胸腺上皮细胞的发育分化及其分子调控

T细胞在胸腺中发育成熟依赖特殊的微环境,而胸腺上皮细胞(TECs)是微环境中最重要的成分之一.TECs主要分为皮质上皮细胞(cTECs)和髓质上皮细胞(mTECs),分别介导胸腺细胞的阳性选择和阴性选择过程.cTECs和mTECs来源于共同的胸腺上皮干细胞(TEPCs),经过一系列发育过程,最终分化为功能及表型成熟的TECs.TECs发育分化过程除受到自身内在基因如转录因子Foxn1和Aire的调控以外,还需要与间质细胞、胸腺细胞相互作用,接受外源信号如TNFR家族成员RANK、CD40和LTβR信号的调节,这些信号尤其对mTECs的发育至关重要.而成纤维细胞生长因子(FGFs)和Wnt通路则对TECs的扩增和功能维持非常重要.本文综述了TECs发育分化过程以及参与调控该过程的信号分子通路.     

胸腺上皮细胞上清液促进85细胞增殖的研究

胸腺是T细胞分化发育的场所。源于骨髓的前T细胞迁入胸腺后,在胸腺微环境作用下,经阳性和阴性选择过程,发育分化成功能性T细胞迁至外周[1]。目前对胸腺基质细胞如何影响成熟T细胞株的研究较少。为此,本文利用体外原代培养人胸腺上皮细胞,比较不同培养条件下细胞生长情况。...     

Wnt信号通路与胸腺发育

胸腺是人体重要的中枢淋巴器官,是T淋巴细胞分化发育的场所。起源于骨髓的淋巴细胞祖细胞,在胸腺中历经阳性选择和阴性选择后发育为成熟的T细胞,然后通过血液循环参与外周细胞免疫。研究表明,Wnt信号通路广泛存在于胸腺上皮细胞和T细胞,它不但影响胸腺上皮细胞的形态、功能,而且对于维持T细胞前体细胞和后期T细胞的分化发育都很重要。最近研究发现,Wnt信号通路参与了胸腺增龄性萎缩过程的调节,Wnt信号通路的改变可引起上皮网络结构的改变,最终导致胸腺微环境的破坏。因此,研究Wnt信号通路在胸腺发育中的作用,对于探索胸腺增龄性萎缩的调控机制和改善老年人的健康状况有重要意义。     

Foxn1在胸腺上皮细胞发育分化中的关键调控作用

胸腺是哺乳动物T细胞发育成熟的关键中枢免疫器官,并可分泌多种胸腺激素及激素类物质.胸腺上皮包括皮质和髓质,提供T细胞发育所必需的胸腺微环境.通常,造血干细胞首先在皮髓交界处进入胸腺,在皮质中增殖,表达TCR基因,产生具有功能的TCRαB链,然后迁出皮质,发育为CD4+CD8+T细胞后再迁入皮质进行阳性选择.随后T细胞经趋化因子CCR7介导进入髓质,剔除自身反应性T细胞,即进行阴性选择,成熟的T细胞移出胸腺至外周.TECs不仅提供肽段/MHC配体支持T细胞选择,还分泌支持T细胞扩增的各种可溶性因子如Wnt、IL-7和干细胞因子,表达各种趋化因子和促进T细胞定向和分化的Notch配体等.TECs的发育依赖于Foxn1的表达,人类和小鼠Foxn1基因突变或缺失可以引起胸腺发育严重障碍或缺失.现主要就Foxn1对TECs发育分化调控的研究进展进行简要综述.     

胸腺微环境及其作用

胸腺是Ｔ淋巴细胞分化发育的场所，胸腺微环境由胸腺基质细胞、细胞外基质和细胞因子等构成。在胸腺基质细胞中，上皮细胞最多，分布最广。上皮细胞的分化、成熟和增殖依赖于胸腺内发育阶段的各Ｔ细胞亚群。位于胸腺内不同区域的基质细胞在Ｔ细胞发育的不同阶段起重要作用。血胸屏障是胸腺微环境中一个特殊结构，前Ｔ细胞可通过粘附分子，在趋化因子等作用下穿过血胸屏障进入胸腺，在胸腺内完成其分化发育过程。     

用单克隆抗体显示小鼠胚胞腺上皮细胞的分化

以小鼠胸腺基质细胞单克隆抗体ＭＴＳ６、５、２０、３３，用免疫酶法观察了小鼠胚（１２～１９ｄ）胸腺上皮细胞的不同亚类和分化。第１２天胚胸腺原基中有少数细胞开始显示ＭＴＳ６弱阳性反应。第１３ｄ胚胸腺皮质中有些胸腺上皮细胞显示ＭＴＳ５阳性。第１５ｄ胸腺皮质和髓质中有些胸腺上皮细胞开始呈ＭＴＳ２０阳性反应。第１７ｄ胚髓质中可见少数胸腺上皮细胞开始呈ＭＴＳ３３阳性反应。第１９ｄＭＴＳ５、６阳性反应的胸腺上皮     

胸腺微环境和T细胞发育

对于胸腺内T 细胞的一系列复杂的分化过程,基质的调控必定也具有同样的复杂性。包括对前体细胞的吸引、T 细胞系的限定、T 细胞受体(TOR)基因重排的诱导、附属分子的表达、T 细胞总体的扩增、以主要组织相容性复合物(MHC)分子为基础的(阳性和阴性)选择、功能性成熟和迁移能力的获得都要受到基质的控制。在本文中,Richard Boyd 和Patricf Hugo结合T 细胞分化和胸腺基质细胞异源性的资料,对于胸腺微环境中的胸腺细胞发生提出了一个综合的观点。     

用单克隆抗体显示小鼠胚胸腺上皮细胞的分化

以小鼠胸腺基质细胞单克隆抗体ＭＴＳ６、５、２０、３３，用免疫酶法观察了小鼠胚（１２～１９ｄ）胸腺上皮细胞的不同亚类和分化。第１２天胚胸腺原基中有少数细胞开始显示ＭＴＳ６弱阳性反应。第１３ｄ胚胸腺皮质中有些胸腺上皮细胞显示ＭＴＳ５阳性。第１５ｄ胸腺皮质和髓质中有些胸腺上皮细胞开始呈ＭＴＳ２０阳性反应。第１７ｄ胚髓质中可见少数胸腺上皮细胞开始呈ＭＴＳ３３阳性反应。第１９ｄ胚ＭＴＳ５、６阳性反应的胸腺上皮细胞分布于皮质和髓质，并相连成网状，ＭＴＳ２０显示出皮质、髓质中一些散在的胸腺上皮细胞呈阳性反应，而ＭＴＳ３３仅在髓质中显示出少数体积较大的胸腺上皮细胞。第１２～１９ｄ胚ＭＴＳ６、５、２０阳性细胞反应逐渐增强，ＭＴＳ３３阳性细胞反应稍有增强。本研究显示，在鼠胚胸腺发育不同阶段，胸腺上皮细胞的不同亚类的分化有所差异，并提示胸腺上皮细胞的早期分化与Ｔ细胞的分化和发育有密切关系。     

T细胞体外定向诱导分化研究进展

本文重点介绍人的造血干 /祖细胞在体外胸腺微环境中产生并分化发育为成熟T淋巴细胞的过程。具体为胸腺功能对T细胞分化的影响 ;胸腺微环境的建立 ,包括胎儿胸腺器官培养 (FetalthymicorgancultureFTOC)体系和胸腺基质细胞 (TSC)培养体系的建立及CellFoam体系 ;T细胞体外诱导分化 ;T细胞分化研究的应用与展望     

胸腺上皮细胞分化发育的研究进展

<正>T淋巴细胞是免疫系统中最主要的免疫细胞,具有直接杀伤靶细胞、扩大免疫效应的作用。以胸腺上皮细胞为主要成分的胸腺微环境是T淋巴细胞发育、分化、成熟的基础。T淋巴细胞在胸腺皮质微环境中经历阳性选择形成了具有主要组织相容性复合体(major histocompatibility complex,MHC)-Ⅰ、Ⅱ类分子限制性识别能力的T细胞,在髓质微环境中经历阴性选择形成了具有自身抗原耐受能力的成熟T细胞和调节性T细胞~([1]),其中不同表型的胸腺上皮细胞是提供T淋巴细胞发育微环境的     

Thymic epithelial cells: antigen presenting cells that regulate T cell repertoire and tolerance development

During thymocyte development bone marrow-derived precursors in the thymus undergo a series of differentiation steps to produce self-tolerant, mature T lymphocytes. The thymus contains two functionally distinct anatomical compartments, consisting of a centrally located medulla surrounded by the thymic cortex. These compartments in turn are comprised of two major cellular components: (1) the T lymphoid compartment of developing thymocytes and (2) the thymic stroma consisting mainly of thymic epithelial cells (TECs). These epithelial cells are further separated into cortical and medullary TECs (cTECs and mTECs) based on their localization within the thymic cortex or medulla respectively. Reciprocal interactions between thymocytes and epithelial cells are required for the development of both cellular components into a functional thymic organ. Thymocytes provide trophic factors for the development of a complex three-dimensional epithelial cell network, while epithelial cells regulate T cell development through expression and presentation of self-antigens on major histocompatibility molecules. Our work focuses on how thymic epithelial cells regulate T cell development and function and on elucidating the mechanisms of thymic epithelial cell differentiation. Here we review current knowledge and provide our own insight into the development, differentiation and antigen presenting properties of TECs. We focus specifically on how mTECs regulate T cell repertoire selection and central tolerance.     

Depletion of Ift88 in thymic epithelial cells affects thymic synapse and T-cell differentiation in aged mice

Primary cilia are ubiquitous hair-like organelles, usually projecting from the cell surface. They are essential for the organogenesis and homeostasis of various physiological functions, and their dysfunction leads to a plethora of human diseases. However, there are few reports on the role of primary cilia in the immune system; therefore, we focused on their role in the thymus that nurtures immature lymphocytes to full-fledged T cells. We detected primary cilia on the thymic epithelial cell (TEC) expressing transforming growth factor β (TGF-β) receptor in the basal body, and established a line of an intraflagellar transport protein 88 (Ift88) knockout mice lacking primary cilia in TECs (Ift88-TEC null mutant) to clarify their precise role in thymic organogenesis and T-cell differentiation. The Ift88-TEC null mutant mice showed stunted cilia or lack of cilia in TECs. The intercellular contact between T cells and the “thymic synapse” of medullary TECs was slightly disorganized in Ift88-TEC null mutants. Notably, the CD4- and CD8-single positive thymocyte subsets increased significantly. The absence or disorganization of thymic cilia downregulated the TGF-β signaling cascade, increasing the number of single positive thymocytes. To our knowledge, this is the first study reporting the physiological role of primary cilia and Ift88 in regulating the differentiation of the thymus and T cells.

     

Thymic generation and regeneration

Summary: The thymus is a complex epithelial organ in which thymocyte development is dependent upon the sequential contribution of morphologically and phenotypically distinct stromal cell compartments. It is these microenvironments that provide the unique combination of cellular interactions, cytokines, and chemokines to induce thymocyte precursors to undergo a differentiation program that leads to the generation of functional T cells. Despite the indispensable role of thymic epithelium in the generation of T cells, the mediators of this process and the differentiation pathway undertaken by the primordial thymic epithelial cells are not well defined. There is a lack of lineage‐specific cell‐surface‐associated markers, which are needed to characterize putative thymic epithelial stem cell populations. This review explores the role of thymic stromal cells in T‐cell development and thymic organogenesis, as well as the molecular signals that contribute to the growth and expansion of primordial thymic epithelial cells. It highlights recent advances in these areas, which have allowed for a lineage relationship amongst thymic epithelial cell subsets to be proposed. While many fundamental questions remain to be addressed, collectively these works have broadened our understanding of how the thymic epithelium becomes specialized in the ability to support thymocyte differentiation. They should also facilitate the development of novel, rationally based therapeutic strategies for the regeneration and manipulation of thymic function in the treatment of many clinical conditions in which defective T cells have an important etiological role.     

Thymus medulla under construction: Time and space oddities

The development of effective T‐cell‐based immunotherapies to treat infection, cancer, and autoimmunity should incorporate the ground rules that control differentiation of T cells in the thymus. Within the thymus, thymic epithelial cells (TECs) provide microenvironments supportive of the generation and selection of T cells that are responsive to pathogen‐derived antigens, and yet tolerant to self‐determinants. Defects in TEC differentiation cause syndromes that range from immunodeficiency to autoimmunity, which makes the study of TECs of fundamental and clinical importance to comprehend how immunity and tolerance are balanced. Critical to tolerance induction are medullary thymic epithelial cells (mTECs), which purge autoreactive T cells, or redirect them to a regulatory T‐cell lineage. In this issue of the European Journal of Immunology, studies by Baik et al. and Mayer et al. [Eur. J. Immunol. 2016. 46: XXXX‐XXXX and 46: XXXX‐XXXX]) document novel spatial–temporal singularities in the lineage specification and maintenance of mTECs. While Baik et al. define a developmental checkpoint during mTEC specification in the embryo, Mayer et al. reveal that the generation and maintenance of the adult mTEC compartment is temporally controlled in vivo. The two reports described new developmentally related, but temporally distinct principles that underlie the homeostasis of the thymic medulla across life.     

A domain of Foxn1 required for crosstalk-dependent thymic epithelial cell differentiation

Thymic epithelial cells (TECs) are required for T cell maturation within the thymus. In the nude (Foxn1(nu/nu)) mouse, TECs fail to differentiate. We have generated a hypomorphic allele called Foxn1(Delta), from which an N-terminal domain was deleted. The phenotype was thymus specific, identifying a tissue-specific activity for this domain. Foxn1(Delta/Delta) mice showed abnormal thymic architecture, lacking cortical and medullary domains. In contrast to thymi in mice with the null allele, the Foxn1(Delta/Delta) thymus promoted T cell development, but with specific defects at both the double-negative and double-positive stages. Thus, initiation and progression of TEC differentiation are genetically separable functions of Foxn1, and the N-terminal domain is required for crosstalk-dependent TEC differentiation.     

FOXN1 recombinant protein enhances T‐cell regeneration after hematopoietic stem cell transplantation in mice

A prolonged period of T‐cell recovery is the major challenge in hematopoietic stem cell transplantation (HSCT). Thymic epithelial cells (TECs) are the major component of the thymic microenvironment for T‐cell generation. However, TECs undergo degeneration over time. FOXN1 plays a critical role in TEC development and is required to maintain adult TECs for thymopoiesis. To investigate the potential application of FOXN1, we have cloned and expressed recombinant FOXN1 protein (rFOXN1) that was fused with cell‐penetrating peptides. We show here that the rFOXN1 protein can translocate from the cell surface into the cytoplasm and nucleus. Administration of rFOXN1 into both congenic and allogeneic HSCT recipient mice increased the number of TECs, resulting in enhanced thymopoiesis that led to an increased number of functional T cells in the periphery. The increased number of TECs is due to the enhanced survival and proliferation of TECs. Our results suggest that rFOXN1 has the potential to be used in enhancing T‐cell regeneration in patients following HSCT.     

Phenotypic characterization of murine thymic microenvironments.

The thymus provides the necessary microenvironments for the differentiation of T lymphocytes. Thymic non-lymphoid cells, such as epithelial cells, macrophages and interdigitating cells are thought to promote sequential stages in T cell differentiation. However, their specific role in each step of T cell differentiation remains to be established. With the development of new monoclonal antibodies it has now become possible to characterize the different thymic stromal cell types. In this review, various aspects of thymic stromal cells and their functions in T cell differentiation are discussed, such as: (1) phenotypic analysis of stromal cells in situ; (2) the application of new "chimeric' monoclonal antibodies which "link' developing thymocytes and stromal cells; (3) perturbation of thymic microenvironments after cyclosporin-A treatment; (4) perturbation of thymic microenvironments in new transgenic mouse lines; (5) phenotypic analysis of in vitro growing stromal cell lines.     

Differentiation from thymic B cell progenitors to mature B cells in vitro

The role of the thymic microenvironment in the development of murine thymic B cells has yet to be fully clarified. We therefore investigate the microenvironment that supports the development of mature thymic B cells (sIg+/B220+/CD43-B cells) from thymic B cell progenitors with immunophenotypes of sIg-/B220med/CD43+ cells. As we have previously reported, thymic B cells generated from these progenitors in the thymus are CD5+ B cells. We next study the in vitro condition that supports the differentiation of thymic B cell progenitors. Stromal cells (from the bone marrow or thymus), thymus-derived cell lines with the character of thymic nurse cells (TNCs) or thymic epithelial cells (TECs), or the bone marrow-derived cell line (MS-5) are tested for their ability to support B-lymphopoiesis from thymic B cell progenitors. Interestingly, thymic stromal cells (but neither stromal cells from the bone marrow nor stromal cell lines) support the differentiation of thymic B cell progenitors into thymic B cells in the presence of IL-7. Cortical epithelia (but not medullary epithelia, thymic macrophages or dendritic cells) are found to contribute to thymic B cell differentiation. Surface phenotype and Ig rearrangement analyses reveal that mature B cells generated in this condition are primarily CD5+ B cells, indicating that the thymic microenvironment (particularly cortical epithelia) determines the differentiation of thymic B cells.     

Thymic crosstalk restrains the pool of cortical thymic epithelial cells with progenitor properties

Cortical (cTEC) and medullary (mTEC) thymic epithelial cells establish key microenvironments for T‐cell differentiation and arise from thymic epithelial cell progenitors (TEP). However, the nature of TEPs and the mechanism controlling their stemness in the postnatal thymus remain poorly defined. Using TEC clonogenic assays as a surrogate to survey TEP activity, we found that a fraction of cTECs generates specialized clonal‐derived colonies, which contain cells with sustained colony‐forming capacity (ClonoTECs). These ClonoTECs are EpCAM+MHCII‐Foxn1lo cells that lack traits of mature cTECs or mTECs but co‐express stem‐cell markers, including CD24 and Sca‐1. Supportive of their progenitor identity, ClonoTECs reintegrate within native thymic microenvironments and generate cTECs or mTECs in vivo. Strikingly, the frequency of cTECs with the potential to generate ClonoTECs wanes between the postnatal and young adult immunocompetent thymus, but it is sustained in alymphoid Rag2‐/‐Il2rg‐/‐ counterparts. Conversely, transplantation of wild‐type bone marrow hematopoietic progenitors into Rag2‐/‐Il2rg‐/‐ mice and consequent restoration of thymocyte‐mediated TEC differentiation diminishes the frequency of colony‐forming units within cTECs. Our findings provide evidence that the cortical epithelium contains a reservoir of epithelial progenitors whose abundance is dynamically controlled by continual interactions with developing thymocytes across lifespan.