A new study has helped to uncover why Covid-19 can lead to abnormal blood clots, a nasty feature of the disease that can cause purplish rashes and swollen limbs, as well as increase the risk of strokes and kidney failures
Reporting in the journal Science Translational Medicine, a team from the University of Michigan put forward new evidence that suggests the unusual amount of blood clots seen in Covid-19 patients is the result of exploding white blood cells and the release of autoimmune antibodies that spark blood clotting.
Known as antiphospholipid autoantibodies, these clot-causing antibodies are seen in patients with the autoimmune disease antiphospholipid syndrome. They are produced by the immune system and target the individual's own cells, triggering clots in the blood vessels.
It’s now clear that the problematic autoimmune antibodies are also common among people hospitalized with Covid-19. The researchers discovered that around half of the patients who were extremely sick with Covid-19 had heightened levels of both the autoantibodies and neutrophil extracellular traps, which are the product of dangerous and explosive forms of white blood cells. However, it's still unclear what is triggering the body to produce these antibodies.
“In patients with Covid-19, we continue to see a relentless, self-amplifying cycle of inflammation and clotting in the body,” Dr Yogen Kanthi, co-corresponding author and assistant professor at the Michigan Medicine Frankel Cardiovascular Center, said in a statement. “Now we’re learning that autoantibodies could be a culprit in this loop of clotting and inflammation that makes people who were already struggling even sicker.”
To back up their hypothesis, the researchers introduced these explosive neutrophils and antibodies into the bodies of mice and, as anticipated, noticed a significant amount of clotting.
“Antibodies from patients with active Covid-19 infection created a striking amount of clotting in animals – some of the worst clotting we’ve ever seen,” said Kanthi. “We’ve discovered a new mechanism by which patients with Covid-19 may develop blood clots.”
Blood clots are jelly-like clumps of cells and proteins that are the body’s way of stopping bleeding. It’s not known how common blood clots are in people infected with SARS-CoV-2, the coronavirus that causes Covid-19. However, studies from the Netherlands and France published earlier this year suggest that clots might arise in around 20 to 30 percent of severely ill patients hospitalized with Covid-19. Another study in America found that blood clots were present in "almost every organ" the researchers looked at.
Fortunately, the researchers have some clues about how to treat this nasty feature of Covid-19 and are pursuing new ways to prevent risky clotting in patients. For example, the researchers speculate that people at high risk of blood clots could potentially be treated with plasmapheresis, a treatment used in severe autoimmune diseases that involves draining blood, filtering it, and replacing it with fresh plasma. They are also embarking on a new randomized clinical trial that’s looking to see whether dipyridamole, an anti-clotting agent, is effective at reducing blood clots in patients with Covid-19.