Q: How do we generate an immune response (via T cells) that recognizes foeign antigen, but not self-antigen?
A: There 2 discrete processes: positive selection and negative selection of maturing B cells.

Q: What are nurse cells and where are they located?
A: dendritic-like cells in the thymus.

Q: What are the 2 zones of the thymus?
A: outer cortex and inner medulla

Q: What kind of T cells are located in wach zone?
A: Most mature cells in medulla and the least mature in the cortex. 

Q: What key marker do the most immature thymocytes lack?
A: CD3

Q: In TCR rearrangement, which chains rearrange first?
A: gamma/delta

Q: When is transcription of CD3 stimulated?
A: Once the TCR genes start to rearrange.

Q: What markers do a double positive cell have?
A: CD4 and CD8

Q: What are T cells saved from if they are positively selected?
A: Death by apoptosis.

Q: What is the instructional model of positive selection?
A: Double positive cells bind either MHC I or MHC II with the TCR. If a close enough match, CD4 or CD8 will engage, leading to of the un-untilized chain.

Q: What is the stochastic model of positive selection?
A: Double positive cells randomly lose the expression of either CD4 or CD8, then must engage a MHC class I or class II correctly or the cell will die.

Q: What is the purpose of negative selection?
A: Removal from the population of T cells those that recognize self MHC when occupied by self antigen.

Q: What happens if a self reactive T cell is not removed by negative selection?
A: That T cell can help B cells produce auto reactive anitbodies, or make CTL’s that kill normal, healthy self cells.

Q: How are T cells that are self reactive eliminated?
A: apoptosis.

Q: What are all naïve, un-activated T cells known as?
A: TH0 cells

Q: What happens if a TH0 cell is activated in the presence of IL-4?
A: It will become a TH2 cell.

Q: What happens if a TH0 cell is activated in the presence of IL-12?
A: It will become a TH1 cell.

Q: What do TH1 cells produce, and what immune response does this drive?
A: IFN-gamma; antibacterial inflammatory response

Q: What is involvet in the antibacterial inflammatory respone?
A: production of opsonizing isotypes of antibody, activation of macrophages, enhanced CTL, NK and neutrophil killing.

Q: What do TH2 cells produce?
A: IL-4, IL-5, IL-10

Q: What are these IL’s involved in?
A: Neutralizing, and part of the allergic response. IL-5 leads to eosinophil proliferation and activation, also push macrophages into anti-inflammatory status.