Analysis of signal-dependent changes in the proteome of Drosophila blood cells during an immune response

Innate immunity is based on the recognition of cell-sur-face molecules of infecting agents. Microbial substances, such as peptidoglycan, lipopolysaccharide, and -1,3-glu-cans, produce functional responses in Drosophila hemo-cytes that contribute to innate immunity. We have used two-dimensional gel electrophoresis and MS to resolve lipopolysaccharide-induced changes in the protein profile of a Drosophila hemocytic cell line. We identified 24 intra-cellular proteins that were up- or down-regulated, or modified, in response to immune challenge. Several pro-teins with predicted immune functions, including lysoso-mal proteases, actin-binding/remodeling proteins, as well as proteins involved in cellular responses to oxidative stress, were affected by the immune assault. Intriguingly, a number of the proteins identified in this study have recently been implicated in phagocytosis in higher ver-tebrates. We suggest that phagocytosis is activated in Drosophila hemocytes by the presence of microbial sub-stances, and that this activation constitutes an evolution-arily conserved arm of innate immunity. In addition, a number of proteins involved in calcium-regulated signal-ing, mRNA processing, and nuclear transport were af-fected, consistent with a possible role in reprogramming of gene expression. In conclusion, the present proteome analysis identified many proteins previously not linked to innate immunity, demonstrating that differential protein profiling of Drosophila hemocytes is a valuable tool for identification of new players in immune-related cellula