T cell antigen processing and presentation

Definition

Target type: biologicalprocess

The process in which a T cell expresses antigen (peptide or lipid) on its cell surface in association with an MHC protein complex. [GOC:add, PMID:11417857, PMID:15120183]

T cell antigen processing and presentation is a critical step in the adaptive immune response, enabling the recognition and destruction of pathogens and infected cells. This process involves the following steps:

1. **Antigen Uptake:**
- Antigen-presenting cells (APCs), such as dendritic cells, macrophages, and B cells, engulf pathogens or cellular debris through phagocytosis, macropinocytosis, or receptor-mediated endocytosis.

2. **Antigen Processing:**
- Within the APC, the internalized antigen is processed into smaller peptide fragments. This processing occurs in two main pathways:
- **MHC class I pathway:** Processes intracellular antigens, such as viral proteins, and presents them to cytotoxic CD8+ T cells.
- **MHC class II pathway:** Processes extracellular antigens, such as bacterial proteins, and presents them to helper CD4+ T cells.

3. **MHC Class I Pathway:**
- **Proteasome Degradation:** The antigen is degraded by the proteasome, a multi-protein complex, into short peptides of 8-10 amino acids.
- **TAP Transport:** These peptides are transported from the cytoplasm into the endoplasmic reticulum (ER) by the transporter associated with antigen processing (TAP).
- **Loading onto MHC I:** In the ER, peptides bind to MHC class I molecules, which are also assembled in the ER. The MHC I molecule-peptide complex is then transported to the cell surface.

4. **MHC Class II Pathway:**
- **Endocytosis:** The antigen is taken up into endosomes.
- **Endosome Maturation:** Endosomes mature into lysosomes, where the antigen is degraded by lysosomal enzymes.
- **MHC II Loading:** Invariant chain (Ii) blocks the binding of peptides to MHC class II molecules in the ER. Ii is degraded in the endosome, allowing the processed peptides to bind to MHC class II.
- **MHC II Presentation:** The MHC class II-peptide complex is then transported to the cell surface.

5. **T Cell Recognition:**
- The MHC-peptide complex on the APC surface is recognized by the T cell receptor (TCR) on a specific T cell. The TCR recognizes both the peptide and the MHC molecule.
- **CD4+ T cells** recognize MHC class II-peptide complexes, while **CD8+ T cells** recognize MHC class I-peptide complexes.

6. **T Cell Activation:**
- Recognition of the MHC-peptide complex activates the T cell, leading to the release of cytokines, proliferation, and differentiation into effector T cells.
- **CD4+ T cells** differentiate into helper T cells, which provide signals to other immune cells, such as B cells.
- **CD8+ T cells** differentiate into cytotoxic T cells, which kill infected or cancerous cells.

7. **Immune Response:**
- The activation of T cells results in the elimination of the pathogen or infected cell, and the establishment of immunological memory for future encounters with the same antigen.'"

Proteins (2)

Compounds (16)