Dectin-1 facilitates lung fungal-mediated pulmonary fibrosis.

Dectin-1 (Clec7a), a C-type lectin receptor for β-glucans, is critical in host defense against fungal infections and has been implicated in allergic responses, yet its role in pulmonary fibrosis remains unclear. In this study, we reveal that bleomycin-induced pulmonary fibrosis was suppressed in Dectin-1-deficient mice, mediated by interactions with the commensal lung fungus Engyodontium. Dectin-1 was predominantly expressed on alveolar macrophages (AMs), correlating with fibrosis severity in both humans and mice. Dectin-1 deficiency reduced Arginase-1 and TGF-β-producing AMs and profibrotic factor expression. Mechanistically, Dectin-1 signaling promoted quiescent AM differentiation into profibrotic AMs via the Raf1-dependent pathway, bypassing CARD9 signaling and mono-macrophage chemotactic recruitment. Therapeutic targeting of Dectin-1 with laminarin or Raf1 inhibitors attenuated fibrosis in mice and reduced profibrotic factors in human AMs and fibroblasts. These findings highlight the Dectin-1-Raf1 axis as a key regulator of pulmonary fibrosis and a promising therapeutic target for fibrotic diseases.