Project Summary/Abstract: Autism Spectrum Disorders (ASD) are behaviorally defined by deficits in communication, social reciprocity, and repetitive stereotypic behaviors. While genetic and environmental factors are likely contributors to these disorders, little is known about the pathophysiology in ASD. Many in vitro studies, post-mortem brain studies and proteomic studies in plasma and cerebral spinal fluid have described the presence of increased immune activation in ASD, whilst clinical and epidemiological studies suggest that there is an increase in immune mediated conditions such as allergies, asthma and autoimmunity. Activation of these immune responses is more prominent in individuals with exacerbated behavioral impairments in ASD. We hypothesize that an underlying mechanism common to this diverse array of findings is the lack of immune control or regulation that can lead to immune activation and inflammation. Our published data and preliminary findings suggest a lack of production of immune regulatory cytokines such as transforming growth factor beta 1 (TGF?1) and interleukin (IL)-10. Decreases in these factors were associated with worse behavioral outcomes and more co-morbidities in ASD. In animal models with face and construct validity to ASD decreases in CD4+FoxP3+ regulatory T cells (Tregs) were observed. However, no studies have yet to address the functional cellular mechanisms of Tregs in ASD or their role in animal models of ASD. We will test the innovative hypothesis that a lack of cellular immune regulation by Tregs is a predictive risk factor for ASD diagnosis, and that targeting immune control mechanisms can alleviate behavioral abnormalities. Parallel clinical and preclinical experiments will be performed. The proposed studies will determine the Tregs cellular mechanisms of immune control in cord blood samples from children that later receive a diagnosis of ASD, and compare this to children with typical development (Aim #1). This proposal will directly assess specific cellular mechanisms for which there are novel therapeutic potential. One of these therapeutic approaches, adoptive transfer of Tregs, will be utilized to rescue the behavioral impairments present in a preclinical mouse model that exhibits many features with relevance to ASD (Aim #2). The proposal will directly assess the relationship of immune dysregulation in ASD and behavior abnormalities. If successful, this research will validate the transformative concept that ASD is, for some, a disorder due to defects in immune regulation and control by Tregs, and will validate a novel mechanism for one of the most visible public health concerns of our time.