Beta-2-microglobulin

Beta-2-microglobulin (B2M) is a 119-amino acid component of the class I major histocompatibility complex (MHC) that plays a central role in antigen presentation to the immune system (UniProt: P61769). The protein facilitates the presentation of peptide antigens and is involved in immune surveillance; its surface export can be modulated by pathogenic factors such as mycobacterial proteins.

B2M is expressed broadly in tissues expressing MHC class I molecules. UniProt associations include immunodeficiency 43 (IMD43), characterized by reduced immunoglobulin and albumin levels, and hereditary systemic amyloidosis type 6 (AMYLD6), in which B2M variants form amyloid deposits affecting the gastrointestinal, cardiac, and nervous systems.

B2M is upregulated in Alzheimer's disease brain tissue. Analysis of post-mortem AD brain compared to age-matched controls using tandem mass tag proteomics across subcellular fractions showed a mean log2 fold-change of 0.64 (Chaparral AD proteomics), indicating modest but consistent elevation. This upregulation may reflect altered immune-inflammatory responses in the AD brain microenvironment.