T-bet、GATA-3 与T 细胞亚群在再障中的相关性研究

目的:探讨外周血中T-bet和GATA-3 mRNA的表达在再生障碍性贫血中的发病机制及意义。方法:入选27例再障患者,其中重型再障15例,轻型再障l2例,25例健康体检者为对照组。采用流式细胞术检测参试者外周血Thl和Th2细胞,RT-PCR检测外周血单核细胞中转录因子T-bet和GATA-3 mRNA的表达。结果:与健康对照组相比,再障患者血浆T-bet mRNA与Th1细胞比例显著升高(P<0.01),GATA-3 mRNA与Th2细胞明显降低(P<0.05、P<0.01)。与轻型再障患者相比,重型再障患者血浆转录因子T-bet mRNA及Th1细胞比例均明显升高(P<0.01),GATA-3 mRNA水平与Th2细胞比例也显著下降(P<0.05、P<0.01)。结论:T-bet与GATA-3异常表达可增强Th1细胞功能,抑制Th2细胞功能,导致患者免疫功能异常,最终引起再障发生、发展。     

糖尿病患者外周血Th17/Treg细胞及相关细胞因子的表达变化

目的:探讨糖尿病患者外周血Th17细胞和Treg细胞数量以及相关细胞因子表达的变化。方法:以本院2013年1月至2015年12月收治的50例糖尿病患者为研究对象,其中1型糖尿病患者25例,2型糖尿病患者25例,同时以25例健康体检人群为正常对照,检测各组外周血Th17/Treg细胞数量以及血清IL-17、IL-10和TGF-β水平。结果:糖尿病患者外周血中Th17细胞比例均显著高于正常对照组(P0.05)而Treg细胞的比例均显著低于正常对照组(P0.05),且1型糖尿病患者Treg细胞比例显著低于2型糖尿病患者(P0.05)。糖尿病患者血清中IL-10和TGF-β水平均显著低于正常对照组(P0.05)而IL-17水平均显著高于正常对照组(P0.05),且1型糖尿病患者的IL-10水平显著低于2型糖尿病患者(P0.05)。结论:糖尿病患者体内Treg细胞数量及相关细胞因子低于正常而Th17细胞数量及相关细胞因子高于正常,这可能与患者体内的自身免疫失调有关。     

特异性免疫治疗对屋尘螨致敏哮喘小鼠NKT细胞的影响

目的:研究特异性免疫治疗(SIT)对哮喘小鼠自然杀伤T(NKT)细胞的影响。方法:24只BALB/C小鼠随机分为对照组(A组)、哮喘模型组(B组)、哮喘免疫治疗(SIT)组(C组),各8只。通过屋尘螨提取液(HDM)诱导建立哮喘小鼠模型并进行SIT治疗。检测各组小鼠的气道反应性、支气管肺泡灌洗液(BAlF)细胞计数及分类、ELISA检测IL-4、IFN-γ以及应用流式细胞仪检测NKT细胞数目,通过RT-PCR方法检测T-bet和GATA-3mRNA表达水平;HE染色观察小鼠肺组织的改变。结果:与B组相比,C组气道反应性明显下降(P0.01);BALF中细胞总数及嗜酸性粒细胞(EOS)数显著减少(P0.01);血清IL-4分泌显著降低(P0.01),IFN-γ显著升高(P0.01);NKT细胞数及其成熟型比例明显升高(P0.05);T-betmRNA表达水平明显升高(P0.01),且与NKT细胞数及其成熟型比例呈正相关性,GATA-3mRNA表达水平明显降低(P0.05),且与NKT细胞数及其成熟型比例呈负相关性。B组肺部管腔周围炎性细胞聚集,组织上皮损伤,组织水肿,而C组肺部变应性炎症明显减轻。C组其他各项指标接近A组。结论:哮喘的发生可能与NKT细胞失调相关,通过改变NKT细胞数目及其成熟型比例来调节GATA-3/T-bet的表达可能是SIT治疗哮喘的作用机制之一。     

外周血白细胞介素-13与干扰素-γ在儿童特应性皮炎中的发病机制研究

目的:探讨外周血白细胞介素-13(IL-13)与干扰素-γ(IFN-γ)在儿童特应性皮炎(AD)发病机制中的作用。方法:选择2016年5月～2018年4月本院收治的AD患儿120例作为观察组,并根据欧洲特应性皮炎评分标准(SCORAD)将其分为轻度组(n=33)、中度组(n=53)、重度组(n=34),采用分层抽样的方法抽取同期在本院进行健康体检的120例健康儿童为对照组。采用酶联免疫吸附法(ELISA)检测外周血IL-13和IFN-γ水平,采用放射免疫法检测免疫球蛋白E(Ig E)水平,比较各组IL-13、IFN-γ与Ig E水平,采用Spearman相关分析IL-13、IFN-γ、Ig E两两之间的相关性。结果:观察组儿童治疗前IL-13、Ig E水平高于对照组体检时,IFN-γ水平低于对照组体检时,差异有统计学意义(P0.05)。治疗前IL-13与Ig E呈正相关关系(r=0.762,P0.05),IFN-γ与Ig E呈负相关关系(r=-0.673,P0.05),IL-13与IFN-γ呈负相关关系(r=-0.672,P0.05)。轻、中、重度组患儿治疗前的IL-13、IFN-γ、Ig E水平整体比较差异有统计学意义(P0.05),重度组、中度组治疗前IL-13、Ig E水平高于轻度组,IFN-γ低于轻度组,且重度组治疗前IL-13、Ig E水平高于中度组,IFN-γ低于中度组,差异均有统计学意义(P0.05)。观察组治疗3、6个月后,IL-13水平和Ig E水平明显低于治疗前,IFN-γ水平明显高于治疗前,差异有统计学意义(P0.05)。结论:AD患儿外周血IL-13水平升高,IFN-γ水平降低,二者可能通过影响Ig E水平,引起辅助性T细胞1/辅助性T细胞2(Th1/Th2)失衡,从而参与AD的发病过程。     

人外周血Th细胞和Tc细胞内IFN-γ及IL-4表达水平与白塞病的关系

目的检测BD患者外周血Th细胞和Tc细胞内INF-γ和IL-4的表达水平,探索BD患者体内的免疫状况。方法采用流式细胞术检测BD活动期患者(n=22),BD稳定期(n=6)以及健康体检者(n=22)外周血T细胞亚群INF-γ和IL-4的表达水平。结果 BD患者活动期外周血细胞Th细胞和Tc细胞经过刺激后胞内合成IFN-γ的水平明显高于正常人水平(Th细胞:22.45%±7.33%vs.16.32±4.96%,P<0.05;Tc细胞:36.74%±13.19%vs.28.67%±11.56%,P<0.05),稳定期患者Th细胞和Tc细胞体外合成IFN-γ的能力与正常人相比无明显差异;稳定期患者Th细胞和Tc细胞胞内合成IL-4的能力相对于正常人均无明显差异:(稳定期Th细胞:3.01%±1.38%vs.2.87%±1.46%,Tc细胞:1.14%±0.28%vs.1.07%±0.32%,P>0.05)。而活动期患者Th细胞和Tc细胞胞内合成IL-4的能力相对于正常人均存在明显差异:(Th细胞:3.54%±1.62%vs.2.87%±1.46%,Tc细胞:1.82%±0.43%vs.1.07%±0.32%,P<0.05);导致Th细胞和Tc细胞有偏向Th1及Tc1的趋势(Th细胞IFN-γ/IL-4:6.34±3.24 vs.5.69±4.72,p>0.05;Tc细胞IFN-γ/IL-4:20.19±13.65 vs.26.79±14.52,P>0.05)。结论 BD患者外周血INF-γ和IL-4的表达水平明显升高,并与疾病活动期存在一定程度相关,可能对白塞病患者的诊断具有重要的临床意义。     

青春双歧杆菌对NOD小鼠1型糖尿病的免疫调节作用

目的 探讨早期应用青春双歧杆菌对NOD小鼠1型糖尿病发病的影响.方法 给予NOD小鼠口服青春双歧杆菌,观察实验组和对照组(PBS)糖尿病发病率,HE染色观察胰岛炎,免疫组化检测胰岛Bcl-2和Bax的表达,RT-PCR测定TNF-α、IFN-γ和IL-10 mRNA表达.结果 实验组胰岛炎程度较对照组明显减轻(P＜0.01),胰岛Bcl-2的表达高于对照组,而Bax的表达低于对照组(P＜0.05);胰腺TNF-α、IFN-γ mRNA表达实验组明显低于对照组(P＜0.05),而IL-10 mRNA表达差异无显著性;实验组发病率低于对照组(P＜0.05).结论 青春双歧杆菌对NOD小鼠1型糖尿病有预防作用,其机制可能与调节Th1/Th2型细胞因子的免疫失衡有关.     

21例侵袭性肺曲霉病患者Th以及Treg细胞的检测

目的：分析侵袭性肺曲霉病患者辅助性T细胞（Th）以及调节性T细胞（Treg）在外周血中单个核细胞中的表达情况及其临床相关性,探讨Th和Treg细胞介导的免疫反应在侵袭性肺曲霉病中的作用。方法分离21例侵袭性肺曲霉病患者及19例健康人外周血的单个核细胞,采用流式细胞术分析Th1、Th2、Th17、Treg细胞群的表达情况,Real-timePCR方法检测相关转录因子T-bet、GATA-3、RORγt以及Foxp3的表达,ELISA法检测血清中相关细胞因子IFN-γ、IL-4、IL-17以及TGF-β的表达。结果与健康人对照组相比,侵袭性肺曲霉病患者Th1细胞以及Treg细胞占CD4＋T细胞的比例较之对照组明显降低;Th1、Th17、Treg细胞相关转录因子T-bet、RORγt、Foxp3以及相关细胞因子IFN-γ、IL-17A、TGF-β与对照组相比表达明显降低。结论IPA患者的Th1、Th17以及Treg细胞所介导的免疫反应受抑制。     

妊娠期肝内胆汁淤积症患者外周血中维生素D受体 与Th1/Th2 型细胞因子的变化

目的:研究妊娠期肝内胆汁淤积症患者外周血中维生素D受体的表达与Th1/Th2型细胞因子干扰素-γ/白细胞介素-4(IFN-γ/IL-4)的变化关系,探讨ICP发病机制。方法:选取ICP患者31例(ICP组),孕周相匹配的正常孕妇31例(正常对照组)。采用酶联免疫吸附试验(ELISA法),检测两组孕妇血清中Th1型细胞因子(IFN-γ)和Th2型细胞因子(IL-4)的水平;采用实时荧光定量逆转录-多聚酶链反应(qRT-PCR),检测两组孕妇外周血单个核细胞维生素D受体(VDR)mRNA的表达水平,采用3-磷酸甘油醛脱氢酶(GAPDH)为内参,根据相对定量公式:2-△△CT分析VDR mRNA的表达水平。结果:(1)ICP组外周血清中IFN-γ的浓度[(230.93±36.04)pg/ml]明显高于正常对照组[(138.37±25.08)pg/ml],差异有统计学意义(P<0.01)。ICP组血清中IL-4浓度[(9.99±3.19)pg/ml]和正常对照组[(8.58±2.43)pg/ml]比较,差异无统计学意义(P>0.05)。ICP组IFN-γ/IL-4比值(24.56±6.91)高于正常对照组(17.13±4.84),差异有统计学意义(P<0.05)。(2)ICP组外周血单个核细胞维生素D受体mRNA的表达明显低于正常对照组(P<0.01),正常对照组VDR的表达定义为1.0,ICP组的表达量为0.4。(3)ICP组外周血中VDR的表达水平与IFN-γ浓度呈明显负相关(r=-0.833,P<0.01),与IL-4浓度无明显相关(r=-0.109,P>0.05),与IFN-γ/IL-4比值呈负相关,但相关性不强(r=-0.356,P=0.049<0.05)。结论:ICP患者外周血Th1/Th2型细胞因子平衡由Th2向Th1偏移,可能与ICP孕妇外周血单个核细胞VDR的表达减少有关。     

IL-2、IFN-γ、TNF-α在膀胱癌患者中的水平变化及意义

目的:探讨白细胞介素-2(IL-2)、γ-干扰素(IFN-γ)、肿瘤坏死因子-α(TNF-α)在膀胱癌患者中的水平变化及意义。方法:选择从2015年2月到2016年12月在我院进行治疗的膀胱癌患者66例纳入本次研究,为膀胱癌组,选择同期在我院治疗的65例腺性膀胱炎患者记为膀胱炎组,另选择同期在我院进行体检的健康体检者65例记为对照组,对比各组患者的IL-2、IFN-γ及TNF-α水平,不同类型和临床分期的膀胱癌患者的IL-2、IFN-γ及TNF-α水平,分析IL-2、IFN-γ及TNF-α水平与其病理类型和临床分期的相关性。结果:膀胱癌组的IL-2和IFN-γ水平均明显低于膀胱炎组和对照组,TNF-α水平明显高于膀胱炎组和对照组,差异均有统计学意义(均P0.05)。不同类型膀胱癌患者的IL-2、IFN-γ及TNF-α水平相比,差异均无统计学意义(均P0.05)。T2~T4膀胱癌患者的IL-2、IFN-γ水平均明显低于Tis~T1者,TNF-α水平明显高于Tis~T1者,差异均有统计学意义(均P0.05)。根据Spearman相关性分析发现,膀胱癌患者的IL-2、IFN-γ与其临床分期均呈负相关(P0.05),TNF-α与其临床分期呈正相关(P0.05),而患者的IL-2、IFN-γ及TNF-α水平与其病理类型则无明显相关性(P0.05)。结论:IL-2、IFN-γ在膀胱癌患者中的表达明显下降,而TNF-α表达明显上升,且患者的上述三种指标与其临床分期有关,但与其病理类型无关。     

Th17及Th1相关细胞因子与支气管哮喘的关系研究

目的:分析外周血Th17、Th1及相关细胞因子表达水平和支气管哮喘(bronchial asthma,BA)发生、发展的相关性研究。方法:回顾选取我院收治的BA病例57份,称作BA组,另选取呼吸系统正常的病例55例为对照组,检测两组入选者的外周血IL-2、TNF-α、Th17、IL-6、Th1指标表达差异,并进行多因素回归分析。结果:BA组Th17(0.62±1.67)%、Th1(1.45±0.48)%及Th1/Th17(2.33±1.28)均显著低于对照组(P均0.05);BA组TNF-α(27.46±8.12)pg/mL、IL-6(11.69±2.14)pg/mL表达量显著高于对照组,IL-2(2.58±3.89)pg/mL、IFN-γ(3.74±6.15)pg/mL含量均显著低于对照组(P均0.05);经Logistic回归分析,TNF-α、IL-6、IFN-γ、Th1/Th17、IL-2均和BA有密切相关性(P均0.05)。结论:IL-2、IFN-γ、Th1/Th17、TNF-α、IL-6表达水平均与BA有密切关联,可能是参与BA发病的主要原因,及早进行Th17、Th1及相关细胞因子检查有助于明确病情。     

Target sequences of Tc1, Tc3 and Tc5 transposons of Caenorhabditis elegans

We report here the consensus target sequence of transposons Tc1, Tc3 and Tc5 of Caenorhabditis elegans. These sequences were obtained by molecular analysis of 1008 random new insertions which have not been exposed to natural selection. This analysis reveals consensus target sites slightly different from those previously reported, and confirms that the mariner elements Tc1 and Tc3 insert in sites which are not preferentially palindromic.     

Relative diabetogenic properties of islet-specific Tc1 and Tc2 cells in immunocompetent hosts

CD8(+) T cells are important effectors, as well as regulators, of organ-specific autoimmunity. Compared with Tc1-type CD8(+) cells, Tc2 cells have impaired anti-viral and anti-tumor effector functions, although no data are yet available on their pathogenic role in autoimmunity. Our aim was to explore the role of autoreactive Tc1 and Tc2 cells in autoimmune diabetes. We set up an adoptive transfer model in which the recipients were transgenic mice expressing influenza virus hemagglutinin (HA) specifically in their pancreatic ss islet cells (rat insulin promoter-HA mice) and islet-specific Tc1 and Tc2 cells were generated in vitro from HA-specific CD8(+) cells of TCR transgenic mice (CL4-TCR mice). One million Tc1 cells, differentiated in vitro in the presence of IL-12, transferred diabetes in 100% of nonirradiated adult rat insulin promoter-HA recipients; the 50% diabetogenic dose was 5 x 10(5). Highly polarized Tc2 cells generated in the presence of IL-4, IL-10, and anti-IFN-gamma mAb had a relatively low, but definite, diabetogenic potential. Thus, 5 x 10(6) Tc2 cells caused diabetes in 6 of 18 recipients, while the same dose of naive CD8(+) cells did not cause diabetes. Looking for the cause of the different diabetogenic potential of Tc1 and Tc2 cells, we found that Tc2 cells are at least as cytotoxic as Tc1 cells but their accumulation in the pancreas is slower, a possible consequence of differential chemokine receptor expression. The diabetogenicity of autoreactive Tc2 cells, most likely caused by their cytotoxic activity, precludes their therapeutic use as regulators of autoimmunity.     

Target site choice of the related transposable elements Tc1 and Tc3 of Caenorhabditis elegans.

We have investigated the target choice of the related transposable elements Tc1 and Tc3 of the nematode C. elegans. The exact locations of 204 independent Tc1 insertions and 166 Tc3 insertions in an 1 kbp region of the genome were determined. There was no phenotypic selection for the insertions. All insertions were into the sequence TA. Both elements have a strong preference for certain positions in the 1 kbp region. Hot sites for integration are not clustered or regularly spaced. The orientation of the integrated transposon has no effect on the distribution pattern. We tested several explanations for the target site preference. If simple structural features of the DNA (e.g. bends) would mark hot sites, we would expect the patterns of the two related transposons Tc1 and Tc3 to be similar; however we found them to be completely different. Furthermore we found that the sequence at the donor site has no effect on the choice of the new insertion site, because the insertion pattern of a transposon that jumps from a transgenic donor site is identical to the insertion pattern of transposons jumping from endogenous genomic donor sites. The most likely explanation for the target choice is therefore that the primary sequence of the target site is recognized by the transposase. However, alignment of the Tc1 and Tc3 integration sites does not reveal a strong consensus sequence for either transposon.     

Tc7, a Tc1-hitch hiking transposon in Caenorhabditis elegans.

We have found a novel transposon in the genome of Caenorhabditis elegans. Tc7 is a 921 bp element, made up of two 345 bp inverted repeats separated by a unique, internal sequence. Tc7 does not contain an open reading frame. The outer 38 bp of the inverted repeat show 36 matches with the outer 38 bp of Tc1. This region of Tc1 contains the Tc1-transposase binding site. Furthermore, Tc7 is flanked by TA dinucleotides, just like Tc1, which presumably correspond to the target duplication generated upon integration. Since Tc7 does not encode its own transposase but contains the Tc1-transposase binding site at its extremities, we tested the ability of Tc7 to jump upon forced expression of Tc1 transposase in somatic cells. Under these conditions Tc7 jumps at a frequency similar to Tc1. The target site choice of Tc7 is identical to that of Tc1. These data suggest that Tc7 shares with Tc1 all the sequences minimally required to parasitize upon the Tc1 transposition machinery. The genomic distribution of Tc7 shows a striking clustering on the X chromosome where two thirds of the elements (20 out of 33) are located. Related transposons in C. elegans do not show this asymmetric distribution.     

Patterns of selection against transposons inferred from the distribution of Tc1, Tc3 and Tc5 insertions in the mut-7 line of the nematode Caenorhabditis elegans

To identify the factors (selective or mutational) that affect the distribution of transposable elements (TEs) within a genome, it is necessary to compare the pattern of newly arising element insertions to the pattern of element insertions that have been fixed in a population. To do this, we analyzed the distribution of recent mutant insertions of the Tc1, Tc3, and Tc5 elements in a mut-7 background of the nematode Caenorhabditis elegans and compared it to the distribution of element insertions (presumably fixed) within the sequenced genome. Tc1 elements preferentially insert in regions with high recombination rates, whereas Tc3 and Tc5 do not. Although Tc1 and Tc3 both insert in TA dinucleotides, there is no clear relationship between the frequency of insertions and the TA dinucleotide density. There is a strong selection against TE insertions within coding regions: the probability that a TE will be fixed is at least 31 times lower in coding regions than in noncoding regions. Contrary to the prediction of theoretical models, we found that the selective pressure against TE insertions does not increase with the recombination rate. These findings indicate that the distribution of these three transposon families in the genome of C. elegans is determined essentially by just two factors: the pattern of insertions, which is a characteristic of each family, and the selection against insertions within coding regions.     

Widespread occurrence of the Tc1 transposon family: Tc1-like transposons from teleost fish

We characterized five transposable elements from fish: one from zebrafish (Brachydanio rerio), one from rainbow trout (Salmo gairdneri), and three from Atlantic salmon (Salmo salar). All are closely similar in structure to the Tel transposon of the nematode Caenorhabditis elegans. A comparison of 17 Tc1-like transposons from species representing three phyla (nematodes, arthropods, and chordates) showed that these elements make up a highly conserved transposon family. Most are close to 1.7 kb in length, have inverted terminal repeats, have conserved terminal nucleotides, and each contains a single gene encoding similar poly peptides. The phylogenetic relationships of the transposons were reconstructed from the amino acid sequences of the conceptual proteins and from DNA sequences. The elements are highly diverged and have evidently inhabited the genomes of these diverse species for a long time. To account for the data, it is not necessary to invoke recent horizontal transmission.     

Tumor-specific Tc1, but not Tc2, cells deliver protective antitumor immunity.

We investigated whether secretion of multiple cytokines by CD8+ T cells is associated with improved protection against tumor challenge. We show that antitumor immunity induced by immunization with dendritic cells and a MHC class I-binding tumor peptide are dependent on secretion of IFN-gamma but not IL-4 or IL-5 by host cells. To further address the role of IL-4 and IL-5 in antitumor immunity, tumor-specific TCR-transgenic CD8+ T cells were activated in vitro to generate cytotoxic T (Tc) 1 cells that secrete high IFN-gamma and no IL-4 or IL-5 or Tc2 cells that secrete IL-4, IL-5, and some IFN-gamma. Both cell types killed target cells in vitro. Tc1 and Tc2 cells were adoptively transferred into syngeneic hosts, and their ability to protect against tumor challenge was compared. Tc1 cells were able to significantly delay tumor growth, whereas Tc2 cells or Tc2 cells from IFN-gamma(-/-) donors had no effect. This was due to neither the inability of Tc2 cells to survive in vivo or to migrate to the tumor site nor their inability to secrete IL-4 and/or IL-5 in the presence of limiting amounts of anti-CD3. However, IFN-gamma secretion by Tc2 cells was triggered inefficiently by restimulation with Ag compared with anti-CD3. We conclude that the ability to secrete "type 2" cytokines, and cytotoxic ability, have a limited role in antitumor immune responses mediated by CD8+ T cells, whereas the capacity to secrete high amounts of IFN-gamma remains the most critical antitumor effector mechanism in vivo.     

A mouse model for neural tube defects: the curtailed (Tc) mutation produces spina bifida occulta in Tc/+ animals and spina bifida with meningomyelocele in Tc/t

Curtailed (Tc), a dominant mutation on mouse chromosome 17, causes a tailless phenotype and occasional hindlimb paralysis in heterozygotes. Histologically, Tc/+ embryos show a variety of abnormalities including budding and ventral duplication of the developing spinal cord, duplication and intermittent absence of the notochord, and partial or complete absence of bony vertebrae, all posterior to midliver level. When Tc is heterozygous with t-haplotypes that contain the "tail interaction factor," tct, the phenotype is more severe, and a dorsal blood blister exists in the lumbosacral area. Our microscopic observations reveal that Tc/tw5 mice have a lumbosacral spina bifida with meningomyelocele. This results from the absence of bony vertebrae, extensive thinning of the dermis dorsally, and the rupturing of the previously closed neural tube, probably by increased cerebrospinal fluid (CSF) pressure on the necrotic, attenuated roof plate. Thinning of the roof plate, which facilitates the rupturing of the spinal cord, is not observed in Tc/+, which suggests that this phenomenon is associated with the interaction of Tc with the t-allele. Later in the development of Tc/tw5 embryos, adjacent blood vessels are ruptured, resulting in hemorrhage into the CSF space to give the external appearance of a blood blister. Tc/+ mice also show an absence of bony vertebrae dorsally in the lumbosacral region, but they lack the dorsal blood blister, and the dermal layer overlying the bony defect retains its normal thickness; these observations describe a spina bifida occulta.     

Mobilization of quiet, endogenous Tc3 transposons of Caenorhabditis elegans by forced expression of Tc3 transposase.

The commonly studied Caenorhabditis elegans strain Bristol N2 contains approximately 15 copies per genome of the transposon Tc3. However, Tc3 is not active in Bristol N2. Tc3 contains one major open reading frame (Tc3A). We have fused this open reading frame to an inducible promoter and expressed it in a transgenic Bristol N2 line. Tc3A expression resulted in frequent excision and transposition of endogenous Tc3 elements. This shows that the Bristol N2 genome contains Tc3 transposons that are cis proficient for transposition, but are immobile because Tc3A is absent. We demonstrate that recombinant Tc3A binds specifically to the terminal nucleotides of the Tc3 inverted repeat, indicating that Tc3A is the Tc3 transposase. Activation of Tc3 transposition in vivo was accompanied by the appearance of extrachromosomal, linear copies of Tc3. These may be intermediates in Tc3 transposition.