Some behavioral problems in children with autism have been traced back to viral infections in their mothers during pregnancy. Studies have shown that "revving up" the mother's immune system during pregnancy results in offspring with altered gene expression in the brain and problems with behavioral development, as well as immune system changes and autoimmune disorders. Dr. Littman and his colleagues suspect that the link between immune function and autism lies in a newly discovered subset of immune cells called Th17 cells which produce the inflammation-inducing signaling molecule interleukin-17. Their normal role is thought to be in fighting bacterial and fungal infections, but if this defense mechanism goes awry, Th17 cells can cause inflammatory tissue damage that eventually leads to autoimmune and inflammatory diseases. Littman and colleagues propose to study the contribution of these cells to autism using both mouse models and clinical samples. The researchers plan is to use experimental mice lacking Th17 cells to shed light on the cells' role in the behavioral changes linked to activation of the maternal immune system. Clinically, the researchers plan to compare levels of Th17 cells and the chemical signals they produce in blood samples from individuals with autism and healthy controls.