Scientists’ May Have Found the Cause of Long COVID
A new study may have found what’s behind long COVID symptoms.
Scientists say a portion of the immune system may stay activated after someone recovers from the virus.
Research into what causes long COVID is ongoing.
Long COVID has mystified the medical community for years, making it a tough condition to diagnose, let alone treat. However, a growing body of research has found more information on what may be behind long COVID, with the hope of eventually finding an effective treatment. Now, a new study has made an interesting discovery on what may cause long COVID symptoms: a change in the immune system that may be detected via a blood test.
That’s the major takeaway from a new study published in the journal Science. For the study, researchers followed 113 patients with COVID-19 and 39 healthy patients as controls. After six months, 40 of the COVID-19 patients developed symptoms of long COVID.
The researchers analyzed blood samples from those patients and found that they had a group of proteins that showed that a portion of the immune system called the complement system was ramped up well after the patients recovered from COVID-19.
The study analyzed 6,596 proteins across 268 blood samples, which were collected during patients’ acute phase and again six months later. Researchers found several differences in the blood of people with long COVID compared to the healthy patients, including an imbalance in proteins involved in blood clotting and inflammation. Researchers also found that those with long COVID had a group of proteins that showed that a portion of the immune system, called the complement system, was ramped up well after the patients recovered from COVID-19.
The researchers concluded that the findings provide “a basis for new diagnostic solutions” for long COVID. Here’s what you need to know about the findings.
What is the complement immune system?
As the name implies, the complement immune system is part of the immune system. “It’s our baseline and first line of immunity,” says Thomas Russo, M.D., professor and chief of infectious disease at the University at Buffalo in New York.
“Complement is an arm of the immune system that ‘complements’ the action of the other arms,” explains infectious disease expert Amesh A. Adalja, M.D., senior scholar at the Johns Hopkins Center for Health Security. “Activities that it performs range from literally attacking the cell membranes of a pathogen to summoning the cells of other immune systems to the site of infection.”
Among other things, your complement immune system cleans up damaged cells, helps your body heal after an injury or infection, and destroys microscopic organisms like bacteria that can make you sick, the Cleveland Clinic notes. The proteins that make up your complement system are created in your liver and move to your tissues and blood, the organization says.
The complement system also activates inflammation in your body to prevent infection, Dr. Russo says. “If it’s dysregulated or constantly activated, that inflammation can continue,” he says.
Here’s the problem with that: If your complement immune system is activated for too long, it puts you at risk for autoimmune or inflammatory conditions like allergic asthma, anemia, leukemia, kidney disease, and rheumatoid arthritis, the Cleveland Clinic notes. And, apparently, long COVID.
In the case of long COVID, this complement immune system activation may be linked to microclots—tiny blood clots—that can form. “These can block the blood vessels and lead to damage,” Dr. Russo says. “That can cause premature cardiac events, dementia, respiratory failure, and renal failure.” Microclots have also been linked to the extreme fatigue some people with long COVID struggle with.
What do these findings mean?
Doctors say that the study’s findings are a big deal. “This is a really important study,” Dr. Russo says. “We’ve been struggling both to diagnose long COVID and to treat it. This study lends some support.”
How? It could help provide a basis for future diagnostic tests and even treatments, Dr. Adalja says. Essentially, once scientists know what causes a condition like long COVID, they can go to work finding ways to heal people who have it. Dr. Adalja also points out: “There are existing drugs that target [the] complement” system.
But while Dr. Russo says the findings are very likely to be helpful to many long COVID patients, he also says the complement system may not be involved in all long COVID patients. “I have no doubt that, with long COVID, one size does not fit all,” he says. “But this has the potential to perhaps be part of a diagnostic test for at least some patients.”
Dr. Russo says that it’s crucial that researchers continue to explore what’s behind long COVID. “Millions of people across the planet have long COVID or will develop it,” he says. “It’s going to be the next major phase of this pandemic. If we don’t learn to diagnose and manage this, we are going to have many people with complications that impact their lives for the long term.”
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