antigen processing and presentation of endogenous antigen

Definition

Target type: biologicalprocess

The process in which an antigen-presenting cell expresses antigen (peptide or lipid) of endogenous origin on its cell surface in association with an MHC protein complex. [GOC:add, ISBN:0781735149, PMID:15771591, PMID:15928678]

Endogenous antigen processing and presentation is a crucial process in the adaptive immune system, enabling the recognition and elimination of infected or cancerous cells. This intricate pathway involves several steps:

1. **Protein Degradation:** Inside the cell, proteins, including viral proteins or tumor antigens, are constantly degraded through the ubiquitin-proteasome system. This system marks proteins for destruction by attaching ubiquitin molecules, leading to their breakdown into smaller peptides.

2. **Transport to the Endoplasmic Reticulum (ER):** The resulting peptides are transported into the ER, a cellular organelle responsible for protein folding and modification.

3. **Loading onto MHC Class I Molecules:** Within the ER, the peptides encounter MHC class I molecules, which are specialized cell surface proteins responsible for presenting antigens to CD8+ T cells. These MHC class I molecules are composed of two polypeptide chains: a heavy chain and a light chain (β2-microglobulin). The heavy chain has a groove where peptides can bind.

4. **Peptide Editing and Quality Control:** The ER chaperone protein tapasin assists in the loading of peptides onto MHC class I molecules. This process involves peptide editing, ensuring that only peptides of appropriate length and sequence bind. The ER also serves as a quality control checkpoint, allowing only properly folded MHC class I-peptide complexes to exit.

5. **Transport to the Cell Surface:** The loaded MHC class I-peptide complexes are then transported from the ER through the Golgi apparatus, where they undergo further modifications, to the cell surface.

6. **Antigen Presentation to CD8+ T Cells:** Once on the cell surface, the MHC class I-peptide complexes are displayed to CD8+ T cells, which express the CD8 co-receptor that recognizes MHC class I molecules. If the presented peptide is recognized as foreign or abnormal, it triggers the activation of the CD8+ T cell, leading to the elimination of the infected or cancerous cell.

This complex process ensures that cells can efficiently present intracellular antigens to the immune system, enabling the detection and elimination of threats before they can spread. The antigen processing and presentation pathway is essential for maintaining immune surveillance and protecting the body from disease.'
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Proteins (1)

Compounds (2)