Differential membrane perturbation caused by the cell penetrating peptide Tp10 depending on attached cargo

The membrane leakage caused by the cell penetrating peptide Tp10, a variant of transportan, was studied in large unilamellar vesicles with the entrapped fluorophore calcein. The vesicles were composed of zwitterionic 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine. A significant decrease in membrane leakage was found when the 55kDa streptavidin protein was attached to Tp10. When a 5.4kDa peptide nucleic acid molecule was attached, the membrane leakage was comparable to that caused by Tp10 alone. The results suggest that direct membrane effects may cause membrane translocation of Tp10 alone and of smaller complexes, whereas these effects do not contribute for larger cargoes.     

Characterization of novel β‐1,3‐glucan recognition proteins from a Tibetan Plateau ghost moth Thitarodes pui (Lepidoptera,Hepialidae)

β‐1,3‐glucan recognition proteins (βGRPs) function as pattern recognition receptors in the innate immune response against invading pathogens. In the present study, we obtain full‐length cDNA clones for two novel putative βGRPs: TpβGRPc and TpβGRPd from the ghost moth Thitarodes pui (Lepidoptera: Hepialidae). Phylogenetic analysis shows a small distinct lineage, βGRP clade 4, consisting of T. pui βGRPs including TpβGRPa and TpβGRPb that have been identified previously. TpβGRPc and TpβGRPd, comprising 488 and 229 amino acids, have calculated molecular masses of 52 596 and 24 589 Da, respectively. TpβGRPc is 85.52% identical in sequence to TpβGRPa. TpβGRPb and TpβGRPd share the same deletion start site located at the conserved residue Pro 43, although TpβGRPd exhibits a much larger deletion of up to approximately 270 residues covering both the N‐ and C‐terminal regions. Affinity purification, associated with subsequent peptide sequencing, confirms the constitutive occurrence of TpβGRPa and TpβGRPc of similar size (approximately 65 kDa) in sixth‐instar larval haemolymph. These two βGRPs show clear binding affinities to curdlan, an insoluble β‐1,3‐glucan. A quantitative real‐time polymerase chain reaction analysis reveals the high‐level constitutive expression of TpβGRPc and TpβGRPd in the fat body of mid‐instar larvae, which are found to be susceptible to fungal pathogens in field investigations. Remarkable induction of both TpβGRPs occurs in response to haemocoelic challenge with entomopathogenic fungus Beauveria bassiana. The results of the present study suggest that TpβGRPs may contribute to the detection and control of fungal infections.     

Escape from CD8+ T cell response by natural variants of an immunodominant epitope from Theileria parva is predominantly due to loss of TCR recognition

Polymorphism of immunodominant CD8(+) T cell epitopes can facilitate escape from immune recognition of pathogens, leading to strain-specific immunity. In this study, we examined the TCR β-chain (TRB) diversity of the CD8(+) T cell responses of cattle against two immunodominant epitopes from Theileria parva (Tp1(214-224) and Tp2(49-59)) and investigated the role of TCR recognition and MHC binding in determining differential recognition of a series of natural variants of the highly polymorphic Tp2(49-59) epitope by CD8(+) T cell clones of defined TRB genotype. Our results show that both Tp1(214-224) and Tp2(49-59) elicited CD8(+) T cell responses using diverse TRB repertoires that showed a high level of stability following repeated pathogenic challenge over a 3-y period. Analysis of single-alanine substituted versions of the Tp2(49-59) peptide demonstrated that Tp2(49-59)-specific clonotypes had a broad range of fine specificities for the epitope. Despite this diversity, all natural variants exhibited partial or total escape from immune recognition, which was predominantly due to abrogation of TCR recognition, with mutation resulting in loss of the lysine residue at P8, playing a particularly dominant role in escape. The levels of heterozygosity in individual Tp2(49-59) residues correlated closely with loss of immune recognition, suggesting that immune selection has contributed to epitope polymorphism.     

Characterization of senescence- and apoptosis-dependent forms of terminin as derived from a precursor found in replicating and nonreplicating cells

Previously we have reported the production of a monoclonal antibody (Mab 1.2) which recognizes a cytoplasmic protein, terminin, in three different molecular weights: 90 (Tp90), 60 (Tp60), and 30 kDa (Tp30) forms. Further characterization shows that Tp90 is found in young growing and nongrowing quiescent fibroblasts, while Tp60 is found in permanently growth-arrested senescent fibroblasts and Tp30 in cells committed to undergo programmed cell death (apoptosis). In tissue, Tp90 is found in embryonic brain; later, in neonatal brain after terminal differentiation is completed, only Tp60 is found. Tp30 is found in crude liver fractions extracted without the protective action of protease inhibitors. In all these circumstances, Tp90 is mostly seen in the detergent-soluble fraction, while Tp60 and Tp30 are detergent-insoluble. We now report that in cultured fibroblasts, as well as in tissues such as brain and liver, Tp60 and Tp30 are derived from the Tp90 polypeptide, indicated by the fact that only the Tp90 species is identified by both immunoblotting and immunoprecipitation assays, when the cell or tissue extracts are prepared in the presence of protease inhibitors. Further evidence shows that immunoprecipitation of in vitro translation products from brain, liver, and cultured fibroblasts also present a single band of Tp90 polypeptide. Pulse-chase experiments show that during apoptosis, Tp90 is processed to Tp60, and eventually to Tp30. However, when the total protein extracts are fractionated, only Tp90 is found in the detergent-soluble fraction, with diminishing quantities during the time course of apoptosis, and Tp30, in contrast, is found as the only protein species in the insoluble fraction, with increasing quantity during the same time course. Newly processed Tp60 is not found in either of the fractions, reflecting its loss during the fractionation procedure. Limited one-dimensional peptide mapping of Tp90 yields three different bands at 30, 28, and 25 kDa, but only the one at 30 kDa is recognized by Mab 1.2. These results lead us to suggest that terminin protein is synthesized in the Tp90 form, and cleaved to lower molecular weight forms depends upon different physiologic conditions, with Tp60 processed in the terminally differentiated or senescent state and rapidly to Tp30 in apoptosis. Our findings further suggest that Tp90's processing to either Tp60 or Tp30 produces insoluble protein forms. Furthermore, the presence of Tp90 in nonapoptotic (either replicating or nonreplicating) cells may reflect the absence of necessary proteolytic action required for the execution of apoptosis. Future experiments will allow us to determine the nature of this proteolytic action, as well as whether this action is due to the autocatalytic action of Tp90 or by other endogenous proteases, and then to determine the significance of this biochemical action in cells. © 1996 Wiley-Liss, Inc.     

The multifunctional role of the pallilysin‐associated Treponema pallidum protein,Tp0750, in promoting fibrinolysis and extracellular matrix component degradation

The mechanisms that facilitate dissemination of the highly invasive spirochaete, Treponema pallidum, are incompletely understood. Previous studies showed the treponemal metalloprotease pallilysin (Tp0751) possesses fibrin clot degradation capability, suggesting a role in treponemal dissemination. In the current study we report characterization of the functionally linked protein Tp0750. Structural modelling predicts Tp0750 contains a von Willebrand factor type A (vWFA) domain, a protein‐protein interaction domain commonly observed in extracellular matrix (ECM)‐binding proteins. We report Tp0750 is a serine protease that degrades the major clot components fibrinogen and fibronectin. We also demonstrate Tp0750 cleaves a matrix metalloprotease (MMP) peptide substrate that is targeted by several MMPs, enzymes central to ECM remodelling. Through proteomic analyses we show Tp0750 binds the endothelial fibrinolytic receptor, annexin A2, in a specific and dose‐dependent manner. These results suggest Tp0750 constitutes a multifunctional protein that is able to (1) degrade infection‐limiting clots by both inhibiting clot formation through degradation of host coagulation cascade proteins and promoting clot dissolution by complexing with host proteins involved in the fibrinolytic cascade and (2) facilitate ECM degradation via MMP‐like proteolysis of host components. We propose that through these activities Tp0750 functions in concert with pallilysin to enable T. pallidum dissemination.     

The Heterochronic Teopod1 and Teopod2 Mutations of Maize Are Expressed Non-Cell-Autonomously

Teopod1 and Teopod2 are dominant, unlinked mutations in maize that cause dramatic morphological abnormalities, including inappropriate expression of juvenile traits in adult vegetative phytomers and the transformation of reproductive structures into vegetative ones. These phenotypes are consistent with the constitutive expression of a juvenile phase of development throughout shoot growth. To investigate the basis of the Tp1 and Tp2 phenotypes we have analyzed their cell-autonomy in mosaic Teopod:wild-type plants. Mosaic plants were generated by three different mechanisms. Tp1 has previously been shown to be non-cell-autonomous; to verify and extend these results, large wild-type sectors were generated on Tp1 plants by the spontaneous loss of a B-A translocation chromosome containing the Tp1 gene. Analysis of Tp2 cell-autonomy was complicated by a lack of useful markers on chromosome 10L proximal to Tp2. To circumvent this problem two strategies were used. A reciprocal translocation was used to link Tp2 the the wild-type allele of lw2. Sectors were induced in plants of this type by irradiation of imbibed seeds. Also, a chromosome-breaking Ds element located proximal to Tp2 was used to generate somatic sectors that uncovered w2, an albino mutation distal to Tp2. Our results demonstrate conclusively that both Tp1 and Tp2 are non-cell-autonomous. The general use of these techniques for clonal analysis in plants and the potential role of a diffusible factor in regulating the juvenile phase of development in maize are discussed.     

嗜线虫致病杆菌血腔毒素Tp40的纯化和特性分析

[目的]嗜线虫致病杆菌是一种昆虫病原线虫共生菌,它能够产生多种杀虫毒素.本研究旨在从嗜线虫致病杆菌Xenorhabdus nematophila HB310菌株的细胞内纯化新的杀虫蛋白毒素,并对其进行基因克隆和序列分析.[方法]应用盐析和制备型非变性凝胶电泳等方法纯化蛋白,再通过对5龄大蜡螟幼虫血腔注射进行活性筛选.对获得的目的蛋白与已知蛋白进行同源分析,克隆出该目的蛋白的基因序列,从而进行相应的基因和氨基酸序列分析.[结果]本研究纯化的Tp40蛋白对大蜡螟LD50为68.54 ng/头,其SDS-PAGE电泳图谱只显示出一条分子量约为42 kDa的多肽.Western印迹分析表明Tp40与已知的Txp40为同源蛋白,并且仅存在于细胞内.编码该蛋白的基因开放读码框全长1107bp(GenBank登录号:EU095326),编码368个氨基酸残基,预测分子量为41.5 kDa,等电点为8.66,与GenBank中的其余13株昆虫病原线虫共生菌所包含的相似基因核苷酸序列及推导的氨基酸序列比较,同源性分别为85%～99%和70%～99%.[结论]Tp40蛋白具有很高的血腔杀虫活性,其基因序列具有较强的保守性,是昆虫病原线虫共生菌复合体杀虫过程中的一种关键因子.     

Methanol oxidation in a spontaneous mutant of Thiosphaera pantotropha with a methanol-positive phenotype is catalysed by a dye-linked ethanol dehydrogenase

Abstract A spontaneous Thiosphaera pantotropha mutant (Tp9002) that is able to grow on methanol has been isolated. With hybridization experiments it has been demonstrated that mxaF , the gene encoding the large subunit of methanol dehydrogenase, is absent from T. pantotropha . In Tp9002, a dye-linked enzyme activity was found with a substrate specificity similar to that of the dye-linked ethanol dehydrogenase from Pseudomonas aeruginosa . The N-terminus of a 26-kDa cytochrome c , exclusively synthesized in Tp9002, is homologous to the N-terminus of the electron acceptor of ethanol dehydrogenase. These results suggest that in Tp9002 a dye-linked ethanol dehydrogenase is responsible for methanol oxidation, using a 26-kDa cytochrome c as electron acceptor.     

Syntheses of Curcumin Bioconjugates and Study of Their Antibacterial Activities against beta-Lactamase-Producing Microorganisms.

In the present study curcumin bioconjugates, viz. di-O-glycinoylcurcumin (I), di-O-glycinoyl-C(4)-glycylcurcumin (II), 5'-deoxy-5'-curcuminylthymidine (5'-cur-T) (IV), and 2'-deoxy-2'-curcuminyluridine (2'-cur-U) (V) have been synthesized and characterized by elemental analysis and (1)H NMR. The turmeric peptide (Tp) was isolated from the aqueous turmeric extract of the turmeric rhizome. The antibacterial activity of these four bioconjugates and also of the turmeric peptide and sodium salt of curcumin (III) have been tested particularly for beta-lactamase-producing microorganisms.     

The Structure of Treponema pallidum Tp0751 (Pallilysin) Reveals a Non-canonical Lipocalin Fold That Mediates Adhesion to Extracellular Matrix Components and Interactions with Host Cells

Syphilis is a chronic disease caused by the bacterium Treponema pallidum subsp. pallidum. Treponema pallidum disseminates widely throughout the host and extravasates from the vasculature, a process that is at least partially dependent upon the ability of T. pallidum to interact with host extracellular matrix (ECM) components. Defining the molecular basis for the interaction between T. pallidum and the host is complicated by the intractability of T. pallidum to in vitro culturing and genetic manipulation. Correspondingly, few T. pallidum proteins have been identified that interact directly with host components. Of these, Tp0751 (also known as pallilysin) displays a propensity to interact with the ECM, although the underlying mechanism of these interactions remains unknown. Towards establishing the molecular mechanism of Tp0751-host ECM attachment, we first determined the crystal structure of Tp0751 to a resolution of 2.15 Å using selenomethionine phasing. Structural analysis revealed an eight-stranded beta-barrel with a profile of short conserved regions consistent with a non-canonical lipocalin fold. Using a library of native and scrambled peptides representing the full Tp0751 sequence, we next identified a subset of peptides that showed statistically significant and dose-dependent interactions with the ECM components fibrinogen, fibronectin, collagen I, and collagen IV. Intriguingly, each ECM-interacting peptide mapped to the lipocalin domain. To assess the potential of these ECM-coordinating peptides to inhibit adhesion of bacteria to host cells, we engineered an adherence-deficient strain of the spirochete Borrelia burgdorferi to heterologously express Tp0751. This engineered strain displayed Tp0751 on its surface and exhibited a Tp0751-dependent gain-of-function in adhering to human umbilical vein endothelial cells that was inhibited in the presence of one of the ECM-interacting peptides (p10). Overall, these data provide the first structural insight into the mechanisms of Tp0751-host interactions, which are dependent on the protein’s lipocalin fold.     

梅毒螺旋体遗传物质和致病机制的研究进展

梅毒螺旋体(Treponema pallidum,Tp)是慢性全身性性传播疾病梅毒的病原体。由于Tp不能持续体外培养,阻碍了对Tp结构及其致病机制的深入研究。目前,Tp(Nicholes株)基因组测序的完成以及分子生物学技术的发展,为Tp的研究提供了机遇。就Tp的遗传物质和致病机制的研究进展进行综述。     

Retrotransposon-like nature of Tp1 elements: implications for the organisation of highly repetitive, hypermethylated DNA in the genome of Physarum polycephalum.

The repetitive fraction of the genome of the eukaryotic slime mould Physarum polycephalum is dominated by the Tp1 family of highly repetitive retrotransposon-like sequences. Tp1 elements consist of two terminal direct repeats of 277bp which flank an internal domain of 8.3kb. They are the major sequence component in the hypermethylated (M+) fraction of the genome where they have been found exclusively in scrambled clusters of up to 50kb long. Scrambling is thought to have arisen by insertion of Tp1 into further copies of the same sequence. In the present study, sequence analysis of cloned Tp1 elements has revealed striking homologies of the predicted amino acid sequence to several highly conserved domains characteristic of retrotransposons. The relative order of the predicted coding regions indicates that Tp1 elements are more closely related to copia and Ty than to retroviruses. Self-integration and methylation of Tp1 elements may function to limit transposition frequency. Such mechanisms provide a possible explanation for the origin and organisation of M + DNA in the Physarum genome.     

Telocytes in pleura: two- and three-dimensional imaging by transmission electron microscopy

Information about the ultrastructure of connective (interstitial) cells supporting the pleural mesothelium is scarce. Our aim has been to examine whether telocytes (TCs) are present in pleura, as in epicardium and mesentery. TCs are a distinct type of cell, characterized by specific prolongations named telopodes (Tp). We have used transmission electron microscopy (TEM) and electron tomography (ET) to determine whether ultrastructural diagnostic criteria accepted for TCs are fulfilled by any of the cell subpopulations existing in the sub-mesothelial layer in mouse and human pleura. TCs have been identified with TEM by their characteristic prolongations. Tp appear long and moniliform, because of the alternation of podomeres (thin segments of less than 0.2 μm) and podoms (small dilations accommodating caveolae, mitochondria, and endoplasmic reticulum). Tp ramifications follow a dichotomic pattern and establish specialized cell-to-cell junctional complexes. TCs, via their Tp, seem to form an interstitial network beneath the mesothelium, covering about two-thirds of the abluminal mesothelial layer. ET has revealed complex junctional structures and tight junctions connecting pleural TCs, and small vesicles at this level in Tp. Thus, pleural TCs share significant similarities with TCs described in other serosae. Whether TCs are a (major) player in mesothelial-cell-induced tissue repair remains to be established. Nevertheless, the extremely long thin Tp and complex junctional structures that they form and the release of vesicles (or exosomes) indicate the participation of TCs in long-distance homo- or heterocellular communication.     

Using the natural evolution of a rotavirus-specific human monoclonal antibody to predict the complex topography of a viral antigenic site

Background

Immunity against the bovine protozoan parasite Theileria parva has previously been shown to be mediated through lysis of parasite-infected cells by MHC class I restricted CD8⁺ cytotoxic T lymphocytes. It is hypothesized that identification of CTL target schizont antigens will aid the development of a sub-unit vaccine. We exploited the availability of the complete genome sequence data and bioinformatics tools to identify genes encoding secreted or membrane anchored proteins that may be processed and presented by the MHC class I molecules of infected cells to CTL.

Results

Of the 986 predicted open reading frames (ORFs) encoded by chromosome 1 of the T. parva genome, 55 were selected based on the presence of a signal peptide and/or a transmembrane helix domain. Thirty six selected ORFs were successfully cloned into a eukaryotic expression vector, transiently transfected into immortalized bovine skin fibroblasts and screened in vitro using T. parva-specific CTL. Recognition of gene products by CTL was assessed using an IFN-γ ELISpot assay. A 525 base pair ORF encoding a 174 amino acid protein, designated Tp2, was identified by T. parva-specific CTL from 4 animals. These CTL recognized and lysed Tp2 transfected skin fibroblasts and recognized 4 distinct epitopes. Significantly, Tp2 specific CD8⁺ T cell responses were observed during the protective immune response against sporozoite challenge.

Conclusion

The identification of an antigen containing multiple CTL epitopes and its apparent immunodominance during a protective anti-parasite response makes Tp2 an attractive candidate for evaluation of its vaccine potential.     

Synthesis, electrochemistry, geometric and electronic structure of oxo-molybdenum compounds involved in an oxygen atom transferring system

The oxygen atom transfer reactivity of Tp( *)MoO(2)(SPh) (1) (where Tp( *)=hydrotris-(3,5-dimethylpyrazol-1-yl)borate) with trimethyl phosphine (PMe(3)) has been investigated. The reaction proceed through a diamagnetic phosphoryl intermediate complex, Tp( *)MoO(SPh)(OPMe(3)) (2), which has been isolated and characterized by IR, NMR, UV-visible spectroscopy, and mass spectrometry. The molecular structure of 2 has been determined by X-ray crystallography. The complex crystallizes in monoclinic (P2(1)/n) space group, a=19.81 (1)A, b=11.1 (4)A, c=18.416 (5)A, beta=121.2 (3) degrees , V=3463.8 (25)A(3) with Z=4. In acetonitrile, complex 2 exchanges its phosphoryl ligand with a solvent molecule resulting in Tp( *)MoO(SPh)(MeCN) (3), which has been isolated and also characterized spectroscopically and by X-ray crystallography. Compound 3 crystallizes in triclinic (P1 ) space group, a=10.159 (6)A, b=18.563 (5)A, c=7.986 (3)A, alpha=96.22 (3) degrees , beta=121.2 (3) degrees , gamma=84.64 (3) degrees , V=1452.4 (11)A(3) with Z=2. The electronic structures of the complexes have been investigated by density functional theory and the redox chemistry has been investigated by cyclic and differential pulse voltammetry. In acetonitrile, complex 2 spontaneously transforms to complex, 3 at a rate of 5.6x10(-4)s(-1).     

Genetic and physical characterization of trimethoprim resistance plasmids from Shigella sonnei and Shigella flexneri

Analysis of six Shigella flexneri and four S. sonnei isolates with trimethoprim (Tp) resistance from clinical cases in Ontario has shown that, in all isolates, the Tp resistance is mediated by gene(s) on conjugative, multiple antibiotic-resistance plasmids. The physical and genetic characterization of these plasmids revealed that there are three different Tp resistance plasmids. One group, composed of all six S. flexneri plasmids, consists of plasmids which are about 70 megadaltons (MDa) and inhibit the fertility of an Escherichia coli Hfr strain (Fi+). A representative member of this group, pPT4, demonstrates a weak incompatibility reaction with IncFl plasmid R455-2. Another group, three of the four S. sonnei plasmids, contains plasmids which are about 43 MDa, Fi-, and mediate propagation of phage PRD1. The third group, the remaining S. sonnei plasmid, is 53 MDa, fi+, mediates propagation of phages fd and MS2, and is incompatible with IncFII plasmid R100. These plasmids also have been differentiated by restriction endonuclease fragment profiles. Analysis of pPT4 has revealed that the Tp resistance of this plasmid is transposable. The transposon, Tn536, is different from previously described Tp resistance transposons; it is 16 MDa, and in addition to Tp, it encodes resistance to mercuric chloride ions, spectinomycin, streptomycin, and sulfonamides.     

Molecular cloning of a chromosomal DNA region encompassing the dihydrofolate reductase gene ofStreptococcus pneumoniae

Natural competence ofStreptococcus pneumoniae was used to locate and enrich DNA restriction fragments, biologically active for transformation of thymidine-deficient to thymidine-proficient cells. Mutations in the dihydrofolate reductase gene are accompanied by resistance to the drug trimethoprim (Tp). A 6.5-kb region of the pneumococcal chromosome encompassing the dihydrofolate reductase gene has been cloned in plasmid pLS1.Escherichia coli mutants, resistant to Tp, became fully sensitive to the drug when they harbored the recombinant plasmid. The pneumococcaldfrA mutation has been mapped within a 500-bp DNA region.     

梅毒螺旋体耐药性的研究进展

梅毒疫情成为全球普遍关注的公共卫生问题。由于缺乏疫苗预防,控制梅毒主要依赖对感染人群的诊断与抗生素治疗。虽然青霉素治疗梅毒仍然有效,但临床上对一线青霉素的替代药大环内酯类抗生素耐药的梅毒螺旋体(Tp)菌株已在许多国家普遍流行。了解Tp耐药性的遗传基础对于加强Tp耐药分子监测十分必要。就Tp对大环内酯类抗生素耐药性的遗传基础和对其他可能严重阻碍梅毒治疗和控制的抗生素潜在的耐药性进行了综述。     

Human bone marrow cells positive for terminal deoxynucleotidyl transferase (TdT), HLA-DR, and a T cell marker may represent prothymocytes

Recent evidence suggests that prothymocytes, which occur in a low frequency in murine bone marrow (BM), are already committed to thymocyte differentiation and discrete from precursor B cells as well as pluripotent hematopoietic stem cells. Furthermore, it was suggested that, in rodents, prothymocytes are positive for the nuclear enzyme terminal deoxynucleotidyl transferase (TdT) and a T cell surface antigen. The human prothymocyte has not been identified as yet. We analyzed human BM cells by double immunofluorescence staining for TdT and the T cell surface markers Tp41 (recognized by the monoclonal antibodies WT1 and 3A1), T11, T1, and T6. In the BM samples tested, neither T1+/TdT+ nor T6+/TdT+ cells were detected, but Tp41+/TdT+ and T11+/TdT+ cells were present in low frequencies. In childhood BM, the frequency was about two to five in 10,000, whereas in adult BM and regenerating BM, these cells were not always detectable, but if detected, their frequency was five- to 10-fold lower. In a triple staining, using fluorescein, rhodamine, and colloidal gold particles as labels, it appeared that all Tp41+/TdT+ cells were also positive for HLA-DR. These Tp41+/HLA-DR+/TdT+ cells were also detectable in low frequencies in the thymus, and occasionally Tp41+/TdT+ and T11+/TdT+ cells were detected in the peripheral blood (PB), suggesting a migration from the BM to the thymus via the PB. The malignant counterpart of the Tp41+/HLA-DR+/TdT+ cell was detected in a patient with acute lymphoblastic leukemia with the Tp41+/T11+/HLA-DR+/TdT+/T1-/T6- phenotype and germ-line immunoglobulin heavy chain genes. We postulate that the Tp41+/T11+/HLA-DR+/TdT+/T1-/T6- cell represents a human prothymocyte.