Janeway Figure 7.12. The correlation of stages of α:β T-cell development with T-cell receptor gene rearrangement and expression of cell-surface proteins. Lymphoid precursors are triggered to proliferate and become thymocytes committed to the T-cell lineage through interactions with the thymic stroma. These negative cells express CD44 and c-Kit and, at a later stage, the α chain of the IL-2 receptor, CD25. After this, the CD44+ CD25+ cells begin to rearrange the β-chain locus, becoming CD44low and c-Kitlow as this occurs. The cells are arrested in the CD44low CD25+ stage until they productively rearrange the β-chain locus; the in-frame β chain then pairs with the surrogate pTα chain and is expressed on the cell surface, which triggers entry into the cell cycle. Expression of pTα:β on the cell surface is associated with small amounts of CD3, and causes the loss of CD25, cessation of β-chain gene rearrangement, cell proliferation, and the expression of CD4 and CD8. After the cells cease proliferating and revert to small CD4+ CD8+ double-positive cells, they begin rearrangement at the α-chain locus. The cells then express low levels of an α:β T-cell receptor and the associated CD3 complex and are ready for selection. Most cells die by failing to be positively selected or as a consequence of negative selection, but some are selected to mature into CD4 or CD8 single-positive cells and eventually to leave the thymus.
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|current||20:18, 10 March 2004||463 × 485 (28 KB)||Tarek||Janeway Figure 7.12. The correlation of stages of α:β T-cell development with T-cell receptor gene rearrangement and expression of cell-surface proteins. Lymphoid precursors are triggered to proliferate and become thymocytes committed to the T-|
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