How immune response triggered by COVID-19 may damage the brain: Findings could give insight into long-term neurological symptoms of COVID-19

A study from the National Institutes of Health describes the immune response triggered by COVID-19 infection that damages the brain’s blood vessels and may lead to short- and long-term neurological symptoms. In a study published in Brain, researchers from the National Institute of Neurological Disorders and Stroke (NINDS) examined brain changes in nine people who died suddenly after contracting the virus.

The scientists found evidence that antibodies — proteins produced by the immune system in response to viruses and other invaders — are involved in an attack on the cells lining the brain’s blood vessels, leading to inflammation and damage. Consistent with an earlier study from the group, SARS-CoV-2 was not detected in the patients’ brains, suggesting the virus was not infecting the brain directly.

Understanding how SARS-CoV-2 can trigger brain damage may help inform development of therapies for COVID-19 patients who have lingering neurological symptoms.

“Patients often develop neurological complications with COVID-19, but the underlying pathophysiological process is not well understood,” said Avindra Nath, M.D., clinical director at NINDS and the senior author of the study. “We had previously shown blood vessel damage and inflammation in patients’ brains at autopsy, but we didn’t understand the cause of the damage. I think in this paper we’ve gained important insight into the cascade of events.”

Dr. Nath and his team found that antibodies produced in response to COVID-19 may mistakenly target cells crucial to the blood-brain barrier. Tightly packed endothelial cells help form the blood-brain barrier, which keeps harmful substances from reaching the brain while allowing necessary substances to pass through. Damage to endothelial cells in blood vessels in the brain can lead to leakage of proteins from the blood. This causes bleeds and clots in some COVID-19 patients and can increase the risk of stroke.

For the first time, researchers observed deposits of immune complexes — molecules formed when antibodies bind antigens (foreign substances) — on the surface of endothelial cells in the brains of COVID-19 patients. Such immune complexes can damage tissue by triggering inflammation.

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