A repulsive view of MHC-restriction.

Recognition of foreign antigens by T lymphocytes is restricted by molecules of the major histocompatibility complex (MHC). This fact is now a corner-stone of immunology, but little is known about the molecular interactions involved in T-cell recognition. Current models attribute MHC molecules with unusual properties, yet biochemically they seem conventional enough proteins. Here Peter Parham offers a reconciliation between the immunological and biochemical findings.