Interplay between the immune and skeletal cells in the regulation of inflammatory bone destruction

The immune and skeletal systems share a number of regulatory molecules including cytokines, signaling molecules, transcription factors and membrane receptors, in common. Consequently, the physiology and pathology of one system may very well affect the other. Research into the cartilage and bone destruction associated with rheumatoid arthritis (RA) has highlighted the importance of the interplay between the immune and skeletal systems. This interdisciplinary field called osteoimmunology has attracted much attention in recent years. Recently, animal models deficient in immunomodulatory molecules have been found frequently to develop an unexpected skeletal phenotype. Receptor activator of NF-κB ligand (RANKL) is an essential factor for the induction of osteoclastogenesis that links the immune and skeletal systems. Thus, osteoimmunology is becoming increasingly important for understanding the pathogenesis of bone destruction in RA and for developing new therapeutic strategies for diseases affecting both systems. Here we summarize recent advances on the study of the regulation of cartilage and bone destruction by the immune system.