Study shows abnormal immune-cell activity with long COVID

People who have long COVID symptoms—those that linger well after the initial SARS-CoV-2 infection—can display signs of abnormal immune-cell activation in many of their organs and tissues, as well as leftover SARS-CoV-2 RNA in the gut, for more than 2 years after infection, according to a small study this week in Science Translational Medicine.

University of California, San Francisco researchers analyzed data on 24 people after their initial COVID-19 illness who underwent whole-body positron emission tomography (PET) imaging at time points ranging from 27 to 910 days (about 2 and a half years) after their acute COVID-19 cases. Eighteen of the patients had long COVID. 

The team used a tracer during PET imaging that selectively tags activated T cells and found that people with long COVID had certain tissues that were enriched for activated T cells in comparison with never-infected people who did not have long COVID (prepandemic controls). 

Furthermore, this T-cell activation correlated with symptoms of long COVID. For example, people who reported persistent lung problems had stronger signs of T-cell immune activation in their lungs.

Viral RNA in gut tissue

In addition, because the gut was one of the sites of activated T-cell enrichment, the scientists analyzed colorectal biopsies from five of the patients with long COVID. All five of these samples contained SARS-CoV-2 RNA.

The authors wrote, “In this first-in-human T cell activation PET imaging study of individuals after SARS-CoV-2 infection, we found evidence of persistent T cell activation in a variety of tissues. In some individuals, this activity may persist for years after initial COVID-19 onset and be associated with systemic changes in immune activation as well as the presence of [long COVID] symptoms.”

“Overall, these observations challenge the paradigm that COVID-19 is a transient acute infection, building on recent observations in blood,” the authors concluded.