Lec 42: Development of T Cells

Question 1

What are the 4 phases of T lymphocyte development in the thymus?

Answer 1

1. Arrival in the thymus and antigen receptor expression
2. Positive selection
3. Negative selection
4. Terminal antigen-stimulated differentiation into effector and memory cells

Question 2

What are the 2 types of diversity that contribute to 1x10^18 combinations of TCRs?

Answer 2

1. Combinatorial diversity - somatic recombination of TCR alpha and beta loci
2. Junctional diversity - generated at joints between gene segments

Question 3

What is the purpose of T lymphocyte positive selection?

Answer 3

To ensure T-cells will recognize self-MHC (and kill those that do not)

Question 4

What is the purpose of T lymphocyte negative selection?

Answer 4

To delete T-cells that would react to self-antigen

Question 5

What is the purpose of thymic epithelial cells in T lymphocyte positive selection?

Answer 5

Thymic epithelial cells present MHC I and II, along with available proteins acting as antigens, to the “T-cell in training” to see how it will react

Question 6

When is a T-cell considered activated (effector T-cell)?

Answer 6

After it encounters antigen

Question 7

What are the 3 possibly destinies for a T lymphocyte (there are more than 3, but what was described in class)?

Answer 7

1. CD4+ Th1 (helper T-cell)
2. CD4+ Th2 (helper T-cell)
3. CD8+ Tc (cytotoxic T-cell)

Question 8

In terms of location, what is different about the development of T-cells as compared to B-cells?

Answer 8

Both originate in the bone marrow, but T-cells are “educated” and matured in the thymus

Question 9

Which live longer - B-cells or T-cells?

Answer 9

T-cells

Question 10

In terms of thymus structure, what general direction do developing T lymphocytes move as they are developing?

Answer 10

From the outer cortex to the inner medulla

Question 11

Review: what cells are considered lymphocytes?

Answer 11

B-cells, T-cells, and Natural Killer (NK) cells

Question 12

At the start of positive selection in the thymus, do T lymphocytes have CD4, CD8, neither, or both expressed on their surface?

Answer 12

Both CD4 and CD8 - “double positive” (TCR is also expressed at this point)

Question 13

During T lymphocyte positive selection in the thymus, is it desired for the TCR to bind weakly/none or moderately/strongly to the presented MHCs?

Answer 13

Moderately or strongly

Question 14

During T lymphocyte negative selection in the thymus, is it desired for the TCR to bind moderately or tightly to the presented MHC:self-peptide complex?

Answer 14

Moderately; if it binds too tightly to the self-peptide:MHC complex, the T lymphocyte is eliminated