In new research out Monday, scientists say they’ve found evidence that our immune system appears more prone to inflammation and other metabolic changes in the aftermath of even a mild case of covid-19. More research will be needed to understand how these changes could be linked to post-covid symptoms, however.
Researchers are continuing to gather clues about the nature of infection from the SARS-CoV-2 coronavirus and how it can affect us months after the initial illness has passed. Inflammation is a key aspect of how our bodies respond to infection from germs like the coronavirus. In some cases of covid-19, though, the immune response becomes a double-edged sword, causing self-inflicted damage throughout the body. Survivors of severe covid-19, in particular, often experience a variety of persistent symptoms, some of which have been linked to ongoing immune dysfunction. But while the risk of long-term symptoms, commonly known as long covid, may be highest for severe cases, studies have found that some people with initially mild illness can experience similar problems.
This new study, published in the journal Mucosal Immunology, attempts to shed light on the immune changes that might be happening in milder covid-19 cases. It was conducted by scientists at the Karolinska Institute in Sweden, as well as the Helmholtz Center Munich and the Technical University of Munich in Germany. They collected blood samples from 68 people previously diagnosed with mild covid and compared them to people without covid; the samples were collected three to five months after infection, as well as a year later.
The scientists specifically focused on people’s macrophages, important white blood cells that detect foreign invaders, alert other immune cells to the infection, and even swallow germs whole. They prodded these macrophages into action by exposing them to mock signals of an infection, then took measurements of how they reacted, which included seeing which genes were being actively turned on.
At the three to five month mark, the macrophages of those with mild covid behaved noticeably different on average than those who had never been exposed to the coronavirus, the researchers found. Specifically, they released greater amounts of molecules known to be involved in causing inflammation.
“Even in mild cases of disease, we observe an altered response in immune cells several months after the resolution of infection,” study author Craig Wheelock, a lecturer at Karolinska’s department of Medical Biochemistry and Biophysics, told Gizmodo in an email. “In other words, even after people return to health, their immune system evidences an altered function for at least several months.”
The study has some caveats. For one, it’s based on a relatively small sample size, though the addition of a control group does lend more credibility. It’s also not clear how relevant these findings are to our understanding of long covid, since those patients weren’t being explicitly studied.
“These findings do not explain the mechanism for long covid, and in particular we cannot directly associate these findings with long covid because none of the individuals in our study received a long covid diagnosis,” Wheelock said.
The authors do note that about 16% of the people in their mild covid group reported persistent symptoms at the three to five month mark, which had dropped to zero people a year later. Interestingly enough, the inflammatory changes seen in these people’s macrophages also appeared to fade away 12 months later.
Perhaps more important is that long covid is suspected to be caused by one or more of several different mechanisms. So even confirming a connection between post-covid inflammation and people’s lingering symptoms may still not explain every single case. Ideally, though, this kind of research may someday point us to better treatments for at least some patients. The team, for their part, hope to keep digging deeper and to add even more groups of people for comparison, which could include people with other respiratory infections like influenza.
“We would like to expand the study into individuals with severe covid as well as long covid. This would enable us to have a better understanding of the role of this altered immune function in the disease course,” Wheelock said. “In addition, our findings highlight a couple of different therapeutic strategies that could be used to treat the symptoms of covid, including inhibiting the production of some of the lipids that we measure in the current study.”
This article has been updated with comments from one of the study’s authors.
