beta 2-Microglobulin and beta 2-microglobulin-binding proteins in inflammatory diseases

Beta 2 microglobulin (beta 2m) is a 11,800 daltons polypeptide non covalently associated with the heavy chain of class I histocompatibility antigens (HLA-A, B and C) at the surface of nearly all cells. Serum beta 2m levels are passively controlled by the glomerular filtration rate. Increased beta 2m production resulting in elevated serum levels despite normal renal function have been reported in malignancies of the lymphoreticular system (e.g. multiple myeloma) and in various autoimmune or chronic inflammatory diseases, including rheumatoid arthritis. In some situations beta 2m levels were shown to be positively correlated with absolute lymphocyte counts in the peripheral blood or with the score of mononuclear cell infiltrates in biopsy specimens. Together with the demonstration that activated T lymphocytes release beta 2m in culture, these data support the hypothesis that increased production of beta 2m in vivo could represent a non specific indication of lymphocyte activation. Follow-up studies of individual patients are needed to define the clinical situations in which beta 2m determination may improve the immunological monitoring, with special reference to the early diagnosis of relapses and the assessment of individual response to treatment.