Figure 1.

Antigen presentation on MHC-II molecule. Extracellular antigens are endocytosed or phagocytosed, and intracellular antigens are translocated to the late-endosome or the lysosome via autophagosome- or LAMP-2A- mediated autophagy. Then these antigens are degraded by asparaginyl endopeptidase and cathepsin. MHC-II is synthesized in ER and mainly pooled at the plasma membrane as MHC-II-Ii chain complex. When the complex translocates from the ER or the plasma membrane to the acidic compartment, Ii chain is degraded into CLIP and driven out by interaction with H2-M. Afterward, antigen peptides bind to the MHC-II and the peptide-MHC-II complex exports to the cell surface.