What Is Antigen Presentation?

Antigen-presenting cells (APC) refer to a class of immune cells that can take up, process, and present processed antigens to T cells. APC mainly includes monocyte-phagocytic cells, dendritic cells, B cells, Langerhans cells, and endothelial cells, tumor cells, and virus-infected target cells (of which dendritic cells have the strongest antigen-presenting ability).

Antigen presenting cell

Can be divided into full-time APC and non-full-time APC. Full-time APC refers to a type of specialized cells that have the ability to ingest, process, process, present extracellular antigens, activate CD4 + T cells, and induce immune responses. These cells must express MHC-II molecules,

Antigen presenting cell exogenous antigen

After exogenous antigen is phagocytosed or swallowed, it is taken up by APC to form phagosomes, which are fused with lysosomes to form phagolysosomes. Antigens are degraded into small molecule polypeptides by proteolytic enzymes in the acidic environment of phagolysosomes, and the immunogenic ones are called antigenic peptides. After the MHC- molecules synthesized in the endoplasmic reticulum enter the Golgi apparatus, they are carried by secretory vesicles and are fused with phagolysosomes to combine the antigen peptide with MHC- molecules in the vesicles to form antigen peptide-MHC Complex. The complex is expressed on the surface of APC and can be recognized and bound by corresponding CD4 + T cells.

Endogenous antigen

Endogenous antigens refer to antigens synthesized by the cell itself, such as tumor antigens and viral protein antigens. After the endogenous antigen is produced in the cell, it can be degraded into small molecule peptides by the proteasomes existing in the cytoplasm, that is, small molecule polymerized polypeptide bodies (LMP); small molecule peptides and heat shock proteins 70/90 are in the cytoplasm After binding, it is transported to the endoplasmic reticulum via the antigen peptide transporter (TAP), and modified into an immunogenic antigenic peptide through processing; the antigen peptide combines with MHC class I molecules synthesized in the endoplasmic reticulum to form the antigen peptide-MHC class Molecular complex; the latter is transferred into the Golgi apparatus and then transported to the surface of the APC via secretory vesicles for the corresponding CD8 + T cells to recognize and bind.