A subset of skin macrophages modulates surveillance and regeneration of local nerves

Host-environment interfaces such as the dermis comprise tissue macrophages as the most abundant resident immune cell type. Diverse tasks, i.e. to resist against invading pathogens, to attract bypassing immune cells from penetrating vessels and to aid tissue development and repair require a dynamic postnatal coordination of tissue macrophages specification. Here, we delineated the postnatal development of dermal macrophages and their differentiation into distinct subsets by adapting single cell transcriptomics, fate-mapping and tissue imaging. We thereby identified a small phenotypically and transcriptionally distinct subset of embryo-derived skin macrophages that was maintained and largely excluded from the overall postnatal exchange by monocytes. These macrophages specifically interacted with dermal sensory nerves, surveilled and trimmed the myelin sheets and regulated axon sprouting after mechanical injury. In summary, our data show long-lasting functional specification of macrophages in the dermis that is driven by step-wise adaptation to guiding structures and ensures codevelopment of ontogenetically distinct cells within the same compartment.