What are B lymphocytes?

Definition – What are B lymphocytes?

B lymphocytes are a specialized type of immune cells, also known as leukocytes. Lymphocytes (B and T lymphocytes) are part of the specific defence of the immune system. This means that during an infection they always specialise in a particular pathogen and fight it in a targeted manner.

In addition, the immune response is divided into the humoral and cellular sections. Roughly explained, the difference lies in whether the defence takes place via the bloodstream, as is the case with the humoral defence, or directly via the cells (cellular). B-lymphocytes belong to the humoral part of the defence.

Their strategy for fighting pathogens is based on the formation of so-called plasma proteins, the antibodies. The antibodies then enter 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 more information on this under:

  • Immune System
  • Lymphocytes – You should definitely know that!

Anatomy of the B lymphocytes

B lymphocytes are mostly circular cells. They have a diameter of about 6 μm. This means that they can only be seen 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 nucleus in their middle. This nucleus is so large because B-lymphocytes always have to read the genes in the nucleus to synthesize antibodies. The cytoplasm is strongly pushed to the edge by the large nucleus and is only very narrow.

Task and function of the B-lymphocytes

Like all immune cells (leukocytes), B lymphocytes serve to defend against pathogens. In doing so, they are geared to the special task of producing antibodies that are directed precisely at specific structures (antigens) of the pathogens. They are therefore part of the specific defence, as they are only effective against a single, specific antigen, but can combat it very effectively.

In addition, they belong to the humoral defence. This means that their effect is not immediately triggered by cells, but by proteins (plasma proteins) dissolved in the blood plasma, the antibodies. B-lymphocytes produce antibodies of the different classes IgD, IgM, IgG, IgE and IgA.

Ig stands for immunoglobulin, another word for antibodies. B lymphocytes that have not yet had contact with their matching antigen are inactive. However, they have already produced antibodies of classes IgM and IgD, which they carry on their surface and which serve as receptors.

If the matching antigen now binds to these antibodies, the B-lymphocyte is activated. This is usually done with the help of T-lymphocytes, but to a lesser extent can also be done without them. The B-lymphocyte then transforms into its active form, the plasma cell.

As a plasma cell, it begins to produce antibodies of other classes. Detailed information on the activation of the B-lymphocytes will follow later. In addition, an activated B-lymphocyte begins to divide, resulting in many cell clones that are all directed against the same antigen.

At first mostly IgM ́s are produced, later the more effective IgG ́s. The antibodies can damage pathogens in various ways. Firstly, they bind to their antigen and thus neutralize it.

For example, it can then no longer bind to cells and penetrate them. In addition, antibodies can activate another part of the defence system, the complement system. And they make pathogens “palatable” to scavenger cells such as macrophages and neutrophil granulocytes.

This process is known as opsonisation; it leads to pathogens or cells that are affected by them being eaten and degraded more quickly. If enough effective antibodies are produced, the pathogens die and the disease heals. However, this takes some time when the body first comes into contact with a pathogen and its antigens.

In addition, B-lymphocytes also have the task of forming the body’s immunological memory. A small proportion of the B-lymphocytes that are created 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 a whole life. On their surface they carry antibodies against the antigen they are specialised in. If the pathogen re-enters the body with this antigen, it immediately activates the memory cell.

The memory cell begins to divide and more B-lymphocytes are created, which become plasma cells. These immediately start producing antibodies. The pathogens are usually killed quickly as soon as suitable antibodies are available.

Therefore, they die before the disease they cause can break out. This is the reason why some illnesses are no longer present once you have had them. Vaccinations also work according to this principle.