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===Function===
 
===Function===
* MHC class II molecules bind antigenic peptides and present them to TCR on CD4+ T-cells
+
*MHC II presents '''exogenous''' (that is, derived from the ECF) peptides
* The antigen-binding groove is larger and more open than that of MHC class I
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*Endocytosed antigen interacts with MHC II in the cytoplasm to form a complex:
** MHC II can therefore interact with larger peptides
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**Antigen is endoycotsed from the ECF
 +
**Lysosomes fuse with primary endosomes to digest the antigen to peptides
 +
**MHC II is meanwhile being produced by the endoplasmic reticulum, along with an invariant chain chaperone
 +
**These pathways (endoytotic and secretory) merge to allow interaction between the antigen and MHC II:
 +
***The invariant chain is digested, leaving a CLIP peptide in the binding groove
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***Foreign antigen then replaces the CLIP peptide
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*The MHC II-antigen complex is then secreted to the cell surface for presentation to [[Lymphocytes - WikiBlood#Helper CD4+|CD4+ T-cells]]
 
* MHC class II are present on those cells that have antigen-processing ability
 
* MHC class II are present on those cells that have antigen-processing ability
** Interact with antigenic peptides originating from an extracellular source
  −
* After synthesis, MHC class II molecules are transported into special endosomes
  −
** These endosomes fuse with lysosomes that contain the digested remnants of phagocytosed microorganisms
  −
*** The peptides from the lysosome interact with the MHC class II molecules
  −
**** The peptide-MHC class II complex gets transported to the cell surface
      
=Interaction of MHC With Antigen=
 
=Interaction of MHC With Antigen=
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