exam2_solutions

exam2_solutions - 20.320 Exam 2 Spring 2006 Name Solutions...

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1 20.320 Exam 2 Name Solutions * S p r i n g 2 0 0 6 1. [40 pts] As discussed in class, T-cell activation in the immune response requires the interaction of T-cells with professional antigen-presenting cells (APCs). This interaction is regulated through peptides associated with MHC (major histocompatibility complex) on the APC and the TCR (T-cell receptor) on the T-cell. “Self”-peptides presented by the MHC tend to have low affinity for the TCR, and under normal conditions, by themselves are incapable of activating T-cells. Interestingly, to achieve full T-cell activation, interactions with both high affinity foreign peptides and low-affinity self peptides appear to be necessary, and it is the total avidity of the complex that defines downstream T-cell response ( e.g. , T-cell activation and proliferation vs. T-cell anergy (a quiescent state) or apoptosis). To estimate the avidity of a given system, Jencks [Proc. Natl. Acad. Sci.USA 78: 4046-4050 {1981}] proposed that the change in free energy of complex formation could
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exam2_solutions - 20.320 Exam 2 Spring 2006 Name Solutions...

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