CD1c-Expression by Monocytes - Implications for the Use of Commercial CD1c+ Dendritic Cell Isolation Kits

Conventional dendritic cells (cDCs) comprise a heterogeneous population of cells that are important regulators of immunity and homeostasis. CD1c(+) cDCs are present in human blood and tissues, and found to efficiently activate naive CD4(+) T cells. While CD1c is thought to specifically identify this subset of human cDCs, we show here that also classical and intermediate monocytes express CD1c. Accordingly, the commercial CD1c (BDCA-1) Dendritic Cell Isolation Kit isolates two distinct cell populations from blood: CD1c(+) CD14 cDCs and CD1c(+) CD14(+) monocytes. CD1c(+) cDCs and CD1c(+) monocytes exhibited strikingly different properties, including their differential regulation of surface marker expression, their levels of cytokine production, and their ability to stimulate naive CD4(+) T cells. These results demonstrate that a commercial CD1c (BDCA-1) Dendritic Cell Isolation Kit isolates two functionally different cell populations, which has important implications for the interpretation of previously generated data using this kit to characterize CD1c(+) cDCs.