CD14

Background: Scar-associated macrophages (SAMs), defined by triggering receptor expressed on myeloid cells 2 (TREM2) and/or glycoprotein-NMB (GPNMB) expression, have been implicated in lung fibrosis. This study investigated the characteristics and functional roles of SAMs in lung tissues from patients with systemic sclerosis-interstitial lung disease (SSc-ILD) and healthy controls (HCs). Methods: SAM-related transcriptional profiles of lung tissues from patients with SSc-ILD and HCs were analyzed using single-cell RNA sequencing (scRNA-seq). Immunofluorescence staining of lung tissues was performed to detect CD68-positive SAMs expressing TREM2 or CCL2. Monocytes from patients with SSc-ILD and HCs were differentiated with granulocyte-macrophage colony-stimulating factor (GM-CSF) or M-CSF. The population of TREM2- and GPNMB-expressing cells was assessed by flow cytometry, and the levels of CCL2 and TGF-β1 in culture supernatants were measured in an ELISA. The fibrotic effects of macrophages on fibroblasts were examined in co-cultures. TREM2 inhibition was used to determine functional relevance. Results: scRNA-seq revealed the expansion of TREM2 macrophages highly expressing SAM-associated genes in the lower lung lobes of SSc-ILD patients. Immunofluorescence showed increased numbers of CD68 Discussion: Our study identified a GM-CSF-TREM2-TGF-β1 axis driving monocytes-derived profibrotic macrophage-fibroblast crosstalk in SSc-ILD. It also showed that, in the lungs of SSc-ILD patients, CD14