Status report from 'double agent HLA': health and disease.

The human major histocompatibility complex is a multi-gene ~4 Mb of DNA including the highly polymorphic HLA genes which are fundamental in effecting a healthy immune response. Detailed knowledge of the structure and function of HLA genes and their alleles and HLA proteins and their allotypes has rapidly evolved because of their role in clinical transplantation. A significant additional finding is the association or linkage of a wide range of diseases with HLA. We review the function of HLA and the history of disease association studies and focus on specific informative examples in the context of recent genome-wide screening analyses.