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Gamma delta T cells (γδ T cells), represent a small subset of T cells that possess a distinct T-cell receptor (TCR) on their surface. Most T cells are αβ (alpha beta) T cells with TCR composed of two glycoprotein chains called α (alpha) and β (beta) TCR chains. In contrast, gamma delta (γδ) T cells have a TCR that is made up of one γ (gamma) chain and one δ (delta) chain. This group of T cells is usually much less common than αβ T cells, but are at their highest abundance in the gut mucosa, within a population of lymphocytes known as intraepithelial lymphocytes (IELs). The antigenic molecules that activate gamma delta T cells are still largely unknown. However, γδ T cells are peculiar in that they do not seem to require antigen processing and major-histocompatibility-complex (MHC) presentation of peptide epitopes, although some recognize MHC class Ib molecules. Furthermore, γδ T cells are believed to have a prominent role in recognition of lipid antigens. They are of an invariant nature and may be triggered by alarm signals, such as heat shock proteins (HSP). There also exists a γδ-T-cell sub-population within the epidermal compartment of the skin of mice. Originally referred to as Thy-1+ dendritic epidermal cells (Thy1+DEC), these cells are more commonly known as dendritic epidermal T cells (DETC). DETCs arise during fetal development and express an invariant and canonical Vγ3 Vδ1 T-cell receptor (Garman nomenclature ). ==Gamma delta T cells in innate and adaptive immunity== The conditions that lead to responses of gamma delta T cells are not fully understood, and current concepts of them as 'first line of defense', 'regulatory cells', or 'bridge between innate and adaptive responses'〔 only address facets of their complex behavior. In fact, gamma delta T cells form an entire lymphocyte system that develops under the influence of other leukocytes, in the thymus and in the periphery. When mature they are divided into functionally distinct subsets that obey their own (mostly unknown) rules and that have countless direct and indirect effects on healthy tissues and immune cells, on pathogens and tissues enduring infections and the host responses to them. Like other 'unconventional' T cell subsets bearing invariant TCRs, such as CD1d-restricted Natural Killer T cells, gamma delta T cells exhibit several characteristics that place them at the border between the more evolutionarily primitive innate immune system that permits a rapid beneficial response to a variety of foreign agents, and the adaptive immune system, where B and T cells coordinate a slower but highly antigen-specific immune response leading to long-lasting memory against subsequent challenges by the same antigen. Gamma delta T cells may be considered a component of adaptive immunity in that they rearrange TCR genes to produce junctional diversity and will develop a memory phenotype. However, the various subsets may also be considered part of the innate immunity where a restricted TCR may be used as a pattern recognition receptor. For example, according to this paradigm, large numbers of (human) Vγ9/Vδ2 T cells respond within hours to common molecules produced by microbes, and highly restricted intraepithelial Vδ1 T cells will respond to stressed epithelial cells bearing sentinels of danger. Recent work has shown that human Vγ9/Vδ2 T cells are also capable of phagocytosis, a function previously exclusive to innate myeloid lineage cells such as neutrophils, monocytes and dendritic cells Clearly, the complexity of gamma delta T cell biology spans definitions of both innate and adaptive immune responses. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Gamma delta T cell」の詳細全文を読む スポンサード リンク
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