Features of B-lymphocytes as an element of the immune system, the reasons for the increase and decrease of this indicator

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2017.08.07
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Leukocytes

Blood consists of uniform elements that support homeostasis. Lymphocytes provide uninterrupted protection of the body against harmful microorganisms and viruses.

Electron microscope view

Attention! The lymphocyte counts are analyzed in a general clinical blood test. Any abnormalities testify to the pathology of various organs. The detection of an increased or decreased number of lymphocytes allows to diagnose diseases at an early stage.

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Content

  • What is B-lymphocytes, and where are they formed?
  • Primary immune response
  • Secondary immune response
  • Functions and properties
  • Normal values ​​of B-lymphocytes in a blood test
  • Why does the content of B-lymphocytes in the blood increase?

What is B-lymphocytes, and where are they formed?

B-lymphocytes (B-cells) are an important component of humoral immunity. They form in the bone marrow and migrate to the spleen or secondary lymphoid tissues. There they mature and differentiate into immunocompetent B cells. B cells are responsible for the generation of antibodies to specific antigens to which they bind via B-cell receptors (SRS).

Activation occurs through the recognition of antigen by stimulated stimulation. This leads to stimulation of the proliferation of B cells and the formation of germinal centers, where they differentiate into plasma cells or memory B-lymphocytes. All B cells derived from a specific precursor represent clones that recognize one antigen. Plasma cells are found in the spleen and lymph nodes and are responsible for the secretion of different classes of unique antibodies.

B-lymphocytes were discovered indirectly due to the detection of specific proteins - antibodies. Identification of serum gammaglobulin as a source of antibodies was the starting point for the detection of B cells. Plasma cells were proposed as sources of antibody synthesis in 1948. Two competing views on the formation of antibodies, the theory of "natural selection" and "cloning" were proposed by 2 giants of immunology of the 20th century: Niels Jerne and McFarlan Vernet. Both scientists subsequently received the Nobel Prize in Physiology or Medicine.

After that, the first experimental data confirming the theory of "cloning" were obtained by studying individual cells. The chemical structure of the antibody molecule was discovered by Gerald Edelman and Rodney Porter, who in 1972 received a Nobel Prize in Physiology or Medicine for this.

Primary immune response

The immune response is possible due to the synthesis of special protein compounds (antibodies) that react to "foreign" peptides - antigens. Detection of foreign components in the blood is not based on the principle of "harmful or not harmful but with the help of special receptors located on the surface of B cells. Upon contact with the antigen, they emit a huge amount of immunoglobulins.

Three types of mature particles are known:

  1. Non-activated B cells that never interacted with the antigen. React weakly to the appearance of a pathogenic microorganism. Immature cells settle in the spleen, and mature cells in the lymph nodes.
  2. B-cells of memory are long-lived immunocompetent particles of the human body. Provide a quick immune response that does not show symptoms. When the antigen is recognized, memory B cells produce a huge amount of immunoglobulins.
  3. Plasma cells are the last stage of development of B cells. A sufficient number of antibodies are located on the cell membranes. However, live plasma cells are small - 3-4 days. Plasmocytes located in the bone marrow can live for several years.

Secondary immune response

After elimination of the foreign body or pathogenic microorganism, most B-lymphocytes return to the lymphoid tissues. They can remain dormant for a long time and be activated in response to the re-emergence of antigen (virus, bacteria or fungus). Memory cells are capable of proliferating, constantly increasing the population size. Therefore, when a foreign body enters, they quickly mobilize and destroy the pathogen.

Immunoglobulins

This type of immune response is called humoral immunity. It differs from the primary immune response in that it provides a quick and intense reaction to a known antigen. A greater number of B-cells are produced and an alien microorganism is effectively eliminated.

There are two subpopulations of B-lymphocytes: B1 and B2. The difference in subpopulations is that each of them synthesizes only specific types of antibodies:

  1. Antibodies that are designed to fight "new" antigens. Such immunoglobulins are denoted by the Latin letter M. B1-lymphocytes are located in places where microorganisms can penetrate most easily if damaged.
  2. This type of antibody is aimed at fighting with known pathogenic microorganisms or foreign particles. Recognized in immunoglobulin G assays. Activation occurs when the pathogen penetrates the human body.

Functions and properties

B cells perform important functions in the human immune system:

  • Identify pathogens.
  • Preserve the homeostasis of autoimmune processes.
  • Metabolize dead cell particles or catabolism products.
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Important! All functions of B-lymphocytes depend on the antibodies they synthesize. At present five types of immunoglobulins are known: E, D, G, A and M.

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Immunoglobulins G (IgG) constitute the majority of immunoglobulins that are produced by mature B cells. These immunoglobulins provide long-term humoral immunity to infectious agents. They participate in the neutralization of toxins of various etiologies, provide passive immunity of the newborn and stimulate the processes of phagocytosis.

IgG are contained in the bloodstream and beyond, where the protective function is performed.

Immunoglobulins M are synthesized in response to a new infectious agent, providing a primary immune response. This is the most ancient class of antibodies, which is synthesized by plasmocytes.

Antibodies A (IgA) provide a local humoral response. Contained in the gastrointestinal tract, in breast milk, mucous membranes, urine, bile. IgA binds to the surface of pathogenic microorganisms and prevents their further spread.

Immunoglobulins E are contained in the blood in a small amount. Their numbers increase with the advent of allergies or parasite infestation.

Penetration of a foreign microorganism (antigen) causes the body to synthesize antibodies of various types. After the detection of the antigen, the enhanced production of the corresponding immunoglobulins begins. After a while, a certain class of antibodies in the blood begins to predominate over others. A certain type of B-cell synthesizes one class of antibodies. This provides an effective immune response and allows the creation of multibillion-cloned cells. Several hundred thousand antibodies of a particular type can be located on the B-cell membrane. Such a number allows the identification of the "enemy" with high accuracy.

Normal values ​​of B-lymphocytes in a blood test

Depending on age and sex, the absolute or relative amount of B-lymphocytes may differ. Lymphocytes in the blood of women are greater than in men. Women must provide the offspring with "strong" immunity, so this trend is observed. Limits of the absolute content of B cells in the blood in adults are 1000-4800 cells per microliter. In children, the number of them is more - 2000-11000 units. on μl.

Why does the content of B-lymphocytes in the blood increase?

They have on the membrane a CD19 protein compound, which is the earliest marker of this type of lymphocyte. The protein ensures the differentiation, development and activation of B-lymphocytes.

Common causes of increased CD19:

  • The initial period of HIV infection.
  • Autoimmune diseases.
  • Chronic leukemia.
  • Infectious mononucleosis.
  • Bacterial, fungal and parasitic pathogens in the acute stage.
  • Diseases of the liver of various etiologies (viral, idiopathic).
  • Re-infection with a specific type of infection.

Increased content indicates the presence of a strong infection in the human body. Occasionally such a condition appears due to oncological diseases. The indicator of B-lymphocytes is a sign of a pathological condition, and not an independent disorder. To find out the reason that caused the increase in B-cells, you need to contact your doctor.

Often, the number of B cells is reduced due to pathological processes, which can worsen the patient's well-being and lead to complications of different etiologies. If the indicator is lowered, this indicates that the following conditions exist:

  • Benign or malignant neoplasms of the immune system.
  • Splenectomy.
  • Insufficiency of the humoral immune system.
  • Hereditary diseases affecting the bone marrow.
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Advice! The reason for the reduced number of B cells is the use of cytostatic and immunosuppressive drugs. When receiving anesthetics before the invasive intervention, the number of B-lymphocytes decreases. Before taking medication, always consult a doctor.

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