Amplifying elements of arthritis and joint destruction

Rheumatoid arthritis (RA) is a systemic autoimmune disease characterised by chronic joint inflammation and variable degrees of bone and cartilage erosion. Studies in animal models of arthritis provide insight into elements which can amplify destructive features. The presence of immune complexes in the joint makes arthritis more erosive. Although considerable bone erosion still occurs in the absence of Fc gamma R triggering by immune complexes, through cytokine-incluced RANKL and direct osteoclast activation, cartilage erosion is heavily dependent on the Fc gamma R pathway. T cell factors suck as IFN gamma and ILI 7 further amplify erosion through upregulation of the damaging Fc gamma RI and stimulation of the influx of granulocytes, respectively. Apart from immune elements, environmental pressure and components of tissue damage contribute through innate pathways. Spontaneous T cell-dependent arthritis in ILI Ra-/- mice is absent under germ-free conditions, and markedly suppressed in TLR4-deficient mice. Moreover, TLRA blocking with a receptor antagonist suppresses erosive arthritis.