Groups of patients with autism or autism spectrum disorders (ASDs) are at risk for developing autoimmune diseases, which are diseases where the immune system attacks cells in its own body. Exposure to environmental contaminants during pregnancy is thought to contribute to autism/ASDs and autoimmune diseases. This suggests a link between environmental contaminants, the immune system, and autism/ASDs. Contaminants that affect cells known as regulatory T cells (Tregs) are likely candidates. Tregs prevent autoimmune diseases by controlling the immune cells, known as autoreactive T cells, from damaging organs in an autoimmune reaction. Contaminants such as perfluorooctanoic acid (PFOA) and perflurooctane sulfonate (PFOS), which impact the immune system, may also affect Tregs. Autism or ASDs may occur when developmental exposure to PFOA or PFOS affects Tregs, leading to disrupted control of autoreactive T cells that can damage the brain. Pregnant mice will be exposed to PFOA or PFOS. In their offspring, the following will be evaluated: numbers of Tregs; the ability of Tregs to secrete chemicals that control autoreactive T cells; levels of antibodies produced by autoreactive T cells that indicate increased risk of autoimmune disease; and changes in brains that may result from actions of autoreactive T cells. If alterations in Treg number and/or function from developmental exposure to PFOA or PFOS lead to brain damage from autoreactive T cells, then subsets of autism or ASD cases may result from altered Treg responses that lead to brain damage from autoreactive T cells.