SAGE library screening reveals ILT7 as a specific plasmacytoid dendritic cell marker that regulates type I IFN production

Plasmacytoid dendritic cells (pDCs) link innate to acquired immune responses by producing high levels of type I IFN upon infection. In order to identify the specific genes that control pDC, we compared serial analysis of gene expression libraries from human pDCs, herpes simplex virus- stimulated pDCs and monocytes. We found that Ig-like transcript ILT7 is specifically expressed on pDC cell surfaces and is down-regulated when pDC mature in response to viral or bacterial 15 stimulation. ILT7 expression on the cell surface required association with the FceRIg adaptor molecule. Although treatment with one anti-ILT7-specific mAb suppressed type I IFN production in response to cytosine-phosphate-guanosice (CpG) stimulation, another anti-ILT7 mAb up-regulated type I IFN production. We conclude that ILT7 is a key regulator of human pDC function.