The Structure and Function of the Thymus Flashcards
Where are T cells produced?
Where do they mature?
- They are produced in the bone marrow.
- They mature in the thymus.
List the chains that form T cell receptors.
Which are analogous to heavy chains and which are analogous to light chains?
1 - TCR alpha chain (analogous to light).
2 - TCR beta chain (analogous to heavy).
3 - TCR gamma chain (analogous to heavy).
4 - TCR delta chain (analogous to light).
List the possible combinations of TCR receptor chains.
1 - Alpha + beta chains.
2 - Gamma + delta chains.
List the genes that encode the T cell receptor chains.
Which of these genes is not used for ‘light’ chains?
Lymphocyte antigen receptor genes:
1 - Variable (V).
2 - Diversity (D).
3 - Joining (J).
4 - Constant (C).
- The diversity gene is not used for ‘light’ chains.
Which process ensures that every lymphocyte expresses a different antigen receptor?
Random recombination of lymphocyte antigen receptor gene segments.
If diversity of lymphocyte antigen receptors is generated at random, how are autoreactive antigen receptors avoided?
- By negatively selecting against self antigen receptors and positively selecting for non-self receptors.
- By negatively selecting against receptors that don’t recognise any antigen.
Give an example of a functional difference between T cell receptors and B cell receptors.
T cell receptors can only recognise antigen presented by MHC, whereas B cell receptors can recognise antigen without MHC.
Describe the organisation of cells in the thymus.
- The cortex contains cortical epithelium.
- Blood vessels and dendritic cells straddle the boundary between the cortex and medulla.
- The medulla contains medullary epithelium.
Describe the process of selection of T cells in the thymus.
1 - T cells begin in the cortex, where they are negatively selected against if they don’t bind to MHC at all.
2 - Surviving T cells continue to the medulla, where the are negatively selected against if they bind to MHC too strongly because these T cells are likely to be self-reactive.
3 - In the medulla, T cells that bind to MHC class 1 commit to the CD8 lineage, whereas T cells that bind to MHC class 2 commit to the CD4 lineage.
List the types of T cell tolerance.
1 - Central tolerance.
2 - Peripheral tolerance.
Where does central T cell tolerance occur?
In the thymus.
List the sources of peripheral T cell tolerance.
1 - Ignorance.
2 - Anergy.
3 - Cell death.
4 - Regulatory T cells.
How do T cell precursors mature into T regulatory cells in the thymus?
- Positive / negative selection of T cells for maturation is determined by the strength of the T cell receptor signal (the binding strength to MHC).
- There is an area between positive selection (moderate binding strength) and negative selection (excessively strong binding strength) where T cells are selected for T regulatory cell maturation.
What is the function of T regulatory cells?
To suppress autoreactive lymphocytes that have escaped negative selection.
List 3 proteins expressed by T regulatory cells.
1 - CD4.
2 - CD25.
3 - FOXP3.
