Human Langerhans cells selectively activated via Toll-like receptor 2 agonists acquire migratory and CD4+T cell stimulatory capacity.

In epidermal Langerhans cells (LCs), the expression pattern and the functions of TLRs have been poorly characterized. By using mAb, we show that LCs from human skin express TLR1, -2, -5, -6, and -9, the cognate receptors for detection of specific bacteria-derived molecules. As compared with other TLR agonists, LCs acquired a more matured phenotype when activated by specific bacterial or synthetic TLR2 agonists. In addition, monocyte-derived Langerin(+)/CD1c(+)LCs (CD1c(+)MoLCs) secreted higher amounts of IL-6 and TNF-alpha by stimulation via TLR2 than by stimulation via TLR3, -4, -5, -8, and -9. In contrast to MoLCs, dendritic cells, generated from the same donor monocytes, were activated by agonists of TLRs other than TLR2 as well. Lipopeptides triggering TLR2 induced IL-1R-associated kinase-1 phosphorylation and migration toward the chemokines CCL19 and CCL21 in epidermal LCs and CD1c(+)MoLCs. Up-regulation of CD86, CD83, and CCR7, TNF-alpha and IL-6, and NF-kappaB activation and proliferation of CD4(+)T cells could be inhibited TLR2-specific blockage using antibodies prior to TLR2 activation. Application of anti-TLR1, anti-TLR6, and anti-TLR2 indicated an exclusive role of TLR2 in IL-6 induction in human LCs. Collectively, our results show that TLR2 expressed by LCs mediates inflammatory responses to lipopeptides, which implicates a central role in sensing pathogens in human skin.