LPS-induced immune response in Drosophila.

The study of the regulation of the inducible synthesis of antimicrobial peptides in Drosophila melanogaster has established this insect as a powerful model in which to study innate immunity. In particular, the molecular characterization of the regulatory pathway controlling the antifungal peptide drosomycin has revealed the importance of Toll receptors in innate immunity. We report here that injection of LPS into flies induces an immune response, suggesting that LPS receptors are used in Drosophila to detect Gram-negative bacteria infection. We have identified in the recently sequenced genome of Drosophila eight genes coding for Toll-like receptors in addition to Toll, which may function as LPS receptors. However, overexpression of a selection of these genes in tissue-culture cells does not result in up-regulation of the antibacterial peptide genes. These results are discussed in light of the recent data from genetic screens aimed at identifying the genes controlling the antibacterial response in Drosophila.