A study led by Dr. Barry McColl, at The Roslin Institute, shows that having a stroke damages immune cells as well as affecting the brain.
Around one-third of stroke patients are stricken by infections, which can lessen their chances of making a good recovery. Therapies that boost the survival of the affected immune cells or compensate for their damage could help improve patient recovery.
Tests in mice revealed that those which experienced a stroke had fewer numbers of specialised immune cells called marginal zone B cells, which produce antibodies. Affected mice were more susceptible to bacterial lung infections.
Loss of the B cells was caused by a chemical called noradrenaline produced by nerves that are activated during stroke. The authors found they could protect the mice from infections using a drug that blocks the effects of noradrenaline.
Noradrenaline is part of the body’s fight or flight response. It helps to prepare the body for action and has a range of effects, such as raising heart rate, boosting blood supply and triggering the release of energy from stores.
Blocking noradrenaline would probably be too dangerous in stroke patients, the researchers caution, but developing therapies that block or bypass the damage to the immune system could offer new approaches reduce the risk of infection after stroke.
The study could also lead to new tests to identify which stroke patients have the highest chances of developing an infection, so that they can be monitored more closely.
The research is published in the journal Nature Communications and was funded by the Biotechnology and Biological Sciences Research Council and the Medical Research Council.
“Our work shows that stroke has damaging effects on the normal ability of the immune system to protect us from infections such as pneumonia, which are particularly life-threatening in stroke patients. This could partly explain why people who have strokes are so prone to getting infections.
“We now plan to build on our findings by developing and testing new treatments that can block or bypass these immune deficits with B cells a particular target.”
Dr Barry McColl, The Roslin Institute
"Infections are a major complication of stroke and lead to a worse outcome for patients. This is an important study which provides new insights about how stroke affects the immune system, which we hope will lead to new approaches to preventing infections after stroke. "
Professor Craig Smith, on behalf of the stroke research group at Salford Royal NHS Foundation Trust
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