Wrapping Up T Cell Development with a Discussion of Death (or Not)

For Immunology Chapter 9 Day 3

1. During the selection process in the thymus, thymocytes mature from CD4+ CD8+ (DP) cells to being single positive (SP) for either CD4 or CD8. Briefly describe the following:
   1. Instructive model
   2. Stochastic (random) model
2. The kinetic signaling model is the currently accepted idea for explaining why cells commit to a CD4+ vs. CD8+ lineage. Which lineage is the default?  What happens when the TCR signal is interrupted on its way to the default lineage?
3. Why would individuals that are lymphopenic have a higher percentage of recent thymic immigrants relative to typical levels?
4. Thinking back to the two-step model for T cell activation (TCR/peptide/MHC interaction + CD28/CD80 or CD86 interaction), describe how recognition (in peripheral tissues) of a self peptide in an MHC molecule may not lead to T cell activation.
5. Discuss two mechanisms (out of four that the book describes) for how T_REG cells prevent autoimmunity. Can you think of an example of when a drug that inhibits these regulatory cells would be useful?
6. What are some characteristics you would detect in a cell undergoing the apoptotic version of programmed cell death? How do these differ from the characteristics of a necrotic cell?
7. T cells and thymocytes often die via apoptosis as an infection is controlled and during selection, respectively. Which of these situations is more likely to use the “extrinsic” (from outside the cell) pathway?  How does the extrinsic pathway differ from the intrinsic pathway?
8. Certain types of B cell leukemia can be caused by translocations of chromosomes. Why would translocation of the bcl-2 gene next to an immunoglobulin heavy chain promoter be “BAD!”?