Detection of M Proteins

Abstract

Monoclonal plasma cell proliferative diseases such as multiple myeloma are characterized by the proliferation of a single clone of plasma cells which may produce and secrete a homogeneous monoclonal immunoglobulin. The monoclonal immunoglobulin is commonly referred to as an M protein. The M protein acts as a serological “tumor” marker that is useful for diagnosis and disease monitoring. The identification and quantitation of M proteins relies predominantly on the ability to differentiate between monoclonal and polyclonal immunoglobulins. This has traditionally been done with electrophoretic assays [1–3]. High-resolution agarose gel protein electrophoresis (PEL) and capillary zone electrophoresis (CZE) are relatively simple procedures that are used to detect and quantitate monoclonal proteins [4–6]. Immunofixation electrophoresis (IFE) in agarose and immuno-subtraction electrophoresis (ISE) in CZE are used to identify and characterize the immunoglobulin heavy and/or light chains. In the last few years additional methods have been developed that complement the electrophoretic assays [7, 8]. Quantitation of serum free light chains (FLC) by nephelometric immunoassays support some of the weaknesses of PEL and IFE, and international guidelines now include all three serum assays [9].