Lecture 4 Flashcards
When does the thymus start to involute? Is it a primary or secondary lymphoid organ?
Puberty
Primary
Which part of the thymus is responsible for positive selection?
Cortex
Which part of the thymus is responsible for negative selection?
Medulla
What is a thymocyte?
In immature, double negative T cell from the bone marrow
Other than thymocytes, name three other cell types in the thymus.
Dendritic cell, macrophage, thymic epithelial cell
Which cytokine drives initial thymocyte differentiation in the cortex of the thymus? Which cell type releases it?
IL-7 - thymic stromal cells
Which parts of the TCR do RAG-1 and RAG-2 re-arrange?
V-alpha and V-beta
Name the two processes which are involved in generating a unique TCR?
Combinatorial diversity
Junctional diversity
Which (alpha or beta) arm of the TCR has all three V, D and J segments?
Beta
Alpha has only V and J
How many different regions does the alpha chain have for possible rearrangement (somatic / combinatorial diversity)?
70 Variable
61 Joining
How many different regions does the beta chain have for possible rearrangement (somatic/combinatorial diversity?
52 Variable
2 Diversity
13 Joining
Which enzymes are involved in somatic recombination?
RAG 1 and RAG 2
Which enzyme is involved in junctional diversity?
Deoxynucleotidyl-transferase
Which locus - Vbeta or V alpha - rearranges first?
V beta
Which enzymes are affected in SCID? What is the result of this?
RAG-1 and RAG-2
No B or T cells at all - no adaptive immunity
Define ‘thymic education’.
The process of selecting for T cells that recognise ‘altered; self (i.e peptide-MHC complex)
What occurs in the ‘positive selection’ phase of thymic education? Which CD molecules to T cells express during this?
T cells are tested for their ability to bind to self-peptide MHC complexes using their newly recombined TCRs. T cells with any degree of affinity for self-peptide+MHC survive. All others apoptose.
Both CD4 and CD8
What occurs in the ‘negative selection’ phase of thymic education?
Double positive T cells are presented peptide by thymic dendritic cells. Those which recognise MHC I or II + peptide with HIGH avidity are deleted by apoptosis. Those which recognise the former with weak affinity survive, and downregulate expression of either CD4 or CD8 depending on which MHC they bound to.
When in an animal’s life does thymic education occur?
Before birth and early in life.
Treg cells are CD4+ T cells with ____ affinity for self-peptide MHC complex?
high/low
High
