Immunoglobulin M (IgM, serum)
Why this test?
- To assess humoral immunity.
- For diagnosis of immunodeficiency states.
- For differential diagnosis of acute and chronic infections (with simultaneous determination of IgG level). For the diagnosis of intrauterine infections.
- For the diagnosis of Waldenström macroglobulinemia.
- To assess the immune system in autoimmune pathologies, blood diseases and neoplasms.
- To evaluate the effectiveness of immunoglobulin preparations.
In what cases is it prescribed?
- When examining children and adults who often suffer from infectious diseases.
- When monitoring the treatment of macroglobulinemia Waldenström.
- When examining patients with autoimmune pathology.
- In a comprehensive study of the immune system.
- In neoplasms of hematopoietic and lymphoid tissues.
- When monitoring patients with immunodeficiencies.
- Before using immunoglobulin preparations, as well as during and after it.
Immunoglobulins are glycoproteins that play an important role in the work of the immune system. There are 5 classes of antibodies (IgA, IgG, IgM, IgE, IgD), which differ in structure and function and are included in the gamma-globulin fractions of blood proteins. They are produced by plasma cells (mature B-cells) in response to exposure to antigens of bacteria, viruses, fungi, parasites and other organic substances that are perceived as "not their own".
When the body is first infected or exposed to foreign substances, the immune system recognizes them and stimulates plasma cells to produce antibodies that bind and neutralize antigens. It is able to "remember" the antigen with which it was previously in contact, and upon its re-entry into the body, it is able to provide a quick reaction and the production of a larger number of immunoglobulins, preventing reinfection and the repeated development of the disease.
This feature of the immune response is the theoretical basis of vaccination.
IgM antibodies are the first immunoglobulins produced at the beginning of the immune response to the entry of a foreign antigen into the body. Their formation does not require the additional participation of T-helper lymphocytes, which are responsible for switching the synthesis to other classes of immunoglobulins, which allows the body's humoral immune defense mechanisms to be quickly launched.
IgM mainly circulate in the bloodstream and make up 5-10% of all blood immunoglobulins.
IgM is a pentamer - consists of five subunits, each of which has two antigen-binding centers. The half-life of IgM in the body is 5 days. These antibodies bind to antigens, opsonize and enhance their phagocytosis, activate the complement system in the classic way. Due to their large molecular weight, IgM cannot pass through the placenta from the mother to the fetus, so their increased number to a certain antigen indicates intrauterine infection of the fetus. IgM includes isohemagglutinins of blood groups (anti A and anti B), heterophilic antibodies and early rheumatoid factor.
Specific IgM are produced in response to exposure to a specific antigen. They begin to be synthesized upon initial contact with an infectious agent or foreign substance, a few days earlier than the first IgG class antibodies appear. The amount of IgM increases during the first weeks after infection and gradually decreases until it disappears completely. IgMs are replaced by IgGs, which provide long-term protection against infections.
Excessive production of immunoglobulin M can be associated with hyperstimulation of all clones of plasma cells or a separate clone of IgM-producing B-cells. This may accompany an active infectious process or some types of immunoproliferative diseases (for example, myeloma, Waldenström's macroglobulinemia).
IgM deficiency can be primary (congenital), which is rarely observed, or secondary (acquired), caused by various factors that deplete humoral immunity.