B lymphocytes are cells of the human immune system, belonging to the so-called white blood cells (leukocytes). The main task of B lymphocytes is to protect our body against infectious agents through the production of protective antibodies. B lymphocytes are also able to transform into immune memory cells, thanks to which they trigger a quick and effective defense reaction during repeated contact with the pathogen. Find out where B lymphocytes are formed, how does their maturation process and how they perform their immune functions? What is the normal concentration of B cells in the blood?

Mechanisms of the human immune system

The defense mechanisms of the human immune system can be divided into two main groups: innate and acquired. Innate immunity is the first line of defense against pathogens - this is how we respond to any infectious agent that tries to attack us.

Cells of innate immunity are primarily concerned with the production of inflammation, the task of which is to remove the cause of the threat. The characteristic symptoms of inflammation include an increase in temperature, a local increase in blood flow, swelling and pain. Other early immune response mechanisms are also:

  • tight connections between the cells of the epidermis and mucous membranes, preventing the penetration of microorganisms
  • natural defenses such as coughing, tearing, sneezing and diarrhea in the event of a gastrointestinal infection
  • presence of bactericidal substances on the surface of the skin
  • secretion of hydrochloric acid by the parietal cells of the stomach
  • permanent colonization of the skin surface and mucous membranes by natural microflora

The innate immune response is very important in the early stages of the body's defense against pathogens. Unfortunately, in many cases it remains insufficient. Then our immune system reaches for the second line of defense - acquired immunity.

The acquired immunity mechanisms are much more effective in fighting infection. The secret of their effectiveness lies in generating a specific response, i.e. individually tailored to each type of pathogen. Cells that produce such "tailor-made"defense, there are lymphocytes.

Lymphocytes have the ability to accurately recognize an infectious agent, select the most effective anti-infective response, and "save" it in the immune memory. This makes the repeated response to the same pathogen even faster and more effective.

Learning about the phenomenon of immunological memory made it possible to invent one of the most effective methods of protection against infectious diseases - preventive vaccinations.

B lymphocytes - the process of formation and maturation

Human lymphocytes can be divided into two groups, differing in maturation process and function. We distinguish among them:

  • T cells
  • B cells

T cells that mature in the thymus are the main cells of the so-called responsescellular immune . The mechanisms of cellular immunity mainly deal with the fight against those pathogens that can penetrate human cells (e.g. viruses).

B lymphocytes participate in the second type of specific response - the so-calledhumoral immunity . Their task is to produce antibodies that enable the destruction of extracellular pathogens (e.g. most bacteria).

The place where B cells are formed is in the bone marrow. Young B lymphocytes learn there to correctly distinguish between their own and foreign structures. For a B cell to be released from the bone marrow into the bloodstream, it must be able to detect pathogens and also tolerate the body's own cells. Otherwise, autoimmune diseases can occur, i.e. those in which the immune system attacks its own tissues as a result of recognizing them as foreign.

After exiting the bone marrow, B cells travel to the peripheral lymphoid organs. These include the spleen and lymph nodes. At these sites, B cells constantly encounter foreign antigens ("tags" that make them recognize microbes).

Recognition of such a marker leads to the activation of B lymphocytes. Then they begin to multiply, which is manifested by enlargement of the lymph nodes during infection. In order for the B lymphocyte to fulfill its target function, i.e. to produce antibodies specific to a given pathogen, it must pass to the last stage of maturation.

During final differentiation, the B lymphocyte can transform into 2 types of cells:

  • plasmocyte (plasma cell), whose task is to produce a large amount of antibodies (immunoglobulins)
  • memory B lymphocyte, i.e. a cell that stores information about a given type of pathogen. Memory B lymphocyte during revisionAfter contact with this microorganism, it quickly transforms into a plasmocyte, producing antibodies specifically directed against it.

Activity and functions of B lymphocytes

Now that we know how B lymphocytes mature to perform their functions, let's take a closer look at their activities in the body. The most important functions of B lymphocytes include:

  • antigen presentation

B lymphocytes not only carry out their own defense activities (by producing antibodies), but also help other cells of the immune system to recognize foreign microbes. This feature is called antigen presentation (antigen="tag" of the microorganism).

When a B lymphocyte recognizes an "intruder", it attaches a fragment of it to its surface and shows it to other immune cells, signaling the need to destroy it. Thanks to this, it is possible to activate multidirectional defense mechanisms.

  • cytokine production

Cytokines are small protein molecules that carry signals about pathogen invasion. A sudden increase in cytokine production sets an "alarm" for the immune system and leads to the activation of its cells. The production of certain types of cytokines enables the switching of the immune response to the one most needed in a given situation (e.g. antibacterial, antiviral or antiparasitic).

  • production of antibodies (immunoglobulins)

Antibody production is a unique feature of mature B lymphocytes. An antibody is a type of protein specially adapted to a given pathogen for the purpose of neutralizing it. An infectious agent (bacteria, virus or extracellular parasite) is no longer dangerous when combined with the antibody. It also becomes an easy target for cells of the immune system (e.g., food cells), which can then recognize it and neutralize it.

B lymphocytes can produce 5 classes of immunoglobulins:

  • IgM - these are antibodies formed in the earliest phase of B lymphocyte response. Although they are formed very quickly, they are not very specific. The presence of IgM antibodies in the blood indicates a recent exposure to the organism.
  • IgA - is a type of antibodies that play important roles in places of direct contact with pathogens. IgA immunoglobulins are secreted onto the surface of the mucous membranes in the digestive system, respiratory tract and the genitourinary system.
  • IgE - these are the main antibodies involved in allergic reactions. The presence of IgE antibodies in the blood against specific allergens can cause symptoms of allergic rhinitis,allergic conjunctivitis or bronchial asthma upon contact with this allergen. IgE antibodies are also the main antibodies responsible for fighting parasites.
  • IgD - this is the least known class of antibodies, constantly present on the surface of B lymphocytes.
  • IgG - these are the most effective antibodies. They arise in the most mature humoral response and are best suited to the pathogen in question. The concentration of IgG antibodies in the blood is the highest among all types of immunoglobulins.

B lymphocytes - normal blood concentration

In most routine blood tests, all lymphocytes (B and T) are measured together.

The normal concentration of lymphocytes is from 1000 to 5000 in 1 μl of blood.

The percentage of lymphocytes in the entire white blood cell population is also important. Lymphocytes should constitute 20-45% of all leukocytes.

Increase in the number of lymphocytes (lymphocytosis) accompanies infections and infections, mainly caused by viruses. Neoplastic growths of these cells may be a less common cause of an excess of lymphocytes. Lymphocytosis is also a symptom of chronic inflammation (for example in autoimmune diseases).

Reducing the number of lymphocytes is called lymphopenia. Lymphopenia can be caused by various types of immunodeficiency. Sometimes the reduction in lymphocyte counts is caused by taking medications (or other substances) that impair bone marrow function and prevent the production of enough lymphocytes.

B lymphocyte dysfunction

Among the diseases related to the abnormal activity of B lymphocytes, we can distinguish disturbances in their number and function. Both the deficiency and the excess of B lymphocytes can have a negative impact on our he alth.

In some diseases, B lymphocytes are present in the right concentration but do not function properly. This is the case, for example, in autoimmune diseases in which B cells incorrectly "reject" the body's own tissues.

  • humoral immunodeficiencies

Congenital humoral immunity deficiencies are diseases associated with a decrease in the number of B lymphocytes or a significant impairment of antibody production. Usually, the first symptoms of immunodeficiency appear already in childhood: recurrent infections and chronic infections that are difficult to treat. Examples of congenital humoral immunodeficiencies are:

  • Bruton's disease , involving the disturbance of the maturation of B lymphocytes. There are traces of B lymphocytes in the blood, practicallyno antibodies are found
  • common variable immunodeficiency (CVID) , characterized by a reduction in the level of antibodies and the coexistence of neoplastic, allergic and autoimmune diseases
  • hyper-IgM syndrome , which is caused by a lack of non-IgM antibody formation. There are significant deficiencies of IgA, IgE and IgG

Unfortunately, no methods of causal treatment of humoral immunity deficiencies have been developed so far. The basic method of therapy is the constant administration of the patients with antibodies from donors (the so-called immunoglobulin substitution).

  • autoimmune diseases

One of the key stages of B-cell maturation in the bone marrow is the so-called negative selection. Its essence is to "teach" B lymphocytes to recognize foreign antigens and eliminate those that recognize their own cells as pathogenic.

The loss of B lymphocyte tolerance to self antigens is one of the causes of autoimmune diseases. B lymphocytes then begin to produce the so-calledautoantibodies , i.e. antibodies directed against the body's own cells. Examples of autoimmune diseases associated with abnormal B cell activity are:

- multiple sclerosis

- rheumatoid arthritis

- Systemic Lupus Erythematosus

  • B-cell hyperplasia

B lymphocytes at any stage of their development may escape the body's natural control mechanisms and begin to multiply uncontrollably. Neoplastic growths of B lymphocytes may take the following forms:

  • lymphomas (in which the cancer cells mainly affect the lymph nodes)
  • leukemias (in which the cancer cells are found in the bone marrow and blood)

The most common neoplasms derived from B lymphocytes (at different stages of maturation) are:

  • acute lymphoblastic leukemia
  • chronic lymphocytic leukemia
  • Hodgkin's lymphoma
  • follicular lymphoma

At this point, it is worth mentioning one more cancer - multiple myeloma. This type of cancer consists in the uncontrolled multiplication of plasmocytes, which produce huge amounts of a specific antibody (the so-called monoclonal antibody).

About the authorKrzysztof BialaziteA medical student at Collegium Medicum in Krakow, slowly entering the world of constant challenges of the doctor's work. She is particularly interested in gynecology and obstetrics, paediatrics and lifestyle medicine.A lover of foreign languages, travel and mountain hiking.

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Category:

Immune system