{"id":4111,"date":"2026-01-22T08:20:58","date_gmt":"2026-01-22T08:20:58","guid":{"rendered":"https:\/\/sites.manchester.ac.uk\/lydia-becker-institute\/?p=4111"},"modified":"2026-01-22T08:54:28","modified_gmt":"2026-01-22T08:54:28","slug":"stroke-fight-or-flight-immune-system-weakness","status":"publish","type":"post","link":"https:\/\/sites.manchester.ac.uk\/lydia-becker-institute\/2026\/01\/22\/stroke-fight-or-flight-immune-system-weakness\/","title":{"rendered":"Stroke and \u201cfight-or-flight\u201d response weakens the immune system"},"content":{"rendered":"

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A new University of Manchester and Edinburgh study published in the journal\u00a0Brain, Behavior and Immunity<\/a>\u00a0has found that people who have had a stroke have fewer of a specific type of immune cell called B cells, which normally produce antibodies to fight off infections. Surprisingly, the same compromising immune changes were seen when healthy B cells were exposed to noradrenaline – a chemical released by the body after stroke, but also during stress, illness, or intense physical activity.<\/p>\n

People who have had a stroke are more likely to develop infections such as pneumonia. These infections can slow recovery and make brain injury worse. Understanding why the immune system becomes weaker after stroke could help doctors prevent these infections and improve patient outcomes.<\/p>\n

Earlier studies by Dr Laura McCulloch and Dr Barry McColl at the University of Edinburgh found that in animal models, stroke activates the system behind the fight-or-flight response, which includes the release of the chemical noradrenaline.<\/p>\n

This activation quickly impairs a group of immune cells called B cells, reducing their ability to produce protective antibodies, and was associated with vulnerability to infection. Until now, it was unclear whether the same thing happens in stroke patients.<\/p>\n

In this study, carried out at the University of Manchester in collaboration with the University of Edinburgh team, researchers analysed blood samples from patients 24 – 48 hours after an ischaemic stroke and compared them with samples from individuals who had not had a stroke (\u2018controls\u2019).<\/p>\n

They found that stroke patients had fewer B cells than control patients and that these remaining cells were also less effective at producing antibodies and special signalling proteins called cytokines, both of which are essential for fighting infections.<\/p>\n

\u201cFindings from this collaborative study confirm that after someone has had a stroke important immune cells that help to fight infection are reduced, limiting the patient\u2019s ability to make protective antibodies. Revealing these changes opens opportunities to develop new treatments that could help reduce the incidence of infection after stroke,\u201d said Clinical Study Lead Prof Craig Smith from The University of Manchester.\u00a0<\/p>\n

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Findings from this collaborative study confirm that after someone has had a stroke, important immune cells that help to fight infection are reduced, limiting the patient\u2019s ability to make protective antibodies. Revealing these changes opens opportunities to develop new treatments that could help reduce the incidence of infection after stroke<\/em><\/p>\n

 <\/p>\n

Professor Craig Smith<\/strong><\/p>\n<\/blockquote>\n

The teams also tested B cells from healthy volunteers. When these cells were exposed to noradrenaline, they showed the same responses as seen in stroke patients: increased cell death and reduced antibody production.<\/p>\n

These findings suggest that activation of the fight-or-flight response itself, not just stroke, can impair immune function. Stress, illness, or extreme physical exertion may all influence how well B cells work.<\/p>\n

\"Stroke<\/p>\n

Reduced numbers of immune cells (B cells) were found in the blood of patients 24\u201348 hours after an ischaemic stroke. When B cells were stimulated with bacterial proteins (mimicking an infection), they were less able to produce protective antibodies and signalling proteins called cytokines.<\/strong><\/p>\n

The researchers are now studying how these immune changes after stroke may affect long-term recovery, including thinking and memory, as well as further damage to the brain\u2019s blood vessels.<\/p>\n

They are also exploring new treatments aimed at protecting or restoring B cell function after stroke, with the goal of reducing infections and improving recovery.<\/p>\n

This research was a collaboration between the University of Manchester (Geoffrey Jefferson Brain Research Centre<\/a> and the Lydia Becker Institute of Immunology and Inflammation<\/a>), the Manchester Centre for Clinical Neurosciences (part of the Northern Care Alliance NHS Foundation Trust) and the University of Edinburgh (including the UK Dementia Research Institute).<\/p>\n

This work was funded by the Medical Research Council, NIHR, Wellcome Trust, The Royal Society, The Kennedy Trust for Rheumatology Research, Leducq Foundation Transatlantic Network of Excellence StrokeIMPaCT and UK Dementia Research Institute.<\/p>\n