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Immunoglobulins of type G (IgG), or type G antibodies, are particularly important as they are the most numerous and persistent antibodies in our body. IgG antibodies protect the body against infections, and errors in their synthesis sometimes result in the formation of antibodies against the body's own tissues. What is the type G immunoglobulin test? What do IgG immunoglobulins below normal and what are elevated?

G-type immunoglobulins (IgG) , also known as G-antibodies, is an immune protein produced by cells of the immune system - plasma cells, which are a type of B lymphocytes. exposure to various chemical molecules (antigens) that the immune system considers foreign.

Antigens can be fragments of bacteria, viruses, fungi, food, pollen, and in some situations the body's own tissues (so-called autoantigens).IgG antibodiesare very specific as they are always directed against a specific antigen and are mainly produced in the later stages of the immune response, replacing the less specific IgM antibodies.

Immunoglobulin type G (IgG) - role in the body

IgG antibodies are produced in the body as one of the last and can thanks to the so-called The immune memory of plasma cells remain in the blood for up to several dozen years. Therefore, they are considered to be the most persistent antibodies.

IgG antibodies are the most abundant type of antibodies in the body, accounting for about 80% of all types of antibodies.

IgG antibodies have the ability to form immune complexes with antigen molecules and activate the complement system, which is a cluster of proteins that initiates inflammation. This process is designed to neutralize the antigen and safely remove it from the body.

Cells of the immune system, incl. macrophages and neutrophils have receptors on their surface that bind to IgG antibody fragments in immune complexes. Thanks to this, they can absorb and break down immune complexes in the process of phagocytosis (it consists in capturing and absorbing microscopic solids by the cell).

IgG antibodies are the only antibodies that cross the placenta. During pregnancy, the womanpasses on to the fetus its IgG antibodies, which remain in the baby for about a year after birth. At the same time, just after giving birth, the baby begins to produce its own IgG antibodies under the influence of environmental antigens.

Type G immunoglobulins (IgG) - types

IgG antibodies have been divided into four subtypes due to the differences in the molecular structure:

  • IgG1 - the most numerous IgG constituting 67 percent all subtypes; IgG1 deficiency usually accompanies a general deficiency of antibodies
  • IgG2 - accounts for 22 percent IgG and has the lowest specificity; the symptom of IgG2 deficiency are recurrent bacterial and viral infections
  • IgG3 - account for 8 percent IgG and activate the complement system the most; a symptom of IgG3 deficiency may be viral infections
  • IgG4 - the smallest subtype of IgG (3%), which protects the body against allergic reactions and is the only one that does not activate the complement system; an increase in IgG4 is observed during allergen immunotherapy (desensitization)

IgG antibodies can also be divided into total and specific. Specific IgG antibodies are produced throughout life after contact with various antigens. The study of specific IgG antibodies is of particular importance in the diagnosis of infectious and autoimmune diseases. All the specific IgG antibodies in the body constitute the pool of total IgG antibodies.

Immunoglobulin type G (IgG) - indications for the test

Indications for testing the level of immunoglobulin G (IgG) are suspicion:

  • genetic inherited immunodeficiencies, e.g. severe combined immunodeficiency (SCID)
  • secondary immunodeficiencies, e.g. AIDS
  • cirrhosis of the liver
  • autoimmune disease, e.g. rheumatoid arthritis, Hashimoto's disease
  • hematological cancers, e.g. multiple myeloma, lymphomas
  • infectious diseases, e.g. Lyme disease, herpes
  • parasitic invasions, e.g. lamblia, ascariasis

Another indication is the diagnosis of serological conflict. In serological conflict, antibodies against the baby's red blood cells are produced and destroyed as IgG antibodies pass through the placenta.

Testing of specific IgG (most often including IgM) can be important information regarding bacterial, viral, fungal infections and parasitic invasions. An example is the diagnosis of Lyme disease, in which the assessment of the level of IgG and IgM antibodies is used. IgG antibodies appear later in the course of the infection and their elevated levels will meanchronic infection.

Tissue-specific IgG testing is a marker of the ongoing autoimmune process. An example is Hashimoto's disease, in which high levels of IgG antibodies to thyroid peroxidase (anti-TPO) are present in over 90% of patients. sick.

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Immunoglobulin type G (IgG) - what is the test?

In laboratory tests, we can assess the concentration of both total and specific IgG antibodies. Both tests can be performed with venous blood and, in special clinical cases, in the cerebrospinal fluid or synovial fluid.

The concentration of specific IgG antibodies is most often determined using enzyme immunoassay methods (eg ELISA test) or immunofluorescence methods. Immunonephelometric and immunoturbidimetric methods are routinely used to determine total IgG antibody levels.

Worth knowing

Immunoglobulin type G (IgG) - norm

The laboratory norm for total IgG is age dependent and is:

  • 1-7 days: 5.83-12.7 g / l
  • 8 days-2 months: 3.36-10.5 g / l
  • 3-5 months: 1.93-5.32 g / l
  • 6-9 months: 1.97-6.71 g / l
  • 10-15 months: 2.19-7.56 g / l
  • 16-24 months: 3.62-12.2 g / l
  • 2-5 years; 4.38-12.3 g / l
  • 5-10 years: 8.53-14.4 g / l
  • 10-14 years: 7.08-14.4 g / l
  • 14-18 years: 7.06-14.4 g / l
  • over 18 years old: 6.62-15.8 g / l

Immunoglobulin type G (IgG) - results. What does elevated level mean?

Too low IgG level can be caused by:

  • extensive burns
  • diseases of the digestive tract, e.g. celiac disease
  • kidney diseases, e.g. nephrotic syndrome
  • cancer, e.g. leukemia
  • drugs, e.g. antimalarials, cytostatic drugs, glucocorticosteroids
  • infections, e.g. HIV, sepsis
  • malnutrition
  • diabetes complications

Increased IgG levels can also be caused by

  • inflammation
  • chronic infections
  • autoimmune diseases, e.g. multiple sclerosis
  • hematological diseases, e.g. lymphomas, multiple myeloma
  • liver diseases, e.g. cirrhosis

Immunoglobulin type G (IgG) - results. What does the reduced level mean?

Deficiency of individual IgG subtypes can also be diagnosed. Deficiencies of particular IgG subtypes are often asymptomatic or may predispose tomore frequent bacterial infections, making them difficult to recognize. It is estimated that about 20 percent. of the population may be deficient in one IgG subtype. IgG2 deficiency is most common in children and IgG3 deficiency in adults.

Immunoglobulin type G (IgG) - diagnostic tests using IgG antibodies

IgG antibodies are commonly used for 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 one 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 IgG antibodies can be modified by attaching enzymes, radioisotopes or fluorescent dyes to them. The methods using IgG antibodies are:

  • ELISA
  • RIA
  • Westernblot
  • flow cytometry
  • immunohistochemistry
  • protein microarray

Immunoglobulin type G (IgG) - the use of IgG antibodies in the treatment

Monoclonal antibodies can also be used to treat various diseases by:

  • killing cancer 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 responses in autoimmune diseases, e.g. Adalimumab (IgG against tumor necrosis factor alpha)

References

  1. Vidarsson G. et al. IgG Subclasses and Allotypes: From Structure to Effector Functions. Front Immunol. 2014, 5, 520.
  2. Agarwal S. and Cunningham-Rundles C. Assessment and clinical interpretation of reduced IgG values. Ann Allergy Asthma Immunol. 2007, 99 (3), 281-283.
  3. Ewa Bernatowska et al. Developmental age immunomodulation in primary care practice - facts and myths. Pediatrics after the Diploma 2013, 17, 1.
  4. Paul W.E. Fundamental immunology, Philadelphia: Wolters Kluwer / Lippincott Williams & Wilkin 2008, 6th edition.
  5. 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
  6. 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