Fibroblast-like synoviocytes (FLS) are resident mesenchymal cells of synovial 
joints that have been recognized to play an increasingly important role in the 
pathogenesis of rheumatoid arthritis (RA). Activation of FLS in the setting of 
RA leads to the production of a broad array of cell surface and soluble 
mediators that help to recruit, retain, and activate both cells of the immune 
system and resident joint cells, leading to the promotion of ongoing 
inflammation and tissue destruction. The ability of FLS to stimulate both 
inflammation and tissue damage suggests that this cell type may be a unique 
target for the treatment of inflammatory arthritis. Greater understanding of how 
FLS are activated and how they interact with other cells in the RA synovium may 
provide insights that allow development of novel agents for RA therapy.