Author, Donkey, Bureaucrats, Administrators
53,803
edits
Changes
no edit summary
{{OpenPagesTop}}
[[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.
<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 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 />
<br />
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).
<br />
<br />
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.
<br><br>
<br><br>
{{Jim Bee 2007}}
{{Jim Bee 2007}}
{{OpenPages}}
[[Category:Lymphocytes|E]]
[[Category:Lymphocytes|E]]
[[Category:Adaptive Immune System|C]]
[[Category:Adaptive Immune System|C]]