β2-Microglobulin belongs to the β-globulin family of human plasma proteins and is the light chain subunit of the class 1 histocompatibility leukocyte antigen complex, which is found on the cell surfaces of all nucleated cells. It is involved in the regulation and rejection of transplanted tissues.
Because of its low molecular weight (11,800kD), β2-Microglobulin is excreted in the urine where increased levels are found in the catabolic dysfunction of the proximal renal tubules and in inflammatory disorders. β2-Microglobulin is also elevated in blood and bone marrow cancers, such as multiple myeloma, lymphoma, and leukemia. In addition, increased levels are associated with multiple myeloma, nasopharyngeal carcinoma, and HIV-1 disease progression.