antigen processing, the process that prepares antigens for presentation to T cells. Exogenous antigens are endocytosed by antigen-presenting cells and degraded in endosomes/lysosomes. The peptides that have formed due to this process bind to major histocompatibility complex class II molecules and are then transported to the cell surface for presentation to CD4+ T cells. Endogenous proteins, including viral proteins in virus-infected cells, are degraded in the proteasome, and the resulting peptides are loaded on major histocompatibility complex class I molecules. The complex will be transported to the cell surface for presentation to CD8+ T cells.
