Antigen processing is a crucial biological process in the immune system that involves the breaking down and presentation of antigens to immune cells such as T cells. Antigens are molecules that can trigger an immune response, and they can be derived from pathogens, cancer cells, or other foreign substances. During antigen processing, antigen-presenting cells such as dendritic cells, macrophages, and B cells internalize antigens and degrade them into smaller fragments. These fragments are then presented on the cell surface bound to major histocompatibility complex (MHC) molecules. This presentation allows T cells to recognize the antigen and initiate an immune response. Antigen processing is essential for the recognition and elimination of pathogens and harmful cells by the immune system. Understanding the mechanisms and regulation of antigen processing is crucial for developing vaccines, immunotherapies, and treatments for immune-related diseases.