Final answer:
The affinity hypothesis suggests that T cells with higher affinity for self-antigens are more likely to undergo negative selection, while the altered peptide hypothesis proposes that the presentation of self-antigens in the thymus may be altered, leading to different outcomes during thymic selection.
Step-by-step explanation:
The affinity hypothesis and altered peptide hypothesis are two theories that explain the thymic selection paradox, which refers to why not all T cells that are positively selected are negatively selected. The affinity hypothesis suggests that T cells with higher affinity for self-antigens are more likely to undergo negative selection, while T cells with lower affinity are more likely to escape negative selection. On the other hand, the altered peptide hypothesis proposes that the presentation of self-antigens in the thymus may be altered, leading to different outcomes during thymic selection.
For example, under the affinity hypothesis, T cells that strongly bind to self-antigens may be negatively selected to prevent autoimmunity. However, T cells with weaker binding affinity may still be allowed to mature and contribute to the immune response. Under the altered peptide hypothesis, changes in the presentation of self-antigens may result in T cells not being recognized as self-reactive, allowing them to escape negative selection.