The cell biology of antigen presentation in dendritic cells

Dendritic cells are the most efficient antigen-presenting cells. They take up antigens and pathogens, generate MHC-peptide complexes, migrate from the sites of antigen acquisition to secondary lymphoid organs and, finally, th ey physically interact with and stimulate T lymphocytes. Indeed, dendritic cells are the only antigen-presenting cells that induce the activation of r esting T cells, both in vitro and in vivo. Thus, dendritic cells initiate a daptive immune responses and determine tolerance. To do so, dendritic cells have developed unique membrane transport pathways. The molecular mechanism s responsible for the control of antigen uptake and processing, for the gen eration of MHC-peptide complexes and for their transport to the cell surfac e have been partially unraveled in the past two years.