Blood contains 3 main types of immunoglobulin (antibodies): each type is composed of one heavy chain and one light chain. The heavy chain is characteristic of the family of antibodies (IgG, IgA, IgM), while the light chain can be of two types, either kappa or lambda. These antibodies are produced by bone marrow plasmocytes, which are white blood cells involved in the normal defence against attacks (infection, etc.). In a normal response to an attack, several types of plasmocyte intervene and produce a wide variety of antibodies (polyclonal elevation). However, a single plasmocyte subtype (clone) sometimes develop in an uncontrolled manner (cancer) and produces an excess of a single antibody (monoclonal elevation). Protein immunofixation is used to confirm whether an abnormality detected by protein electrophoresis may have been caused by monoclonal phenomena.
The presence of a monoclonal fraction may signal the presence of bone marrow cancer, lymphoma or multiple myeloma. Some myeloma are called “MGUS” for monoclonal gammopathy of undetermined significance. Monoclonal elevations of IgM are often associated with a thickening of the blood, particularly when the skin is exposed to cold (Waldenstrom macroglobulinemia).