Two Dutch immunologists’ discovery that auto-antibodies are one of the possible causes of post covid syndrome, or Long Covid, has prompted a trial to see if removing them by filtering the blood can offer a solution.

Jeroen den Dunnen and Niels Eijkelkamp, who work at teaching hospitals Amsterdam UMC and UMC Utrecht, started the search five years ago. They based it on the presence of auto-antibodies in the blood of sufferers and whether or not they were a cause or a consequence of the syndrome.

A study on mice showed that an injection with the antibodies from patients caused health problems in the mice, such as a heightened sensitivity to pain and lethargy.

An auto-antibody is an antibody (a type of protein) made against substances formed by a person’s own body. Auto-antibodies can directly destroy cells that have the substances on them or can make it easier for other white blood cells to destroy them.

The study, which was published in medical journal Cell Reports Medicine on Tuesday, but had been pre-published two years ago on a preprint website, drew the attention of international scientists.

“We know so little about this disease that when we suggested something, everybody paid attention,” Den Dunnen told the Volkskrant.

Outcomes of similar investigations by three foreign teams, including that of world-renowned immunologist Akiko Iwasaki, yielded similar results.

Extensive blood tests have since shown that there are dozens of auto-antibodies that only occur in the blood of Long Covid patients.

One in five Long Covid patients makes antibodies that attack their own body but why that happens remains unclear, Eijkelkamp said.

The mice study was “pioneering”, they said. They now know that the pain sensitivity in mice was connected with nerve damage, which is also present in half of Long Covid sufferers.

Measuring methods have since been refined and brain fog, another Long Covid symptom, can now be ascertained in mice as well. The tests will now also include people with the similarly debilitating long-term consequences of Lyme’s disease and Q fever.

The blood filtering method, if effective, may help some of the patients. According to Brent Appelman, who is conducting the trial at Amsterdam UMC, it won’t become the standard treatment. “It is invasive, expensive, and only has a temporary effect: the antibodies quickly return,” he said.

Den Dunnen said antibodies are just one of many possible causes of Long Covid. “It may be that they are part of a chain of things that go wrong in the body,” he said.