The immunoglobulin-like transcript (ILT) 7 is a surface molecule selectively expressed by human plasmacytoid dendritic cells (pDCs). ILT7 cross-linking suppresses pDC activation and type I interferon (IFN-I) secretion following Toll-like receptors (TLR)7/9 engagement. The bone marrow stromal cell antigen 2 (BST2, aka HM1.24, tetherin or CD317) is expressed by different cell types upon exposure to IFN-I and is a natural ligand for ILT7. Here we show that ILT7 expression decreased spontaneously in pDCs upon in vitro culture, which correlates with pDC differentiation measured as increased side scatter properties and CCR7 expression. TLR7/9 Ligands , as well as HIV, induced BST2 upregulation on all tested cell types except T cells, which required TCR stimulation to respond to TLR9L-induced IFN-I. IFN-γ, IL-4, IL-10 and TNF-α had only marginal effects on BST2 expression in blood leukocytes compared to TLR9L. Pre-incubation with ILT7-crosslinking Ab inhibited IFN-I production in PBMCs treated with TLR7/9L or HIV, whereas BST2 blockade did not affect IFN-I responses even when BST2 upregulation was further boosted with TCR agonists or immunoregulatory cytokines. Our data indicate that BST2-mediated ILT7 cross-linking may act as a homeostatic regulatory mechanism on immature circulating pDC, rather than a negative feedback for activated mature pDCs which have downregulated ILT7.