T memory cell

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T memory cells or memory T cells are a subgroup ( subpopulation ) of the T-lymphocytes . They have the function of an immunological memory and improve the protection of an individual in the event of renewed infection with the same pathogen (reinfection). As former T-helper cells (T H1 or T H2 ), the memory cells have stored the specific immune reaction that has been learned . When the organism is confronted with the same antigen again , the memory T cells trigger a fast and effective immune response. In some cases, they are then transformed again into T helper cells.

history

The existence of memory cells could be assumed by epidemiological observations during a measles epidemic in the 19th century on the Faroe Islands . At that time, after a single virus exposure and obviously no renewed exposure in the intervening period, protection from new diseases was found in the residents who were originally infected with measles, even after 30 years or more.

properties

After the adaptive immune system has been stimulated by an antigen , the specific T cells multiply 10 to 100 times. Of these, some can mediate a faster and more efficient secondary response upon renewed contact with the same antigen. This memory function can be taken over by CD4 -positive and CD8 -positive T memory cells.

From naive T cells by differentiation resulting effector cells usually have a short life time and usually die after a immune response by activation-induced cell death ( AICD , Eng. Activation-induced cell death ), a process of programmed cell death . Various mechanisms are involved in this program, including the provision of Fas -mediated signals (CD95), intracellular pro-apoptotic molecules and the loss of growth factors .

Less than 5% of all effector cells are excluded from this programmed cell death of the T memory cells formed during the specific immune response. The cellular and molecular influences that determine that as a result of activation, naive T cells differentiate into short-lived effector cells on the one hand and long-lived memory cells on the other, are only partially known. The following models for the differentiation of T memory cells are discussed:

  • A model assumes the existence of two different naive T-cell subsets, one of which has the potential to mature into T-effector cells, while the other can only develop into T-memory cells. Convincing experimental data to support this model are currently lacking.
  • In another model, different signals when naive T cells are activated determine whether an effector cell or a T memory cell is formed. Costimulator- mediated signals convey whether a short-lived effector cell should arise as a result of strong activation or a long-lived memory cell after weak signals. This model is supported by animal experiments.
  • In the third model, a subgroup of activated effector cells survives as T memory cells because they either receive signals that record this differentiation or because they evade the signals that would otherwise initiate programmed cell death. It remains to be seen whether these additional stimuli act randomly ( stochastically ) on the T effector cells or only act on certain cells through selective provision. Animal experiment results are compatible with this model.

Types

As with naive T cells, memory T cells are divided into CD4 and CD8 positive cells. In addition, a distinction is made between at least two functionally different groups within these two types. These are (Engl. For an effector-memory T cells effector memory T cells , T EM ) and central to other memory T cells (Engl. Central memory T cells , T CM ). Both groups can occur in both CD4 and CD8 positive memory T cells. The effector memory T cells are reactivated upon renewed contact with the antigen and, through several divisions, provide many functional effector cells. The central memory T cells, on the other hand, rest in the secondary lymphatic organs and initially have no effector function at the focus of infection. However, once the antigen reappears, they can easily be activated to develop into effector cells. The division of labor between effector memory T cells and central memory T cells is similar to that between plasma cells and memory B cells.

  • Human effector memory T cells are phenotypically characterized by the fact that they do not express CCR7 and usually not CD62L , two markers that are typically expressed on naive T cells. Effector memory T cells can be activated particularly quickly by their antigen and then secrete IFN-γ , IL-4 , and IL-5 within a few hours .
  • Central memory T cells have, in addition to the memory T cell marker CD45R0 (naive T cells express CD45RA), also CCR7 and CD62L. These cells are more easily activated than naïve T cells and require less costimulation to be activated. They upregulate the expression of CD40L on their cell surface, which makes them easier to activate by dendritic cells or B cells . After activation of the T-cell receptor , these cells mainly produce interleukin-2 , after an initial phase of reproduction they differentiate into effector cells, which also produce IFN-γ (with T H 1) or IL-4 (with T H 2).

literature

  • GA Holländer: Immunology, basics for clinics and practice . 1st edition. Elsevier, Munich 2006, ISBN 3-437-21301-6 .
  • MJ Owen, JR Lamb: Immune Recognition . Thieme, Stuttgart 1991, ISBN 3-13-754101-8 .
  • Nicole Menche, Bernd Guzek, Hubert Hasel, Herbert Renz-Polster: Biology, Anatomy, Physiology . 6th edition. Munich 2007, ISBN 978-3-437-26801-4 .

Individual evidence

  1. ↑ RD Michalek, JC Rathmell: The metabolic life and times of a T-cell. In: Immunol Rev . (2010), Volume 236, pp. 190-202. PMID 20636818 ; PMC 2983473 (free full text).
  2. ^ KK McKinstry, TM Strutt, SL Swain: Hallmarks of CD4 T cell immunity against influenza. In: J Intern Med. (2011), Volume 269 (5), pp. 507-518. doi: 10.1111 / j.1365-2796.2011.02367.x . PMID 21362069 ; PMC 3395075 (free full text).
  3. ^ R. Arens, SP Schoenberger: Plasticity in programming of effector and memory CD8 T-cell formation. In: Immunol Rev. (2010), Volume 235 (1), pp. 190-205. PMID 20536564 ; PMC 2937176 (free full text).
  4. ^ Haven Emerson: Panum on Measles: Observations Made During the Epidemic of Measles on the Faroe Islands in the Year 1846. In: Am J Public Health Nations Health. 1940, Volume 30, Number 10, pp. 1245-1246. (Translation of an article by Peter Ludwig Panum from 1938 from Danish) PMC 1530953 (free full text)
  5. ↑ a b c Federica Sallusto, Jens Geginat, Antonio Lanzavecchia : Central Memory and Effector Memory T cell Substets: Function, Generation, and Maintenance. In: Annu Rev Immunol . (2004). Volume 22, pp. 745-763.