Biomedical subjects

Leslie L Sharp

Publications and source records attributed to Leslie L Sharp.

7 recordsLinked to original sources

PubMed2006

Altered development of CD8+ T cell lineages in mice deficient for the Tec kinases Itk and Rlk.

Mutations affecting the Tec kinases Itk and Rlk decrease T cell receptor-induced Ca(2+) mobilization and Erk kinase activation and impair both positive and negative thymic selection. Itk(-/-) and Rlk(-/-)Itk(-/-) mice also have decreased CD4:8 T cell ratios, suggestive of altered CD4:8 lineage commitment. Nonetheless, we find that CD8 single-positive (SP) thymocytes and peripheral CD8(+) T cells in these mice do not resemble conventional CD8(+) T cells. Instead, these cells express memory markers, rapidly produce interferon-gamma, and can be selected on hematopoietically derived cells, similar to MHC class Ib-restricted "innate-type" lymphocytes. Itk deficiency also greatly increases the number of cells selected by MHC class Ib. Expression of a hypersensitive Erk2 mutant partially corrects the CD8(+) T cell phenotypes in Itk(-/-) mice, arguing that altered signaling permits development of this innate-type CD8(+) cell population. Our results suggest that Tec kinases differentially regulate development of conventional versus nonconventional lymphocytes.

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PubMed2005

Active Ca2+/calmodulin-dependent protein kinase II gamma B impairs positive selection of T cells by modulating TCR signaling.

T cell development is regulated at two critical checkpoints that involve signaling events through the TCR. These signals are propagated by kinases of the Src and Syk families, which activate several adaptor molecules to trigger Ca(2+) release and, in turn, Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) activation. In this study, we show that a constitutively active form of CaMKII antagonizes TCR signaling and impairs positive selection of thymocytes in mice. Following TCR engagement, active CaMKII decreases TCR-mediated CD3zeta chain phosphorylation and ZAP70 recruitment, preventing further downstream events. Therefore, we propose that CaMKII belongs to a negative-feedback loop that modulates the strength of the TCR signal through the tyrosine phosphatase Src homology 2 domain-containing phosphatase 2 (SHP-2).

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PubMed2005

Gammadelta T cell-induced hyaluronan production by epithelial cells regulates inflammation.

Nonhealing wounds are a major complication of diseases such as diabetes and rheumatoid arthritis. For efficient tissue repair, inflammatory cells must infiltrate into the damaged tissue to orchestrate wound closure. Hyaluronan is involved in the inflammation associated with wound repair and binds the surface of leukocytes infiltrating damaged sites. Skin gammadelta T cells play specialized roles in keratinocyte proliferation during wound repair. Here, we show that gammadelta T cells are required for hyaluronan deposition in the extracellular matrix (ECM) and subsequent macrophage infiltration into wound sites. We describe a novel mechanism of control in which gammadelta T cell-derived keratinocyte growth factors induce epithelial cell production of hyaluronan. In turn, hyaluronan recruits macrophages to the site of damage. These results demonstrate a novel function for skin gammadelta T cells in inflammation and provide a new perspective on T cell regulation of ECM molecules.

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PubMed2005

Dendritic epidermal T-cell activation.

Although gammadelta T cells compose a small proportion of lymphocytes in lymphoid compartments and peripheral blood, they are the major T-cell population present in epithelial tissues. However, the role played by gammadelta TCR expressing intraepithelial lymphocytes (IEL) has been enigmatic. The location of tissue-resident IEL suggests that they are important members of the first line of defense against insult for organs exposed to the environment, including the skin, gut, lungs, and reproductive system. Dendritic epidermal T cells (DETC) are the skin-resident gammadeltaIEL and serve as a model system for gammadeltaIEL in other locations. DETC have demonstrated importance in the modulation of immune responses, surveillance and repair of tissue, and resistance to infection. This work discusses recent developments in understanding DETC activation.

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PubMed2004

Dendritic epidermal T cells regulate skin homeostasis through local production of insulin-like growth factor 1.

A fine balance between rates of proliferation and apoptosis in the skin provides a defensive barrier and a mechanism for tissue repair after damage. Vgamma3(+) dendritic epidermal T cells (DETCs) are primary modulators of skin immune responses. Here we show that DETCs both produce and respond to insulin-like growth factor 1 (IGF-1) after T cell receptor stimulation. Mice deficient in DETCs had a notable increase in epidermal apoptosis that was abrogated by the addition of DETCs or IGF-1. Furthermore, DETC-deficient mice had reduced IGF-1 receptor activation at wound sites. These findings indicate critical functions for DETC-mediated IGF-1 production in regulating skin homeostasis and repair.

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PubMed2004

Regulation of skin cell homeostasis by gamma delta T cells.

Although innate T lymphocytes such as gamma delta T cells have been extensively studied, their biological role has remained an enigma to researchers for many years. However, recent advances have begun to explain their complex role in the immune system. Gamma delta T cells are often the major T cell population in epithelial tissues such as the skin, gut, and lung where they have been implicated in maintaining tissue integrity, defending against pathogens, and regulating inflammation. The gamma delta T cells that reside in the skin are a prototypical intra-epithelial lymphocyte (IEL) population. These skin gamma delta T cell receptor (TCR)-expressing cells are named dendritic epidermal T cells (DETC) for their unique dendritic morphology. Using their gamma delta TCR, DETC recognize an unknown ligand expressed by stressed or damaged keratinocytes. Activated DETC exhibit effector functions such as cytokine production, cytolysis, and proliferation in vitro. Recent findings have shown that upon activation by damaged keratinocytes, DETC produce a key keratinocyte growth factor for wound repair called fibroblast growth factor 7 (FGF-7). FGF-7 is produced in vitro and in vivo, suggesting that DETC might play an important role in the biological function of wound repair. Indeed a delay in wound closure and a decrease in the proliferation of keratinocytes at the wound site have been observed in mice lacking gamma delta T cells. In addition to effector functions attributed to DETC, it has also been suggested that gamma delta T cells such as DETC have regulatory roles such as initiating or inhibiting inflammation. This is supported by the findings that DETC produce chemokines and cytokines. Control of the inflammatory response in the epithelium may provide another mechanism to reestablish homeostasis after a biological insult such as wound infliction. Understanding the function of DETC may be useful in the development of future therapies for chronic wounds and the maintenance of skin homeostasis.

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PubMed2004

Preferential activation of an IL-2 regulatory sequence transgene in TCR gamma delta and NKT cells: subset-specific differences in IL-2 regulation.

A transgene with 8.4-kb of regulatory sequence from the murine IL-2 gene drives consistent expression of a green fluorescent protein (GFP) reporter gene in all cell types that normally express IL-2. However, quantitative analysis of this expression shows that different T cell subsets within the same mouse show divergent abilities to express the transgene as compared with endogenous IL-2 genes. TCR gamma delta cells, as well as alpha beta TCR-NKT cells, exhibit higher in vivo transgene expression levels than TCR alpha beta cells. This deviates from patterns of normal IL-2 expression and from expression of an IL-2-GFP knock-in. Peripheral TCR gamma delta cells accumulate GFP RNA faster than endogenous IL-2 RNA upon stimulation, whereas TCR alpha beta cells express more IL-2 than GFP RNA. In TCR gamma delta cells, IL-2-producing cells are a subset of the GFP-expressing cells, whereas in TCR alpha beta cells, endogenous IL-2 is more likely to be expressed without GFP. These results are seen in multiple independent transgenic lines and thus reflect functional properties of the transgene sequences, rather than copy number or integration site effects. The high ratio of GFP: endogenous IL-2 gene expression in transgenic TCR gamma delta cells may be explained by subset-specific IL-2 gene regulatory elements mapping outside of the 8.4-kb transgene regulatory sequence, as well as accelerated kinetics of endogenous IL-2 RNA degradation in TCR gamma delta cells. The high levels and percentages of transgene expression in thymic and splenic TCR gamma delta and NKT cells, as well as skin TCR gamma delta-dendritic epidermal T cells, indicate that the IL-2-GFP-transgenic mice may provide valuable tracers for detecting developmental and activation events in these lineages.

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