The study of the HLA system was primarily initiated to understand the basis for the histocompatibility between recipients and tissue donors. HLA typing methods are being continuously improved and biochemical and molecular typing, in particular, are expected to provide precise typing of the HLA system. Conventional HLA typing methods can define antigen specificities, while biochemical and molecular methods will provide direct allele typing that is based on the actual sequence polymorphism. The precise tissue typing will definitely improve the outcome of transplantation. Structural studies have revealed the highly polymorphic nature of the HLA system and given insight to understanding the molecular basis of the HLA polymorphism. One big immunological puzzle remaining to be answered is how T-cell receptor molecules recognize peptide antigen in conjunction with the HLA molecule. The crystallization of the T-cell receptor molecule, an experiment currently underway, will eventually reveal the structural basis of the trimolecular interaction.
Animals ; Genes, MHC Class I ; Genes, MHC Class II ; Histocompatibility Antigens Class I/analysis/chemistry/*physiology ; Histocompatibility Antigens Class II/analysis/chemistry/*physiology ; Human ; Polymorphism (Genetics) ; Protein Conformation

OBJECTIVEThis review focuses on the current knowledge on the implication and significance of beta 2 microglobulin (β2M), a conservative immune molecule in vertebrate.

DATA SOURCESThe data used in this review were obtained from PubMed up to October 2015. Terms of β2M, immune response, and infection were used in the search.

STUDY SELECTIONSArticles related to β2M were retrieved and reviewed. Articles focusing on the characteristic and function of β2M were selected. The exclusion criteria of articles were that the studies on β2M-related molecules.

RESULTSβ2M is critical for the immune surveillance and modulation in vertebrate animals. The dysregulation of β2M is associated with multiple diseases, including endogenous and infectious diseases. β2M could directly participate in the development of cancer cells, and the level of β2M is deemed as a prognostic marker for several malignancies. It also involves in forming major histocompatibility complex (MHC class I or MHC I) or like heterodimers, covering from antigen presentation to immune homeostasis.

CONCLUSIONSBased on the characteristic of β2M, it or its signaling pathway has been targeted as biomedical or therapeutic tools. Moreover, β2M is highly conserved among different species, and overall structures are virtually identical, implying the versatility of β2M on applications.

Antigens, CD1 ; physiology ; Hemochromatosis Protein ; analysis ; Histocompatibility Antigens Class I ; physiology ; Humans ; Receptors, Fc ; physiology ; beta 2-Microglobulin ; blood ; chemistry ; deficiency ; physiology