Recent evidence suggests that the immune system, which normally protects the body against many diseases, may malfunction in people with autism and actually contribute to or produce this disorder. "Adaptive" immune "T" cells are summoned by ‘innate" immune cells to attack invaders. Immune T cells in some people, however, mistake the body's own tissues as foreign and attack them, a process called "autoimmunity." Immune T cells also can over-react to otherwise harmless substances, such as pollen, and produce allergies. Usually these potentially errant responses by immune T cells are kept under control by ‘regulatory T cells." Regulatory T cells are produced by the Foxp3 gene. According to the collaborating researchers, who combine expertise in autism, immunity, and patterns of disease ("epidemiology"), a disproportionate number of children with autism have immune system malfunctions that are similar to those seen in autoimmunity, allergy, or both conditions. They hypothesize that regulatory T cells in people with autism may be too few, or too weak, to provide a generalized ability to control errant immune responses, which contributes to, or causes, autism. The collaborators will study immune T cells, which circulate through the bloodstream, in blood samples taken from 20 children with autism and 20 healthy ("control") children. They will compare the number of regulatory T cells, and how effectively these cells control the "attacker" T cells, in blood samples from the two groups of children. The investigators also will find out whether differences exist in the two groups of blood samples in the amount of chemicals, called ‘cytokines," produced by attacking T cells. Excessive amounts of these cytokines, suggesting incomplete control of T cells by their regulators, may have consequences for the brain, providing a link between immune dysfunction and autism. Alternatively, some other factor may be common to both immune regulation and to autism. Significance: If this study indicates that a failure to properly regulate immune T cells is involved in autism, the research will provide a better understanding of immune system involvement in autism. The findings also may provide an immune "marker" to diagnose autism, and lead to development of specific immune-based therapies to prevent or treat autism.