Given that T cell receptors (TCRs) are randomly generated during the maturation process, how are new T cells selected that can recognize self-antigens and other immune cells appropriately?

Question

What will be an ideal response?

Answer 1

Answer: Positive selection selects for T cells that can recognize and respond appropriately to MHC-peptide complexes. Positive selection requires the interaction of new T cells in the thymus with the thymic self-antigens. Using their TCRs, some T cells bind to MHC-peptide complexes on the thymic tissue. The T cells that do not bind MHC-peptide complexes undergo apoptosis and are permanently eliminated. By contrast, those T cells that bind thymic MHC proteins receive survival signals and continue to divide and grow. Positive selection retains T cells that recognize MHC-peptide and deletes T cells that do not recognize MHC-peptide and would therefore be unable to recognize MHC-peptide outside the thymus. In the second stage of T cell maturation, T cells must be able to separate from the MHC-peptide complexes in order to continue to divide and grow. If they bind too strongly at this stage, they will not grow or finish maturation and will die. This prevents T cells that may cause immune reactions to self-antigens from maturing and entering the circulation.