File:Janeway-7.30.gif

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Janeway Figure 7.30. Thymic cortical epithelial cells mediate positive selection. The expression of MHC class II molecules in the thymus of normal and mutant strains of mice is shown by coloring the stromal cells only if they are expressing MHC class II molecules. In the thymus of normal mice (first panels), which express MHC class II molecules on epithelial cells in the thymic cortex (blue) as well as on medullary epithelial cells (orange) and bone marrow-derived cells (yellow), both CD4 (blue) and CD8 (red) T cells mature. Double-positive thymocytes are shown as half red/half blue. The second panels represent mutant mice in which MHC class II expression has been eliminated by targeted gene disruption; in these mice, few CD4 T cells develop, although CD8 T cells develop normally. In MHC class II-negative mice containing an MHC class II transgene engineered so that it is expressed only on the epithelial cells of the thymic cortex (third panels), normal numbers of CD4 T cells mature. The MHC class II molecule needs to be able to interact with the CD4 protein, as mutant MHC class II molecules with a defective CD4 binding site do not allow the positive selection of CD4 T cells (fourth panels). Thus, the cortical epithelial cells are the critical cell type mediating positive selection.

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current05:22, 11 March 2004Thumbnail for version as of 05:22, 11 March 2004701 × 264 (30 KB)Tarek (talk | contribs)Janeway Figure 7.30. Thymic cortical epithelial cells mediate positive selection. The expression of MHC class II molecules in the thymus of normal and mutant strains of mice is shown by coloring the stromal cells only if they are expressing MHC class II
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