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**** Function chiefly in the defence against extracellular bacteria.
**** Function chiefly in the defence against extracellular bacteria.
** Therefore, one of the major biological functions of the activation of either TH subset is cytokine-controlled reactive haematopoiesis.
** Therefore, one of the major biological functions of the activation of either TH subset is cytokine-controlled reactive haematopoiesis.
==Cytotoxic T-Cells==
* Viruses are intracellular pathogens that use the host cell machinery for pathogen protein synthesis.
** Viral peptides associate with MHC class I and are expressed on the cell surface.
*** CD8+ cytotoxic T-lymphocytes (CTL) recognise the antigen-MHC complex.
* Cytotoxic T-cells secrete a pattern of cytokines similar to that of TH<sub>1</sub> cells.
** I.e. IFNγ but not IL-2.
*** The IFNγ shifts the balance of the immune response in favour of TH<sub>1</sub> cells.
**** There is therefore an increased level of T-cell proliferation.
***** The initiation of the immune response via CTL leads to the selective proliferation of CTL - enhances the main mechanism of killing of virally-infected cells.
===Killing Mechanism===
* The CTl killing mechanism is initiated by direct CTL-target cell contact.
* The cells involved bind by antigen/MHC class I-TcR interaction.
** This results in the CTL's intracellular granules becoming localised to the area of contact.
*** These granules contain most of the molecules responsible for cytotoxicity.
* Direct cell contact stimulates the release of the granule contents into the area of contact between the two cells.
* The granules contain two groups of cytotoxic molecules.
** Perforin.
*** Structurally related to the [[Complement - WikiBlood|complement]] component, C9.
*** Forms pores in the cell membrane.
** Granzymes.
*** Proteolytic enzymes.
*** Target cell nucleases.
*** Cause programmed cell death.
==T-Cell Activation==
==T-Cell Activation==
[[B cell differentiation - WikiBlood|B Cell Development]]
[[B cell differentiation - WikiBlood|B Cell Development]]
[[Lymphocytes - WikiBlood#Cytotoxic CD8+|Lymphocytes - WikiBlood]]
<big><center>[[Leukopoiesis - WikiBlood|'''BACK TO LEUKOPOIESIS''']]</center></big>
<big><center>[[Leukopoiesis - WikiBlood|'''BACK TO LEUKOPOIESIS''']]</center></big>
<big><center>[[Immunology - WikiBlood|'''BACK TO IMMUNOLOGY''']]</center></big>
<big><center>[[Immunology - WikiBlood|'''BACK TO IMMUNOLOGY''']]</center></big>