1. M protein detection and characterization
M protein detection and characterization. A) Serum protein electrophoresis. In this test, serum proteins are separated based on size and charge by electrophoresis in an agarose gel, which is then stained with a protein dye. Lanes marked with an asterisk contain a sharply focused band within the region of the gel to which immunoglobulin (Ig) migrates, an appearance that is indicative of the presence of a monoclonal immunoglobulin (an M protein). Note that each M protein migrates differently, reflecting the fact that each has its own unique amino acid sequence. The amount of M protein is quantified based on its staining intensity. B) Once an M protein is detected, it is further characterized by immunofixation. In this assay, the same sample is loaded in multiple lanes and separated by electrophoresis as in A. One lane is stained for total protein (SP), whereas the other individual lanes are incubated with antibodies specific for various immunoglobulin heavy chains (G, A, or M) and light chains (κ, kappa or λ, lambda) and then washed extensively. Any antibody-antibody complexes that form in the gel are resistant to removal during washing; these "immunofixed" proteins are detected with a protein stain. Immunoglobulins in normal serum (left panel) are of many different types and therefore appear as a broad smear. In contrast, in multiple myeloma, a single major sharp immunoglobulin band is seen in the lanes stained for IgG heavy chain and kappa light chain, indicating the presence of an IgG-kappa M protein. Note also that normal immunoglobulins are suppressed in this sample, a hallmark of myeloma. The right hand panel contains serum from a patient with lymphoplasmacytic lymphoma (LPL) that is associated with production of an IgM-lambda M protein. Unlike the myeloma sample, this serum has relatively preserved levels of polyclonal immunoglobulin.
Source: Multiple Myeloma and Related Disorders, Pathophysiology of Blood Disorders
Citation: Bunn H, Aster JC. Pathophysiology of Blood Disorders; 2011 Available at: Accessed: September 26, 2017
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