Selective depletion of CD11b-positive monocytes/macrophages potently suppresses bleomycin-induced pulmonary fibrosis.

• Idiopathic Pulmonary Fibrosis (IPF) is a fatal lung disease without effective treatments. • CD11B-positive monocytes/macrophages increase in the fibrotic lungs and is correlated with pulmonary fibrosis progression. • CD11b conditional depletion suppresses bleomycin-induced pulmonary fibrosis. • CD11b contributes to pulmonary fibrosis via altering macrophages polarization and the sphingosine 1-phosphate receptor 2 (S1PR2)-sphingosine kinase 2 (SphK2) signaling. • CD11b may represent a potential therapeutic target for pulmonary fibrosis. The understanding of pathogenesis underlying idiopathic pulmonary fibrosis (IPF) is still limited presently. Monocytes or macrophages are involved in progression of the pulmonary injury and repair. The aim of this study is to investigate the roles of CD11b+ monocytes/macrophages in the progression of pulmonary fibrosis. In this study, the expression levels of CD11B gene and inflammatory genes in the IPF patients are evaluated using the available datasets. CD11b cells are conditionally depleted in a CD11b-diptheria toxin receptor (CD11b-DTR) mouse by administration of diptheria toxin (DT). Pulmonary fibrosis in mice is induced using intranasal bleomycin. The mRNAs and proteins expression in lung tissues are determined by quantitative real-time polymerase chain reaction (qRT-PCR), immunofluorescence (IF) staining and Western-blot assays. It shows that the expression of CD11B mRNA is up-regulated in fibrotic lungs and alveolar macrophages of IPF patients and bleomycin-treated rodents. Selective depletion of CD11b+ monocytes / macrophages in CD11b-DTR mice potently halts bleomycin-induced pulmonary fibrosis progression. CD11b depletion inhibits the polarization of macrophages in the fibrotic lungs. Mechanically, CD11b deficiency represses the activation of sphingosine 1-phosphate receptor 2 (S1PR2)/sphingosine kinase 2 (SphK2) signaling during pulmonary fibrosis. In conclusion, our data suggest that CD11b+ monocytes/macrophages contribute to pulmonary fibrosis and represent a potential therapeutic target for IPF. [ABSTRACT FROM AUTHOR]