Memory T cells
Encyclopedia
Infection
An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...
- as well as potentially cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
-fighting T cell
T cell
T cells or T lymphocytes belong to a group of white blood cells known as lymphocytes, and play a central role in cell-mediated immunity. They can be distinguished from other lymphocytes, such as B cells and natural killer cells , by the presence of a T cell receptor on the cell surface. They are...
s (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
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
or virus
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...
es, as well as cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
cells. Memory T cells have become "experienced" by having encountered antigen during a prior infection, encounter with cancer, or previous vaccination
Vaccination
Vaccination is the administration of antigenic material to stimulate the immune system of an individual to develop adaptive immunity to a disease. Vaccines can prevent or ameliorate the effects of infection by many pathogens...
. 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-selectinL-selectin
L-selectin, also known as CD62L, is a cell adhesion molecule found on leukocytes. It belongs to the selectin family of proteins, which recognize sialylated carbohydrate groups...
(CD62L) .
- Central memory TCM cells express L-selectinL-selectinL-selectin, also known as CD62L, is a cell adhesion molecule found on leukocytes. It belongs to the selectin family of proteins, which recognize sialylated carbohydrate groups...
and the 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.
More recently, other sub-populations have been explored using co-stimulatory molecules CD27
CD27
CD27 is a tumor necrosis factor receptor.-Interactions:CD27 has been shown to interact with SIVA1, TRAF2 and TRAF3.-External links:...
and CD28
CD28
CD28 is one of the molecules expressed on T cells that provide co-stimulatory signals, which are required for T cell activation. CD28 is the receptor for CD80 and CD86 . When activated by Toll-like receptor ligands, the CD80 expression is upregulated in antigen presenting cells...
expression in addition to CCR7 and CD62L .
Function
AntigenAntigen
An antigen is a foreign molecule that, when introduced into the body, triggers the production of an antibody by the immune system. The immune system will then kill or neutralize the antigen that is recognized as a foreign and potentially harmful invader. These invaders can be molecules such as...
-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
CD8
CD8 is a transmembrane glycoprotein that serves as a co-receptor for the T cell receptor . Like the TCR, CD8 binds to a major histocompatibility complex molecule, but is specific for the class I MHC protein. There are two isoforms of the protein, alpha and beta, each encoded by a different gene...
-positive) subset, similar populations appear to exist for both the helper T cells (CD4
CD4
CD4 is a glycoprotein expressed on the surface of T helper cells, monocytes, macrophages, and dendritic cells. It was discovered in the late 1970s and was originally known as leu-3 and T4 before being named CD4 in 1984...
-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 phosphorylationPhosphorylationPhosphorylation is the addition of a phosphate group to a protein or other organic molecule. Phosphorylation activates or deactivates many protein enzymes....
of an important transcription factorTranscription factorIn molecular biology and genetics, a transcription factor is a protein that binds to specific DNA sequences, thereby controlling the flow of genetic information from DNA to mRNA...
known as STAT5STAT5STAT5 refers to two highly related proteins, STAT5A and STAT5B, which are encoded by separate genes, but are 90% identical at the amino acid level....
. 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 maintaining 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.
A recent study in Science found that T-cells in the spleen can synthesize acetylcholine
Acetylcholine
The chemical compound acetylcholine is a neurotransmitter in both the peripheral nervous system and central nervous system in many organisms including humans...
in response to vagus nerve stimulation
Vagus nerve stimulation
Vagus nerve stimulation is an adjunctive treatment for certain types of intractable epilepsy and treatment-resistant depression.- Mechanism of action :...
. (Science Sept 15, 2011. DOI : 10.1126/science.1209985)
It is thought that this mechanism may play a role in down-regulating inflammation
Inflammation
Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...
via
TNF-alpha via macrophage
Macrophage
Macrophages are cells produced by the differentiation of monocytes in tissues. Human macrophages are about in diameter. Monocytes and macrophages are phagocytes. Macrophages function in both non-specific defense as well as help initiate specific defense mechanisms of vertebrate animals...
s.