Diagram depicting the multiple dendritic cell-lymphocyte interactions that take place in the immune cascade following antigen processing and presentation by DCs. Dendritic cell activation of NK T cells through self ligands (not shown) and IL-12 results in IFN-γ release and subsequent activation of CD4+ and CD8+ T cells. CD4 and CD8 T cell receptors (TCR) interact with peptide-MHC II and I complexes, respectively. CD40L-CD40 interactions between CD4+ T cells and a DC and CD28-B7 interactions between CD8+ T cells and a DC are critical costimulatory interactions that must occur for appropriate T-cell signaling and immune responsiveness.

Schematic of dendritic cell antigen processing and presentation via distinct MHC-I and MHC-II targeted pathways. Foreign antigens are sampled from the environment via dendritic cell phagocytosis or pinocytosis. Once vacuolized, antigen-containing vesicles are directed down one of two MHC pathways that result in cell surface presentation. A) Antigen containing vesicle encounters endoplastmic reticulum-phagosome. Antigen is retro-translocated into the cytoplasm via Sec 61 where proteosome complexes mediate peptide degradation. The resultant epitopes are translocated back into the ER-phagosome via the transporter-associated protein (TAP), where they are loaded onto MHC-I complexes and extruded for membrane integration and antigen presentation on the cell surface. B) Antigen-containing vesicle encounters lysosome which cleaves peptides using acid proteases. MHC-II complexes formed within the ER and subsequently processed and extruded from the Golgi apparatus are transported to peptide containing endosomes for antigen loading.