beta2-Microglobulins.

A low-molecular-weight protein, beta2-mu, isolated from urine and other biological fluids was shown to have an amino acid sequence related to constant regions of the immunoglobulin heavy chain--to CH3 comain in particular. Several homologues of this protein were also isolated and partially sequenced. The protein was shown to be localized in the membranes of nucleated cells and found to be associated with HL-A antigens. Its biological and/or immunological function is still unknown; however, it binds to complement and is cytophilic to guinea pig macrophages as well as to other cells. Antibodies to beta1-mu can act as mitogens and can blcok stimulation in MLCs but not recognition by "killer" lymphocytes.