Researchers think they’ve figured out why some people develop long COVID after an initial coronavirus infection.
Evidence from patients’ blood suggests that one part of the human immune system – called the complement system – sometimes remains active even after the body has successfully fought off a COVID infection.
Where Black Americans are more likely to report symptoms of long COVID compared to their white counterparts, this could be an important breakthrough.
“In patients with long COVID, the complement system no longer returns to its basal (resting) state, but remains activated and, thus, also damages healthy body cells,” senior researcher Onur Boyman, a professor of immunology at the University of Zurich in Switzerland, said in a university news release.
Long COVID is a syndrome that typically occurs about a month after a person has gotten over their infection.
The patient can experience a wide variety of symptoms that can last months or even years, including fatigue, shortness of breath, altered sense of smell or taste, heart palpitations, and “brain fog” — confusion, forgetfulness and a lack of focus and mental clarity.
For this study, researchers followed 113 COVID patients for up to a year after their initial infection. After six months, 40 of them had developed active long COVID.
They analyzed more than 6,500 proteins in the blood of both the study participants and a healthy control group of 39 people, to see if there were any differences in those with long COVID.
It turned out that people with long COVID had measurable changes in blood proteins linked to the complement system.
“The analyses of which proteins were altered in long COVID confirmed the excessive activity of the complement system,” lead author Dr. Carlo Cervia-Hasler, a postdoctoral researcher in Boyman’s team, said in the news release.
The complement system is made up of about 50 proteins in blood plasma constantly circulating throughout the body, according to the Cleveland Clinic.
The system serves as the first line of defense for the immune system, activating inflammation and targeting and removing foreign invaders like viruses and bacteria.
“When you have a viral or bacterial infection, the complement system becomes activated and binds to these viruses and bacteria and then eliminates them,” Boyman told NBC News.
The proteins also are involved in blood clotting and the repair of tissue damage, researchers said.
But if the complement system doesn’t shut down following an infection, it can itself start damaging healthy cells throughout the body, researchers said.
This could lead to the wide variety of symptoms in long COVID patients, due to tissue and organ damage as well as micro clots in the blood.
“Patients with active long COVID disease also had elevated blood levels indicating damage to various body cells, including red blood cells, platelets and blood vessels,” Cervia-Hasler said.
Additionally, researchers found that the plasma proteins in long COVID patients returned to normal within six months of recovering from the syndrome.
“Our work not only lays the foundation for better diagnosis, but also supports clinical research into substances that could be used to regulate the complement system,” Boyman said. “This opens up new avenues for the development of more targeted therapies for patients with long COVID.”
The findings were published Jan. 19 in the journal Science.
The U.S. Centers for Disease Control and Prevention has more about long COVID.
SOURCE: University of Zurich, news release, Jan. 18, 2024.