Control of MHC II–peptide endocytosis and MHC II synthesis in immature, maturing, and mature DCs. Schematic representation of MHC II trafficking in immature (top left), maturing (early, top right; late, bottom left), and mature (bottom right) DCs. See “Discussion” for details. The triangles represent self antigens endocytosed by DCs in the steady state (open) or foreign antigens captured in the presence of inflammatory stimuli (closed). The width of the arrows represents the relative flow of MHC II molecules between compartments; the size of the compartments represents the relative amount of MHC II contained in each major subcellular location at each stage of maturation.