18 Questions
What is the key role of the thymus in T-cell maturation?
Selective removal of T cells reactive against self-antigens
Where in the thymus do mature T lymphocytes exit by passing through the walls of venules and efferent lymphatics?
Medulla
What is the outcome of positive selection in the thymus?
Increased expression of CD4 and CD8
In the thymic medulla, what determines the survival of pre-T lymphocytes?
Recognition of self-antigens
Which cells within the thymus present MHC molecules with antigens to pre-T lymphocytes in the cortex?
Cortical epithelial cells
What happens to pre-T lymphocytes in the thymus that recognize self-antigens during negative selection?
They die by apoptosis
What is the main function of squamous thymic epithelial cells (TECs) in the cortex of the thymus?
Forming a layer that surrounds the microvasculature to create an isolated cortical compartment
What prevents unregulated exposure of thymocytes to antigens in the thymus?
Blood-thymus barrier formed by squamous TECs
What is the role of stellate TECs in the thymus?
Forming a cytoreticulum for attachment of macrophages and developing lymphocytes
Which cell type in the thymus express MHC class II molecules and secrete cytokines for T-cell development?
Stellate TECs
What is the function of the cortical epithelial cells in the thymus during T-cell maturation?
Providing a microenvironment for positive and negative selection of T cells
Which feature distinguishes squamous thymic epithelial cells (TECs) from stellate TECs in the thymus?
Contain keratin tonofilaments joined by desmosomes
What is the main function of Hassall corpuscles in the thymic medulla?
Secrete cytokines that control activity of local dendritic cells
Which cell type is less densely packed in the thymic medulla compared to the cortex?
Dendritic cells
What is the primary role of squamous cortical TECs in the thymus?
Form a functional corticomedullary barrier
What is the unique feature of thymic corpuscles in the medulla?
Secrete factors promoting development of regulatory T cells
Which structure forms a boundary between the cortex and medulla in the thymus?
Cytoreticulum
What characterizes secondary nodules in lymphoid organs?
Larger, more euchromatic cells centrally
Explore the role of the thymus in T-cell maturation and selection process, including the secretion of cytokines by cortical epithelial cells and the exit of mature T lymphocytes from the medulla. Understand how the thymus facilitates T-lymphocyte differentiation and eliminates T cells reactive to self-antigens.
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