Specialization and complementarity in microbial molecule recognition by human myeloid and plasmacytoid dendritic cells.

Following encounter with pathogens, dendritic cells (DC) mature and migrate from peripheral tissues to the T cell areas of secondary lymphoid organs, where they produce regulatory cytokines and prime naive T lymphocytes. We investigated in two subsets of human peripheral blood DC the expression of Toll-like receptors (TLR1 through TLR9) and the regulation of chemokine receptors and cytokine production in response to different maturation stimuli. Myeloid DC express all TLR except TLR7 and TLR9, which are selectively expressed by plasmacytoid DC. Myeloid and plasmacytoid DC respond to pathogen-associated molecular patterns according to their TLR expression. In response to the appropriate stimuli both DC types up-regulate CCR7, a receptor that drives DC migration to the T cell areas. Type I IFN was produced only by plasmacytoid DC and at early time points after stimulation. Furthermore, its production was elicited by some of the maturation stimuli tested. These results reveal a remarkable specialization and complementarity in microbial molecule recognition as well as a flexibility in effector function among myeloid and plasmacytoid DC.