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T cell exhaustion can be triggered by several factors like persistent antigen exposure and lack of CD4 T cell help. [64] Antigen exposure also has effect on the course of exhaustion because longer exposure time and higher viral load increases the severity of T cell exhaustion. At least 2–4 weeks exposure is needed to establish exhaustion. [65]
[2] [28] In older children and adults, which have a functioning lymphatic system with mature T cells also situated in other lymphoid organs, the effect is reduced, but includes failure to mount immune responses against new antigens, [2] an increase in cancers, and an increase in all-cause mortality.
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.
T-cell growth factors acronym: TCGF(s) are signaling molecules collectively called growth factors which stimulate the production and development of T-cells. A number of them have been discovered, among them many members of the interleukin family. The thymus is one organ which releases TCGFs. TCGFs have been able to induce T-cell production ...
Majority of human naive T cells are produced very early in life when infant's thymus is large and functional. 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 earlier in life.
Thymocytes are classified into a number of distinct maturational stages based on the expression of cell surface markers. The earliest thymocyte stage is the double negative stage (negative for both CD4 and CD8), which more recently has been better described as Lineage-negative, and which can be divided into four substages.
In 1989, two scientific groups came up with the hypothesis that the thymus expresses genes which are in the periphery, strictly expressed by specific tissues (e.g.: Insulin produced by β cells of the pancreas) to subsequently present these so-called "tissue-restricted antigens" (TRAs) from almost all parts of the body to developing T cells in order to test which TCRs recognize self-tissues ...
Diagram showing the development of different blood cells from haematopoietic stem cell to mature cells. Haematopoiesis (/ h ɪ ˌ m æ t ə p ɔɪ ˈ iː s ɪ s, ˌ h iː m ə t oʊ-, ˌ h ɛ m ə-/; [1] [2] from Ancient Greek αἷμα (haîma) 'blood' and ποιεῖν (poieîn) 'to make'; also hematopoiesis in American English, sometimes h(a)emopoiesis) is the formation of blood cellular ...