PS2_KEY

PS2_KEY - Bi114 Problem Set 2 ANSWER KEY 50 points total 1....

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Bi114 Problem Set 2 ANSWER KEY 50 points total 1. [24 total points] Read Sun and Bevan. 2003. Science (a) [5points] The mouse strains used in this study were either wild type or MHCII- deficient (class II -/- ). Given that peptides are presented to CD8 T cells via MHC-I molecules, why would the authors have used MHCII-deficient mice to study CD8 T cell memory? The authors used MHCII-deficient mice because these mice lack CD4 T cell function and therefore allow for the study of memory CD8 T cell generation in the absence of any help from CD4 T cells. 2.5 points: MHCII-deficient mice lack CD4 T cell function 2.5 points: studying memory CD8 T cell generation in absence of CD4 T cell help (b) [5points] In Figure 1A we see that even the wild type mice took at least 7 days to clear a rLmOva infection. Why did the authors measure CFUs after only 3 days in Figure 1B? In Figure 1B, the mice have already experienced a primary rLmOva infection (ie they have been immunized) and the authors are now measuring the mouse’s ability to clear a secondary infection, which the wild type mice were clearly able to do within 3 days. 2.5 points: authors measuring the mouse’s ability to clear a secondary infection 2.5 points: this should occur more quickly than 7 days in a wild type mouse (c) [5points] In Figure 1C, memory CD8 + T cells were measured via staining with K b /OVA tetramers. The tetramers used by the authors were bound to the ovalbumin- derived peptide SIINFEKL. If the authors knew the antigen sequence, why did they use labeled tetramers to quantify antigen-specific T cells instead of just a labeled antigen? In your answer explain the choice of MHC molecules used in these tetramers. T cells cannot be activated by an antigen alone. Their activation requires an appropriate peptide:MHC complex which can be presented via tetramers. Because CD8 T cells can only be activated by a peptide presented by a class I MHC molecule and the authors were measuring CD8 T cell activation, they had to use class I MHC molecules in these tetramers. 2.5 points: T cells activation requires peptide:MHC complex, can be presented via tetramers. 2.5 points: class I MHC molecules used in tetramers because measuring CD8 T cell activation
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(d) [9points] Explain how and why cytotox ic activity was measured in figure 2D ( general terms are fine, specific reagents not necessary ). Why is a loss of function only detected
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PS2_KEY - Bi114 Problem Set 2 ANSWER KEY 50 points total 1....

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