MedWire News: Researchers have discovered an immune system mechanism that may explain the increased risk of asthma among people with gastro-oesophageal reflux disease.

Previous research has suggested a link between gastro-oesophageal reflux disease and asthma. Indeed, studies have shown that 50-90% of asthma patients experience reflux symptoms, and that asthma is very common condition among reflux patients, explain Dr Shu Lin and team from Duke University Medical Center in Durham, North Carolina, USA.

However, they add that uncertainty surrounds the nature of the relationship between the two disorders.

To investigate, the researchers injected tiny amounts of stomach acid into the lungs of mice over a period of 8 weeks. The experiment was designed to mimic 'micro-aspiration' in humans with reflux disease, in which small amounts of stomach acid in the food pipe are breathed into the lungs.

The team then compared the immune systems of these mice with those of mice that were exposed to allergens, but not stomach acid.

The researchers found that the immune systems of the two groups of mice responded very differently.

Indeed, the immune systems of mice exposed to stomach acid overreacted and developed a "T-helper type 2 response' - a type of immune system reaction characteristic of asthma. In contrast, the immune systems of the other mice mounted a more balanced response, consisting of both T-helper type 1 and T-helper type 2 responses.

"These data suggest that chronic micro-aspiration of gastric fluid can drive the immune system toward an asthmatic response," said Dr Lin. "This is the first experimental evidence in a controlled, laboratory setting linking these two very common conditions."

However, co-researcher Dr William Parker added: "This does not mean that everyone with gastro-oesophageal reflux disease is going to develop asthma, by any means. But it may mean that people with gastro-oesophageal reflux disease may be more likely to develop asthma.

"If there is an upside to this, it is that developing gastro-oesophageal reflux disease is something we can pretty much treat and control."

The research is published in the European Journal of Clinical Investigation.