Changes

*Viral proteins are broken down to peptides by the proteasome and transferred to the endoplasmic reticulum via TAP (Transporters associated with Antigen Processing) molecules

*Viral proteins are broken down to peptides by the proteasome and transferred to the endoplasmic reticulum via TAP (Transporters associated with Antigen Processing) molecules

*In the ER peptides are processed with empty MHC I molecules and exported to the cell surface for presentation

*In the ER peptides are processed with empty MHC I molecules and exported to the cell surface for presentation

* MHC class I molecules present these to the T-cell receptors of [[Lymphocytes - WikiBlood#Cytotoxic CD8+|'''CD8+ T-cells''']]

* MHC class I molecules present these to the T-cell receptors of [[Lymphocytes#Cytotoxic CD8+|'''CD8+ T-cells''']]

==MHC II==

==MHC II==

===Structure===

===Structure===

* MHC class II is expressed mainly on [[Macrophages - WikiBlood|macrophages]], [[T cell differentiation - WikiBlood#Antigen Presentation by Dendritic Cells|dendritic cells]] and [[Lymphocytes - WikiBlood#B Cells|B-lymphocytes]]

* MHC class II is expressed mainly on [[Macrophages - WikiBlood|macrophages]], [[T cell differentiation - WikiBlood#Antigen Presentation by Dendritic Cells|dendritic cells]] and [[Lymphocytes#B Cells|B-lymphocytes]]

* MHC class II consists of membrane-associated α and β chains

* MHC class II consists of membrane-associated α and β chains

**  Each chain is a transmembrane glycoprotein

**  Each chain is a transmembrane glycoprotein

***The invariant chain is digested, leaving a CLIP peptide in the binding groove

***The invariant chain is digested, leaving a CLIP peptide in the binding groove

***Foreign antigen then replaces the CLIP peptide

***Foreign antigen then replaces the CLIP peptide

*The MHC II-antigen complex is then secreted to the cell surface for presentation to [[Lymphocytes - WikiBlood#Helper CD4+|CD4+ T-cells]]

*The MHC II-antigen complex is then secreted to the cell surface for presentation to [[Lymphocytes#Helper CD4+|CD4+ T-cells]]

=Interaction of MHC With Antigen=

=Interaction of MHC With Antigen=

** These MHC amino acids associate with amino acids near the ends of the peptides

** These MHC amino acids associate with amino acids near the ends of the peptides

*** The intervening stretch of peptide folds into a helix within the groove

*** The intervening stretch of peptide folds into a helix within the groove

*** Is the target for [[Lymphocytes - WikiBlood#T Cells|T cell]] receptor recognition

*** Is the target for [[Lymphocytes#T Cells|T cell]] receptor recognition

*MHC molecules have the capacity to bind to trillions of different peptides

*MHC molecules have the capacity to bind to trillions of different peptides

**Adopt a flexible '''floppy''' conformation until a peptide binds

**Adopt a flexible '''floppy''' conformation until a peptide binds

==TCR-MHC Interaction==

==TCR-MHC Interaction==

[[Image:MHC T cell Interaction.jpg|thumb|right|150px|Molecules of T lymphocyte recognition - Copyright Prof Dirk Werling DrMedVet PhD MRCVS]]

[[Image:MHC T cell Interaction.jpg|thumb|right|150px|Molecules of T lymphocyte recognition - Copyright Prof Dirk Werling DrMedVet PhD MRCVS]]

* Only peptide associated with self-MHC will interact with and activate [[Lymphocytes - WikiBlood#T Cells|T cells]]

* Only peptide associated with self-MHC will interact with and activate [[Lymphocytes#T Cells|T cells]]

** [[Lymphocytes - WikiBlood#T Cells|T cells]] cannot be activated by a peptide on a foreign cell

** [[Lymphocytes#T Cells|T cells]] cannot be activated by a peptide on a foreign cell

** [[Lymphocytes - WikiBlood#T Cells|T cells]] will react against foreign MHC molecules

** [[Lymphocytes#T Cells|T cells]] will react against foreign MHC molecules

*** This is the basis of graft rejection

*** This is the basis of graft rejection