**5.7 Osteoporosis**

IL-6 levels are significantly higher (30 to 1000-fold) in synovial fluid than in sera (Desgeorges et al., 1997), and IL-6 drives osteoclastgenesis (Le Goff et al., 2010). Since osteoclasts are primarily involved in bone resorption, reduction in their number would be anticipated to reduce bone loss. This expectation is supported by the results of Axmann et al (2009) who demonstrated that blockade of IL-6R dose dependently decreased the joint osteoclast count and the number of bone erosions. They concluded that the mechanism for this effect was that blockade of IL-6R negatively affects osteoclast differentiation (Axmann et al., 2009).
