Final answer:
Intracellular antigens are processed in the cytosol by the proteasome enzyme complex and brought into the endoplasmic reticulum by the TAP system, where they interact with class I MHC molecules. The antigen-MHC complex is then transported to the cell surface.
Step-by-step explanation:
Intracellular antigens, which are typical of viruses and certain intracellular parasites and bacteria, are processed in the cytosol by an enzyme complex called the proteasome. The proteasome degrades the intracellular antigens into short peptide fragments. After degradation, the fragments are brought into the endoplasmic reticulum by the transporter associated with antigen processing (TAP) system, where they interact with class I MHC molecules. Eventually, the antigen-MHC complex is transported to the cell surface by a transport vesicle.