Antigen Processing and Presentation | Part II | The Endocytic Pathway
Antigen processing and presentation is when a foreign protein antigen is degraded into peptides and becomes MHC associated peptide fragments on a infected cell surface for display to T cells. This is because , in order for a foreign protein antigen to be recognised by T cells, it must be degraded into small antigenic peptides which forms complexes with Class I or Class II MHC molecule. T cells on their own cannot recognise the antigen alone, it must be presented on MHC molecule.
When an Antigen Presenting Cell (APC) such as macrophages, dendritic cells or B cells, takes up the exogenous antigen by phagocytosis or endocytosis, It will degrade it into peptides within the compartments of the endocytic processing pathway and makes antigen Class II MHC complex which would display antigen to T helper cells.
Have you ever wondered how antigen presenting cell (APC) does not get confused between whether to present Ag on MHC I or MHC II since it can express both? Let’s find out about it and more in this video.
@ 00:14 introduction, @ 09:51 endocytic pathway – overview, @ 13:26 explanation of how the APC knows on which MHC molecule to display the Ag @ 17:50 explanation of endocytic pathway.
Binding of antigenic peptide to MHC II molecule in exchange of CLIP (Class II Associated Invariant Chain Peptide) requires a non classical MHC II molecule called HLA-DM.
Here’s the first part Antigen Processing and Presentation | Part I | The Cytosolic Pathway?