Changes

* CD4 binds MHC class II - [[T_cells#Helper_CD4.2B|CD4+ T-cells]] recognise antigen only in association with [[Major Histocompatability Complexes#MHC II|MHC class II]].  

* CD4 binds MHC class II - [[T_cells#Helper_CD4.2B|CD4+ T-cells]] recognise antigen only in association with [[Major Histocompatability Complexes#MHC II|MHC class II]].  

* CD8 binds MHC class I - [[T_cells#Cytotoxic_CD8.2B|CD8+ T-cells]] recognise antigen only in association with [[Major Histocompatability Complexes#MHC I|MHC class I]].  

* CD8 binds MHC class I - [[T_cells#Cytotoxic_CD8.2B|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''' is the interaction of the TcR with the antigenic peptide/[[Major Histocompatability Complexes|MHC]] complex on the antigen presenting cell.  

*** The interaction of the TcR with the antigenic peptide/[[Major Histocompatability Complexes|MHC]] complex on the antigen presenting cell.  

*'''Signal 2''' is the interaction of CD28 on the T cells with its ligand, CD80, on the antigen-presenting cell.  

** '''Signal 2'''

*** The interaction of CD28 on the [[Lymphocytes#T cells|T cells]] with its ligand, CD80, on the antigen-presenting cell.  

**** APC expression of CD80 only occurs after:

**** APC expression of CD80 only occurs after:

***** The engagement of pattern recognition or Fc receptors.  

***** The engagement of pattern recognition or Fc receptors.