Air pollution may do more than aggravate heart problems. It also can shut down the immune system over time, according to a new study.

Pollutants in ozone, long associated with pulmonary and cardiovascular problems and deaths, can also affect the lungs and the rest of the body, making it more susceptible to illnesses, including the entry of bacteria and other foreign invaders in the body, Duke University Medical Center researchers found.

Pulmonary researchers used mice to study the effects of ozone and unhealthy pollutants on the immune system and found they enhance lung injuries in response to bacteria and cell death in immune system cells, which are used to fight off foreign toxins in the body.

The researchers had mice breathe room air with levels of ozone that an active human would inhale on an unhealthy ozone-level day.

“Small amounts of inhaled foreign material can be relatively harmless, since they stimulate an appropriate innate immune response that protects the lungs,” said Dr. John Hollingsworth, a pulmonologist and lead author of the study, in a news release.

“However, it appears that ozone causes the innate immune system to overreact, killing key immune system cells, and possibly making the lungs more susceptible to subsequent invaders, such as bacteria," said Hollingsworth.

Future studies out of Duke will focus on how the pollutants interfere with system-wide immune system responses.