Antigen-bearing Dendritic Cells Research Articles

Chemokine CCL19 promotes type 2 helper T cell differentiation and allergic airway inflammation

Abstract Allergic asthma is largely driven by the actions of allergen-specific CD4 +type 2 T helper (Th2) cells. Following allergen inhalation, these cells are induced by the interaction of naïve CD4 +T cells with antigen-bearing dendritic cells (DCs) in lung-draining lymph nodes (LNs). The molecular mechanisms underlying the induction of T helper cells have been well studied and include the migration of allergen-bearing DCs from the lung to regional LNs in a manner dependent on the chemokine receptor, CCR7. Previous studies have demonstrated that CCL21, a CCR7 ligand, is required for the accumulation of naïve T cells and activated DCs in the LNs, but the function of another ligand, CCL19, has been unknown. In the present study, we investigated the role of CCL19 in allergic airway inflammation using CCL19-deficient mice. In a mouse model of asthma, eosinophils and lymphocytes were significantly reduced in airways of CCL19-deficient mice compared with those of wildtype (WT) animals, and production of IL-4 and IL-13 in the lung was significantly diminished, suggesting that CCL19 is required for type 2 immune responses. Co-cultures of naïve WT CD4 +T cells with CCL19-deficient DCs produced less type 2 cytokines than did T cells co-cultured with WT DCs. Further, fibroblastic reticular cells (FRCs) from CCL19-deficient mouse LNs produced less Th2 cytokine production compared with WT FRCs. Addition of recombinant CCL19 to the culture of naïve CD4 +T cells increased phosphorylation of STAT5 and gene expression of Il2, Il2ra, Il2rb, Il2rg, Sta5a, Stat5b and Stat6. Together, our findings suggest that CCL19 produced by DCs and FRCs promotes Th2 differentiation through the activation of STAT5-signaling, and that this promotes allergic airway inflammation. This work was supported by Intramural Research Program of NIEHS, NIH (ZIA ES102025-09).

CCL5-producing migratory dendritic cells guide CCR5+ monocytes into the draining lymph nodes.

Dendritic cells (DCs) and monocytes capture, transport, and present antigen to cognate T cells in the draining lymph nodes (LNs) in a CCR7-dependent manner. Since only migratory DCs express this chemokine receptor, it is unclear how monocytes reach the LN. In steady-state and following inhalation of several PAMPs, scRNA-seq identified LN mononuclear phagocytes as monocytes, resident, or migratory type 1 and type 2 conventional (c)DCs, despite the downregulation of Xcr1, Clec9a, H2-Ab1, Sirpa, and Clec10a transcripts on migratory cDCs. Migratory cDCs, however, upregulated Ccr7, Ccl17, Ccl22, and Ccl5. Migratory monocytes expressed Ccr5, a high-affinity receptor for Ccl5. Using two tracking methods, we observed that both CD88hiCD26lomonocytes and CD88-CD26hi cDCs captured inhaled antigens in the lung and migrated to LNs. Antigen exposure in mixed-chimeric Ccl5-, Ccr2-, Ccr5-, Ccr7-, and Batf3-deficient mice demonstrated that while antigen-bearing DCs use CCR7 to reach the LN, monocytes use CCR5 to follow CCL5-secreting migratory cDCs into the LN, where they regulate DC-mediated immunity.

Heparin Specifically Interacts with Basic BBXB Motifs of the Chemokine CCL21 to Define CCR7 Signaling.

Chemokines are critically involved in controlling directed leukocyte migration. Spatiotemporal secretion together with local retention processes establish and maintain local chemokine gradients that guide directional cell migration. Extracellular matrix proteins, particularly glycosaminoglycans (GAGs), locally retain chemokines through electrochemical interactions. The two chemokines CCL19 and CCL21 guide CCR7-expressing leukocytes, such as antigen-bearing dendritic cells and T lymphocytes, to draining lymph nodes to initiate adaptive immune responses. CCL21-in contrast to CCL19-is characterized by a unique extended C-terminus composed of highly charged residues to facilitate interactions with GAGs. Notably, both chemokines can trigger common, but also ligand-biased signaling through the same receptor. The underlying molecular mechanism of ligand-biased CCR7 signaling is poorly understood. Using a series of naturally occurring chemokine variants in combination with newly designed site-specific chemokine mutants, we herein assessed CCR7 signaling, as well as GAG interactions. We demonstrate that the charged chemokine C-terminus does not fully confer CCL21-biased CCR7 signaling. Besides the positively charged C-terminus, CCL21 also possesses specific BBXB motifs comprising basic amino acids. We show that CCL21 variants where individual BBXB motifs are mutated retain their capability to trigger G-protein-dependent CCR7 signaling, but lose their ability to interact with heparin. Moreover, we show that heparin specifically interacts with CCL21, but not with CCL19, and thereby competes with ligand-binding to CCR7 and prevents signaling. Hence, we provide evidence that soluble heparin, but not the other GAGs, complexes with CCL21 to define CCR7 signaling in a ligand-dependent manner.

Motility Dynamics of T Cells in Tumor-Draining Lymph Nodes: A Rational Indicator of Antitumor Response and Immune Checkpoint Blockade.

Simple SummaryImmune checkpoint blockade (ICB) therapies are attracting much attention for the clinical treatment of tumors. Combination therapies are being developed to enhance the effects of ICBs, and the importance of tumor-draining lymph nodes (TDLNs) has been reevaluated in antitumor responses via ICB therapy. The migration and motility status of T cells and their functional interaction with antigen-bearing dendritic cells are key factors for inducing adaptive immunity in LNs. Although immune checkpoint molecules are known to regulate T cell motility, their actual influence on T cell dynamics in TDLNs, particularly in ICBs, is poorly understood. In this review, we summarize the relevance of T cell dynamics and immune responses in draining LNs, and discuss the alteration of T cell motility under ICB. To develop better immunotherapies using ICBs, studying T cell dynamics in TDLNs can provide a good indicator to evaluate the efficacy of antitumor therapy.The migration status of T cells within the densely packed tissue environment of lymph nodes reflects the ongoing activation state of adaptive immune responses. Upon encountering antigen-presenting dendritic cells, actively migrating T cells that are specific to cognate antigens slow down and are eventually arrested on dendritic cells to form immunological synapses. This dynamic transition of T cell motility is a fundamental strategy for the efficient scanning of antigens, followed by obtaining the adequate activation signals. After receiving antigenic stimuli, T cells begin to proliferate, and the expression of immunoregulatory receptors (such as CTLA-4 and PD-1) is induced on their surface. Recent findings have revealed that these ‘immune checkpoint’ molecules control the activation as well as motility of T cells in various situations. Therefore, the outcome of tumor immunotherapy using checkpoint inhibitors is assumed to be closely related to the alteration of T cell motility, particularly in tumor-draining lymph nodes (TDLNs). In this review, we discuss the migration dynamics of T cells during their activation in TDLNs, and the roles of checkpoint molecules in T cell motility, to provide some insight into the effect of tumor immunotherapy via checkpoint blockade, in terms of T cell dynamics and the importance of TDLNs.

Discordant requirements for CD11c+ APCs in priming CD8 T cell responses against H-2Kb versus H-2Db restricted TMEV-associated peptides

Abstract CD8 T cell priming after viral infection of the central nervous system (CNS) is incompletely understood. In peripheral infections, T cell priming generally relies upon stimulation by antigen-bearing dendritic cells (DCs) migrating into draining lymph nodes. The parenchyma of the brain, however, is largely devoid of dendritic cells and evidence demonstrating that activated DCs leave the brain parenchyma is lacking. We therefore sought to understand the role of DCs and specific MHC class I molecules in priming CD8 T cells following CNS infection. We employed H-2Db−/− H-2Kb−/− (MHC-I deficient) mice that express a floxed H-2Db or floxed Kb molecule, a unique transgenic mouse system developed by our research program. Crossed with an MHC class I deficient CD11c-Cre expressing animal results in DC-specific ablation of Db or Kb Class I restricted antigen presentation ability. We found that CD11c+ APCs are critical for the early priming of CD8 T cells against the Db restricted VP2121–130 epitope of the model pathogen, TMEV. However, DCs are ultimately dispensable for long-term development of these antigen specific T cells. Discordantly, the loss of MHC class I restricted antigen presentation ability on CD11c+ APCs does not impact the priming of T cells against the H-2Kb restricted OVA257–264 epitope following intracranial TMEV-OVA infection, but does impact the ability of these T cells to successfully occupy the CNS. This work suggests that differing patterns of MHC class I restriction for CNS pathogen-derived epitopes might have functional consequences on the APC requirements for a successful CD8 T cell response against neurotropic viruses.

Marshallagia marshalli Antigen Strengthens Dendritic Cell Medi-ated T Lymphocyte Regulation on Asthmatic Patients

The current study was conducted to investigate the antigenic effect of Marshallagia marshalli on the treatment of asthma by measuring the secreted inhibitory cytokine. Case patients and controls were selected from clinics in Mashhad, Khorasan Razavi Province, Northeastern Iran in 2017-18. In this experimental study, peripheral blood mononuclear cells (PBMCs) were isolated from 15 patients with asthma and 10 healthy controls and were cultured. PBMCs were then converted to tolerogenic DCs through exposure to GM-CSF, IL-4 and M. marshalli antigen. Then, tolerogenic DCs were exposed to autologous T cells for five days and finally, the level of secreted TGF-β1 was measured. The mean TGF-β1 level in the control and control groups was 210.2 ± 8.2 and 225.4 ± 6.1 pq/ml, respectively. The results showed that TGF-β1 levels in both groups significantly increased in both groups (P<0.001). In addition, TGF-β1 levels in the case group were significantly higher than the control group (P<0.001). M. marshalli antigen increase the level of TGF-β1 and can create antigen-bearing dendritic cells and shift T lymphocytes to the regulatory type. This parasite can be used in dendritic cell therapy to control allergic diseases.

Mouse CD8+NKT-like cells exert dual cytotoxicity against mouse tumor cells and myeloid-derived suppressor cells

Our previous work has demonstrated the high efficiency of CD8+ natural killer T (NKT)-like cells in killing antigen-bearing dendritic cells. To evaluate their role in the tumor microenvironment, we performed in vitro and in vivo antitumor experiments to investigate whether CD8+NKT-like cells could kill Yac-1 and B16 cells like NK cells and kill EL4-OVA8 cells in an antigen-specific manner like cytotoxic T lymphocytes (CTLs). Unlike NK1.1−CTLs, CD8+NKT-like cells also exhibit the capability to kill myeloid-derived suppressor cells (MDSCs) in an antigen-specific manner, indicative of their potential role in clearing tumor antigen-bearing MDSCs to improve the antitumor microenvironment. In vitro blocking experiments showed that granzyme B inhibitor efficiently suppressed the cytotoxicity of CD8+NKT-like cells against tumor cells and MDSCs, while Fas ligand (FasL) or tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) inhibition failed to produce similar effects. Transcriptomic and phenotypic analyses of CD8+NKT-like cells, NK cells, and NK1.1−CTLs indicated that CD8+NKT-like cells expressed both T-cell activation markers and NK cell markers, thus bearing features of both the activated T cells and NK cells. Taken together, CD8+NKT-like cells could exert NK- and CTL-like antitumor effects through the elimination of both tumor cells and MDSCs in a granzyme B-dependent manner.

Role of T Cell-To-Dendritic Cell Chemoattraction in T Cell Priming Initiation in the Lymph Node: An Agent-Based Modeling Study.

The adaptive immune response is initiated in lymph nodes by contact between antigen-bearing dendritic cells (DCs) and antigen-specific T cells. A selected number of naïve T cells that recognize a specific antigen may proliferate into expanded clones, differentiate, and acquire an effector phenotype. Despite growing experimental knowledge, certain mechanistic aspects of T cell behavior in lymph nodes remain poorly understood. Computational modeling approaches may help in addressing such gaps. Here we introduce an agent-based model describing T cell movements and their interactions with DCs, leading to activation and expansion of cognate T cell clones, in a two-dimensional representation of the lymph node paracortex. The primary objective was to test the putative role of T cell chemotaxis toward DCs, and quantitatively assess the impact of chemotaxis with respect to T cell priming efficacy. Firstly, we evaluated whether chemotaxis of naïve T cells toward a nearest DC may accelerate the scanning process, by quantifying, through simulations, the number of unique T cell—DC contact events. We demonstrate that, in the presence of naïve T cell-to-DC chemoattraction, a higher total number of contacts occurs, as compared to a T cell random walk scenario. However, the forming swarm of naïve T cells, as these cells get attracted to the neighborhood of a DC, may then physically restrict access of additional T cells to the DC, leading to an actual decrease in the cumulative number of unique contacts between naïve T cells and DCs. Secondly, we investigated the potential role of chemotaxis in maintaining cognate T cell clone expansion. The time course of cognate T cells number in the system was used as a quantitative characteristic of the expansion. Model-based simulations indicate that inclusion of chemotaxis, which is selective for already activated (but not naïve) antigen-specific T cells, may strongly accelerate the time of immune response occurrence, which subsequently increases the overall amplitude of the T cell clone expansion process.

Percutaneous sensitization is limited by in situ inhibition of cutaneous dendritic cell migration through skin-resident regulatory T cells

Percutaneous sensitization is associated with various allergic diseases, including asthma and food allergies. However, the immunologic mechanisms underlying how the skin regulates percutaneous sensitization are still unclear. We aimed to investigate whether and how CD4+Foxp3+ regulatory T (Treg) cells residing in the skin regulate percutaneous sensitization in the skin. Selective reduction of numbers of cutaneous Treg cells was achieved by means of intradermal injection of diphtheria toxin into the ear skin of Foxp3DTR mice, in which Treg cells specifically express the diphtheria toxin receptor fused with green fluorescent protein. Thirty percent to 40% of cutaneous Treg cells were capable of IL-10 production in both mice and human subjects. Selective reduction of cutaneous Treg cells at the sensitization site promoted migration of antigen-bearing dendritic cells (DCs) to the draining lymph nodes (dLNs). Accordingly, sensitization through the skin with reduced numbers of Treg cells led to enhanced antigen-specific immune responses in the dLNs, including both effector T-cell differentiation and T cell-dependent B-cell responses, such as the development of germinal center B cells expressing IgG1 and IgE. Furthermore, antigen-bearing cutaneous DC migration was enhanced in mice with IL-10 deficiency restricted to the cutaneous Treg cell compartment, suggesting an important role of cutaneous IL-10+ Treg cells in limiting percutaneous sensitization. Treg cells with a skin-homing phenotype in skin dLNs expressed high levels of IL-10, suggesting that they contribute to renewal and maintenance of the cutaneous IL-10+ Treg cell population. Skin-resident Treg cells limit percutaneous sensitization by suppressing antigen-bearing DC migration through in situ IL-10 production.

Engineering of Nanobodies Recognizing the Human Chemokine Receptor CCR7.

The chemokine receptor CCR7 plays a pivotal role in health and disease. In particular, CCR7 controls homing of antigen-bearing dendritic cells and T cells to lymph nodes, where adaptive immune responses are initiated. However, CCR7 also guides T cells to inflamed synovium and thereby contributes to rheumatoid arthritis and promotes cancer cell migration and metastasis formation. Nanobodies have recently emerged as versatile tools to study G-protein-coupled receptor functions and are being tested in diagnostics and therapeutics. In this study, we designed a strategy to engineer novel nanobodies recognizing human CCR7. We generated a nanobody library based on a solved crystal structure of the nanobody Nb80 recognizing the β2-adrenergic receptor (β2AR) and by specifically randomizing two segments within complementarity determining region 1 (CDR1) and CDR3 of Nb80 known to interact with β2AR. We fused the nanobody library to one half of split-YFP in order to identify individual nanobody clones interacting with CCR7 fused to the other half of split-YFP using bimolecular fluorescence complementation. We present three novel nanobodies, termed Nb1, Nb5, and Nb38, that recognize human CCR7 without interfering with G-protein-coupling and downstream signaling. Moreover, we were able to follow CCR7 trafficking upon CCL19 triggering using Nb1, Nb5, and Nb38.

Type 1 alveolar epithelial cell-derived chemokine CCL19 promotes airway inflammation

Abstract Allergic asthma is largely driven by the actions of allergen-specific CD4+T helper cells. Following allergen inhalation, these cells are induced by the interaction of naïve CD4+ T cells with antigen-bearing dendritic cells (DCs) in lung-draining lymph nodes. The molecular mechanisms underlying the induction of T helper cells have been well studied, and include the migration of allergen-bearing DCs to lung-draining lymph nodes in a manner dependent on the chemokine receptor, CCR7. However, comparatively little is known regarding how these effector T cells become activated following their subsequent encounter with allergen in the lung. This knowledge would be useful in the design of novel therapies for asthma, especially for neutrophilic asthma, which is refractory to inhaled glucocorticoids. We recently noticed that lung DCs migrating to lymph nodes originate from the large airways, whereas DCs associated with small airways, parenchyma and subpleural areas are non-migratory. Video confocal analysis of precision cut lung slices revealed that these non-migratory DCs form tight interactions with OVA-specific T cells and stimulate T cell receptor signaling, as measured by activation of a Nur77-gfpreporter gene. Furthermore, Ccl19, which encodes a CCR7-ligand, is highly expressed by type 1 alveolar epithelial cells, and in mouse model of asthma, airway inflammation was significantly diminished in CCL19-deficient mice compared with WT mice. Together, our findings suggest that CCL19 produced by type I epithelial cells acts to position lung DCs in the distal area of the lung where they interact with effector T cells, thereby promoting allergic airway inflammation.

Dendritic Cells and T Cells Interact Within Murine Afferent Lymphatic Capillaries.

Afferent lymphatic vessels contribute to immunity by transporting antigen and leukocytes to draining lymph nodes (LNs) and are emerging as new players in the regulation of peripheral tolerance. Performing intravital microscopy in inflamed murine ear skin we found that migrating dendritic cells (DCs) and antigen-experienced effector T cells spend considerable time arresting or clustering within afferent lymphatic capillaries. We also observed that intralymphatic T cells frequently interacted with DCs. When imaging polyclonal T cells during an ongoing contact-hypersensitivity response, most intralymphatic DC-T cell interactions were short-lived. Conversely, during a delayed-type-hypersensitivity response, cognate antigen-bearing DCs engaged in long-lived MHCII-(I-A/I-E)-dependent interactions with antigen-specific T cells. Long-lived intralymphatic DC-T cell interactions reduced the speed of DC crawling but did not delay overall DC migration to draining LNs. While further consequences of these intralymphatic interactions still need to be explored, our findings suggest that lymphatic capillaries represent a unique compartment in which adaptive immune interaction and modulation occur.

Histone deacetylase 6 inhibitor enhances resistance to Mycobacterium tuberculosis infection through innate and adaptive immunity in mice.

Interleukin (IL)-10 plays a key role in immune response following mycobacterial infection, which can be inhibited by histone deacetylase (HDAC) 6. In this study, we explored whether Tubastatin A, a HDAC6 inhibitor, could enhance immune response and restrain mycobacterial growth. We established a mouse model using attenuated Mycobacterium tuberculosis (M.tbH37Ra) infection. The growth of mycobacteria was evaluated using colony form unit assays. Immune response statues were investigated using flow cytometry. Chromatin immunoprecipitation was used to study the influence of HDAC6 on IL10 transcription. Tubastatin A significantly inhibited the growth of M.tbH37Ra in the lungs of mice. In parallel, the levels of tumor necrosis factor-α, IL-12p40 and interferon-γ were up-regulated, while the level of IL-10 was down-regulated. Tubastatin A accelerated the delayed innate cellular immune response by recruiting more macrophages, dendritic cells (DCs) and neutrophils into the lungs. More antigen-bearing DCs and primed Th1 cells were observed in the draining lymph nodes in mice treated with Tubastatin A. Tubastatin A reduced HDCA6 recruitment on IL10 promoter. Tubastatin A enhanced innate and adaptive immune responses against the mycobacteria by suppressing IL-10 expression and consequently delayed mycobacterial growth. The experiments were extended to the H37Rv strain on the insistence of the Editor.

Priming of dendritic cells by DNA-containing extracellular vesicles from activated T cells through antigen-driven contacts

Interaction of T cell with antigen-bearing dendritic cells (DC) results in T cell activation, but whether this interaction has physiological consequences on DC function is largely unexplored. Here we show that when antigen-bearing DCs contact T cells, DCs initiate anti-pathogenic programs. Signals of this interaction are transmitted from the T cell to the DC, through extracellular vesicles (EV) that contain genomic and mitochondrial DNA, to induce antiviral responses via the cGAS/STING cytosolic DNA-sensing pathway and expression of IRF3-dependent interferon regulated genes. Moreover, EV-treated DCs are more resistant to subsequent viral infections. In summary, our results show that T cells prime DCs through the transfer of exosomal DNA, supporting a specific role for antigen-dependent contacts in conferring protection to DCs against pathogen infection. The reciprocal communication between innate and adaptive immune cells thus allow efficacious responses to unknown threats.

Toll-Like Receptor 4, but Not Neutrophil Extracellular Traps, Promote IFN Type I Expression to Enhance Th2 Responses to Nippostrongylus brasiliensis.

The induction of Th2 responses is thought to be multifactorial, and emerge from specific pathways distinct from those associated with antagonistic antibacterial or antiviral Th1 responses. Here, we show that the recognition of non-viable Nippostrongylus brasiliensis (Nb) in the skin induces a strong recruitment of monocytes and neutrophils and the release of neutrophil extracellular traps (NETs). Nb also activates toll-like receptor 4 (TLR4) signaling with expression of Ifnb transcripts in the skin and the development of an IFN type I signature on helminth antigen-bearing dendritic cells in draining lymph nodes. Co-injection of Nb together with about 10,000 Gram-negative bacteria amplified this TLR4-dependent but NET-independent IFN type I response and enhanced the development of Th2 responses. Thus, a limited activation of antibacterial signaling pathways is able to boost antihelminthic responses, suggesting a role for bacterial sensing in the optimal induction of Th2 immunity.

Persistence and Adaptation in Immunity: T Cells Balance the Extent and Thoroughness of Search.

Effective search strategies have evolved in many biological systems, including the immune system. T cells are key effectors of the immune response, required for clearance of pathogenic infection. T cell activation requires that T cells encounter antigen-bearing dendritic cells within lymph nodes, thus, T cell search patterns within lymph nodes may be a crucial determinant of how quickly a T cell immune response can be initiated. Previous work suggests that T cell motion in the lymph node is similar to a Brownian random walk, however, no detailed analysis has definitively shown whether T cell movement is consistent with Brownian motion. Here, we provide a precise description of T cell motility in lymph nodes and a computational model that demonstrates how motility impacts T cell search efficiency. We find that both Brownian and Lévy walks fail to capture the complexity of T cell motion. Instead, T cell movement is better described as a correlated random walk with a heavy-tailed distribution of step lengths. Using computer simulations, we identify three distinct factors that contribute to increasing T cell search efficiency: 1) a lognormal distribution of step lengths, 2) motion that is directionally persistent over short time scales, and 3) heterogeneity in movement patterns. Furthermore, we show that T cells move differently in specific frequently visited locations that we call “hotspots” within lymph nodes, suggesting that T cells change their movement in response to the lymph node environment. Our results show that like foraging animals, T cells adapt to environmental cues, suggesting that adaption is a fundamental feature of biological search.

Skin tumor immunity: Site does matter for antigen presentation by DCs.

The immune system has the ability to specifically identify and eliminate tumors, but the underlying mechanisms responsible for this phenomenon are not fully understood. A study published in this issue of the European Journal of Immunology now provides new insights into this important problem. Joncker et al. [Eur. J. Immunol. 2016. 46: 609-618] show that the timely mobilization of tumor antigen-bearing dendritic cells (DCs) from the periphery to the lymph nodes is critical for effective antitumor T-cell immunity, and that DCs present tumor antigens much more efficiently when encountered in the skin rather than in the subcutaneous tissues.

CCR7 Controls Thymus Recirculation, but Not Production and Emigration, of Foxp3(+) T Cells.

SummaryCurrent models of Foxp3+ regulatory T cell (Treg) development involve CCR7-mediated migration of thymocytes into the thymus medulla to enable essential interactions with medullary epithelium. However, increased Foxp3+ thymic Treg numbers in Ccr7−/− mice challenge this view, and the role of CCR7 in Treg development, emigration, and/or recirculation is unknown. Here, we have examined CCR7 and Rag2pGFP levels during Treg development and generated Rag2pGFPCcr7−/− mice to study its impact on the intrathymic Treg pool. We reveal surprising developmental heterogeneity in thymocytes described as Treg precursors, showing that they contain recirculating CCR6+CCR7−Rag2pGFP− T cells. Although CCR7 defines bona fide Rag2GFP+ Treg precursors, it is not required for Treg production and emigration. Rather, we show that lack of CCR7 renders the thymus more receptive to Treg thymus homing. Our study reveals a role for CCR7 in limiting Treg recirculation back to the thymus and enables separation of the mechanisms controlling Treg production and thymic recirculation.

Thymic regulatory T cell niche size is dictated by limiting IL-2 from antigen-bearing dendritic cells and feedback competition.

Thymic regulatory T (Treg) cell production requires interleukin 2 (IL-2) and agonist TCR ligands, and is controlled by competition for a limited developmental niche, but the thymic sources of IL-2 and the factors that limit access to the niche are poorly understood. Here we show that IL-2 produced by antigen-bearing dendritic cells plays a key role in Treg cell development, and that existing Treg cells limit new Treg cell development by competing for IL-2. . Our data suggest that antigen-presenting cells that can provide both IL-2 and a TCR ligand comprise the thymic niche, and that competition by existing Treg cells for a limited supply of IL-2 provides negative feedback for new Treg cell production.

Vaginal type-II mucosa is an inductive site for primary CD8⁺ T-cell mucosal immunity.

The structured lymphoid tissues are considered the only inductive sites where primary T cell immune responses occur. The naïve T cells in structured lymphoid tissues, once being primed by antigen -bearing dendritic cells, differentiate into memory T cells and traffic back to the mucosal sites through the bloodstream. Contrary to this belief, here we show that the vaginal type-II mucosa itself, despite lack of structured lymphoid tissues, can act as an inductive site during primary CD8+ T cell immune responses. We provide evidence that the vaginal mucosa supports both the local immune priming of naïve CD8+ T cells and the local expansion of antigen-specific CD8+ T cells, thereby demonstrating a different paradigm for primary mucosal T cell immune induction.