Dendritic cell origins: Puzzles and paradoxes

In the present review, a series of studies on the origins of dendritic cell s of mice and humans are summarized. Several subsets of mature dendritic ce lls found in vivo are described and these may correspond to distinct lineag es. There is evidence that some dendritic cells are myeloid-derived and tha t others are lymphoid-derived. The different ways of generating dendritic c ells are examined and an attempt to reconcile the differences seen using mo use and human culture models is made. The particular case of Langerhans cel ls is discussed and an historical overview of the biology of the plasmacyto id T cells, which may represent a distinct 'lymphoid-related' dendritic cel l lineage, is given. It is concluded that three or four different pathways lead to the development of different subtypes of dendritic cells.