Development of accessory phenotype and function during the differentiation of monocyte-derived dendritic cells

Dendritic cells (DCs) are professional antigen-presenting cells (APCs), and classical DCs, such as Langerhans cells (LCs) or interdigitating DCs (IDCs) are known to be the most potent stimulators of T lymphocytes. Earlier, several groups described the generation of DCs from monocytes, starting with peripheral blood mononuclear cells (PBMCs), adherent cells or magnetic bead-purified CD14+ cells. Although modifications of the original protocols have already been described, some questions relevant to clinical application and basic studies have not yet been addressed. Granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL4) appear to be necessary, but are not sufficient for the differentiation of monocyte-derived dendritic cells (MoDCs), as indicated by the failure to generate such cells under serum-free conditions. Using adherence purified monocytes, we first investigated the amount of GM-CSF and IL4 required for the differentiation of DCs. Consecutive kinetic studies during the differentiation period were designed to demonstrate how monocytes acquire the phenotype and function of DCs. The results showed that small amounts of GM-CSF and IL4 were required to generate MoDC which acquired their phenotype and function within 4 days. IL13 may substitute for IL4, whereas IL10, TNF alpha or IFN gamma inhibited the generation of MoDCs.