The Drosophila TNF ortholog eiger is required in the fat body for a robust immune response

Eiger is the sole TNF family member found in Drosophila melanogaster. This signaling molecule is induced during infection and is required for an appropriate immune response to many microbes; however, little is known about where eiger is produced. Here, we show that eiger is made in the fly's fat body during a Salmonella typhimurium infection. Using tissue-specific knockdown, we found that eiger expression in the fat body is required for all of the phenotypes we observed in eiger null mutant flies. This includes reduced melanization, altered antimicrobial peptide expression and reduced feeding rates. The effect of eiger on feeding rates alone may account for the entire phenotype seen in eiger mutants infected with S. typhimurium.