Epitopes

T- and B-cell epitopes differ fundamentally in the way they are recognized by the immune system. B-cell epitopes are recognized as three-dimensional structures on the surface of native antigens. T-cell epitopes are parts of internalized and processed antigens that are presented to T lymphocytes in association with molecules of the major histocompatibility complex. Since in a biological system T- and B-cell receptors or antibody molecules face a virtual infinite number of structures, cognate interactions with epitopes are the basis of the primordial intelligence that drives the teleological choices of the immune system. Although theoretically any antigen comprises a myriad of potential epitopes, the immune response will focus only on a few of them by a phenomenon termed immunodominance. Understanding the mechanisms that govern epitope selection is important for epitope prediction and vaccine design.