Memory T Cells

For other uses, see Memory cell (disambiguation).


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.

Sub-populations

Within the overall memory T cell population, at least three distinct subpopulations have been described and can be recognised by the differential expression of chemokine receptor CCR7 and L-selectin (CD62L).[1]

  • Effector memory TEM cells, however, do not express L-selectin or CCR7 but produce effector cytokines like IFNγ and IL-4.

More recently, other sub-populations have been explored using co-stimulatory molecules CD27 and CD28 expression in addition to CCR7 and CD62L.[2]

Function

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.

  • central memory (TCM). The TCM cells are thought to contain some properties associated with memory cells stem cells. TCM display a capacity for self-renewal due to high levels of phosphorylation of an important transcription factor known as STAT5.[3] In mice, TCM cells have been shown to confer superior protection against viruses,[4] bacteria,[4] and cancer[5] 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.[6][7] 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 maintaining themselves. In preclinical studies, adoptively transferred TSCM confer superior immunity compared with other T memory subsets.[7] Whether such a population is found in humans is the subject of active investigation.

See also

References

Further reading

External links

  • T-cell Group - Cardiff University