Guided monocyte fate to FRβ/CD163+ S1 macrophage antagonises atopic dermatitis via fibroblastic matrices in mouse hypodermis

Macrophages are versatile myeloid leukocytes with flexible cellular states to perform diverse tissue functions beyond immunity. This plasticity is however often hijacked by diseases to promote pathology. Scanning kinetics of macrophage states by single-cell transcriptomics and flow cytometry, we observed atopic dermatitis drastically exhausted a resident subtype S1. Characterized by FRβ/CD163 expression, S1 exhibited strong efferocytosis and chemoattracted monocytes and eosinophils. Here we have delineated mechanisms regulating monocyte decision to acquire S1 identity in skin. During M-CSF driven macrophage differentiation in healthy skin, FRβ was expressed via intrinsic control of STAT6 and ALK5 activities, and did not require heterotypic cellular crosstalk. In contrast, CD163 expression required exposure to fibroblastic secretion. This process depended on SHP1 activity and involved STAT5 inactivation. Suppressed STAT5 activity caused CD163 expression and rendered macrophage insensitive to further induction by fibroblasts. Parsing coculture experiments with in silico ligand expression, we identified laminin-α2 and type-V collagen secreted by hypodermal fibroblasts as CD163-driving factors. S1 identity loss in AD followed a stepwise cascade: reduced laminins availability first dampened CD163 expression, IL4 and TGFβ subsequently acted on CD163^lo/- cells to downregulate FRβ. In AD skin, we showed that imitating this fibroblast-macrophage crosstalk with exogenous laminin-211 encouraged monocyte differentiation to S1 macrophages, fostered homeostatic commitment of extravasated eosinophils, and alleviated dermatitis. Hence, we demonstrated that reinforcing a steady-state cue from hypodermal fibroblasts could override maladaptive pressure on macrophage and restored tissue homeostasis.