chapter_1_part2

chapter_1_part2 - Chapter 1 part 2, slides 35 to the end...

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Chapter 1 part 2, slides 35 to the end
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Immunoglobulins (i.e., antibodies) Constant regions Variable regions Antigen binding site
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What about the TCR effector function ? Cell plasma membrane
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Immunoglobulin and TCR variable region genes are made from gene segments by gene rearrangements . This contributes to the building of the antigen- recognition repertoire of B and T cells. Other mechanisms also contribute to the generation of diversity in the antigen- binding receptors
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1. Gene rearrangements (combinatorial diversity ) 2. Junctional diversity 3. Light chain-heavy chain pairing (L-H pairing) (combinatorial diversity ) 4. For B cells only, somatic hypermutation The generation of diversity (i.e., the generation of a diverse antigen-binding repertoire for Ab and TCRs)
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What is achieved by gene rearrangements and other mechanisms for the generation of diversity? 1. Relatively few gene segments can combine to make millions of different receptors (large repertoire ) (i.e., 100s of gene segments can be assembled to make millions of variable regions for Igs and TCRs). 2. Different cells can have different antigen receptors. 3. Somatic progeny of a cell with a gene rearrangement will inherit the gene rearrangement and thus inherit the antigen recognition specificity of the parent cell.
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The down-side is that it is slower to respond than innate immunity because lymphocytes must divide to produce enough cells to mount an effective response and differentiate into effector cells. Antigen-activated, dividing lymphocytes are lymphoblasts . Lymphoblasts divide every 6-8-12 hours. Eventually (usually 4-7 days), lymphoblasts will differentiate into effectors and memory cells. B cells plasma cells T cells active CTL (killers), T H 1 or T H 2 cells also B and T cells memory B and T cells Clonal selection Clonal selection solves the problem of a repertoire that is too large to be fully functional all the time. It is also the basis of immunological memory and tolerance (self/non-self discrimination).
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Effector cells have limited life-spans (maybe 7 days) and clonal expansion will continue only in the presence of antigen. Therefore, when antigen is gone 1. Activation (division and differentiation) ends. 2. Effectors die off and are not replaced, or lose effector function 3. The response subsides Adaptive immune responses are limited by the concentration of antigens. As long as antigen is present, the response continues. When antigen is gone, the response subsides; however, memory memory cells cells remain .
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chapter_1_part2 - Chapter 1 part 2, slides 35 to the end...

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