English: HLA-DM is synthesized in the endoplasmic reticulum (ER) of antigen presenting cells (APCs), and transported in endosomes while binding to HLA-DO. The HLA-DM containing endosome fuses with an MHC class II containing endosome, which then subsequently fuses with an antigen-containgin endosome. Once in the presence of antigen, HLA-DM associates with MHC class II and releases CLIP form the peptide binding groove. HLA-DO degrades, and HLA-DM facilitates peptide exchange to ensure high affinity binding between the MHC class II and it's peptide. The late endosome then fuses with the plasma membrane to present MHC class II + peptide on its surface. This can be recognized by other immune cells and initiate a response.