Biomedical subjects

A P Chidgey

Publications and source records attributed to A P Chidgey.

4 recordsLinked to original sources

PubMed2002

Analysis of thymic stromal cell populations using flow cytometry.

The complexity of the lymphostromal interplay that is essential to alphabetaT-cell development is reflected by the heterogeneity of both lymphocytes and thymic stromal cells. While panels of monoclonal antibodies have described many of the cellular components of these microenvironments, the means to quantify stromal cell subsets using flow cytometry remains poorly defined. This study refines and compares various stromal cell isolation procedures and determines the effects of various digestion enzymes on important surface molecules. Three- and four-color flow cytometry is used to correlate established and novel stromal cell markers to define thymic fibroblasts, epithelium and a unique subset of thymic endothelium that express MHC class II. This work provides a basis for the purification of thymic stromal cells for further phenotypic, functional and genetic analysis.

Animals↗

PubMed1998

Positive selection of low responsive, potentially autoreactive T cells induced by high avidity, non-deleting interactions.

Using a novel cell suspension model we investigated the relative abilities of nominal peptide and variants thereof to modulate de novo positive selection of lymphocytic choriomeningitis virus (LCMV)-specific TCR transgenic T cells. Confirming our earlier findings intermediate concentrations (10(-7) to 10(-5) M) of the nominal agonist peptide, p33, induced CD8 co-receptor down-modulation at the level of the entire receptor and the CD8beta chain as a consequence of high but non-deleting signal interactions. Agonist peptide variants caused down-modulation of the CD8beta chain but to a lesser degree. An antagonist peptide capable of inducing positive selection did not cause such modifications of the co-receptor. The positively selected TCRhiCD8alpha alpha and TCRhiCD8- cells were functional but not as efficient as TCRhiCD8alphabeta cells, presumably due to lower avidity interactions in the absence of the CD8beta chain or entire co-receptor. CD8beta mRNA was absent in these cells and was not up-regulated when further stimulated with fresh antigen-presenting cells pulsed with 10(-5) M p33. Effectively our data suggest that it is not the agonist or antagonist nature of a peptide per se but the overall strength of signalling that determines whether a cell will be positively or negatively selected, or die by neglect. Furthermore the agonist/antagonist properties of peptides defined at the level of mature T cell function do not unequivocally predict their effect on positive/negative selection. The ability of the T cell to down-modulate its CD8 co-receptor in response to high but non-deleting peptide interactions during positive selection allows the survival of T cells with a broader range of affinities and represents a possible mechanism by which low responsive but potentially autoreactive cells may escape into the periphery.

Acetyltransferases↗

PubMed1998

An adult thymic stromal-cell suspension model for in vitro positive selection.

Presented here is a cell-suspension model for positive selection using thymocytes from alphabeta-TCR (H-2Db-restricted) transgenic mice specific to the lymphocytic choriomeningitis virus (LCMV) on a nonselecting MHC background (H-2d or TAP-1 -/-), cocultured with freshly isolated adult thymus stromal cells of the selecting MHC type. The thymic stromal cells alone induced positive selection of functional CD4- CD8+ cells whose kinetics and efficiency were enhanced by nominal peptide. Fibroblasts expressing the selecting MHC alone did not induce positive selection; however, together with nonselecting stroma and nominal peptide, there was inefficient positive. These results suggest multiple signaling in positive selection with selection events able to occur on multiple-cell types. The ease with which this model can be manipulated should greatly facilitate the resolution of the mechanisms of positive selection in normal and pathological states.

Animals↗

PubMedDate not supplied

Thymic stromal cells and positive selection.

The intrathymic differentiation events leading to the development and export of mature T cells tolerant to self yet capable of responding to foreign peptide antigen in the context of self-MHC are clearly both dynamic and complex. The changing phenotype of the developing thymocyte as it migrates through and interacts with the heterogeneous thymic microenvironment and the intracellular signalling events associated with such interactions are being extensively studied, yet many aspects remain poorly defined, such as the precise relationship between stromal cells and thymic selection. Positive and negative selection are crucial events in the development of T cells, leading to a diverse yet non-autoreactive immune system. A breakdown in either of these processes could lead to either a reduced T cell repertoire or the escape into the periphery of autoreactive T cells - both clearly having deleterious consequences for the health of the individual. This review aims to summarise the current status of research in thymic positive selection with emphasis on the role of different cell types and peptides.

Animals↗