IMMUNESYSTEM5_Lectureppt_Ch07

Where do T cells develop?

T cells develop in the thymus after migrating from the bone marrow.

What is the role of thymic epithelial cells in T cell development?

Thymic epithelial cells form a nurturing network around developing thymocytes, supporting their maturation.

What are thymocytes, and how are they organized in the thymus?

Thymocytes are immature T cells. They are found in the cortex, while mature thymocytes reside in the medulla.

What is the significance of Hassall's corpuscles in the thymus?

Hassall's corpuscles in the thymic medulla are believed to be involved in the destruction of thymocytes that fail to mature.

How does the production of T cells in the thymus change with age?

The production decreases as thymic tissue is gradually replaced by fatty tissue in a process called thymic involution.

At what stage do thymocytes commit to the T-cell lineage?

Thymocytes commit to the T-cell lineage before rearranging their T-cell receptor (TCR) genes.

What is the role of the Notch1 receptor in T cell development?

The Notch1 receptor drives T cell development by binding to its ligand on thymic epithelium and activating genes essential for T-cell development.

What are the two lineages of T cells, and how do they arise?

αβ and γδ T cells arise from a common thymocyte progenitor, depending on gene rearrangement outcomes.

What happens to immature T cells that undergo apoptosis?

They are ingested by macrophages in the thymic cortex.

How is a pre-T-cell receptor formed?

A pre-T-cell receptor is formed when a successful β-chain gene rearrangement occurs, and it signals the cell to proliferate and express CD4 and CD8.

How are T cells that recognize self-MHC molecules selected?

They undergo positive selection in the thymus and survive if their T-cell receptor binds to a self-MHC molecule.

How does the thymus-specific proteasome affect positive selection?

It produces peptides that are essential for the positive selection process of T cells in the thymus.

What determines whether a T cell becomes a CD4 or CD8 T cell?

Interaction with MHC class I or class II molecules during positive selection determines if the T cell will express CD4 or CD8.

What is negative selection of T cells?

Negative selection removes T cells that bind too tightly to self-antigens, preventing autoimmunity.

How are tissue-specific proteins involved in negative selection?

These proteins are expressed in the thymus and help in the selection of T cells that do not react to self-antigens.

What is the role of regulatory CD4 T cells?

Regulatory CD4 T cells are a distinct lineage that helps regulate immune responses, preventing autoimmunity.

How do T cells further differentiate after antigen recognition?

They differentiate in secondary lymphoid tissues, becoming fully functional immune cells after antigen exposure.

What happens to double-negative thymocytes in T cell development?

Double-negative thymocytes undergo gene rearrangements that lead to the assembly of either a γδ receptor or a pre-T-cell receptor.

What is the significance of CD4+CD8+ αβ cells?

These are double-positive thymocytes, the stage after rearranging a functional αβ T-cell receptor, before becoming single-positive CD4 or CD8 cells.

How are nonproductive β-chain rearrangements rescued?

Successive rearrangements at the β-chain locus allow cells to attempt multiple productive rearrangements.

What is the function of the pre-T-cell receptor?

It signals the thymocyte to proliferate and start the recombination of the α-chain gene.

How is the δ-chain locus deleted?

t is deleted during α-chain gene rearrangement as part of a small circular DNA that is removed from the genome.

What are the stages of αβ T-cell development?

These stages are marked by changes in T-cell receptor gene rearrangement and the expression of specific proteins.

What is positive selection, and how does it relate to MHC molecules?

Positive selection ensures that T cells can recognize self-MHC molecules. Cells that fail this process undergo apoptosis.

What happens during negative selection at the boundary between the cortex and medulla?

Dendritic cells test thymocytes for reactivity to self-antigens, leading to the elimination of self-reactive T cells.

What role do dendritic cells play in negative selection?

Dendritic cells present self-antigens to thymocytes to ensure only non-self-reactive cells survive.

How do T cells recirculate in the body?

Mature T cells leave the thymus and recirculate between the blood, secondary lymphoid tissues, and lymph, unless activated by a specific antigen.

What are the two checkpoints in T-cell development?

The first checkpoint tests the β-chain rearrangement, and the second tests the α-chain rearrangement.

How does continuing α-chain rearrangement influence positive selection?

It increases the chance that T cells will be positively selected by allowing multiple rearrangement attempts

What are double-negative thymocytes?