This ADRN-CRC application brings together seasoned clinical and laboratory investigators in atopic dermatitis (AD), with expertise in clinical research, immunology, S aureus biology, dermatology, and statistics. The investigators have long track records in implementing multi-center and single-center clinical trials and observational studies in allergic diseases, including AD, to the standards of NIH funded clinical research networks, in conducting NIH fundamental research on disease mechanisms in AD and in training generations of investigators in AD research In part A we demonstrate that we have the personnel and facilities to conduct ADRN network-wide and CRC center-specific research on pediatric and adult AD patient populations recruited from the allergy and dermatology clinics at Boston Children's Hospital and collaborating adult centers at the Brigham and Women's Hospital Mas General Hospital and Boston University Medical Center and Hospital, and from our just completed, as well as ongoing, NIH-funded studies of schoolchildren with allergic diseases. We have a highly experienced team, IRB-approved protocols for recruitment and clinical characterization of AD patients, an infrastructure which includes clinical research facilities, investigational pharmacy services, a laboratory facility capable of processing, storing and shipping human samples, a state-of-the-art immunology research laboratory with a 25 year focus on AD, and a data management facility with quality control plans, and capability to upload data into the NIAID designated repositories and biostatistical support. Project I in part B will draw on an already genotyped local population of AD patients to test the hypothesis that the IL-4Rα R576 polymorphism is associated with increased AD severity and alterations in the function and gene expression of epidermal and immune cells. We will also use a mouse model of AD to test the hypothesis that both epidermal and immune cells contribute to the increased antigen allergic skin inflammation observed in mice with the IL-4Rα R576R polymorphism. Project II in part B will test the hypothesis that S. aureus skin decolonization in AD will reduce disease severity and favorably alter the function and gene expression of epidermal and immune cells that contribute to disease severity. We will also test the hypothesis that S. aureus skin colonization promotes the development of antigen-driven allergic skin inflammation, and its reactivation, using a mouse model of AD. Our proposal will contribute extensively to the ADRN as a Clinical Research Unit and, as an ADRN-CRC will help elucidate the role of genetic and microbial modifiers in AD. !