Monash scientists find bad guy blood cells vital to gut health

Professor Nicola Harris, from Monash's Central Clinical School, made the surprising discovery working with study co-lead, Professor Kathy McCoy from the University of Calgary, and scientists from Switzerland.

Their paper was published in Immunity.

"The study showed a critical role for eosinophils in facilitating mutualistic interactions between host and microbiota, the millions of bacteria in the gut," Prof Harris said.

"It turns our views of eosinophil function on its head and will no doubt spur a lot more research into these relatively rare cells."

Eosinophils make up about 1-2 per cent of circulating white blood cells in healthy people in developed countries but are present in increased numbers in people who are severely allergic.

"They play a tissue-destructive, pathological role in these allergies, they're the bad guys," Prof Harris said.

Around 10-15 years ago scientists realised that eosinophils accounted for 10 - 30 per cent of white blood cells in the gastrointestinal tract and asked why. Prof Harris said the answer has remained a mystery.

"We set out to answer why these supposedly tissue-destructive cells were sitting in the gut."

The scientists investigated the possible role of eosinophils in the main functions of the small intestine using germ-free animal models and advanced 3D microscopy. They found that eosinophils coordinated the gut's response to bacteria.

"They were limiting overt inflammation and by doing that they were limiting tissue damage," Prof Harris said. "The most important factor of this damage is the length of the villi, the finger-like projections that come up from the wall of the intestine, which absorb nutrients.

"We found eosinophils kept those villi intact and without them the villi became much shorter and lipid uptake was reduced.

"So, they were helping to maintain this absorptive area that allowed extraction of nutrients from the diet at a proper level."

The study also found that gut motility was dysregulated in the absence of eosinophils and that they could impact the structure of tissue.

"These cells are a lot more complicated than previously believed - we need to think about them in an entirely different way," Prof Harris said. "They're doing a lot that's completely unexplored."

Prof Harris said the findings had many implications for those studying the cells in both the clinical and basic research spheres.

Co-first authors on the paper were Dr Aline Ignacio from the University of Calgary and Dr Kathleen Shah from the Global Health Institute, Swiss Federal Institute of Technology, Lausanne, Switzerland.