T Lymphocyte Recognition Restrictions
In their development in the thymus, T lymphocytes are selected to recognize MHC molecules of the host but not recognize other self antigens. Following selection each T lymphocyte shows dual specificity: The T cell receptor (TCR) recognizes self MHC but only non-self antigens.
MHC restriction occurs during lymphocyte development in the thymus through a process known as positive selection. T cells that do not receive a positive survival signal — mediated mainly by thymic epithelial cells presenting self peptides bound to MHC molecules — to their TCR undergo apoptosis. Positive selection ensures that mature T cells can functionally recognize MHC molecules in the periphery (i.e. elsewhere in the body).
The TCRs of T lymphocytes recognise only sequential epitopes, also called linear epitopes, of only peptides and only if coupled within an MHC molecule. (Antibody molecules secreted by activated B cells, on the other hand, ligate diverse epitopes—peptide, lipid, carbohydrate, and nucleic acid—and recognize conformational epitopes, which have 3D structure.)
Read more about this topic: Major Histocompatibility Complex
Famous quotes containing the word recognition:
“By now, legions of tireless essayists and op-ed columnists have dressed feminists down for making such a fuss about entering the professions and earning equal pay that everyone’s attention has been distracted from the important contributions of mothers working at home. This judgment presumes, of course, that prior to the resurgence of feminism in the ‘70s, housewives and mothers enjoyed wide recognition and honor. This was not exactly the case.”
—Mary Kay Blakely (20th century)