Circulating monocytes from systemic sclerosis patients with progressive interstitial lung disease preferentially express M2 phenotype markers: in vitro and ex vivo study

Objective To characterise phenotype and functional profibrotic M2 markers in circulating monocytes and cultured monocyte-derived macrophages (MDMs) from systemic sclerosis (SSc) patients (pts) with progressive interstitial lung disease (ILD) (prog-ILD), non-progressive ILD (no-prog-ILD) and without ILD (no-ILD).Methods Fifty-five SSc pts and 20 age-matched healthy controls were evaluated. In 36 SSc pts, circulating monocytes expressing toll-like receptor-4 (TLR4, M1 marker) and M2 phenotype markers (CD204, CD206, CD163) were detected by flow cytometry. Moreover, MDMs of 29 SSc pts were analysed by quantitative real-time PCR and Western blotting for gene expression and protein synthesis with regard to the production of profibrotic mediators: transforming growth factor-ß1 (TGFß1), Mer tyrosine kinase receptor (MerTK) and arginase-1 (ARG1). Interleukin-6 and 4 (IL6, IL4), as well as C-C motif chemokine ligand 2 and 18 (CCL2/MCP1 and CCL18) from culture medium, were evaluated by enzyme-linked immunosorbent assay (ELISA).Results Prog-ILD SSc pts showed a higher percentage of TLR4+CD204+CD206+CD163+ monocytes versus no-prog-ILD, and significantly higher compared with no-ILD SSc pts.Interestingly, MDMs from prog-ILD SSc pts showed a significantly higher gene expression and protein synthesis of TGFβ1, and a significantly higher protein synthesis of MerTK, CD206, IL4 and CCL18 compared with no-prog-ILD SSc pts. Finally, gene expression and protein synthesis of TGFβ1, TLR4, CD206, CD163, ARG1, MerTK and IL6 were significantly increased in prog-ILD SSc versus no-ILD SSc MDMs.Conclusions Cultured MDMs from circulating monocytes in SSc pts with prog-ILD show markedly increased profibrotic biomarkers and mediator expression, indicating an enhanced fibrotic phenotype compared to non-prog and no-ILD SSc pts.