β2 -Microglobulin and Its Relationship to the Immune System

Abstract β 2 -Microglobulin has been isolated from several species, but only bovine β 2 -microglobulin, previously known as lactollin, has been crystallized. An improved method for its isolation from colostrum is described. The bovine homologue exhibits a concentration-dependent aggregation behavior. β 2 -Microglobulin is related to both immune and histocompatibility antigen systems. It exhibits homology with the constant domains of the immunoglobulin-G light and heavy chains and is an integral part of histocompatibility antigens bound to cell surface. β 2 -Microglobulin also occurs in the free state in various body fluids including milk and colostrum. The possible relationship of elevated free β 2 -microglobulin to pathological conditions is suggested for future research.