Regulatory T (T-reg) cells suppress the development of inflammatory disease, but our knowledge of transcriptional regulators that control this function remains incomplete. Here we show that expression of Id2 and Id3 in T-reg cells was required to suppress development of fatal inflammatory disease. We found that T cell antigen receptor (TCR)-driven signaling initially decreased the abundance of Id3, which led to the activation of a follicular regulatory T (T-FR) cell-specific transcription signature. However, sustained lower abundance of Id2 and Id3 interfered with proper development of T-FR cells. Depletion of Id2 and Id3 expression in T-reg cells resulted in compromised maintenance and localization of the T-reg cell population. Thus, Id2 and Id3 enforce T-FR cell checkpoints and control the maintenance and homing of T-reg cells.

In chronic viral infections, persistent antigen presentation causes progressive exhaustion of virus-specific CD8+ T cells. It has become clear, however, that virus-specific naïve CD8+ T cells newly generated from the thymus can be primed with persisting antigens. In the setting of low antigen density and resolved inflammation, newly primed CD8+ T cells are preferentially recruited into the functional memory pool. Thus, continual recruitment of naïve CD8+ T cells from the thymus is important for preserving the population of functional memory CD8+ T cells in chronically infected animals. Friend virus (FV) is the pathogenic murine retrovirus that establishes chronic infection in adult mice, which is bolstered by the profound exhaustion of virus-specific CD8+ T cells induced during the early phase of infection. Here we show an additional evasion strategy in which FV disseminates efficiently into the thymus, ultimately leading to clonal deletion of thymocytes that are reactive to FV antigens. Owing to the resultant lack of virus-specific recent thymic emigrants, along with the above exhaustion of antigen-experienced peripheral CD8+ T cells, mice chronically infected with FV fail to establish a functional virus-specific CD8+ T cell pool, and are highly susceptible to challenge with tumor cells expressing FV-encoded antigen. However, FV-specific naïve CD8+ T cells generated in uninfected mice can be primed and differentiate into functional memory CD8+ T cells upon their transfer into chronically infected animals. These findings indicate that virus-induced central tolerance that develops during the chronic phase of infection accelerates the accumulation of dysfunctional memory CD8+ T cells.

Polycomb group gene Bmi1 plays an essential role in HSCs and the BM microenvironment. Recent reports also pointed to the importance of Bmi1 in thymocyte development. However, little is known about its role in the development of the thymic microenvironment. Here, we examined the function of Bmi1 in thymic epithelial cells (TECs) by using the engraftment of fetal thymus (FT) lobes under the kidney capsule. The engrafted Bmi1(-/-) FT lobes were clearly smaller and the number of thymocytes in these lobes was significantly decreased compared with control FT lobes. Analysis of the cell cycle status of TECs in the reconstituted lobes revealed that the reduction of thymus size in Bmi1(-/-) FT grafts was caused by less proliferation of TECs during the early expansion stage. Unlike cases with hematopoietic stem cells or thymocytes, the deletion of p16Ink4a and p19Arf could not restore the defects in Bmi1(-/-) TEC, indicating a distinct role for Bmi1 in TECs. In conclusion, epigenetic regulator polycomb group gene Bmi1 plays a role in the thymic microenvironment in a regeneration process by supporting TEC growth, and thereby contributes to the control of thymus size for T-cell growth in mice.

ABSTRACTMoxibustion is a technique used in traditional oriental medicine, the aim of which is to cure and/or prevent illness by activating a person's ability for self‐healing. In this study, we assessed how moxibustion would affect the immune system and whether it would augment protective immunity. Mice were treated with moxibustion at Zusanli (ST36) acupoints; we analyzed mortality and cytokine activity in sera after infection with herpes simplex virus type 1 (HSV‐1), and cytokine gene expression in the skin and the spleen without a virus challenge. Our study demonstrates that pretreatment of BALB/c mice with moxibustion resulted in a marked increase in the survival rate after infection with lethal doses of HSV‐1, and elevated serum levels of IL‐1β and IFN‐γ on days 1 and 6 post‐infection with HSV‐1. Semi‐quantitative RT‐PCR assay showed that moxibustion treatment augmented the expression of IL‐1α, IL‐1β, IL‐6, universal‐IFN‐α, MIP‐1α, and TNF‐α mRNA in the skin, and IL‐1α, IL‐1β, IL‐12p40, IL‐15, u‐IFN‐α, MIP‐1α, and TNF‐α mRNA in the spleen. Moreover, moxibustion induces augmentation of natural killer cell activity. Collectively, our study demonstrates that moxibustion activates protective responses against HSV‐1 infection through the activation of cytokine production including IFN, and of NK cells.

The Global Thymus Network (GTN) is a series of linked international meetings dedicated to the study of the thymus and T-cell biology (Table 1). The four meetings and organizing regions that compose the GTN are: the Rolduc Workshop (Europe), KTCC (Japan), ThymOz (Australia) and ThymUS (USA). Over time, the participants and organizers of the individual meetings realized that their coordination was both logical and mutually beneficial to all. Therefore, it was agreed that from 2005, each of these meetings should be held every four years, and from this year, the meetings are coordinated by the unified governing board, composed of representative organizers of each of the conferences (see list of authors of this article). Here, we would like to introduce the GTN and highlight the common and specific flavors of the four conferences.Table 1The four meetings of the Global Thymus Network.MeetingRegionFoundedMost recentUpcomingWebsiteKTCCJapan199120052009http://ktcc.umin.jpThymOzAustralia199520062010http://www.thymoz.comRolducEurope198920072011http://www.rolduc-thymus.orgThymUSCaribbean/US200120082012http://www.thymus-conference.orgNote: authors of this article are listed in the order in which the respective conferences are being held from now on. Please address correspondence to any one of them (via the addresses on the above websites) regarding individual conferences or this article. Open table in a new tab Individual meetings and their historiesThe first thymus-centered meeting was the Rolduc Workshop on T-cell biology, originally held in 1989 at the 12th century Rolduc Abbey. Over the years, Hergen Spits and his core Dutch group played a key part in facilitating the organization of Rolduc with researchers from other European countries rotated as the academic organizers. Although T-cell and thymus-centric, Rolduc is known as a ‘workshop’ for the phenotypic classification of thymus stromal cells and their structural and functional contribution to the microenvironment controlling T-cell development.The KTCC (Kyoto T-cell conference) was founded by Yoshimoto Katsura in 1991, and is held in the historic city of Kyoto. It has provided an opportunity for researchers in Japan and Asia working on T cells and related fields to exchange scientific ideas through intensive discussions with, and between, internationally acclaimed research groups. KTCC hosts annual domestic meetings and an international workshop once every four years.The ThymOz (Thymus Australia) series of international conferences was founded by Richard Boyd and Ann Chidgey in 1995, with the aim of creating a stimulating and conducive environment ‘down under’ that would catalyze a vigorous exchange of recent data, based around the thymus. The first conference was aptly opened by, and in honor of, Jacques Miller. ThymOz is held on Heron Island, a unique national marine park on the Great Barrier Reef, with attendees ranging from international experts to new students. The sixth ThymOz (March, 2010) will incorporate stem cell biology into the understanding and function of the thymus and the clinical translation of fundamental research.The ThymUS conference, co-founded by Janko Nikolich-Zugich and Howard Petrie, was first held in 2001, and is focused on countries of the Caribbean region. It was founded as a sister conference to ThymOz, with which it has been coordinated since its inception. Like ThymOz, ThymUS does not sponsor its speakers, but rather subsidizes all attendees, with a special focus on trainees. A characteristic feature of the ThymUS conference is a focus on events that occur within the thymus, and how they affect peripheral T-cell homeostasis and immunity, in addition to disease states such as immunosenescence, autoimmunity and cancer.Common essential features of the GTN conferencesIn addition to the common focus on the formation and function of the thymus, T-cell development and T-cell biology, the four meetings share other important components, which the organizers believe to be vital for successful conferences of this type. First, they each have shorter (∼20 min) presentations, eliminating the need for speakers to expend precious time introducing the basic terms and background literature. Second, they all host ∼100 to 175 attendees in a single scientific activity, and promote interactions in an informal and comfortable atmosphere, including highly interactive poster sessions. Third, deliberate steps are taken to retain speakers on site throughout the duration of the conference, providing further cohesion and interaction. Fourthly, all four meetings are solely and exclusively run by the scientists and for the scientists in the field and do not involve large conference organizations. In summary, the GTN meetings offer a detailed and personalized experience for those specifically interested in the T-cell development field. Finally, strong efforts are made to ensure diversity of the meetings and to support participation of post-docs and students by providing various subsidies. We feel that mentoring young scientists ensures critical rejuvenation of the field. Consistent with this, the KTCC 2009 held 1–4 June this year, marks the fifth anniversary of the GTN and has a travel bursary to encourage post-doc and student attendance. The conference promises exciting science and lively discussion with topics including: thymus microenvironments, lymphoid progenitors and lineage commitment, selection and differentiation, recognition and activation, immune response and memory, immune regulation and diseases. The Global Thymus Network (GTN) is a series of linked international meetings dedicated to the study of the thymus and T-cell biology (Table 1). The four meetings and organizing regions that compose the GTN are: the Rolduc Workshop (Europe), KTCC (Japan), ThymOz (Australia) and ThymUS (USA). Over time, the participants and organizers of the individual meetings realized that their coordination was both logical and mutually beneficial to all. Therefore, it was agreed that from 2005, each of these meetings should be held every four years, and from this year, the meetings are coordinated by the unified governing board, composed of representative organizers of each of the conferences (see list of authors of this article). Here, we would like to introduce the GTN and highlight the common and specific flavors of the four conferences. Note: authors of this article are listed in the order in which the respective conferences are being held from now on. Please address correspondence to any one of them (via the addresses on the above websites) regarding individual conferences or this article. Individual meetings and their historiesThe first thymus-centered meeting was the Rolduc Workshop on T-cell biology, originally held in 1989 at the 12th century Rolduc Abbey. Over the years, Hergen Spits and his core Dutch group played a key part in facilitating the organization of Rolduc with researchers from other European countries rotated as the academic organizers. Although T-cell and thymus-centric, Rolduc is known as a ‘workshop’ for the phenotypic classification of thymus stromal cells and their structural and functional contribution to the microenvironment controlling T-cell development.The KTCC (Kyoto T-cell conference) was founded by Yoshimoto Katsura in 1991, and is held in the historic city of Kyoto. It has provided an opportunity for researchers in Japan and Asia working on T cells and related fields to exchange scientific ideas through intensive discussions with, and between, internationally acclaimed research groups. KTCC hosts annual domestic meetings and an international workshop once every four years.The ThymOz (Thymus Australia) series of international conferences was founded by Richard Boyd and Ann Chidgey in 1995, with the aim of creating a stimulating and conducive environment ‘down under’ that would catalyze a vigorous exchange of recent data, based around the thymus. The first conference was aptly opened by, and in honor of, Jacques Miller. ThymOz is held on Heron Island, a unique national marine park on the Great Barrier Reef, with attendees ranging from international experts to new students. The sixth ThymOz (March, 2010) will incorporate stem cell biology into the understanding and function of the thymus and the clinical translation of fundamental research.The ThymUS conference, co-founded by Janko Nikolich-Zugich and Howard Petrie, was first held in 2001, and is focused on countries of the Caribbean region. It was founded as a sister conference to ThymOz, with which it has been coordinated since its inception. Like ThymOz, ThymUS does not sponsor its speakers, but rather subsidizes all attendees, with a special focus on trainees. A characteristic feature of the ThymUS conference is a focus on events that occur within the thymus, and how they affect peripheral T-cell homeostasis and immunity, in addition to disease states such as immunosenescence, autoimmunity and cancer. The first thymus-centered meeting was the Rolduc Workshop on T-cell biology, originally held in 1989 at the 12th century Rolduc Abbey. Over the years, Hergen Spits and his core Dutch group played a key part in facilitating the organization of Rolduc with researchers from other European countries rotated as the academic organizers. Although T-cell and thymus-centric, Rolduc is known as a ‘workshop’ for the phenotypic classification of thymus stromal cells and their structural and functional contribution to the microenvironment controlling T-cell development. The KTCC (Kyoto T-cell conference) was founded by Yoshimoto Katsura in 1991, and is held in the historic city of Kyoto. It has provided an opportunity for researchers in Japan and Asia working on T cells and related fields to exchange scientific ideas through intensive discussions with, and between, internationally acclaimed research groups. KTCC hosts annual domestic meetings and an international workshop once every four years. The ThymOz (Thymus Australia) series of international conferences was founded by Richard Boyd and Ann Chidgey in 1995, with the aim of creating a stimulating and conducive environment ‘down under’ that would catalyze a vigorous exchange of recent data, based around the thymus. The first conference was aptly opened by, and in honor of, Jacques Miller. ThymOz is held on Heron Island, a unique national marine park on the Great Barrier Reef, with attendees ranging from international experts to new students. The sixth ThymOz (March, 2010) will incorporate stem cell biology into the understanding and function of the thymus and the clinical translation of fundamental research. The ThymUS conference, co-founded by Janko Nikolich-Zugich and Howard Petrie, was first held in 2001, and is focused on countries of the Caribbean region. It was founded as a sister conference to ThymOz, with which it has been coordinated since its inception. Like ThymOz, ThymUS does not sponsor its speakers, but rather subsidizes all attendees, with a special focus on trainees. A characteristic feature of the ThymUS conference is a focus on events that occur within the thymus, and how they affect peripheral T-cell homeostasis and immunity, in addition to disease states such as immunosenescence, autoimmunity and cancer. Common essential features of the GTN conferencesIn addition to the common focus on the formation and function of the thymus, T-cell development and T-cell biology, the four meetings share other important components, which the organizers believe to be vital for successful conferences of this type. First, they each have shorter (∼20 min) presentations, eliminating the need for speakers to expend precious time introducing the basic terms and background literature. Second, they all host ∼100 to 175 attendees in a single scientific activity, and promote interactions in an informal and comfortable atmosphere, including highly interactive poster sessions. Third, deliberate steps are taken to retain speakers on site throughout the duration of the conference, providing further cohesion and interaction. Fourthly, all four meetings are solely and exclusively run by the scientists and for the scientists in the field and do not involve large conference organizations. In summary, the GTN meetings offer a detailed and personalized experience for those specifically interested in the T-cell development field. Finally, strong efforts are made to ensure diversity of the meetings and to support participation of post-docs and students by providing various subsidies. We feel that mentoring young scientists ensures critical rejuvenation of the field. Consistent with this, the KTCC 2009 held 1–4 June this year, marks the fifth anniversary of the GTN and has a travel bursary to encourage post-doc and student attendance. The conference promises exciting science and lively discussion with topics including: thymus microenvironments, lymphoid progenitors and lineage commitment, selection and differentiation, recognition and activation, immune response and memory, immune regulation and diseases. In addition to the common focus on the formation and function of the thymus, T-cell development and T-cell biology, the four meetings share other important components, which the organizers believe to be vital for successful conferences of this type. First, they each have shorter (∼20 min) presentations, eliminating the need for speakers to expend precious time introducing the basic terms and background literature. Second, they all host ∼100 to 175 attendees in a single scientific activity, and promote interactions in an informal and comfortable atmosphere, including highly interactive poster sessions. Third, deliberate steps are taken to retain speakers on site throughout the duration of the conference, providing further cohesion and interaction. Fourthly, all four meetings are solely and exclusively run by the scientists and for the scientists in the field and do not involve large conference organizations. In summary, the GTN meetings offer a detailed and personalized experience for those specifically interested in the T-cell development field. Finally, strong efforts are made to ensure diversity of the meetings and to support participation of post-docs and students by providing various subsidies. We feel that mentoring young scientists ensures critical rejuvenation of the field. Consistent with this, the KTCC 2009 held 1–4 June this year, marks the fifth anniversary of the GTN and has a travel bursary to encourage post-doc and student attendance. The conference promises exciting science and lively discussion with topics including: thymus microenvironments, lymphoid progenitors and lineage commitment, selection and differentiation, recognition and activation, immune response and memory, immune regulation and diseases.

The development and maintenance of thymic microenvironments depends on sustained crosstalk signals derived from developing thymocytes. However, the molecular basis for the initial phase in the lymphoid dependent development of thymic epithelial cells (TECs) remains unclear. Here we show that similarly to regular thymocytes, developing B cells enforced to express the Notch ligand Delta-like-1 (DLL1) efficiently induce the non-polarized, three-dimensional (3D) meshwork architecture of cortical TECs in fetal thymic organ culture. Moreover, the DLL1-overexpressing B cells induce well-developed distinct medullae. Such medullae also arose in lobes reconstituted with Rag2−/− thymocytes overexpressing DLL1. Our present findings thus strongly suggest that Notch signaling from thymocytes to TECs induces TEC development at an early phase of thymic organogenesis. The present approach using non-T lineage cells for the in vitro construction of thymic environments may also provide a novel tool for thymus regeneration and T cell production in immunocompromised individuals.

Thymic epithelial cells (TECs), derived from polarized two-dimensional (2D) oriented endodermal cells, are distinguished from other epithelial cells by their unique three-dimensional (3D) phenotype. However, some polarized epithelial cells remain present in the normal thymus, forming thymic cysts at the cortico-medullary junction. Here, we analyse the dynamics, origin and phenotype of such thymic cysts. In time-course experiments, we show a reverse correlation between thymic cyst expansion and the presence of thymocytes, suggesting a default pathway for the development of TECs in the absence of thymocytes. By transplanting isolated TEC populations into E15 fetal thymic lobes, we provide evidence that medullary thymic epithelial cells (mTECs), rather than cortical thymic epithelial cells (cTECs) contribute to the formation of thymic cysts. Finally, thymi of reporter mice reveal that the cysts originate from epithelia committed to a thymic fate, as indicated by the expression of Foxn1. The 2D-phenotype of cyst-lining TECs is not caused by a downregulation of Foxn1 expression, since a significant proportion of these cells in the embryonic and adult thymus continues to express Foxn1 at the protein level.

Foxn1 transcription factor is known to be essential for development of the thymic organ. We analyzed whether Foxn1 expression in thymic epithelial cells is necessary for the expression of functional molecules such as Delta-like 4 (Dll4) and CCL25, and whether maintenance of these molecular expressions depends on the Foxn1 transcription factor. We show that almost all thymic epithelial cells in the early thymus anlagen express Foxn1, and Dll4 and CCL25 are limitedly expressed in Foxn1-positive epithelial cells. The results are consistent with previous reports suggesting the indispensability of Foxn1 for epithelial cell differentiation which enables these cells to induce the expressions of CCL25 (Bleul, C. C. and Boehm, T. 2000. Chemokines define distinct microenvironments in the developing thymus. Eur. J. Immunol. 30:3371), Dll1 and Dll4 (Tsukamoto, N., Itoi, M., Nishikawa, M. and Amagai, T. 2005. Lack of Delta like 1 and 4 expressions in nude thymus anlages. Cell. Immunol. 234:77). On the other hand, the expression of Foxn1 was not detectable in a large number of post-natal thymic epithelial cells. Both Foxn1-positive and -negative epithelial cells seem to express Dll4 and CCL25. Therefore, the expressions of Dll4 and CCL25 are independent of Foxn1 transcription factor in the post-natal thymus. These results indicate that in the post-natal thymus, epithelial cells may maintain the expressions of those functional molecules without the aid of Foxn1 transcription factor.

Epithelial-mesenchymal interactions have essential roles in thymus organogenesis. Mesenchymal cells are known to be required for epithelial cell proliferation. However, the contribution of mesenchymal cells to thymic epithelial cell differentiation is still unclear. In the present study, we have investigated the roles of mesenchymal cells in functional development of epithelial cells in the thymus anlage in patch (ph) mutant mice, which have a primarily defect in mesenchymal cells caused by the absence of platelet-derived growth factor receptor alpha expression. In the ph/ph thymus anlage, T cell progenitors migrate normally among the epithelial cells, however, they are severely impaired to proliferate and differentiate to CD25-positive cells. Epithelial cells of the ph/ph thymus anlage show severely impaired proliferation and expression of functional molecules, such as SCF, Delta-like 4 and MHC class II, which have crucial roles in T cell development. Moreover, the cultured ph/ph thymus anlage fails to develop into a mature organ supporting full T cell development. Addition of intact thymic mesenchymal cells to organ culture induces development of the ph/ph thymus anlage. In the cultured lobes, added mesenchymal cells contribute to form not only the capsule but also the meshwork structure mingled with epithelial cells. Our present results strongly suggest the roles of mesenchymal cells in functional development of epithelial cells in thymus organogenesis. In addition, our data suggest that mesenchymal cells are required to create the thymic microenvironment and to maintain epithelial architecture and function.

It is known that selected populations of lymphoid cells migrate into and from the adult thymus through blood vessels at the cortico-medullary junction and in the medulla. Here, we show that in the perivascular spaces (PVS) of mice surrounding large blood vessels, CD117-positive hematopoietic progenitor cells, CD4 single-positive (SP) and CD8SP T cells are located. However, developing thymocytes, CD25-positive cells and CD4 and CD8 double-positive cells, are not detectable in the PVS. After intravenous (i.v.) injection of CD117-positive bone marrow (BM) cells from C57BL/6 mice into non-irradiated RAG2 mutant mice i.v., donor-derived cells first preferentially migrate into the PVS within 30 min, and then the number of donor-derived cells in the thymic parenchyma increases. Likewise, newly developed mature T cells in the thymic parenchyma of RAG2 mutant mice transferred with wild-type BM cells migrate to the PVS, before leaving the thymus to the circulation. Accumulation of mature T cells was observed after treatment with sphingosine-1 phosphate receptor agonist FTY720 not only in the medulla but also in the thymic PVS. These results suggest that the PVS is a transit pathway for progenitor cells to immigrate into the thymus and for mature T cells to emigrate from the thymus.

Notch signaling is required for the early steps in T cell development. However, distribution of Notch ligands in the thymus anlages is not clear. We investigated the expressions of Delta like (Dll) 1 and Dll4 in the mouse thymus anlages. In the normal thymus anlages on embryonic day 13, Dll4 is strongly expressed throughout the epithelial region, but Dll1 is expressed only in scattered cells. In contrast, epithelial cells of the nude thymus anlages express neither Dll1 nor Dll4. These results indicate that expressions of Dll1 and Dll4 in thymic epithelial cells are regulated by Foxn1 transcriptional factor.

Polycomb group (PcG) proteins play a role in the maintenance of cellular identity throughout many rounds of cell division through the regulation of gene expression. In this report we demonstrate that the loss of the PcG gene mel-18 impairs the expansion of the most immature T progenitor cells at a stage before the rearrangement of the TCR beta-chain gene in vivo and in vitro. This impairment of these T progenitors appears to be associated with increased susceptibility to cell death. We also show that the expression of Hes-1, one of the target genes of the Notch signaling pathway, is drastically down-regulated in early T progenitors isolated from mel-18(-/-) mice. In addition, mel-18(-/-) T precursors could not maintain the Hes-1 expression induced by Delta-like-1 in monolayer culture. Collectively, these data indicate that mel-18 contributes to the maintenance of the active state of the Hes-1 gene as a cellular memory system, thereby supporting the expansion of early T progenitors.

It remains controversial whether the thymus-colonizing progenitors are committed to the T cell lineage. A major problem that has impeded the characterization of thymic immigrants has been that the earliest intrathymic progenitors thus far identified do not necessarily represent the genuine thymic immigrants, because their developmental potential should have been influenced by contact with the thymic microenvironment. In the present study, we examined the developmental potential of the ontogenically earliest thymic progenitors of day 11 murine fetus. These cells reside in the surrounding mesenchymal region and have not encountered thymic epithelial components. Flow cytometric and immunohistochemical analyses demonstrated that these cells are exclusively Lin(-)c-kit(+)IL-7R(+). Limiting dilution analyses disclosed that the progenitors with T cell potential were abundant, while those with B cell potential were virtually absent in the region of day 11 thymic anlage. Clonal analyses reveled that they are restricted to T, NK, and dendritic cell lineages. Each progenitor was capable of forming a large number of precursors that may clonally accommodate highly diverse TCRbeta chains. These results provide direct evidence that the progenitors restricted to the T/NK/dendritic cell lineage selectively immigrate into the thymus.

The functions of a chemokine CXC chemokine ligand (CXCL) 12/stromal cell-derived factor-1/pre-B cell growth stimulating factor and its physiologic receptor CXCR4 in T cell development are controversial. In this study, we have genetically further characterized their roles in fetal and adult T cell development using mutant and chimeric mice. In CXCL12(-/-) or CXCR4(-/-) embryos on a C57BL/6 background, accumulation of T cell progenitors in the outer mesenchymal layer of the thymus anlage during initial colonization of the fetal thymus was comparable with that seen in wild-type embryos. However, the expansion of CD3(-)CD4(-)CD8(-) triple-negative T cell precursors at the CD44(-)CD25(+) and CD44(-)CD25(-) stages, and CD4(+)CD8(+) double-positive thymocytes was affected during embryogenesis in these mutants. In radiation chimeras competitively repopulated with CXCR4(-/-) fetal liver cells, the reduction in donor-derived thymocytes compared with wild-type chimeras was much more severe than the reduction in donor-derived myeloid lineage cells in bone marrow. Triple negative CD44(+)CD25(+) T cell precursors exhibited survival response to CXCL12 in the presence of stem cell factor as well as migratory response to CXCL12. Thus, it may be that CXCL12 and CXCR4 are involved in the expansion of T cell precursors in both fetal and adult thymus in vivo. Finally, enforced expression of bcl-2 did not rescue impaired T cell development in CXCR4(-/-) embryos or impaired reconstitution of CXCR4(-/-) thymocytes in competitively repopulated mice, suggesting that defects in T cell development caused by CXCR4 mutation are not caused by reduced expression of bcl-2.

I. はじめに 今 回の企画では、Systematic Reviewに よって 「鍼の疾病予防 ・保健増 進に対する効果について の研究の現状について具体性を持って総括 し、今 後の研究の方向性を検討する。」という重い提起 がされた。生体の自然治癒力を担 うものの1つ と しての広い意味での免疫学の観点から、本稿では 免疫系の関わる疾患の予防 ・治療における鍼灸の 意義を、臨床研究と基礎研究の現状 と展開の方向 性を考えながら可能な範囲で現段階を総括 してみた。 まず最初に人を対象 とした近年の免疫系疾患に 対する臨床的なランダム化比較試験(RCT)の 例 を見てみたい。David1)ら によるリウマチへの鍼 灸の効果に関するRCTで は彼 らはLI3へ4分 間週 1回 計5回 の治療 を評価 し無効 としている(表 1)。 この点にはTukmachi2)がLettertoEditorで 治 療法と治療期間について批判 している。他方、変 形性関節症の鍼灸治療では十分検討 された治療法 と治療期間を用いたRCTに よって痙痛緩和などで の効果が示 されている3)。 また多 くのRCTで は、 東洋医学的診断による疾病分類が無視 されている ことが多 く、さらに治療法の画一化や治療成績の 評価法の上での問題点も多い。画一的RCTの 結果 として、vickers4)ら のReviewに あるように 『正 確な』?RCTで は多 くの疾患で鍼灸は有効 とはい えないという結論が引き出されているのではない かと思われる。近年臨床研究における統計処理 と RCTの 重要性が声高に議論され、それ自体は大変

Development of a mature T-cell repertoire in the thymus depends on lympho-stromal interaction between thymocytes and stromal cells. To facilitate intercellular contact, the epithelium in the thymus has differentiated into a unique three-dimensionally (3D)-oriented network. Here we analyze factors influencing induction and maintenance of the 3D configuration of the epithelial network in fetal thymic lobes in vitro. We show that the 3D configuration of the thymic stroma depends on (a) the oxygen pressure in vitro and (b) permanent physical contact between stromal cells and developing thymocytes. This latter feature is demonstrated by incubation of fetal thymic lobes with deoxyguanosine (d-Guo), inducing a 2D-organized thymic stroma, with thymic cysts appearing. Reconstitution of d-Guo-treated lobes with a limited number of flow-sorted T-cell progenitors restores the 3D configuration of the thymic epithelium, but only at high oxygen pressure. This study underlines the plasticity of thymic epithelium and shows that the unique organization of the thymic epithelium is dependent on both oxygen and crosstalk signals derived from developing thymocytes.

Thymic epithelial cells, which create a three-dimensionally organized meshwork structure peculiar to the thymus, develop from simple epithelia of the third pharyngeal pouch and cleft during organogenesis. We comparatively investigated the thymus anlages of normal and nude mice by immunohistochemical analysis with regard to epithelial organization and distribution of hematopoietic progenitor cells at early stages of organogenesis. Our results show that development of the mouse thymus anlage at early stages can be subdivided into at least two stages by the differences in epithelial organization, i.e. stratified epithelial stage on embryonic day (Ed) 11 and clustered epithelial stage on Ed12. At the former stage, hematopoietic progenitor cells are accumulated in the mesenchymal layer of the thymus anlage, and at the latter stage progenitor cells enter the epithelial cluster and proliferate. In nude mice, hematopoietic progenitor cells are found in the mesenchymal layer on Ed11.5, but they are not observed among epithelial cells on Ed12, even though epithelial cells form a cluster structure. The present results suggest that aberrant development of the nude mouse thymus anlage occurs at the clustered epithelial stage and that epithelial cells of the nude anlage lack the ability to induce the entrance of hematopoietic progenitor cells into the epithelial cluster.