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. Author manuscript; available in PMC: 2009 Feb 1.
Published in final edited form as: Cytokine Growth Factor Rev. 2008 Feb;19(1):41–52. doi: 10.1016/j.cytogfr.2007.10.004

Fig. 1.

Fig. 1

Dendritic cells are composed of subsets. DC progenitors originate from bone marrow CD34+FLT3+ hematopoietic progenitor cells (HPCs). A myeloid pathway generates both Langerhans cells (LCs), found in stratified epithelia such as the skin, and interstitial (int)DCs, found in all other tissues. It also generates mDCs circulating in the blood. Upon inflammation monocytes can yield mDCs. Another pathway generates plasmacytoid DCs (pDCs), which secrete large amounts of IFN-α/β after viral infection. Activated (mature) mDCs and pDCs traffic to secondary lymphoid organs either via afferent lymphatics (mDCs) or blood (pDCs). Langerhans DCs home to cell zones while interstitial DCs home to follicles consistent with their functional specialization, i.e. generation of cellular (Langerhans DCs) and humoral (interstitial DCs) immunity, respectively. The origin of resident lymph node DCs remains to be determined.