Human astrocytes express a limited repertoire of Toll-like re-ceptor (TLR) family members including TLR1-4, which are expressed on the cell surface. Also, TLR3 but not TLR4 acti-vation on astrocytes induces expression of several factors involved in neuroprotection and down-regulation of inflam-mation rather than in the onset of traditional pro-inflamma-tory reactions. The notion that astrocyte TLR may thus play a role not only in host defense but also in tissue repair responses prompted us to examine the possibility that en-dogenous TLR agonists could be expressed in the human central nervous system to regulate the apparently dual astrocyte functions during trauma or inflammation. As a potential source of endogenous agonists, a cDNA library derived from several human brain tumor cell lines was used. Gene pools of this library were transfected into COS-7 cells and the expression products were screened for their ability to induce TLR activation in human primary astrocytes. The screening resulted in the identification of soluble CD14. By using a panel of TLR-transfected HEK293 cells, we found that signaling by soluble CD14 was TLR2 dependent. More-over, the CD14-triggered TLR2-mediated response in astro-cytes lead to the production of CXCL8, IL-6, and IL12p40, whereas typical TLR-induced pro-inflammatory cytokines, like TNF-a and IL-1b, were not produced at detectable levels. In conclusion, our data indicate that apart from its well-known ability to act as a co-receptor for TLR-dependent signaling by peptidoglycans or LPS, soluble CD14 can also act as a direct agonist for TLR2. V V C 2007 Wiley-Liss, Inc.