Anatomy-Lexicon

What are B lymphocytes?

Definition - What are B lymphocytes?

B lymphocytes are a specialized type of immune cell, also called leukocytes. Lymphocytes (B and T lymphocytes) belong to the specific defense of the immune system. This means that they always specialize in a certain pathogen during an infection and fight it in a targeted manner.

In addition, a distinction is made between the humoral and cellular sections of the immune reaction. Roughly explained, the difference lies in whether the defense takes place via the bloodstream, as is the case with the humoral defense, or directly via the cells (cellular). B lymphocytes are part of the humoral part of the immune system. Their strategy for combating pathogens is based on the formation of so-called plasma proteins, the antibodies. The antibodies then get into the blood and fight, among other things, foreign material in the body. The synthesis of antibodies, together with the formation of memory cells, is the main task of the B lymphocytes.

Would you like to know exactly how the human immune system works? You can find out more about this at:

immune system
Lymphocytes - What You Should Know!

Anatomy of the B lymphocytes

B-lymphocytes are mostly circular cells. They have a diameter of approx. 6 µm. This means that you can only see them under a microscope. B-lymphocytes generally show the same structure as most other cells. They can be recognized by the fact that they have a very large cell nucleus in their middle. This is so large that B lymphocytes always have to read the genes in the cell nucleus for the synthesis of antibodies. The cytoplasm is strongly pushed to the edge by the large nucleus and is only very narrow.

To learn more about the intricacies of a cell, also read: histology

Role and function of the B lymphocytes

Like all immune cells (leukocytes), B-lymphocytes serve to ward off pathogens. They are geared towards the special task of producing antibodies that target specific structures (antigens) of the pathogens. So they belong to the specific defense, as they are only effective against a single, specific antigen, but can fight this very effectively.

They are also counted as part of the humoral defense. This means that their effect does not unfold directly via cells, but via proteins (plasma proteins), the antibodies, that are dissolved in the blood plasma. B lymphocytes produce antibodies of the various classes IgD, IgM, IgG, IgE and IgA. The Ig stands for immunoglobulin, another word for antibodies.

B lymphocytes that have not yet had contact with their matching antigen are inactive. But they have already produced antibodies of the IgM and IgD classes, which they carry on their surface and which serve as receptors. If the appropriate antigen binds to these antibodies, the B lymphocyte is activated. This is usually done with the help of T lymphocytes, but to a lesser extent it can also be done without them. The B-lymphocyte then converts to its active form, the plasma cell. As a plasma cell, it begins to produce antibodies of other classes as well. Detailed information on the activation of the B-lymphocytes follows in the further course.

In addition, an activated B-lymphocyte begins to divide, so that many cell clones arise, all of which are directed against the same antigen. Initially, mostly IgMs are produced, later the more effective IgGs. The antibodies can damage pathogens in a number of ways. On the one hand, they bind to their antigen and thereby neutralize it. For example, it can then no longer bind to cells and penetrate them. Antibodies can also activate another part of the immune system, the complement system. And they make pathogens "palatable" for phagocytes such as macrophages and neutrophils. This process is called opsonization, it means that pathogens or cells that are infected by them are eaten and broken down more quickly.

If enough effective antibodies are produced, the pathogens die and the disease heals up. However, this takes some time when the body comes into contact with a pathogen and its antigens for the first time.

In addition, B-lymphocytes also have the task of building the body's immunological memory. A small fraction of the B lymphocytes that arise after activation do not become plasma cells. Instead, they develop into memory cells. These cells can survive in the body for a very long time, sometimes for decades or an entire life. They carry antibodies against the antigen they specialize in on their surface. If the pathogen with this antigen penetrates the body again, it activates the memory cell immediately. This begins to divide and further B-lymphocytes develop, which become plasma cells. These immediately start producing antibodies. The pathogens are usually killed quickly as soon as suitable antibodies are available. That is why they die before the disease they cause can break out. This is the reason why, once you have had some diseases, you no longer get it. Vaccinations also work according to this principle.

Would you like to stimulate this function of the lymphocytes and escape disease faster? The most important information can be found at: How can you strengthen the immune system?

Normal values of the B lymphocytes

The values of the B-lymphocytes are usually determined in the complete blood count. This measures the number and type of immune cells. However, no distinction is made between T and B lymphocytes, so that the normal values apply to the sum of both types of lymphocytes.
Typically, there are between 1,500 and 4,000 lymphocytes per microliter of blood. The total proportion of lymphocytes in all immune cells (leukocytes) normally fluctuates between 20% and 50%.

What can be the cause if the B-lymphocytes are increased?

An increased number of lymphocytes is called lymphocytosis. This is usually determined on the basis of a complete blood count, in which, among other things, the immune cells are counted and divided according to their different types. Normally, no distinction is made between B and T lymphocytes in the blood count; this is only done if certain diseases are suspected.

Since lymphocytes are immune cells, an increase in the number of lymphocytes may indicate an infection that is either ongoing or healing. Children in particular quickly develop lymphocytosis, but it also occurs in adults. The triggering diseases can be viral infections (e.g. measles) or bacterial infections (e.g. whooping cough). Here, disease-specific symptoms usually also occur. Lymphocytosis can also occur in some diseases that could be autoimmune (e.g. Crohn's disease). Here, too, accompanying symptoms are to be expected that are typical for this disease.

In addition, excessive, abnormal growth of lymphocytes can also lead to an increase in these cells. This is the case, for example, with leukemia (e.g. chronic lymphocytic leukemia / CLL) or lymphomas. These types of cancer often cause fewer symptoms. If they do occur, it can be night sweats, weight loss, fever, enlarged lymph nodes, susceptibility to infection, shortness of breath or bleeding.

You can find additional information at:

What is determined in a blood count?
What infectious diseases are there?
How do you recognize leukemia?

What can be the cause if the B-lymphocytes are low?

A low number of lymphocytes is called lymphocytopenia. Lymphocytopenia is also diagnosed with the help of the complete blood count. A low number of lymphocytes can arise in situations that overwhelm or damage the immune system.

This includes, for example, simply stressful situations. During stress, the stress hormone cortisol is released, which suppresses the immune system.

Lymphocytopenia can also occur during therapy with cortisone, the drug form of cortisol.

Therapies that inhibit cell division (chemotherapy, radiation therapy) can also have this effect.

Infection with pathogens that damage the immune system can also reduce the number of lymphocytes. This includes, for example, the HI virus (human immunodeficiency virus). An infection is initially noticeable with flu-like symptoms, but then often has few symptoms for a long time.

Certain types of cancer can also lead to lymphocytopenia, especially those that affect the lymphatic system. This includes, for example, non-Hodgkin lymphoma. This form of cancer causes night sweats, weight loss, fever, and swelling of the lymph nodes, for example.

You can read more important information here:

Side effects of cortisone
Chemotherapy side effects

How do B lymphocytes mature?

B-lymphocytes are formed in the bone marrow from so-called blood stem cells (haematopoietic stem cells). These cells can still develop into any blood cell. However, as they develop into fully developed cells (differentiation), they lose this ability.

Pro-B-cells represent a further development stage of B-lymphocytes. These then further develop into pre-B-cells. They differ from B lymphocytes mainly in that they do not yet produce antibodies and can carry them on their surface. That is why they do not yet have a receptor and cannot be activated. This is because the genes needed to produce antibodies cannot yet be read. Only after the genes have been rearranged are they released for reading. This creates immature B lymphocytes that can only produce IgM antibodies. After they become mature B-lymphocytes, they can also make IgD antibodies.

In this state, they leave the bone marrow. They are still called naive because they had no contact with their antigen. Only after this contact are they activated and can now also produce the other antibody classes.

How are B lymphocytes activated?

There are two different ways that B lymphocytes can be activated. In both cases, the antibody on the cell surface, which serves as a receptor, must be in contact with its matching antigen.

In the case of T-cell-independent activation, the B-cell receptors network and this is how activation occurs. With this type of activation, however, no memory cells are formed, and only antibodies of the IgM class are then formed.

In the case of T-cell-dependent activation, a T-lymphocyte has to interact with its receptor and signaling molecules with the B-cell. The resulting activation leads to the formation of memory cells, and more types of antibodies can then be produced. So it is much more effective.

Further information on this: Superantigens.

Lifespan of a B lymphocyte

The lifespan of B lymphocytes can vary greatly depending on whether the lymphocyte develops into a plasma cell or a memory cell.

Plasma cells only live for about 2-3 days. During this time, however, they divide very often, so that their cell clones take over their task after them.

Memory cells can remain in the body for decades or even a lifetime. As long as they are alive, there is protection from the pathogen against which their antibodies are directed.