Chapter 5

I wasn't in class last week but I was informed we are expected to focus our posts on chapter 5, as that's where we are in lecture.

1. The first half of chapter 5 discusses T cell receptor development. The gene rearrangement process which takes place here is quite similar to that found in B cells, but the way in which the rearrangements occur is more complex: first it is determined if a T cell will express an Alpha Beta or a Gamma Delta receptor, based on if a successful Beta-chain gene rearrangement occurs before a successful rearrangement of the the Gamma and Delta chains (this statistically leads to the majority of T cells differentiating to become Alpha Beta), once the successful Beta chain is expressed the T cell than proliferates before attempting to express a successful Alpha chain and also expresses the co-receptors CD4 and CD8, successful rearrangement leads to a "double positive"T cell which is then selected for to insure no self-antigen reactivity. In the initial "positive selection"portion of this stringent selection process, T Cells are tested for their capability to recognize the antigen-presenting MHC molecules of the host, and those with receptors that can interact with the MHC molecules are kept (at most 2%) while the rest are left to die by apoptosis. T cells then undergo negative selection, wherein they interact with dendritic cells and macrophages--profesional antigen-presenting cells--and are induced to undergo apoptosis if they interact with any self antigens.

2. I think my biggest challenge throughout both the B and T cell chapters has been conceptualizing the genetic machinery which facilitates rearrangement and all of the particulars of the V, D, and J segments, how they are arranged, how RAG actually facilitates this, and how, exactly, it is possible for T cells to rearrange up to four times. Also much of the medical terminology when describing locations within the body, particularly concerning the thymus (such as subcapsular epithelium, cortico-medullary junction, etc...) did little to further my understanding of the nature of these spaces.

3. I found it particularly interesting that the Thymus is a somewhat transitive organ, working primarily during development and childhood and becoming almost unnecessary be 30 years of age--is this perhaps a function of immune memory? Like the body decidind it has encountered as many new infections as it will and that the current memory immune cells can maintain the body's T-cell immunity without further novel T cell synthesis? It would be interesting to see how maintaining human Thymus function after the age of 30 might affect immunity, and other factors such as metabolism (as it seems perhaps the thymus is "discontinued"for energy reasons).