Fig. 7
From: The activin-follistatin anti-inflammatory cycle is deregulated in synovial fibroblasts
Possible mechanisms involved in reduced invasiveness of activin A overexpressing RASF in the SCID mouse model. RASF and monocytes/macrophages activate each other specifically at sites of cartilage invasion by secretion of pro-inflammatory cytokines (e.g., IL-1β, TNFα produced by macrophages, IL-6 produced by fibroblasts). IL-1β increases the invasiveness of RASF in the SCID mouse model. Activin A decreases the IL-1β production in monocytes/macrophages. In contrast, activin A increases TIMP-1 expression in chondrocytes. Additionally, the expression of follistatin, an antagonist of activin A, is reduced in RASF by activin A