The vapor from e-cigarettes may boost the production of inflammatory chemicals in the lungs, while disabling key cellular defenders against infection, a new study suggests.

In a series of laboratory experiments, researchers found that e-cigarette vapor impairs the activity of cells called macrophages, which normally remove allergens, bacteria and other particles that have made their way into the lungs, according to the report published in Thorax.

For the cultured cells, exposure to e-cigarette vapor induced many of the same changes in lung macrophages that have been seen in cigarette smokers and patients with COPD, the researchers note.

The concern is that long-term vaping might lead to breathing problems. Earlier studies looked just at the effect on cells of the liquid that goes into an e-cigarette rather than at the vaporized chemicals.

To determine what effect vaporizing might have, researchers at the University of Birmingham in the U.K. extracted macrophages from lung tissue samples from eight non-smokers who had never had asthma or COPD. One third of those cells were exposed to e-cigarette fluid, another third to vaporized liquid and the remaining third to nothing.

After 24 hours, the researchers saw cells dying in the groups exposed to fluid and vaporized e-cigarette liquid. But the vaporized liquid killed cells at lower doses than the unvaporized liquid.

The researchers also noted that when macrophages were exposed to doses too low to kill, the cells spewed out 50-fold higher amounts of oxygen-free radicals, the “rust” of the biological world, compared to unexposed cells. The cells exposed to vaped liquid also secreted a host of inflammation-inducing molecules.

Cells exposed to vaporized liquid also were not as good at battling bacteria, suggesting that e-cigarette users’ lungs might have more trouble fighting off infections.