The thymus gland is an organ of the immune system located behind the sternum and below the neck that produces T-lymphocytes, or T cells. This lymphoid organ is primarily active during the early years of life. After puberty, it atrophies and regresses until it ceases to function completely in adulthood.
The thymus gland is also responsible for giving instructions regarding the endocrine system in addition to the immune system. More hormones are produced by the thymus gland than all other glands combined, and they target the pituitary gland, adrenal glands and ovaries. They also instruct the body how to develop and increase its size so that it can function effectively.
The thymus gland is responsible for the maturation of T lymphocytes, an important component of the adaptive immune system. Over 80% of the thymus gland is occupied by T cells, and it produces a large number of T cells. After puberty, the thymus begins to atrophy and begins to regress until it ceases to function completely in adulthood.
Lymphoid Organ Responsible for the Maturation of T Lymphocyte :
1. How many T lymphocytes can be produced by the thymus?
T cells are produced by the thymus in large numbers. The thymus can produce two to five billion T cells per day. These cells are then transported to the lymph nodes and other lymphoid organs where they receive further education. By the age of 20, a human will have about 250 billion T cells.
2. What type of education does the thymus give to T cells?
The education provided by the thymus is necessary for the proper functioning of T-cells. The thymus provides negative selection, positive selection and clonal deletion. The thymus selects which antigens should be attacked or “presented” to them via MHC proteins (antigen presenting cells), and it also instructs how immature T cells should respond once they encounter antigen presenting cells expressing foreign antigens (danger signals).
3. How many T lymphocytes are there in a normal adult?
Only one to ten million T cells are produced daily in a normal adult with full participation of their immune system and only less than 10% of these cells survive long enough to leave the bone marrow and reach their target.
4. How many T cells are produced daily in the thymus?
The thymus can produce two to five billion T cells per day. These cells are then transported to the lymph nodes and other lymphoid organs where they receive further education (negative selection, positive selection and clonal deletion). By the age of 20, a human will have about 250 billion T cells.
5. Is there a correlation between the health of a thymus gland and that of an individual?
Structural damage to the thymus gland can be caused by radiation therapy, therapeutic irradiation, or surgery involving radiation exposure near the gland. A large reduction in the functionality of the thymus gland can be caused by surgery or irradiation of the head area.
Abnormal functioning of the thymus can be caused by infectious diseases (e.g. tuberculosis) and is also associated with diseases such as AIDS and Crohn’s disease, a chronic inflammatory disorder of the gastrointestinal tract which causes severe intestinal damage, ulcers and potential perforation.
6. Why does tumor necrosis factor alpha (TNF-α) cause atrophy in this organ?
TNF-alpha is one of many cytokines involved in inflammation responses. It has pro-inflammatory and anti-inflammatory functions, and is sometimes detrimental during the process of healing. In the thymus, TNF-alpha creates a favorable environment for T lymphocytes to mature, but is also detrimental if too much TNF-alpha is produced and prevents the thymus from maturing.
7. What does clonal deletion mean?
Clonal deletion means that an immature T lymphocyte has been identified by the thymus as being a “good” cell type and will be allowed to mature in other parts of the body such as the bone marrow. The immature cell then matures into a mature cell type (e.g., a gamma or alpha T cell). If the thymus decides that the cell is not good, it will be destroyed or “deleted”.
8. What is the role of the thymus gland in the protection of an individual from infection?
The thymus produces two types of lymphocytes: gamma and alpha cells. Gamma cells protect against intracellular pathogens such as fungi and mycobacteria. The alpha cells are involved in humoral immunity, which involves antibodies to fight extracellular pathogens like bacteria, viruses, and toxins. Therefore, the thymus helps with protection against infection by producing T lymphocytes that can fight off intracellular and extracellular infections.
9. Does the production of T cells slow down in older people?
The production of T cells slows down in older individuals. This is related to a reduction in the functionality of the thymus, which results from atrophy and loss of thymic tissue.