Developmental control of inflammatory memory in atopic dermatitis-like skin disease - Abstract Atopic dermatitis (AD) is a chronic skin condition characterized by T cell-driven Type 2 inflammation. The MC903- induced dermatitis model has enabled dissection of pathways driving acute AD-like disease such as keratinocyte TSLP production and Th2 signaling; however, its ability to model persistent disease states remains unexplored. Using a repeated-challenge protocol with MC903, we found that adult mice undergoing a primary bout of AD-like inflammation develop persistent, tissue-specific inflammatory memories in skin that manifest as exaggerated pathologic responses during secondary MC903 challenge. This aligns with the emerging idea that AD chronicity stems from local memories of inflammation that persist in healed lesions and exacerbate future disease flares. However, AD in childhood follows a distinct course, with a unique immune composition and lower incidence of chronic disease. We thus tested our model in neonatal mice, and despite observing similar primary response kinetics to MC903-treated adults, we strikingly saw no signs of aggravated pathology during secondary MC903 challenge. This suggests that AD-like inflammatory memory fails in early life. Characterizing the cellular and molecular mediators of these divergent skin phenotypes will be the focus of our proposed work. Our data suggests that inflammatory memory in adults is driven by the emergence of Type 1 (T1) immune features in skin such as T1 tissue-resident memory T cells (Trms), mirroring recent findings in human AD. Transcriptional profiling suggests fibroblasts help to organize these networks by supporting T cell positioning and Trm development within inflamed adult skin. Given emerging data to suggest that neonatal T cells and fibroblasts exhibit distinct inflammatory behaviors from their adult counterparts, we hypothesize that inflammatory memory is impaired in neonatal skin due to age-related differences in T cell and fibroblast function. To test this, we will first use lineage tracing to define the fates and phenotypes of adult and neonatal T cells during AD-like inflammation in developing and adult skin (Aim 1). Subsequently, we will interrogate fibroblast-T cell interactions in the atopic skin of adult and neonatal mice using in vivo profiling via scRNA-seq and immunofluorescence staining as well as in vitro functional assays involving fibroblast-T cell co-cultures. Our work is conceptually innovative and clinically relevant, especially given the growing incidence of chronic AD in adults. Completion of the proposed work will clarify the basic mechanisms by which neonatal skin escapes inflammatory memory, potentially aiding in the identification of new therapeutic interventions for chronic AD.
