The new study, posted as a preprint last week, was modest in size, examining just 99 people with Long Covid. “But it went very deep, it went into granular aspects of the T cells, the antibody response,” says Eric Topol, director of the Scripps Research Translational Institute, who was not involved in the work. “This is exploratory, but it’s the foundation for much bigger studies.”

The Long Covid patients, most of them struggling with intense fatigue, brain fog, and other symptoms, had low levels of cortisol, a stress hormone that helps the body control inflammation, glucose, sleep cycles, and more. Features of their T cells indicated their immune system was battling unidentified invaders, perhaps a reservoir of SARS-CoV-2 or a reactivated pathogen such as Epstein-Barr virus.

https://www.science.org/content/article/blood-abnormalities-found-people-long-covid