Immune response of Drosophila melanogaster to infection with the flagellate parasite Crithidia spp.

Insects are able to recognize invading microorganisms and to mount an immun e response to bacterial and fungal infections. Recently, the fruitfly Droso phila melanogaster has emerged as a promising invertebrate model to investi gate innate immunity because of its well-characterized genetics. Insects ar e also Vectors of numerous parasites which can trigger an immune response. We have investigated the interaction of Drosophila melanogaster with the fl agellate protozoan Crithidia spp. We show that a per os parasitic infection triggers the synthesis of several antimicrobial peptides. By reverse phase HPLC and mass spectrometry, peptides were shown to be present in the hemol ymph and not in the gut tissue, suggesting the presence of immune messenger s between the site of the infection, namely the gut, and the fat body, the main site of synthesis for antimicrobial peptides. Interestingly, we have i dentified one molecule which is specifically induced in the hemolymph after infection with Crithidia, but not with bacteria, suggesting that Drosophil a can discriminate between pathogens. When flagellates were injected into t he hemolymph, a low synthesis of antimicrobial peptides was observed togeth er with phagocytosis of parasites by circulating hemocytes. The data presen ted here suggest that Drosophila-Crithidia spp. represents an interesting m odel to study host defense against protozoan parasites. (C) 2001 Elsevier S cience Ltd. All rights reserved.