E-cigarette vapour disables key immune cells in the lung that keep the air spaces clear of potentially harmful particles, say scientists who warn that vaping may be more harmful than traditional smoking.

The vapour impairs the activity of alveolar macrophages, which engulf and remove dust particles, bacteria, and allergens that have evaded the other mechanical defences of the respiratory tract.

The findings, published online in the journal Thorax, suggest that while further research is needed to better understand the long term health impact of vaping, e-cigarettes may be more harmful than we think, as some of the effects were similar to those seen in regular smokers and people with chronic lung disease.

Vaping is increasing in popularity, but most of the current body of research has focused on the chemical composition of e-cigarette liquid before it is vaped.

Researchers from the University of Birmingham and Swansea University in the UK devised a mechanical procedure to mimic vaping and produce condensate from the vapour.

They extracted alveolar macrophages from lung tissue samples provided by eight non-smokers who had never had asthma or chronic obstructive pulmonary disease (COPD).

A third of the cells were exposed to plain e-cigarette fluid, a third to different strengths of the artificially vaped condensate with and without nicotine, and a third to nothing for 24 hours.

The results showed that the condensate was significantly more harmful to the cells than e-cigarette fluid and that these effects worsened as the 'dose' increased.

After 24 hours of exposure, the total number of viable cells exposed to the vaped condensate was significantly reduced compared to the untreated cells, and condensate containing nicotine exaggerated this effect.

Exposure to the condensate increased cell death and boosted production of oxygen free radicals by a factor of 50, and it significantly increased the production of inflammatory chemicals - more so when the condensate contained nicotine.

What is more, the ability of cells exposed to vaped condensate to engulf bacteria was significantly impaired, although treatment with an antioxidant restored this function and helped lessen some of the other harmful effects.

The researchers conclude that the vaping process itself can damage vital immune system cells, at least under laboratory conditions.

"Importantly, exposure of macrophages to [e-cigarette vapour condensate] induced many of the same cellular and functional changes in [alveolar macrophage] function seen in cigarette smokers and patients with COPD," they said.