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==T-Cell Activation==
 
==T-Cell Activation==
 
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T cells function only after recent activation by an antigen.
* [[Lymphocytes#T cells|T cells]] function only after recent activation by antigen.
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* CD4 binds [[Major Histocompatability Complexes#MHC II|MHC class II]] - [[Lymphocytes#Helper CD4+|CD4+ T-cells]] recognise antigen only in association with [[Major Histocompatability Complexes#MHC II|MHC class II]].
* CD4 binds [[Major Histocompatability Complexes#MHC II|MHC class II]].
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* CD8 binds [[Major Histocompatability Complexes#MHC I|MHC class I]] - [[Lymphocytes#Cytotoxic CD8+|CD8+ T-cells]] recognise antigen only in association with [[Major Histocompatability Complexes#MHC I|MHC class I]].  
** [[Lymphocytes#Helper CD4+|CD4+ T-cells]] therefore recognise antigen only in association with [[Major Histocompatability Complexes#MHC II|MHC class II]]  
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* CD8 binds [[Major Histocompatability Complexes#MHC I|MHC class I]].
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** [[Lymphocytes#Cytotoxic CD8+|CD8+ T-cells]] recognise antigen only in association with [[Major Histocompatability Complexes#MHC I|MHC class I]].  
   
* Activation of [[Lymphocytes#T cells|T cells]] requires two distinct signals.  
 
* Activation of [[Lymphocytes#T cells|T cells]] requires two distinct signals.  
 
** '''Signal 1'''
 
** '''Signal 1'''
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