Antigen uptake and presentation by dendritic leukocytes.

Dendritic leukocytes are required for the initiation of T cell mediated immune responses. These cells, in different stages of maturation, are distributed throughout lymphoid and most non-lymphoid tissues. Immature cells may be localized predominantly within non-lymphoid tissues, and are responsible for endocytosis and processing of antigens. Inflammatory mediators are thought to promote their maturation and migration, via lymph and blood, into secondary lymphoid tissues. Here the mature cells present foreign peptide-MHC complexes to T cells, and deliver unique signals for T cell activation (immunostimulation). Within the thymus, however, these cells may be important for inducing T cell tolerance to self peptide-MHC complexes.