In recent years, scientists have uncovered just how vital our gut microbiome is to our overall health. It influences everything from how we react to fear and stress, to our weight, mental well-being, and even our likelihood of developing autoimmune conditions like lupus and type 1 diabetes.

Now, new research published in The Journal of Immunology adds to this growing body of knowledge. The study, conducted using animal models, points to a link between the gut microbiome and autism—but surprisingly, it’s not the child’s microbiome that matters most. According to the researchers, it’s the mother’s microbiome that could play a key role.

“The microbiome can shape the developing brain in multiple ways,” said lead researcher John Lukens, a PhD student at the University of Virginia School of Medicine.

“The microbiome is really important to the calibration of how the offspring’s immune system is going to respond to an infection or injury or stress.”

The study focuses on a molecule called interleukin-17a (IL-17a), produced by the immune system. IL-17a has already been linked to autoimmune disorders like rheumatoid arthritis and multiple sclerosis. It’s known to help fight fungal infections, but it also appears to influence how the brain develops in the womb.

To test their theory, the research team blocked IL-17a in pregnant mice. They studied two groups of female mice: one group had a type of gut bacteria that triggered an IL-17a inflammatory response, and the other group (the control) did not.

When IL-17a was blocked in both groups, the offspring showed normal, neurotypical behaviors. But when the process was left to occur naturally, pups born to the first group of mothers (with the inflammatory gut bacteria) developed autism-like traits, especially in their social and repetitive behaviors.

To further test their findings, researchers transferred fecal matter from the first group of mice to the second group, essentially altering the second group’s gut microbiome to resemble the first. The result? Their pups also developed autism-like behaviors—strong evidence pointing to the mother’s gut microbiota as a key influence.

Although these are still early findings based on animal studies, the implications are significant. The study opens up a new direction in autism research, suggesting that the state of the mother’s gut health during pregnancy might play a part in neurodevelopmental outcomes.

Next, Lukens and his team plan to investigate whether similar patterns can be observed in humans and identify what specific elements in the maternal microbiome might be involved. He also notes that IL-17a is likely just one piece of a much larger and more complex puzzle.