Though many people with autism experience gut-related symptoms including inflammation, there was no mechanistic explanation to link the two conditions until a 2021 study in Immunity by Picower Institute Associate Professor Gloria Choi and Harvard Immunologist Jun Huh.

Previously the pair had teamed up to show that among mothers who harbored certain bacteria in their microbiome, infection during pregnancy could lead to overexpression of the immune system molecule IL-17a. Upon reaching receptors in brain cells of the fetus the molecule hindered proper development, leading to hyperexcitation in the S1DZ region of the cortex. That, in turn, led to autism-like social behaviors in the offspring as adults.

In the new study they found that overexpression of IL-17a alters the pregnant dam’s microbiome. The changes, in turn, influence the immune system development of her newborn pup, making certain immune cells more prone to express the molecule when fighting an infection later in life. So the same overabundant molecule that leads to abnormal brain development in utero, also leads after birth to abnormal immune system development during infancy. Blocking IL-17a in moms prevented the inflammation problems in the pups.

By identifying these specific molecular interactions, the team has shown how autism and inflammatory symptoms are linked in the offspring of mothers who experience infection during pregnancy.