重组白细胞介素2促进小鼠胸腺细胞发育及辐射损伤小鼠免疫功能的恢复

经亚致死量照射的BALB/c小鼠胸腺内残留的胸腺干细胞经历与胚胎胸腺发育十分相似的过程,体内给予IL-2(6×10~5u/kg)可明显促进胸腺细胞由CD4~-CD8~-向CD4~+CD8~+再向CD4~+CD8~-/CD4~-CD8~-分化并明显促进胸腺细胞增殖和亚致死量照射小鼠脾细胞对ConA、LPS 的增殖能力,促进同种异型细胞的混合淋巴细胞反应(MLR)和绵羊红细胞(SRBC)的抗体形成细胞数(PFC)等多项免疫功能的恢复。     

miR-126基因敲减对小鼠胸腺淋巴细胞发育的影响

目的研究miR-126基因敲减对小鼠胸腺细胞发育的影响,并初步探讨其意义。方法观察miR-126基因敲减(KD)小鼠胸腺的体积、重量和细胞总数;Real-time PCR检测小鼠胸腺miR-126表达水平;HE染色观察小鼠胸腺形态学结构;FACS检测胸腺中淋巴细胞比例、核抗原Ki-67的表达以及细胞凋亡的变化;最后,Western blot检测胸腺中磷酸化AKT(p-AKT)和磷酸化ERK1/2(p-ERK)的表达。结果 WT和miR-126KD小鼠胸腺体积大小、重量以及细胞总数均无明显差异,但miR-126KD小鼠胸腺miRNA-126表达水平显著下调(P0.05)。miR-126KD小鼠胸腺组织结构出现形态学异常。与WT小鼠相比,miR-126KD小鼠胸腺CD4~+SP细胞比例及细胞绝对数明显增加(P0.05),而CD4~+CD8~+(DP)细胞比例及绝对数则显著减少(P0.05),miR-126KD小鼠胸腺CD4~+SP细胞核抗原Ki-67表达显著增加(P0.05),且细胞凋亡明显减少(P0.05),而DP细胞Ki-67表达则明显减少(P0.05)。最后,miR-126KD小鼠胸腺淋巴细胞中磷酸化AKT和磷酸化ERK1/2的表达水平明显下调(P0.05)。结论 miR-126基因敲减可显著影响胸腺细胞特别是CD4~+SP细胞的发育,为后续进一步深入探讨miR-126对T淋巴细胞发育以及功能的影响提供重要的实验基础。     

NF-κB诱导激酶基因突变对CD4+CD25+调节性T细胞产生的影响

目的：探讨NIK基因变异鼠—aly鼠自身免疫病的产生与CD4^ CD25^ 调节性T细胞的相关性。方法：利用NIK基因自然突变鼠—aly／aly鼠做为动物模型，aly／ 小鼠做为NIK基因正常对照鼠；CN4^ CD25^ T细胞亚群鉴定采用流式细胞分析仪(FACS)；用免疫组织化学方法观察胸腺结构。结果：aly小鼠的CD4 CD25^ CD8^-胸腺细胞数量和脾脏CD4^ CD25^ CD8^-T淋巴细胞的数量明显低于aly／ 小鼠；aly小鼠胸腺髓质缺少UEA—1阳性细胞。结论：NIK基因突变的aly小鼠CD4^ CD25^ 胸腺细胞和脾脏T淋巴细胞的数量明显降低可能是aly小鼠自身免疫病产生的原因；UEA—1阳性细胞很可能在CN4^ CD25^ 调节性T细胞选择中发挥作用。     

CD3~-CD4~-CD8~ 小鼠胸腺细胞表型的研究

目的　分析CD3-CD4-CD8 胸腺细胞的表型特征 ,阐明其在胸腺发育中所处地位。方法　分离纯化小鼠CD4-CD8 单阳性胸腺细胞 ,进行CD3与其他表面标志的染色 ,然后进行FACS分析。结果　CD3-CD4-CD8 细胞体积较大 ,对可的松敏感 ,TCRαβ阴性 ,高度表达不成熟标志 6C10和HSA ,不表达活化标志CD6 9和成熟标志Qa 2。结论　CD4-CD8 单阳性胸腺细胞可明显分为CD3 和CD3-两个亚群 ,后者代表了胸腺发育过程中由CD4-CD8-双阴性细胞向CD4 CD8 双阳性细胞转变的过渡状态。     

年龄、性别在幼鼠胸腺T细胞增殖中的作用

目的：分析年幼小鼠性别、年龄与CD3、CD4、CD8免疫参数表达的关系。方法：分离3—9周小鼠胸腺、脾脏T淋巴细胞，FACS分析细胞表面CD3、CD4、CD8的表达；CFSE标记后细胞，加入ConA、抗TCR抗体、PMA IONO刺激剂培养72小时，流式细胞仪分析的方法比较不同刺激剂作用下雌、雄小鼠T细胞的增殖。结果：结果胸腺和脾脏表面CD3、CD4、CD8的表达与性别无明显关系，6-9周小鼠脾脏CD3^ 细胞明显多于3—4周小鼠；胸腺细胞的增殖与年龄、性别无关，而3周雌性小鼠脾细胞对PMA IONO刺激后的增殖应答比雄性明显，4-6周雄性小鼠脾细胞的增殖能力强于雌性小鼠，7—8周雌性小鼠脾细胞对抗TCR抗体的应答能力明显减小。结论：免疫系统的雌雄异型可能早于青春期。     

去细胞人羊膜基质的制备及免疫原性

目的制备去细胞人羊膜基质(AHAM)并分析其移植至小鼠体内后的免疫反应,评价去细胞人羊膜基质作为细胞移植支架的免疫原性。方法利用胰蛋白酶-EDTA消化人羊膜(HAM),去除人羊膜上皮细胞,制备新鲜去细胞人羊膜基质;新鲜去细胞人羊膜基质置于含硫酸软骨素及甘油的冷冻保护液中,-80℃保存;使用前经PBS复水处理后即冷冻去细胞人羊膜基质;免疫细胞化学分析去细胞人羊膜基质中人类白细胞抗原的表达情况;将冷冻的去细胞人羊膜基质移植至BALB/c小鼠肝脏内4周后,分析脾脏组织中CD4~+、CD8~+T淋巴细胞比例的变化。结果新鲜及冷冻保存后的去细胞人羊膜基质均不表达人类白细胞抗原;冷冻的去细胞人羊膜基质移植至小鼠体内后,脾脏组织中CD4~+、CD8~+T淋巴细胞无明显变化。结论去细胞人羊膜基质的免疫原性较低,移植后不会引起由T细胞介导的特异性排斥反应,可以作为免疫安全性的生物支架用于疾病的细胞移植治疗。     

Smad4基因条件性敲除对T细胞发育的影响

目的:探讨特异性地在T细胞中敲除Smad4基因后,对T细胞发育的影响。方法:制备小鼠胸腺单细胞悬液,通过流式细胞术检测表面标记分子CD4、CD8、TCRβ、NK1.1、γδT CR和核因子Foxp3的表达情况。结果:Smad4在T细胞中的缺失不影响CD4~-CD8~-、CD4~+CD~8+、CD4~+SP、CD8~+SP、TCRβ~(hi)、NK1.1~+TCRβ~-、NK1.1~+TCRβ~+、CD8~-γδT~+、CD8~+γδT~+、CD4~+Foxp3~+ nTreg等细胞亚群在胸腺细胞中的比例与绝对数。结论:Smad4基因在T细胞中的条件性敲除不影响T细胞的发育。     

CD3/TCR复合物抗体诱导不成熟胸腺细胞亚群的凋亡

目的：采用AnnexinV,PI染色，流式细胞仪分析的方法、DNA琼脂糖电泳法检测不同CD3/TCR复合物抗体对小鼠胸腺T淋巴细胞亚群的促凋亡作用。方法：新鲜分离胸腺细胞，加入PMA、anti-TCR anti-CD28 mAb,anti-TCR mAb等培养20小时，AnnexinV,PI,CD4,CD8细胞染色以及TCR三染，进行FACS分析，同时抽提培养细胞DNA进行琼脂糖电泳。结果：PMA IONO诱导胸腺T细胞的凋亡作用最强，anti-TCR anti-CD28 mAb次之，anti-TCR mAb最弱。结论：AnnexinV,PI细胞染色，流式细胞仪分析的方法可以灵敏检测T淋巴细胞的凋亡；anti-TCR anti-CD28 mAb能明显增强anti-TCR mAb促不成熟的CD4^ CD8^ TCR^ 和CD4^ TCR^ 细胞的凋亡作用；不成熟T细胞经TCR与自身抗原结合的活性过程能产生克隆删除从而产生自我耐受。     

卵巢切除对成年小鼠免疫系统淋巴细胞亚群组成的影响

目的: 研究卵巢切除对成年小鼠胸腺和外周淋巴器官淋巴细胞亚群组成的影响。方法: 用双色免疫荧光结合流式细胞仪, 检测成年小鼠双侧卵巢切除 14d后, 胸腺、脾脏和腹腔淋巴细胞亚群的比例。结果: 与伪手术组相比较, 卵巢切除的成年小鼠胸腺CD4 CD8 T细胞的比率显著升高(P<0. 05), CD4- CD8- T细胞和CD4 CD8- T细胞的比率显著降低(P<0. 05); 脾脏和淋巴结中CD4 CD8- T细胞的比率显著降低(P<0. 05)。结论: 成年小鼠切除卵巢后, 可明显影响免疫系统淋巴细胞亚群的组成; 对于胸腺T细胞的发育及向外周输出也有一定的影响。     

脐血CD34+细胞体外定向诱导分化为T淋巴细胞的实验研究

目的：建立利用人造血干／祖细胞体外定向诱导分化为T淋巴细胞的方法，为研究T细胞生物学特性及细胞免疫提供技术平台。方法：MACS方法分离人脐带CD34^ 细胞接种到人胎儿胸腺基质单层细胞上，IMDM液体培养基含20％人AB血清并加入FL、IL-12、IL-7和IL-2细胞因子组合，于培养7、14、21、28、35、42天取非贴壁细胞利用流式细胞仪对细胞表型进行检测，并进行细胞形态学分析。结果：2周后，CD4^ CD8^ 非成熟T淋巴细胞占细胞总数的0．3％-13．3％，4-5周CD4^ CD8^ T淋巴细胞达到高峰占16．6％-26．5％，且CD3^ CD4^ CD8^ 和CD3^ CD4^-CD8^ T淋巴细胞逐渐增多，6周后达26．5％～64．9％和11．6％-38．9％。培养成熟的T淋巴细胞经PHA IL-2刺激后瑞氏染色鉴定可见大原始淋巴细胞存在。结论：利用人脐血CD34^ 在体外人胎儿胸腺基质单层细胞上加FL、IL-12、IL-7和IL-2细胞因子组合条件下，可诱导分化出T淋巴细胞，并且培养的T细胞对有丝分裂素刺激有增殖反应。     

Expression of a gp33/27,000 MW activation inducer molecule (AIM) on human lymphoid tissues. Induction of cell proliferation on thymocytes and B lymphocytes by anti-AIM antibodies.

We have recently described several monoclonal antibodies (mAb) that recognize a heterodimeric structure (gp33/27,000 MW) expressed on the surface of human peripheral blood T lymphocytes upon activation with different mitogenic stimuli. Such mAb, when used in combination with submitogenic doses of phorbol ester, were capable of triggering T-cell proliferation. The antigen has been designated as activation inducer molecule (AIM). In the present study we have investigated the expression of the AIM in different lymphoid and non-lymphoid tissues. In addition, we have analysed the ability of lymphocyte subsets derived from thymus and tonsil to proliferate in response to anti-AIM mAb. The presence of AIM on subpopulations of lymphoid cells from thymus, tonsil, lymph node and spleen has been demonstrated by immunoprecipitation, flow cytometry and immunoperoxidase staining of tissue sections. By contrast, non-lymphoid cells from tissue such as brain, kidney, liver, lung or skin did not react with anti-AIM mAb. In thymus, the AIM expression was restricted to a subset of CD3+ medullary thymocytes, whereas CD1+ CD3- cortical thymocytes did not express this antigen. Nevertheless, the majority of both purified CD1- and CD3- thymocytes expressed AIM antigen after treatment with PMA. In tonsil and lymph node, a strong staining of a subset of CD3+ T lymphocytes located in the germinal centre was observed by immunohistochemical labelling with anti-AIM mAb. Certain T cells from the paracortical zone and CD19+ B lymphocytes from mantle region were also reactive. Both purified tonsillar T and B lymphocytes strongly expressed AIM after activation with PMA. The anti-AIM mAb was able to induce a strong proliferative response on purified CD1- thymocytes as well as on both purified tonsillar T and B lymphocytes in the presence of submitogenic doses of PMA. By contrast, no proliferative response was induced through the AIM in the CD3- immature thymocyte subset.     

Abnormal distribution of IL-6 receptor in aged MRL/lpr mice: elevated expression on B cells and absence on CD4+ cells.

A mAb against murine IL-6 receptor (IL-6R), KMH7, was obtained by immunization of hamster with recombinant soluble murine IL-6R. Flow cytometry analysis of IL-6R distribution on lymphocytes in BALB/c showed that IL-6R was expressed on peripheral lymph node (LN) T cells of either CD4+ or CD8+ phenotype, and Peyer's patch IgA+ B cells, but not on splenic B cells and thymocytes. A similar distribution was observed in 5 week old MRL/lpr and 16-week-old MRL/n mice. In contrast, in 16 week old MRL/lpr mice of both sexes, IL-6R was expressed on splenic IgM+ cells. Peripheral LN CD4+ T cells in 16 week old female MRL/lpr mice did not express IL-6R. Thymocytes in any population with a phenotype of CD4+ or CD8+, double negative, and double positive were not stained with KMH7 in both BALB/c and MRL/lpr mice. In both strains, IL-6R was induced in CD4+ or CD8+ thymocytes after 2 days of culture, suggesting that CD4+ thymocytes in MRL/lpr have a potential to express IL-6R. Our results suggest that overexpression of IL-6R on B cells and absence of IL-6R on peripheral CD4+ cells are concurrent with, or may contribute to, B cell hyperreactivity and T cell abnormality in this strain.     

Analysis of recent thymic emigrants with subset- and maturity-related markers

The thymus plays an integral role in the development and production of T lymphocytes. However, thymocytes differ markedly in their phenotypic characteristics from the T cells normally found in the peripheral lymphoid organs. We have examined the phenotypic characteristics of recent thymic emigrants and compared them with both mature phenotype thymocytes (CD4+ CD8-CD3+ and CD4-CD8+ CD3+) and lymph node T cells. Recent thymic emigrants were defined as those fluorescein-positive cells found in the lymph node up to 16 h after intrathymic injection of fluorescein. Most cells emigrating from the thymus expressed CD3 and either CD4 or CD8, indicating maturity. Recent thymic emigrants, like mature phenotype thymocytes, were slightly larger on average than peripheral T cells, but this differential was lost within 24 h of emigration. Also like mature thymocytes but unlike peripheral T cells, some recent emigrants expressed heat-stable antigen. This did not change within 24 h of emigration. The antigen CD44 (Pgp-1, Ly-24) was expressed on a proportion of mature thymocytes, recent thymic emigrants, and peripheral T cells, and its expression did not show any clear relationship to maturity. The antigen CD45R also did not show marked changes associated with maturity, but our data do not parallel the published data of the expression of CD45R in the human. We conclude that recent thymic emigrants are phenotypically mature with respect to some antigens but not others. None of the antigens we investigated could have been used to uniquely distinguish recent thymic emigrants from peripheral T cells or from mature thymocytes.     

A lymphocyte differentiation and activation antigen, CZ-1, that distinguishes between CD8+ and unstimulated CD4+ T lymphocytes.

We report the generation and cellular reactivity of a novel rat IgM monoclonal antibody (mAb), CZ-1, made against mouse natural killer (NK) cells activated in vivo. mAb CZ-1 recognizes a molecule whose properties are consistent with that of a trypsin-sensitive, non-phosphatidyl inositol-linked sialoglycoprotein. The expression of the antigen recognized by mAb CZ-1 is restricted mostly to cells of the lymphoid lineage. The antigen is expressed on 10%-25% of bone marrow cells and 3%-5% of thymocytes. Analysis of thymocyte subpopulations indicates expression of the CZ-1 antigen on 100% of the NK1.1+, 27% of the CD4-CD8-, 1.1% of the CD4+CD8+, 1.1% of the CD4+CD8-, and 33% of the CD4-CD8+ cells. In the spleen, the CZ-1 antigen is expressed on B lymphocytes, NK cells, and virtually all CD8+ T lymphocytes. Most unstimulated CD4+ splenic T lymphocytes, monocytes and polymorphonuclear cells, with the notable exception of basophils, do not react with mAb CZ-1. CD4+ T cells activated in vivo by virus infection or in vitro by anti-CD3 and interleukin-2 express the CZ-1 antigen. These results indicate that mAb CZ-1 identifies a novel inducible lymphocyte activation/differentiation antigen that distinguishes between thymic and unstimulated splenic CD4+ and CD8+ T lymphocytes. This mAb will be a useful tool in the identification of lymphocyte subpopulations and in the study of the ontogeny and activation of these cells.     

Guinea pig T lymphocyte development analyzed by enzyme histocytochemistry, monoclonal antibodies, and flow cytometry

Studies of T (thymus-derived) lymphocyte ontogeny in the guinea pig have been hampered by the lack of suitable antigenic or other markers for various T cell subpopulations in this species. Monoclonal antibodies that recognize three distinct surface proteins of guinea pig T cells and react with all peripheral T cells have been used in combination with membrane alkaline phosphatase (AP) to characterize stages of guinea pig T cell development and to determine anatomical localization of different T cell subpopulations. Flow cytofluorographic analysis of thymus, spleen, and lymph node lymphocytes was used to characterize monoclonal antibody specificity. Cortical thymocytes in tissue sections expressed membrane AP activity and contained nuclear terminal deoxynucleotidyl transferase; medullary thymocytes reacted strongly with one of the monoclonal antibodies (8BE6), minimally with a second (5CD2), and not at all with a third (11AE3). In contrast, polyclonal rabbit antiguinea pig T cell antiserum reacted with both cortical and medullary thymocytes. Staining of tissue sections of lymph node and spleen revealed AP+ lymphocytes to be present peripheral to the mantle region of lymph node follicles and to be randomly scattered throughout the splenic red pulp. T cells reactive with monoclonal antibodies were located primarily in paracortical regions of lymph node and the central region around the periarteriolar regions of the spleen. Dual staining of frozen sections and cell suspension of guinea pig lymphoid tissues for AP activity and surface proteins unique to T cells showed that AP+ cells lacked T cell markers. Dual staining for AP activity and surface immunoglobulins or esterase activity showed that AP+ cells are not likely to be derived from either B cell or monocyte-macrophage lineages. AP+ cells in guinea pig secondary lymphoid tissue may represent a unique subset of lymphocytes of unknown function.     

7株小鼠胸腺基质细胞系诱导裸鼠骨髓干细胞表达CD4及CD8分子

为研究胸腺微环境在Ｔ细胞发育中的作用，我室在体外建立了７株小鼠胸腺基质细胞系，命名为ＭＴＥＣＩ～ＭＴＥＣ７。通过初步分离得到裸鼠骨髓富含干细胞的细胞群，表面ＣＤ４及ＣＤ８分子均为阴性。将分离的骨髓干细胞与胸腺基质细胞共育３天后，经双色荧光抗体染色，ＦＡＣＳ分析发现胸腺基质细胞可诱导裸鼠骨髓干细胞表达ＣＤ４ＣＤ８分子。ＭＴＳＣ－ＳＮ及ＭＴＳＣ主要诱导的是ＣＤ４＋ＣＤ８－细胞，部分ＣＤ４＋ＣＤ８＋细胞，而ＣＤ４－ＣＤ８＋细胞极少，这种诱导特点可能和基质细胞系的类型有关。     

Monoclonal antibody to a human leukocyte-specific membrane glycoprotein probably homologous to the leukocyte-common (L-C) antigen of the rat

The monoclonal antibody (F10–89–4) described in this study recognizes an antigen which by quantitative absorption analysis is absent from human brain, kidney, liver, heart, erythrocytes, platelets and normal serum, but is present on spleen, lymph node, chronic lymphatic leukemia cells, bone marrow, thymus and granulocytes at a ratio of 1 : 1 : 0.8 : 0.3 : 0.3 : 0.1, respectively. Analysis with the fluorescence-activated cell sorter showed that 100% of thymocytes, lymph node lymphocytes, blood mononuclear cells and granulocytes carry the antigen, while 83% of bone marrow cells are positive. There was marked heterogeneity in the amount of labeling of thymocytes, with 3 major peaks. There was also heterogeneity of labeling of blood mononuclear cells and lymph node lymphocytes, with a weakly staining hump containing approximately 20% of the cells in the case of lymph node lymphocytes. Double labeling experiments demonstrated that the weakly staining cells of blood and lymph node were B lymphocytes, while frozen sections of thymus showed that the antigen was expressed most weakly in subcapsular cortical thymocytes, and most strongly on medullary thymocytes. Biochemical studies established that the antigen bound to lentil lectin columns, and sodium dodecyl sulfate polyacrylamide gel electrophoresis studies using NaB³ H₄-labeled blood mononuclear cells established that the antigen was a major glycoprotein of lymphocytes, and that its molecular weight was in the region of 190 000 to 215 000.     

Flow microfluorometric analysis of alloantigen expression during T cell development

The fluorescence-activated cell sorter (FACS) was used to examine the expression of several alloantigens on T cells: Thy-1, Lyt-1.1, Lyt-2.1, Ly-5, Ly-6 and Ly-7. Antibodies secreted by monoclonal cell lines were used to characterize the Thy-1.2, Lyt-1.1 and Lyt-2.1 antigenic determinants, whereas Ly-5.1, Ly-6.2 and Ly-7.2 determinants were identified with alloantisera raised by conventional hyperimmunization. Using indirect immunofluorescence with fluorescein isothiocyanate-conjugated reagents, the profiles obtained with the FACS demonstrated that: (a) the expression of Thy-1 is greater on normal thymocytes than on cortisone-resistant thymocytes (CRT), lymph node and spleen cells; (b) in contrast to Thy-1, the expression of Ly-1 on normal thymocytes is less than on CRT, lymph node and spleen cells; (c) about 90% of normal thymocytes but < 50% of CRT, spleen and lymph node T cells are Lyt-2⁺ and (d) although weakly expressed on normal thymocytes, the amount of Ly-6 and Ly-7 present on peripheral T cells was considerably increased. The significance of these findings and the potential for further analysis of T cell developmental pathways is discussed.     

Three distinct subpopulations of sheep T lymphocytes

Monoclonal antibodies reactive with distinct T lymphocyte subpopulations have been described in man, mouse and rat and structural analyses of these antigens have demonstrated a high degree of evolutionary conservation. This report describes the reactivity of three monoclonal antibodies (mAb), 19-19, alpha SBU-T4 and alpha SBU-T8, which define T cell subpopulations in the sheep. The mAb alpha SBU-T4 and alpha SBU-T8 define the sheep CD4 and CD8 molecules, respectively. These two antigens show similar tissue distributions, molecular weights and fluorescence-activated cell sorter profiles to human, mouse and rat CD4 and CD8 molecules. The mAb 19-19 is reactive with a subpopulation of T lymphocytes which displays a tissue distribution unlike that reported for a T cell subset in any other species. 19-19 stains 7% of efferent lymph lymphocytes, 15% of peripheral blood lymphocytes but only 1-3% of lymph node lymphocytes. Two-color immunofluorescence demonstrates that the 19-19+ T cell subset is SBU-T4- and SBU-T8-, and thus defines a third T cell subpopulation in sheep. Immunohistology on frozen lymph node tissue sections localizes 19-19 mAb-reactive cells to the subcapsular region of the lymph node and lymph node trabeculae. Only 1% of thymocytes are 19-19+ and these cells are located mainly in the medulla and often arranged as foci around blood vessels. The 19-19 mAb immunoprecipitates from sheep lymphocytes an antigen with an apparent molecular mass of 215 kDa under both reducing and nonreducing conditions. It is concluded that alpha SBU-T4 and alpha SBU-T8 recognize the sheep homologues of the human T4 and T8 antigens, respectively, whereas 19-19 recognizes an antigen (termed SBU-T19) which has not been reported in any other species.     

Functional and phenotypic analysis of thymic B cells: role in the induction of T cell negative selection.

The phenotype of mouse thymic B cells and their capacity to induce T cell negative selection in vitro were analyzed. Thymic B cells expressed B cell markers such as IgM, Fc gamma receptor, CD44, heat-stable antigen, LFA-1 and CD40. In addition, they were positive for the activation molecule CD69 and displayed high levels of B7-2. Although thymic B cells expressed CD5 on their surface, no CD5-specific mRNA was detected. Moreover, thymic B cells induced a stronger deletion of TCR-transgenic (TG) thymocytes than splenic B cells, which had low CD69 and B7-2 levels. Interestingly, CD40-activated splenic B cells up-regulated CD69 and B7-2 and acquired a capacity to induce T cell deletion comparable to that of thymic B cells. Moreover, thymic B cells from CD40-deficient mice displayed lower CD69 and B7-2 levels than control thymic B cells, and lower capacity to induce the deletion of TCR TG thymocytes. These results support the hypothesis that CD40-mediated activation of thymic B cells determines a high efficiency of antigen presentation, suggesting that within the thymus B cells may play an important role in the elimination of autoreactive thymocytes.