The overall goal of this proposal is to address immune function in children with autism, including the response to vaccine challenge, and how that relates to behavior. Evidence suggests that autism is associated in some cases with altered immune function, but the response of the immune system in children with autism to specific immune challenges, such as vaccines, has not been investigated directly. While it has been reported that some children with autism respond poorly following vaccination with symptoms ranging from rash, diarrhea, irritability, seizures, and loss of skills, no careful, thorough approach has been undertaken to fully characterize this issue, both at the biology and behavior level. We propose to use our current CHARGE (Childhood Autism Risks from Genetics and the Environment) and Autism Phenome Project (APP) study population to address this critical issue. The overall approach would include an examination of the immune response to both viral and bacterial vaccines in children with autism, as compared to typically developing age-matched controls, in real time following vaccination at 5 years of age. Vaccines have advantages for directly studying the immune response as they provide a known, scheduled immune challenge, whose dose is well characterized - making it possible to collect and interpret immune response data at the time that it occurs. Therefore, we think that exposure to an immune challenge with vaccine would result in an increase in inflammation compared to controls in a subpopulation of children with autism. However, we also anticipate that some children will respond to vaccine challenge differently, depending on form of the vaccine, i.e. viral vs. bacterial. Thus, we propose to address the issue of immune function in children with autism through a careful analysis of the immune system, medical and mitochondrial issues, and behavioral response to both viral and bacterial vaccines.