Functional complement activity is decisive for the development of chronic synovitis, osteophyte formation and processes of cell senescence in zymosan-induced arthritis.

Synovial inflammation plays a critical role in the symptoms and structural progression of arthritis which leads to irreversible damage of the adjacent cartilage and bone. Activation of complement system is strongly implicated as a factor in the pathogenesis of chronic synovitis in human rheumatoid arthritis (RA). In this study, we show that the depletion of functional complement activity at the time of the initiation of zymosan-induced arthritis, significantly reduced the expression of TGF-beta1/3, BMP2 and pSmad2 and decreased the number of Sudan Black B positive cells in the synovium. Also, the excessive synthesis of proteoglycans and glycosaminoglycans was diminished. The appearance of apoptotic and senescent cells among the adherent bone marrow cells cultivated in vitro was not observed in complement depleted mice. Therefore, the lack of functional complement prevented the development of chronic synovitis, osteophyte formation and the generation of pathologic senescent arthritic cells.