PubMed Health⌕ Search

Biomedical subjects

H S Teh

Publications and source records attributed to H S Teh.

At least 37 records · Page 2Linked to original sources
PubMed1998

T cells expressing receptors of different affinity for antigen ligands reveal a unique role for p59fyn in T cell development and optimal stimulation of T cells by antigen.

Signaling from the TCR involves the protein tyrosine kinase p59fyn (Fyn). Previous studies have shown that T cell development occurs normally in Fyn-/- mice. In this study, we investigated the requirement for Fyn in the development and function of T cells expressing either the transgenic 2C TCR, with high affinity for its Ag ligand, or the transgenic H-Y TCR, representative of a low affinity TCR. Although Fyn was not essential for positive selection of thymocytes expressing either the 2C or the H-Y TCR, it facilitated the down-regulation of the heat-stable Ag in positively selected CD4-CD8+ thymocytes in both 2C and H-Y mice. Negative selection of thymocytes expressing the H-Y TCR also occurs efficiently in Fyn-/- mice. However, in Fyn-/- mice, there was a preferential survival of thymocytes that expressed higher levels of the CD8 coreceptor and the transgenic TCR. Positively selected CD4-CD8+ thymocytes and peripheral T cells expressing either the 2C or the H-Y TCR differed in their requirement of Fyn for optimal proliferation responses to stimulation by antigenic ligands. Whereas 2C Fyn-/- or 2C Fyn+/+ thymocytes and peripheral T cells responded optimally to stimulation by the specific Ag, H-Y Fyn-/- thymocytes and peripheral T cells were hyporesponsive compared with Fyn+/+ cells. Significantly, in response to a defined low affinity ligand, both 2C Fyn-/- thymocytes and peripheral T cells required Fyn for optimal response to Ag stimulation. Thus, Fyn plays a role during thymocyte development and is required for optimal responses to low affinity/avidity ligands.

Animals↗
PubMed1998

Positive selection of thymocytes expressing the same TCR by different MHC ligands results in the production of functionally distinct thymocytes distinguished by differential expression of the heat stable antigen.

The issue of whether the signaling process during positive selection can affect the efficiency by which the positively selected T cells respond to antigenic stimulation has not been addressed. We approached this question by determining the consequences of positive selection of a particular transgenic TCR (2C TCR) in the H-2b and the H-2k thymus. The H-2b thymus provides a strong positive-selecting environment for the 2C TCR, whereas the H-2k thymus selects weakly for the 2C TCR. Although the positively selected CD8 thymocytes from the H-2b or H-2k thymus expressed similar levels of the CD8 coreceptor molecule, those for the H-2k thymus expressed a slightly lower level of the 2C TCR. This lower level of 2C TCR expression by H-2k CD8 thymocytes was not a result of coexpression of endogenous TCRs. Interestingly, CD8 thymocytes from H-2k mice were hyporesponsive to Ag stimulation compared with those from the H-2b mice. The functional maturity of positively selected CD8 thymocytes from the H-2b or H-2k thymus was inversely correlated with the level of heat stable Ag expressed by these cells. Furthermore, TCR-derived signals appear to be more efficiently coupled to downstream pathways leading to proliferation and cytokine production in CD8 thymocytes from H-2b 2C mice than those derived from H-2k 2C mice. These results provide the first demonstration that the intensity of the signaling process during positive selection affects the efficiency by which TCR-derived signals in positively selected thymocytes are coupled to downstream effector pathways.

Animals↗
PubMed1998

Naturally occurring low affinity peptide/MHC class I ligands can mediate negative selection and T cell activation.

The affinity/avidity model for T cell development postulates that ligands with high affinity for the TCR are efficient in negative selection, whereas those with lower affinity/avidity favor positive selection. Using the 2C TCR transgenic model, we evaluated the efficacy of ligands with widely differing affinity for the TCR (3 x 10(3) to 2 x 10(6) M(-1)) in mediating thymocyte deletion. The relative affinities of the 2C TCR for the p2Ca/Ld, dEV-8/Kb, p2Ca-A3/Ld, and p2Ca/Kb ligands are approximately 1000:50:10:1, respectively. Here we show, using an in vitro assay, that the deletion of 2C CD4+ CD8+ thymocytes is mediated not only by p2Ca/Ld, but also by the lower affinity ligands dEV-8/Kb, p2Ca-A3/Ld, and p2Ca/Kb, albeit at relatively higher peptide concentrations. Deletion mediated by low affinity ligands required CD8, whereas high affinity ligand-mediated deletion was CD8 independent. The p2Ca/Kb and dEV-8/Kb ligands are naturally occurring in H-2b mice, and others have shown that p2Ca/Kb can induce the maturation of CD4- CD8+ 2C-TCR(high) thymocytes in fetal thymic organ culture. In this study we showed that in addition to deletion, the p2Ca/Kb and dEV-8/Kb ligands, in the presence of exogenous IL-2, induced mature 2C T cell proliferation, albeit at a lower level than that induced by the high affinity p2Ca/Ld ligand. Thus, the same low affinity ligands that can effect negative selection and, in the case of p2Ca/Kb, the maturation of CD8 single-positive thymocytes can also induce the activation of mature CD8 T cells.

Animals↗
PubMed1998

Anti-IL-4 treatment prevents dermal collagen deposition in the tight-skin mouse model of scleroderma.

The tight-skin (Tsk/+) mutant mouse, a putative murine model of scleroderma, is characterized primarily by the excessive deposition of collagen and other extracellular matrix molecules in the dermis, and also by a developmentally acquired defect in pulmonary architecture. Passive transfer experiments have suggested an etiologic role for the immune system in Tsk/+ dermal pathology. In addition, CD4+ T lymphocytes have been shown to be required for the excessive accumulation of dermal collagen in these mice. As IL-4, a product of differentiated CD4+ T cells, is capable of regulating the synthesis of various matrix molecules (including type I collagen) by fibroblasts in vitro, we investigated the potential role of IL-4 in mediating Tsk/+ dermal fibrosis. Confirming that Tsk/+ cells are capable of responding to IL-4, we found receptors for this cytokine on Tsk/+ embryonic fibroblasts and a dermal fibroblast cell line derived from these mice. Furthermore, IL-4 receptors on Tsk/+ fibroblasts were functional since IL-4 stimulation in vitro increased type I collagen secretion from these cells. These results demonstrated the potential for IL-4 to be directly involved in the excessive deposition of dermal collagen in Tsk/+ mice. Critical insight into the role played by IL-4 in mediating the dermal phenotype, however, was obtained following the administration of neutralizing anti-lL-4 antibodies to Tsk/+ mice. This treatment prevented the development of dermal fibrosis, leading to normalization of dermal collagen content. Given the requirement for CD4+ T cells in Tsk/+ dermal fibrosis, our results suggest that Th2 cells and/or factors elaborated by this T cell subset may play a key role in regulating dermal collagen content in this strain.

Animals↗
PubMed1998

Contrast-enhanced magnetic resonance imaging of the internal auditory canals and posterior fossa.

A retrospective review of 314 cases of contrast-enhanced magnetic resonance imaging (MRI) of the posterior fossa and internal auditory canals was carried out correlating the presenting symptoms with the scan findings. 7.2% of the cases showed findings on the MRI which could account for the patients' symptoms. Patients with sensorineural hearing loss were more likely to have a positive scan than those presenting with vertigo and/or tinnitus without hearing loss. Acoustic schwannoma was the most common lesion detected. Labyrinthine lesions e.g. cochlear schwannoma, labyrinthitis, congenital labyrinthine abnormality, and central lesions e.g. multiple sclerosis, brainstem glioma were some of the other lesions detected.

Adolescent↗
PubMed1997

CD28-induced cytokine production and proliferation by thymocytes are differentially regulated by the p59fyn tyrosine kinase.

CD28 is a 44-kDa homodimeric receptor that is expressed on the majority of T cells. Engagement of the CD28 receptor by soluble anti-CD28 mAb in conjunction with phorbol ester (PMA) induces the production of cytokines and the proliferation of resting T cells via signal transduction pathways independent of the TCR. Evidence is provided herein that CD28 signals leading to cytokine production do not require the p59fyn (Fyn) tyrosine kinase, whereas CD28-mediated proliferation is dependent on the presence of the Fyn kinase in thymic, but not lymph node, cells. The defect in proliferation is not due to failure of IL-2R signaling, since addition of high concentrations of exogenous IL-2 can overcome the proliferative defect. Analysis of CD28-directed induction of the IL-2R alpha (CD25)-chain, which confers high affinity binding to IL-2, showed that Fyn-deficient thymocytes, but not lymph node cells, failed to up-regulate CD25 expression following anti-CD28 and PMA stimulation. Thus, the Fyn tyrosine kinase is critically required for thymic CD28-mediated CD25 expression and proliferation but not for CD28-mediated cytokine production.

Animals↗
PubMed1997

High concentrations of antigenic ligand activate and do not tolerize naive CD4 T cells in the absence of CD28/B7 costimulation.

We evaluated whether signals transmitted through the T cell receptor (TCR) can activate naive CD4 T cells expressing a transgenic TCR specific for a defined peptide/MHC ligand in the absence of CD28/B7 costimulation. Our results showed that CD28/B7 costimulation was required at low, but not at high, concentrations of antigenic ligand. This was the case whether the CD28/B7 costimulatory pathway was blocked by CTLA-4 Ig fusion protein or by the chemical fixation of antigen-presenting cells. Naive CD4 cells stimulated with high concentrations of antigen and without CD28 costimulation produced low but detectable amounts of IL-2 and interferon-gamma. Furthermore, naive CD4 T cells activated for a 7-day period by either low or high concentrations of antigen with or without CD28 costimulation were functionally similar, indicating that signals transmitted through the TCR were not intrinsically tolerogenic for CD4 T cells.

Abatacept↗
PubMed1997

CD2 regulates the positive selection and function of antigen-specific CD4- CD8+ T cells.

The CD2 glycoprotein has been implicated in both positive and negative regulation of T-cell mitogenesis. To study the involvement of CD2 in T-lymphocyte development and immune responses, we have analyzed two lines of CD2-null mice, each expressing a distinct class I major histocompatibility complex (MHC)-restricted T-cell receptor (TCR). In both situations, the absence of CD2 appeared to promote the positive selection of cells in a manner that is similar to that which occurs in the absence of CD5. Consistent with this, compound homozygotes that lacked both CD2 and CD5 showed evidence of enhanced positive selection even in the absence of a transgenic TCR. Despite the observed enhancement of positive selection, the lack of CD2 was associated with defects in proliferative responses and interferon-gamma production when transgenic thymocytes and mature T lymphocytes were stimulated with the appropriate antigens. These findings raise the possibility that impaired sensitivity to selecting ligands in the thymus may provide a selective advantage that improves the efficiency of positive selection for certain TCRs. Furthermore, the results highlight the potential for a differential role for CD2 in thymocyte selection and T-cell immune responses.

Animals↗
PubMed1997

CD45 enhances positive selection and is expressed at a high level in large, cycling, positively selected CD4+CD8+ thymocytes.

T-cell development is arrested at the CD4+CD8+ (DP; double-positive) stage of thymocyte development in CD45 null mice. However, the mechanism by which CD45 participates in the positive selection of T cells remains to be investigated. In this report we describe a DP thymocyte population that associates positive selection with expression of high levels of CD45, CD4 and CD8. DP thymocytes of this phenotype are large, cycling cells and represent approximately 20% of DP thymocytes in normal mice. In mice expressing a transgenic T-cell receptor (TCR) specific for the male antigen presented by H-2Db (H-Y TCR), the up-regulation of TCR, CD5 and CD69 in this large DP population occurred in a major histocompatibility complex (MHC)-restricted manner. To investigate further the role of CD45 in positive selection, we determined whether thymocytes that expressed a transgenic CD45RO molecule under the control of the proximal lck promoter can influence the positive selection of T cells in H-Y TCR transgenic mice. It was found that in female H-Y TCR transgenic mice, MHC-restricted positive selection of CD4- CD8+ H-Y TCR+ thymocytes was enhanced by increased CD45RO expression. Thus, CD45 increases the efficacy of positive selection of CD4- CD8+ thymocytes that express H-Y TCR.

Animals↗
PubMed1997

Influence of the affinity of selecting ligands on T cell positive and negative selection and the functional maturity of the positively selected T cells.

Interaction of the TCR on immature thymocytes with ligands on antigen presenting cells can lead to different fates including positive and negative selection. The affinity of the selecting ligands plays an important role in determining these outcomes. We used the 2C TCR transgenic model to evaluate the efficacy of ligands with widely differing affinity (3 x 10(3) - 2 x 10(6) M-1) for the 2C TCR in mediating thymic negative and positive selection. Our results support the conclusions that the deletion of immature thymocytes is not only mediated by high-affinity ligands but also by low-affinity/avidity ligands. However, high- and low-affinity ligands differ in their requirements for negative selection. We also present evidence that positive selection is not an all or none process but depending on the strength of interaction between the ligand and the TCR during the positive selection process can result in single positive thymocytes that are at different stages of functional maturity.

Animals↗
PubMed1996

The CD43 130-kD peripheral T-cell activation antigen is downregulated in thymic positive selection.

Specific glycoforms of CD43, the major O-glycosylated cell-surface protein on T lymphocytes, can affect cell adhesion according to the types of carbohydrate side chains carried. In the peripheral immune system, CD43 130 kD, which carries core 2 O-glycan structures on its surface, is an activation antigen expressed on both CD4 and CD8 single-positive (SP) T cells. We have previously shown that the 115-kD resting and 130-kD activation glycoforms of murine CD43 are differentially regulated on peripheral SP T cells. In this study, we used transgenic mice expressing T-cell receptors (TCRs) specific for antigens presented by class I and class II major histocompatibility complex (MHC) molecules to determine whether CD43 glycoforms are involved in thymocyte differentiation. Positive selection in these mice results in an increase in the production of CD8 and CD4 SP T cells, respectively, which express the transgenic TCR. Positive selection is also accompanied by the upregulation of TCR, CD69, and CD5. Using these markers to define stages of thymocyte maturation, we found that CD43 130 kD was downregulated in the positive selection of CD4 CD8 double-positive thymocytes expressing a class I but not class II MHC-restricted TCR. These data suggest that core 2 glycosyltransferase (C2GnT) modulated expression of CD43 glycoforms may be involved in thymic selection events.

Animals↗
PubMed1996

Differential activation of phospholipase C-gamma 1 and mitogen-activated protein kinase in naive and antigen-primed CD4 T cells by the peptide/MHC ligand.

In this study, we determined the functional and biochemical differences in naive and primed CD4 T cells that expressed a TCR specific for the pigeon cytochrome c (pcc) peptide presented by I-Ek MHC class II molecules. Naive CD4 T cells expressing the transgenic TCR were isolated from the peripheral lymphoid organs of transgenic mice and stimulated with pcc peptide and IL-2 for 10 to 14 days. After this culture period, the Ag-primed cells were quiescent, as judged by the lack of expression of the early activation marker CD69, low expression of CD25 (IL-2R), and failure to incorporate thymidine. The primed cells required 10-fold less peptide than naive cells to achieve the same degree of proliferation and for the induction of CD69. Primed cells also mobilized calcium more efficiently with regard to Ag dose and magnitude of the response. The biochemical signal-transduction events in naive and primed T cells were compared by stimulating them with different concentrations of pcc peptide presented by adherent Ek-transfected fibroblasts. It was found that tyrosine phosphorylation and activation of mitogen-activated protein kinase (MAPK) in primed cells required 10-fold less Ag and occurred more rapidly and intensively. Interestingly, peptide stimulation induced tyrosine phosphorylation of phospholipase C (PLC)-gamma 1 exclusively in primed cells. RasGAP was also more efficiently tyrosine phosphorylated in primed cells. By contrast, Shc was tyrosine phosphorylated to the same extent in naive and primed cells. PI3Kp85 was not tyrosine-phosphorylated in naive and primed cells either before or after peptide stimulation. We propose that the higher sensitivity of the primed cells to Ag stimulation is most likely dependent, at last in part, on the more efficient activation of PLC-gamma 1, MAPK, and calcium-dependent pathways.

Animals↗
PubMed1996

Increase in the specific activity of p50csk in proliferating T cells correlates with decreased specific activity of p56lck and p59fyn and reduced phosphorylation of CD3 subunits.

Depending on their prior antigen recognition history, mature T cells respond with different functional outcomes to T cell receptor (TCR) stimulation. These functional outcomes include proliferation, anergy and cell death. The biochemical basis underlying differential responses by mature T cells at different stages of their developmental pathway to TCR stimulation remains to be determined. We have previously shown that proliferating but not naive T cells were susceptible to apoptosis after TCR stimulation and that the tyrosine phosphorylation of TCR zeta, CD3 gamma, and CD3 epsilon in proliferating T cells was decreased after TCR stimulation. In this study. We determined whether differences in phosphorylation between naive and proliferating T cells were due to altered regulation of p56lck (Lck) or p59fyn (Fyn) by their positive or negative regulators, CD45 or p5Ocsk (Csk), respectively. We found that Lck was expressed at the same level and had the same phosphotyrosine content in naive and proliferating T cells. However, its autophosphorylation activity was lower in proliferating cells, corresponding to a 2-fold decrease in its specific kinase activity. Similarly, the specific kinase activity of Fyn was also decreased by about 2-fold in proliferating T cells. In contrast, although Csk was expressed at the same level in both cell types its specific kinase activity was increased by 6-fold in proliferating T cells. The tyrosine phosphatase CD45, a positive regulator of src-family kinases, was overexpressed by 3- to 6-fold in proliferating cells. However, the specific activity of CD45 in naive and proliferating T cells was the same. Therefore, although the protein expression level of CD45 was increased in proliferating T cells it only partially compensated for the hyperactivity of Csk resulting in a 2-fold reduction in the specific activity of Lck and Fyn in proliferating T cells.

Animals↗
PubMed1996

Differential regulation of p72syk expression in naive and proliferating CD4-CD8+ T cells.

A well-known consequence of TCR stimulation in proliferating T cells is cell death by apoptosis. We have previously shown that the extent of tyrosine phosphorylation of TCR zeta, CD3 gamma, and CD3 epsilon subunits in proliferating CD4-CD8+ T cells after TCR stimulation was decreased when compared to similarly stimulated naive T cells expressing the same TCR. Furthermore, these differences correlated with a decrease in the specific kinase activity of p56lck and p59fyn, with a corresponding increase in the specific kinase activity of p50rsk, a negative regulator of src-family tyrosine kinases. In this study we determined whether kinases that bind tyrosine phosphorylated TCR zeta chain were differentially regulated in naive and proliferating cells. Chemically synthesized cytoplasmic domains of the TCR zeta chain were fully phosphorylated in vitro with p56lck and used to precipitate TCR zeta binding proteins in naive and proliferating cells. Using this method we found that both ZAP-70 and p72syk bound tyrosine phosphorylated TCR zeta very efficiently. More interestingly, p72syk was found to be expressed only in naive but not proliferating cells. Kinetic studies indicate that more than 48 hr of activation was required for ceasation of p72syk expression. We also showed that the inability to detect p72syk expression in proliferating cells was not due to its translocation to cytoskeletal compartments in proliferating cells. We propose that the differential regulation of ZAP-70 and p72syk in naive and proliferating cells may contribute to the uncoupling of the TCR signaling pathway from downstream signaling events leading to distinct functional outcomes in these two cell types after TCR stimulation.

Animals↗
PubMed1996

Fas (CD95)-independent regulation of immune responses by antigen-specific CD4-CD8+ T cells.

Antigen-activated T cells of the CD4(+)CD8(-) phenotype are susceptible to antigen receptor-stimulated cell death. This form of apoptotic cell death has been shown to be dependent on the expression of the Fas (CD95) antigen and can occur via an autocrine mechanism involving the concomitant up-regulation of Fas and its ligand on activated T cells. Mutation in genes encoding Fas (Ipr) and the Fas ligand (gld) contribute to the development of an autoimmune syndrome similar to systemic lupus erythematosus in mice. These observations led to the suggestion that the Fas signaling pathway is an important regulator of immune responses in vivo. Here we evaluated the importance of the Fas pathway in regulating immune responses by male antigen-specific CD4(-)CD8(+) T cells. We found that the in vivo elimination of these activated cells was independent of Fas expression by these cells. However, the elimination of these activated cells was inhibited by the transgenic expression of Bcl-2, a protein that inhibits multiple forms of apoptotic cell death. The transgenic Bcl-2 protein also inhibited the death of male antigen-activated cells following IL-2 deprivation. Cell death resulting from IL-2 deprivation occurred efficiently in male antigen-activated Fas- cells. We propose that the rapid deletion of male antigen-activated Fas- cells in vivo is due to limiting amounts of IL-2 that are available in the microenvironment of the activated cells at the peak of the response.

Animals↗
PubMed1995

Distinct differentiative stages of CD4+CD8+ thymocyte development defined by the lack of coreceptor binding in positive selection.

Cortical CD4+CD8+ thymocytes mature into CD4+ or CD8+ thymocytes through a process termed positive selection. To better define differentiative stages of CD4+CD8+ thymocyte development in positive selection, we performed a phenotypic analysis of CD4+CD8+ thymocytes from H-Y mice mated to various genetic backgrounds. We have previously shown that coordinate binding of the H-Y TCR and the CD8 coreceptor to the restricting Db MHC class I molecule is required for the efficient positive selection of this TCR. In this study we have used TCR, CD5, and CD45 expression levels as markers for thymocyte maturation. Lack of CD8/Db interaction was achieved by introducing a mutation that abrogates CD8 binding in the alpha 3 domain of Db. We found that the absence of coreceptor ligation prevented TCR up-regulation in CD4+CD8+ thymocytes and resulted in a developmental arrest characterized by low levels of TCR and CD45. We have previously shown that deletion of CD4+CD8+ thymocytes expressing the H-Y TCR is facilitated by CD8 coreceptor ligation. Here we show that expression of the deleting ligand in the absence of coreceptor ligation caused CD5 up-regulation without concomitant TCR or CD45 up-regulation in CD4+CD8+ thymocytes. In a beta 2-microglobulin null background, introduction of the H-Y TCR caused the majority of CD4+CD8+ thymocytes to express an unusually low level of of the CD5 activation marker, suggesting that a low-affinity or noncognate TCR/MHC interaction may be required for initial CD5 up-regulation to intermediate levels. Collectively, these observations favor a maturational process in positive selection in which CD5 up-regulation precedes CD45 and TCR up-regulation.

Animals↗
PubMed1995

Isolation of a gene encoding a developmentally regulated T cell-specific protein with a guanine nucleotide triphosphate-binding motif.

In this study, we describe a novel full length cDNA clone designated Tgtp that encodes a predicted 415-amino acid a T cell-specific guanine nucleotide triphosphate-binding protein (TGTP) bearing the characteristic motifs of a guanine nucleotide triphosphate (GTP) binding protein. Tgtp is expressed preferentially, if not exclusively, in T cells, and is up-regulated in both unfractionated and in purified CD4+8+ thymocytes upon TCR cross-linking. In contrast, expression of Tgtp is peripheral T cells is maintained at relatively high levels and is not grossly affected by TCR cross-linking. Antiserum generated against synthetic peptides from the predicted TGTP amino acid sequence recognized a single protein with a molecular mass of approximately 50 kDa, corresponding well with the computed molecular mass of 47 kDa. The only known relative of Tgtp is MUSGTP, which is reportedly expressed in B cells and bears a GTP binding motif. Thus, the discovery of Tgtp resolves a subfamily of molecules with GTP binding motifs and apparent lymphoid lineage-restricted expression. Given the restricted expression pattern in T cells, the up-regulated expression observed in response to TCR signaling in immature thymocytes, and the presence of the motifs characteristic of GTP binding proteins, we suggest that TGTP may have an important function in T cell development and/or T cell activation.

Amino Acid Sequence↗