The lung tissue of people with chronic obstructive pulmonary disease contains triple the sootlike particle buildup found in similar tissue in smokers’ lungs, a recent analysis finds.

The study found that COPD patients’ alveolar macrophages — a type of lung cell that removes dust, particles and microorganisms from the lungs — contain more carbon than those of smokers. The carbon-containing alveolar macrophages in COPD patients’ lungs were also larger than macrophages without visible carbon, the study found.

Published in ERJ Open Research, the study looked at carbon deposits in the cells. Alveolar macrophages are an important part of the immune system, activating other immune defense cells to protect the body from inhaled invaders. People with COPD have inflamed airways and more alveolar macrophages than healthy people.

Researchers looked at lung tissue from 28 COPD patients and 15 smokers who underwent surgery for suspected or confirmed lung cancer, measuring alveolar macrophages against those of smoker controls.

People with COPD had more than three times the carbon in their alveolar macrophages than smokers, with carbon-containing cells enlarged compared to those without carbon.

The carbon buildup was linked to potential inflammation and worse lung function in COPD patients, the researchers write.

If the immune response of those with COPD is impaired, they note, COPD patients could be more susceptible to bacterial infections that exacerbate the condition.

The study does not prove what caused the changes in the COPD patients’ lung tissue. Those with COPD may be less able to clear carbon from their lungs, the researchers write, or perhaps those with a reduced ability to clear carbon are likelier to develop COPD. Pollution or indoor particulate matter may also be to blame, they conclude.