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Ly6C(hi) Monocytes Direct Alternatively Activated Profibrotic Macrophage Regulation of Lung Fibrosis

Lookup NU author(s): Professor John SimpsonORCiD


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Rationale: Idiopathic pulmonary fibrosis (IPF) is a devastating disease. Antiinflammatory therapies, including corticosteroids, are of no benefit. The role of monocytes and macrophages is therefore controversial. Objectives: To define the role of monocytes and macrophages during lung fibrogenesis and resolution, and explore the phenotype of the cells involved. Methods: We used multiple in vivo depletional strategies, backed up by adoptive transfer techniques. Further studies were performed on samples from patients with IPF. Measurements and Main Results: Depletion of lung macrophages during fibrogenesis reduced pulmonary fibrosis as measured by lung collagen (P = 0.0079); fibrosis score (P = 0.0051); and quantitative polymerase chain reaction for surrogate markers of fibrosis Col1 (P = 0.0083) and alpha-smooth muscle actin (P = 0.0349). There was an associated reduction in markers of the profibrotic alternative macrophage activation phenotype, Ym1 (P = 0.0179), and Arginase1. The alternative macrophage marker CD163 was expressed on lung macrophages from patients with IPF. Depletion of Ly6C(hi) circulating monocytes reduced pulmonary fibrosis (P = 0.0052) and the number of Ym1-positive alternatively activated lung macrophages (P = 0.0310). Their adoptive transfer during fibrogenesis exacerbated fibrosis (P 0.0304); however, adoptively transferred CD45.1 Ly6C(hi) cells were not found in the lungs of recipient CD45.2 mice. Conclusions: We demonstrate the importance of circulating monocytes and lung macrophages during pulmonary fibrosis, and emphasize the importance of the alternatively activated macrophage phenotype. We show that Ly6C(hi) monocytes facilitate the progression of pulmonary fibrosis, but are not obviously engrafted into lungs thereafter. Finally, we provide empirical data to suggest that macrophages may have a resolution-promoting role during the reversible phase of bleomycin-induced pulmonary fibrosis.

Publication metadata

Author(s): Gibbons MA, MacKinnon AC, Ramachandran P, Dhaliwal K, Duffin R, Phythian-Adams AT, Van Rooijen N, Haslett C, Howie SE, Simpson AJ, Hirani N, Gauldie J, Iredale JP, Sethi T, Forbes SJ

Publication type: Article

Publication status: Published

Journal: American Journal of Respiratory and Critical Care Medicine

Year: 2011

Volume: 184

Issue: 5

Pages: 569-581

Print publication date: 16/06/2011

ISSN (print): 1073-449X

ISSN (electronic): 1535-4970

Publisher: American Thoracic Society


DOI: 10.1164/rccm.201010-1719OC


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