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Thymic involution is the shrinking of the thymus with age, resulting in changes in the architecture of the thymus and a decrease in tissue mass. [1] Thymus involution is one of the major characteristics of vertebrate immunology, and occurs in almost all vertebrates, from birds, teleosts, amphibians to reptiles, though the thymi of a few species of sharks are known not to involute.
Thymic involution is common in most mammals; in humans it begins after puberty, as the immunological defense against most novel antigens is necessary mainly during infancy and childhood. [ 11 ] The major characteristic of the immunosenescent phenotype is a shift in T-cell subpopulation distribution.
The thymus continues to grow after birth reaching the relative maximum size by puberty. [2] It is most active in fetal and neonatal life. [9] It increases to a mass of 20 to 50 grams by puberty. [3] It then begins to decrease in size and activity in a process called thymic involution. [4]
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 (basal lamina), leading to epithelial regression and apoptosis, with accompanying stromal fibrosis. The consequent reduction in cell number and reorganization of stromal ...
The majority of human naive T cells are produced very early in life when the thymus is large and functional. The subsequent decrease in naive T cell production due to involution of the thymus with age is compensated by so called "peripheral proliferation" or "homeostatic proliferation" of naive T cells which have emigrated from the thymus ...
Cortical thymic epithelial cells (cTECs) form unique parenchyma cell population of the thymus which critically contribute to the development of T cells. Thymus tissue is compartmentalized into cortex and medulla and each of these two compartments comprises its specific thymic epithelial cell subset. cTECs reside in the outer part- cortex, which ...
Hassall's corpuscles (also known as thymic bodies) are structures found in the medulla of the human thymus, formed from eosinophilic type VI thymic epithelial cells arranged concentrically. These concentric corpuscles are composed of a central mass, consisting of one or more granular cells, and of a capsule formed of epithelioid cells.
Similarly, there is SLA (Swine leukocyte antigens), BoLA (Bovine leukocyte antigens), DLA for dogs, etc. However, historically, the MHC in mice is called the Histocompatibility system 2 or just the H-2, whereas it has been referred to as the RT1 complex in rats, and the B locus in chickens. [citation needed]