Toll signaling pathways in the innate immune response.

The Toll signaling pathway, which is required for the establishment of the dorsal-ventral axis in Drosophila embryos, plays an important role in the response of larval and adult Drosophila to microbial infections. Recent genetic evidence has shown that a mammalian Toll-like receptor, mouse Tlr4, is the signal transducing receptor activated by bacterial lipopolysaccharide. Thus, Toll-like receptors appear to detect a variety of microbial components and to trigger a defensive reaction in both Drosophila and mammals. Genetic data from both Drosophila and mice have defined components required for activation of Toll-like receptors and for the downstream pathways activated by the Toll-like receptors.