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ABSTRACT: Contraction is a critical phase of immunity whereby the vast majority of effector T cells die by apoptosis, sparing a population of long-lived memory cells. Where, when, and why contraction occurs has been difficult to address directly due in large part to the rapid clearance of apoptotic T cells in vivo. To circumvent this issue, we introduced a genetically encoded reporter for caspase-3 activity into naive T cells to identify cells entering the contraction phase. Using two-photon imaging, we found that caspase-3 activity in T cells was maximal at the peak of the response and was associated with loss of motility followed minutes later by cell death. We demonstrated that contraction is a widespread process occurring uniformly in all organs tested and targeting phenotypically diverse T cells. Importantly, we identified a critical window of time during which antigen encounters act to antagonize T cell apoptosis, supporting a causal link between antigen clearance and T cell contraction. Our results offer insight into a poorly explored phase of immunity and provide a versatile methodology to study apoptosis during the development or function of a variety of immune cells in vivo.
Cell reports. 11/2012;
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ABSTRACT: NK cells become activated during viral infection in response to cytokines or to engagement of NK cell activating receptors. However, the identity of cells sensing viral particles and mediating NK cell activation has not been defined. Here, we show that local administration of a Modified Vaccinia virus Ankara vaccine in mice results in the accumulation of NK cells in the subcapsular area of the draining lymph node and their activation, a process that is strictly dependent on type I IFN signaling. NK cells located in the subcapsular area exhibited reduced motility and were found associated with CD169(+) positive subcapsular sinus (SCS) macrophages and collagen fibers. Moreover, depletion of SCS macrophages using clodronate liposomes abolished NK cell accumulation and activation. Our results identify SCS macrophages as primary mediators of NK cell activation in response to lymph born viral particles suggesting that they act as early sensors of local infection or delivery of viral-based vaccines.
Blood 10/2012; · 9.90 Impact Factor
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ABSTRACT: CD8(+) T cell responses generate effector cells endowed with distinct functional potentials but the contribution of early events in this process is unclear. Here, we have imaged T cells expressing a fluorescent reporter for the activation of the interferon-γ (IFN-γ) locus during priming in lymph nodes. We have demonstrated marked differences in the efficiency of gene activation during stable T cell-dentritic cell (DC) contacts, influenced in part by signal strength. Imaging the first cell division, we have demonstrated that heterogeneity in T cell functional potential was largely apparent as T cells initiated clonal expansion. Moreover, by analyzing the fate of single activated T cells ex vivo, we have provided evidence that these early differences resulted in clonal progenies with distinct functional properties. Thus, the early set of T cell-DC interactions in lymph nodes largely contribute to the heterogeneity of T cell responses through the generation of functionally divergent clonal progenies.
Immunity 09/2010; 33(3):412-23. · 21.64 Impact Factor
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ABSTRACT: Tumor cell vaccination with irradiated autologous tumor cells is a promising approach to activate tumor-specific T cell responses without the need for tumor Ag identification. However, uptake of dying cells by dendritic cells (DCs) is generally a noninflammatory or tolerizing event to prevent the development of autoreactive immune responses. In this study, we describe the mechanisms that confer the potent T cell priming capacity of a recently identified a population of DCs (merocytic DCs [mcDCs]) that potently primes both CD8(+) and CD4(+) T cells to cell-associated Ags upon uptake of apoptotic cells. mcDCs acquired cell-associated materials through a process of merocytosis that is defined by the uptake of small particles that are stored in nonacidic compartments for prolonged periods, sustained Ag presentation, and the induction of type I IFN. T cells primed by mcDCs to cell-associated Ags exhibit increased primary expansion, enhanced effector function, and increased memory formation. By using transgenic T cell transfer models and endogenous models, we show that treatment of tumor-bearing mice with mcDCs that have been exposed to dying tumor cells results in tumor suppression and increased host survival through the activation of naive tumor-specific CD8(+) T cells as well as the reinvigoration of tumor-specific T cells that had been rendered nonresponsive by the tumor in vivo. The potent capacity of mcDCs to prime both CD4(+) and CD8(+) T cells to cell-associated Ags under immunosuppressive conditions makes this DC subset an attractive target for tumor therapies as well as interventional strategies for autoimmunity and transplantation.
The Journal of Immunology 09/2010; 185(6):3337-47. · 5.79 Impact Factor
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ABSTRACT: Understanding the mechanisms leading to effective priming of lymphocytes with regulatory properties is crucial for the manipulation of immune responses. CD8alphaalpha(+)TCRalphabeta(+) T cells are a special subset of innate-like lymphocytes that have been shown to be involved in immune regulation. These cells can recognize self-peptides in the context of a class Ib molecule, Qa-1. How self-Ags are processed in the Qa-1 pathway and presented to CD8alphaalpha(+)TCRalphabeta(+) T cells is not understood. In this study we demonstrate a cross-presentation pathway by which bone marrow-derived dendritic cells (DCs) capture apoptotic CD4(+) T cells and process and present TCR-derived peptides in the context of Qa-1 to prime CD8alphaalpha(+)TCRalphabeta(+) T cells. The priming ability of the DCs is enhanced following TLR signaling using TLR3, TLR4, and TLR9 agonists. DC-mediated cross-presentation is inhibited in the presence of endosomal and proteasomal Ag-processing antagonists. Importantly, DCs loaded with apoptotic T cells prime CD8alphaalpha(+)TCRalphabeta(+) T cells in vivo, which in turn provides protection from CD4(+) T cell-mediated autoimmune disease. These data provide a key insight related to processing and presentation of self-Ags in the Qa-1 pathway for priming of CD8alphaalpha(+)TCRalphabeta(+) T cells and have implications for a DC-based immunotherapeutic approach to inflammatory diseases.
The Journal of Immunology 07/2009; 182(11):6959-68. · 5.79 Impact Factor
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ABSTRACT: Early during infection, CMV targets dendritic cells (DC) and alters their functions. Herein we show that CMV-infected DC maintain the ability to present both virus-derived and exogenous Ags, but that they actively induce tolerance or anergy in Ag-specific T cells. CMV accomplishes this by selectively maintaining high-level expression of the negative costimulatory molecule programmed death ligand-1 (PD-L1), while commensurately down-regulating positive costimulatory molecules and MHC on the DC surface. Consequently, CD4 and CD8 T cells activated by these infected DC have a stunted phenotype, characterized by poor proliferation, effector function. and recall responses. Blocking PD-L1, but not PD-L2, during direct priming of naive T cells by infected DC significantly restores Ag-specific T cell functions. Using systems where direct and cross-priming of T cells can be distinguished revealed that PD-L1/PD-1 signaling contributes only when naive T cells are primed directly by infected DC, and not upon cross-presentation of viral Ags by uninfected DC. These data suggest that murine CMV programs infected DC during acute infection to inhibit early host adaptive antiviral responses by tipping the balance between negative and positive cosignals.
The Journal of Immunology 05/2008; 180(7):4836-47. · 5.79 Impact Factor
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ABSTRACT: T lymphocytes receive activation signals during their encounters with antigen-bearing dendritic cells (DCs) in secondary lymphoid organs. With the recent application of two-photon imaging to visualize immune responses as they happen, the dynamics of T cell-DC interactions have been dissected in several mouse models. As we are integrating the results of these new studies, we are learning that the dynamics of T cell-DC interactions are regulated by multiple immunological parameters and, most importantly, that the spatiotemporal characteristics of these cell-cell contacts encode part of the T-cell fate.
Immunological Reviews 03/2008; 221:182-7. · 11.15 Impact Factor
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Bianca R Mothé,
Barbara S Stewart,
Carla Oseroff,
Huynh-Hoa Bui,
Stephanie Stogiera, Zacarias Garcia,
Courtney Dow,
Maria Pilar Rodriguez-Carreno,
Maya Kotturi,
Valerie Pasquetto,
Jason Botten,
Shane Crotty,
Edith Janssen,
Michael J Buchmeier,
Alessandro Sette
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ABSTRACT: Activation of CD4(+) T cells helps establish and sustain CD8(+) T cell responses and is required for the effective clearance of acute infection. CD4-deficient mice are unable to control persistent infection and CD4(+) T cells are usually defective in chronic and persistent infections. We investigated the question of how persistent infection impacted pre-existing lymphocytic choriomeningitis virus (LCMV)-specific CD4(+) T cell responses. We identified class II-restricted epitopes from the entire set of open reading frames from LCMV Armstrong in BALB/c mice (H-2(d)) acutely infected with LCMV Armstrong. Of nine epitopes identified, six were restricted by I-A(d), one by I-E(d) and two were dually restricted by both I-A(d) and I-E(d) molecules. Additional experiments revealed that CD4(+) T cell responses specific for these epitopes were not generated following infection with the immunosuppressive clone 13 strain of LCMV. Most importantly, in peptide-immunized mice, established CD4(+) T cell responses to these LCMV CD4 epitopes as well as nonviral, OVA-specific responses were actively suppressed following infection with LCMV clone 13 and were undetectable within 12 days after infection, suggesting an active inhibition of established helper responses. To address this dysfunction, we performed transfer experiments using both the Smarta and OT-II systems. OT-II cells were not detected after clone 13 infection, indicating physical deletion, while Smarta cells proliferated but were unable to produce IFN-gamma, suggesting impairment of the production of this cytokine. Thus, multiple mechanisms may be involved in the impairment of helper responses in the setting of early persistent infection.
The Journal of Immunology 08/2007; 179(2):1058-67. · 5.79 Impact Factor
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ABSTRACT: The regulation of T cell-dendritic cell (DC) contacts during clonal expansion is poorly defined. Although optimal CD4 T cell responses require prolonged exposure to antigen (Ag), it is believed that stable T cell-DC interactions occur only during the first day of the activation process. Here we show that recently activated CD4 T cells are in fact fully competent for establishing contact with Ag-bearing DC. Using two-photon imaging, we found that whereas prolonged interactions between activated T cells and Ag-bearing DCs were infrequent at high T cell precursor frequency, they were readily observed for a period of at least 2 days when lower numbers of T cells were used. We provide evidence that, when present in high numbers, Ag-specific T cells still gained access to the DC surface but were competing for the limited number of sites on DCs with sufficient peptide-MHC complexes for the establishment of a long-lived interaction. Consistent with these findings, we showed that restoration of peptide-MHC level on DCs at late time points was sufficient to recover interactions between activated T cells and DCs. Thus, the period during which CD4 T cells continue to establish stable interactions with DCs is longer than previously thought, and its duration is dictated by both Ag levels and T cell numbers, providing a feedback mechanism for the termination of CD4 T cell responses.
Proceedings of the National Academy of Sciences 04/2007; 104(11):4553-8. · 9.68 Impact Factor
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ABSTRACT: In order to evaluate the permanent chromatin remodeling in plant allowing their high developmental plasticity, three sugarbeet cell lines (Beta vulgaris L. altissima) originating from the same mother plant and exhibiting graduate states of differentiation were analyzed. Cell differentiation has been estimated by the cell redox state characterized by 36 biochemical parameters as reactive oxygen species steady-state levels, peroxidation product contents and enzymatic or non-enzymatic protective systems. Chromatin remodeling has been estimated by the measurement of levels of DNA methylation, histone acetylation and corresponding enzyme activities that were shown to differ between cell lines. Furthermore, distinct loci related to proteins involved in cell cycle, gene expression regulation and cell redox state were shown by restriction landmark genome scanning or bisulfite sequencing to display differential methylation states in relation to the morphogenic capacity of the lines. DNA methylating, demethylating and/or histone acetylating treatments allowed to generate a collection of sugarbeet cell lines differing by their phenotypes (from organogenic to dedifferentiated), methylcytosine percentages (from 15.0 to 43.5%) and acetylated histone ratios (from 0.37 to 0.52). Correlations between methylcytosine or acetylated histone contents and levels of various parameters (23 or 7, respectively, out of 36) of the cell redox state could be established. These data lead to the identification of biomarkers of sugarbeet morphogenesis in vitro under epigenetic regulation and provide evidence for a connection between plant morphogenesis in vitro, cell redox state and epigenetic mechanisms.
Planta 10/2006; 224(4):812-27. · 3.00 Impact Factor
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ABSTRACT: The cellular orchestration underlying help provided by CD4 T lymphocytes to CD8 T cell responses is not fully understood. We documented that the formation of three-cell clusters occurred as soon as day 1 and relied on long-lasting CD4 and CD8 T cell interactions with dendritic cells (DCs). The influence of CD4 help on CD8 T cell differentiation could be observed as early as the second round of cell division. Importantly, our results identify a new facet to the phenomenon of CD4 help in which DCs, upon cognate interactions with CD4 T cells, increase their ability to attract/retain Ag-specific CD8 T cells. Our results support a model in which CD4 help operates rapidly, in part by favoring CD8 T cells recruitment around those DCs that are the most competent for priming.
The Journal of Immunology 09/2006; 177(3):1406-10. · 5.79 Impact Factor
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ABSTRACT: The cellular mode of T cell priming in vivo remains to be characterized fully. We investigated the fate of T cell-dendritic cell (DC) interactions in the late phase of T cell activation in the lymph node. In general, CD4 T cells detach from DCs before undergoing cell division. Using a new approach to track the history of antigen (Ag)-recognition events, we demonstrated that activated/divided T cells reengage different DCs in an Ag-specific manner. Two-photon imaging of intact lymph nodes suggested that T cells could establish prolonged interactions with DCs at multiple stages during the activation process. Importantly, signals that are delivered during subsequent DC contacts are integrated by the T cell and promote sustained IL-2Ralpha expression and IFN-gamma production. Thus, repeated encounters with Ag-bearing DCs can occur in vivo and modulate CD4 T cell differentiation programs.
Journal of Experimental Medicine 12/2005; 202(9):1271-8. · 13.85 Impact Factor
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ABSTRACT: The lineage relationships of central-memory T cells (T(CM)) cells and effector-memory T cells (T(EM)), as well as their homeostasis and recall capacities, are still controversial. We investigated these issues in a murine model using two complementary approaches: T cell receptor repertoire analysis and adoptive transfer experiments of purified H-Y-specific T(CM) and T(EM) populations. Repertoire studies showed that approximately two thirds of T(CM) and T(EM) clones derived from a common naive precursor, whereas the other third was distinct. Both approaches highlighted that T(CM) and T(EM) had drastically distinct behaviors in vivo, both in the absence of antigen or upon restimulation. T(CM) clones were stable in the absence of restimulation and mounted a potent and sustained recall response upon secondary challenge, giving rise to both T(CM) and T(EM), although only a fraction of T(CM) generated T(EM). In contrast, T(EM) persisted for only a short time in the absence of antigen and, although a fraction of them were able to express CD62L, they were unable to mount a proliferative response upon secondary challenge in this model.
Journal of Experimental Medicine 03/2005; 201(4):579-90. · 13.85 Impact Factor
