Recognizes a protein of 12kDa, identified as beta-microglobulin. Beta--microglobulin non-covalently associates with the 44kDa chain to form the HLA Class I antigen complex. Human beta-2 microglobulin associated with HLA Class I antigens is expressed on many types of cells including lymphocytes, thymocytes, monocytes, granulocytes, platelets, endothelial cells, and epithelial cells. It is absent on erythrocytes. This MAb is specific to human beta-2 microglobulin and does not react with non-human primate cells. This antibody reacts with all cell types excluding erythrocytes. Detection of beta-2 microglobulin in body fluids has been used as a tumor marker and for monitoring patients with HIV infection.