Lungs enlist immune cells to fight infections in capillaries

ON TRACK Neutrophils (red) crawl along the walls of capillaries in a mouse lung (tracks shown in blue). In mice deficient in a key protein, these immune cells couldn’t move as far (left) as those in mice that had the protein (right).

Immune cells in the lungs provide a rapid counterattack to bloodstream infections, a new study in mice finds. This surprising discovery pegs the lungs as a major pillar in the body’s defense during these dangerous infections, the researchers say.

“No one would have guessed the lung would provide such an immediate and strong host defense system,” says Bryan Yipp, an immunologist at the University of Calgary in Canada. Yipp and his colleagues report their findings online April 28 in Science Immunology.

The work may offer ways to target and adjust our own immune defense system for infections, says Yipp. “Currently, we only try to kill the bacteria, but we are running out of antibiotics because of resistance.”

The research uncovers some of the mechanisms that drive the rapid activation of neutrophils, says immunologist Andrew Gelman of Washington University School of Medicine in St. Louis. “This is critical in removing bacteria from sequestered spaces in the lung,” he says.

Generally, clearing bacteria out of the bloodstream falls to macrophages that reside in the liver and the spleen. But macrophages aren’t found in vessels of the lungs. So the lungs’ blood vessel network gives pathogens a place to hide and escape the body’s usual removal efforts.