Beta-2 microglobulin

β2 microglobulin is a component of MHC class I molecules, which are present on almost all cells of the body (red blood cells are a notable exception). β2 microglobulin lies lateral to the α3 chain on the cell surface. Unlike α3, β2 has no transmembrane region. Directly above β2 (i.e. away from the cell) lies the α1 chain, which itself is lateral to the α2. β2 microglobulin associates not only with the alpha chain of MHC class I molecules, but also with class I-like molecules such as CD1 and Qa.



In patients on long-term hemodialysis, it can aggregate into amyloid fibers that deposit in joint spaces, a disease known as dialysis-related amyloidosis.

Mice models deficient for the β2 microglobulin gene have been engineered. These mice demonstrate that β2 microglobulin is necessary for cell surface expression of MHC class I and stability of the peptide binding groove. In fact, in the absence of β2 microglobulin, very limited amounts of MHC class I (classical and non-classical) molecules can be detected on the surface. In the absence of MHC class I, CD8 T cells cannot develop. CD8 T cells are a subset of T cells involved in the development of acquired immunity.