antigen processing and presentation of exogenous peptide antigen via MHC class I

Definition

Target type: biologicalprocess

The process in which an antigen-presenting cell expresses a peptide antigen of exogenous origin on its cell surface in association with an MHC class I protein complex. The peptide antigen is typically, but not always, processed from a whole protein. Class I here refers to classical class I molecules. [GOC:add, ISBN:0781735149, PMID:15771591]

The process of antigen processing and presentation of exogenous peptide antigen via MHC class I, also known as cross-presentation, is a crucial mechanism by which the immune system recognizes and responds to pathogens. Here's a detailed explanation:

1. **Antigen Uptake**: Exogenous antigens, such as those from viruses, bacteria, or parasites, enter the cell through various pathways:
* **Endocytosis**: The cell engulfs the antigen through specialized membrane invaginations forming vesicles.
* **Phagocytosis**: Immune cells like macrophages and dendritic cells engulf large particles like bacteria.
* **Macropinocytosis**: Cells take up fluid and dissolved solutes, potentially containing antigens.

2. **Antigen Processing**: Once inside the cell, the antigen undergoes processing to generate peptides suitable for MHC class I presentation:
* **Degradation**: The antigen is broken down into smaller peptides by proteasomes, multi-protein complexes that degrade proteins.
* **TAP Transport**: The peptides generated by the proteasome are transported into the endoplasmic reticulum (ER) via the transporter associated with antigen processing (TAP) complex.

3. **MHC Class I Loading**: In the ER, the peptides interact with MHC class I molecules:
* **Assembly**: MHC class I molecules, composed of α and β2 microglobulin chains, assemble in the ER.
* **Peptide Loading**: The peptide binds to the MHC class I molecule in a groove within the α chain.
* **Chaperones**: Chaperone proteins like calnexin and calreticulin assist in the folding and peptide loading of MHC class I molecules.

4. **MHC Class I Trafficking**: The peptide-loaded MHC class I complex exits the ER and is transported to the cell surface via the Golgi apparatus:
* **Vesicle Transport**: The complex travels within transport vesicles through the Golgi.
* **Quality Control**: The Golgi apparatus ensures proper folding and peptide loading before further transport.

5. **Presentation on the Cell Surface**: The MHC class I complex is displayed on the cell surface, making the peptide accessible to CD8+ T cells:
* **Recognition**: CD8+ T cells, also known as cytotoxic T lymphocytes (CTLs), possess T cell receptors (TCRs) that recognize specific peptides presented by MHC class I molecules.
* **Activation**: Upon TCR engagement, the CD8+ T cell becomes activated, leading to the production of effector molecules that eliminate infected or cancerous cells.

This process is critical for the immune system to recognize and eliminate pathogens that reside within cells. The ability to present exogenous antigens via MHC class I allows the immune system to effectively target a wide range of threats.'
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Proteins (3)

Compounds (14)