How stress can weaken the immune system

The busy life of modern society makes 'stress' or 'stress' a common term everywhere. Anyone has been, is, and will be able to fall into a state of stress. Contrary to what many people think, stress not only causes psychological damage, but also has an extremely negative impact on our physical health.

According to a new clinical study on mice published in the journal Cell on August 8, prolonged stress makes our bodies feel sick, and bacteria in the gut may be the cause. Scientists have discovered that stress in the brain directly shuts down specific glands in the intestines. This is the organ responsible for secreting chemicals, releasing them inside or outside the body, thereby affecting the intestinal flora and the body's broader immune system.

Neuroscientist John Cryan from University College Cork Ireland said the discovery "is a technical marvel". Most previous research has focused on how bacteria affect the brain, but now we're looking at the opposite mechanism: How the brain's psychological states may influence the microbiome , but specifically in the intestinal tract.

Scientists have long known that the gut and brain have the ability to 'talk' to each other. When stressed, the brain promotes the release of hormones that can cause intestinal conditions such as inflammatory bowel disease. Conversely, some bacteria in the gut can also release chemical signals that affect the brain and body's behavior.

However, neural pathways are less well understood. To learn more about this issue, neuroscientist Ivan de Araujo at the Max Planck Institute in Germany and his colleagues focused on small organs called Brunner's glands located in the wall of the small intestine. Until now, scientists knew little about the workings of these glands, other than that they produce mucus and contain many nerve cells.

De Araujo's research team found that removing Brunner's glands in mice made the animals more susceptible to infection. It also increases markers of inflammation, a variety of immune and cellular chemicals that can cause tissue damage. The team saw a similar effect in humans: people who had tumors removed from the part of the intestine containing Brunner's glands had higher levels of white blood cells — a marker of inflammation — than the general population.

Further analysis showed that removing Brunner's glands from mice also caused bacteria in the Lactobacillus genus living in the small intestine to disappear. This is a type of probiotic that plays an important role in maintaining the intestinal barrier. In a healthy digestive tract, Lactobacilli stimulate the production of proteins that act as mortar between the cells lining the intestines, keeping most substances in the intestines, while allowing certain nutrients to enter the bloodstream. When Lactobacilli disappear, the intestines become "leaky", releasing some toxic substances into the blood. The immune system attacks these foreign molecules, causing inflammation and disease as observed in mice lacking Brunner's glands.

The researchers then examined the gland's nerve cells. They discovered that Brunner's glands are directly connected to the amygdala, the brain region involved in emotions and stress responses, via the vagus nerve. When mice are chronically stressed, Brunner's glands are inhibited, leading to Lactobacillus depletion and increased inflammation, similar to when the glands are completely removed.

Dr. De Araujo said the findings have important implications for the treatment of stress-related disorders such as inflammatory bowel disease. His team is currently studying whether chronic stress from the mother affects infants who receive Lactobacillus through breast milk.