Autoimmune antibodies may cause blood clots in COVID-19

Autoimmune antibodies may cause blood clots in COVID-19

Written by Eleanor Bird, M.S. on November 16, 2020 — Fact checked by Catherine Carver, MPH

A new study shows that the novel coronavirus can trigger the production of clot-causing autoantibodies. This finding may explain the high rate of blood clots among COVID-19 patients.


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Alongside the respiratory features of COVID-19, many people with the illness have experienced thromboses, better known as blood clots.

Some estimates suggest that the novel coronavirus causes blood clots in 30% of critically ill patients, which can lead to serious complications, including strokes.

These findings have motivated researchers to test whether existing blood-thinning drugs typically used to prevent blood clots after a heart attack, for example, could improve outcomes for people with COVID-19. However, precisely what causes the blood clots to form in people with the illness remains unclear.

Stay informed with live updates on the current COVID-19 outbreak and visit our coronavirus hub for more advice on prevention and treatment.

New research led by a team from the University of Michigan suggests that a type of autoantibody usually seen in people with the autoimmune disease antiphospholipid syndrome could be behind blood clots in people with COVID-19.

The researchers found the clot-causing antibodies in more than half of the COVID-19 patients in their analysis, and these antibodies were also associated with impaired renal function.

The study could lead to new treatment options and is available in the journal Science Translational Medicine.

aPL autoantibodies

Scientists have proposed various explanations for the presence of blood clots in people with COVID-19, including the “cytokine storm” generated by an excessive immune response, blockages to blood vessels caused by very low oxygen levels, and direct damage to blood vessels caused by SARS-CoV-2, the virus responsible for COVID-19.

The present study, however, investigated a new mechanism that involves a type of antibody called an autoantibody, which attacks lipids in the body.

These antibodies, known as antiphospholipid (aPL) autoantibodies, are a feature of the autoimmune disease antiphospholipid syndrome, which is associated with blood clots in veins and arteries.

aPL antibodies activate various factors in the blood, including platelets, to trigger the blood clotting process. Viral infections can lead to the production of these antibodies, including — according to recent case reports — the infection that causes COVID-19.

However, data on aPL antibodies and their ability to trigger blood clots in people with COVID-19 are still limited. To add to the evidence, this study tested for aPL antibodies in 172 people receiving inpatient treatment COVID-19.

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