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Main Pathways and Endogenous/Exogenous Antigens – Antigen Processing and Presentation

by Peter Delves, PhD
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    So how are these peptides actually generated? Well they’re generated by antigen processing. And that antigen can come from two locations. The action can be within a cell, in that case we refer to it as endogenous antigen. And processing of antigens that are within the cell; endogenous antigens produces peptides that are eight to nine amino acids long. And this is a necessary length for presentation by MHC Class I because the peptide binding groove in MHC Class I specifically binds peptides of this length. In contrast, antigen that is present outside of cells, exogenous antigen that is then taken up for example by a phagocytic cell. These are processed into peptides that are rather longer, approximately 15 amino acids, can be 20 or so. But typically around about 15 amino acids, sometimes a little bit shorter but you know on average around about 15 amino acids long for presentation by MHC Class II. Let’s look now at the actual enzymes and structures that are involved in this processing of protein antigen. So here we have an example of an endogenous antigen. It could be a protein from a virus that’s infecting a cell for example. The first thing that happens is that this protein becomes ubiquitinated. It has a tag, an ubiquitine tag added to it. This causes it to be fed into a structure that is called the proteasome. Now all cells have proteasomes in them and they are complexes of enzymes that form a tube-like structure and proteins are fed in at one end and come out the other end being chopped up. And it’s a way in which cells get rid of sort of worn out proteins. But when cells become infected with viruses or other pathogens, they actually modify the constitutive proteasome. They add...

    About the Lecture

    The lecture Main Pathways and Endogenous/Exogenous Antigens – Antigen Processing and Presentation by Peter Delves, PhD is from the course Adaptive Immune System. It contains the following chapters:

    • The Main Pathways of Antigen Processing
    • Endogenous Antigen Processing and Presentation
    • Exogenous Antigen Processing and Presentation

    Included Quiz Questions

    1. Invariant chain (Ii)
    2. TAP1
    3. Erp57
    4. CLIP
    5. Tapasin
    1. Endogenous creates peptides that are 8-9 amino acids long for MHC Class I Exogenous creates peptides that are approximately 15 amino acids long for MHC Class II
    2. Endogenous creates peptides that are 8-9 amino acids long for MHC Class II Exogenous creates peptides that are approximately 15 amino acids long for MHC Class I
    3. Endogenous creates peptides that are 15 amino acids long for MHC Class I Exogenous creates peptides that are approximately 8-9 amino acids long for MHC Class II
    4. Endogenous creates peptides that are 15 amino acids long for MHC Class II Exogenous creates peptides that are approximately 8-9 amino acids long for MHC Class I
    5. Endogenous creates peptides that are 8-9 amino acids long for MHC Class I and MHC Class II Exogenous creates peptides that are approximately 15 amino acids long for MHC Class II
    1. ...it marks the protein so that the proteasome can recognize it.
    2. ...it inactivates the protein.
    3. ...it allows the cell to recognize the protein as an antigen.
    4. ...it directly generates peptides.
    5. ...it prepares the protein for presentation on the MHC Class II molecule.
    1. Immunoproteasomes break down proteins into peptides of a specific length
    2. Immunoproteasomes are always present in every cell
    3. Immunoproteasomes do not recognize proteins that have been ubiquitinated
    4. Immunoproteasomes do not recognize self proteins
    5. Immunoproteasomes can only process viral proteins
    1. Transport processed peptides out of the cytosol, through the endoplasmic reticulum, to be presented by the MHC Class I molecule
    2. Transport peptides from the cytoplasm to the immunoproteasome
    3. Form the nonpolymorphic region of the MHC Class I molecule
    4. Break down proteins that have been ubiquitinated
    5. Process proteins into peptides with the correct amount of amino acids

    Author of lecture Main Pathways and Endogenous/Exogenous Antigens – Antigen Processing and Presentation

     Peter Delves, PhD

    Peter Delves, PhD


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