Lecture 4

Question 1

When does the thymus start to involute? Is it a primary or secondary lymphoid organ?

Answer 1

Puberty

Primary

Question 2

Which part of the thymus is responsible for positive selection?

Answer 2

Cortex

Question 3

Which part of the thymus is responsible for negative selection?

Answer 3

Medulla

Question 4

What is a thymocyte?

Answer 4

In immature, double negative T cell from the bone marrow

Question 5

Other than thymocytes, name three other cell types in the thymus.

Answer 5

Dendritic cell, macrophage, thymic epithelial cell

Question 6

Which cytokine drives initial thymocyte differentiation in the cortex of the thymus? Which cell type releases it?

Answer 6

IL-7 - thymic stromal cells

Question 7

Which parts of the TCR do RAG-1 and RAG-2 re-arrange?

Answer 7

V-alpha and V-beta

Question 8

Name the two processes which are involved in generating a unique TCR?

Answer 8

Combinatorial diversity

Junctional diversity

Question 9

Which (alpha or beta) arm of the TCR has all three V, D and J segments?

Answer 9

Beta

Alpha has only V and J

Question 10

How many different regions does the alpha chain have for possible rearrangement (somatic / combinatorial diversity)?

Answer 10

70 Variable

61 Joining

Question 11

How many different regions does the beta chain have for possible rearrangement (somatic/combinatorial diversity?

Answer 11

52 Variable

2 Diversity

13 Joining

Question 12

Which enzymes are involved in somatic recombination?

Answer 12

RAG 1 and RAG 2

Question 13

Which enzyme is involved in junctional diversity?

Answer 13

Deoxynucleotidyl-transferase

Question 14

Which locus - Vbeta or V alpha - rearranges first?

Answer 14

V beta

Question 15

Which enzymes are affected in SCID? What is the result of this?

Answer 15

RAG-1 and RAG-2

No B or T cells at all - no adaptive immunity

Question 16

Define ‘thymic education’.

Answer 16

The process of selecting for T cells that recognise ‘altered; self (i.e peptide-MHC complex)

Question 17

What occurs in the ‘positive selection’ phase of thymic education? Which CD molecules to T cells express during this?

Answer 17

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

Question 18

What occurs in the ‘negative selection’ phase of thymic education?

Answer 18

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.

Question 19

When in an animal’s life does thymic education occur?

Answer 19

Before birth and early in life.

Question 20

Treg cells are CD4+ T cells with ____ affinity for self-peptide MHC complex?

high/low

Answer 20

High