Study finds cause of inflammation, clotting in severe Covid patients

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Scientists have discovered that “rogue” antibodies found circulating in the blood of Covid-19 patients have the potential to cause cells to lose their resistance to clotting.

A team from the University of Michigan found higher-than-expected levels of antiphospholipid autoantibodies, which can trigger blood clots in the arteries and veins of patients with autoimmune disorders, including lupus and antiphospholipid syndrome.

Antibodies typically help the body neutralise infections. Autoantibodies are antibodies produced by the immune system that mistakenly target and sometimes damage the body’s own systems and organs.

In a 2020 study, the research group found that autoantibodies from patients with active Covid-19 infections caused “a striking amount of clotting” in mice.

For the new study the team studied the blood samples of nearly 250 patients hospitalised for Covid-19.

The team found that the autoantibodies appear to stress the endothelial cells that make up the inner lining of blood vessels and, in doing so, cause the cells to lose their ability to prevent blood clots from forming.

The results are published in Arthritis and Rheumatology.

“This provides an even stronger connection between autoantibody formation and clotting in Covid-19,” said Hui Shi, lead author and rheumatology research fellow at Michigan Medicine.

“When endothelial cells are activated, they cause healthy blood vessels to become ‘sticky’, attracting other cells to the vessel walls and becoming more prone to thrombosis. This can affect many of the body’s essential organs,” Shi added.

The researchers found that when they removed the antiphospholipid autoantibodies from Covid-19 blood samples, the endothelial cell activation that promotes clotting was lost.

While the link is strong, future studies must be done to find whether these autoantibodies are the precise cause of thrombosis that contributes to clotting and increased severity of Covid-19, said Jason Knight, Associate Professor of rheumatology at Michigan Medicine.

“We must do more research to decide if it is beneficial to screen patients with severe Covid-19 for these autoantibodies to evaluate their risk of clotting and progressive respiratory failure,” Knight said.

This may help to repurpose treatments used in traditional cases of antiphospholipid syndrome for Covid-19, he noted.

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