Transcriptional and functional characterization of dendritic cell differentiation induced by CD137 ligand reverse signaling in human monocytes

The contribution of monocyte-derived dendritic cells (DC) to an immune response is essential for the elimination of pathogens. In vitro DC can be generated by treatment of monocytes with GM-CSF + IL-4 but it is unknown what stimuli induce the differentiation of monocytes to DC in vivo. CD137L-DC are human monocyte-derived DC that are generated by CD137 ligand (CD137L) signaling. Since CD137 is only expressed at sites of inflammation it would be a suitable signal for the induction of monocyte-derived DC. Here we report on gene expression analysis of CD137L-DC, immature and mature classical DC, monocytes and macrophages which indicates that CD137L-DC have a gene signature that is most similar to that of classical DC. Additionally, CD137L-DC signature genes are highly enriched in monocyte-derived DC which were isolated from sites of inflammation. Also cell surface marker expression and cytokine secretion of CD137L-DC are highly similar to that of inflammatory monocyte-derived DC. CD137L-DC express high levels of adhesion molecules, display strong attachment and employ the adhesion molecule ALCAM to stimulate T cell proliferation. This study identifies a physiological stimulus for the generation of monocyte-derived DC in vivo. A total of 30 expression profiles were obtained, on 6 APC subtypes from 5 different donors