3. The figure below shows the range of TCR affinities for self-peptide: self-MHC

Question

3. The figure below shows the range of TCR affinities for self-peptide: self-MHC of thymocytes. The range of TCR affinities has been divided into four levels, labeled A-D. i) What is the fate of thymocytes with each of four labeled TCR affinity levels (i.e. what happens to these cells). Your response should have four (4) answers (one for A B C D) (4 pts) i) Briefly describe the mechanism that leads to the fates of thymocytes in levels A and D. Your response should have two (2) answers (one for A...). (4 pts) TCR affinity for self peptide:self MHC

Explanation / Answer

i) The blue and green bar shows the negative (blue) and positive (green) threshold.

Region A: Eliminated by negative selection, because of low affinity.

Region B: Survives, as these have moderate affinity.

Region C: Undergoes apoptosis due to high affinity, though it lies in the threshold region.

Region D: Eliminated by neglect during thymic selection.

ii) A: Because of very low affinity, these T cell would not bind to any pMHC molecules. So they are eliminated in positive selection.

D: These thymocytes have very high affinity which could lead to self-reacting T cells and results in autoimmune disease. So these thymocytes are eliminated through negative selection.

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