Systemic sclerosis.

Systemic sclerosis (SSc) is a multisystem autoimmune disease characterized by vasculopathy and tissue fibrosis of the skin and various internal organs. A series of genetic and epidemiological studies have demonstrated that SSc onset is determined by the accumulation of predisposing factors related to environmental influences, while genetic factors affect the susceptibility to and the severity of this disease. This notion has been confirmed by recent advance in animal models. The initial trigger of SSc is believed to be autoimmune attacks to endothelial cells, which occur in individuals with the genetic susceptibility to autoimmune diseases and/or the cumulative exposure to certain SSc-related environmental influences. Then, endothelial cells are aberrantly activated or damaged, leading to the development of vascular structural changes, such as destructive vasculopathy and proliferative obliterative vasculopathy, and tissue fibrosis. In parallel, inflammatory cells activate SSc fibroblasts and modify the metabolism of extracellular matrix by soluble factors and autoantibodies. Prior to or during these processes, SSc fibroblasts acquire the ability to selectively respond to profibrotic growth factors and cytokines, persistently producing excessive amount of extracellular matrix. SSc fibroblasts also modify immune responses, at least those of CD4+ T cells, in the microenvironment through the secretion of immune regulatory molecules. Thus, various types of individually activated cells interact with each other and coordinately drive an SSc-specific disease cascade, leading to the development of unique clinical symptoms. This article provides an overview of the current understanding of the pathogenesis of SSc with the recent advance in the research field of this disease.