A study published Tuesday by scientists at the US National Institutes of Health (NIH) suggests that the immune response triggered by coronavirus infections damages blood vessels in the brain and may be responsible for long-lasting symptoms.

The paper, published in the journal Brain, was based on brain autopsies of nine people who died suddenly after contracting the virus.

Instead of detecting evidence of Covid-19, the team found that it was people’s own antibodies that attacked the cells lining the brain’s blood vessels, causing inflammation and damage.

This finding may explain why some people suffer lingering effects of the infection — such as headache, fatigue, loss of taste and smell, sleeping difficulties and “mental fog” — and may also help create treatments for long-term Covid.

Scientist Avindra Nath, senior author of the paper, said in a statement that “Patients often develop neurological complications with Covid-19, but the underlying pathophysiological process is not well understood.”

“We had already shown damage to blood vessels and inflammation in the brains of patients at autopsy, but we didn’t understand the cause of the damage. I think in this article we gained important insights into this cascade of events,” he said.

The nine subjects, ages 24 to 73, were selected from the team’s previous study because they showed evidence of damage to brain blood vessels, according to scans.

Their brains were compared to those of ten controls. The team examined neuroinflammation and immune responses using a technique called immunohistochemistry.

Scientists found that antibodies produced against Covid-19 mistakenly targeted cells that form the “blood-brain barrier”, a structure designed to keep harmful invaders out of the brain while allowing necessary substances to pass through.

Damage to these cells can cause protein leakage, bleeding, and clots, which increase the risk of stroke.

Leaks also trigger immune cells called macrophages to rush to the site and repair the losses, causing inflammation.

The team found that normal cellular processes in the targeted areas of the attack were severely disrupted, which had implications for things like the ability to detoxify and regulate metabolism.

The findings offer clues to the biology at play in patients with long-term neurological symptoms and could inform new treatments. For example, a drug that acts on the accumulation of antibodies in the blood-brain barrier.

“It is quite possible that this same immune response persists in patients with long-term Covid, resulting in neuronal injury,” said Nath.

That is, a drug that reduces this immune response could help these patients. “So these findings have very important therapeutic implications,” she emphasized.