HLA-B27 and HLA-A2 subtypes: structure, evolution and function.

Beyond the resolution of tissue typing serology, HLA class I antigens display a certain level of structural microheterogeneity, that allows their subdivision into subtypes. The structure of these subtypes shows that multiple mechanisms operate in the generation of HLA polymorphism and suggests possible evolutionary pathways for subtype diversification. In addition, subtype polymorphism critically affects cellular allorecognition and antigen presentation to self-restricted T cells. These properties are used to define the structure and diversity of T-cell epitopes. In this review, José López de Castro discusses the nature and evolution of this polymorphism and its modulation of antigen recognition by cytolytic T lymphocytes.