β2 Microglobulin

β2 microglobulin also known as B2M is a component of MHC class I molecules, which are present on all nucleated cells (excludes red blood cells). In humans, the β2 microglobulin protein is encoded by the B2M gene. β2 microglobulin lies beside the α3 chain on the cell surface. Unlike α3, β2 has no transmembrane region. Directly above β2 (that is, further away from the cell) lies the α1 chain, which itself is next 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. Low levels of β2 microglobulin can indicate non-progression of HIV. Levels of β2 microglobulin can be elevated in multiple myeloma and lymphoma, though in these cases primary amyloidosis (amyloid light chain) and secondary amyloidosis (amyloid associated protein) are more common. The normal value of β2 microglobulin is <2 mg/L. However, with respect to multiple myeloma, the levels of β2 microglobulin may also be at the other end of the spectrum.