Insect immunity: Inducible antibacterial activity in Drosophila

Adult Drosophila melanogaster were found to produce an inducible antibacterial activity as a response to an injection (vaccination) of the non-pathogenic bacterium, Enterobacter cloacae. Vaccinated flies showed an increased survival time after a second injection with an insect-pathogenic bacterium, Pseudomonas aeruginosa. This immune response was blocked by cycloheximide, an inhibitor of eukaryotic protein synthesis, a fact which indicates de novo synthesis of the antibacterial factor operating in vivo. Electrophoretic mobility at pH 4 in combination with antibacterial assay and immunological cross reactivity was used to demonstrate attacin-like factors in hemolymph and cecropin-like factors in cell-free extracts of whole flies. Extract of flies also contained lysozyme but this enzyme could not be induced. Some active material is pre-existing and can be released by treatment of whole flies with ultrasound (sonication) or microwaves. Compared to wild-type flies, a mutant strain deficient in leucine aminopeptidase showed much higher values for antibacterial activity and lysozyme.