Negative Selection Ensures Self Tolerance

The population of MHC-restricted thymocytes that survive positive selection comprises some cells with low-affinity receptors for self-antigen presented by self-MHC molecules and other cells with high-affinity receptors. The latter thy-mocytes undergo negative selection by an interaction with thymic stromal cells. During negative selection, dendritic cells and macrophages bearing class I and class II MHC molecules interact with thymocytes bearing high-affinity receptors for self-antigen plus self-MHC molecules or for self-MHC molecules alone (see Figure 10-5). However, the precise details of the process are not yet known. Cells that experience negative selection are observed to undergo death by apoptosis. Tolerance to self-antigens encountered in the thymus is thereby achieved by eliminating T cells that are reactive to these antigens.

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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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