Role of Macrophages in Promoting Inflammation and Fibrosis in Systemic Sclerosis

Abstract

Systemic sclerosis (SSc) is a severe autoimmune disease characterized by chronic inflammation, vascular damage and fibrosis. The hallmark clinical manifestation is fibrotic skin thickening; however, the clinical outcome is determined by the extent of internal organ fibrosis. Macrophages, integral to the innate immune system, play a crucial role in phagocytosing invading pathogens and efferocytosis of apoptotic cells, while also contributing significantly to tissue homeostasis and repair. These highly adaptable cells, particularly in the M2-like polarization state, have been associated with a pro-fibrotic environment, implicated in various fibrotic disorders as well as cancer invasion. In SSc, these cells may be dysfunctional, having the potential to produce inflammatory and pro-fibrotic cytokines, recruit other inflammatory cells and stimulate fibroblast differentiation into myofibroblast, thus promoting extracellular matrix (ECM) deposition and fibrosis. Accordingly, we hypothesize that abnormally activated macrophages have a central role in SSc, promoting inflammation and fibrosis, and driving the disease process.