Antibody tests - what are they?
The content of the article:
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Analyzes depending on the types of antibodies
- Antibodies to viral and bacterial infections
- Antibodies to allergens
- Antibodies to parasite antigens
- Antibodies to sexually transmitted infections
- Antibodies to thyroid proteins
- Autoantibodies
- Antibodies to Rh factor
- Antisperm antibodies
- How is the test for antibodies
- Antibodies and their functions
An antibody test not only determines the level of antibodies in the blood, but also establishes their type, allowing you to identify a specific infection and the approximate time of infection.
Antibodies (immunoglobulins) are protein compounds that are produced by the body's immune system in response to the appearance of antigens (animal bacteria, viruses, toxic substances, etc.). Antibodies are formed with the participation of B-lymphocytes. Their production begins when the antigen of one or another pathogen enters the bloodstream. The body remembers antigens and when they re-enter the body, it is easier to cope with the disease. It is on this ability of the body that the principle of action of vaccines is based: to produce certain antibodies in an amount sufficient to form immunity, a person is injected with a certain amount of antigen, which provokes the production of antibodies to it.
Analyzes depending on the types of antibodies
For a detailed diagnosis, an analysis is performed for each specific type of antibody.
Antibodies are specific proteins produced by the body's immune system in response to the ingress of antigens, infectious and not only
Antibodies to viral and bacterial infections
By testing the level of IgM and IgG in the blood, the presence of most infections can be determined. So, specific IgM antibodies to measles can be detected already by the second day of the onset of the rash, antibodies to chickenpox (chickenpox) begin to be produced within 4-5 days from the onset of the rash, IgM immunoglobulins to poliomyelitis are formed in the blood after 7 days from the moment of infection, and rubella antibodies appear 3-4 weeks after infection.
For the diagnosis of hepatitis, both the direct isolation of the virus in the blood and the determination of indirect signs of its presence in the body are used: anti-HAV IgM - antibodies to the hepatitis A virus, the presence of the HbsAg antigen in the blood is a marker of hepatitis B, the markers of hepatitis C are total antibodies to the virus HCV.
IgG persists after infectious diseases for life, and by their presence in the blood, one can judge the resistance to these diseases.
Antibodies to allergens
Antibodies of class E serve as a marker of allergic reactions. Analysis for lgE reveals a hereditary predisposition to allergies and assess the risk of its occurrence.
Antibodies to parasite antigens
An additional diagnostic method that allows you to determine the presence of antibodies to lamblia, ascaris, toxoplasma, Trichomonas, causative agents of opisthorchiasis, etc.
Antibodies to sexually transmitted infections
The enzyme immunoassay allows you to diagnose genital infections (syphilis, toxoplasma, mycoplasma, ureaplasma, etc.) by detecting antigens to them. So, the determination of antibodies is included in the complex of treponemal tests, at the beginning of the onset of clinical symptoms, most patients with syphilis have IgM and IgG antibodies to treponema pale in their blood.
Antibodies to thyroid proteins
In clinical practice, antibodies to thyroperoxidase (antibodies to TPO), to thyroglobulin (antibodies to TG) and to TSH (antibodies to the TSH receptor) are determined. The thyroid antibody test is used as a complementary test in the diagnosis of inflammatory autoimmune thyroid diseases.
Autoantibodies
Serves as an indicator of most autoimmune diseases. They are called autoantibodies, as they are produced against healthy tissues of their own body, for example, against components of cell membranes. The determination of autoantibodies usually includes tests for antibodies to phospholipids and antinuclear antibodies.
Antibodies to Rh factor
The Rh test is performed during pregnancy in women with a negative Rh factor. If the level of antibodies in the blood is increased, it means that the mother's body perceives the child's cells as foreign.
Antisperm antibodies
In the diagnosis of immunological causes of infertility, which can be detected in men and women, an analysis of antisperm antibodies is used. In immunological infertility, the immune system identifies the sperm cells as hostile cells and neutralizes them, which excludes conception.
How is the test for antibodies
The study requires blood from a vein. There should be at least four hours between the last meal and the blood draw. On the eve of the test, it is recommended to exclude physical activity, smoking, alcohol, fatty and fried foods, carbonated drinks. You can drink water.
As a rule, antibodies are determined by the enzyme-linked immunosorbent assay (ELISA), an ultrasensitive test based on an antigen-antibody reaction.
In the laboratory, blood serum is examined on an automatic analyzer using a labeled reagent (conjugate). A small amount of blood serum and purified antigens of the suspected pathogen are introduced into the well of a special microplate. The interaction between them leads to the formation of an immune complex, in which the active center of the immunoglobulin affects a specific site of the antigen.
After that, an appropriate reagent is added, which, by specifically binding to antibodies, stains the immune complex. The intensity of its color is proportional to the amount of antibodies detected.
The analysis results are deciphered by a specialist in combination with information obtained using other diagnostic methods.
The study of antibodies is carried out using the ELISA method - enzyme immunoassay
Antibodies and their functions
Five classes of immunoglobulins are distinguished depending on the biological and physicochemical properties:
- antibodies of class G (IgG) provide long-term and persistent immunity to infections, activate phagocytosis and provide a basic immune response. They are highly active, can penetrate the placenta into the fetus and form passive immunity in newborns. IgG begin to be produced several weeks after infection and remain active for a long time;
- antibodies of class M (IgM) are produced first in response to infection, then decrease to an insignificant level within several months. They stimulate various links of immunity, participate in the activation of complement, agglutinate gram-negative bacteria and viruses, enhance the processes of destroying antigens;
- antibodies of class A (IgA) are contained mainly in the secretion of the mucous membrane and provide its protection against viruses. Immunoglobulins of the IgA class are not capable of agglutination and precipitation of antigens, do not activate complement. Their main task is to neutralize viruses and bacterial poisons. IgA appears in the blood 1-2 weeks after the onset of the disease and disappears after 2-3 months;
- antibodies of class E (lgE) are produced in response to allergens;
- antibodies of class D (lgD) and are contained in blood serum in small amounts and have no diagnostic value.
The main functions of antibodies:
- recognition - the ability to identify a variety of antigens and bind exactly to the one that stimulated their synthesis;
- opsonization - attachment to the outer walls of bacteria, changes in their physical and chemical structure;
- agglutination - adhesion of cells carrying antigens. As a result, particles are formed that precipitate in the form of flakes. Then these conglomerates are attacked by phagocytes;
- fixation - antibodies attach to a foreign cell, activating the complement system, causing cell lysis or starting the process of inflammation;
- neutralization - antibodies block parts of the surface of viruses and toxins, preventing them from moving to the places of their optimal existence;
- sedimentation - the adhesion of soluble antigens, which then precipitate in the form of lumps (precipitation phenomenon) and are attacked by phagocytic cells. In contrast to the agglutination reaction, soluble (molecular) compounds serve as antigen for the precipitation reaction.
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Anna Kozlova Medical journalist About the author
Education: Rostov State Medical University, specialty "General Medicine".
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