Activation of Toll-like receptor 2 on human dendritic cells triggers induction of IL-12, but not IL-10

Mammalian Toll-like receptors (TLRs) are required for cell activation by ba cterial lipoproteins (bLP) and LPS, Stimulation of monocytes with bLP and L PS results in a TLR-dependent induction of immunomodulatory genes leading t o the production of pro-inflammatory cytokines. In this paper, we compared the expression and response of TLRs on monocytes and dendritic cells (DC). TLR2, but not TLR4, was detected on peripheral blood monocytes and DC, in l ymphoid tissue CD1a(+) DC as well as on in vitro monocyte-derived DC. Upon stimulation with bLP or LPS, monocytes produced IL-12 and IL-10 at similar levels, whereas monocyte-derived DC produced comparable levels of IL-12, bu t little IL-10. Greater than 90% of the bLP-induced production of IL-12 was blocked by anti-TLR2 mAb. Thus, DC express TLR2 and activation of this rec eptor by bLP provides an innate mechanism by which microbial pathogens pref erentially activate cell-mediated immunity.