A study published in Frontiers in Immunology that analyzed samples of intestine from people who died after being diagnosed with COVID-19 during the first wave of the pandemic showed the impact of the virus on the gut immune system, specifically an area known as Peyer’s Patch.

The study was conducted by researchers from King’s College of London with funding by the Medical Research Council via the U.K. Coronavirus Immunology Consortium, and support from the NIHR Guy’s and St Thomas’ BRC.

Lymphoid tissue in the gut normally maintains healthy intestinal microbial populations which are essential to health. Researchers observed that the system that would normally regulate the composition of the microbial communities—otherwise known as Peyer’s Patches—were significantly disrupted in severe COVID-19. This was irrespective of whether there was evidence of virus present in the gut or not.

While severe COVID-19 can lead to breathing problems and high fever, some patients can experience diarrhea, nausea and vomiting, which suggests involvement of the gastrointestinal tract.

Observations of the samples found the structure and cellularity in Peyer’s Patches—a grouping of lymphoid follicles that lines the small intestines—had been altered independent of the local levels of the virus. This included depletion of the germinal centers, which normally propagate antibody producing cells, in patients who died with COVID-19.

This resulting poor local immunity could lead to a reduction in microbial diversity, known as dysbiosis. Researchers also noted the findings suggest that oral vaccination may not be effective if the patient is already ill, as the gut immune system is already compromised.

Jo Spencer, professor of experimental medicine at King’s College said, “In the future it will be important to understand factors driving such lymphoid tissue dysregulation in severe inflammatory responses.”