Abstract: Atopic dermatitis (AD) is one of the most common inflammatory skin diseases with an estimated prevalence approaching 5% in adults and is typically characterized by pediatric onset, pruritis and persistance. Research has indicated that AD is associated with an impaired epithelial barrier that promotes sensitization to environmental antigens and a type II immune response. Despite advances in AD research, the causative mechanism(s) leading to the persistent type II immune response remain unclear. Our recent publication and Prel Data indicate that the dermis and subcutis contain fibroblasts that appear to be involved in establishing type II inflammatory reactions in skin. Understanding how dysregulation of skin fibroblasts contributes to downstream events that they may intitiate formation of inflammatory AD-like lesions is the focus of this proposal. Our Prel Data show that dysregulation of NF-kB signaling in Prx1+ fibroblasts leads to upregulation of CEBPb in fibroblasts, upregulation of CCL11 and tissue eosinophilia followed by type II skin lesions resembling human AD. Our mouse model shares many similarities with human AD-like lesions involving both the dermis and epidermis at the histologic, cellular and molecular levels. Prel Data compares single cell RNAseq analysis from our study with published scRNAseq databases from human AD lesions. scRNAseq analysis from our model and human AD show fibroblast dysregulation involving CCL11 and CEBPb. Moreover, using RNAScope we have also shown that validated human AD samples contain increased numbers of dermal fibroblasts co-expressing CEBPb and CCL11 compared to matched control human skin, also consistent with our murine model. Thus, we propose novel preclinical and translational studies (Aim 1) to define molecular mechanisms by which fibroblast dysregulation mediated by CEBPb induces an inflammatory phenotype in these cells. Aim 2 will determine the role of eosinophil infiltration as a key intermediate for triggering type II immune response in AD-like skin. Aim 3 will use spatial transcriptomics (GeoMX) and RNA seq to explore equivalent mechanisms in human fibroblasts and AD specimens and translational studies using inhibitors as potential treatments for AD. We expect the proposed studies along with recent reports in the literature to contribute to a paradigm shift in understanding AD pathogenesis regarding fibroblast dysregulation and contribute to development of new therapeutic interventions that may prevent the development of AD.