Cells fall on sword to stop Legionnaire's

Like a deadly stowaway, Legionella pneumophila, the bacterium that causes Legionnaire’s disease, (see photo) hides inside cells to evade detection by the immune system. Holed up in sealed vacuoles, the germs multiply, causing fatal pneumonia in up to a quarter of those infected.

But the immune system usually outwits Legionella. In the March issue of the journal Nature Immunology, Associate Professor of Microbial Pathogenesis Craig R. Roy, Ph.D., and colleagues show that immune cells detect Legionella and destroy it by inducing cells to commit suicide.

Roy’s team found that a protein called Birc1e detects any bits of bacteria that escape vacuoles and activates the caspase-1 protease, a master regulator of cell death. Caspase-1 degrades proteins in infected cells, starting a cascade of events that end with the cell’s demise—and the elimination of Legionella.

“Identification of Birc1e and the caspase cascade gives us information about the process of how the body fights off infection by a potentially lethal microbe, as well as possible targets for treatments,” says Roy.