Type I IFN-activated lung monocytes and macrophages as initiators and drivers of fibrosis at the alveolar barrier in IPF

Idiopathic pulmonary fibrosis (IPF) is a progressive and fatal lung disease with limited therapeutic options. Although macrophages have been implicated in pathogenesis in murine models, their role in human disease remains unclear. Here, we present a comprehensive, unbiased single-cell transcriptomic and regulon atlas of myeloid cells from the alveolar barrier and lung tissue. We demonstrate that alveolar barrier macrophages are transcriptionally distinct from their lung tissue counterparts, exhibiting a striking upregulation of type I interferon (IFN) signalling in IPF. Circulating monocytes from IPF patients are primed for type I IFN responses, particularly in early disease, and monocytes are enriched with type I IFN-associated genes at lung sites of early fibrosis. These findings suggest a central role for type I IFN-activated monocytes in the initiation of fibrosis, and for alveolar barrier-related, type I IFN-activated macrophages in perpetuating fibrosis. These insights provide a rationale for therapeutically targeting monocytes in early stages of IPF.