Researchers Theorize Long COVID May Be an Autoimmune Disease

In a study published in September, researchers suggested some people who get COVID-19 develop autoantibodies that attack their own proteins, a hallmark of many autoimmune diseases, which leads to inflammation that could trigger long COVID. Now, the National Institutes of Health is conducting a $470 million study to determine why COVID-19 symptoms persist for so long among many patients.

In the study, the researchers analyzed blood samples from 32 COVID-19 patients who donated plasma to the University of Arkansas, and another 15 who had been hospitalized there. Approximately 81 percent of the plasma donors and 93 percent of the hospitalized patients had developed a particular autoantibody that inhibited their ACE2 enzymes, which serve as ports of entry for the coronavirus to invade the body’s cells, but they’re also vital to calming the immune system down. When not enough ACE2 is present, the immune system can produce too much inflammation. “It’s the inhibition of that ACE2 enzyme that basically is plugging up the system,” said John Arthur, MD, PhD, a researcher at the University of Arkansas for Medical Sciences. “It’s like if you’ve got a bunch of hair in the drain and the water starts to accumulate on top.”

However, more research is needed to determine whether these ACE2 antibodies cause long COVID. Researchers also aren’t sure yet whether severe infections produce more autoantibodies than mild ones. A May study found that to be the case, but Dr. Arthur noted that long COVID is also common among people whose infections were initially mild.

If the theory that long COVID is an autoimmune disease, it would have implications for COVID-19 treatments. Certain blood-pressure medications, for instance, could be used to stifle the harmful cascade of inflammation. And there’s already some evidence that vaccines help alleviate long COVID symptoms, perhaps because they help regulate the antibody response.