Australian researchers have defined a new cell type responsible for attacking Legionella pneumophila in the lungs. With this discovery, they have dissected the complex roles of legions of immune cells that interact to destroy the bacterium.

Legionella pneumophila is the bacterium that causes legionnaire’s disease. The bacterium preferentially grows within pond amoebae, but can ‘accidentally’ cause serious lung infections in susceptible humans.

Researchers uncovered a new population of immune cells that was playing a significant role: the monocyte-derived cells (MCs) and showed that MCs responded to Legionella within 24 hours of infection and were present in over 10-fold the numbers of macrophages in the lung by 48 hours after infection.