Flashcards in Lec 42: Development of T Cells Deck (14):
What are the 4 phases of T lymphocyte development in the thymus?
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
What are the 2 types of diversity that contribute to 1x10^18 combinations of TCRs?
1. Combinatorial diversity - somatic recombination of TCR alpha and beta loci
2. Junctional diversity - generated at joints between gene segments
What is the purpose of T lymphocyte positive selection?
To ensure T-cells will recognize self-MHC (and kill those that do not)
What is the purpose of T lymphocyte negative selection?
To delete T-cells that would react to self-antigen
What is the purpose of thymic epithelial cells in T lymphocyte positive selection?
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
When is a T-cell considered activated (effector T-cell)?
After it encounters antigen
What are the 3 possibly destinies for a T lymphocyte (there are more than 3, but what was described in class)?
1. CD4+ Th1 (helper T-cell)
2. CD4+ Th2 (helper T-cell)
3. CD8+ Tc (cytotoxic T-cell)
In terms of location, what is different about the development of T-cells as compared to B-cells?
Both originate in the bone marrow, but T-cells are "educated" and matured in the thymus
Which live longer - B-cells or T-cells?
In terms of thymus structure, what general direction do developing T lymphocytes move as they are developing?
From the outer cortex to the inner medulla
Review: what cells are considered lymphocytes?
B-cells, T-cells, and Natural Killer (NK) cells
At the start of positive selection in the thymus, do T lymphocytes have CD4, CD8, neither, or both expressed on their surface?
Both CD4 and CD8 - "double positive" (TCR is also expressed at this point)
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?
Moderately or strongly