The discovery underscores the intricate relationship between gut microbiota and the immune system, particularly in early life development. Serotonin, typically associated with mood regulation, has now been found to play a crucial role in immune system education, mediated by specific gut bacteria. The promotion of T-regulatory cells by serotonin-producing bacteria suggests a mechanism by which the microbiome influences immune tolerance, potentially reducing the risk of autoimmune diseases and allergic reactions later in life. This study highlights the importance of early microbial colonization in shaping immune function and underscores the potential for microbiome-targeted interventions in preventing immune-related disorders.

“The gut is now known as the second human brain as it makes over 90 per cent of the neurotransmitters in the human body. While neurotransmitters such as serotonin are best known for their roles in brain health, receptors for neurotransmitters are located throughout the human body,” explained the study’s senior author, Dr. Melody Zeng, an assistant professor of immunology in the Gale and Ira Drukier Institute for Children’s Research and the Department of Pediatrics at Weill Cornell Medicine.

The establishment of a human infant stool biobank, in collaboration with the Neonatal Intensive Care Unit at the NewYork-Presbyterian Alexandra Cohen Hospital for Women and Newborns, marks a significant advancement in understanding early gut microbiota development. The utilization of this biobank, with appropriate consent and de-identification procedures, allows researchers to explore the intricate interactions between gut bacteria and neurological processes in newborns.

The findings indicating that certain gut bacteria may supply neurotransmitters necessary for critical biological functions before the neonatal gut can independently produce them sheds light on the complex interplay between the microbiome and early development. This suggests a potential symbiotic relationship between gut microbes and the developing nervous system, influencing crucial physiological processes during the neonatal period.

  • Gut Bacteria in Babies Provide a Helping Hand

The researchers observed that the neonatal mouse gut had much higher levels of neurotransmitters, including serotonin, than the adult gut. “So far, almost all studies of gut neurotransmitters were conducted in adult animals or human subjects, where a specific gut cell type called enterochromaffin cells produce neurotransmitters,” stated Dr. Zeng. “However, we discovered that this isn’t the case in the newborn gut where most of the serotonin is made by bacteria that are more abundant in the neonatal gut.”

“We found that gut bacteria in young mice not only directly produce serotonin but also decrease an enzyme called monoamine oxidase that normally breaks down serotonin, thus keeping gut serotonin levels high,” stated the study’s lead author Dr Katherine Sanidad, a postdoctoral associate in paediatrics at Weill Cornell Medicine.

  • Healthy Immune System Helps Later in Life

immune system, particularly in infants. Babies in developed countries, with higher antibiotic usage and limited exposure to diverse microbes, may lack the necessary abundance of serotonin-producing bacteria in their intestines, leading to reduced levels of Tregs and an increased risk of immune reactions, including allergies to food. This phenomenon potentially contributes to the rising prevalence of food allergies in children in developed nations. Proper education of the immune system during infancy could mitigate these issues, allowing it to distinguish between harmless and harmful substances, thereby potentially reducing the risk of both food allergies and autoimmune diseases later in life.

The team’s future research plans involve analyzing bacteria in human infant stool samples to quantify their production of serotonin, as well as other neurotransmitters and molecules that could play a role in training the immune system. By examining these factors, they aim to gain a deeper understanding of how early microbial colonization influences immune system development and its implications for preventing immune-related diseases such as allergies, infections, and even cancer. This research holds promise for uncovering novel therapeutic strategies aimed at modulating the gut microbiome to promote lifelong immune health and reduce the incidence of immune-related disorders.

“It’s essential to understand how the immune system is trained during early life, but this is understudied in newborns and children. Further studies of these developmental periods may hopefully lead us to mitigation approaches to reduce the risk of inflammatory diseases like food allergies and inflammatory bowel disease later in life,” Dr Sanidad stated.


The information contained in this article is for educational and informational purposes only and is not intended as a health advice. We would ask you to consult a qualified professional or medical expert to gain additional knowledge before you choose to consume any product or perform any exercise.

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