UCSF researchers profiled colorectal biopsies and blood from 44 people with long COVID and 13 recovered controls, using multiomic and spatial techniques to look for viral remnants and immune changes in tissue rather than blood alone. They found SARS-CoV-2 RNA in the gut biopsies of a subset of long COVID participants at a notably higher rate than in controls.
In tissue carrying viral material, the immune picture was lopsided: innate myeloid signaling was driving chronic inflammation while the adaptive mechanisms needed to clear infected cells appeared blunted. The authors describe this as a reservoir the immune system can sense but cannot eliminate.
Notably, these signatures were far weaker in peripheral blood than in tissue, which may help explain why blood-based tests have struggled to capture long COVID biology. This is a preprint and has not yet completed peer review.