Mature dendritic cells use endocytic receptors to capture and present antigens

In response to inflammatory stimuli, dendritic cells (DCs) trigger maturation, a terminal differentiation program required to initiate T lymphocyte responses. A hallmark of maturation is downregulation of endocytosis, widely assumed to restrict the ability of mature DCs to capture and present antigens encountered after the initial stimulus. We found that mature DCs continue to internalize antigens, especially by receptor-mediated endocytosis and phagocytosis. These antigens were transported to lysosomal compartments, loaded onto MHCII, and presented efficiently to T cells, both in vitro and in vivo. Antigens were also presented on MHCI with high efficiency. While mature DCs down-regulate macropinocytosis, they capture antigens via endocytic receptors and, in principle, remain able to initiate immune responses during the course of an infection.