New research from RCSI University of Medicine and Health Sciences has found that white blood cells which ‘remember’ past inflammation events are quick to overreact, raising the risk of blood clots.

People living with inflammatory conditions, such as inflammatory bowel disease, blood cancers and sickle cell anaemia, can have a higher risk of blood clots.

The new study, published in the high-impact journal Science Advances, explores how episodes of inflammation in such diseases can result in the production of white blood cells called myeloid cells that have increased blood-clotting activity, which persists long after the inflammation took place.

Immune memories are important, according to researcher Dr Aisling Rehill, Senior Postdoctoral Fellow at the Irish Centre for Vascular Biology, RCSI. “Certain immune cells can ‘remember’ past encounters with inflammation or infection, a concept known as trained immunity. This memory allows them to respond more aggressively to future threats,” says Dr Rehill.

But this ‘shortened fuse’ could have consequences that are not desirable and actual contribute to disease, she adds.

“Our study found that this heightened response can have unintended consequences. When these myeloid cells in the immune system have been trained by prior exposure to specific inflammatory agents, they also become more likely to promote blood clotting. Similarly, mice trained by exposure to specific inflammatory agents experience changes in their bone marrow that mean they produce new immune cells with a lower threshold to start blood clotting weeks after the original exposure.”

The research, which was carried out by experts at RCSI, FutureNeuro, Trinity College Dublin and Children’s Health Ireland, could help to explain why people living with inflammatory disease can have a relatively high risk of blood clots and the complications they bring, according to lead researcher on the study Professor Roger Preston.

“If this was translated to humans, the study suggests that while trained immunity can boost the body’s defence against infections, it may also contribute to the risk of blood clot-related complications in individuals with inflammatory disease,” says Professor Preston, who is an Associate Professor at RCSI School of Pharmacy and Biomolecular Sciences.

“The findings suggest that periods of inflammation during disease could cause the generation of immune cells with increased clotting activity long after the original inflammatory event has taken place.”

The authors also suggest that the insights from the study could form the basis for targeted treatments to help prevent or manage conditions where the immune system and clotting system are overly active.

The research was funded by Research Ireland, the Health Research Board and Children’s Health Foundation and the paper ‘Trained hypercoagulability in myeloid cells’ is published in the journal Science Advances.