Thymus hyperplasia

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Thymus hyperplasia
Other namesThymic hyperplasia
Specialty Immunology   OOjs UI icon edit-ltr-progressive.svg

Thymus hyperplasia refers to an enlargement ("hyperplasia") of the thymus. [1]

It is not always a disease state. The size of the thymus usually peaks during adolescence and atrophies in the following decades. Before the immune function of the thymus was well understood, the enlargement was sometimes seen as a cause for alarm, and justification for surgical reduction. This approach is much less common today.

It can be associated with myasthenia gravis. [2] [3] MRI can be used to distinguish it from thymoma. [4]

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Autoimmune regulator A transcription factor expressed in the medulla (inner part) of the thymus. It is part of the mechanism which eliminates self-reactive T cells that would cause autoimmune disease.

The autoimmune regulator (AIRE) is a protein that in humans is encoded by the AIRE gene. It is a 13kb gene on chromosome 21q22.3 that has 545 amino acids. AIRE is a transcription factor expressed in the medulla of the thymus. It is part of the mechanism which eliminates self-reactive T cells that would cause autoimmune disease. It exposes T cells to normal, healthy proteins from all parts of the body, and T cells that react to those proteins are destroyed.

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Involution is the shrinking or return of an organ to a former size. At a cellular level, involution is characterized by the process of proteolysis of the basement membrane, leading to epithelial regression and apoptosis, with accompanying stromal fibrosis. The consequent reduction in cell number and reorganization of stromal tissue leads to the reduction in the size of the organ.

One of the major characteristics of vertebrate immunology is thymic involution, the shrinking (involution) of the thymus with age, resulting in changes in the architecture of the thymus and a decrease in tissue mass. This process is genetically regulated, with the nucleic material responsible being an example of a conserved sequence — one maintained through natural selection since it arose in a common ancestor of all species now exhibiting it, via a phenomenon known to bioinformaticists as an orthologic sequence homology. The thymus involutes in almost all vertebrates, from birds, teleosts, amphibians to reptiles, though the thymi of a few species of sharks are known not to involute. T-cells are named for the thymus where T-lymphocytes migrate from the bone marrow to mature. Its regression has been linked to the reduction in immunosurveillance and the rise of infectious disease and cancer incidence in the elderly . Though thymic involution has been linked to immunosenescence, it is not induced by senescence as the organ starts involuting from a young age: in humans, as early as the first year after birth.

Thymus transplantation is a form of organ transplantation where the thymus is moved from one body to another.

References

  1. "eMedicine - Surgery of the Thymus Gland : Article by Said Fadi Yassin". 2019-02-26.Cite journal requires |journal= (help)
  2. "Thymus, hyperplasia". Medcyclopaedia. GE.
  3. Murakami M, Hosoi Y, Negishi T, et al. (November 1996). "Thymic hyperplasia in patients with Graves' disease. Identification of thyrotropin receptors in human thymus". J. Clin. Invest. 98 (10): 2228–34. doi:10.1172/JCI119032. PMC   507671 . PMID   8941638.
  4. Inaoka T, Takahashi K, Mineta M, et al. (June 2007). "Thymic hyperplasia and thymus gland tumors: differentiation with chemical shift MR imaging". Radiology. 243 (3): 869–76. doi:10.1148/radiol.2433060797. PMID   17463136.
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