Circulating mast cell progenitors migrate to atopic dermatitis-like skin then adapt locally

Background Mast cells (MCs) are tissue-resident immune cells that are classified into two subsets in mice: connective tissue-type MCs (CTMCs) and mucosal type MCs (MMCs). Although both CTMCs and MMCs can be induced from bone marrow (BM)-derived hematopoietic stem cells (HSCs) in vitro, recent research on MC ontogeny has revealed that MMCs are maintained with a supply of BM-derived HSCs, while CTMCs are maintained locally by self-proliferation in steady state in vivo . However, how CTMCs, such as skin MCs, are maintained in an inflammatory state such as atopic dermatitis (AD) remains to be fully elucidated. Methods: MC903-induced AD model was used to identify BM-derived MCs in the skin. The infiltration and proliferation of MCs were evaluated by flow cytometry using CD45.1 BM-chimera mice and parabiosis. BM-derived MCs in AD-like skin were compared to resident MCs (rMCs) in gene expressions by RNA sequence analysis. The fate of BM-derived MCs in AD-like skin was investigated for expressions of CTMC markers and responses to compound 48/80. Results: In AD-like skin, significant increase of both rMCs and BM-derived MCs was observed. BM-derived MCs were derived from circulating MC progenitors (MCps) and were distinguished from rMCs by integrinβ7 expression, which was gradually downregulated in the skin. RNA sequence analysis showed that integrinβ7+ MCs in the skin shared characteristics of both MMC and CTMC. Integrinβ7+ MCs proliferated in situ and acquired the CTMC phenotypes in AD-like skin. Conclusions: Skin MCs are maintained in AD-like skin by both local proliferation of rMCs and infiltration/proliferation of BM-derived MCs, which differentiate toward CTMC in the skin. ### Competing Interest Statement The authors have declared no competing interest.