SCIENTISTS in Edinburgh have discovered that immune cells in the brain seem to encourage tumour cells to grow rather than destroy them – a discovery that came to light using tropical fish.

The team at the Cancer Research UK centre at Edinburgh University used a fluorescent microscope to examine the brains of transparent zebrafish.

They recorded video footage using zebrafish that showed the specialised cells, called microglia, interact with cells from glioblastoma, the most common type of brain tumour which is also the hardest to treat. Around 265 people are diagnosed with glioblastoma every year in Scotland.

Microglia usually “eat” up anything that could cause harm to the brain, such as cancer cells.

However, the footage, shot at the Centre for Neuroregeneration at the University of Edinburgh, shows that rather than engulfing and destroying glioblastoma cells, the microglia infiltrate the brain tumour and interact with the cancer cells, helping them to grow and spread.

The team was led by Dr Dirk Sieger, who said: “Looking at the interactions between microglia and glioblastoma cells, the microglia appear to be friendly towards the tumour.

“We call this ‘nursing’ because these immune cells really help and support the cancer cells to develop.”

But the scientists detected that the microglia in zebrafish brains reacted very differently when they came into contact with a different type of cancer cell.

They looked at how these immune cells interacted with fibrosarcoma cells in zebrafish brains, and found that the microglia started engulfing and breaking down these cancer cells.

The scientists hope their discovery can be used as a new way to test experimental immunotherapy drugs as a treatment for brain tumours.

Sieger added: “From the different behaviours of microglia that we have seen in zebrafish, we now know what to look for when testing new immunotherapy drugs for brain tumours.

“If we can make a drug that can alter microglia’s alliance, then we should be able to see these immune cells attacking tumour cells.”

Sieger and his team also hope that using their zebrafish and fluorescent microscope will help them find out even more about the relationship between microglia and brain tumours.

They also want to work out what causes the microglia to abandon their usual mission of destroying cancer cells and instead encouraging them to grow.

He said: “If we can figure this out then the zebrafish will help us understand how these immune cells can be made to fight the tumour, and which drugs cause this behaviour.”

Cancer Research UK spent more than £33 million in Scotland last year on some of the UK’s leading scientific and clinical research, including nearly £5m on cutting-edge research in Edinburgh.

Dr Áine McCarthy, senior science information officer at Cancer Research UK, said: “Glioblastoma is one of the most aggressive forms of brain tumour that is very difficult to treat. Survival rates are stubbornly low so more research is needed to find new treatments for the disease.

“This research provides some exciting new insights into how immune cells in the brain interact with glioblastoma cells.

“The findings could help scientists design and develop new drugs to help the immune system turn its full force on brain tumours.”