Fig. 1

The MHC class I antigen processing and presentation pathway. The classical MHC class I antigen processing and presentation pathway is divided into four major steps: (1) the generation of antigenic peptides by proteasomal degradation, (2) the ATP-dependent peptide transport from the cytosol in the ER via the TAP heterodimer, (3) the assembly of MHC class I HC, β₂-m and peptides, which is assisted by various chaperones (e.g., Erp57, tapasin and calreticulin), and (4) the export and presentation of the trimeric MHC/peptide complex.