A lymphocyte is a 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.

Memory T cells are a specific type of infection-fighting T cell (also known as a T lymphocyte) that can recognize foreign invaders such as bacteria or viruses, that were encountered during a prior infection or 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. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... A scanning electron microscope (SEM) image of a single human lymphocyte. ... Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Naive T cell refers to a T cell that has differentiated in bone marrow, and successfully undergone the positive and negative processes of central selection in the thymus. ... An antigen or immunogen is a molecule that stimulates an immune response. ... T cells belong to a group of white blood cells known as lymphocytes and play a central role in cell-mediated immunity. ... This does not adequately cite its references or sources. ... Cytokines are a group of proteins and peptides that are used in organisms as signaling compounds. ... A helper (or TH) T cell is a T cell (a type of white blood cell) which has on its surface antigen receptors that can bind to fragments of antigens displayed by the Class II MHC molecules found on professional antigen-presenting cells (APCs). ... A cytotoxic T cell (also known as TC, CTL or killer T cell) belongs to a sub-group of T lymphocytes (a type of white blood cell) which are capable of inducing the death of infected somatic or tumor cells; they kill cells that are infected with viruses (or other... An infection is the detrimental colonization of a host organism by a foreign species. ... T cells are a subset of lymphocytes that play a large role in the immune response. ... T cells are a subset of lymphocytes that play a large role in the immune response. ... Phyla Actinobacteria Aquificae Chlamydiae Bacteroidetes/Chlorobi Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Lentisphaerae Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Verrucomicrobia Bacteria (singular: bacterium) are unicellular microorganisms. ... This article is about biological infectious particles. ... A vial of the vaccine against influenza. ... A request has been made on Wikipedia for this article to be deleted in accordance with the deletion policy. ...

Sub-populations

Within the human cytotoxic T cell population, three distinct sub-populations have now been described:

• central memory (T_CM). The T_CM cells are thought to represent memory stem cells. T_CM display a capacity for self-renewal due to high levels of phosphorylation of an important transcription factor known as STAT5. ^[1]
• two highly related effector memory sub-types, which strongly express genes for molecules essential to the cytotoxic function of CD8 T cells:
  • effector memory (T_EM)
  • effector memory RA (T_EMRA)

Memory T cells can be recognized by the differential expression of certain molecules. Mouse embryonic stem cells. ... A phosphorylated serine residue Phosphorylation is the addition of a phosphate (PO4) group to a protein or a small molecule or the introduction of a phosphate group into an organic molecule. ... In molecular biology, a transcription factor is a protein that binds DNA at a specific promoter or enhancer region or site, where it regulates transcription. ... STAT5 refers to two highly related proteins, STAT5a and STAT5b. ... Cytotoxicity is the quality of being poisonous to cells. ...

• Central memory T_CM cells express L-selectin and the chemokine receptor CCR7, they secrete IL-2, but not IFNγ or IL-4.

• Effector memory T_EM 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 T_CM and T_EM subsets. Although most information is currently based on observations in the Cytotoxic T cells (CD8-positive) subset, similar populations appear to exist for Helper T cells (CD4-positive). L-selectin, also known as CD62L, is a cell adhesion molecule found on leukocytes. ... Typical structure of a chemokine receptor, with seven transmembrane domains and a characteristic DRY motif in the second intracellular domain. ... CC chemokine receptors are integral membrane proteins that specifically bind and respond to cytokines of the CC chemokine family. ... Interleukin-2 (IL2) is an interleukin, a type of biological response modifier that can improve the bodys natural response to disease. ... Expression pattern Orthologs Human Mouse Entrez Ensembl Uniprot Refseq Location Interferon-gamma (IFN-γ) is a dimerized soluble cytokine that is the only member of the type II class of interferons. ... Interleukin-4, abreviated IL-4, is a lymphokine that stimulates the proliferation of activated B-cells and T-cells, among other effects. ... Cytokines are small protein molecules that are the core of communication between immune system cells, and even between immune system cells and cells belonging to other tissue types. ... An antigen or immunogen is a molecule that stimulates an immune response. ... A microorganism or microbe is an organism that is so small that it is microscopic (invisible to the naked eye). ... A cytotoxic (or TC) T cell is a T cell (a type of white blood cell) which has on its surface antigen receptors that can bind to fragments of antigens displayed by the Class I MHC molecules of virus (or other intracellular pathogen) infected somatic cells and tumor cells. ... CD8 (cluster of differentiation 8) is a molecule that is expressed on the surface of cytotoxic T cells. ... A T helpered cell (or TH) cell, is a T cell (a type of white blood cell or leukocyte) which has on its surface antigen receptors that can bind to fragments of antigens displayed by the Class II MHC molecules found on professional antigen-presenting cells (APCs). ... CD4 (cluster of differentiation 4) is a molecule that is expressed on the surface of T helper cells (as well as regulatory T cells and dendritic cells). ...

See also

• Naive T cell
• V(D)J recombination of DNA
• Memory B cell

Naive T cell refers to a T cell that has differentiated in bone marrow, and successfully undergone the positive and negative processes of central selection in the thymus. ... V(D)J recombination is a mechanism of DNA recombination used by humans and other vertebrates for immunological protection against attacks by bacterial, viral, and parasitic invaders. ... Memory B cells are a B cell sub-type that are formed following primary infection. ...

References

1. ^ Willinger T, Freeman T, Hasegawa H, McMichael A, Callan M (2005). "Molecular signatures distinguish human central memory from effector memory CD8 T cell subsets". J Immunol 175 (9): 5895-903. PMID 16237082. 

Further reading

• Janeway CA, Jr. et al (2005). Immunobiology., 6th ed., Garland Science. ISBN 978-0-443-07310-6. 

• Cellular and Molecular Immunology (5th Ed.) Abbas AK, and Lichtman, Editor: Saunders, Philadelphia, 2003.