Immune Response From the Gut May Not Provide Systemic Immunity to COVID-19

An analysis of blood samples from patients infected with SARS-CoV-2 revealed that immune cells circulating in the blood triggered by the gut's response to infection were limited in number compared to immune cells that had been triggered elsewhere in the body, according to a study published in Frontiers in Immunology. According to the researchers, this suggests the gut may not provide long-lasting systemic immunity from COVID-19.

“Although the gut is considered an important portal of entry for the virus, the immune response in the blood of COVID-19 patients is dominated by lymphocytes—cells that protect the body from infection—that have been triggered by other areas of the body,” said study author Dr. Sebastian Zundler, research group leader at the Department of Medicine 1, University Hospital Erlangen, Germany, in a press release. “Further work is needed, but these findings may have implications for oral COVID-19 vaccines.”

The researchers used flow cytometry to detect and measure the different types of immune cells that were found in the blood samples of patients currently positive for COVID-19, patients who had recovered from COVID-19, and individuals who had never been infected.

“There is a special mechanism in the lymphoid tissue of the gut that triggers the production of an imprint marker called ‘a4b7 integrin.’ This marker causes T cells to head towards the gut to fight infection. We can use this marker to identify whether there are lymphocytes circulating in the blood that were triggered by the gut's immune response,” said Dr. Tanja Müller, lead author of this study, in the release. “We found relatively few immune cells with this marker in the blood of patients with COVID-19. This could be because of the ‘dilution’ by cells generated at other sites of infection—most probably the lung—or alternatively by the selective attraction of these gut-imprinted immune cells to organs other than the gut, since there was no difference between patients with and without symptoms that suggested an intestinal element to their infection.”

There is a possibility that if the gut-imprinted immune cells are diluted in comparison to immune cells triggered by other parts of the body, there could be implications for the oral-based COVID-19 vaccines currently under development, according to the study authors. However, further research is required to establish the significance of the findings.

“Our study adds to our understanding of the human immune response to SARS-CoV-2 infection, but we cannot yet finally answer the question about the fate of the gut-imprinted immune cells—whether they are ‘diluted’ or ‘attracted’ elsewhere,” Zundler said in the release. “Assessing biopsy samples from the gut and autopsy samples from the lungs will help us to answer this important question.”

REFERENCE

Gut's immune response in COVID-19 may not provide efficient protection of other organs [news release]. EurekAlert; April 20, 2021. Accessed April 23, 2021. https://www.eurekalert.org/pub_releases/2021-04/f-gir041521.php