beta 2-Microglobulin: Proteins and Enzymes

beta 2-Microglobulin (B2M) forms the light chain of Class I MHC molecules. It has been measured in a variety of body fluids, including serum/plasma, saliva, CSF, and urine. B2M freely passes through the glomerular membrane, but it is nearly completely reabsorbed and degraded in proximal tubule cells. Clinically, serum B2M is elevated in rheumatoid arthritis, systemic lupus erythematosus, viral infections, and conditions associated with decreased glomerular filtration.