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In the image, the Y-shaped blue antibody, or immunoglobulin, is the M protein.
The big round object behind it is a plasma cell, which makes the antibodies. Not all M proteins are whole antibodies like the one shown. Sometimes, the myeloma’s M protein is only one piece of an antibody.
Other References to M Protein
In the context of myeloma, M protein refers to the abnormal production of your body’s antibody-producing plasma cells. Unfortunately, “M protein” may be laden with different meanings in medicine, depending on the topic or illness that is being discussed.
The M protein may also be described using terms as follow:
In this article, we are talking mostly about the M protein that relates to cancer—and, more specifically, to certain types of blood cancer and precancerous conditions of the blood and bone marrow. However, some other notable M proteins occur in medicine, especially in regard to infectious pathogens as shown here:
Blood Cancer
Where It Comes From
In multiple myeloma, the M protein comes from a great excess of plasma cells. Ordinarily, plasma cells will produce a wide range of antibodies. In the normal or healthy state, the population of plasma cells capable of producing a wide array of different antibodies—so-called polyclonal antibodies, or polyclonal immunoglobulins. When plasma cells become cancerous, often there is a single, very bad cell that has given rise to many identical minions. All of the minions are clones of the same cell, and they make only the same monoclonal proteins. Since there are a lot of plasma cells, multiplying abnormally, they make a lot of this monoclonal protein. The abundance, or spike, in the volume of just one protein, can be detected in lab tests.
Structure of Monoclonal Antibodies
Each antibody is made up of four parts. There are two long chains on the inside, and two shorter chains on the outside. In the image, you can see a plasma cell with an antibody and many other tiny antibodies in the background.
The light chains, or the shorter, outside lines in the “blue Y” in the picture, are also called aBence Jones proteins, orfree immunoglobulin light chains. In this case, it is just a small piece of the huge antibody. When the M protein is a light chain, it is small enough, in fact, that it may pass through the kidneys and enter into the urine. So, if only a blood test is done the light chains can be missed since they have entered the urine.
On the other hand, if the M protein is a whole immunoglobulin—the whole big Y in the picture—then it can be detected in the blood since it is too large to pass to the urine. And because these large proteins are retained, excessive buildup of such M protein in the kidney may cause kidney disease.
Importance
Blood and Marrow Conditions That Have an Increased M Protein
Conditions that may result in an elevated level of M proteins on a urine test include:
In some cases, cells causing the M-protein are malignant, and they may invade the bone, lymph nodes, liver, spleen, or other organs. This is the case in multiple myeloma, solitary plasmacytoma, and Waldenström macroglobulinemia.
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A Word From Verywell
Many conditions can cause a monoclonal gammopathy, a spike in one protein product; and, not all of these conditions are cancerous. You can have M protein with certain connective tissue disorders, like systemic lupus erythematosus, rheumatoid arthritis, and psoriatic arthritis. You can have it with Hepatitis C virus infection and HIV/AIDS. You can even have it with acquiredvon Willebrand disease, a rare bleeding disorder. Thus, in many instances, the cause of the M protein is more important than the mere presence of this finding.
4 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Leukemia and Lymphoma Society.Diagnosis.International Myeloma Foundation.Tests to assess monoclonal protein.University of Rochester.Bence-Jones protein.Leukemia and Lymphoma Society.Waldenstrom macroglobulinemia facts.Additional ReadingPapanikolaou X, Rosenthal A, Dhodapkar M, et al.Flow cytometry defined cytoplasmic immunoglobulin index is a major prognostic factor for progression of asymptomatic monoclonal gammopathies to multiple myeloma (subset analysis of SWOG S0120).Blood Cancer J. 2016;6(3):e410. doi:10.1038/bcj.2016.19
4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Leukemia and Lymphoma Society.Diagnosis.International Myeloma Foundation.Tests to assess monoclonal protein.University of Rochester.Bence-Jones protein.Leukemia and Lymphoma Society.Waldenstrom macroglobulinemia facts.Additional ReadingPapanikolaou X, Rosenthal A, Dhodapkar M, et al.Flow cytometry defined cytoplasmic immunoglobulin index is a major prognostic factor for progression of asymptomatic monoclonal gammopathies to multiple myeloma (subset analysis of SWOG S0120).Blood Cancer J. 2016;6(3):e410. doi:10.1038/bcj.2016.19
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
Leukemia and Lymphoma Society.Diagnosis.International Myeloma Foundation.Tests to assess monoclonal protein.University of Rochester.Bence-Jones protein.Leukemia and Lymphoma Society.Waldenstrom macroglobulinemia facts.
Leukemia and Lymphoma Society.Diagnosis.
International Myeloma Foundation.Tests to assess monoclonal protein.
University of Rochester.Bence-Jones protein.
Leukemia and Lymphoma Society.Waldenstrom macroglobulinemia facts.
Papanikolaou X, Rosenthal A, Dhodapkar M, et al.Flow cytometry defined cytoplasmic immunoglobulin index is a major prognostic factor for progression of asymptomatic monoclonal gammopathies to multiple myeloma (subset analysis of SWOG S0120).Blood Cancer J. 2016;6(3):e410. doi:10.1038/bcj.2016.19
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