Biomedical subjects

Helen C O'Neill

Publications and source records attributed to Helen C O'Neill.

7 recordsLinked to original sources

PubMed2004

A role for niches in the development of a multiplicity of dendritic cell subsets.

Although most studies on murine dendritic cell (DC) differentiation concentrate on the nature of the DC precursor population and the lineage relationship between DC and other hematopoietic cell types, very little research addresses the nature of the microenvironments necessary for DC hematopoiesis. Evidence supporting a major contribution of niches in DC differentiation within hematopoietic tissues is reviewed. A model is presented that identifies a potential role for multiple hematopoietic niches in DC differentiation. It is proposed that multiple DC subsets develop from one or a small number of DC progenitor types that lodge in various niches within different tissue sites. Implications of a niche-mediated model for differentiation of DC precursors are discussed in the context of both physiological and pathological situations.

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PubMed2004

In vitro hematopoiesis produces a distinct class of immature dendritic cells from spleen progenitors with limited T cell stimulation capacity.

The study of dendritic cells (DC) has been hampered by the difficulty of isolating rare cells for analysis of their phenotype and function. Interpretation of the DC lineage has been largely influenced by studies on cell populations which can be readily isolated and amplified in the presence of cytokines. Long term cultures (LTC) from murine spleen have been shown to support continuous in vitro hematopoiesis of DC dependent on interaction with a stromal cell monolayer. LTC-DC represent a single, stable class of DC derived by constant turnover of spleen DC progenitors maintained within stroma. They represent a resident DC population in spleen. The functional characteristics of LTC-DC have been studied in terms of capacity to stimulate T cells and response to activation by environmental stimuli. LTC-DC have many morphological, phenotypic and functional properties reflecting an immature or partially mature, marginal zone-like CD4(-)CD8(-) splenic DC subset. They are highly endocytic and can process and present protein antigen to naive hen egg lysozyme (HEL)-specific MHC-II-restricted TCR-Tg CD4(+) T cells. They do not, however, induce T cell proliferation in a mixed lymphocyte reaction. LTC-DC do not respond in a typical fashion to common DC activators like LPS and CD40L. They upregulate MHC-I and CD80/CD86 but not MHC-II and CD40. They reflect an endogenous, immature DC subset in spleen with properties distinct from immature DC located in peripheral tissues.

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PubMed2004

Germline transcription of multiple TCR-Vbeta genes in cloned T-cell lines.

The functional significance of germline transcription of T cell receptor (TCR) beta chain variable (V) region genes is under investigation. The accepted model is that transcriptional activation of germline TCR genes is associated with the rearrangement process during T-cell development. By this model, germline expression of a subset of TCR-Vbeta genes might be expected in early T cells which have not yet undergone rearrangement. Germline transcription of TCR-Vbeta genes was analysed using the reverse transcriptase (RT)-PCR in a clonal T-cell precursor line C1-V13D, a clonal pre-B cell line RAW112 and a mature T helper cell line D10.G4.1. Evidence is presented for germline transcription of TCR-Vbeta8.2 and TCR-Vbeta2.1 genes in all three cell lines, although expression in RAW112 was very weak. C1-V13D cells expressed very high levels of the whole range of transcripts including Vbeta2.1, Vbeta5.1, Vbeta5.2, Vbeta6.1, Vbeta7.1, Vbeta8.1, Vbeta8.2, Vbeta8.3 and Vbeta13.1. However, D10.G4.1 cells expressed a subset of transcripts with apparently lower levels of expression, including Vbeta2.1, Vbeta5.1, Vbeta5.2, Vbeta6.1, Vbeta8.2 and Vbeta8.3. These results raise questions about the significance and possible function of germline transcripts and/or their encoded products in early lymphoid cells and in T cells at different stages of development.

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PubMed2004

Dendritic cell development in long-term spleen stromal cultures.

The cellular microenvironments in which dendritic cells (DCs) develop are not known. DCs are commonly expanded from CD34+ bone marrow precursors or blood monocytes using a cocktail of growth factors including GM-CSF. However, cytokine-supported cultures are not suitable for studying the intermediate stages of DC development, since progenitors are quickly driven to become mature DCs that undergo limited proliferation and survive for only a short period of time. This lab has developed a long-term culture (LTC) system from spleen which readily generates a high yield of DCs. Hematopoietic cells develop under more normal physiological conditions than in cultures supplemented with cytokines. A spleen stromal cell monolayer supports stem cell maintenance, renewal, and the specific differentiation of only DCs and no other hematopoietic cells. Cultures maintain continuous production of a small population of small-sized progenitors and a large population of fully developed DCs. Cell-cell interaction between stromal cells and progenitor cells is critical for DC differentiation. The progenitors maintained in LTC appear to be quite distinct from bone marrow-derived DC progenitors that respond to GM-CSF. The majority of cells produced in LTC are large-sized cells with a phenotype reflecting myeloid-like DC precursors or immature DCs. These cells are highly endocytotic and weakly immunostimulatory for T cells. This model system predicts in situ production of DCs in spleen from endogenous progenitors, as well as a central role for spleen in DC hematopoiesis.

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PubMed2003

Identification of differentially expressed genes representing dendritic cell precursors and their progeny.

The development of dendritic cells (DCs) from hematopoietic progenitors is not well understood. Using a spleen-derived long-term culture (LTC) system, it has been possible to continuously generate DCs from progenitors maintained in culture. The nonadherent LTC-DC population is composed of 2 major subsets. These are the small LTC-DC or DC precursors and their progeny, the large LTC-DCs that phenotypically resemble immature DCs. In this study, subtracted cDNA libraries were generated containing sequences differentially expressed in small or large LTC-DCs. Differential screening was then used on plated library clones to select genes expressed in either the small or the large cell population. Real-time polymerase chain reaction (PCR) has been used to verify the selection procedure for several genes of particular interest. Known genes isolated from subtracted libraries were related to stages in DC development and supported previous findings regarding the function of small and large LTC-DCs. Large LTC-DCs expressed a number of immunologically important genes encoding CD86, CCR1, osteopontin, and lysozyme. Small LTC-DCs resembled progenitor DCs expressing genes related to the organization of the cytoskeleton, the regulation of antigen processing, and a number of mitochondrial and ribosomal proteins. Novel transcripts were isolated from small and large LTC-DC-subtracted libraries that could encode novel proteins important in DC development. This study describes changes in gene expression related to the development of CD11c+CD11b+ major histocompatibility complex 2 low (MHC2lo) CD8alpha- DCs from precursors in a stroma-dependent culture system in the absence of exogenous cytokines.

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PubMed2003

Dynamics of dendritic cell development from precursors maintained in stroma-dependent long-term cultures.

Two distinct subsets of dendritic cells are produced within the non-adherent cell population of the stroma-dependent long-term culture system. These are the small subset containing dendritic cell precursors and their progeny, large long-term culture-dendritic cells, which resemble immature CD11c+CD11b+MHCIIloCD8alpha- dendritic cells. The replicative and developmental potential of cells produced in long-term culture were investigated as a model for production of dendritic cells from progenitors. Cell proliferation and apoptosis were examined by labelling with bromodeoxyuridine and Annexin-V, respectively. The developmental potential of cells was analysed following transfer on to stromal monolayers or into in vitro colony and transwell assays. Results demonstrate that small long-term culture-dendritic cells are stromal cell-dependent. In the absence of stroma, they become apoptotic and die. Furthermore, direct contact with stromal cells is necessary for the differentiation and proliferation of small precursor cells. The small cell subset contains no long-term self-renewing cells, but instead appears to contain cells committed to developing into large long-term culture dendritic cells. The large long-term culture dendritic cell subset also contains dividing cells. Survival of large long-term culture-dendritic cells is dependent on soluble stroma-derived factor(s) and not direct contact with the stromal layer. All data suggest that the long-term culture system supports dendritic cell development from a self-renewing progenitor population resident within the stroma that gives rise to committed dendritic cell precursors and immature dendritic cells.

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PubMed2003

Murine dendritic cell development: difficulties associated with subset analysis.

Dendritic cells are bone marrow-derived professional antigen presenting cells that play major roles in both the induction of primary immune responses and tolerance. It has become clear that dendritic cells are a heterogeneous group of cells that vary in cell surface marker expression and function. Multiple dendritic cell subsets have now been defined in mouse lymphoid organs and peripheral tissues. A knowledge of the function and relationship between dendritic cell subsets will be essential for understanding the regulation of immune homeostasis, immune responses and tolerance. While an increasing number of dendritic cell progenitors are being identified, the pathways that connect them remain unclear. In addition, it is unclear whether the functional divisions reflect maturation status, subset specialization or functional plasticity in response to specific pathogen and environmental signals. This review summarizes the current knowledge about the function and lineage relationship of dendritic cell subsets. It also discusses some of the difficulties associated with dendritic cell subset analysis.

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