Lymph follicle

Lymph follicle play a major role in the human immune system. They contain a large number of B lymphocytes, which multiply to form immune cells when they come into contact with pathogens.

What are lymph follicles?

Lymph follicles are part of the lymphatic system. Under the light microscope these can be seen as a spherical cluster of B lymphocytes.

The lymph follicles are involved in certain processes of the immune system. They take on the task of multiplying and specializing the B lymphocytes into plasma cells. They mainly occur in the lymph nodes, where a particularly large number of pathogens are located. In the human body, it is the spleen and the pharynx in particular that have to deal with a large number of antigens.

The lymph follicles are also found in the reticular connective tissue of various organs. These include the mucous membranes of the digestive tract, the organs of the respiratory system and the urinary and sexual organs. Lymph follicles arise as a reaction to local stimuli, temporarily form solitary follicles and appear as fixed components of lymphatic organs.

Anatomy & structure

The appearance of the lymph follicles varies depending on their stage of development. The primary follicles, also called primary nodules, have a diameter of up to one millimeter.

At this stage, the lymph follicles have not yet experienced any antigen-antibody contact. Instead, they are characterized by an even distribution of small lymphocytes. The secondary follicles or secondary nodules, on the other hand, have a bright center, which is also referred to as the germinal or reaction center. Contact with pathogens causes the primary lymph follicles to become secondary follicles. The germinal center of the secondary follicles is surrounded by a dense cortex with a high concentration of T lymphocytes. This cortex is also called the parafollicular space in technical terms.

In the germinal center of the secondary follicle there are activated B-lymphocytes, which are differentiated into plasma cells. Finally, solitary follicles are those lymphatic follicles that are located in the tela submucosa. These enlarge in the case of infections in the mucous membrane and can even grow to the size of a pin. So-called solitary follicle formations occur in individual areas of the human body, which aggregate to form the folliculi lymphatici aggregati. These can be found as Peyer's plaques in the ileum mucosa.

Function & tasks

As soon as pathogens penetrate certain organs of the body, the body triggers a specific immune reaction. As part of the lymphatic system, the lymph follicles are responsible for fighting the invaders. The functions of lymph follicles differ according to their functional stage.

A high concentration of immature B-lymphocytes is formed in the polar caps of primary follicles. These B-lymphocytes are also called naive B-cells because they have not yet come into contact with antigens. After antigen contact, the primary follicle becomes a reaction follicle with a lighter inner zone, which is a reaction center with few cells. At this stage the lymph follicles are called secondary follicles. They are now surrounded by a dark wall of lymphocytes. In addition, there are still undifferentiated B lymphocytes in the lymph follicles. If these come into contact with the memory cells and helper cells, they can form specific antibodies.

Another task of secondary follicles is to mitotically multiply and differentiate the B lymphocytes after exposure to the antigen. Since the B-lymphocytes are already characterized by the different developmental stages with specific characteristics, these are relevant for the later processes in the immune system. Now the increased and differentiated B cells mature within the lymph follicles. Then when intrafollicular T lymphocytes come into contact with follicular dendritic cells, the B lymphoblasts are formed. These eventually migrate out of the lymph follicles to develop into antibody-producing plasma cells.

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Diseases

Common diseases that occur in connection with the lymph follicles are tonsillitis, appendix infections, and swelling of the lymph nodes and spleen.

The tonsillitis, in medical jargon as angina tonsillaris or tonsillitis for short, is an acute, bacterial infection of the tonsils, the tonsils or the tonsils. These are all located in the pharynx, with the tonsils most likely to be affected by tonsillitis. If pathogens penetrate the tonsils, they swell and often cause severe pain in those affected.

A tonsillitis is often caused by streptococci, pneumococci, Haemophilius influenzae, or staphylococci. This disease particularly affects children and adults with a weakened immune system. If tonsillitis is common and the patient often has difficulty breathing, surgery is an option.

In appendicitis, the worm-shaped end of the appendix is ​​inflamed. It is true that appendicitis is spoken of in everyday language, but not the entire appendix is ​​affected by the infection. To avoid life-threatening consequences for the patient, the appendix 10 centimeters long and 1 centimeter thick is removed after the diagnosis. This contains a large amount of lymph follicles, which sets the defense going, especially in childhood, when an infection occurs. The inflammation occurs particularly in children and adolescents from 10 years of age. Adults are prone to appendicitis up to the age of 30. The symptoms of appendix infections include loss of appetite, nausea, vomiting, and a high fever.

When the lymph nodes and spleen swell, it is called mantle cell lymphoma. Not only the healthy but also defective B-lymphocytes are increased. These have a similar appearance to lymphocytes that are otherwise located in the edge area of ​​the lymph follicles. These cells are tumor cells that increasingly grow in the lymph nodes and in the spleen and have no defense function. However, unlike the two above, this condition does not arise from infection. So far there is also no evidence of a hereditary cause, although about 85 percent of all patients have a genetic change.