By Nicoletta Lanese - Live Sciene
A new study hints that the coronavirus infects fat cells and certain immune cells in fat.
The coronavirus SARS-CoV-2 may directly infect fat cells and specific immune cells found in fat tissue, The New York Times reported.
In a recent study, posted to the preprint database bioRxiv on Oct. 25, scientists experimented with fat tissue obtained from bariatric surgeries, to see if the tissue could be infected by the coronavirus. They found that fat cells, known as adipocytes, could become infected and developed a low level of inflammation. They also found that immune cells housed within the fat tissue, called macrophages, also became infected and kicked off a much more intense inflammatory response.
In addition to these experiments, the team examined fat tissue from patients who died from COVID-19 infections and found coronavirus particles 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; several experts told the Times that SARS-CoV-2 could theoretically do something similar, making fat a reservoir for the virus.
The new research has not yet been peer-reviewed or published in a scientific journal, but assuming its results stand up to scrutiny, "the bottom line is, 'Oh my god, indeed, the virus can infect fat cells directly,'" Philipp Scherer, a scientist who studies fat cells at UT Southwestern Medical Center in Dallas, who was not involved in the research, told the Times.
Since the early days of the pandemic, people with obesity have faced a higher risk of developing severe symptoms, requiring hospitalization and dying from COVID-19, Live Science previously reported. A number of theories have tried to explain why fat increased the risk of bad COVID-19 outcomes.
For starters, excess fat in the abdomen can push on the diaphragm and so restrict airflow in the lungs; if people are already struggling to get enough oxygen into their lungs on a good day, they may fare worse against COVID-19, Science reported. In addition, obese people's blood tends to clot more easily than those with lower fat levels — another major problem in the context of COVID-19, which can trigger extensive blood clotting.
In addition, as fat builds up in the body, fat cells infiltrate the spleen, bone marrow and thymus, where many immune cells are produced. This can weaken the immune system by both reducing the number and undermining the efficacy of immune cells produced. Excess fat can also spur chronic, low-grade inflammation throughout the body, as fat cells release inflammatory substances called cytokines and macrophages do the same, in an effort to clear dead fat cells from the body, Science reported.
While all these factors may worsen COVID-19 outcomes for people with obesity, now there's this new evidence that the virus infects fat cells directly.
"This could well be contributing to severe disease," senior author Dr. Catherine Blish, a translational immunologist and professor of medicine at the Stanford University School of Medicine, told the Times. "We're seeing the same inflammatory cytokines that I see in the blood of the really sick patients being produced in response to infection of those [fat] tissues."