Diversity of gamma delta T-cell receptors on murine intestinal intra-epithelial lymphocytes

Interplay between Microbiota and γδ T Cells: Insights into Immune Homeostasis and Neuro-Immune Interactions

The gastrointestinal (GI) tract of multicellular organisms, especially mammals, harbors a symbiotic commensal microbiota with diverse microorganisms including bacteria, fungi, viruses, and other microbial and eukaryotic species. This microbiota exerts an important role on intestinal function and contributes to host health. The microbiota, while benefiting from a nourishing environment, is involved in the development, metabolism and immunity of the host, contributing to the maintenance of homeostasis in the GI tract. The immune system orchestrates the maintenance of key features of host-microbe symbiosis via a unique immunological network that populates the intestinal wall with different immune cell populations. Intestinal epithelium contains lymphocytes in the intraepithelial (IEL) space between the tight junctions and the basal membrane of the gut epithelium. IELs are mostly CD8+ T cells, with the great majority of them expressing the CD8αα homodimer, and the γδ T cell receptor (TCR) instead of the αβ TCR expressed on conventional T cells. γδ T cells play a significant role in immune surveillance and tissue maintenance. This review provides an overview of how the microbiota regulates γδ T cells and the influence of microbiota-derived metabolites on γδ T cell responses, highlighting their impact on immune homeostasis. It also discusses intestinal neuro-immune regulation and how γδ T cells possess the ability to interact with both the microbiota and brain.

Expansion of MAIT cells in the combined absence of NKT and γδ-T cells

Mucosal-associated invariant T (MAIT) cells, natural killer T (NKT) cells, and γδT cells are collectively referred to as 'unconventional T cells' due to their recognition of non-peptide antigens and restriction to MHC-I-like molecules. However, the factors controlling their widely variable frequencies between individuals and organs are poorly understood. We demonstrated that MAIT cells are increased in NKT or γδT cell-deficient mice and highly expand in mice lacking both cell types. TCRα repertoire analysis of γδT cell-deficient thymocytes revealed altered Trav segment usage relative to wild-type thymocytes, highlighting retention of the Tcra-Tcrd locus from the 129 mouse strain used to generate Tcrd-/- mice. This resulted in a moderate increase in distal Trav segment usage, including Trav1, potentially contributing to increased generation of Trav1-Traj33+ MAIT cells in the Tcrd-/- thymus. Importantly, adoptively transferred MAIT cells underwent increased homeostatic proliferation within NKT/gdT cell-deficient tissues, with MAIT cell subsets exhibiting tissue-specific homing patterns. Our data reveal a shared niche for unconventional T cells, where competition for common factors may be exploited to collectively modulate these cells in the immune response. Lastly, our findings emphasise careful assessment of studies using NKT or γδT cell-deficient mice when investigating the role of unconventional T cells in disease.

The intestinal γδ T cells: functions in the gut and in the distant organs

Located in the frontline against the largest population of microbiota, the intestinal mucosa of mammals has evolved to become an effective immune system. γδ T cells, a unique T cell subpopulation, are rare in circulation blood and lymphoid tissues, but rich in the intestinal mucosa, particularly in the epithelium. Via rapid production of cytokines and growth factors, intestinal γδ T cells are key contributors to epithelial homeostasis and immune surveillance of infection. Intriguingly, recent studies have revealed that the intestinal γδ T cells may play novel exciting functions ranging from epithelial plasticity and remodeling in response to carbohydrate diets to the recovery of ischemic stroke. In this review article, we update regulatory molecules newly defined in lymphopoiesis of the intestinal γδ T cells and their novel functions locally in the intestinal mucosa, such as epithelial remodeling, and distantly in pathological setting, e.g., ischemic brain injury repair, psychosocial stress responses, and fracture repair. The challenges and potential revenues in intestinal γδ T cell studies are discussed.

Divergent roles for the gut intraepithelial lymphocyte GLP-1R in control of metabolism, microbiota, and T cell-induced inflammation

Gut intraepithelial lymphocytes (IELs) are thought to calibrate glucagon-like peptide 1 (GLP-1) bioavailability, thereby regulating systemic glucose and lipid metabolism. Here, we show that the gut IEL GLP-1 receptor (GLP-1R) is not required for enteroendocrine L cell GLP-1 secretion and glucose homeostasis nor for the metabolic benefits of GLP-1R agonists (GLP-1RAs). Instead, the gut IEL GLP-1R is essential for the full effects of GLP-1RAs on gut microbiota. Moreover, independent of glucose control or weight loss, the anti-inflammatory actions of GLP-1RAs require the gut IEL GLP-1R to selectively restrain local and systemic T cell-induced, but not lipopolysaccharide-induced, inflammation. Such effects are mediated by the suppression of gut IEL effector functions linked to the dampening of proximal T cell receptor signaling in a protein-kinase-A-dependent manner. These data reposition key roles of the L cell-gut IEL GLP-1R axis, revealing mechanisms linking GLP-1R activation in gut IELs to modulation of microbiota composition and control of intestinal and systemic inflammation.

Comparing Mouse and Human Tissue-Resident γδ T Cells

Circulating immune cell compartments have been extensively studied for decades, but limited access to peripheral tissue and cell yield have hampered our understanding of tissue-based immunity, especially in γδ T cells. γδ T cells are a unique subset of T cells that are rare in secondary lymphoid organs, but enriched in many peripheral tissues including the skin, uterus, and other epithelial tissues. In addition to immune surveillance activities, recent reports have revealed exciting new roles for γδ T cells in homeostatic tissue physiology in mice and humans. It is therefore important to investigate to what extent the developmental rules described using mouse models transfer to human γδ T cells. Besides, it will be necessary to understand the differences in the development and biogenesis of human and mouse γδ T cells; to understand how γδ T cells are maintained in physiological and pathological circumstances within different tissues, as well as characterize the progenitors of different tissue-resident γδ T cells. Here, we summarize current knowledge of the γδ T phenotype in various tissues in mice and humans, describing the similarities and differences of tissue-resident γδ T cells in mice and humans.

Three Layers of Intestinal γδ T Cells Talk Different Languages With the Microbiota

The mucosal surfaces of our body are the main contact site where the immune system encounters non-self molecules from food-derived antigens, pathogens, and symbiotic bacteria. γδ T cells are one of the most abundant populations in the gut. Firstly, they include intestinal intraepithelial lymphocytes, which screen and maintain the intestinal barrier integrity in close contact with the epithelium. A second layer of intestinal γδ T cells is found among lamina propria lymphocytes (LPL)s. These γδ LPLs are able to produce IL-17 and likely have functional overlap with local Th17 cells and innate lymphoid cells. In addition, a third population of γδ T cells resides within the Peyer´s patches, where it is probably involved in antigen presentation and supports the mucosal humoral immunity. Current obstacles in understanding γδ T cells in the gut include the lack of information on cognate ligands of the γδ TCR and an incomplete understanding of their physiological role. In this review, we summarize and discuss what is known about different subpopulations of γδ T cells in the murine and human gut and we discuss their interactions with the gut microbiota in the context of homeostasis and pathogenic infections.

GVHD, IBD and primary immunodeficiencies: The gut as a target of immunopathology resulting from impaired immunity

The intestinal tract is the largest immunological organ in the body and has a central function of regulating local immune responses, as the intestinal epithelial barrier is a location where the immune system interacts with the gut microbiome including bacteria, fungi and viruses. Impaired immunity in the intestinal tract can lead to immunopathology, which manifests in different diseases such as inflammatory bowel disease (IBD) or intestinal graft-versus-host disease (GVHD). A disturbed communication between epithelial cells, immune cells and microbiome will shape pathogenic immune responses to antigens, which need to be counterbalanced by tolerogenic mechanisms and repair mechanisms. Here, we review how impaired intestinal immune function leads to immunopathology with a specific focus on innate immune cells, the role of the microbiome and the resulting clinical manifestations including intestinal GVHD, IBD and enteropathy in primary immunodeficiency. This article is protected by copyright. All rights reserved.

Innate and adaptive γδ T cells: How, when, and why

γδ T cells comprise the third cell lineage of lymphocytes that use, like αβ T cells and B cells, V(D)J gene rearrangement with the potential to generate a highly diverse T cell receptor (TCR) repertoire. There is no obvious conservation of γδ T cell subsets (based on TCR repertoire and/or function) between mice and human, leading to the notion that human and mouse γδ T cells are highly different. In this review, we focus on human γδ T cells, building on recent studies using high-throughput sequencing to analyze the TCR repertoire in various settings. We make then the comparison with mouse γδ T cell subsets highlighting the similarities and differences and describe the remarkable changes during lifespan of innate and adaptive γδ T cells. Finally, we propose mechanisms contributing to the generation of innate versus adaptive γδ T cells. We conclude that key elements related to the generation of the γδ TCR repertoire and γδ T cell activation/development are conserved between human and mice, highlighting the similarities between these two species.

Gut γδ T cells as guardians, disruptors, and instigators of cancer

Colorectal cancer is the third most common cancer worldwide with nearly 2 million cases per year. Immune cells and inflammation are a critical component of colorectal cancer progression, and they are used as reliable prognostic indicators of patient outcome. With the growing appreciation for immunology in colorectal cancer, interest is growing on the role γδ T cells have to play, as they represent one of the most prominent immune cell populations in gut tissue. This group of cells consists of both resident populations-γδ intraepithelial lymphocytes (γδ IELs)-and transient populations that each has unique functions. The homeostatic role of these γδ T cell subsets is to maintain barrier integrity and prevent microorganisms from breaching the mucosal layer, which is accomplished through crosstalk with enterocytes and other immune cells. Recent years have seen a surge in discoveries regarding the regulation of γδ IELs in the intestine and the colon with particular new insights into the butyrophilin family. In this review, we discuss the development, specialities, and functions of γδ T cell subsets during cancer progression. We discuss how these cells may be used to predict patient outcome, as well as how to exploit their behavior for cancer immunotherapy.

The Role of Tissue-resident T Cells in Stress Surveillance and Tissue Maintenance

While forming a minor population in the blood and lymphoid compartments, T cells are significantly enriched within barrier tissues. In addition to providing protection against infection, these tissue-resident T cells play critical roles in tissue homeostasis and repair. T cells in the epidermis and intestinal epithelium produce growth factors and cytokines that are important for the normal turnover and maintenance of surrounding epithelial cells and are additionally required for the efficient recognition of, and response to, tissue damage. A role for tissue-resident T cells is emerging outside of the traditional barrier tissues as well, with recent research indicating that adipose tissue-resident T cells are required for the normal maintenance and function of the adipose tissue compartment. Here we review the functions of tissue-resident T cells in the epidermis, intestinal epithelium, and adipose tissue, and compare the mechanisms of their activation between these sites.

Mechanisms of activation of innate-like intraepithelial T lymphocytes

Intraepithelial T lymphocytes (T-IEL) contain subsets of innate-like T cells that evoke innate and adaptive immune responses to provide rapid protection at epithelial barrier sites. In the intestine, T-IEL express variable T cell antigen receptors (TCR), with unknown antigen specificities. Intriguingly, they also express multiple inhibitory receptors, many of which are normally found on exhausted or antigen-experienced T cells. This pattern suggests that T-IEL are antigen-experienced, yet it is not clear where, and in what context, T-IEL encounter TCR ligands. We review recent evidence indicating TCR antigens for intestinal innate-like T-IEL are found on thymic or intestinal epithelium, driving agonist selection of T-IEL. We explore the contributions of the TCR and various co-stimulatory and co-inhibitory receptors in activating T-IEL effector functions. The balance between inhibitory and activating signals may be key to keeping these highly cytotoxic, rapidly activated cells in check, and key to harnessing their immune surveillance potential.

Recasting the Tissue-Resident Lymphocyte in Celiac Disease

In a recent issue of Cell, Mayassi et al. (2019) show that chronic inflammation in celiac disease (CeD) patients changes the repertoire and functional phenotype of intestinal TCR γδ⁺ intraepithelial lymphocytes. These changes are not reversed by gluten-free dietary regimens, suggesting that they might underlie the long-term sensitivity of CeD patients to gluten.

Tissue Adaptations of Memory and Tissue-Resident Gamma Delta T Cells

Epithelial and mucosal barriers are critical interfaces physically separating the body from the outside environment and are the tissues most exposed to microorganisms and potential inflammatory agents. The integrity of these tissues requires fine tuning of the local immune system to enable the efficient elimination of invasive pathogens while simultaneously preserving a beneficial relationship with commensal organisms and preventing autoimmunity. Although they only represent a small fraction of circulating and lymphoid T cells, γδ T cells form a substantial population at barrier sites and even outnumber conventional αβ T cells in some tissues. After their egress from the thymus, several γδ T cell subsets naturally establish residency in predetermined mucosal and epithelial locations, as exemplified by the restricted location of murine Vγ5⁺ and Vγ3Vδ1⁺ T cell subsets to the intestinal epithelium and epidermis, respectively. Because of their preferential location in barrier sites, γδ T cells are often directly or indirectly influenced by the microbiota or the pathogens that invade these sites. More recently, a growing body of studies have shown that γδ T cells form long-lived memory populations upon local inflammation or bacterial infection, some of which permanently populate the affected tissues after pathogen clearance or resolution of inflammation. Natural and induced resident γδ T cells have been implicated in many beneficial processes such as tissue homeostasis and pathogen control, but their presence may also exacerbate local inflammation under certain circumstances. Further understanding of the biology and role of these unconventional resident T cells in homeostasis and disease may shed light on potentially novel vaccines and therapies.

γδ T cells in homeostasis and host defence of epithelial barrier tissues

Epithelial surfaces line the body and provide a crucial interface between the body and the external environment. Tissue-resident epithelial γδ T cells represent a major T cell population in the epithelial tissues and are ideally positioned to carry out barrier surveillance and aid in tissue homeostasis and repair. In this Review, we focus on the intraepithelial γδ T cell compartment of the two largest epithelial tissues in the body - namely, the epidermis and the intestine - and provide a comprehensive overview of the crucial contributions of intraepithelial γδ T cells to tissue integrity and repair, host homeostasis and protection in the context of the symbiotic relationship with the microbiome and during pathogen clearance. Finally, we describe epithelium-specific butyrophilin-like molecules and briefly review their emerging role in selectively shaping and regulating epidermal and intestinal γδ T cell repertoires.

Lung-resident γδ T cells and their roles in lung diseases

γδ T cells are greatly enriched in mucosal and epithelial sites, such as the skin, respiratory, digestive and reproductive tracts, and they are defined as tissue-resident immune cells. In these tissues, the characteristics and biological roles of γδ T cells are distinguished from each other. The lungs represent the most challenging immunological dilemma for the host, and they have their own effective immune system. The abundance of γδ T cells, an estimated 8-20% of resident pulmonary lymphocytes in the lung, maintains lung tissue homeostasis. In this review, we summarize the recent research progress regarding lung-resident γδ T cells, including their development, residency and immune characteristics, and discuss the involvement of γδ T cells in infectious diseases of the lung, including bacterial, viral and fungal infections; lung allergic disease; lung inflammation and fibrosis; and lung cancer.

Characterization of γδ T Cells from Zebrafish Provides Insights into Their Important Role in Adaptive Humoral Immunity

γδ T cells represent an evolutionarily primitive T cell subset characterized by distinct T cell receptors (TCRs) and innate and adaptive immune functions. However, the presence of this T cell subset in ancient vertebrates remains unclear. In this study, γδ T cells from a zebrafish (Danio rerio) model were subjected to molecular and cellular characterizations. The constant regions of zebrafish TCR-γ (DrTRGC) and δ (DrTRDC) were initially identified. Zebrafish γδ T cells accounted for 7.7–20.5% of the total lymphocytes in spleen, head kidney, peripheral blood, skin, gill, and intestine tissues. They possess typical morphological features of lymphocytes with a surface phenotype of γ⁺δ⁺CD4⁻CD8⁺. Zebrafish γδ T cells functionally showed a potent phagocytic ability to both soluble and particulate antigens. They can also act as an antigen-presenting cell to initiate antigen (KLH)-specific CD4⁺ T_KLH cell activation and to induce B cell proliferation and IgM production. Particularly, zebrafish γδ T cells also play a critical role in antigen-specific IgZ production in intestinal mucus. These findings demonstrated that γδ T cells had been originated as early as teleost fish, which providing valuable insights into the evolutionary history of T cell subset. It is anticipated that this study would be used as a guide to develop a zebrafish model for the cross-species investigation of γδ T cell biology.

The burgeoning family of unconventional T cells

While most studies of T lymphocytes have focused on T cells reactive to complexes of peptide and major histocompatibility complex (MHC) proteins, many other types of T cells do not fit this paradigm. These include CD1-restricted T cells, MR1-restricted mucosal associated invariant T cells (MAIT cells), MHC class Ib-reactive T cells, and γδ T cells. Collectively, these T cells are considered 'unconventional', in part because they can recognize lipids, small-molecule metabolites and specially modified peptides. Unlike MHC-reactive T cells, these apparently disparate T cell types generally show simplified patterns of T cell antigen receptor (TCR) expression, rapid effector responses and 'public' antigen specificities. Here we review evidence showing that unconventional T cells are an abundant component of the human immune system and discuss the immunotherapeutic potential of these cells and their antigenic targets.

Gamma delta T cell reconstitution is associated with fewer infections and improved event-free survival after hematopoietic stem cell transplantation for pediatric leukemia

After hematopoietic stem cell transplantation (HSCT), successful engraftment and immune recovery is necessary to protect the patient from relapse and infection. Many studies highlight the importance of conventional αβ T cell recovery after HSCT, but the impact of γδ T cell recovery has not been well described. Here, we investigate the recovery of γδ T cells in 102 pediatric patients with acute leukemia in first clinical remission who underwent allogeneic HSCT at St. Jude Children's Research Hospital from 1996 to 2011. Mean patient age was 10.5 ± 5.9 years (range, .6 to 25.2), and mean survivor follow-up was 2.7 ± 1.8 years (range, .12 to 6.0). Diagnoses included 59% patients with acute lymphoblastic leukemia and 41% patients with acute myelogenous leukemia. Multivariate analysis demonstrated significant impact of the maximum number of CD3(+), CD4(+), and CD8(+) T cells and donor source on the γδ T cell recovery (P < .0001, P < .0001, P < .0001, and P < .004, respectively). Univariate and multivariate models found the number of γδ T cells after HSCT to be associated with infections (P = .026 and P = .02, respectively). We found the probability of infections for patients with an elevated number of γδ T cells was significantly lower compared with patients with low or normal γδ T cells after HSCT (18% versus 54%; P = .025). Bacterial infections were not observed in patients with elevated γδ T cells. Finally, event-free survival was significantly higher in patients with enhanced γδ T cell reconstitution compared with patients with low/normal γδ T cell reconstitution after HSCT (91% versus 55%; P = .04). Thus, γδ T cells may play an important role in immune reconstitution after HSCT.

γδ T cells exhibit multifunctional and protective memory in intestinal tissues

The study of T cell memory and the target of vaccine design have focused on memory subsumed by T cells bearing the αβ T cell receptor. Alternatively, γδ T cells are thought to provide rapid immunity, particularly at mucosal borders. Here, we have shown that a distinct subset of mucosal γδ T cells mounts an immune response to oral Listeria monocytogenes (Lm) infection and leads to the development of multifunctional memory T cells capable of simultaneously producing interferon-γ and interleukin-17A in the murine intestinal mucosa. Challenge infection with oral Lm, but not oral Salmonella or intravenous Lm, induced rapid expansion of memory γδ T cells, suggesting contextual specificity to the priming pathogen. Importantly, memory γδ T cells were able to provide enhanced protection against infection. These findings illustrate that γδ T cells play a role with hallmarks of adaptive immunity in the intestinal mucosa.

Close link between development and function of gamma-delta T cells

Murine γδ T cells develop as the first T-cell lineage within the fetal thymus and disproportionately localize in mucosal tissues such as lung, skin, uterus, and intestine of adult mice. These unique developmental features and distribution patterns of γδ T cells enable rapid functioning against various insults from pathogens. γδ T cells are also able to respond to local inflammation and consequently regulate the pathogenesis of autoimmune disorders and development of tumors in mice and humans. Hence, it is clinically important to understand the mechanisms that regulate γδ T cell functions. Recent evidence has shown that generations of effector γδ T cell subsets producing IFN-γ, IL-4, and IL-17 are programmed in the murine thymus before their migration to peripheral tissues. This review outlines our current understanding of the development and function of γδ T cells as they influence both innate and acquired immunity.

Development of interleukin-17-producing γδ T cells is restricted to a functional embryonic wave

γδ T cells are an important innate source of interleukin-17 (IL-17). In contrast to T helper 17 (Th17) cell differentiation, which occurs in the periphery, IL-17-producing γδ T cells (γδT17 cells) are probably committed during thymic development. To study when γδT17 cells arise during ontogeny, we used TcrdH2BeGFP reporter mice to monitor T cell receptor (TCR) rearrangement and IL-17 production in the embryonic thymus. We observed that several populations such as innate lymphoid cells and early T cell precursors were able to produce IL-17 prior to (and thus independent of) TCR recombination. γδT17 cells were absent after transplantation of IL-17-sufficient bone marrow into mice lacking both Il17a and Il17f. Also, γδT17 cells were not generated after genetic restoration of defective Rag1 function in adult mice. Together, these data suggested that these cells developed exclusively before birth and subsequently persisted in adult mice as self-renewing, long-lived cells.

Intraepithelial lymphocytes in celiac disease immunopathology

Celiac disease is a T cell-mediated immune disorder induced by dietary gluten that is characterized by the development of an inflammatory anti-gluten CD4 T cell response, anti-gluten antibodies, and autoantibodies against tissue transglutaminase 2 and the activation of intraepithelial lymphocytes (IELs) leading to the destruction of the intestinal epithelium. Intraepithelial lymphocytes represent a heterogeneous population of T cells composed mainly of cytotoxic CD8 T cells residing within the epithelial layer, whose main role is to maintain the integrity of the epithelium by eliminating infected cells and promoting epithelial repair. Dysregulated activation of IELs is a hallmark of CD and is critically involved in epithelial cell destruction and the subsequent development of villous atrophy. In this review, we compare and contrast the phenotype and function of human and mouse small intestinal IELs under physiological conditions. Furthermore, we discuss how conditions of epithelial distress associated with overexpression of IL-15 and non-classical MHC class I molecules induce cytotoxic IELs to become licensed killer cells that upregulate activating NKG2D and CD94/NKG2C natural killer receptors, acquiring lymphokine killer activity. Pathways leading to dysregulated IEL activation could eventually be targeted to prevent villous atrophy and treat patients who respond poorly to gluten-free diet.

Epithelial barrier biology: good fences make good neighbours

The external surfaces of the body, such as the skin and the gastrointestinal mucosal membrane, are an important line of defence preventing the invasion of microorganisms and their products. Mucosal immune cells, especially intraepithelial lymphocytes, are involved in maintaining the integrity of these epithelial barriers. They contribute towards the tolerance to commensal organisms, which occupy these same sites, and to the immune responses against harmful organisms and their products. The composition of the microbiota is influenced by immune cells as well as external environmental factors, especially the use of antibiotics and diet. There is an increasing appreciation that the microbiota affects systemic immune responses in addition to local immunity. Failure to control the occupancy by microorganisms may result in the disruption of the delicate homeostasis between beneficial and harmful microorganisms and contribute to inflammatory pathologies. This review will discuss some of our current understanding of the impact of immune cells and diet on the microbiota.

The light and dark sides of intestinal intraepithelial lymphocytes

The intraepithelial lymphocytes (IELs) that reside within the epithelium of the intestine form one of the main branches of the immune system. As IELs are located at this critical interface between the core of the body and the outside environment, they must balance protective immunity with an ability to safeguard the integrity of the epithelial barrier: failure to do so would compromise homeostasis of the organism. In this Review, we address how the unique development and functions of intestinal IELs allow them to achieve this balance.

Mouse and human intestinal immunity: same ballpark, different players; different rules, same score

The study of animal immune physiology and animal models of human disease have accelerated many aspects of translational research by allowing direct, definitive investigations. In particular, the use of mice has allowed genetic manipulation, adoptive transfer, immunization, and focused cell and tissue sampling, which would obviously be unthinkable for studies in humans. However, the disease relevance of some animal models may be uncertain and difficulties in interpretation may occur as a consequence of immunological differences between the two species. In this review, we will consider general differences in the structure and development of human and mouse mucosal lymphoid microenvironments and then discuss species differences in mucosal B- and T-cell biology that relate to the current concepts of intestinal immune function.

Distribution and development of the postnatal murine Vδ1 T-cell receptor repertoire

Murine γ/δ T cells express canonical Vγ5Vδ1 chains in the epidermis and Vγ6Vδ1 chains at reproductive sites. Both subsets carry an identical Vδ1-Dδ2-Jδ2 chain which completely lacks junctional diversity. These cells are thought to monitor tissue integrity via recognition of stress-induced self antigens. In this study, we showed by reverse transcription-polymerase chain reaction (RT-PCR), complementarity determining region 3 (CDR3) spectratyping and sequencing of the junctional regions of Vδ1 chains from C57BL/6 mice (aged 1 day to 14 months) that the canonical Vδ1-Dδ2-Jδ2 chain is also consistently present at other sites such as the thymus, gut, lung, liver, spleen and peripheral blood. In addition, we found multiple Vδ1 chains with fetal type rearrangements which were also shared among organs and among animals. These Vδ1 chains were typically characterized by a conserved amino acid motif, 'GGIRA'. Furthermore, by analysing the early postnatal period at days 10 and 16, we demonstrated that the diversification of the thymic Vδ1 repertoire is not paralleled by a diversification of extrathymic Vδ1+γ/δ T cells. This indicates that only fetal type rearrangements survive at extrathymic sites. In conclusion, γ/δ T cells expressing the canonical Vδ1-Dδ2-Jδ2 chain are not unique to the skin and reproductive sites. Furthermore, we found other γ/δ T cells expressing fetal type Vδ1 chains which were shared among different organs and animals. Thus, γ/δ T cells expressing conserved Vδ1 chains are likely to have important functions. We suggest a model in which this subset continuously recirculates throughout the organism and rapidly responds to stress-induced self antigens.

Accessibility control of TCR Vγ region by STAT5

The signal of the IL-7R and signal transducers and activators of transcription (STAT) 5 plays an essential role in gammadelta T-cell development by inducing V-J recombination in the TCRgamma locus. Previously, we have shown that STAT5 binds to the Jgamma promoters and controls chromatin accessibility by histone acetylation. However, little is known on control mechanism of Vgamma region by the IL-7R. To elucidate the regulation by STAT5, we first analyzed the chromatin status of Vgamma region in primary thymocytes. The levels of histone H3 acetylation are high at Vgamma5, HsA element and Vgamma2 in Rag2(-/-) thymocytes but low in IL-7R alpha-chain (IL-7Ralpha)-deficient early thymocytes, suggesting that IL-7R signaling controls the accessibility of the Vgamma region. In addition, high levels of histone H3 acetylation and germ line transcription were induced at Vgamma5 and HsA by cytokine and STAT5 in cytokine-dependent Ba/F3 and other hematopoietic cell lines. Importantly, the chromatin accessibility of Vgamma5 gene is increased by cytokine signal. Furthermore, STAT5 was not recruited to a non-canonical STAT-binding motif in the endogenous chromatin of the Vgamma5 promoter by cytokine stimulation, while STAT5 binds to a consensus motif in the HsA element. In accordance with this result, STAT5 does not directly activate the Vgamma5 promoter by reporter assay. These results suggested that while STAT5 directly binds to HsA element and induces its histone acetylation, STAT5 indirectly activates the Vgamma5 promoter. Thus, this study implies a potential role of STAT5 in accessibility control of Vgamma region, especially at Vgamma5 and HsA.

Mechanisms determining cell membrane expression of different gammadelta TCR chain pairings

We investigated the ability of the most common TCR-gamma and delta chains to express on the cell surface. Vgamma1Cgamma4 and Vgamma7Cgamma1 chains paired with all TCR-delta chains tested, whereas Vgamma4Cgamma1 chains were found with Vdelta4 and Vdelta5, but not with Vdelta2 or Vdelta6 chains, and Vgamma2Cgamma2 chains were expressed only with Vdelta5. Mapping studies showed that up to four polymorphic residues influence the different co-expressions of Vgamma1 and Vgamma2 chains with Vdelta chains. Unexpectedly, these residues are not located in the canonical gamma/delta interface, but in the outer part of the gammadelta TCR complex exposed to the solvent. Expression of functional Vdelta4 or Vdelta6 chains in Vgamma2/Vdelta5(+) cells or of functional Vgamma2Cgamma2 in Vgamma1(+) cells reduced cell-surface expression of the gammadelta TCR. Taken together, these data show that (i) the Vgamma/Vdelta repertoire of mouse gammadelta T cells is reduced by physical constraints in their associations. (ii) Lack of Vgamma2/Vdelta expression is due to the formation of aberrant TCR complexes, rather than to an intrinsic inability of the chains to pair and (iii) despite not being expressed at the cell surface, the presence of a functionally rearranged Vgamma2 chain in gammadelta T cells results in reduced TCR levels.

Intestinal T cells: facing the mucosal immune dilemma with synergy and diversity

The epithelium of the gastrointestinal tract, which represents the greatest body surface area exposed to the outside environment, is confronted with a plethora of foreign and potentially harmful antigens. Consequently, the immune system of the gut faces the daunting task of distinguishing harmless dietary proteins and commensal bacteria from potentially dangerous pathogens, and of then responding accordingly. Mucosal T cells play a central role in maintaining barrier function and controlling the delicate balance between immune activation and immune tolerance. This review will focus on the unique features of mucosal T cell subsets that reside in the epithelium and lamina propria of the gut.

Characterization and TCR variable region gene use of mouse resident nasal gammadelta T lymphocytes

Tissue-resident gammadelta T lymphocytes, such as dendritic epidermal T cells, intestinal intraepithelial lymphocytes (IEL), and resident pulmonary lymphocytes, are known to support local tissue homeostasis and host defense. Inhaled antigens, toxins, and microorganisms first interact with the immune system through contact with the nasal mucosa. Herein, we characterized two populations of resident nasal lymphocytes (RNL) that are present in the nasal mucosa: nasal IEL (nIEL) and nasal lamina propria lymphocytes (nLPL). gammadelta TCR+ and alphabeta TCR+ nIEL and nLPL were detected by immunofluorescent staining. Mononuclear cells (5-15%) were CD3+ RNL by FACS analysis. Among the CD3+ RNL, 20-30% were GL3+ gammadelta T cells, which were double-negative for CD4 and CD8 and predominantly expressed a Vgamma4/Vdelta1 TCR. These results demonstrate that RNL might be crucial for the host defense and tissue homeostasis in the nasal mucosa.

T cells developing in fetal thymus of T-cell receptor alpha-chain transgenic mice colonize gammadelta T-cell-specific epithelial niches but lack long-term reconstituting potential

The gammadelta T cells generated during mouse fetal development are absolutely dependent on their invariant T-cell receptors (TCRs) for their function. However, there is little information on whether the epithelial homing properties of fetal T cells might also be developmentally induced by factors unrelated to TCR specificity. We have previously described TCR alpha-chain transgenic (2B4 TCR-alpha TG) mice, in which the transgenic TCR alpha-chain is expressed early, already at embryonic day 14 (E14). These mice have a large population of 'gammadelta T-cell-like' CD4- CD8- (double-negative; DN) alphabeta T cells, some of which develop during E14-E18 contemporarily to intraepithelial lymphocytes (IELs) expressing invariant TCR-gammadelta. Using the 2B4 TCR-alpha TG mouse model we have been able to more precisely study the impact of a variant TCR expression on IEL development and homing. In this study we show that TCR-alpha TG and TCR-alpha TG crossed to TCR-delta-deficient mice (TCR-alpha TG x TCR-delta-/-) carry TG TCR-alpha+ dendritic epidermal T cells (DETCs) and TCR-alpha TG+ IELs in the small intestine. The TG+ DETCs develop and seed the epidermis with similar kinetics as Vgamma5+ DETCs of normal mice, in contrast to the TCR-alphabeta+ DETCs found in TCR-delta-/- mice. However, whereas the intestinal TCR-alpha TG+ IELs persist in old mice (> 20 months), the TCR-alpha TG+ DETCs do not. The data in this study indicate that the timing of TCR expression and thereby development during ontogeny regulates the specific homing potential for fetal T cells but not their subsequent functions and properties.

Highly restricted diversity of TCR delta chains of the amphibian Mexican axolotl (Ambystoma mexicanum) in peripheral tissues

Gammadelta T cells localize at mammalian epithelial surfaces to exert both protective and regulatory roles in response to infections. We have previously characterized the Mexican axolotl (Ambystoma mexicanum) T cell receptor delta (TRD) chain. In this study, TRD repertoires in spleen, liver, intestine and skin from larvae, pre-adult and adult axolotls were examined and compared to the thymic TRD repertoire. A TRDV transcript without N/D diversity, TRDV1S1-TRDJ1, dominates the TRD repertoires until sexual maturation. In adult tissues, this canonical transcript is replaced by another dominant TRDV1S1-TRDJ1 transcript. In the thymus, these two transcripts are detected early in development. Our results suggest that gammadelta T cells that express the canonical TRDV1S1-TRDJ1 transcript emerge from the thymus and colonize the peripheral tissues, where they are selectively expanded by recurrent ligands. This particular situation is probably related to the neotenic state and the slow development of the axolotl. In thymectomized axolotls, TRD repertoires appear different from those of normal axolotls, suggesting that extrathymic gammadelta T cell differentiation could occur. Gene expression analysis showed the importance of the gut in T cell development.

gammadelta T cells: firefighters or fire boosters in the front lines of inflammatory responses

Intradermal inoculation of cloned self-reactive alphabeta T cells into the footpads of mice induced cutaneous graft-versus-host disease (GVHD), and after recovery from GVHD, the epidermis became resistant to subsequent attempts to induce GVHD. Resistance to GVHD was not induced in the epidermis of T-cell receptor delta-deficient (TCRdelta(-/-)) mice that lacked gammadelta T cells bearing canonical Vgamma5/Vdelta1(+)gammadeltaTCRs, known as dendritic epidermal T cells (DETCs), and resistance was restored by reconstitution of these mutant mice with precursors of Vgamma5(+) DETCs. Pulmonary infection by Cryptococcus neoformans induced an increase of gammadelta T cells in the lung, and in comparison with wildtype mice, TCRdelta(-/-) mice eliminated C. neoformans more rapidly and synthesized more interferon-gamma in the lung. In the mouse small intestine, the absence of gammadelta T cells is associated with a reduction in epithelial cell turnover and downregulation of the expression of major histocompatibility complex class II molecules. The protective role of gammadelta T cells was verified in a dextran sodium sulfate-induced inflammatory bowel disease (IBD) model, whereas in a spontaneous model of IBD, gammadelta T cells were involved in the exacerbation of colitis in TCRalpha(-/-) mice. Taken together, in addition to the homeostatic regulation of epithelial tissues, gammadelta T cells appear to play a pivotal role in the modification of inflammatory responses induced in many organs containing epithelia.

Repertoire of the alpha beta T-cell receptor in the intestine

The majority of T cells in the human and mouse intestine express the T-cell receptor (TCR) as an alphabeta heterodimer on their cell surface. As the major recognition element of antigens in the context of major histocompatibility complex-derived proteins, an examination of the structure of the alpha beta TCR in intestines has provided significant insights into the potential function of these cells and the major determinants that drive their selection. Studies in the human intestine have shown that the repertoires of intraepithelial lymphocytes (IELs), and likely lamina propria lymphocytes, are polyclonal before and shortly after birth, with the repertoire becoming oligoclonal in adults. Similarly, in adult mice the repertoire is oligoclonal, while in the newborn it is polyclonal. Investigations in mice have shown that some T cells may evade thymic selection. The population size and oligoclonality of IELs is influenced by the microbial content of the luminal microenvironment. This microenvironment probably directly determines the TCR repertoire. Studies in human inflammatory bowel disease (IBD) indicate that inflammation further skews the TCR repertoire. We speculate that dominant antigens associated with the pathogenesis of IBD are responsible for such skewing and that identifying the antigenic drivers may shed light on the environmental factors that trigger or potentiate human IBD.

Human CD8+intraepithelial lymphocytes: a unique model to study the regulation of effector cytotoxic T lymphocytes in tissue

The epithelium of the human small intestine contains a large population of intraepithelial cytolytic alphabeta T-cell receptor (TCR) CD8 alpha beta T lymphocytes (IE-CTLs), whose main role is to sustain epithelial integrity by rapidly eliminating infected and damaged cells. In mouse, the recognition of inducible/modified self-molecules, i.e. non-classical major histocompatibility complex (MHC) class I molecules, is mediated by the TCR and natural killer receptors (NKRs) co-expressed on the cell surface of a non-conventional autoreactive CD8 alpha alpha alpha beta TCR cell subset. In contrast, in humans, the recognition of non-classical MHC class I molecules induced by stress and inflammation on intestinal epithelial cells (IECs) is principally mediated by NKRs expressed on conventional CD8 alpha beta alpha beta TCR cells. By sensing microenvironmental signals of inflammation and stress through NKRs, IE-CTLs fine tune their TCR activation threshold. Furthermore, IE-CTLs under particular conditions, involving interleukin-15 upregulation, acquire the capacity to kill distressed intestinal epithelial cells in an antigen non-specific manner. Adaptive IE-CTLs appear hence to have autoreactive properties and modulate their immune response based on innate signals, reflecting the fitness of the tissue.

Distribution and leukocyte contacts of γδ T cells in the lung

Pulmonary gammadelta T cells protect the lung and its functions, but little is known about their distribution in this organ and their relationship to other pulmonary cells. We now show that gammadelta and alphabeta T cells are distributed differently in the normal mouse lung. The gammadelta T cells have a bias for nonalveolar locations, with the exception of the airway mucosa. Subsets of gammadelta T cells exhibit further variation in their tissue localization. gammadelta and alphabeta T cells frequently contact other leukocytes, but they favor different cell-types. The gammadelta T cells show an intrinsic preference for F4/80+ and major histocompatibility complex class II+ leukocytes. Leukocytes expressing these markers include macrophages and dendritic cells, known to function as sentinels of airways and lung tissues. The continuous interaction of gammadelta T cells with these sentinels likely is related to their protective role.

Targeting T cell responses by selective chemokine receptor expression

Immune responses require the orchestrated migration of T cells throughout the body. Conventional CD4+ and CD8+ alphabeta T cells undergo clonal expansion in the secondary lymphoid tissues, during which they are programmed to migrate into specific non-lymphoid tissues and other lymphoid effector sites such as B cell follicles. By contrast, T cell populations expressing receptors with limited diversity (i.e. gammadelta T cells and NK T cells) appear to be preprogrammed to localize in non-lymphoid tissues where they monitor tissue integrity or serve regulatory functions. By promoting chemotaxis and integrin activation, chemokines and their receptors (in conjunction with surface adhesion molecules) control these T cell homing events. Thus, expression of chemokine receptors defines T cells with tropism for particular tissues and/or microenvironments, and identifies T cell subsets with distinct functional properties.

A keratinocyte-responsive gamma delta TCR is necessary for dendritic epidermal T cell activation by damaged keratinocytes and maintenance in the epidermis

A unique population of T lymphocytes, designated dendritic epidermal T cells (DETC), homes to the murine epidermis during fetal development. DETC express a canonical gammadelta TCR, Vgamma3/Vdelta1, which recognizes Ag expressed on damaged, stressed, or transformed keratinocytes. Recently, DETC were shown to play a key role in the complex process of wound repair. To examine the role of the DETC TCR in DETC localization to the epidermis, maintenance in the skin, and activation in vivo, we analyzed DETC in the TCRdelta(-/-) mouse. Unlike previous reports in which the TCRdelta(-/-) skin was found to be devoid of any DETC, we discovered that TCRdelta(-/-) mice have alphabeta TCR-expressing DETC with a polyclonal Vbeta chain repertoire. The alphabeta DETC are not retained over the life of the animal, suggesting that the gammadelta TCR is critical for the maintenance of DETC in the skin. Although the alphabeta DETC can be activated in response to direct stimulation, they do not respond to keratinocyte damage. Our results suggest that a keratinocyte-responsive TCR is necessary for DETC activation in response to keratinocyte damage and for DETC maintenance in the epidermis.

Production of a soluble gammadelta T-cell receptor to identify ligands for the murine intestinal intraepithelial gammadelta T cell population

Although the functions and antigen recognition requirements of alphabeta T cells are well characterised, the antigens recognised by gammadelta T cells and the consequences of this recognition are unclear. gammadelta T cells are enriched within epithelia, where they eradicate transformed epithelial cells and regulate inflammation. To understand how this occurs, we need to understand the cellular ligands recognised by the gammadelta cell through the gammadelta T-cell receptor (TCR). We have therefore generated a soluble TCR (sTCR) to identify ligands for the murine gammadelta intestinal intraepithelial lymphocyte (IEL) population. sTCR was produced in the baculovirus expression system and purified by affinity chromatography on an anti-TCRdelta affinity column. sTCR was recognised by a panel of conformation-specific anti-TCRgammadelta antibodies. We will now use our sTCR to directly test the binding of putative ligands to the TCR using surface plasmon resonance, and to isolate the ligand biochemically.

Modulation of gamma delta T cells in mouse buccal epithelium following antigen priming

T cells using the gamma delta T cell receptor (TCR) are abundant in mucosal and epidermal tissues in mice. Most studies of mucosal gamma delta T cells, however, have examined cells from the intestinal mucosa, whereas little is known about the presence or function of gamma delta T cells in the oral cavity. To better understand the involvement of oral gamma delta T cells in immunity, we have characterized TCR variable gamma-gene usage in the buccal epithelium from normal mice, and from mice challenged locally with a non-replicating antigen (bovine serum albumin [BSA]) or by influenza-virus infection as a replicating antigen. Our findings demonstrate a restricted use of V gamma genes by buccal gamma delta T cells, consisting primarily of V gamma 1.2, V gamma 3, and V gamma 5, with minimal use of V gamma 2 and V gamma 4 genes. Of particular interest, 3-4 days post-antigen challenge with BSA, there was a precipitous drop in the level of expression of V gamma 1.2, V gamma 3, and V gamma 5 genes, and to a lesser extent for the V gamma 2 gene, whereas V gamma 4 gene expression increased between days 1 and 2 post-priming. In influenza-infected mice, a similar pattern was observed for the V gamma 2 and V gamma 5 genes, but not other V gamma genes. The immune-modulating effects of oral antigen exposure on buccal gamma delta T cells suggest that these cells are functionally involved in the local immune response to both replicating and non-replicating antigens in oral mucosal surfaces.

A role for CCR9 in T lymphocyte development and migration

CCR9 mediates chemotaxis in response to CCL25/thymus-expressed chemokine and is selectively expressed on T cells in the thymus and small intestine. To investigate the role of CCR9 in T cell development, the CCR9 gene was disrupted by homologous recombination. B cell development, thymic alphabeta-T cell development, and thymocyte selection appeared unimpaired in adult CCR9-deficient (CCR9(-/-)) mice. However, competitive transplantation experiments revealed that bone marrow from CCR9(-/-) mice was less efficient at repopulating the thymus of lethally irradiated Rag-1(-/-) mice than bone marrow from littermate CCR9(+/+) mice. CCR9(-/-) mice had increased numbers of peripheral gammadelta-T cells but reduced numbers of gammadeltaTCR(+) and CD8alphabeta(+)alphabetaTCR(+) intraepithelial lymphocytes in the small intestine. Thus, CCR9 plays an important, although not indispensable, role in regulating the development and/or migration of both alphabeta(-) and gammadelta(-) T lymphocytes.

Characterization of T cell differentiation in the murine gut

Gut intraepithelial CD8 T lymphocytes (T-IEL) are distinct from thymus-derived cells and are thought to derive locally from cryptopatch (CP) precursors. The intermediate stages of differentiation between CP and mature T-IEL were not identified, and the local differentiation process was not characterized. We identified and characterized six phenotypically distinct lineage-negative populations in the CP and the gut epithelium: (a) we determined the kinetics of their generation from bone marrow precursors; (b) we quantified CD3-epsilon, recombination activating gene (Rag)-1, and pre-Talpha mRNAs expression at single cell level; (c) we characterized TCR-beta, -gamma, and -alpha locus rearrangements; and (d) we studied the impact of different mutations on the local differentiation. These data allowed us to establish a sequence of T cell precursor differentiation in the gut. We also observed that the gut differentiation varied from that of the thymus by a very low frequency of pre-Talpha chain mRNA expression, a different kinetics of Rag-1 mRNA expression, and a much higher impact of CD3 epsilon/delta and pre-Talpha deficiencies. Finally, only 3% of CP cells were clearly involved in T cell differentiation, suggesting that these structures may have additional physiological roles in the gut.

Transgenic mouse model of intestine-specific mucosal injury and repair

Most studies of injury and repair to mucosal tissue have used nonspecific mediators to induce injury. Damage to the mucosal epithelium resulting from chemical or radiation treatment associated with cancer therapy may fall into this category of injury. When such treatments are applied, it is generally not possible to predict or control the extent of possible injury. This fact makes analysis of inductive and reparative processes difficult. In addition, the role of the immune system in the etiology and subsequent healing of mucosal tissue following cancer therapy with or without bone marrow transplantation remains unclear. To study tissue- and antigen-specific immune damage of intestinal mucosal tissue, we generated transgenic mice that express a nominal antigen exclusively in intestinal epithelial cells. The transfer of antigen-specific CD8 T cells with concomitant virus infection resulted in the destruction of intestinal epithelial cells and disease. The destructive phase in some cases was followed by complete recovery and tolerance induction. This model will provide a system that can be regulated for analysis of the mediators of mucosa-specific tissue damage and repair.

Attributes of gammadelta intraepithelial lymphocytes as suggested by their transcriptional profile

gammadelta T lymphocytes in the intestinal intraepithelial layer (gammadelta IELs) are thought to contribute to immune competence, but their actual function remains poorly understood. Here we used DNA microarrays to study the gene expression profile of gammadelta IELs in a Yersinia infection system to better define their roles. To validate this approach, mesenteric lymph node CD8(+) alphabeta T cells were similarly analyzed. The transcription profiles show that, whereas lymph node CD8(+) alphabeta T cells must be activated to become cytotoxic effectors, gammadelta IELs are constitutively activated and appear to use different signaling cascades. Our data suggest that gammadelta IELs may respond efficiently to a broad range of pathological situations irrespective of their diverse T cell antigen receptor repertoire. gammadelta IELs may modulate local immune responses and participate in intestinal lipid metabolism, cholesterol homeostasis, and physiology. This study provides a strong basis for further investigations of the roles of these cells as well as mucosal immune defense in general.

V gamma 2 TCR repertoire overlap in different anatomical compartments of healthy, unrelated rhesus macaques

Gammadelta T cells show preferential homing that is characterized by biased TCR repertoire at different anatomical locations. The processes that regulate this compartmentalization are largely unknown. A model that allows repeated multiple sample procurement under different conditions and enables with relatively straightforward extrapolation to a human situation will facilitate our understanding. The peripheral blood Vgamma2 T cell population is the best-characterized human gammadelta T cell subset. To determine its diversity at multiple immunocompartments matching blood, colon, and vagina samples from rhesus macaques were investigated. Four joining segments used in Vgamma2-Jgamma transcripts were identified, including one segment with no human counterpart. Like in humans, the rhesus peripheral blood Vgamma2 TCR repertoire was limited and contained common sequences that were shared by genetically heterogeneous animals. Furthermore, this subset comprised several phylogenetically conserved Vgamma2 complementarity-determining region 3 (CDR3) motifs between rhesus and humans. Common sequences were also found within the colon and vagina of the same animal, and within the peripheral blood and intestine of different unrelated animals. These results validate rhesus macaques as a useful model for gammadelta TCR repertoire and homing studies. Moreover, they provide evidence that the concept of limited but overlapping Vgamma TCR repertoire between unrelated individuals can be extended including the mucosa of the digestive and reproductive tract.

Gut cryptopatches: direct evidence of extrathymic anatomical sites for intestinal T lymphopoiesis

Athymic cytokine receptor gamma chain mutant mice that lack the thymus, Peyer's patches, cryptopatches (CP), and intestinal T cells were reconstituted with wild-type bone marrow cells. Bone marrow-derived TCR(-) intraepithelial lymphocytes (IEL) first appeared within villous epithelia of small intestine overlying the regenerated CP, and these TCR(-) IEL subsequently emerged throughout the epithelia. Thereafter, TCR(+) IEL increased to a comparable number to that in athymic mice and consisted of TCRgammadelta and TCRalphabeta IEL. In gut-associated lymphoid tissues of wild-type mice, only CP harbored a large population of c-kit(high)IL-7R(+)CD44(+)Thy-1(+/-)CD4(+/-)CD25(low/-)alpha(E) beta(7)(-)Lin(-) (Lin, lineage markers) lymphocytes that included cells expressing germline but not rearranged TCRgamma and TCRbeta gene transcripts. These findings provide direct evidence that gut CP develop progenitor T cells for extrathymic IEL descendants.

Development of dendritic epidermal T cells with a skewed diversity of gamma delta TCRs in V delta 1-deficient mice

One of the most intriguing features of gammadelta T cells that reside in murine epithelia is the association of a specific Vgamma/Vdelta usage with each epithelial tissue. Dendritic epidermal T cells (DETCs) in the murine epidermis, are predominantly derived from the "first wave" Vgamma5+ fetal thymocytes and overwhelmingly express the canonical Vgamma5/Vdelta1-TCRs lacking junctional diversity. Targeted disruption of the Vdelta1 gene resulted in a markedly impaired development of Vgamma5+ fetal thymocytes as precursors of DETCs; however, gammadeltaTCR+ DETCs with a typical dendritic morphology were observed in Vdelta1-/- mice and their cell densities in the epidermis were slightly lower than those in Vdelta1+/- epidermis. Moreover, the Vdelta1-deficient DETCs were functionally competent in their ability to up-regulate cytokines and keratinocyte growth factor-expression in response to keratinocytes. Vgamma5+ DETCs were predominant in the Vdelta1-/- epidermis, though Vgamma5- gammadeltaTCR+ DETCs were also detected. The Vgamma5+ DETCs showed a typical dendritic shape, gammadeltaTCR(high), and age-associated expansion in epidermis as observed in conventional DETCs of normal mice, whereas the Vgamma5- gammadeltaTCR+ DETCs showed a less dendritic shape, gammadeltaTCR(low), and no expansion in the epidermis, consistent with their immaturity. These results suggest that optimal DETC development does not require a particular Vgamma/Vdelta-chain usage but requires expression of a limited diversity of gammadeltaTCRs, which allow DETC precursors to mature and expand within the epidermal microenvironment.