Immunoglobulins (antibodies) are the most important proteins in the specific immune response, and their task is to protect the body against threats, among others. from microorganisms. Deficiency or excess of antibodies can be a sign of various pathologies, therefore their determination in blood is an important element in the diagnosis of many diseases. Moreover, the progress of biomedical sciences made it possible to use synthetic antibodies in the treatment of certain diseases.

Immunoglobulins , also known asantibodies , or gamma globulins, are immune proteins produced by cells of the immune system - plasma cells, which are a type of B lymphocytes.

Antibodies are present in the body fluids of all vertebrates and are produced by contact with chemical particles (antigens), e.g. bacteria, viruses, and in some cases even by contact with your own tissues (so-called autoantigens).

Antibodies are part of the humoral immune response and act very specifically, as they are always directed against a specific antigen.

The name "humoral" comes from the humoral theory that was common in medicine in ancient times and assumed the presence of body fluids (humors) in the human body. Although this theory has long been disproved, some of its formulations are still used in medical terminology.

The humoral immune response consists of B lymphocytes (including plasma cells) and the antibodies they produce. The humoral expression alludes to the fact that the elements of the immune system that include it are found in body fluids (humors) such as lymph or plasma.

Immunoglobulins (antibodies) - types and structures

Antibodies have the shape of the letter "Y" and consist of two pairs of protein chains - light and heavy, which are linked together by disulfide bonds. Based on the differences in the structure of heavy chains, several classes (types) of antibodies have been distinguished:

  • immunoglobulin type A (IgA) - (alpha heavy chain) is an antibody that is secreted mainly through the mucous membranes, e.g. intestines, respiratory tract, and secretions e.g. saliva, providing local humoral immunity
  • immunoglobulin type D (IgD) - (heavy chain delta) is the least known antibody and accounts for up to 1 percent.all antibodies in the blood
  • immunoglobulin type E (IgE) - (epsilon heavy chain) is only 0.002 percent. all antibodies in the blood and has the unique property of activating mast cells and basophils, leading to their release, among others. histamines
  • immunoglobulins of type G (IgG) - (gamma heavy chain) are the most numerous (80% of all antibodies) and the most persistent antibodies in the body, as they can remain in the blood even several decades after contact with the antigen
  • type M immunoglobulins (IgM) - (mi heavy chain) are produced first in the course of the immune response, are less persistent and are gradually replaced by IgG antibodies

Most antibodies (IgG, IgD, IgE) exist as a single "Y" molecule (monomer). The exception is the IgA antibody, which is in the double form (dimer) and the IgM antibody, which forms the shape of the so-called snowflake (pentamer).

Antibodies in the light and heavy chain region have a variable region, which is a specific amino acid sequence that matches almost perfectly with that on the antigen. This region is called the paratope and is responsible for the specific antigen binding specificity of each antibody.

Consequently, each antibody fits the antigen like a key and a lock, and by combining with each other they form the so-called immune complex. However, it should be remembered that antibodies nevertheless show flexibility to bind to different antigens, which means that they can be matched to different antigens, which can result in cross-reactions. This phenomenon is seen very often in allergies.

  • CROSS ALLERGY - symptoms. Cross-allergen table

Immunoglobulins (antibodies) - role in the body

The role of all antibodies in the body is to participate in immune responses. Antibodies are able to form immune complexes with antigen molecules and activate the complement system and inflammation. This is to neutralize the antigen and remove it safely from the body.

Due to their diverse biochemical properties, different classes of antibodies can perform specialized functions:

  • neutralize parasites (IgE)
  • neutralize microorganisms (IgM, IgG)
  • protect against falling ill, e.g. mumps (IgG)
  • protect mucous membranes with microorganisms and allergens (IgA)
  • participate in the maturation and development of lymphocytes (IgD)
  • confer immunity to the fetus (IgG) and the newborn (IgA)

Immunoglobulins(antibodies) - immune memory

There is a primary and a secondary response in the immune response.Primary immune responsedevelops the first time it comes into contact with an antigen, then the body produces mainly IgM antibodies, which are gradually replaced by more specific and more persistent IgG antibodies, andsecondary response immunologicalis formed on repeated contact with the same antigen. It is more intense than the primary response, and the antibody concentration reaches higher levels than in the primary response. immune memory and the presence of memory B lymphocytes. Such cells live in the body for years and when they come into contact with the antigen again, they begin to divide very intensively and produce specific antibodies.

Immunoglobulins (antibodies) - antigenic variability of antibodies

One of the most fascinating phenomena in the field of antibodies is the process of their formation and the enormous variety they are able to achieve, since the number of antibody combinations is estimated at up to a trillion. The secret lies in the structure of the genes encoding antibodies and the processes of recombination of antibody genes and their hypermutation.

These processes can be referred to as the controlled introduction of mutations into the genome for the sake of trial and error matching of the appropriate antibodies. Although it does not sound too complicated, it is actually a very complex process that requires extreme precision and in case of mistakes it can even lead to the formation of neoplasms.

Immunoglobulins (antibodies) - vaccines

Antibodies play a key role in the development of immunity after vaccination. When it comes into contact with the antigen contained in the vaccine, the cells of the immune system produce antibodies.

First, less persistent and specific IgM, then persistent and persistent for years in the blood IgG. For example, during vaccination against hepatitis B virus (HBV), three doses of the vaccine are given at intervals to induce sustained immunity. The measure of the effectiveness of such a vaccination is the measurement of the level of IgG antibodies against the virus antigens in the blood.

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Immunoglobulins (antibodies) - serological conflict

One of the most important tests in pregnant women is the assessment of the presence and monitoring of antibodies against antigens of fetal red blood cells. In serological conflict, such antibodies can cross the placenta to the fetus and destroy its red blood cells, causing haemolytic disease. This happens when the mother has Rh (-) blood type and the fetus is Rh (+).

Immunoglobulins (antibodies) - tests

Antibodies make up 12-18% of serum proteins. In order to assess the amount of individual protein fractions, including antibodies, a proteinogram is performed. This test is based on electrophoresis of serum proteins, i.e. their separation in an electric field.

Antibody testing is performed from venous blood (IgM, IgG, IgE, IgA) or saliva and feces (IgA). In selected clinical situations, an examination of a different material, e.g. cerebrospinal fluid, can be performed.

Total IgG, IgM, IgA, and antibody light chain concentrations are routinely determined by immunonephelometric and immunoturbidimetric methods. In contrast, the total concentration of IgE antibodies is most often tested using immunochemiluminescent methods.

Immunoturbidimetric and immunonephelometric methods use the ability to cloud solutions and scatter light by forming antigen-antibody complexes. The immunonephelometric method measures the intensity of light scattered by the test solution, and the immunoturbidimetric method measures the intensity of light passing through the test solution. These methods are used, among others. for determining the total concentration of different classes of antibodies.

Pathological forms of antibodies can also be marked in the laboratory. An example is a monoclonal antibody (M protein), which is an incomplete antibody (e.g., lacking a heavy or light chain fragment) found in monoclonal gammapathies or lymphomas. Another example is the Bence-Jones protein found in the urine of people with multiple myeloma.

Worth knowing

Immunoglobulins (antibodies) - norms

The norms for total blood antibody levels are age dependent and for adults are:

  • IgG - 6.62-15.8 g / l
  • IgM - 0.53-3.44 g / l
  • IgA - 0.52-3.44 g / l
  • IgE - up to 0.0003 g / l
  • IgD - up to 0.03 g / l

Immunoglobulins (antibodies) - results and their interpretation

Many clinical situations may result in an increase in antibody levels (hypergammaglobulinemia) or a decrease in antibodies (hypogammaglobulinemia).

Increase or decreaseit can apply to the total amount of antibodies as well as to selected classes only. Also of clinical significance is the determination of the presence of specific antibodies directed against specific microorganisms or one's own tissues.

Immunoglobulin (antibodies) - what does elevated antibody level mean?

Polyclonal hypergammaglobulinemia results from the overproduction of many classes of antibodies by various plasma cells and may result from:

  • acute and chronic inflammation
  • parasitic, bacterial, viral or fungal diseases
  • autoimmune diseases
  • cirrhosis of the liver
  • sarcoidosis
  • AIDS

Immunoglobulin (antibodies) - which means low antibody level?

Monoclonal hypergammaglobulinemia results from the excessive production of antibodies by one clone of the cancer cell and may result from:

  • multiple myeloma
  • Unknown Cause Gammapatii (MGUS)
  • lymphoma
  • Walderström's macroglobulinemia

Hypogammaglobulinemia can be caused by:

  • genetic inherited immunodeficiencies, e.g. severe combined immunodeficiency (SCID)
  • drugs, e.g. antimalarials, cytostatic drugs, glucocorticosteroids
  • malnutrition
  • infections e.g. HIV, EBV
  • cancer e.g. leukemias, lymphomas
  • nephrotic syndrome
  • extensive burns
  • severe diarrhea

Immunoglobulins (antibodies) - application in laboratory diagnostics

Antibodies (mainly IgG) are commonly used in laboratory research. Such antibodies are obtained under laboratory conditions and are called monoclonal antibodies. They come from a single cell clone and are directed against a specific antigen.

The basic method of producing monoclonal antibodies uses laboratory mice and cell cultures. It is a combination of two types of cells: cancer cells (myeloma) and B lymphocytes that produce specific antibodies.

Then the monoclonal antibodies can be modified by attaching enzymes, radioisotopes and fluorescent dyes to them. Antibody methods use the ability to specifically bind to an antigen.

  • ELISA method

ELISA (enzyme-linked immunosorbent assay) is one of the most frequently used methods in diagnostic and scientific research. The ELISA method uses monoclonal antibodies that are linked to the enzyme. For herwith the aid, it is possible to quantify various antigens in biological material. The advantage of the ELISA method is its simplicity and high sensitivity. The ELISA method is performed using special plastic plates with wells filled with e.g. Borrelia antigens and specific monoclonal antibodies, which are designed to detect antibodies in a patient sample.

  • RIA method

The radioimmunoassay (RIA) method consists in detecting antigens with the use of antibodies labeled with radioactive isotopes, eg with 14C carbon. However, due to the safety of work with radioactive substances, the ELISA method is more often used.

  • Westernblot method

The Westernblot method consists in separating the tested antigen in an electric field and then transferring it to a special membrane. Specific antibodies labeled with a dye or an enzyme are then applied to the antigen membrane. The Westernblot method allows for a very specific detection of antigens, which is why it is used in tests that confirm inconclusive results, e.g. in the serological diagnosis of Lyme disease.

  • Flow cytometry

The method consists in detecting specific markers on the surface of cells (immunophenotyping). Fluorescently labeled monoclonal antibodies specific for a particular surface marker on the cell are used in cytometry. The labeled cells are then detected with a detector. Flow cytometry is used e.g. in the CD57 test.

  • Immunohistochemistry

Thanks to immunohistochemical methods, it is possible to detect antigens in tissue fragments using labeled antibodies, which are then observed under a microscope.

  • Protein microarray

Protein microarray is a modern method, the principle of which is similar to the ELISA method. Thanks to miniaturization and the possibility of one-time detection of up to several hundred different proteins, it has found application in scientific research and allergology.

Immunoglobulins (antibodies) - use in therapy

Monoclonal antibodies can also be used in the treatment of certain diseases. They were first used in 1981 in the treatment of lymphoma. Monoclonal antibodies are used in:

  • killing tumor cells e.g. Ofatumumab (IgG against the CD20 marker)
  • inhibition of selected cells of the immune system in transplantation, e.g. Muronomab (IgG against the CD3 marker)
  • inhibition of immune reactions in autoimmune diseases, e.g. Adalimumab (IgG against the necrosis factorcancer alpha)

Bibliography:

  1. Pietrucha B. Selected issues in clinical immunology - antibody deficiencies and cellular deficiencies (part I) Pediatr Pol, 2011, 86 (5), 548-558.
  2. Paul W.E. Fundamental immunology, Philadelphia: Wolters Kluwer / Lippincott Williams & Wilkin 2008, 6th edition.
  3. Laboratory diagnostics with elements of clinical biochemistry, a textbook for medical students edited by Dembińska-Kieć A. and Naskalski J.W., Elsevier Urban & Partner Wydawnictwo Wrocław 2009, 3rd edition
  4. Internal diseases, edited by Szczeklik A., Medycyna Praktyczna Kraków 2010
About the authorKarolina Karabin, MD, PhD, molecular biologist, laboratory diagnostician, Cambridge Diagnostics Polska A biologist by profession, specializing in microbiology, and a laboratory diagnostician with over 10 years of experience in laboratory work. A graduate of the College of Molecular Medicine and a member of the Polish Society of Human Genetics. Head of research grants at the Laboratory of Molecular Diagnostics at the Department of Hematology, Oncology and Internal Diseases of the Medical University of Warsaw. She defended the title of doctor of medical sciences in the field of medical biology at the 1st Faculty of Medicine of the Medical University of Warsaw. Author of many scientific and popular science works in the field of laboratory diagnostics, molecular biology and nutrition. On a daily basis, as a specialist in the field of laboratory diagnostics, he runs the content department at Cambridge Diagnostics Polska and cooperates with a team of nutritionists at the CD Dietary Clinic. He shares his practical knowledge on diagnostics and diet therapy of diseases with specialists at conferences, training sessions, and in magazines and websites. She is particularly interested in the influence of modern lifestyle on molecular processes in the body.

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Immune system