An autoimmune antibody circulating through the blood is attacking healthy cells and has been found to cause microscopic blood clots in people hospitalised with COVID-19, according to scientists at Michigan Medicine Frankel Cardiovascular Center (Michigan Medicine), US. In COVID-19, clots may restrict blood flow in the lungs, impair oxygen exchange, and ultimately cause life-threatening complications such as strokes in people already struggling with the disease.

These clot-causing antibodies are typically seen in patients who have the autoimmune disease antiphospholipid syndrome, so it was quite unexpected that the antibodies could be a culprit in COVID-19 clotting and inflammation; at least half of COVID-19 patients exhibited a combination of high levels of the antibodies and destructive neutrophils, which explode white blood cells – the scientists were first to report the incidence of higher levels of neutrophil extracellular traps in the blood and severe COVID-19.

The scientists also studied the dangerous combination further in mouse models, only to find a striking amount of clotting in animals who received antibodies from patients with active COVID-19 infection.

“[The antibodies] created some of the worst clotting we’ve ever seen,” said Yogen Kanthi, an assistant professor Michigan Medicine. Kanthi and colleagues at Michigan Medicine now want to know whether severely ill patients with high levels of these antibodies would have better outcomes if the antibodies are blocked or removed.

If so, that might warrant an aggressive treatment like plasmapheresis, commonly used for severe autoimmune diseases. Internal medicine specialist Yu Zuo explained that plasmapheresis involved draining a patients’ blood through an IV, filtering it and replacing it with fresh plasma that doesn’t contain antibodies associated with blood clots.

The scientists suggest using convalescent plasma and anti-clotting agents as possible COVID-19 treatments – they are currently testing a well-known anti-clotting agent, dipyridamole, in patients with COVID-19 to see if it can reduce excessive blood clots.

“FDA-approved dipyridamole is an old drug that is safe, inexpensive, and scalable. We only recently discovered its potential to block this specific type of inflammation that occurs in COVID,” said Kanthi.