During obesity, a person's own fat cells set off a complex inflammatory chain reaction that can drive to disrupt metabolism and weaken immune response. This can potentially place people at higher risk of poor outcomes from a variety of diseases and infections, including COVID-19.

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The study was led by scientists at Cincinnati Children's and the University of Cincinnati College of Medicine and was published in Nature Communications. The team reports that type I interferons, a class of substances produced by immune cells also are produced by fat cells called adipocytes. These interferons drive a constant low-level, chronic immune response that amplifies "vigor" to a cycle of inflammation within white adipose tissue (WAT). More commonly known as white fat, this is the type of fat that expands to form most of the unwanted bulges around our thighs, arms, and bellies. This inflammation, in turn, appears to drive a cascade of cellular responses that promote obesity-related disease, especially type 2 diabetes and non-alcoholic fatty liver disease (NAFLD).

"Our novel study reveals how Type I Interferon sensing by adipocytes uncovers their dormant inflammatory potential and exacerbates obesity-associated metabolic arrangements," said Senad Divanovic, PhD, corresponding author and a researcher in the Division of Immunobiology at Cincinnati Children's. "Further, our findings highlight a previously underappreciated role for adipocytes as a contributor to the overall inflammation in obesity," Divanovic added.

The new study shows how type 1 interferons operate along an axis of interaction with IFNa receptors (IFNAR) to trigger a vicious cycle of inflammation. Among the effects: changes in expression of several genes associated with inflammation, glycolysis, and fatty acid production.

For example, mice fed an obesity-inducing diet displayed an augmented type I IFN signature including increases in Ifnb1, Ifnar1, Oas1a, and Isg15 gene expression, the team reported. Importantly, many of the metabolic changes documented in mice were found to be conserved in human adipocytes. This activity was unexpected because until now most scientists have studied type 1 interferons in relation to viral infections and immune cell function.

"Our observations suggest that the type I Interferon axis can alter adipocyte core inflammatory programming to converge them closer to that of an inflammatory immune cell. Additionally, type I Interferons modify the metabolic circuit of adipocytes, which to our knowledge is the first depiction of immune-mediated modulation of adipocyte core metabolism," Divanovic said.

Further investigation continues into the specific mechanisms that type I Interferons employ to modify adipocyte core metabolism. In addition, researchers continue to study the full extent of how adipocytes can "mimic" inflammatory immune cell capabilities. "These findings directly impact an extensive number of patients, both adult and pediatric," Divanovic added. Beyond diabetes and NAFLD, the interplay between obesity and the immune system appears to increase the risk of preterm birth and may reduce the body's ability to fight off infections--including viruses such as COVID-19.