A prolonged immune response may contribute to the formation of blood clots after COVID-19

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Serious complications due to blood clots, such as heart attack and stroke, which some COVID-19 survivors have, can be caused by a long-lasting immune response in the blood vessels after recovery, a study published today in eLife.

The findings may help explain why some COVID-19 survivors, so-called ‘long-term carriers’, report persistent symptoms of COVID-19 or why some experience strokes and heart attacks for weeks or months after recovery. They can also suggest potential strategies to prevent these complications.

“During the initial stages of infection, SARS-CoV-2, the virus that causes COVID-19, can attack the lining of blood vessels, which can trigger inflammation and an immune response. This can result in blood vessel damage in the short term,” explains first author Florence Chioh, researcher. at Lee Kong Chian Medical School (LKCMedicine), Nanyang University of Technology, Singapore. “For our study, we wanted to investigate what happens in the long-term blood vessels of COVID-19 survivors.”

Chioh and colleagues collected blood samples from COVID-19 survivors within a month of recovery and discharge from the hospital. They found that, compared to healthy individuals, COVID-19 survivors had twice as many damaged blood vessel cells, called circulating endothelial cells, that float in their blood. Even more of these damaged blood vessel cells were found in survivors who had conditions such as hypertension or diabetes that could also damage blood vessels.

In addition to the signs of blood vessel damage, the team found that the survivors had an abundance of inflammatory proteins called cytokines produced by immune cells. They also discovered an unusually large number of immune cells called T cells, which help destroy the virus, despite the fact that the virus has already disappeared.

“We show that an overactive immune system is a likely cause of blood vessel damage seen in some COVID-19 survivors,” says Chioh. “It can cause blood vessels to leak, which increases the risk of blood clots.”

“Our work suggests that patients with COVID-19, especially those with underlying chronic conditions, could benefit from close follow-up after recovery,” adds senior author Christine Cheung, assistant professor and chair of medical care at LKCMedicine. “This would help identify high-risk individuals who may need blood thinners or preventative therapy to protect them from the debilitating complications of blood clotting.”

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eLife is a non-profit organization created by financiers and led by researchers. Our mission is to accelerate the discovery by working of a platform for research communication that encourages and recognizes the most responsible behaviors. We aim to publish work to the highest standards and importance in all areas of biology and medicine, including cell biology, immunology, and inflammation, as we explore new creative ways to improve the way research is evaluated and published. eLife receives financial support and strategic guidance from the Howard Hughes Medical Institute, the Knut and Alice Wallenberg Foundation, the Max Planck Society and Wellcome. Learn more at https: //elifesciences.org /o.

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