Mixed-Up Microflora

The relationship between an animal host and the complex mixture of microbes it carries in its gut is a delicate one, and the exact role the host immune system plays in maintaining commensal homeostasis remains unclear. Ryu et al . (see the Perspective by Silverman and Paquette) examined the expression of antimicrobial proteins in the gut of the fruit fly, Drosophila melanogaster . Although the key immune transcriptional regulator nuclear factor κB (NF-κB) was chronically activated in the flies by indigenous gut microflora, only a subset of NF-κB-regulated antimicrobial genes was actually expressed because of transcriptional repression exerted by the intestinal homeobox gene Caudal . Disruption of Caudal expression resulted in the expression of a different subset of antimicrobial peptides, as well as a dramatic change in the composition of the intestinal microflora that led to the apoptosis of intestinal epithelial cells and loss of host viability. J.-H. Ryu, S.-H. Kim, H.-Y. Lee, J. Y. Bai, Y.-D. Nam, J.-W. Bae, D. G. Lee, S. C. Shin, E.-M. Ha, W.-J. Lee, Innate immune homeostasis by the homeobox gene Caudal and commensal-gut mutualism in Drosophila . Science 319 , 777-782 (2008). [Abstract][Full Text] N. Silverman, N. Paquette, The right resident bugs. Science 319 , 734-735 (2008). [Abstract][Full Text]