Objective

To characterize the role of interleukin (IL)-1β and skin microvascular endothelial cells (MECs) in the generation of alternatively-activated macrophages (AAMs) and explore their fibrotic role during systemic sclerosis (SSc).

Methods

Conditioned medium from MECs purified from healthy donors (HD) or SSc patient’s skin were used to generate monocytes-derived macrophages. Flow cytometry, multiplex protein assessment, RT-qPCR and tissue immunofluorescence were used to characterize MEC-induced AAM polarization. Co-culture experiments were conducted to assess the role of MEC-induced AAM on fibroblast activation. AAMs were characterized in skin of healthy donors and SSc patients using multiparametric immunofluorescence and multiplexed measurements of gene expression. A skin AAM-specific score was developed to perform correlations with clinical features.

Results

IL-1β-activated MECs from SSc patients induced monocytes to differentiate into DC-SIGN+ AAMs, which produced high levels of CCL18, CCL2, and CXCL8 but low level of IL-10. DC-SIGN+ AAMs favor pro-inflammatory fibroblasts and were enriched in perivascular regions of highly fibrotic SSc skin. A novel transcriptomic macrophage signature defined from our findings correlated with the extent of skin fibrosis (Spearman r = 0.6; p=0.0018) and was associated with early disease and lung involvement.

Conclusion

Our work sheds new light on the vicious circle implicating IL-1β unabated secretion, microvascular endothelial cells activation and generation of DC-SIGN+ AAM in fibrosis during scleroderma.