Blood clots continue to wreak havoc in patients with severe COVID-19 infection, and a new study explains what can cause them in up to half of patients.
The culprit: an autoimmune antibody that circulates in the blood, attacks cells and causes clots in arteries, veins and microscopic vessels. Blood clots can cause life-threatening events such as stroke. In COVID-19, microscopic clots can restrict blood flow in the lungs and impair oxygen exchange.
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Outside of a novel coronavirus infection, these clot-causing antibodies typically appear in patients with the antiphospholipid syndrome, an autoimmune disease. The link between autoantibodies and COVID-19 was unexpected, says co-author Dr. Yogen Kanthi, Assistant Professor at the Frankel Cardiovascular Center of Michigan Medicine and Lasker Investigator at the National Heart, Lung, and Blood Institute of the National Institutes of Health.
“In patients with COVID-19, we continue to see a relentless, self-reinforcing cycle of inflammation and clots in the body,” says Kanthi. “Now we are learning that autoantibodies can be a culprit in this loop and inflammation loop that makes people who have already had problems even sicker.”
“Some of the worst clots we’ve ever seen”
Corresponding author Jason Knight, MD, Ph.D., a rheumatologist with Michigan Medicine, has been studying antibodies to antiphospholipid syndrome in the general population for years.
“Half of the patients hospitalized with COVID-19 were positive for at least one of the autoantibodies, which was quite a surprise,” said Knight, also an associate professor of internal medicine and the leading expert on autoantibody-induced diseases.
In the new Scientific translational medicine Upon release, they found that about half of the patients who were severely ill with COVID-19 had a combination of high levels of both the dangerous antibodies and super-activated neutrophils, which are destructive, exploding white blood cells. In April, the team first reported that patients hospitalized for severe COVID-19 had higher levels of extracellular neutrophil traps in their blood.
To learn more, they worked together to study the explosive neutrophils and COVID-19 antibodies in mouse models to see if this could be the dangerous combination behind the clots.
“Antibodies from patients with active COVID-19 infection caused a remarkable amount of clotting in animals – some of the worst clots we have ever seen,” says Kanthi. “We discovered a new mechanism by which patients with COVID-19 can develop blood clots.”
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