Secrets of a stowaway bug

When harmful bacteria enter the body, white blood cells known as macrophages engulf them and sequester them in capsules called phagosomes. These capsules then fuse with lysosomes, spheres packed with enzymes that destroy the bacterium.

But some bacteria can survive and continue to cause illness by blocking this process. Scientists have long known that pathogens like Legionella pneumophila, the cause of Legionnaire’s disease, secrete proteins into macrophages, but it has been unclear what those proteins do.

In the June 20 issue of Science, a School of Medicine team led by Craig R. Roy, Ph.D., associate professor of microbial pathogenesis, reported that L. pneumophila proteins known as Anks disrupt the transport of endosomes—vesicles that eventually develop into bacteria-killing lysosomes—along intracellular conduits known as microtubules.

Because L. pneumophila and related bacteria behave somewhat like viruses, in that they inject Ank proteins into cells, Roy says they might be vulnerable to a vaccine that targets Anks, allowing macrophages to do their job.