In a research paper published in the scientific journal Frontiers in Immunology, researchers from Erlangen, Germany, see evidence that oral vaccination may have no benefit.
The intestine is one of the most important organs for the human immune system. According to the German Pharmacist Newspaper (DAZ), about 80 percent of immune cells are hosted by the intestine. Moreover, next to the lungs, it is the largest target of the human health system in a SARS Cov-2 infection. However, as Friedrich Alexander University in Erlangen-Nuremberg (FAU) has now discovered, the immune power of the gut alone is not sufficient to actually fight off a COVID-19 infection.
The scientists’ study was published in the journal “Frontiers in Immunology”. The researchers examined blood samples from COVID-19 patients. Significant differences became apparent. “The number of defense cells produced in response to the infection by the intestine was significantly lower than at other sites in the body,” says Dr. Sebastian Zundler. Zundler leads the team at Medical Clinic 1 that is responsible for gastroenterology, pneumology and endocrinology, among other areas.
Coronavirus attacks the body through the intestine and lungs
It is known that the coronavirus, SARS-CoV-2, can infect the body through both the lungs and the intestines. That’s why experts also recommend general hygiene rules, such as keeping your distance and washing your hands frequently. Zunder’s team, however, set a goal to get further into the mode of action of the virus. The researchers investigated the possibility of creating systemic immunity against the virus.
“We usually do research on the immune response as well as cell migration in the context of inflammatory bowel disease. However, since infection with COVID-19 is also possible through the intestine, we decided to apply our methods to the virus,” Zundler said, explaining the reason for the research. The university researchers used a technique called “flow cytometry.” This can be used to detect and measure different types of immune cells. To do this, they examined the blood of people who have contracted COVID-19, patients who have recovered from COVID-19, and people who have never been infected.
“There is a specific mechanism in the lymphoid tissue of the gut that triggers the production of a marker called ‘a4b7 integrin.’ This marker causes T cells (white blood cells) to move toward the gut to fight infection. Using this marker, we can detect whether there are lymphocytes circulating in the blood that have been generated by the intestinal immune response,” describes the e first author of the study, Dr. Tanja Müller. She, too, conducts research at the University Hospital Erlangen.
Few antibodies found in the gut
“Regardless of whether patients had gastrointestinal symptoms as part of their disease or not, we found relatively few immune cells with this marker in the blood of COVID-19 patients. This could be due to “dilution” by cells produced at other sites of infection, such as the lungs. It is also conceivable that these cells migrate to other organs,” Müller continues.
The scientists are convinced that these results may be of importance for any oral vaccines that are being developed.
“If only relatively few immune cells are imprinted by the virus in the intestine, the intestine might also not be able to produce enough antibodies to maintain immunity when an oral vaccination against coronavirus is given,” the researcher says.
Zundler cautions that more research needs to be done to understand the significance of the findings. “Our study contributes to our understanding of the human immune response to SARS-CoV-2 infection, but we cannot yet definitively answer some questions about the immune cells formed in the gut. Evaluation of samples from the gut and lungs will help us answer this important question,” the expert says.