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Clues to Immune System’s Role in Autism

Many persons with autism show signs of brain inflammation and other immune problems. Researchers also know that the immune system affects early brain development. However, its role in the development of autism remains little understood. A new study, funded in part by Autism Speaks, sheds new light on the role of molecules that may be involved. It’s published online in the journal Biological Psychiatry.

In their investigation, the researchers looked at chemicals that help immune cells enter the brain. They found low levels of these chemicals in toddlers and preschoolers with autism, as compared to age-matched children without autism.

“We are becoming more aware that there are important interactions between neurons [brain nerve cells] and immune cells,” says lead author Paul Ashwood, Ph.D. “Changes in the immune system can affect how neurons grow, migrate and form connections with other neurons,” he explains. Dr. Ashwood is an immunologist at the M.I.N.D. Institute of the University of California, Davis.

Previous studies have shown that certain immune cells must migrate into the brain for its normal development. However, these cells depend on special adhesion molecules to cross the tight blood-brain barrier. Research with high-functioning adults with autism revealed that they have low levels of these adhesion molecules. In his new study, Dr. Ashwood tested whether these reduced levels exist during the age period when children tend to develop autism symptoms.

He measured levels of several adhesion molecules in the blood samples of 80 children, ages 2 to 4. Of these, 49 had ASD and 31 were developing typically. Overall, the children with autism had a 25 percent lower level of two types of the adhesion molecules (sPECAM-1 and the sP-selectin) as compared to the typically developing group.

The researchers then looked at how these levels related to behavior. They associated lower levels of sPECAM-1 with increased repetitive behaviors among the children with autism.

“The results provide further evidence that immune dysfunction may occur in children with autism,” says Dr. Ashwood. “Though more research is needed, levels of these adhesion molecules might someday be used as part of a blood test for biological signatures to help in the diagnosis of autism and possibly in monitoring the effectiveness of therapies.”

“Many changes in brain-immune function have been associated with many diseases and conditions including autism," says Daniel Smith, Ph.D., Autism Speaks senior director of discovery neuroscience. “The importance of this study is that it builds on the specific relationship between autism and molecules that carry immune cells into the brain. Once inside the brain, they could affect behavior and much, much more. It will be exciting to see how levels of adhesion molecules in blood relate to markers of brain inflammation, behavioral symptom progression and therapeutic intervention in people with autism.”

Autism Speaks considers the association between the immune system and autism a high-priority area of research. It is likewise a top priority among Autism Speaks supporters, as reflected in the organization’s recent MyResearchIdeas survey.

You can explore Autism Speaks research projects on immune factors in autism using this website’s Grant Search. This research is made possible by the generous and passionate support of Autism Speaks’ community of families, donors and volunteers.  

Reported by Autism Speaks science writer Laurie Tarkan