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| [[Image:TH1-2.jpg|thumb|right|200px|TH1 and 2 selection is influenced by infection - B. Catchpole, RVC 2008]] | | [[Image:TH1-2.jpg|thumb|right|200px|TH1 and 2 selection is influenced by infection - B. Catchpole, RVC 2008]] |
| ==Introduction== | | ==Introduction== |
| [[T cells|T cells]] are long lived and are involved in '''cell mediated immunity'''. Functionally they are divided by the expression of CD4<sup>+</sup> or CD8<sup>+</sup> markers. CD4<sup>+</sup> T helper cells recognise antigens bound to MHC II complexes and are involved with the control of intracellular and extracellular pathogens; they can interact with CD8<sup>+</sup>, NK and dendritic cells or with B cells. Cytotoxic CD8<sup>+</sup> T cells recognise the MHC I complex and destroy infected or neoplastic cells. | | [[T cells|T cells]] are long lived and are involved in '''cell mediated immunity'''. Functionally they are divided by the expression of CD4<sup>+</sup> or CD8<sup>+</sup> markers. CD4<sup>+</sup> T helper cells recognise antigens bound to MHC II complexes and are involved with the control of intracellular and extracellular pathogens; they can interact with CD8<sup>+</sup>, NK and dendritic cells or with B cells. Cytotoxic CD8<sup>+</sup> T cells recognise the MHC I complex and destroy infected or neoplastic cells. |
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− | Within the blood and lymphoid organs the majority of T cells are antigen-naive T cells; only a small proportion are memory T cells. Naive T cells have yet to encounter antigen and can only be activated by antigen that is presented by dendritic cells. After initial antigenic activation, naïve T-cells develop into an intermediate stage cell called the TH<sub>0</sub> cell which can then be activated by any antigen-presenting cell, e.g. Dendritic cells, [[Macrophages|macrophages]] or [[B cells]]. | + | <br /> |
− | | + | Within the blood and lymphoid organs the majority of T cells are antigen-naive T cells; only a small proportion are memory T cells. Naive T cells have yet to encounter antigen and can only be activated by antigen that is presented by dendritic cells. After initial antigenic activation, naïve T-cells develop into an intermediate stage cell called the T<sub>H</sub>0 cell which can then be activated by any antigen-presenting cell, e.g. Dendritic cells, [[Macrophages|macrophages]] or [[B cells]]. |
− | The T<sub>H</sub>0 cells have the capacity to differentiate into T<sub>H</sub>1, T<sub>H</sub>2 cells and a very recently described subtype T<sub>H</sub>17 cells. The type of cell that develops depends on the antigen presenting cell type. [[Macrophages|Macrophages]] cause the T<sub>H</sub>0 cell to develop into a T<sub>H</sub>1 cell induced by IL-12 production following macrophage-antigen interaction. B cells cause the T<sub>H</sub>0 cell to develop into a T<sub>H</sub>2 cell induced by IL-10 production following B cell-antigen interaction. On antigenic stimulation the T<sub>H</sub>1 or T<sub>H</sub>2 cells become activated, undergo clonal expansion and secrete a range of different cytokines. The third most recently described subset, T<sub>H</sub>17, form in the presence of IL-6 and TGF-β which are produced in the prescence of infection, and by either of the Antigen Presenting Cells (APCs). | + | <br /> |
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| + | The T<sub>H</sub>0 cells have the capacity to differentiate into T<sub>H</sub>1, T<sub>H</sub>2 cells and a very recently described subtype T<sub>H</sub>17 cells. The type of cell that develops depends on the antigen presenting cell type. [[Macrophages|Macrophages]] cause the T<sub>H</sub>0 cell to develop into a T<sub>H</sub>1 cell induced by IL-12 production following macrophage-antigen interaction. B cells cause the T<sub>H</sub>0 cell to develop into a T<sub>H</sub>2 cell induced by IL-10 production following B cell-antigen interaction. On antigenic stimulation the T<sub>H</sub>1 or T<sub>H</sub>2 cells become activated, undergo clonal expansion and secrete a range of different cytokines. The third most recently described subset, T<sub>H</sub>17, form in the presence of IL-6 and TGF-β which are produced in the prescence of infection, and by either of the Antigen Presenting Cells (APCs). The importance of CD4<sup>+</sup> T<sub>H</sub> cells is very clear in immunity. An example of a disease that targets CD4<sup>+</sup> T cells is the Human Immunodeficieny Viruses (HIV) and Simian Immunodeficieny Viruses (SIV) which, when the CD4<sup>+</sup> T cells are overwhelmed, causes Advanced Immunodeficiency Syndrome (AIDS). |
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| For any one cell the cytokine-secreting activation state is short-lived, lasting between 4 - 40 hours. After this time these cells either die or mature into the long-lived memory cells. The proliferation of [[T cells]] continues until the presentation of antigen ceases. | | For any one cell the cytokine-secreting activation state is short-lived, lasting between 4 - 40 hours. After this time these cells either die or mature into the long-lived memory cells. The proliferation of [[T cells]] continues until the presentation of antigen ceases. |
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| **Helminths (SEA, ES 62) | | **Helminths (SEA, ES 62) |
| *Endogenous | | *Endogenous |
− | **Inflammatory mediators (IL-1/TNF-a, hsp, FcR) | + | **Inflammatory mediators (IL-1/TNFα, hsp, FcR) |
| **Immune cells (CD40L, CD47, FasL) | | **Immune cells (CD40L, CD47, FasL) |
| [[Image:Maturation of Dendritic Cells.jpg|thumb|right|300px|Maturation of Dendritic Cells - Copyright Prof Dirk Werling DrMedVet PhD MRCVS]] | | [[Image:Maturation of Dendritic Cells.jpg|thumb|right|300px|Maturation of Dendritic Cells - Copyright Prof Dirk Werling DrMedVet PhD MRCVS]] |
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| ''Still under investigation'' | | ''Still under investigation'' |
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− | The T<sub>H</sub>17 cells which form when T<sub>H</sub>0 cells are challenged with IL-6 and TGF-β produce a number of cytokines that enhance the innate immune response. The [[Cytokines|cytokines]] produced enhance the extravasation and chemotaxis of [[Neutrophils|neutrophils]] to the site of infection, in the aim of combating extracellular bacteria. These cytokines include: | + | The T<sub>H</sub>17 cells form when T<sub>H</sub>0 cells are challenged with IL-6 and TGF-β to produce a number of cytokines that enhance the innate immune response <ref>{{citation|initiallast = Korn|initialfirst = T|2last = Bettelli|2first = E|3last = Oukka|3first = M|finallast = Kuchroo|finalfirst = V.K|year = 2009|jtitle = IL-17 and Th17 Cells|jor = Annual Reviews of Immunology|vol = 27|range = 485-517}}</ref>. The [[Cytokines|cytokines]] produced enhance the extravasation and chemotaxis of [[Neutrophils|neutrophils]] to the site of infection, in the aim of combating extracellular bacteria. These cytokines include: |
| *IL-17 | | *IL-17 |
| *IL-17F | | *IL-17F |
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| TH cells secrete cytokines for only a short period after they have been activated; the range of cytokines that T<sub>H</sub> cells secrete after activation chiefly determines their function. Different T-helper cell subpopulations (T<sub>H</sub>1, T<sub>H</sub>2 and T<sub>H</sub>17 cells) secrete different sets of cytokines. | | TH cells secrete cytokines for only a short period after they have been activated; the range of cytokines that T<sub>H</sub> cells secrete after activation chiefly determines their function. Different T-helper cell subpopulations (T<sub>H</sub>1, T<sub>H</sub>2 and T<sub>H</sub>17 cells) secrete different sets of cytokines. |
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| + | ==References== |
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| <br><br> | | <br><br> |
| {{Jim Bee 2007}} | | {{Jim Bee 2007}} |
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| + | {{OpenPages}} |
| [[Category:Lymphocytes|E]] | | [[Category:Lymphocytes|E]] |
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| [[Category:Adaptive Immune System|C]] | | [[Category:Adaptive Immune System|C]] |