Editor’s note: This article first ran on Dec. 9, 2021, after an earlier version of the study was posted to the preprint database bioRxiv (opens in new tab). The article was updated on Sept. 23, 2022 to reflect the new information contained in the peer-reviewed journal.
The coronavirus SARS-CoV-2 directly infects fat cells and specific immune cells found in fat tissue, sparking inflammation that can then spread to uninfected “bystander” cells nearby.
In a study, published Sept. 22 in the journal Science Translational Medicine (opens in new tab), scientists experimented with fat tissue obtained from patients undergoing bariatric, heart and chest surgeries, to see if the tissue could be infected by the coronavirus. They found that the virus could infect and replicate within mature fat cells, known as adipocytes, and these infected cells became inflamed. They also found that specific subsets of immune cells housed within the fat tissue, called macrophages, also became infected and kicked off a much more intense inflammatory response.
Notably, the virus could not make new copies of itself inside the macrophages — the pathogen could break into the immune cells, but the buck stopped there. However, even this short-lived invasion triggered a significant change in the macrophages, causing them to spew inflammatory substances into the surrounding tissue. There, immature fat cells, called pre-adipocytes, reacted to the onslaught of chemical signals by becoming inflamed themselves.
These pre-adipocytes cannot be directly infected by SARS-CoV-2, the team found, but through this chain reaction, they were indirectly affected by the virus.
In addition to these experiments, the team examined fat tissue from patients who died from COVID-19 infections and found coronavirus genetic material in the fat that surrounded various organs. Viruses like HIV and influenza can squirrel themselves away in fat tissue, as a way of hiding from the immune system. Similarly, “adipose tissue could serve as a potential reservoir for SARS-CoV-2,” and in theory, this hidden reservoir could contribute to the enduring symptoms seen in people with long COVID, the team wrote in their report.
What’s more, in two patients who died of COVID-19, the team found inflammatory immune cells had assembled around infected adipocytes in the fat tissue surrounding the heart. “This was of great concern to us, as…