A viral attack during the first trimester of pregnancy may increase risk for autism. Researchers from Caltech have found a link between an overactive immune system and autism like behavior.

"We have long suspected that the immune system plays a role in the development of autism spectrum disorder. In our studies of a mouse model based on an environmental risk factor for autism, we find that the immune system of the mother is a key factor in the eventual abnormal behaviors in the offspring," said Paul Patterson, the Anne P. and Benjamin F. Biaggini Professor of Biological Sciences at Caltech, authors of the study.

Researchers from Caltech, led by Elaine Hsiao, graduate student in Patterson's lab, induced a viral infection in pregnant mice during the first trimester, by injecting a viral mimic. The mother's body reacted the same way as it would have towards a real viral infection.

"In mice, this single insult to the mother translates into autism-related behavioral abnormalities and neuropathologies in the offspring," said Hsiao.

They found that the offspring displayed some classic symptoms of autism-like behavior that include delayed learning, lack of socializing and compulsive behavior.

They also found that mice, whose mothers were infected, had the same kind of changes in their immune systems as those found in autistic people. These mice had lower levels of regulatory T cells that help suppress the immune system.

Researchers were able to correct some autistic behaviors in mice by conducting a bone-marrow transplant. The new bone-marrow corrected the immune system and some autistic behavior

Bone marrow Replacement for Autism- Not Likely

Researchers say that they wouldn't recommend bone-marrow replacement as an option to treat autism because their study was conducted entirely on mice models. However, immune system manipulation might be a good target for treating autism in the future and even then these manipulations would only reduce some of the developmental delays associated with autism, they say.

The study was published in the Proceedings of the National Academy of Sciences.