Minor histocompatibility antigens.

Histocompatibility antigens have been studied for over 50 years because they form a major obstacle to clinical transplantation. Human minor histocompatibility antigens remain ill-defined, but minor histocompatibility loci have been mapped on nearly every mouse chromosome. Recent molecular definition of several transplantation antigens suggests that they are by-products of an immune system poised to present viral antigens, and a mutation in any gene may give rise to a new minor histocompatibility antigen.