atopic march," indicates that keratinocyte-produced TSLP may represent an important factor in the link of atopic dermatitis to asthma.

International audience; The thymus provides a specialized environment allowing the differentiation of T lymphocytes from bone marrow-derived progenitor cells. We and others have demonstrated that gene transfer into distinct thymocyte populations can be obtained, both in vivo and ex vivo, using lentiviral vectors. Here, we describe techniques for intrathymic lentiviral transduction in mice, using a surgical approach wherein the thoracic cavity is exposed as well as a significantly less invasive strategy wherein virions are directly injected through the skin. Moreover, thymocyte differentiation from murine and human progenitors is now feasible in vitro, under conditions wherein the Notch and IL-7 signaling pathways are activated. We describe methods allowing transduction of murine and human progenitors and their subsequent differentiation into more mature thymocytes. Conditions for lentiviral gene transfer into more differentiated human thymocyte subsets are also presented. Optimization of technologies for HIV-based gene transfer into murine and human thymocyte progenitors will advance strategies aimed at modulating T-cell differentiation and function in-vivo; approaches potentially targeting patients with genetic and acquired immunodeficiencies as well as immune-sensitive tumors. Furthermore, this technology will foster the progression of basic research aimed at elucidating molecular aspects of T-cell differentiation in mice and humans.

Udgivelsesdato: 2009-Aug-19 We showed previously that Lyn is a substrate for caspases, a family of cysteine proteases, involved in the regulation of apoptosis and inflammation. Here, we report that expression of the caspase-cleaved form of Lyn (LynDeltaN), in mice, mediates a chronic inflammatory syndrome resembling human psoriasis. Genetic ablation of TNF receptor 1 in a LynDeltaN background rescues a normal phenotype, indicating that LynDeltaN mice phenotype is TNF-alpha-dependent. The predominant role of T cells in the disease occurring in LynDeltaN mice was highlighted by the distinct improvement of LynDeltaN mice phenotype in a Rag1-deficient background. Using pan-genomic profiling, we also established that LynDeltaN mice show an increased expression of STAT-3 and inhibitory members of the NFkappaB pathway. Accordingly, LynDeltaN alters NFkappaB activity underlying a link between inhibition of NFkappaB and LynDeltaN mice phenotype. Finally, analysis of Lyn expression in human skin biopsies of psoriatic patients led to the detection of Lyn cleavage product whose expression correlates with the activation of caspase 1. Our data identify a new role for Lyn as a regulator of psoriasis through its cleavage by caspases.

International audience; The thymus is the primary site of T-cell development and plays a key role in the induction of self-tolerance. We previously showed that the intrathymic (i.t.) injection of a transgene-expressing lentiviral vector (LV) in mice can result in the correction of a T cell-specific genetic defect. Nevertheless, the efficiency of thymocyte transduction did not exceed 0.1-0.3% and we were unable to detect any thymus transduction in macaques. As such, we initiated studies to assess the capacity of recombinant adeno-associated virus (rAAV) vectors to transduce murine and primate thymic cells. In vivo administration of AAV serotype 2-derived single-stranded AAV (ssAAV) and self-complementary AAV (scAAV) vectors pseudotyped with capsid proteins of serotypes 1, 2, 4, 5, and 8 demonstrated that murine thymus transduction was significantly enhanced by scAAV2/8. Transgene expression was detected in 5% of thymocytes and, notably, transduced cells represented 1% of peripheral T lymphocytes. Moreover, i.t. administration of scAAV2/8 particles in macaques, by endoscopic-mediated guidance, resulted in significant gene transfer. Thus, in healthy animals, where thymic gene transfer does not provide a selective advantage, scAAV2/8 is a unique tool promoting the in situ transduction of thymocytes with the subsequent export of gene-modified lymphocytes to the periphery.

Bovine leukemia virus (BLV), one of the most common infectious viruses of cattle, is endemic in many herds. Approximately 30–40% of adult cows in the United States are infected by this oncogenic C-type retrovirus and 1–5% of animals will eventually develop a malignant lymphoma. BLV, like the human and simian T cell leukemia viruses, is a deltaretrovirus but, in contrast with the latter, the BLV receptor remains unidentified. In this study, we demonstrate that the amino-terminal 182 residues of the BLV envelope glycoprotein surface unit encompasses the receptor-binding domain. A bona fide interaction of this receptor-binding domain with the BLV receptor was demonstrated by specific interference with BLV, but not human T cell leukemia virus, envelope glycoprotein-mediated binding. We generated a rabbit Ig Fc-tagged BLV receptor-binding domain construct and ascertained that the ligand binds the BLV receptor on target cells from multiple species. Using this tool, we determined that the BLV-binding receptor is expressed on differentiating pro/pre-B cells in mouse bone marrow. However, the receptor was not detected on mature/quiescent B cells but was induced upon B cell activation. Activation of human B and T lymphocytes also induced surface BLV-binding receptor expression and required de novo protein synthesis. Receptor levels were down-regulated as activated lymphocytes returned to quiescence. In the human thymus, BLV-binding receptor expression was specifically detected on thymocytes responding to the IL-7 cytokine. Thus, expression of the BLV-binding receptor is a marker of enhanced metabolic activity in B cells, T cells, and thymocytes.

International audience; Patients with mutations in the Artemis gene display a complete absence of T- and B lymphocytes, together with increased cellular radiosensitivity; this leads to a radiosensitive severe combined immunodeficiency (RS-SCID). Allogenic hematopoietic stem-cell (HSC) transplantation is only partially successful in the absence of an human leukocyte antigen-genoidentical donor, and this has prompted a search for alternative therapeutic approaches such as gene therapy. In this study, a self-inactivated lentiviral vector expressing Artemis was used to complement the Artemis knockout mouse (Art(-/-)). Transplantation of Artemis-transduced HSCs into irradiated Art(-/-) mice restored a stable (over a 15-month period of follow-up) and functional T- and cell repertoire that was comparable to that of control mice. The success of secondary transplantations demonstrated that the HSCs had been transduced. One of thirteen mice developed a thymoma 6 months after gene therapy. Although thymic cells were seen to be carrying two lentiviral integration sites, there was no evidence of lentivirus-driven oncogene activation. The Art(-/-) mice were found to be prone to develop T-cell lymphomas, either spontaneously or after irradiation. These data indicate that the observed lymphoproliferation was probably the consequence of the chromosomal instability associated with the Artemis-deficient background. As a whole, our work provides a basis for supporting the gene therapy approach in Artemis-deficient SCID.

International audience; Antigen recognition by T cell antigen receptors (TCRs) is thought to 'unmask' a proline-rich sequence (PRS) present in the CD3epsilon cytosolic segment, which allows it to trigger T cell activation. Using 'knock-in' mice with deletion of the PRS, we demonstrate here that elimination of the CD3epsilon PRS had no effect on mature T cell responsiveness. In contrast, in preselection CD4+CD8+ thymocytes, the CD3epsilon PRS acted together with the adaptor protein SLAP to promote CD3zeta degradation, thereby contributing to downregulation of TCR expression on the cell surface. In addition, analysis of CD4+CD8+ thymocytes of TCR-transgenic mice showed that the CD3epsilon PRS enhanced TCR sensitivity to weak ligands. Our results identify previously unknown functions for the evolutionarily conserved CD3epsilon PRS at the CD4+CD8+ developmental stage and suggest a rather limited function in mature T cells.

International audience; A young boy with a confirmed complete DiGeorge Syndrome (cDGS) underwent a peripheral blood mononuclear cell transplantation (PBMCT) from his HLA-identical sister at 4.5 years of age, without a conditioning regimen. Eight years later, he is healthy with good immunological functions in the presence of a stable mixed T-cell chimerism. Absence of recent thymic emigrants is confirmed. We observe an inverted CD4+/CD8+ ratio, related to the CD8 subset expansion, a skewing of the TCR repertoire, especially on the CD8+ subset and a telomere loss on the CD8+ cells compared to the donor. However, these anomalies do not seem to have an impact on functional immunity. PBMCT in cDGS using an HLA-matched sibling donor provides good long-lasting immunity and is an easy alternative to bone marrow transplantation and to thymic transplantation.

International audience; Partial purification of the DNA ligase from three human tissues (liver, thymus and lymphoblasts) revealed that each cell type contains several different polypeptides bearing a DNA ligase I activity. Their apparent molecular weights estimated after SDS PAGE, 130 kDa, 100 kDa and 80 kDa, are in agreement with previous reports. These polypeptides are related by proteolysis to a single higher molecular weight protein of 200 kDa which does not show DNA ligase activity but that could be a preprotein.

A system under homeostatic control tends to maintain its structure and functions by establishing dynamic equilibriums controlled by multiple regulatory mechanisms. We have shown that this is the case for immune system. Several different mechanisms seem to participate in the homeostatic control of T cell numbers and population distribution. In other words, besides a quantitative dimension, there is also a qualitative dimension in T cell homeostasis. This is achieved through competition by driving the specialization of sub-populations of lymphocytes to occupy specific niches in the peripheral pool and by developing independent homeostatic mechanisms for each particular cell sub-set. Thus, the sizes of the naive and memory T cell compartments are governed by independent homeostatic mechanisms, which preserve the capacity to deal with any novel infection (conferred by the presence of naive T cells) whilst ensuring the efficacy of memory responses when dealing with recurring antigens. Peripheral T cell homeostasis also depends on the integrity of sub-population structure and the presence of regulatory CD4+ CD25+ T cells. The indexation of regulatory CD4+ CD25+ T cell numbers to the numbers of peripheral activated CD4+ T cells is another mechanism of homeostasis that has major advantages in the control of immune responses. It ensures continuous regulation of T cell numbers throughout immune responses, allowing for increases in cell numbers as long as the proportion of CD4+ CD25+ regulatory T cells is kept.

doi : 10.1016/j.molimm.2007.02.017; International audience; The size of the available human alphabeta T cell repertoire is difficult to determine and is open to debate. Empirical analysis of TCR beta-chain diversity reveals approximately 10(6) different beta chains in peripheral blood. Due in part to locus complexity, comparable information for TCR alpha is lacking. Rather, current estimates for human TCR alpha diversity, and hence, total repertoire diversity, are based on theoretical analyses that assume equal probabilities of rearrangement between any V alpha gene and J alpha gene. Here, we report on a systematic locus-wide rearrangement analysis of the TCR alpha-chain in human T cells. We first demonstrate that the V-J alpha recombination in the thymus is not random but depends on the reciprocal V alpha and J alpha position within the locus. Characterization of the frequency of gene usage combined with identification of five previously unrecognized pseudogenes enables us to empirically estimate the human TCR alpha combinatorial repertoire. The number of V-J alpha combinations achieved is approximately 44-56% of the total combinatorial possibilities, significantly lower than theoretical estimates. We also demonstrate that TCR alpha-chain diversity in peripheral T lymphocytes mimics the same general patterns of rearrangement as observed in the thymus, and these patterns appear conserved among different individuals. This unexpected observation indicates that, unlike the TCR beta locus, the human TCR alpha-chain repertoire is primarily predetermined by genetic recombination and its size is restricted by limits on the combinatorial repertoire rather than post-thymic selection.

International audience; The nature and lineage potential, particularly that for B cells, of thymus settling progenitors (TSP) in the adult mouse has been the subject of considerable debate. Lack of B cell potential would suggest pre-thymic, whereas its presence would suggest intra-thymic loss of B cell potential. Using limiting dilution analysis (LDA) in vitro and transfer experiments in vivo, we show that the B cell potential of TSP is critically dependent on mouse age, reaching a maximum of about 1 in 20 cells at birth, decreasing 50-fold in adult mice. Cells with a TSP phenotype can be found in the neonatal blood. Furthermore, using LDA, we show that Notch ligand signaling of TSP results in the loss of B cell potential with a half-life of approximately 12 h. Taken together, these results indicate that loss of B cell potential by TSP is an intra-thymic event and highlight the developmental pressure acting on the immune system to rapidly colonize primary lymphoid organs with functional progenitors. This critical time coincides with birth in the mouse. In the adult mouse, we estimate than only about 5 TSP cells/day would be required to maintain steady-state thymopoiesis.

International audience; Understanding natural killer (NK) cell developmental pathways is crucial for harnessing the potential therapeutic benefits of this specialized lymphocyte subset. The bone marrow (BM) plays a major role in NK cell development, providing the appropriate environmental cues for NK cell commitment and subsequent NK cell differentiation. Nevertheless, the molecular signals provided in this context remain enigmatic. It is widely assumed that BM seeds the periphery with NK cells. However, the precise origins of NK cells found in lymphoid organs and tissues are not defined. Recently, we found that thymic NK cells bear molecular markers and functional attributes that distinguish them from most peripheral NK cells. We find that NK cells are actively exported from the thymus to the periphery, suggesting that thymus-derived NK cells may have unique roles both intrathymically and in secondary lymphoid organs. Here we compare the properties of thymic NK cells with properties of other NK cell subsets that have been identified in the mouse. We propose that heterogeneity in NK cell function can be achieved through distinct thymic and bone marrow pathways of NK cell development.

International audience; Natural killer (NK) cell development is thought to occur in the bone marrow. Here we identify the transcription factor GATA-3 and CD127 (IL-7R alpha) as molecular markers of a pathway of mouse NK cell development that originates in the thymus. Thymus-derived CD127+ NK cells repopulated peripheral lymphoid organs, and their homeostasis was strictly dependent on GATA-3 and interleukin 7. The CD127+ NK cells had a distinct phenotype (CD11b(lo) CD16- CD69(hi) Ly49(lo)) and unusual functional attributes, including reduced cytotoxicity but considerable cytokine production. Those characteristics are reminiscent of human CD56(hi) CD16- NK cells, which we found expressed CD127 and had more GATA-3 expression than human CD56+ CD16+ NK cells. We propose that bone marrow and thymic NK cell pathways generate distinct mouse NK cells with properties similar to those of the two human CD56 NK cell subsets.

Free Full Text : http://www.smw.ch/docs/pdf200x/2006/4/smw-11413.pdf; International audience; Haematopoietic stem cells (HSCs), a very rare cell type in the bone marrow, are responsible for the life-long production of all cells of the blood including T and B cells. Until recently, it was thought that the differentiation of HSCs into the various haematopoietic cells was rather hierarchical in that differentiation along a given lineage was associated with a progressive loss of potential to give rise to other blood cell lineages. The recent development of very sensitive and quantitative in vitro assays, together with the identification of new progenitor subpopulations, has challenged this idea. Thus, lymphocyte progenitors can be shown to keep their developmental potential to give rise to myeloid, dendritic and NK cells until just prior to their final commitment stage. Here we review these new findings and concepts.

In pre-Tα (pTα) gene-deleted mice, the positively selectable CD4+CD8+ double-positive thymocyte pool is only 1% that in wild-type mice. Consequently, their peripheral T cell compartment is severely lymphopenic with a concomitant increase in proportion of CD25+FoxP3+ regulatory T cells. Using mixed bone marrow chimeras, where thymic output was 1% normal, the pTα−/− peripheral T cell phenotype could be reproduced with normal cells. In the pTα−/− thymus and peripheral lymphoid organs, FoxP3+CD4+ cells were enriched. Parabiosis experiments showed that many pTα−/−CD4+ single-positive thymocytes represented recirculating peripheral T cells. Therefore, the enrichment of FoxP3+CD4+ single-positive thymocytes was not solely due to increased thymic production. Thus, the pTα−/− mouse serves as a model system with which to study the consequences of chronic decreased thymic T cell production on the physiology of the peripheral T cell compartment.

International audience; NK cells constitute an essential element of the innate immune system; however, the cellular and molecular mechanisms that guide their early development are still poorly understood. Here, we demonstrate that in addition to its known crucial role in T cell development, Notch signaling can also be involved in NK cell development. Thus, upon co-culture on OP9 stroma expressing the Notch ligand Delta-like 1 (OP9-DL1), Pax5-deficient pro-B cells, which have multi-lineage potential, efficiently differentiate into T and NK cells. Upon DL-1 signaling, Pax5-deficient pro-B cells down-regulate both surface CD93 expression and transcripts for B cell-specific genes and concomitantly up-regulate T lineage gene transcripts. Subsequent transfer of DL-1-signaled Pax5-deficient pro-B cells onto OP9 stroma in the presence of IL-2 leads to their efficient differentiation into NK1.1(+), functional NK cells. Moreover, bone marrow early progenitor with lymphoid and myeloid differentiation potential (EPLM), which we have previously described as the normal in vivo-equivalent of Pax5-deficient pro-B cells, also gain the ability to differentiate into effector NK cells following transient DL1 Notch-mediated signaling. The potential involvement of Notch signaling in the generation of the NK cell repertoire in vivo is discussed.

International audience; OBJECTIVE: To investigate whether mature human articular chondrocytes (AC) exhibit an antiproliferative effect on activated peripheral blood mononuclear cells (PBMC) and to compare this effect with other cells of mesenchymal origin. METHODS: AC from healthy cadaveric cartilage were grown for different passages, in the absence (control) or presence of factors enhancing cell de-differentiation (transforming growth factor (TGF)beta1, fibroblast growth factor (FGF)-2, and platelet derived growth factor (PDGF)bb-TFP medium). Cell ability to suppress PBMC proliferation driven by anti-CD3 antibody was measured by tritiated thymidine uptake following incubation for 48 h at different PBMC:AC ratios and expressed as percent of residual proliferation (RP). AC antiproliferative effect was compared to that of control dermal fibroblasts (DF) and bone marrow stromal cells (BMSC). RESULTS: AC exhibited a cell number-dependent antiproliferative effect. The strongest effect (up to 2% RP) was measured using the least expanded AC cultures. The use of TFP medium for AC expansion resulted in a significantly lower antiproliferative effect, in the range of that induced by BMSC (up to 18% RP). Also DF induced a marked antiproliferative effect (up to 11% RP). CONCLUSION: We report for the first time that human AC have a marked antiproliferative effect on anti-CD3 stimulated PBMC, which is reduced upon culture in medium-inducing extensive cell de-differentiation. These results reflect the immunosuppressive properties observed for other different mesenchymal cell types and raise the question of a potential common physiological role in local tissue protection.

We have recently described a CD19– B220+CD117low bone marrow subpopulation with B, T, and myeloid developmental potential, which we have called “early progenitors with lymphoid and myeloid potential” or EPLM. These cells also expressed Fms-like tyrosine kinase 3, Flt3, or CD135. Treatment of mice with the corresponding ligand, Flt3L, showed a 50-fold increase in EPLM. In addition to the expected increase in dendritic cell numbers, Flt3L treatment had a reversible inhibitory effect on B lymphopoiesis. Limiting dilution analysis of sorted EPLM from Flt3L-treated mice showed that B-lymphocyte progenitor activity was reduced 20-fold, but that myeloid and T-cell progenitor activity was largely preserved. EPLM from treated mice transiently reconstituted the thymus and bone marrow of recipient mice, generating cohorts of functional T and B cells in peripheral lymphoid organs. Thus, Flt3L treatment results in a dramatic increase in a novel bone marrow cell with lymphoid and myeloid progenitor activity.

CD4+CD25+ regulatory T lymphocytes play a crucial role in inhibition of autoimmune pathology. In accordance with this physiological role, it is now well established that the repertoire of these lymphocytes is strongly enriched in autospecific cells. However, despite extensive investigation, the thymic mechanisms involved in development of regulatory T cells remain incompletely defined. To address the issue of selection of regulatory T cell precursors in mice with a naturally diverse TCR repertoire, we have analyzed development of superantigen-specific regulatory T cells in hemopoietic chimeras in which endogenous super-antigens are exclusively presented by thymic epithelial cells. Our results demonstrate that recognition of agonist ligands expressed by thymic epithelium does not lead to deletion but substantially enhances development of mature regulatory T cells. Interestingly, also development of a small subpopulation of CD25-expressing T cells lacking expression of the transcription factor Foxp3, thought to be autospecific, is enhanced by expression of the agonist ligand on thymic epithelium. Based on quantitative arguments, we propose that commitment to the regulatory T cell lineage is not dictated by the specificity of precursors, but that recognition of the agonist ligand expressed by thymic epithelium substantially enhances their positive selection.

The checkpoint in gammadelta cell development that controls successful T cell receptor (TCR) gene rearrangements remains poorly characterized. Using mice expressing a reporter gene 'knocked into' the Tcrd constant region gene, we have characterized many of the events that mark the life of early gammadelta cells in the adult thymus. We identify the developmental stage during which the Tcrd locus 'opens' in early T cell progenitors and show that a single checkpoint controls gammadelta cell development during the penultimate CD4- CD8- stage. Passage through this checkpoint required the assembly of gammadelta TCR heterodimers on the cell surface and signaling via the Lat adaptor protein. In addition, we show that gammadelta selection triggered a phase of sustained proliferation similar to that induced by the pre-TCR.

E.J.-M, V.A.-A. and C.A.-G. contributed equally to this work.; International audience; Cellular prion protein (PrP(C)) is an ubiquitously expressed glycoprotein whose roles are still widely discussed, particularly in the field of immunology. Using TgA20- and Tg33-transgenic mice overexpressing PrP(C), we investigated the consequences of this overexpression on T cell development. In both models, overexpression of PrP(C) induces strong alterations at different steps of T cell maturation. On TgA20 mice, we observed that these alterations are cell autonomous and lead to a decrease of alphabeta T cells and a concomitant increase of gammadelta T cell numbers. PrP(C) has been shown to bind and chelate copper and, interestingly, under a copper supplementation diet, TgA20 mice presented a partial restoration of the alphabeta T cell development, suggesting that PrP(C) overexpression, by chelating copper, generates an antioxidant context differentially impacting on alphabeta and gammadelta T cell lineage.

E.J.-M, V.A.-A. and C.A.-G. contributed equally to this work.; International audience; Cellular prion protein (PrP(C)) is an ubiquitously expressed glycoprotein whose roles are still widely discussed, particularly in the field of immunology. Using TgA20- and Tg33-transgenic mice overexpressing PrP(C), we investigated the consequences of this overexpression on T cell development. In both models, overexpression of PrP(C) induces strong alterations at different steps of T cell maturation. On TgA20 mice, we observed that these alterations are cell autonomous and lead to a decrease of alphabeta T cells and a concomitant increase of gammadelta T cell numbers. PrP(C) has been shown to bind and chelate copper and, interestingly, under a copper supplementation diet, TgA20 mice presented a partial restoration of the alphabeta T cell development, suggesting that PrP(C) overexpression, by chelating copper, generates an antioxidant context differentially impacting on alphabeta and gammadelta T cell lineage.

International audience; The precise roles played by the transmembrane receptor tyrosine kinase c-kit and its ligand stem cell factor in early T cell development are difficult to study. Using cloned Pax5-deficient progenitor B cells, we show that following Notch signaling, which induces their commitment to the T cell developmental pathway, c-kit expression is rapidly up-regulated at both the transcriptional and cell surface level. Using either an anti-c-kit monoclonal antibody or Gleevec, a pharmacological inhibitor of c-kit signaling, we show that the Notch-induced T cell differentiation of either Pax5-deficient progenitor B cells, or the equivalent cell from the bone marrow of normal mice, is strictly dependent on c-kit signaling, whereas the differentiation of normal progenitors into the B cell lineage is not. Moreover, we show that the Notch and IL-7 signaling-induced proliferation and differentiation of CD44+CD25-c-kit(high) and CD44+CD25+c-kithigh thymocytes along the T cell, but not natural killer cell or macrophage, pathway also requires c-kit signaling, whereas the Notch-induced proliferation and differentiation of CD44-CD25+c-kitint cells along the T cell pathway is independent of c-kit. These results further highlight the complex inter-relationships existing between c-kit, Notch and IL-7 receptor signaling that control the proliferation and differentiation of early T cell progenitors.