Children with autism commonly have gastrointestinal comorbidities; Elaine Y. Hsiao and her colleagues now show that treating a maternal immune–mediated mouse model of autism with probiotics can restore both gut barrier function and behavioral abnormalities in the mice (Cell 155, 1451–1463, 2013).

The researchers activated the immune system of pregnant mice by injecting them with a viral-like molecule. The offspring exhibited many behavioral features of autism, such as enhanced anxiety and decreased ultrasonic vocalizations, as well as gut barrier dysfunction and a shift in some bacterial species in the gut. When the young offspring were treated with the human gut commensal organism Bacteroides fragilis as a probiotic, the bacterial balance was restored, as was gut barrier function and autism-like behavioral symptoms.

One particular serum metabolite produced by some mouse gut bacteria, 4-ethylphenylsulfate, was markedly increased in the autism model offspring, and the amounts were after treatment with the probiotic. Injection of this metabolite into normal mice resulted in a subset of behavioral abnormalities that had been seen in the autism model offspring, such as anxiety, suggesting that this metabolite, perhaps in combination with others, affects some neural circuits linked to autism. The direct relevance of this study to other mouse models of autism remains to be determined.