A novel mode of induction of the humoral innate immune response in <i>Drosophila</i> larvae

Abstract

<i>Drosophila</i> adults have been utilized as a genetically tractable model organism to decipher the molecular mechanisms of humoral innate immune responses. In an effort to promote the utility of <i>Drosophila</i> larvae as an additional model system, in this study, we describe a novel aspect of an induction mechanism for innate immunity in these larvae. By using a fine tungsten needle created for manipulating semi-conductor devices, larvae were subjected to septic injury. However, although Toll pathway mutants were susceptible to infection with Gram-positive bacteria as had been shown for <i>Drosophila</i> adults, microbe clearance was not affected in the mutants. In addition, <i>Drosophila</i> larvae were found to be sensitive to mechanical stimuli with respect to the activation of a sterile humoral response. In particular, pinching with forceps to a degree that might cause minor damage to larval tissues could induce the expression of the antifungal peptide gene <i>Drosomycin</i>; notably, this induction was partially independent of the Toll and immune deficiency pathways. We therefore propose that <i>Drosophila</i> larvae might serve as a useful model to analyze the infectious and non-infectious inflammation that underlies various inflammatory diseases such as ischemia, atherosclerosis and cancer.