Immunoglobulin G (IgG, serum)
Why this test?
- To assess local humoral immunity.
- For diagnosis of immunodeficiency states.
- To diagnose the causes of relapses of bacterial, viral, fungal and parasitic infections.
- For diagnosing the state of the immune system in autoimmune pathologies, blood diseases and neoplasms.
In what cases is it prescribed?
- When examining children and adults prone to frequent recurrent respiratory, intestinal and / or urogenital infections.
- When monitoring the treatment of IgG-type myeloma.
- When examining patients with autoimmune pathology.
- In a comprehensive study of the state of the immune system.
- In neoplasms of hematopoietic and lymphoid tissues.
- When monitoring patients with immunodeficiencies.
- Before, during and after the use of immunoglobulin preparations.
Immunoglobulins are glycoproteins that play an important role in the body's immune system.
There are 5 classes of antibodies (IgA, IgG, IgM, IgE, IgD), which differ in their structure and functions 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.
The immune system is able to "remember" the antigen with which it was previously in contact, and quickly react to its re-entry into the body, producing a greater number of immunoglobulins, which prevents reinfection and the repeated development of the disease.
The main immunoglobulins that provide long-term humoral protection against re-infection are class G immunoglobulins. IgG makes up 70-80% of all blood immunoglobulins. Their half-life in the body is 21-24 days. They neutralize toxins, viruses, opsonizing antigens, enhancing their phagocytosis, and activate the complement system in the classic way. This class of antibodies is able to penetrate into the extravascular space and perform a protective function in tissues.
IgG is the only type of immunoglobulin that penetrates through the placenta from the mother to the fetus and protects the child during the first 4-6 months of life from infectious agents with which the mother was previously in contact.
Specific IgG 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, but later than IgM antibodies. Then, the amount of IgG gradually increases during several weeks after the onset of infection and then decreases to a level that normally remains in the blood for many years.
Repeated exposure to the antigen causes rapid production of a large amount of IgG, which prevents new infection. This feature of the work of the immune system is taken as a basis for vaccination using antigens of various microorganisms.
There are several subclasses of IgG: IgG-1, IgG-2, IgG-3, IgG-4. A decrease in the level of certain subclasses is the cause of recurrent infections.
At the same time, the deficiency is sometimes so difficult to detect, since the total IgG index can be within the reference values. Deficiency or hyperproduction of total IgG can be isolated or combined with a change in the level of other classes of immunoglobulins.
For example, insufficient levels of IgG-2 and IgG-4 often accompany IgA deficiency.
Excessive production of immunoglobulin G can be associated with hyperstimulation of all clones of plasma cells or a separate clone of IgG-producing B-cells. This, in turn, may be associated with an active infectious process or some types of immunoproliferative diseases (for example, myeloma).
IgG deficiency can be primary (congenital), which is rarely observed, or secondary (acquired), caused by various factors that deplete humoral immunity.
In severe immunodeficiencies with low or no IgG, parenteral administration of immunoglobulin preparations may be required.