As discussed in the previous lecture, T cells see fragmented, linear antigenic peptides when these are bound to proteins encoded by MHC genes. There are two major subsets of T lymphocytes that differ in effector function , MHC restriction and accessory molecule usage.
T cells express a clonal antigen-specific receptor.
It has 2 paired polypeptide chains both of which have constant and variable portions and both of which are composed of immunoglobulin-like domains. It exists only as a cell surface receptor and has no counterpart to secreted antibody. The accessory molecules CD4 and CD8 define the effector function and MHC restriction of a T cell. These molecules bind to MHC molecules at a different site to the TCR but form an important part of the TCR complex. Immature thymocytes begin life as emigrants from the bone marrow.