The Intricate Process of Antigen Degradation and Loading onto MHC Molecules by APCs: A Crucial Step in Immune Response

Antigens are degraded into _____ after being captured by APCs before being loaded onto MHC molecules

Antigens are degraded into peptide fragments after being captured by Antigen-Presenting Cells (APCs) before being loaded onto Major Histocompatibility Complex (MHC) molecules

Antigens are degraded into peptide fragments after being captured by Antigen-Presenting Cells (APCs) before being loaded onto Major Histocompatibility Complex (MHC) molecules.

APCs, such as dendritic cells, macrophages, and B cells, play a crucial role in the immune response by capturing foreign antigens and presenting them to T-cells. When an APC engulfs an antigen, it forms an intracellular compartment called a phagosome. Within the phagosome, the antigen is broken down into smaller peptide fragments through a process known as antigen processing.

Antigen processing involves the actions of proteolytic enzymes, including proteasomes and lysosomal enzymes, which cleave the antigen into smaller fragments. Proteasomes primarily generate peptide fragments from proteins that have been marked for degradation by the attachment of a small protein called ubiquitin. These peptide fragments are further fragmented by proteases within the phagosome or lysosome.

The resulting peptide fragments are then transported from the phagosome or lysosome into the endoplasmic reticulum by the transporter associated with antigen processing (TAP) molecules. Within the endoplasmic reticulum, the peptide fragments associate with MHC molecules, which are specialized proteins that bind to and present antigens on the surface of cells.

The loading of the peptide fragments onto MHC molecules is a highly specific process and involves the binding of the peptides to a specific binding groove on the MHC molecule. This binding is guided by the amino acid sequence and structure of the peptide fragments. The MHC molecules loaded with antigenic peptides are then transported to the cell surface, where they are recognized by T-cells.

So, in summary, antigens are degraded into peptide fragments by proteolytic enzymes in APCs before being loaded onto MHC molecules. This process is essential for the immune system to effectively present antigens to T-cells and initiate an appropriate immune response.

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