Antigen presentation
![](http://upload.wikimedia.org/wikipedia/commons/thumb/4/4d/Antigen_presentation.svg/240px-Antigen_presentation.svg.png)
Antigen presentation is a vital
Presentation of intracellular antigens: Class I
![](http://upload.wikimedia.org/wikipedia/commons/thumb/d/d7/MHC_Class_I_processing.svg/220px-MHC_Class_I_processing.svg.png)
Cytotoxic T cells (also known as Tc, killer T cell, or cytotoxic T-lymphocyte (CTL)) express CD8 co-receptors and are a population of T cells that are specialized for inducing programmed cell death of other cells. Cytotoxic T cells regularly patrol all body cells to maintain the organismal homeostasis. Whenever they encounter signs of disease, caused for example by the presence of viruses or intracellular bacteria or a transformed tumor cell, they initiate processes to destroy the potentially harmful cell.[1] All nucleated cells in the body (along with platelets) display class I major histocompatibility complex (MHC-I molecules). Antigens generated endogenously within these cells are bound to MHC-I molecules and presented on the cell surface. This antigen presentation pathway enables the immune system to detect transformed or infected cells displaying peptides from modified-self (mutated) or foreign proteins.[5][6]
In the presentation process, these proteins are mainly degraded into small peptides by cytosolic proteases in the proteasome, but there are also other cytoplasmic proteolytic pathways. Then, peptides are distributed to the endoplasmic reticulum (ER) via the action of heat shock proteins and the transporter associated with antigen processing (TAP) which translocates the cytosolic peptides into the ER lumen in an ATP-dependent transport mechanism. There are several ER chaperones involved in MHC-I assembly, such as calnexin, calreticulin, Erp57, protein disulfide isomerase (PDI),[7] and tapasin. Specifically, the complex of TAP, tapasin, MHS Class 1, ERp57, and calreticulin is called the peptide-loading complex (PLC).[8] Peptides are loaded to MHC-I peptide binding groove between two alpha helices at the bottom of the α1 and α2 domains of the MHC class I molecule. After releasing from tapasin, peptide-MHC-I complexes (pMHC-I) exit the ER and are transported to the cell surface by exocytic vesicles.[9][10]
Naïve anti-viral
Cross-presentation is a special case in which MHC-I molecules are able to present extracellular antigens, usually displayed only by MHC-II molecules. This ability appears in several APCs, mainly plasmacytoid dendritic cells in tissues that stimulate CD8+ T cells directly. This process is essential when APCs are not directly infected, triggering local antiviral and anti-tumor immune responses immediately without trafficking the APCs in the local lymph nodes.[6]
Presentation of extracellular antigens: Class II
![](http://upload.wikimedia.org/wikipedia/commons/thumb/f/f0/MHC2.svg/220px-MHC2.svg.png)
Antigens from the extracellular space and sometimes also endogenous ones,
APCs usually internalise exogenous antigens by
MHC-II molecules are transported from the ER to the MHC class II loading compartment together with the protein
APCs undergo a process of maturation while migrating, via
Alternative pathway of endogenous antigen processing and presentation over MHC-II molecules exists in
Presentation of native intact antigens to B cells
B-cell receptors on the surface of B cells bind to intact native and undigested antigens of a structural nature, rather than to a linear sequence of a peptide which has been digested into small fragments and presented by MHC molecules. Large complexes of intact antigen are presented in lymph nodes to B cells by follicular dendritic cells in the form of immune complexes. Some APCs expressing comparatively lower levels of lysosomal enzymes are thus less likely to digest the antigen they have captured before presenting it to B cells.[14][15]
See also
References
- ^ a b Janeway Jr CA, Travers P, Walport M, Shlomchik MJ (2001-01-01). "Chapter 5 Antigen Presentation to T Lymphocytes". Immunobiology: The Immune System in Health and Disease. 5th edition. Garland Science.
- PMID 27060633.
- ^ Janeway Jr CA, Travers P, Walport M, Shlomchik MJ (2001-01-01). "The major histocompatibility complex and its functions". Immunobiology: The Immune System in Health and Disease (5th ed.). Garland Science.
- PMID 34065814.
- PMID 14511229.
- ^ S2CID 460907.
- ^ "Antigen Processing and Presentation | British Society for Immunology". www.immunology.org. Retrieved 2021-11-27.
- PMID 28228754.
- ^ ISBN 9788189781095.
- S2CID 234948691, retrieved 2021-12-02
- PMID 26107264.
- ^ PMID 27018930.
- PMID 11298823.
- S2CID 2413048.
- PMID 21283653.
External links
- ImmPort - Gene summaries, ontologies, pathways, protein/protein interactions and more for genes involved in antigen processing and presentation
- antigen+presentation at the U.S. National Library of Medicine Medical Subject Headings (MeSH)