Memory T cell
From Wikipedia, the free encyclopedia
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.
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. In mice, TCM cells have been shown to confer superior protection against viruses, bacteria, and cancer 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. 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. 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.
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- ^ 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:10.1038/nm.1982. PMID 19525962.
- 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.
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