What is Antigen processing and presentation?

Antigen processing and presentation is the process by which antigens are taken up by antigen-presenting cells (APCs), processed into smaller fragments, and then presented on the cell surface in a form that can be recognized by T cells. This process is essential for the adaptive immune response to occur.

The first step in antigen processing is the uptake of antigens by APCs. APCs can be either professional APCs, such as dendritic cells, macrophages, and B cells, or non-professional APCs, such as epithelial cells and endothelial cells. Professional APCs are more efficient at taking up and processing antigens than non-professional APCs.

Once the antigen has been taken up by the APC, it is processed into smaller fragments by a variety of enzymes, including proteases, cathepsins, and lysosomal enzymes. These fragments are then complexed with major histocompatibility complex (MHC) molecules and transported to the cell surface.

MHC molecules are cell surface proteins that are expressed by all cells in the body. Each individual has a unique set of MHC molecules, which are inherited from their parents. MHC molecules bind to specific T cell receptors (TCRs) on the surface of T cells. When an antigen is presented on the cell surface in complex with an MHC molecule, it can be recognized by a TCR on a T cell. This interaction triggers the activation of the T cell, which can then proliferate and differentiate into effector T cells.

Effector T cells can then kill infected cells, produce cytokines to help other immune cells fight the infection, or help to memory T cells that can provide long-term immunity to the antigen.

Antigen processing and presentation is a complex and essential process for the adaptive immune response. It allows the immune system to recognize and respond to a wide variety of pathogens.