Unbalanced levels of bone resorption promoting factors in bone marrow from patients with rheumatoid arthritis in comparison to osteoarthritis

RANKL and IL-6 participate in osteoclast differentiation and activation, and therefore regulate bone resorption. The biological activity of RANKL is inhibited by its natural decoy receptor osteoprotegerin (OPG), while IL-6 activity is either enhanced by soluble IL-6 receptor (sIL-6R) or inhibited by soluble glycoprotein 130 (sgp130), an extracellular domain of the signaling chain of the IL-6 receptor complex.