Studies in mice demonstrate that signals from the bacteria that harmlessly — and often beneficially — inhabit the human gastrointestinal tract boost the immune system’s ability to kill a major respiratory pathogen, Klebsiella pneumoniae, according to a paper published online ahead of print in the journal Infection and Immunity.

The research is yet another example of how important these “commensal” bacteria are to human health and physiology, said author Thomas B. Clarke, of Imperial College London, UK.

“Alveolar macrophages are the lungs’ first line of defense against bacterial infection,” says Clarke. “I found that the production of reactive oxygen molecules by these cells was enhanced by these signals from the commensal bacteria.”