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Memory T cell
From Wikipedia, the free encyclopedia
For other uses, see Memory cell.
A lymphocyte is shown in the center of this picture
1. After the naive T cell (N) encounters an antigen it becomes activated and begins to proliferate (divide) into many clones or daughter cells.
2. Some of the T cell clones will differentiate into effector T cells (E) that will perform the function of that cell (e.g. produce cytokines in the case of helper T cells or invoke cell killing in the case of cytotoxic T cells).
3. Some of the cells will form memory T cells (M) that will survive in an inactive state in the host for a long period of time until they re-encounter the same antigen and reactivate.
2. Some of the T cell clones will differentiate into effector T cells (E) that will perform the function of that cell (e.g. produce cytokines in the case of helper T cells or invoke cell killing in the case of cytotoxic T cells).
3. Some of the cells will form memory T cells (M) that will survive in an inactive state in the host for a long period of time until they re-encounter the same antigen and reactivate.
Memory T cells are a subset of infection- as well as potentially cancer-fighting T cells (also known as a T lymphocyte) that have previously encountered and responded to their cognate antigen; thus, the term antigen-experienced T cell is often applied. Such T cells can recognize foreign invaders, such as bacteria or viruses, as well as cancer cells. Memory T cells have become "experienced" by having encountered antigen during a prior infection, encounter with cancer, or previous vaccination. At a second encounter with the invader, memory T cells can reproduce to mount a faster and stronger immune response than the first time the immune system responded to the invader. This behaviour is utilized in T lymphocyte proliferation assays, which can reveal exposure to specific antigens.
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Sub-populations
Within the overall memory T cell population, at least three distinct sub-populations have been described:
- central memory (TCM). The TCM cells are thought to contain some properties associated with memory stem cells. TCM display a capacity for self-renewal due to high levels of phosphorylation of an important transcription factor known as STAT5.[1] In mice, TCM cells have been shown to confer superior protection against viruses,[2] bacteria,[2] and cancer[3] in several different model systems compared with TEM cells.
- two highly related effector memory sub-types, which strongly express genes for molecules essential to the cytotoxic function of CD8 T cells:
- effector memory (TEM)
- effector memory RA (TEMRA)
- More recently, antigen-experienced CD8+ T cells with apparent self-renewal capabilities have been described in mice.[4][5] This population, now termed stem cell memory (TSCM), can be identified by the markers CD44(low)CD62L(high)CD122(high)sca-1(+) and are capable of generating TCM and TEM subsets while maintaing themselves. In preclinical studies, adoptively transferred TSCM confer superior immunity compared with other T memory subsets.[5] Whether such a population is found in humans is the subject of active investigation.
Memory T cells can be recognized by the differential expression of certain molecules.
- Central memory TCM cells express L-selectin and the chemokine receptor CCR7, they secrete IL-2, but not IFNγ or IL-4.
- Effector memory TEM cells, however, do not express L-selectin or CCR7 but produce effector cytokines like IFNγ and IL-4.
Antigen-specific memory T cells against viruses or other microbial molecules can be found in both TCM and TEM subsets. Although most information is currently based on observations in the cytotoxic T cells (CD8-positive) subset, similar populations appear to exist for both the helper T cells (CD4-positive) and the cytotoxic T cells.
See also
References
- ^ Willinger T, Freeman T, Hasegawa H, McMichael AJ, Callan MF (November 2005). "Molecular signatures distinguish human central memory from effector memory CD8 T cell subsets". Journal of Immunology 175 (9): 5895–903. PMID 16237082. http://www.jimmunol.org/cgi/pmidlookup?view=long&pmid=16237082.
- ^ a b Wherry EJ, Teichgräber V, Becker TC, et al. (March 2003). [Expression error: Missing operand for > "Lineage relationship and protective immunity of memory CD8 T cell subsets"]. Nature Immunology 4 (3): 225–34. doi:. PMID 12563257.
- ^ Klebanoff CA, Gattinoni L, Torabi-Parizi P, et al. (July 2005). [Expression error: Missing operand for > "Central memory self/tumor-reactive CD8+ T cells confer superior antitumor immunity compared with effector memory T cells"]. Proceedings of the National Academy of Sciences of the United States of America 102 (27): 9571–6. doi:. PMID 15980149.
- ^ Zhang Y, Joe G, Hexner E, Zhu J, Emerson SG (December 2005). [Expression error: Missing operand for > "Host-reactive CD8+ memory stem cells in graft-versus-host disease"]. Nature Medicine 11 (12): 1299–305. doi:. PMID 16288282.
- ^ a b Gattinoni L, Zhong XS, Palmer DC, et al. (July 2009). [Expression error: Missing operand for > "Wnt signaling arrests effector T cell differentiation and generates CD8+ memory stem cells"]. Nature Medicine 15 (7): 808–13. doi:. PMID 19525962.
Further reading
- Janeway, Charles (2005). Immunobiology: the immune system in health and disease. New York: Garland Science. ISBN 978-0-443-07310-6.
- Lichtman, Andrew H.; Abbas, Abul K. (2003). Cellular and molecular immunology. Philadelphia: Saunders. ISBN 0-7216-0008-5.
External links
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