Thymic Maturation Research Articles

Thymic function in MHC class II–deficient patients

MHC class II (MHC-II) molecules play a pivotal role in the development, activation, and homeostasis of CD4(+) TH cells in the thymus. The absence of MHC-II molecules causes severe T-cell immunodeficiency. We sought to study thymic function, including T-cell receptor excision circle (TREC) quantification, in patients with MHC-II deficiency. Eight MHC-II-deficient patients underwent a thorough T-cell immunologic work-up, including thymic activity, which was estimated based on TREC levels and T-cell receptor (TCR) genes, as well as analysis of several sequential human TCR gene rearrangements. Invitro responses to mitogens were normal or only slightly reduced, and flow cytometric evaluations of the TCR-Vβ repertoires of total CD3(+) lymphocytes were normal in all patients. However, both the flow cytometric evaluation of the TCR-Vβ repertoire on CD4(+) cells and spectratyping evaluation of the TCR-Vγ repertoire on total CD3(+) lymphocytes showed clonal abnormalities. TRECs were present in all patients in both total lymphocytes and sorted CD4(+) cells. Additionally, TRECs were detected in genomic DNA obtained from Guthrie cards with dried blood spots. Quantitative RT-PCR assessment of different TCR gene rearrangement events revealed lower levels in MHC-II-deficient patients compared with levels seen in healthy control subjects. This was irrespective of the total lymphocyte numbers, suggesting a reduced global thymic activity. Our report highlights potential pitfalls in diagnosing MHC-II deficiency and emphasizes the probable importance of MHC-II molecules in the normal thymic maturation process of T cells. Patients with MHC-II deficiency have detectable TRECs and might therefore be missed by a TREC-based newborn screening program.

Post-transcriptional regulation of CD83 expression by AUF1 proteins

Mature dendritic cells (DC), activated lymphocytes, mononuclear cells and neutrophils express CD83, a surface protein apparently necessary for effective DC-mediated activation of naïve T-cells and T-helper cells, thymic T-cell maturation and the regulation of B-cell activation and homeostasis. Although a defined ligand of CD83 remains elusive, the multiple cellular subsets expressing CD83, as well as its numerous potential implications in immunological processes suggest that CD83 plays an important regulatory role in the mammalian immune system. Lately, nucleocytoplasmic translocation of CD83 mRNA was shown to be mediated by direct interaction between the shuttle protein HuR and a novel post-transcriptional regulatory element (PRE) located in the CD83 transcript’s coding region. Interestingly, this interaction commits the CD83 mRNA to efficient nuclear export through the CRM1 protein translocation pathway. More recently, the cellular phosphoprotein and HuR ligand ANP32B (APRIL) was demonstrated to be directly involved in this intracellular transport process by linking the CD83 mRNA:HuR ribonucleoprotein (RNP) complex with the CRM1 export receptor. Casein kinase II regulates this process by phosphorylating ANP32B. Here, we identify another RNA binding protein, AUF1 (hnRNP D) that directly interacts with CD83 PRE. Unlike HuR:PRE binding, this interaction has no impact on intracellular trafficking of CD83 mRNA-containing complexes; but it does regulate translation of CD83 mRNA. Thus, our data shed more light on the complex process of post-transcriptional regulation of CD83 expression. Interfering with this process may provide a novel strategy for inhibiting CD83, and thereby cellular immune activation.

Oligodendrocytes Enforce Immune Tolerance of the Uninfected Brain by Purging the Peripheral Repertoire of Autoreactive CD8+ T Cells

Myelin-specific CD8(+) Tcells are thought to contribute to the pathogenesis of multiple sclerosis. Here we modeled this contribution in mice with CD8(+) Tcells recognizing ovalbumin (OVA) expressed in oligodendrocytes (ODCs). Surprisingly, even very high numbers of activated OVA-reactive CD8(+) Tcells failed to induce disease and were cleared from the immune system after antigen encounter inthe centralnervous system (CNS). Peripheral infection with OVA-expressing Listeria (Lm-OVA) enabled CD8(+) Tcells to enter the CNS, leading to the deletion of OVA-specific clones after OVA recognition on ODCs. In contrast, intracerebral infection allowed OVA-reactive CD8(+) Tcells to cause demyelinating disease. Thus, in response to infection, CD8(+) Tcells also patrol the CNS. If the CNS itself is infected, they destroy ODCs upon cognate antigen recognition in pursuit of pathogen eradication. In the sterile brain, however, antigen recognition on ODCs results in their deletion, thereby maintaining tolerance.

Subcellular distribution of Lck during CD4 T-cell maturation in the thymic medulla regulates the T-cell activation threshold

Mature peripheral T cells respond to foreign but not to self-antigens. During development in the thymus, deletion of high-affinity self-reactive immature thymocytes contributes to tolerance of mature T cells. However, double-positive thymocytes are positively selected to survive if they respond to self-peptide-MHC complexes; thus, there must be mechanisms to prevent overt reactivity to those same complexes in the periphery. "Developmental tuning" is the active process through which T-cell receptor (TCR)-associated signaling pathways of single-positive (SP) thymocytes are attenuated to respond appropriately to self-peptide-MHC complexes in the periphery. We previously showed that MHC class II expression in the thymic medulla was necessary to tune CD4(+) SP (CD4 SP) thymocytes. CD4 SP thymocytes from mice lacking medullary MHC class II expression had inappropriately enhanced proximal TCR signaling to low-affinity self-ligands that was associated with altered cellular distribution of the tyrosine kinase Lck. Now, we report that activation of both tuned and untuned CD4 SP thymocytes is Lck-dependent. Untuned CD4 SP cells contain a pool of Lck with increased basal phosphorylation that is not associated with the CD4 coreceptor. Phosphorylation of this pool of Lck decreases with tuning. Immunogold transmission electron microscopy of membrane sheets permitted direct visualization of Lck. In the absence of tuning, a significant proportion of Lck and the TCR subunit CD3ζ are expressed on the same protein island; this close association of Lck and the TCR probably explains the enhanced activation of untuned CD4 SP cells. Thus, changes in membrane topography during thymic maturation determine the set point for TCR responsiveness.

TLX Homeodomain Oncogenes Mediate T Cell Maturation Arrest in T-ALL via Interaction with ETS1 and Suppression of TCRα Gene Expression

Acute lymphoblastic leukemias (ALLs) are characterized by multistep oncogenic processes leading to cell-differentiation arrest and proliferation. Specific abrogation of maturation blockage constitutes a promising therapeutic option in cancer, which requires precise understanding of the underlying molecular mechanisms. We show that the cortical thymic maturation arrest in T-lineage ALLs that overexpress TLX1 or TLX3 is due to binding of TLX1/TLX3 to ETS1, leading to repression of Tcell receptor (TCR) α enhanceosome activity and blocked TCR-Jα rearrangement. TLX1/TLX3 abrogation or enforced TCRαβ expression leads to TCRα rearrangement and apoptosis. Importantly, the autoextinction of clones carrying TCRα-driven TLX1 expression supports TLX "addiction" in TLX-positive leukemias and provides further rationale for targeted therapy based on disruption of TLX1/TLX3.

Peroxisome-derived lipids are self antigens that stimulate invariant natural killer T cells in the thymus

The development and maturation of semi-invariant natural killer T cells (iNKT cells) rely on the recognition of self antigens presented by CD1d restriction molecules in thymus. The nature of the stimulatory thymic self lipids remains elusive. We isolated lipids from thymocytes and found that ether-bonded mono-alkyl glycerophosphates and the precursors and degradation products of plasmalogens stimulated iNKT cells. Synthetic analogs showed high potency in activating thymic and peripheral iNKT cells. Mice deficient in the peroxisomal enzyme glyceronephosphate O-acyltransferase (GNPAT), essential for the synthesis of ether lipids, had significant alteration of the thymic maturation of iNKT cells and fewer iNKT cells in both thymus and peripheral organs, which confirmed the role of ether-bonded lipids as iNKT cell antigens. Thus, peroxisome-derived lipids are nonredundant self antigens required for the generation of a full iNKT cell repertoire.

T-regs/Th17 function defect in systemic autoimmunity as a result of "recent thymic emigrants" maturation defect

T-regs and Th17 cells are the new generation of CD4+T-cells which play crucial role in autoimmunity. Both of subsets can influence each other and probably have common precursor. A key question for understanding the mechanism of autoimmunity is to recognize how T-regs and Th17 cells turn from self-protection to autoreactivity. Based on literature data and own observations, we have constructed a conception of age-dependent thymic T-cells maturation peripherialisation as cause of errors in Th17-T-reg cells interrelations. The connection of T-regs with thymus is determined currently. Connection of Th17 cells with thymus remains to be determined properly. Main, there may be naturally occurring Tregs of thymic origin that are resistant to cell death and serve as reserve pool for autoimmunity protective suppressors. This mechanism could be affected by external factors producing profound lymphopenia [1]. Previously we found that RA patients with numerous rheumatoid nodules (RN) and lymphopenia had statistically reliable decrease of CD3+T-cells level. We found definite negative correlation between CD3+PBL amount and RN number (p = 0,029). In all RA patients with and without RN we didn't found the decrease of CD4 receptor. Hereby we expected to find unusual CD3-4+ and CD3-8+ cells in RA. Otherwise the percentage of CD3+4+ and CD3+8+ cells was normal in general. But in 4 RA patients after magnetic separation of CD3+T-cells we detected reliable amount of CD3-4+ lymphocytes (25-28%) These cells were not detected before separation. One of possible explanation of this phenomenon is CD3 molecule modulation after the contact with anti-CD3 antibodies conjugated with magnetic particles. So the presence of T-cells with unusual phenotype in peripheral blood of RA patients doesn't give absolute evidence of T-cells maturation disorders. According to our viewpoint recent thymic emigrants (RTE) fraction presence among T-regs and hypothetically among Th17-cells is the sign of normal Th17/T-regs function. Otherwise the absence of RTE among them leads to immunopathology. CD31 receptor and T cell receptor rearrangement excision circles (TREC) are now markers of RTE. We investigated the number of CD4+CD31+T-cells in RA patients. The preliminary results permit us to suggest the diminution of RTE in RA (less then 1%/ml) We also found the diminution of TREC amount in PBL of 22 rheumatoid arthritis patients, (Median 0,035539 units). FOXP3, RORγ, RORα and CD31 expression in RA will permit to establish role of RTE in autoimmunity.

Omenn Syndrome: inflammation and autoimmunity

Background Omenn Syndrome (OS) is a rare inherited disorder presenting with early-onset generalized erythrodermia, alopecia, chronic diarrhea, lymphoadenopathy, failure to thrive, and recurrent infections. The immunological phenotype is characterized by eosinophilia, virtual absent circulating B cells but elevated IgE serum levels. T cells are normal or increased and display a highly restricted, oligoclonal TCR repertoire. Because of overwhelming infections and loss of proteins, the disease is fatal, unless treated with allogeneic bone marrow transplantation, which is variably successful. We have previously demonstrated that mutations in either RAG1 and RAG2, impairing, but not abolishing, the first steps of V(D)J recombination, are the main cause of this syndrome [1]. Nonetheless, a compelling explanation for the autoimmune features of OS has proven elusive. The pathogenesis is likely multifactorial. We have shown that the reduced thymopoiesis in OS patients is accompanied by defects in thymic epithelial cell maturation and/or homeostasis, impaired expression of autoimmune regulator (aire) protein and poor generation of thymic CD4+CD25 +Foxp3+ natural regulatory T cells [2,3]. While these observations emphasize the potential role of T cell tolerance impairments in sustaining the immune dysregulation of OS, a possible contribution of defects in other immune cells, such as antigen presenting cells, has not been investigated. In addition, numerous questions remain surrounding the disease pathogenesis. To gain insights into the mechanisms underlying autoimmunity, we have recently generated a murine model (the Rag2mouse) carrying in Rag2 gene a mutation responsible for OS in many patients. This mouse model recapitulates the phenotype and many of the clinical manifestations of OS patients [4]. We have used this model to further investigate T and B cell contribution in the pathogenesis of autoimmune manifestations in OS.

Changes in thymic regulatory T-cell maturation from birth to puberty: Differences in atopic children

Characterization of regulatory immune pathways is a research priority for both the pathogenesis of allergic disease and potential therapeutic strategies. The thymus is a rich source of regulatory T (Treg) cells, which offers a novel opportunity to document the maturation of these pathways beyond limited studies on small volumes of peripheral blood available from young children. Thymus tissue was collected from children undergoing cardiac surgery (age, 1 week to 14 years), and skin prick testing was performed from 12 months of age. The ontogeny of Treg cell maturation and function was examined in atopic (n = 20) and nonatopic (n = 20) children by assessing their phenotype, enumeration, proliferation, and suppressive ability. Age-related changes in the thymic cytokine milieu paralleled the changes seen in peripheral immune function. Specifically, the thymic microenvironment is similarly T(H)2 skewed during the early postnatal period, and this undergoes age-related suppression as the T(H)1 (IFN-γ) response increased. We detected CD4(+)CD25(+)CD127(lo/-) forkhead box protein 3 (FOXP3)-positive Treg cells in the neonatal thymus. These cells suppressed the proliferative response to allogeneic stimulation of CD4(+)CD25(-) T cells dose dependently. In nonatopic children Treg cell turnover and suppressive function increased with age and paralleled the increase in global thymic FOXP3 mRNA expression, whereas in atopic children Treg cell maturation was significantly delayed compared with that seen in age-matched nonatopic children. These data suggest that the developmental changes in the thymus parallel the recognized changes in peripheral blood responses. There is also a developmental delay in the function of thymic regulatory cells in atopic compared with nonatopic children. These differences are fundamental to understanding early events that lead to immune dysregulation and might predispose to allergic disease.

The Molecular Signature Underlying the Thymic Migration and Maturation of TCRαβ+CD4+CD8- Thymocytes

BackgroundAfter positive selection, the newly generated single positive (SP) thymocytes migrate to the thymic medulla, where they undergo negative selection to eliminate autoreactive T cells and functional maturation to acquire immune competence and egress capability.Methodology/Principal FindingsTo elucidate the genetic program underlying this process, we analyzed changes in gene expression in four subsets of mouse TCRαβ+CD4+CD8- thymocytes (SP1 to SP4) representative of sequential stages in a previously defined differentiation program. A genetic signature of the migration of thymocytes was thus revealed. CCR7 and PlexinD1 are believed to be important for the medullary positioning of SP thymocytes. Intriguingly, their expression remains at low levels in the newly generated thymocytes, suggesting that the cortex-medulla migration may not occur until the SP2 stage. SP2 and SP3 cells gradually up-regulate transcripts involved in T cell functions and the Foxo1-KLF2-S1P1 axis, but a number of immune function-associated genes are not highly expressed until cells reach the SP4 stage. Consistent with their critical role in thymic emigration, the expression of S1P1 and CD62L are much enhanced in SP4 cells.ConclusionsThese results support at the molecular level that single positive thymocytes undergo a differentiation program and further demonstrate that SP4 is the stage at which thymocytes acquire the immunocompetence and the capability of emigration from the thymus.

Altered Proportions of Naïve, Central Memory and Terminally Differentiated Central Memory Subsets among CD4+ and CD8+ T Cells Expressing CD26 in Patients with Type 1 Diabetes

Type 1 diabetes is an autoimmune process predominantly T-cell mediated. CD26 plays a role in T-cell costimulation, migration, memory development, thymic maturation and emigration patterns. In peripheral blood from 55 patients with type 1 diabetes and 20 healthy controls, CD4(+) and CD8(+) T cells expressing CD26 were differentiated into naïve (N, CD45RA(+)CCR7(+)), central memory (CM, CD45RA(-)CCR7(+)), effector memory (EM, CD45RA(-)CCR7(-)), and terminally differentiated effector memory (TEMRA, CD45RA(+)CCR7(-)). In type 1 diabetes, CD4(+) and CD8(+) T cells expressing CD26 showed a distinctive differentiation profile: percentages and absolute numbers of CM and N cells were reduced, whereas those of TEMRA cells were markedly increased. The indices of intermediate- and long-term glycaemic control were associated negatively with the number of CM and N cells while positively with the number of TEMRA cells. The considerable accumulation of TEMRA T cells in our patients suggests life-long stimulation by protracted antigen exposure (viruses, other agents or residual self-antigens?) or a homeostatic defect in the regulation/contraction of immune responses.

IL-15Rα of Radiation-Resistant Cells Is Necessary and Sufficient for Thymic Invariant NKT Cell Survival and Functional Maturation

The development of invariant NKT (iNKT) cells depends on the thymus. After positive selection by CD4(+)CD8(+)CD1d(+) cortical thymocytes, iNKT cells proceed from CD44(low)NK1.1(-) (stage 1) to CD44(high)NK1.1(-) (stage 2), and then to CD44(high)NK1.1(+) (stage 3) cells. The programming of cytokine production occurs along the three differentiation stages, whereas the acquisition of NK receptors occurs at stage 3. Stage 3 thymic iNKT cells are specifically reduced in Il15ra(-/-) mice. The mechanism underlying this homeostatic deficiency and whether the IL-15 system affects other thymic iNKT cell developmental events remain elusive. In this study, we demonstrate that increased cell death contributed to the reduction of stage 3 cells in Il15ra(-/-) mice, as knockout of Bim restored this population. IL-15-dependent upregulation of Bcl-2 in stage 3 cells affected cell survival, as overexpression of hBcl-2 partially restored stage 3 cells in Il15ra(-/-) mice. Moreover, thymic iNKT cells in Il15ra(-/-) mice were impaired in functional maturation, including the acquisition of Ly49 and NKG2 receptors and the programming of cytokine production. Finally, IL-15Rα expressed by radiation-resistant cells is necessary and sufficient to support the survival as well as the examined maturation events of thymic iNKT cells.

MicroRNA miR-150 regulates thymic NKT cell development and function (153.38)

Abstract CD1d-restricted invariant natural killer T (iNKT) cells play an important role in the regulation of diverse immune responses. MicroRNAs (miRNAs), a class of 21-25 nt single-stranded non-coding small RNAs, are increasingly being recognized as important regulators of gene expression through the inhibition of effective mRNA translation. We recently reported that miRNAs expressed in iNKT cell lineage are potent regulators of iNKT cell development, maturation, and function. However, the role of specific miRNAs in the iNKT cells has not been addressed so far. Using miRNA arrays, we found that the expression of miR-150 was significantly upregulated in mature iNKT cells compared to immature iNKT cells in the thymus. Interestingly, mice with miR-150 deficiency have a defect in iNKT cell development in the thymus and iNKT cell maturation was blocked at developmental stage 1 and 2, while the peripheral iNKT cells maturated normally. Furthermore, miR-150-deficient peripheral iNKT cells produce more cytokine interferon-gamma compared to that from wild type after PMA/Ionomycin stimulation. Thus, our results suggest that miR-150 controls iNKT cell thymic maturation and regulates iNKT cell function.

Abnormalities of Thymic Stroma may Contribute to Immune Dysregulation in Murine Models of Leaky Severe Combined Immunodeficiency

Lymphostromal cross-talk in the thymus is essential to allow generation of a diversified repertoire of T lymphocytes and to prevent autoimmunity by self-reactive T cells. Hypomorphic mutations in genes that control T cell development have been associated with immunodeficiency and immune dysregulation both in humans and in mice. We have studied T cell development and thymic stroma architecture and maturation in two mouse models of leaky severe combined immune deficiency, carrying hypomorphic mutations in rag1 and lig4 genes. Defective T cell development was associated with abnormalities of thymic architecture that predominantly affect the thymic medulla, with reduction of the pool of mature medullary thymic epithelial cells (mTECs). While the ability of mTECs to express autoimmune regulator (Aire) is preserved in mutant mice, the frequency of mature mTECs expressing Aire and tissue-specific antigens is severely reduced. Similarly, the ability of CD4+ T cells to differentiate into Foxp3+ natural regulatory T cells is preserved in rag1 and lig4 mutant mice, but their number is greatly reduced. These data indicate that hypomorphic defects in T cell development may cause defective lymphostromal cross-talk and impinge on thymic stromal cells maturation, and thus favor immune dysregulation.

Subchronic Oral Toxicity Study of Furan in Fischer-344 Rats

Rodent studies have shown that furan is a hepatocarcinogen. Previous studies conducted with high doses showed tumors at nearly 100% incidence at all doses. In this paper, a ninety-day gavage experiment conducted with lower doses (0.0, 0.03, 0.12, 0.5, 2.0, and 8.0 mg/kg bw) to identify a no-observed adverse effect level for hepatotoxicity and to characterize non-neoplastic effects including gross changes and histopathology, clinical biochemistry, hematology, and immunotoxicology is reported. As indicated by changes in serum biomarkers, increased liver weights and gross and histological lesions, the liver is the major target organ affected by furan. There were no changes in body weights, food consumption, or histology in other organs. Some of the serum electrolyte markers, including phosphorus, were altered. There was a significant increase in serum thyroxine and triidothyronine in males. This increase was not accompanied by histological thyroid changes. Immunophenotypic analysis showed that thymic lymphocyte maturation was altered in male rats. Although altered clinical biochemistry and hematological parameters were observed at a dose of > 0.5 mg/kg bw, mild histological lesions in the liver were observed at > 0.12 mg/kg bw. Based on this finding, a furan dose of 0.03 mg/kg bw was proposed as the no-observed adverse effect level for hepatic toxicity.

CD4+ recent thymic emigrants are biased to the Th2 lineage (99.14)

Abstract Following intra-thymic development, T cells exit the thymus and join the peripheral T cell pool. These newly generated cells, termed recent thymic emigrants (RTEs), undergo phenotypic and functional maturation for the first 3 weeks they reside in the periphery. Using mice transgenic (Tg) for green fluorescent protein (GFP) driven by the Rag2 promoter (RAG2p-GFP Tg), in which GFP reliably distinguishes RTEs from their more mature naïve (MN) counterparts, our lab is able to isolate untouched RTEs for functional and phenotypic analysis. Activated CD4+ RTEs exhibit defects in IL-2Rα upregulation, proliferation and IL-2 production. We now show that CD4+ RTEs are defective in T helper (Th) 0, Th1, Th17 and regulatory T cell lineage commitment, with dampened cytokine production and transcription factor expression. RTE Th lineage commitment is not globally impaired, however, as CD4+ RTES are biased toward the Th2 lineage, with IL-4, IL-5 and IL-13 production that is enhanced compared to that by identically treated mature T cells. This bias in RTEs likely results from dampened negative regulation of the Th2 lineage by diminished levels of T-bet, a key Th1 transcription factor. CD4+ RTEs are thus a transitional population defined by their distinct interpretation of, and response to, immunological cues. These characteristics may be beneficial during the post-thymic maturation period to avoid inappropriate immune responses, particularly in lymphopenic neonates and adults.

Arrested bone marrow resident T cell committed progenitors in athymic nu/nu mice can give rise to alpha-beta T cells in an OP9DL1 co-culture system. (36.34)

Abstract Bone marrow-resident committed T cell progenitors (CTP) are arrested at a Thy1.2hiLin-CD2- stage in athymic nu/nu mice. In WT mice, CTP progress to a Thy1.2hiLin-CD2+ intermediate stage that then can produce mature, function single positive T cells through thymic and extrathymic maturation pathways. The nu/nu bone marrow microenvironment, therefore, likely disrupts the T cell competence of these precursors during the transition from hematopoietic stem cell (HSC) to CTP prior to these cells leaving the bone marrow for the thymus or periphery. This defect is currently not characterized. We investigated the developmental potential of the arrested CTP from nu/nu bone marrow in a hyper-Notch signal environment induced by the OP9DL1 co-culture system that is able to support the development of mature single-positive T cells from HSCs, embryonic stem cells (ESC) and double negative thymocytes. We found that the OP9DL1 co-culture microenvironment allows the arrested nu/nu CTP to progress to the Thy1.2+Lin-CD2+ intermediate stage as well as to double positive CD4+CD8+ and single positive CD4 and CD8 αβ T cells. It is likely therefore that Notch signaling is compromised in the bone marrow of nu/nu mice and this dysregulated signaling results in the absence of acquisition of T cell competence by early hematopoietic precursors in the bone marrow of these congenitally athymic mice.

Tissue microarray를 이용한 사이모신 베타4(Thymosin β4)와 vascular endothelial cell growth factor (VEGF)의 정상 인간 조직 발현 양상 연구

사이모신 베타 4와 VEGF의 발현을 여러 인간 조직에서 tissue microarray를 사용하여 조사하였다. 사이모신 베타 4는 간, 이자, 침샘의 관상피, 심장에서 강한 발현을 보였으며 피부, 폐, 이자, 림프절, 갑상선, 요관, 폐와 부신의 혈관 내피세포 등에서 중간 수준의 발현 양상을 보였다. VEGF의 발현 양상은 대체적으로 사이모신 베타 4와 동일하였으며 이자, 요관, 유선, 간, 식도, 신장, 폐, 부신 등의 혈관 내피세포에서 강하게 발현되었다. 이러한 결과를 통해 사이모신 베타 4는 간, 이자, 침샘의 관상피, 심장에서 중요한 역할을 담당하며 VEGF와 같은 발현 양상을 보여 혈관 신생작용에 관여함을 확인하였다. Thymosin <TEX>${\beta}4$</TEX>, a small protein containing 43 amino acids, has multi-functional roles in cell physiology. It was first identified as a thymic maturation factor and recently has been shown to accelerate wound healing, hair growth, angiogenesis, tumor growth, and metastasis. It was also reported to play a key role in developing organs, including the nervous system and heart. Thymosin <TEX>${\beta}4$</TEX> induces the expression of vascular endothelial cell growth factor (VEGF), laminin-5, and other important biologically active genes. Using tissue microarray analysis, we investigated the expression patterns of thymosin <TEX>${\beta}4$</TEX> and VEGF in various normal human adult tissues. Thymosin <TEX>${\beta}4$</TEX> was highly expressed in the liver, pancreas, ductal epithelium of the salivary gland, and heart, and moderately expressed in the skin, lung, spleen, lymph node, thymus, ureter, and blood endothelial cells in both the lung and adrenal gland. The expression of VEGF generally co-localized with thymosin <TEX>${\beta}4$</TEX> and VEGF was highly expressed in the pancreas, ureter, mammary gland, liver, esophagus, and blood endothelial cells in both the lung and adrenal gland. These results suggest that thymosin <TEX>${\beta}4$</TEX> plays an important role in the function of various organs and since the expression pattern of thymosin <TEX>${\beta}4$</TEX> co-localized with VEGF, part of that function may be to induce or maintain angiogenesis.

Stage-specific Arf tumor suppression in Notch1-induced T-cell acute lymphoblastic leukemia

AbstractFrequent hallmarks of T-cell acute lymphoblastic leukemia (T-ALL) include aberrant NOTCH signaling and deletion of the CDKN2A locus, which contains 2 closely linked tumor suppressor genes (INK4A and ARF). When bone marrow cells or thymocytes transduced with a vector encoding the constitutively activated intracellular domain of Notch1 (ICN1) are expanded ex vivo under conditions that support T-cell development, cultured progenitors rapidly induce CD4+/CD8+ T-ALLs after infusion into healthy syngeneic mice. Under these conditions, enforced ICN1 expression also drives formation of T-ALLs in unconditioned CD-1 nude mice, bypassing any requirements for thymic maturation. Retention of Arf had relatively modest activity in suppressing the formation of T-ALLs arising from bone marrow–derived ICN1+ progenitors in which the locus is epigenetically silenced, and all resulting Arf+/+ tumors failed to express the p19Arf protein. In striking contrast, retention of Arf in thymocyte-derived ICN1+ donor cells significantly delayed disease onset and suppressed the penetrance of T-ALL. Use of cultured thymocyte-derived donor cells expressing a functionally null Arf-GFP knock-in allele confirmed that ICN1 signaling can induce Arf expression in vivo. Arf activation by ICN1 in T cells thereby provides stage-specific tumor suppression but also a strong selective pressure for deletion of the locus in T-ALL.

Early defects in human T-cell development severely affect distribution and maturation of thymic stromal cells: possible implications for the pathophysiology of Omenn syndrome

AbstractThymocytes and thymic epithelial cell (TEC) cross-talk is crucial to preserve thymic architecture and function, including maturation of TECs and dendritic cells, and induction of mechanisms of central tolerance. We have analyzed thymic maturation and organization in 9 infants with various genetic defects leading to complete or partial block in T-cell development. Profound abnormalities of TEC differentiation (with lack of AIRE expression) and severe reduction of thymic dendritic cells were identified in patients with T-negative severe combined immunodeficiency, reticular dysgenesis, and Omenn syndrome. The latter also showed virtual absence of thymic Foxp3+ T cells. In contrast, an IL2RG-R222C hypomorphic mutation permissive for T-cell development allowed for TEC maturation, AIRE expression, and Foxp3+ T cells. Our data provide evidence that severe defects of thymopoiesis impinge on TEC homeostasis and may affect deletional and nondeletional mechanisms of central tolerance, thus favoring immune dysreactive manifestations, as in Omenn syndrome.