Important insights that explain why our ability to ward off infection declines with age are published in a new research report in the July 2012 issue of the Genetics Society of America’s journal, GENETICS (http://www.genetics.org/). A team of U.S. scientists identified genes responsible for this decline by examining fruit flies – a model organism often used to study human biology in an experimentally tractable system – at different stages of their lives. They found that a completely different set of genes is responsible for warding off infection at middle age than during youth. Many of the genes identified are also present in humans, so this study opens doors to understanding genetic interactions that underlie why older people have more trouble fighting off infections than do younger people.