2007HW3KEY Micro - Bio 221 Fall 2007 Homework #3 Key 1....

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Bio 221 Fall 2007 Homework #3 Key 1. Assume for a moment that the only requirement for T cell activation was to bind antigen attached to an MHC. What would be the result of this situation? How does the requirement for the “second signal” (CD28/B7) avoid this problem? Two problems here. First, if T C cells could become activated by binding to any antigen on an MHC, you would end up killing most of your cells, since internal proteins are being presented all the time by most of the cells in your body. Secondly, many non-pathogens are phagocytized and their antigens presented on MHC2. If this automatically activated T H cells, you would have many Type IV hypersensitivity reactions. The “second signal” requirement ensures that a PMP (molecular signal associated with a pathogen) has been recognized before a T cell can be activated. 2. One of Streptococcus pneumoniae ’s virulence factors is a capsule. How does your immune system raise antibodies against S. pneumoniae ? After a first infection with this
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This note was uploaded on 04/07/2008 for the course BIOL 221 taught by Professor Walter during the Spring '08 term at Purdue University-West Lafayette.

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2007HW3KEY Micro - Bio 221 Fall 2007 Homework #3 Key 1....

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