The Role of Human Class II Molecules in Activation of T4 Lymphocytes

While B lymphocytes can bind antigen directly, T lymphocytes recognize antigen only when presented together with major histocompatibility complex (MHC)-en-coded class I or II molecules in the membrane of antigen-presenting cells (APC). This is called MHC restriction and was first shown in animal studies (see [5, 25] for references). The parts of the MHC molecule which are co-recognized together with antigen are often called restriction elements.