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T A Barrett

Publications and source records attributed to T A Barrett.

30 records · Page 2Linked to original sources
PubMed1994

Developmental expression of the alpha IEL beta 7 integrin on T cell receptor gamma delta and T cell receptor alpha beta T cells.

A novel monoclonal antibody, 2E7, was shown by immunoprecipitation to be reactive with the alpha IEL beta 7 integrin and was employed to analyze the expression of this integrin in lymphocyte subsets and during T cell ontogeny. In adult lymph nodes, alpha IEL was expressed at low levels by 40-70% of CD8+ T cells and < 5% of CD4+ T cells. However, virtually all intestinal intraepithelial lymphocytes and approximately 20% of lamina propria CD4+ T cells were 2E7+, indicating a preferential expression of this integrin on mucosal T cells. Examination of alpha IEL integrin expression during thymus ontogeny revealed that approximately 3-5% of fetal or adult thymocytes were 2E7+. Interestingly, early in fetal thymus ontogeny, approximately 40% of 2E7+ cells expressed T cell receptor (TcR)-gamma delta and this subset persisted through birth. A developmental switch occurred such that 2E7+ TcR- CD4-8+ cells detected on fetal day 19 were followed by 2E7+ TcR-alpha beta CD4-8+ cells in the neonatal thymus. The latter population persisted throughout thymus ontogeny into adulthood. Interestingly, a subset of TcR-gamma delta V gamma 3+ day 16 fetal thymocyte dendritic epidermal cell (DEC) precursors were 2E7+, but all mature DEC expressed high levels of alpha IEL integrin, suggesting that the alpha IEL integrin was acquired late in DEC maturation. This possibility was strengthened by immunohistochemical localization of the majority of 2E7+ gamma delta and alpha beta T cells to the medullary regions of the thymus. Overall, the results demonstrate a developmentally ordered expression pattern of the alpha IEL beta 7 integrin that suggests a common function for this integrin during TcR-gamma delta and -alpha beta CD4-8+ T cell thymocyte development or perhaps in effector functions for these subsets.

Animals↗
PubMed1993

The gamma chain of the high-affinity receptor for IgE is a major functional subunit of the T-cell antigen receptor complex in gamma delta T lymphocytes.

T-cell activation is a consequence of the clonotypic T-cell antigen receptor (TCR) binding to an antigen followed by signal transduction via the invariant subunits of the TCR/CD3 complex. gamma delta TCR cells are a small subset of T cells that populate both the epithelial and lymphoid tissues and have unique antigen specificity and function. However, the composition of invariant chains within the gamma delta TCR/CD3 complex has not been well characterized. Here we report that, unlike the majority of alpha beta T cell, gamma delta T cells isolated from spleen and intestinal epithelial tissue express high levels of the gamma chain of the high-affinity receptor for IgE (Fc epsilon RI gamma) as one invariant subunit of their TCR/CD3 complex. Fc epsilon RI gamma exists as both a homodimer and a heterodimer associated with the TCR zeta chain. Moreover, stimulation of the gamma delta TCR results in rapid tyrosine phosphorylation of Fc epsilon RI gamma. Our results suggest that utilization of distinct receptor signaling components may enable the coupling of antigen stimulation to the activation of different signal transduction pathways in alpha beta and gamma delta T cells.

Animals↗
PubMed1993

CD28-mediated costimulation is necessary for the activation of T cell receptor-gamma delta+ T lymphocytes.

The role of costimulation in the activation of TCR-gamma delta cells in normal mice and mice transgenic (tg) for a TCR-gamma delta receptor was investigated. Activation of TCR-gamma delta cells required two signals. One signal was mediated by TCR occupancy, whereas a second signal was provided by accessory cells. The importance of the CD28/B7 interaction in the delivery of the second signal was demonstrated in multiple ways. First, addition of a soluble fusion protein homolog of CD28, CTLA4Ig, significantly inhibited the activation of G8 tg splenic TCR-gamma delta lymphocytes and intestinal epithelial TCR-gamma delta lymphocytes by Ag-bearing lymphocytes during primary stimulation. Similarly, both proliferation and IFN-gamma production were inhibited by addition of CTLA4Ig to secondary antigenic stimulation of G8 tg TCR-gamma delta cells. Second, an Ag-bearing thymoma, EL-4, was only able to stimulate expanded G8 tg TCR-gamma delta cells when the thymoma expressed B7. This stimulation was blocked by both CTLA4Ig and anti-B7 antibody. Third, antibodies to CD28 were able to mimic the costimulatory affect of APC. TCR-gamma delta cells cultured with either Ag-bearing fixed stimulator cells or submitogenic concentrations of immobilized anti-pan TCR-gamma delta mAb proliferated only in the presence of anti-CD28 mAb. Finally, G8 tg cells produced IL-2 only in the presence of APC costimulation or anti-CD28 antibodies, and the addition of exogenous rIL-2 overcame the need for costimulation. Thus, autocrine IL-2 production is one of the major consequences of TCR-gamma delta cell costimulation. Together these data demonstrate that costimulation is necessary for the activation of TCR-gamma delta cells and can occur through CD28 interaction.

Animals↗
PubMed1993

Tolerance of T cell receptor gamma/delta cells in the intestine.

The present study examined the mechanism(s) of tolerance induction for intestinal intraepithelial lymphocytes (iIELs) using an alloantigen (Ag)-specific gamma/delta T cell receptor (TCR gamma/delta) transgenic (Tg) model. In Tg Ag-bearing H-2b/d mice (Tgb/d), Tg iIELs were Thy-1-, CD44+, CD45R (B220)+, and CD5+, whereas in syngeneic Tgd/d mice, iIELs were Thy-1+, CD44-, and CD45R- with a subset of CD5+ cells. Previously, we had shown that tolerance for Tgb/d iIELs involved functional anergy and deletion (Barrett, T. A., M. L. Delvy, D. M. Kennedy, L. Lefrancois, L. A. Matis, A. L. Dent, S. M. Hedrick, and J. A. Bluestone. 1992. J. Exp. Med. 175:65). In this study we demonstrate that Tgb/d iIELs expressing dull levels of Thy-1 proliferated in the presence of exogenous rIL-2. A direct precursor-product relationship between the Thy-1+-responsive iIELs and the tolerant Thy-1dul/- iIELs was demonstrated by adoptive transfer into severe combined immunodeficient (SCID) mice. Tg Thy-1+ iIELs reconstituting Ag+ but not Ag- SCID mice downregulated Thy-1 after Ag exposure in vivo. Analysis of bone marrow (BM) chimeras demonstrated the persistence of Tg IELs in all Ag+ chimeras although a modest degree of clonal deletion was apparent. The greatest percentage of Tg IELs were detected when Ag was restricted to radioresistant cells (e.g., epithelial cells) compared with BM-derived antigen-presenting cells (APC). This was especially apparent in thymectomized chimeric mice. Consistent with the notion that Ag-bearing epithelial cells may be poor APC, isolated intestinal epithelial cells from Ag-bearing mice failed to stimulate Tg iIELs compared with splenic APC. These studies suggest that the major population of TCR gamma/delta iIELs were probably extrathymically derived and encountered self-Ag on intestinal epithelial cells. The induction of tolerance likely involved an activation event resulting in downregulation of Thy-1. These mechanisms of tolerance for TCR gamma/delta iIELs led to the persistence of a reservoir of self-reactive T cells with the potential for mediating autoimmune disease.

Animals↗
PubMed1992

Differential function of intestinal intraepithelial lymphocyte subsets.

It has been proposed that intestinal intraepithelial lymphocytes (I-IEL) perform immune surveillance of the epithelial layer (1) and regulate mucosal humoral responses to exogenous Ag (2). To better understand the functional potential of this unique population, purified murine I-IEL were analyzed phenotypically and functionally. Initial studies determined that I-IEL could be distinguished based on several phenotypic characteristics including: TCR (TCR-alpha beta vs TCR-gamma delta); Thy-1, CD45R/B220, CD5, and CD8 (CD8 alpha alpha vs CD8 alpha beta) expression. Using anti-TCR mAb, individual I-IEL subsets were activated and examined functionally. Both TCR-alpha beta and TCR-gamma delta I-IEL were found to synthesize an array of lymphokines that included IL-2, IL-3, and IL-6 but not IL-4 or IL-5. Additionally, a number of lymphokines were detected that directly influence epithelial function (IFN-gamma, TNF-alpha, and TGF-beta 1). However, the majority of the I-IEL function was localized within the Thy-1+, CD45R/B220- I-IEL subset. In addition those TCR-alpha beta I-IEL expressing the CD8 alpha beta heterodimer were more easily activated. Thus, a subset of I-IEL have the capacity to respond to TCR-mediated stimuli. The functional activities of these cells may influence both local immune cell populations as well as epithelial differentiation.

Animals↗
PubMed1992

Mechanism of self-tolerance of gamma/delta T cells in epithelial tissue.

The present study examined mechanisms of tolerance for T cell receptor gamma/delta (TCR-gamma/delta) cells. Using a transgenic (Tg) model, we demonstrate that although alloantigen (Ag)-specific TCR-gamma/delta cells are deleted in the thymus and spleen of Ag-bearing mice, intraepithelial lymphocytes (IELs) expressing normal levels of the Tg TCR were present. However, Tg+ IELs from Ag-bearing mice were unresponsive to activation. Furthermore, self-reactive Tg+ IELs decreased in number over time. Thus, in epithelial tissue, Tg TCR-gamma/delta cells are eliminated subsequent to and most likely as a result of the induction of clonal anergy.

Animals↗
PubMed1991

Control of self-reactivity in the intestine.

In the intestine maintenance of self-tolerance may involve tissue-specific self-Ags, APCs, 'second signals', and extrathymic pathways of T cell maturation. These factors combine to create a unique environment where autoimmune tissue destruction is prevented despite local inflammatory influences. In this review we summarize our findings using a TCR-gamma delta transgenic model where self-tolerance was maintained by clonal deletion for cells localizing to peripheral lymphoid tissue and by clonal anergy for cells localizing to the intraepithelial compartments. Several possible explanations exist for these results but in general, these findings have implications for the maintenance of self-tolerance of normal TCR-alpha beta and TCR-gamma delta IELs in epithelial tissues such as the intestine.

Animals↗
PubMed1991

Repertoire development and ligand specificity of murine TCR gamma delta cells.

During the past several years, we have been studying the circulating TCR gamma delta cells expressed in peripheral lymphoid tissues. Biochemical and molecular characterization of the TCR gamma delta heterodimers present on these TCR gamma delta cells identified 3 TCR gamma proteins, V gamma 2-C gamma 1, V gamma 1.2-C gamma 2, and V gamma 1.1-C gamma 4. In addition, at least 6 different V delta gene products (V delta 2,4,5,6,V alpha 10, V alpha 11) are expressed in peripheral lymphoid tissue. Nucleotide sequence analysis has revealed a great deal of junctional diversity present among the different V gamma and V delta proteins. Thus, compared to other nonlymphoid tissues (e.g., skin), this population of TCR gamma delta cells appears quite extensive. The development and specificity of TCR gamma delta cells has been pursued by two approaches. First, different TCR gamma delta cells clones were generated which recognize MHC-encoded gene products. One clone recognizes an unconventional TL-encoded antigen, whereas others have been shown to recognize either classical MHC class I or class II antigens. The TCR gamma delta receptor genes have been cloned from the TL-specific TCR gamma delta cell and used to construct transgenic mice to examine the development of TCR gamma delta cells. Although the Tg+ TCR gamma delta cells are tolerized by thymic clonal tolerance similar to TCR alpha beta cells, the epithelial Tg+ TCR gamma delta cells are subjected to non-deletional tolerance (anergy). A second approach towards examining the development of TCR gamma delta cells has been to compare the repertoire of TCR gamma delta splenocytes in a variety of inbred and MHC-congenic strains of mice using subset-specific anti-murine TCR gamma delta mAb. The percentage of individual subsets of splenic TCR gamma delta cells differ widely between different inbred strains of mice due to both MHC- and TCR-encoded genetic differences. In summary, these studies provides a basis for understanding and determining the ligand(s) of the TCR gamma delta heterodimer and the factors which shape the peripheral TCR gamma delta repertoire.

Animals↗
PubMed1990

Chemotactic peptide effects on intestinal electrolyte transport.

The bacterial-derived chemotactic peptide N-formylmethionyl-leucyl-phenylalanine (fMLP) increases short-circuit current (Isc) and arachidonic acid metabolism (AAM) in rabbit ileum and distal colon. Serosal (s) or mucosal (m) addition of fMLP transiently increases Isc. Half-maximally effective dose and maximal increases in Isc were 32 nM and 84 microA/cm2 in ileum and 234 nM and 80 microA/cm2 in colon, respectively. Piroxicam, a cyclooxygenase inhibitor, diminished the Isc response by 97% in colon and 69% in ileum. Changes in Isc were dependent on Cl- and HCO3- in the bathing media. In ileum, fMLP inhibited m-to-s 36Cl- fluxes and stimulated s-to-m 36Cl- fluxes. These changes in Cl- flux were also inhibited by piroxicam. fMLP stimulated prostaglandin E2 (PGE2) release in intact tissue and in isolated subepithelial components. Increased tissue adenosine 3',5'-cyclic monophosphate levels were detected in intact tissue but not in isolated components. Previous desensitization of ileum to PGE1 inhibited fMLP stimulation of Isc in ileum by 88%. Desensitization to fMLP in ileum failed to alter the effect of PGE1 (10 microM) on Isc. In isolated microsomal membranes of ileal enterocytes, fMLP binding sites could not be demonstrated, suggesting that fMLPs action was initially mediated via stimulation of nonepithelial cell cyclooxygenase activity. The above results indicate that fMLP stimulates net secretion in both ileum and colon probably by the activation of AAM.

1-Methyl-3-isobutylxanthine↗
PubMed1987

Purification and partial characterization of the multicomponent dextranase complex of Streptococcus sobrinus and cloning of the dextranase gene.

The presence of proteases in culture supernatant fluids and on the cell surface of Streptococcus sobrinus and the aggregation of multicomponent enzyme complexes make the isolation and characterization of cell surface proteins difficult. We report a simple purification procedure for dextranase and the cloning of the dextranase structural gene. S. sobrinus culture supernatant fluids were precipitated with 70% ammonium sulfate, and the precipitate was dialyzed against sodium acetate buffer and loaded onto a hemoglobin-Sepharose 4B column connected to a blue dextran-agarose column at 4 degrees C. After being washed with low concentrations of salt, the dextranase and the dextran-binding proteins were eluted with 5 M KI and further purified by gel filtration. Two dextranases (molecular weights, 175,000 and 160,000) were purified and partially characterized. The structural gene for the dextranase of S. sobrinus 6715 strain UAB66, serotype g, was cloned into the cosmid vector, pHC79. Clones were selected for expression of dextranase activity by detection of zones of enzyme-mediated hydrolysis of a blue dextran substrate incorporated into minimal medium agar plates. Release of dextranase was achieved by induction of thermoinducible, excision-defective Escherichia coli K-12 lysogens containing recombinant cosmid molecules of S. sobrinus DNA. Recombinant cosmid molecules were repackaged simultaneously into infectious lambdoid particles. Recombinant clones expressing dextranase activity which varied in size from the high-molecular-weight protein produced by S. sobrinus (i.e., 175,000) to lower-molecular-weight forms expressed by S. sobrinus have been identified and partially characterized.

Bacterial Proteins↗
PubMedDate not supplied

Instrumented measurement of the posterolateral corner.

A new device called the Lars Rotational Laxiometer (Lars Inc, Dijon, France) is introduced to aid in the diagnosis of posterolateral rotatory instability of the knee. This device assigns a quantitative value for tibial external rotation. Three examiners each evaluated a separate group of 30 different subjects (total 180 knees) to obtain side-to-side differences. The subjects had no history of injury, pain, or instability. An external rotation measurement was performed at 30 degrees and 90 degrees of knee flexion. At 90 degrees, the mean side-to-side difference was 4.4 degrees (range, 3.7 degrees to 5.1 degrees); at 30 degrees it was 5.5 degrees (range, 4.7 degrees to 6.3 degrees). There was no significant difference with gender or age. The purpose of this study is to establish baseline side-to-side values for the posterolateral complex in normal knees. Objective values are obtainable with the Laxiometer.

Adolescent↗