For nearly all of 2020, news of COVID-19 dominated the headlines. The first U.S. lockdowns associated with the viral pandemic occurred in March. Now, in November, the novel coronavirus is linked to nearly 49.5 million cases and 1.25 million deaths worldwide; in America alone, there are 9.83 million cases and 237,000 associated deaths. As the pandemic progressed, researchers were stumped by some of the outcomes: strokes in seemingly healthy patients; tiny but widespread blood clots. In fact, these blood clots have contributed to dangerous blockages and have, in some cases, even been fatal. But now, researchers believe that they discovered the cause to these blood clots: autoantibodies. Find the full research in Science Translational Medicines.

Autoantibodies

So what are autoantibodies? An antibody is a type of immune protein that is produced to protect against a specific antigen. An antigen is a foreign invader in the body. For example, cancer cells express a certain antigen. Now, targeted therapies are being created to target those antigens. But, as LabTestsOnline explains:

Autoantibodies are antibodies (immune proteins) that mistakenly target and react with a person’s own tissues or organs. When the immune system ceases to recognize one or more of the body’s normal constituents as “self,” it may produce autoantibodies that react with its own cells, tissues, and/or organs, [causing] inflammation, damage, and/or [organ dysfunction].

In the case of COVID-19, researchers believe that autoantibodies are attacking blood vessels, causing repeated and worsening clotting and inflammation.

The Research

Originally, the researchers associated with this study analyzed blood vessel clots in the lungs. In an article in JCI Insight, researchers shared how the clots were full of neutrophils, a type of white blood cell associated with the immune system. In patients with COVID-19, neutrophils explode within the blood vessels, causing blockages and blood clots. The more these occurred, the more severe COVID-19 was.

Now, researchers furthered their understanding of COVID-related clotting by analyzing autoantibodies. 172 hospitalized patients with COVID-19 participated in the study. Of these, around half had autoantibodies. Next, researchers also injected lab mice with autoantibodies. As they hypothesized, the mice went on to develop blood clots.

Patients with severe COVID-19 develop the same autoantibodies found in patients with antiphospholipid syndrome, a rare autoimmune condition in which the immune system mistakenly attacks blood proteins. Thus, researchers wonder if COVID-19 blood clots are just a more severe version of antiphospholipid syndrome or related conditions.